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  • Books  (13)
  • Articles  (800,845)
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  • 1
    Electronic Resource
    Electronic Resource
    Application of the continuous wavelet transform to the fluctuations and electric field analysis in the H-1 heliac : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 503-505 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We apply the continuous wavelet transform (CWT) and a CWT spectral technique to the analysis of the time-resolved fluctuation-driven particle flux in the H-1 heliac. The results confirm that in some cases the outward radial flux reverses its direction. In addition, time-resolved frequency spectra of fluctuation signals obtained by CWT show that the dominant frequency component as a function of time closely follows changes in the radial electric field. This suggests that the VE×B drift velocity dominates the poloidal phase velocity of the fluctuations in the laboratory frame, in which case the time-resolved frequency can be used to characterize the radial electric field. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1310583
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  • 2
    Electronic Resource
    Electronic Resource
    Observations of radial wild cables in tokamak plasmas (abstract) : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 506-506 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The results of processing the plasma images with the help of the method of multilevel dynamical contrasting (MDC)1 are presented. The images are taken in visible light, with space resolution ∼100 μm and time resolution ∼10 μs, in various tokamaks (TM-2, T-4, T-6, and T-10). The presence of rigid-body filamentary structures is found. They are similar to those structures formerly found in a Z-pinch, whose long life was proven2 in tracing their dynamics. The reliability of results is supported by the rich statistics and considerable similarity of the structures in various facilities and regimes, as well as by the insensitivity of observed structuring to a specific way of imaging (strick camera, fast photography, etc.). Sometimes the structuring may be seen without MDC processing (in such cases, the MDC allows fine resolution of structuring). The most typical structure is a straight cylindrical block varying in length from few centimeters up to a diameter of plasma column. The diameter of such a block varies, respectively, from a few millimeters to several centimeters. The most attention is paid to radially directed filaments which, together with toroidal and poloidal filaments, form a network. Detailed analysis of individual cylindrical blocks of several centimeters in diameter revealed them to be a coaxial tubular structure with an inner rod (which may be of tubular form as well) of a few millimeters diameter. The similarity of the above structures to coaxial cables may appear to not be occasional: according to the hypothesis3 the elementary coaxial block of diameter not exceeding few millimeters, is a "wild cable" in which the propagating high-frequency (HF) electromagnetic wave produces a vacuum channel around the hypothetical microsolid skeleton2 and thus protects the skeleton from the ambient high-temperature plasma. An analysis of measurements of HF electric fields, both inside and outside the plasma column in tokamak T-10, reveals their reasonable agreement with predictions based on the hypothesis.3 © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1323474
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  • 3
    Electronic Resource
    Electronic Resource
    Newly developed double neural network concept for reliable fast plasma position control : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 513-516 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Neural network is considered as a parameter estimation tool in plasma controls for next generation tokamak such as ITER. The neural network has been reported to be so accurate and fast for plasma equilibrium identification that it may be applied to the control of complex tokamak plasmas. For this application, the reliability of the conventional neural network needs to be improved. In this study, a new idea of double neural network is developed to achieve this. The new idea has been applied to simple plasma position identification of KSTAR tokamak for feasibility test. Characteristics of the concept show higher reliability and fault tolerance even in severe faulty conditions, which may make neural network applicable to plasma control reliably and widely in future tokamaks. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1323251
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of film development on uniformity and modulation transfer function of the gated/fast x-ray imagers data : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 521-524 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have been investigating the different phenomena that affect the modulation transfer function response of the gated x-ray imagers and fast x-ray imagers that we use to record subnanosecond x-ray images at different laser facilities. As part of that investigation, we noticed that there is definite nonuniformity to the recorded images, even when the incident radiation was uniform. After a significant effort to track down that effect we found that the automatic developing processors, which process the film along the length of the roll, cause the effect. Manual development, which depends primarily on transverse agitation in the developer, and automatic processors that do not use a feed mechanism but emulate this agitation, do not introduce such artifacts. We recommend that for absolutely critical missions, such as target symmetry measurements, certain automatic machines should not be used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1310585
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  • 5
    Electronic Resource
    Electronic Resource
    Accessing TJ-II data with remote procedure call : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 525-529 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new software, based on the de facto standard Open Network Computing Remote Procedure Call (ONC RPC) has been developed for TJ-II database access. This software solution replaces a previous development based on Berkeley sockets in which the client implementation had the drawback that was platform dependent. From the user point of view, the access to the TJ-II database can be done from codes running in the central server or from any other computer in the network in exactly the same way. From the development point of view, the ONC RPC tools allow to generate source code for the clients in an easy and flexible manner, thus reducing the work needed to maintain/upgrade the library for different platforms. The access to the database is managed by a concurrent server program, running on the central server, which implements each access routine as a service on the network. This allows controlling the accesses to the database. A client library has been developed to provide connection with the data server. This library implements a client routine per service, that interchanges parameters between client and server programs using External Data Representation. The client library has been installed in different UNIX and UNIX-like platforms, including ALPHA AXP/Digital UNIX, Sparc/SOLARIUS, INTEL/LINUX and CRAY/UNICOS and in Windows (NT/95/98) platforms. The support for Windows platforms allows autonomous PC-based acquisition systems to integrate experimental data into the data base. A basic in-house developed identification system is used to control client connections. An access policy has been defined in order to assign different permissions to different clients. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1316757
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  • 6
    Electronic Resource
    Electronic Resource
    Precision metrology of NSTX surfaces using coherent laser radar ranging : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 533-536 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A frequency modulated Coherent Laser Radar ranging diagnostic is being used on the National Spherical Torus Experiment (NSTX) for precision metrology. The distance (range) between the 1.5 μm laser source and the target is measured by the shift in frequency of the linearly modulated beam reflected off the target. The range can be measured to a precision of 〈100 μm at distances of up to 22 m. A description is given of the geometry and procedure for measuring NSTX interior and exterior surfaces during open vessel conditions, and the results of measurements are elaborated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1310586
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  • 7
    Electronic Resource
    Electronic Resource
    Design and application of a zone plate monochromator for laboratory soft x-ray sources (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 53-57 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this article we describe the test of a zone plate monochromator for a laboratory soft x-ray source which is a laser produced plasma on a liquid jet target. The monochromator consists of a zone plate and a pinhole. Due to the special zone plate used (condensor zone plate KZP7) the monochromator is particularly suitable for laboratory sources since it collects a relatively large solid angle in the present setup. Depending upon the diameter of the pinhole a monochromaticity of up to λ/Δλ=600 can be achieved. The usefulness of the linear monochromator was proven on the basis of a filter transmission measurement. The monochromator can be used for several applications. In particular it is suitable for time-resolved x-ray absorption spectroscopy and pump and probe experiments. The use for such investigations is discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1329901
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  • 8
    Electronic Resource
    Electronic Resource
    Optical characterization of plasma facing mirrors for a Thomson scattering system of a burning plasma experiment : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 540-544 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The general requirements for a plasma facing mirror (PFM) of a Thomson scattering system (TS) for a burning plasma experiment are (i) high and approximately constant reflectivity in the wavelength spectral range 400–800 nm; (ii) low sputtering yield and low erosion; (iii) high power damage threshold; (iv) good thermo-mechanical properties to preserve quality imaging. Rhodium-coated mirrors are chosen because they meet these requirements. Rhodium coated mirror were realized with substrates of copper and vanadium. The detailed optical characterization of these mirrors is presented: i.e., surface planarity measurements as well as roughness and reflectivity figures are presented. These data can be used for the choice of the PFM of a TS system for international thermonuclear experimental reactor. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1316759
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  • 9
    Electronic Resource
    Electronic Resource
    Diagnostic requirements for high power auxiliary heating on NSTX (abstract) : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 551-551 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: National Spherical Torus Experiment (NSTX) has recently completed its first phase of operation. The primary objective for the baseline diagnostic1 set during this phase has been to aid in plasma control and machine operation, which successfully led to attainment of 1 MA of plasma current and some encouraging initial results with coaxial helicity injection (CHI). This first set of diagnostics relied on techniques previously established on tokamaks and related plasma devices. In the next phase of operation, strong auxiliary heating will become available in the form of rf heating through high harmonic fast waves (HHFWs) and neutral beam injection (NBI) for a combined total power of 11 MW. With intense auxiliary heating, accurate and reliable measurements of the plasma parameters for both machine operation and characterization of the plasma performance over a wide range of conditions will require an extended set of diagnostics. Profile diagnostics will be particularly important in this phase, and in some cases this capability can be achieved by upgrading existing diagnostics. However, many new diagnostic approaches must be implemented which take into account the constraints of a spherical torus device. An overview of the full complement of diagnostics planned for NSTX will be presented, and issues related to implementing each diagnostic will be discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1323478
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  • 10
    Electronic Resource
    Electronic Resource
    Plasma diagnostics for the sustained spheromak physics experiment : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 556-561 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this article we present an overview of the plasma diagnostics operating or planned for the sustained spheromak physics experiment device now operating at Lawrence Livermore National Laboratory. A set of 46 wall-mounted magnetic probes provide the essential data necessary for magnetic reconstruction of the Taylor relaxed state. Rogowski coils measure currents induced in the flux conserver. A CO2 laser interferometer is used to measure electron line density. Spectroscopic measurements include an absolutely-calibrated spectrometer recording extended domain spectrometer for obtaining time-integrated visible ultraviolet spectra and two time-resolved vacuum monochrometers for studying the time evolution of two separate emission lines. Another time-integrated spectrometer records spectra in the visible range. Filtered silicon photodiode bolometers provide total power measurements, and a 16 channel photodiode spatial array gives radial emission profiles. Two-dimensional imaging of the plasma and helicity injector is provided by gated television cameras and associated image-processing software. An array of fiber-coupled photodetectors with H alpha filters view across the midplane and in the injector region to measure neutral hydrogen concentrations. Several novel diagnostics are being fielded including a transient internal probe (TIP) and an ultrashort-pulse reflectometer (USPR) microwave reflectometer. The TIP probe fires a very high velocity optical bullet through the plasma and will provide fairly nonpertabative internal magnetic field and current measurements to compare with an equilibrium code model fitted to wall-mounted probes. The USPR is being designed to study edge density and turbulent fluctuations. A multipoint Thomson scattering system is currently being installed to give radial temperature and density profiles. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1318246
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  • 11
    Electronic Resource
    Electronic Resource
    Calibration and initial operation of the HIBP on the MST : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 564-567 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: For the first time, a heavy ion beam probe (HIBP) has been installed on a reversed field pinch, i.e., Madison symmetric torus (MST), to measure the plasma potential profile, potential, and electron density fluctuations, etc. The application of a HIBP on MST has presented new challenges for this diagnostic. The primary sources of difficulty are small access ports, high plasma, and, ultraviolet (UV) flux and a confining magnetic field produced largely by plasma currents. The requirement to keep ports small so as to avoid magnetic field perturbations led to the development of the cross-over sweep system. The effectiveness and calibration of this sweep system will be reported. In addition, this diagnostic is now operating with greater plasma/UV loading effects than most previous Rensselaer HIBPs. The plasma flux is reduced by using a magnetic suppression structure. The UV flux appears to be the dominant cause of the remaining loading, which is substantial. The magnetic field being largely produced by the plasma makes determination of measurement locations exclusively from trajectory calculations difficult. Initial operation results have shown that the magnetic field model we are using to calculate our ion trajectories has an inaccuracy of about 10%, and thus subsequent development of improved confining field models is important. Secondary signals have been detected, and the levels are smaller than that from the UV induced noises. Methods to increase the signal levels are discussed. A very rough estimation of the potential at a typical MST core location is 0.8–2 kV. Fluctuations in the frequency range 100–20 kHz have also been observed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1310590
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  • 12
    Electronic Resource
    Electronic Resource
    Modified biased split detectors for the HIBP electrostatic energy analyzer : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 575-578 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In electrostatic energy analyzers of heavy ion beam probes the required accuracy of plasma potential measurements is provided by differential detection of the ion beam on the split detector. Secondary electrons created on the detector surface by the analyzed ions and ultraviolet plasma radiation can strongly disturb the measurements. In this article we consider the influence on analyzer operation of secondary electrons emitted from the detector, describe the relation for corresponding errors in the plasma potential measurements, and present two modified biased split detectors which avoid these errors. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1310592
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  • 13
    Electronic Resource
    Electronic Resource
    Compact soft x-ray reflectometer based on a line-emitting laser-plasma source (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 58-62 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe a compact soft x-ray reflectometer for in-house characterization of water-window multilayer optics. The instrument is based on a line-emitting, liquid-jet, laser-plasma source in combination with angular scanning of the studied multilayer optics. With a proper choice of target liquid and thin-film filters, one or a few lines of well-defined wavelength dominate the spectrum and multilayer periods are measured with an accuracy of 0.003 nm using a multi-line calibration procedure. Absolute reflectivity may also be estimated with the instrument. The typical measurement time is currently 10 min. Although the principles of the reflectometer may be used in the entire soft x-ray and extreme ultraviolet range, the current instrument is primarily directed towards normal-incidence multilayer optics for water-window x-ray microscopy, and is thus demonstrated on W/B4C multilayers for this wavelength range. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1327307
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  • 14
    Electronic Resource
    Electronic Resource
    Rutherford scattering diagnostic for the Madison symmetric torus reversed-field pinch : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 598-601 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The technique of Rutherford scattering (RS) has been used (for the first time on a reversed-field pinch) to measure the bulk majority ion temperature on the Madison symmetric torus (MST). RS has been in routine operation on MST since December 1999. The neutral beam source and electrostatic energy analyzers which comprise the RS diagnostic were built by the Budker Institute of Nuclear Physics (Novosibrsk, Russia). The source is described in another paper (Abdrashitov et al., these proceedings) and the analyzers are described. A data analysis routine has been developed which yields accurate fits to the data, and estimates of errors in the fit parameters. Typical results are shown. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1321737
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  • 15
    Electronic Resource
    Electronic Resource
    First results of reverse field experiment vertical time-of-flight : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 607-610 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The charge exchange neutral particle outfluxes and ion temperature are important quantities for the determination of the power balances and the plasma's energetic content; therefore they constitute a long term issue of reversed field pinch research. In order to improve the experimental knowledge of these plasma quantities, in the reversed field experiment a vertical time-of-flight (TOF) neutral particle analyzer (NPA) has been recently installed. It sees the plasma along a vertical chord, whose impact parameter is about half radius, and it is meant to complement the other two NPAs, which are installed on the equatorial plane. In this article, the new vertical TOF is reported, with particular attention to its more original components. An "in situ" method to calibrate the electron multiplier gain absolutely is described in detail. The first measurements of the ion temperature are reported, showing the reliable operation of the system and the acceptable signal-to-noise ratio obtained up to now. The results are also compared with the measurements of the horizontal NPAs mainly in the experimental regime of high plasma density. Possible improvements of the new diagnostic and its use in combination with a neutral particle beam are also briefly described and discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1316760
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  • 16
    Electronic Resource
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    Omegatron mass spectrometer for analysis of ion concentrations in hydrogenic plasmas : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 623-626 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe an omegatron-type mass spectrometer used for measurement of the molecular and atomic ion concentrations as well as the ion species temperatures in hydrogenic plasmas. The experiments were performed in the PISCES-A linear plasma experiment with electron densities n(approximate)1011–1012 cm−3, ion temperatures Ti(approximate)2–8 eV, electron temperatures Te(approximate)3–30 eV, and magnetic fields B=0.8–1.9 kG. The resulting mass spectra show clear evidence of atomic hydrogen H+, as well as of the molecular ions H2+ and H3+, with H+ and H3+ usually being dominant. It is found that large electron repeller voltages ((approximate)−200 V) are important for preventing electrons from entering the diagnostic region and ionizing the residual gas. The relative peak heights for the different ions are found to vary as a function of ion repeller voltage, probably due to differences in ion temperature. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1310594
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  • 17
    Electronic Resource
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    Electron beam generation from semiconductor photocathodes (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 63-67 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Several measurements on a variety of semiconductor photocathodes were performed in order to determine their photoelectric quantum efficiency. Two different excimer lasers (XeCl and KrCl) and a pulsed Xe lamp were used as light sources for electron photoextraction from doped and undoped samples of cadmiun telluride, indium antimonide, and indium phosphide. Large current densities were obtained up to the limit of the Child–Langmuir law. This suggests the use of these materials for the production of intense electron sources, which could also be used for purity measurements of noble liquids. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1333042
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  • 18
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    X-ray imaging techniques on Z using the Z-Beamlet laser : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 657-662 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The Z-Beamlet laser backlighter system at Sandia National Laboratories, which will be operational in 2001, will create a point or area source of high (or moderate) energy x rays behind a Z-accelerator [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] -driven target. In the former case with 〉2 kJ in up to four pulses of 〈2 ns total duration in a 20 ns interval, and 〉80% of the 2ω energy in a ∼50-μm-diam focal spot, the resulting 〉4×1016 W/cm2 irradiances will generate ≥8.950, 8.999 keV (zinc He-α, etc.) x rays. This high-energy source, as either a single point or four separate spots, will be used directly for four-frame point-projection x-ray imaging, and will attain spatial resolutions and signal-to-noise levels significantly better than presently possible on Z using existing methods. In combination with a ∼1 cm field of view, the technique will be well suited to the large, relatively opaque objects characteristic of Z experiments. This addition is anticipated to have a major impact upon the basic physics of z-pinch implosions, and therefore, possibly the ultimate x-ray powers and hohlraum (vacuum or dynamic) radiation temperatures that may be attainable. Furthermore, in combination with a slightly defocused point source and a medium-energy grazing-incidence microscope, Z-Beamlet may allow various inertial confinement fusion and high-energy-density physics experiments to be studied at even higher spatial resolution and signal-to-noise levels. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1315645
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  • 19
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    One-dimensional x-ray imaging using a spherically bent mica crystal at 4.75 keV : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 674-677 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: One-dimensional x-ray imaging of static gold bars using a spherically bent mica crystal is presented for the first time at an x-ray energy of 4.75 keV. X rays are produced using 1-ns-square pulses on the TRIDENT laser facility driving the He-like resonance transition in solid titanium disks. Time-integrated images of square profile parallel gold bars are recorded on direct exposure film with a magnification of ∼10. Rising edge measurements of the bars demonstrate resolutions of about 6–7 μm over a 400 μm field of view. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1315648
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  • 20
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    Fluorescence concerns in high energy x-ray yield scaling and imaging studies : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 682-685 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: X rays at high photon energies are needed to backlight and image large objects of high opacity on large lasers, such as the National Ignition Facility, or large pulsed power facilities, such as ATLAS. Attenuators and filters are usually used to bring the signals to scale and to filter the x rays from un-needed low energy components. As the x-ray energy increases, the secondary effect of the interactions of the x rays with the filter or attenuator material must be addressed. This is especially true when one considers using the very high energy x rays from the hot electrons generated during the interaction of intense lasers with high Z materials. We will show how these concerns can be quantified and reduced in at least one case; an experiment on the OMEGA laser facility, designed to investigate the scaling of absolute x-ray yield and conversion efficiency with laser energy and power. This investigation is part of the study to determine the feasibility of high-energy backlighters using Ge emission near 10.3 keV. We will also show how these results apply to imaging at larger x-ray energies.
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    URL: http://dx.doi.org/10.1063/1.1318252
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    Development and characterization of a single-line-of-sight framing camera : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 694-697 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present initial characterization data from a new single-line-of-sight (SLOS) x-ray framing camera. The instrument uses an image-dissecting structure inside an electron optic tube to produce up to four simultaneous dc images from a single image incident on the cathode and a microchannel plate-based device to provide the temporal gating of those images. A series of gated images have been obtained using a short-pulse UV laser source, and the spatial resolution of those images is compared to those obtained using a more traditional-microchannel plate based system. © 2001 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1318254
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    The large format x-ray imager : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 701-704 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We introduce a new Large Format X-ray Imaging Camera (LFC) for the Los Alamos National Laboratory (LANL) Inertial Confinement Fusion/Radiation Physics (ICF/RP) program. This instrument is intended as a prototype for use at the National Ignition Facility (NIF), but is capable of operating at LANL's Trident and the University of Rochester's OMEGA laser systems. The LFC is based upon similar x-ray camera architecture and is currently in the final design stages. It is constructed around a mosaic of 3 large (35×105 mm2) microchannel plate (MCP) detectors, primarily to give a larger field of view, but also for greater temporal coverage and higher magnification while maintaining spatial resolution. The camera is designed to have 30 data channels, six 13-mm-wide microstrips, continuous temporal coverage of 4.2 ns, adjustable electrical gate width, and variable gain on each microstrip and magnifications up to 20×. In the process of designing the LFC we scrutinized every element of the gated x-ray imaging process and designed optimization experiments for many of these elements. From the results of two of these experiments, improvements were made in impedance matching to MCPs and, in another, optimization of phosphor on faceplates. © 2001 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1326005
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    Imaging of laser–plasma x-ray emission with charge-injection devices : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 713-716 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This work details the method of obtaining time-integrated images of laser–plasma x-ray emission using charge-injection devices (CIDs), as has been demonstrated on the University of Rochester's 60-beam UV OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. The CID has an architecture similar to a charge-coupled device. The differences make them more resistant to radiation damage and, therefore, more appropriate for some application in laser–plasma x-ray imaging. CID-recorded images have been obtained with x-ray pinhole cameras, x-ray microscopes, x-ray spectrometers, and monochromatic x-ray imaging systems. Simultaneous images obtained on these systems with calibrated x-ray film have enabled determination of the absolute detection efficiency of the CIDs in the energy range from 2 to 8 keV. © 2001 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1318257
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    Soft x-ray detector array for the study of magnetohydrodynamics instabilities in the compact helical system heliotron/torsatron : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 721-723 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A 20 channel PIN-photodiode array is installed on the compact helical system (CHS) heliotron/torsatron to measure the radial profiles of soft x-ray (SXR) emission and fluctuations. In neutral beam injection (NBI) heated plasma on CHS, sawtooth oscillations are often observed in the SXR signals. The sawtooth has a characteristic feature of the off-axis sawtooth crash that takes place first near the 1/q=1/2 rational surface located at the normalized minor radius ρ(approximate)0.4−0.6, where q is the safety factor. In most of cases high frequency precursor and low frequency postcursor oscillations having m/n=2/1 mode structure (m, n: the poloidal and toroidal mode numbers) appear before and after the crash. The total plasma beta derived from the measurement of SXR emission-peak position is slightly but clearly decreased by the sawtooth crash. This reduction suggests rapid transport of energetic beam ions from the core region toward the plasma edge region. © 2001 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1318259
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    Operation of the ultrasoft x-ray system on NSTX (abstract) : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 731-731 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The ultrasoft x-ray imaging system on National Spherical Torus Experiment (NSTX) became operational and provided the first data in the filtered diode slow bow tie configuration. Using different band pass filters on each of three arrays allows an approximate spectroscopic estimate of the plasma impurity content, as well as of the electron temperature. Magnetohydrodynamics (MHD) activity from different plasma regions is also observed. The soft x-ray emission profiles are well behaved until an Internal Reconnection Event occurs. Examples of NSTX MHD phenomena seen in the ultrasoft x-ray emission under different operational regimes will be presented. From a technical point of view, we point out that the industrial PC based data acquisition system was not adversely affected by stray magnetic fields due to its close proximity to the NSTX device. Also, the surface barrier diodes withstood baking to 100 °C relatively well.© 2001 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1323483
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    Monochromatic x-ray imaging with bent crystals for laser fusion research : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 744-747 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Monochromatic x-ray imaging with toroidally bent crystals has been applied to investigate critical issues in laser fusion research in collaboration with Jena University [for example, I. Uschmann et al., Rev. Sci. Instrum. 66, 734 (1995)]. Described in this article is the study on x-ray diagnostics to provide simultaneously time, space, and spectral resolutions for the laser fusion experiments by the use of toroidally bent crystals. A monochromatic x-ray imager was developed, which consists of two sets of identical five bent crystals and a fast x-ray framing camera. The attained spatial resolution of 6 μm, time resolution of 34 ps, and spectral resolution of 10 eV are high enough to observe temporal evaluation and temperature distribution of the laser fusion hot core. In addition, a new x-ray imager with bent crystal was developed to investigate hydrodynamic instabilities occurring in laser-driven planer targets as one of the most critical issues in laser fusion research. The imager was so designed as to match the experiments using rather thick, massive targets irradiated under the same condition as in the high-gain experiments. Configuration and specifications of the imager are presented. © 2001 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1318261
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    National Ignition Facility core x-ray streak camera : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 748-750 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The National Ignition Facility (NIF) core x-ray streak camera will be used for laser performance verification experiments as well as a wide range of physics experiments in the areas of high-energy-density science, inertial confinement fusion, and basic science. The x-ray streak camera system is being designed to record time-dependent x-ray emission from NIF targets using an interchangeable family of snouts for measurements such as one-dimensional (1D) spatial imaging or spectroscopy. the NIF core x-ray streak camera will consist of an x-ray-sensitive photocathode that detects x rays with 1D spatial resolution coupled to an electron streak tube to detect a continuous time history of the x rays incident on the photocathode over selected time periods. A charge-coupled-device (CCD) readout will record the signal from the streak tube. The streak tube, CCD, and associated electronics will reside in an electromagnetic interference, and electromagnetic pulse protected, hermetically sealed, temperature-controlled box whose internal pressure is approximately 1 atm. The streak tube itself will penetrate through the wall of the box into the target chamber vacuum. We are working with a goal of a spatial resolution of 15 lp/mm with 50% contrast transfer function at the photocathode and adjustment sweep intervals of 1–50 ns. The camera spectral sensitivity extends from soft x rays to 20 keV x rays, with varying quantum efficiency based on photocathode selection. The system will have remote control, monitoring, and Ethernet communications through an embedded controller. The core streak camera will be compatible with the instrument manipulators at the OMEGA (University of Rochester) and NIF facilities. © 2001 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1318262
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    Nuclear diagnostics for the National Ignition Facility (invited) : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 773-779 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The National Ignition Facility (NIF), currently under construction at the Lawrence Livermore National Laboratory, will provide unprecedented opportunities for the use of nuclear diagnostics in inertial confinement fusion experiments. The completed facility will provide 2 MJ of laser energy for driving targets, compared to the approximately 40 kJ that was available on Nova and the approximately 30 kJ available on Omega. Ignited NIF targets are anticipated to produce up to 1019 DT neutrons. In addition to a basic set of nuclear diagnostics based on previous experience, these higher NIF yields are expected to allow innovative nuclear diagnostic techniques to be utilized, such as neutron imaging, recoil proton techniques, and gamma-ray-based reaction history measurements. © 2001 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1319356
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    Fast ion loss diagnostic plans for the National Spherical Torus Experiment : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 784-787 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The prompt loss of neutral beam ions from the National Spherical Torus Experiment is expected to be between 12% and 42% of the total 5 MW of beam power. There may, in addition, be losses of fast ions arising from high harmonic fast wave (HHFW) heating. Most of the lost ions will strike the HHFW antenna or the neutral beam dump. To measure these losses in the 2000 experimental campaign, thermocouples in the antenna, several infrared camera views, and a Faraday cup lost ion probe will be employed. The probe will measure loss of fast ions with E〉1 keV at three radial locations, giving the scrape-off length of the fast ions. © 2001 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1319358
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    A thin film device as a low energy, high flux charged particle spectrometer : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 792-795 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We are continuing our investigation of the use of stacks of electrically isolated thin metal foils as spectrometers for lost ions from tokamak fusion plasmas. Devices of this type in which the foil thicknesses were a few micrometers were installed on the Joint European Torus during the recent first deuterium–tritium experiment in an effort to observe lost energetic alpha particles. While there was no convincing evidence of lost alpha particles in this experiment, we did observe significant fluxes of low energy (〈500 keV) charged particles. In an effort to provide an instrument for the investigation of this phenomenon and of escaping relatively low energy (〈100 keV) ions from other fusion plasma devices, we have developed alternative devices with very thin (few hundred nanometers) alternating layers of conductor and insulator. Four such devices have been fabricated and tested for protons with energies between 20 and 160 keV and demonstrated good energy resolution (typically about 10%) for proton bombarding energies between about 40 and 120 keV. One of the devices, consisting of deposited layers of Al, Ti, and SiO2 was operated up to a current density of about 100 m/cm2 at an energy of 100 keV, corresponding to a power volume density of 100 kW/cm3 © 2001 American Institute of Physics.
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    High-yield neutron activation system for the National Ignition Facility : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 818-821 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The most accurate absolutely calibrated measurement of the total yield of neutrons from experiments on the National Ignition Facility will be from activation of threshold nuclear reactions. The high-yield neutron activation system is being designed to provide high-accuracy (similar to the ±7% achieved on other fusion experiments) linear measurements over a 9-order-of-magnitude dynamic range from the facility limit of ∼1019 neutrons/shot down to a minimum of ∼3×1010 neutrons/shot. The system design requirements are presented, and a conceptual design to meet those requirements described. © 2001 American Institute of Physics.
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    Time-of-flight neutron spectrometer for JT-60U : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 828-831 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The authors have developed a 2.45 MeV neutron double crystal time-of-flight (DC–TOF) spectrometer for deuterium plasmas in JT-60U. The DC–TOF neutron spectrometer consists of two fast plastic scintillators (BC-408 made by Bicron, 50 cm2 and 1800 cm2, thickness 2 cm), located on constant TOF spheres. The constant TOF spheres have a radius of 1 m which gives a neutron flight length of 1.64 m and a TOF of 92 ns for 2.45 MeV neutrons. The calculated spectrometer efficiency and resolution are 2.8×10−2 cm2 and 100 keV, respectively. The energy resolution corresponds to a time resolution of 2.0 ns. The spectrometer has been installed in the basement of JT-60U, 10 m away from the plasma center with vertical line-of-sight. Neutron energy spectra have been obtained when the neutron yield from the plasma is ∼1015 neutrons/s. © 2001 American Institute of Physics.
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    Neutron emission study of DT plasmas heated with tritium neutral beams : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 832-835 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The neutron emission energy spectrum from deuterium–tritium fusion reactions has been measured in experiments carried out at the Joint European Torus for plasmas heated with high power neutral beam (NB) injection of tritium beams at Eb(approximate)150 keV using a magnetic proton recoil neutron spectrometer. High quality data were obtained in which up to three spectral components due to different ion reactions could be distinguished with the help of dedicated model calculations of the fusion neutron emission based on Monte Carlo simulations. The analysis model involved neutrons from reactions of NB ions on passing and trapped orbits interacting with thermal bulk ions. Moreover, a narrow Gaussian component, due to neutrons from thermal d+t→α+n reactions, could be resolved in some cases. Results are presented and the plasma information obtained is discussed as an illustration of the capabilities of neutron emission spectroscopy diagnostics. © 2001 American Institute of Physics.
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    A sensitive neutron spectrometer for the National Ignition Facility : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 846-849 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We are developing a sensitive neutron spectrometer for the National Ignition Facility laser at Livermore. The spectrometer will consist of a 1020 channel single-neutron-interaction time-of-flight detector array fielded 23 m from the neutron-producing target. It will use an existing detector array together with upgraded electronics for improved time resolution. Measurements of neutron yield, ion and electron temperatures, and density-radius product are all possible under certain conditions using one-, two-, or three-step reaction processes. The locations of the most important potential sources of scattered neutron backgrounds are determined as the first step in designing collimation to reduce these backgrounds. © 2001 American Institute of Physics.
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    Optimal foil shape for neutron time-of-flight measurements using elastic recoils : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 859-862 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The basis for a time-of-flight neutron spectrometer for inertial confinement fusion (ICF) experiments using recoils from a shaped scattering foil is presented. It is shown that the number of elastic recoils can be substantially increased by utilizing a large scattering foil in the shape of an ellipsoid, with the curvature of the ellipsoid being determined by the mass of the recoil particle. This shape allows the time-of-flight dispersion — present originally in the neutrons — to be maintained in the recoils despite the large foil area. The feasibility of using this design on current ICF experiments is discussed. © 2001 American Institute of Physics.
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    Development of a neutron imaging diagnostic for inertial confinement fusion experiments : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 865-868 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Pinhole imaging of the neutron production in laser-driven inertial confinement fusion experiments can provide important information about the performance of various capsule designs. This requires the development of systems capable of spatial resolutions on the order of 5 μm or less for source strengths of 1015 and greater. We have initiated a program which will lead to the achievement of such a system to be employed at the National Ignition Facility (NIF) facility. Calculated neutron output distributions for various capsule designs will be presented to illustrate the information which can be gained from neutron imaging and to demonstrate the requirements for a useful system. We will describe the lines-of-sight available at NIF for neutron imaging and explain how these can be utilized to reach the required parameters for neutron imaging. We will describe initial development work to be carried out at the Omega facility and the path which will lead to systems to be implemented at NIF. Beginning this year, preliminary experiments will be aimed at achieving resolutions of 30–60 μm for direct-drive capsules with neutron outputs of about 1014. The main thrust of these experiments will be to understand issues related to the fabrication and alignment of small diameter pinhole systems as well as the problems associated with signal-to-background ratios at the image plane. Subsequent experiments at Omega will be described. These efforts will be aimed at achieving resolutions of about 10 μm. Proposed developments for new imaging systems as well as further refinement of pinhole techniques will be presented. © 2001 American Institute of Physics.
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    Synergy of multiviewing spectroscopic diagnostics on COMPASS-D (invited) : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 881-887 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In the COMPASS-D tokamak three multiviewing diagnostic systems are combined by using the same collection optics. HeI line ratios from a helium thermal jet provide detailed edge Te(r) and ne(r) profiles. The spectrometer also provides the Dα profile. A Doppler spectrometer system provides Ti and Vθ profiles using HeII emission. The Te and ne profiles are used in extracting neutral densities from the Dα emissivities, and the radial electric field from the Doppler measurements. The behavior of Te(r), ne(r), 2nD(r), Er, and Vθ and their gradients can now be compared in detail to investigate the H-mode transition physics. © 2001 American Institute of Physics.
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    Diagnostics for advanced tokamak research (invited) : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 906-914 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Advanced tokamak research seeks to find the ultimate potential of the tokamak as a magnetic confinement system. Achieving this potential involves optimizing the plasma cross-sectional shape, current density, and pressure profiles for stability to magnetohydrodynamic (MHD) modes while simultaneously controlling the current density, pressure, and radial electric field profiles to minimize the cross field transport of plasma energy. In its ultimate, steady-state incarnation, the advanced tokamak also requires pressure profiles that have been adjusted to achieve the maximum possible bootstrap current, subject to the constraints of MHD stability. This simultaneous, nonlinear optimization of shape, current, pressure, and electric field profiles to meet multiple goals is a grand challenge to plasma physics. To keep the plasma at peak performance, active feedback control will almost certainly be required. Diagnostic measurements play a crucial role in advanced tokamak research both for developing the scientific understanding underlying the optimization and for serving as sensors for real time feedback control. One outstanding example of this is the way motional Stark effect (MSE) measurements of the internal magnetic field revolutionized work on current profile shaping. Improved diagnostic measurements are essential in testing theories which must be validated in order to apply advanced tokamak results to next step devices. © 2001 American Institute of Physics.
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    Digital-image capture system for the IR camera used in Alcator C-Mod : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 927-930 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An infrared imaging system, based on an Amber Radiance 1 infrared camera, is used at Alcator C-Mod to measure the surface temperatures in the lower divertor region. Due to the supra-linear dependence of the thermal radiation with temperature it is important to make use of the 12-bit digitization of the focal plane array of the Amber camera and not be limited by the 8 bits inherent to the video signal. It is also necessary for the image capture device (i.e., fast computer) to be removed from the high magnetic field environment surrounding the experiment. Finally, the coupling between the digital camera output and the capture device should be nonconductive for isolation purposes (i.e., optical coupling). A digital video remote camera interface (RCI) coupled to a PCI bus fiber optic interface board is used to accomplish this task. Using this PCI-RCI system, the 60 Hz images from the Amber Radiance 1 camera, each composed of 256×256 pixels and 12 bits/pixel, are captured by a Windows NT computer. An electrical trigger signal is given directly to the RCI module to synchronize the image stream with the experiment. The RCI can be programmed from the host computer to work with a variety of digital cameras, including the Amber Radiance 1 camera.
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    Applications of visible CCD cameras on the Alcator C-Mod tokamak : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 935-939 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Five 7 mm diameter remote-head visible charge-coupled device (CCD) cameras are being used on Alcator C-Mod for several different diagnostic purposes. All of the cameras' detectors and optics are placed inside a magnetic field of up to 4 T. Images of the cameras are recorded simultaneously using two three-channel color framegrabber cards. Two CCD cameras are used typically to generate two-dimensional emissivity profiles of deuterium line radiation from the divertor. Interference filters are used to select the spectral line to be measured. The local emissivity is obtained by inverting the measured brightnesses assuming toroidal symmetry of the emission. Another use of the cameras is the identification and localization of impurity sources generated by the ion cyclotron radio frequency (ICRF) antennas, which supply the auxiliary heating on Alcator C-Mod. The impurities generated by the antennas are identified by correlating in time the injections seen at the cameras with measurements made with core diagnostics. Fibers whose views aligned with the camera views and whose outputs are coupled to a visible spectrometer are also used to identify the species of the impurities injected. © 2001 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1321010
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    Reconstruction of time-resolved continuum intensity profile of nonaxisymmetric laser-produced plasma : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 948-951 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A single laser pulse is used to produce weakly nonideal plasma from a metallic aluminum target immersed in a dense neutral gas. The attendant increase in plasma density due to neutral gas confinement precipitates interfacial instability when the gas density exceeds a threshold value. This is accompanied by large fluctuations in the total attenuation of the laser beam by the laser-produced plasma plume. We have developed a new diagnostic method utilizing two mutually orthogonal side-view streak photographs of plasma continuum luminosity at a fixed distance from the target surface. The lack of axial symmetry is overcome by using a front-view luminosity image of the plasma at time zero as a two-dimensional weighting factor. The resulting profile at one time is used as the weighting factor for the next time segment. The time-resolved reconstructed plasma profiles clearly exhibit the near-threshold behavior of Rayleigh–Taylor type instability. © 2001 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1327296
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    Spectroscopy diagnostics of a low temperature laser ablated LiAg plasma plume : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 957-960 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In experiments performed at Sandia National Laboratories, laser-generated LiAg plasma plumes were produced by irradiation of solid targets using a 10 ns pulse duration, 1×108 W/cm2 intensity Nd YAG laser. Time- and spatially resolved (along a direction normal to the target's surface) optical spectra were recorded with a framing spectrograph. The observed spectra consist of optical line emission in Li and Ag atoms. Evidence of ions in the plume is suggested by the presence of a forbidden line and Stark-broadened line shapes. A spectroscopic model based on time-dependent collisional-radiative atomic kinetics that self-consistently calculate the Li and Ag level populations in conjunction with detailed line shapes and radiation transport is used to interpret the data. From this analysis, temperature, density, and ionization in the plume as a function of time and position along the normal to the target surface are extracted. © 2001 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1326899
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    Laser interferometric experiments for the TJ-II stellarator electron-density measurements (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 96-102 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Laser two-color heterodyne interferometry is a proven method to measure electron density in fusion plasmas. Though only used in tokamaks with high electron densities, the idea of also using two-color laser interferometers for stellarators and small machines to replace far-infrared laser interferometers is being proposed. This will lead to low-cost, reliable, and easy to operate diagnostics for electron-density measurements. In this article, we present the interferometric experiments we have used for calibration of a two-color laser heterodyne system for electron-density measurements in the TJ-II stellarator. These experiments have been based on the use of a novel interferometric scheme: the heterodyne/homodyne interferometer. Finally, we describe the interferometer we have installed in the TJ-II stellarator and present the first results on mechanical-vibration subtraction and electron-density measurements with a two-color laser interferometer in a stellarator (TJ-II, Madrid, Spain). © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1333040
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    Real-time measurement of toroidal rotation (abstract) : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 966-966 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: One of the important goals in Columbia's HBT-EP tokamak program is the improvement in the stability of tokamak plasmas by controlling the bulk plasma flow relative to the conducting wall. The method for active plasma flow control in HBT-EP is the application of oscillating resonant magnetic perturbations to oppose the velocity of magnetic islands at the q=2 surface. Real time (10 kHz) feedback control without inserting a material probe necessitates the use of an optical toroidal rotation measurement whose data is available during the shot. This is being accomplished in a novel way by seeding the deuterium plasma with 5%–10% helium and measuring the Doppler shift of the chord-integrated emission of the He II (n=4→3) line at 4686 Å. Since the electron temperature is expected to be about 30 eV at the q=2 surface, helium is not fully stripped. The shift in wavelength is calculated by measuring the change in intensity as the line moves across the passband of an interference filter that varies linearly. Filters with less than 0.2% variation from a perfectly linear slope have been obtained. Fluctuations in the plasma emission are removed by having two detectors observe the same volume of plasma. This is achieved by splitting the optical view with a ‘Y' composed of randomized optical fibers. One detector views the plasma through a filter whose passband has a negative slope and the other channel views it through a positive-slope filter. Systematic differences such as detector sensitivity, amplifier gain, fiber losses, etc. are compensated by normalizing each signal to the signal at a particular reference time. The ratio of signals at two different times does not depend on any detector or circuit characteristic that remains constant. The Doppler shift, relative to the reference time, is a function only of the slope of the filter's transmission. The Doppler shift at the He II impurity emisson line is 0.25 Å for a toroidal rotation of 3 km/s, and the slope of the filter passband is 8%–10% per Å, resulting in a 4% variation in signal level relative to the other channel. © 2001 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1323495
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    Near to backscattered light imaging diagnostic on the National Ignition Facility : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 976-978 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The National Ignition Facility (NIF) is being built at Lawrence Livermore National Laboratory for the U.S. Department of Energy Stockpile Stewardship Program. It will perform experiments for inertial confinement fusion ignition, high energy density science, and basic science. A target diagnostic is being developed for the NIF that will image nearly all the light scattered near the laser axis, (i.e., just outside the laser focusing lens). The diagnostic is called the near backscatter imager (NBI) and is presently required to measure stimulated Brillouin (SBS) and stimulated Raman (SRS) scattering so that the backscatter fraction will be determined with a goal of 30% uncertainty, and SBS and SRS temporal response with ∼200 ps resolution. The NBI will also provide an option to measure temporally resolved spectrum with 50 ps and ∼1 nm resolution. The diagnostic will obtain SBS and SRS scatter plate images with a retro-viewing optical digital camera placed inside the target chamber. Time integrated optical diodes and fast optical diodes will be placed at several locations on the scatter plate to obtain the power and total energy data, as well as a calibration for the scatter plate image at several points. Fibers will be placed near the diodes to provide the option to make spectral measurement. A calibration system using a low power laser, in situ, to illuminate a series of points on the plate while recording the plate image with an external camera system is also being considered. © 2001 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1319601
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    Full aperture backscatter diagnostic for the NIF laser facility (abstract) : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 975-975 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The current schemes for achieving ignition on the National Ignition Facility require efficient coupling of energy from 192 laser beams to the deuterium–tritium fuel capsule. Each laser beam must propagate through a long scalelength plasma region before being converted to x rays (indirect drive) or being absorbed on the capsule (direct drive). Laser-plasma instabilities such as stimulated Brillouin and stimulated Raman scattering (SBS and SRS) will scatter a fraction of the incident laser energy out of the target leading to an overall reduction in the coupling efficiency. It is important to measure the character of this scattered light in order to understand it and to develop methods for reducing it to acceptable levels. We are designing a system called the full aperature backscatter diagnostic with the capability to measure the time-dependent amplitude and spectral content of the light which is backscattered through the incident beam focusing optic. The backscattered light will be collected over about 85% of the full beam aperture and separated into the SBS wavelength band (348–354 nm) and the SRS wavelength band (400–700 nm). Spectrometers coupled to streak cameras will provide time-resolved spectra for both scattered light components. The scattered light amplitude will be measured with fast and slow diodes. The entire system will be routinely calibrated. Analysis of the data will provide important information for reducing scattered power, achieving power balance, and finally achieving ignition. © 2001 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1329656
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    2D turbulence imaging in DIII-D via beam emission spectroscopy : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 988-991 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Two-dimensional measurements of density fluctuations have been performed in DIII-D using the beam emission spectroscopy diagnostic. The 32 spatial channels are arranged to image a 5×6 cm2 (radial×poloidal) region in the plasma cross section, at a nominal 1 cm spatial resolution and separation. The typical decorrelation time, poloidal and radial correlation lengths, as well as a time-averaged flow field plot are obtained from spatial and temporal correlation analyses. A biorthogonal decomposition algorithm is applied to expand the data set into a set of modes that are orthogonal in time and in space, thus providing a simultaneous analysis of the space and time dependencies of fluctuation data. © 2001 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1321739
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    Simulations of beam-emission spectroscopy on Alcator C-Mod (abstract) : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 987-987 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An eight-channel beam-emission-spectroscopy (BES)1 system has been installed on the Alcator C-Mod tokamak, intended for use with a diagnostic neutral hydrogen beam (DNB). Capable of localized measurements from the plasma edge to the plasma core, the BES diagnostic collects light from the first Balmer transition (Hα) resultant from beam/plasma collisions. The Hα line splits into several components whose central wavelengths depend on the viewing geometry, the magnetic field, and the beam energy. This is due to the Doppler shifts from viewing the beam off perpendicular, the different velocities of the three mass components of the beam (H, H2, H3), and the large motional Stark effect. Optimal signal-to-noise requires collecting these components while attenuating all other emission: primarily bremsstrahlung and Dα radiation (from plasma D0/e− collisions). Tunable bandpass filters are thus required. A BES simulation code has been developed that calculates the brightnesses (bremsstrahlung, Dα, Hα) versus wavelength using plasma profile data from the C-Mod MDSplus database,2 a computation of the beam penetration, the viewing and DNB geometries, and bandpass filter characteristics. The model was first used to estimate signal levels and choose the optimal BES bandpass filters; its ultimate purpose is to determine the shot-to-shot tuning requirements of the filters for different discharge conditions. Comparisons of measured and predicted background bremsstrahlung and Dα brightnesses are presented, as are first measurements and calculations of the beam emission. The code is written in the IDL programming language3 utilizing the "widget" graphical user interface. Designed for geometrical and spectral flexibility, it can be modified to simulate other beam diagnostics such as motional-Stark-effect plasma current measurements and charge-exchange recombination spectroscopy, as well as passive diagnostics measuring chord-averaged spectral emission. © 2001 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1326010
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    Apparatus for in situ x-ray absorption fine structure studies on catalytic systems in the energy range 1000 eV〈E〈3500 eV (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3260-3266 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new apparatus for in situ x-ray absoprtion fine structure measurements in the medium energy range of 1000–3500 eV has been developed. Measurements can be performed in a gaseous environment (max. pressure 1 bar) at temperatures ranging from 80 to 750 K. Pre-treatments can be performed at 5 bar and 750 K in the same cell, after which XAFS measurements can be done without exposing the sample to ambient air. In a modular set-up several detector systems can be used: fluorescence detection using a gas proportional counter, a photodiode or a microstrip detector. All detectors are highly integrated into the cell, gaining solid angle for detection. Electron yield detection can be used simultaneously using conversion electron yield or total electron yield. The performance of the new apparatus is demonstrated by a study of the K edge of Al in Zeolite Beta. The Al content is as low as 2 wt%. It will be shown that octahedral framework Al is formed while adding gaseous water at room temperature after ammonia removal (at 450 °C) of an NH4-Beta. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1287634
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    Log spiral of revolution highly oriented pyrolytic graphite monochromator for fluorescence x-ray absorption edge fine structure (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3267-3273 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have constructed an x-ray monochromator based on a log spiral of revolution covered with highly oriented pyrolytic graphite. Such a monochromator is used for obtaining x-ray absorption edge fine structure by the fluorescence method, and is particularly useful for measuring the fine structure of dilute element A in a concentrated matrix of element B, where B is to the left of A in the Periodic Table. Using the log spiral monochromator, we measure good Cr x-ray fine structure in an alloy of 1% Cr in a V matrix, whereas the corresponding spectrum is severely distorted by the V background if nonmonochromatized fluorescence is used. We also obtain excellent rejection of Mn fluorescence relative to Cr fluorescence in a Cr80Mn20 alloy, and can tune the monochromator such that the entire Mn step height is significantly smaller than the Cr x-ray absorption edge fine structure oscillations for this system. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1287753
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    Active length control of two phase locked CO2 lasers with a digital signal processor (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3298-3305 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Two CO2 lasers are phase locked together by injection locking, where radiation between the two lasers is exchanged using a copper prism as a beam folding device in the resonators. Extraction of the output radiation is achieved by a common output coupler. As this method is only utilizing reflective optics (except for the output coupler), it is also practical as a technique for phase-locking lasers with powers in the multikilowatt range. Single frequency oscillation is only achieved if the lengths of both resonators are within a so-called locking range. This can only be fulfilled if the length of one resonator is actively controlled. The method of detection of the phase difference between the lasers and actively controlling the length of one resonator is presented as well as its implementation into a digital signal processor. Stable phase locked operation is achieved and proved through detection of twice the intensity in the far field in the phase-locked regime. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1288263
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    Novel device for the generation of controlled prepulses in a Ti:sapphire laser amplifier chain (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3313-3316 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: For the generation of a well defined prepulse in high intensity laser plasma interactions, we implemented a newly developed prepulse device into a multiterawatt titanium:sapphire amplifier system. The temporal delay between the prepulse and main pulse is variable between −350 ps and + 100 ps. If the laser pulse is focused on a target, the spatial overlap of the two pulses in the focal point is corrected automatically over the entire range. It is possible to attenuate the main pulse as well as the prepulse independently of each other by more than one order of magnitude. We investigated the dependence of the Kα emission of the laser produced plasma of a silicon target on the delay between the prepulse and main pulse. An increase of the yield of the Kα emission by a factor of 2 for a temporal delay of several tens of picoseconds between the prepulse and main pulse was measured. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1287049
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    A technique for accurate measurements of ion beam current density using a Faraday cup (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3326-3330 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have performed measurements of the spatial distribution of current in various alkali and reactive ion beams over the energy range 5–600 eV using a Faraday cup. Ion beam current densities have been extracted from these measurements using a simple deconvolution procedure. Our results reveal that the beams are Gaussian in shape with a constant width, σ, for energies greater than approximately 75 eV and for all ion species investigated. This width is consistent with that determined from the distribution of oxygen on a Cu(001) crystal after an O+ ion beam deposition, measured using Auger electron spectroscopy. Using the measurement technique outlined in this article, together with the linear relationship between current density and Faraday cup current, it is possible to determine the beam current density using a single current measurement. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1287635
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    Plasma generation and confinement in a toroidal magnetic cusp (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3351-3361 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The first measurements of plasma parameters in a discharge created by electron cyclotron resonance heating in a toroidal cusp configuration are discussed along with the predictions of particle orbits and confinement from a guiding center model. The configuration appears to be suitable for basic investigations of the physics of plasma flows and instabilities around a magnetic null, hence of magnetic reconnection. © 2000 American Institute of Physics.
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    Simple and inexpensive current-driven magnetic multipole plasma homogenizer (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3373-3376 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Magnetic multipole plasma confinement geometries employing permanent magnets are commonly used to confine laboratory plasmas and improve uniformity. Here we describe the design and operation of a particularly simple and low-cost kind of current-driven multipole system that makes use of a similar magnetic field structure but does not require permanent magnets. The magnetic field is generated by current carrying wires attached to the inside wall of a cylindrical supporting structure to provide a magnetic field resembling that of permanent multipole magnetic homogenizers. We demonstrate the use of the current-driven homogenizer to improve the uniformity of the radial density profile of a vacuum arc generated metal plasma. Our configuration of metal plasma gun, macroparticle filter, and current-driven homogenizer was used for thin film deposition, and was able to produce a relatively homogeneous film thickness profile while maintaining a deposition rate comparable to that at the peak point of the freely expanded beam at the same location. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1287751
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    Simultaneous soft x-ray emissivity profile measurements in poloidally separate locations of the Alcator C-Mod edge plasma (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3385-3390 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Two high resolution edge x-ray imaging diagnostics have been installed in the Alcator C-Mod tokamak. One array measures the radial soft x-ray emissivity profiles at the top of the plasma with 1.2 mm radial resolution, mapped along flux surfaces to the midplane, whereas the other measures the radial soft x-ray emissivity profiles at the outboard edge with 1.5 mm radial resolution mapped to the midplane. The two diagnostics measure the chord brightness profiles, which are then inverted to get soft x-ray emissivity simultaneously with a 12 μs sampling time. This allows us to determine if the soft x-ray emissivity, and therefore the fluorine density, is constant on a flux surface during steady state high confinement mode conditions, as well as during fast transient edge events, such as edge localized modes or transitions from the high confinement mode to the low confinement mode. Measurements are presented showing that the soft x-ray emissivity is not constant on a flux surface, but instead shows a large poloidal variation, contrary to what is assumed in the inversion routine. The effects of the poloidal variation on the inversion accuracy are estimated numerically. It is found that the emissivity is systematically overestimated at the top, and underestimated at the outboard edge, by less than 15%. The width of the x-ray emissivity pedestal is accurate to within 15%, and the location of the pedestal is accurate to within 1 mm. Measurements showing a poloidal propagation delay for the onset of the transition from high confinement mode (H mode) to low confinement mode (L mode) are also presented. © 2000 American Institute of Physics.
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    A new method for searching for free fractional charge particles in bulk matter (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3409-3414 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present a new experimental method for searching for free fractional charge in bulk matter; this new method derives from the traditional Millikan liquid drop method but allows the use of much larger drops, 20–100 μm in diameter, compared to the traditional method that uses drops less than 15 μm in diameter. These larger drops provide the substantial advantage that it is then much easier to consistently generate drops containing liquid suspensions of powdered meteorites and other special minerals. These materials are of great importance in bulk searches for fractional charge particles that may have been produced in the early universe. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1308268
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    Triode electron bombardment evaporation source for ultrahigh vacuum thin film deposition (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3444-3450 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new electron bombardment evaporation source for ultrahigh vacuum (UHV) thin film deposition is presented. It is based on an original electrodes configuration (modeled on that of a vacuum triode) featuring, besides anode and filament, a biased grid acting as a power modulator. The presence of a polarized grid helps to minimize space charge problems, to improve electron focusing and to fine control the dissipation on the evaporating material, governing the sublimation rate. The electrodes geometry was optimized by studying electron trajectories and electrical field distribution in the electrodes zone with ray-tracing analysis. Mechanical solutions and electrodes geometry were designed to ensure low outgassing and UHV compatibility, as well as to facilitate maintenance and source cleaning. The evaporator is water cooled and a mechanically operated shutter is present. The working principles and the technical details are presented together with operating data and evaporation performances. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1287624
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    Multichannel ellipsometer for real time spectroscopy of thin film deposition from 1.5 to 6.5 eV (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3451-3460 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A rotating polarizer multichannel ellipsometer has been optimized for operation well into the ultraviolet (UV) spectral range. With this instrument, 132 spectral points in the ellipsometric parameters (ψ, Δ) over the photon energy range from 1.5 eV (827 nm) to 6.5 eV (191 nm) can be collected in a minimum acquisition time of 24.5 ms, corresponding to one optical cycle of the rotating polarizer. Averages over two and 80 optical cycles (obtained in 49 ms and 1.96 s, respectively) give standard deviations in (ψ, Δ) of less than (0.04°, 0.08°) and (0.007°, 0.015°), respectively, for the energy range from 3.5 to 6.0 eV, as determined from successive measurements of a stable thermally oxidized silicon wafer. Key modifications to previous instrument designs include: (i) a tandem in-line Xe/D2 source configuration for usable spectral output from 1.5 to 6.5 eV; (ii) MgF2 Rochon polarizers for high transmission in the UV without the need for optical activity corrections; (iii) a spectrograph with a grating blazed at 250 nm and two stages of internally mounted order-sorting filters; and (iv) nonuniform grouping of the pixels of the photodiode array detector for a more uniform spectral resolution versus photon energy, with energy spreads per pixel group ranging from 0.02 eV at 1.6 eV to 0.05 eV at 5.1 eV. As an example of the application of this instrument, results of real time spectroscopic ellipsometry studies are reported for the deposition of an amorphous silicon nitride thin film by radio-frequency magnetron sputtering onto a silicon wafer substrate. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288260
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    Langmuir–Taylor surface ionization of alkali (Li, Na, K) and alkaline earth (Ca, Sr, Ba) atoms attached to helium droplets (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3480-3484 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A beam of superfluid helium droplets (HeN, N(approximate)104) doped with alkali and alkaline earth atoms is detected by Langmuir–Taylor surface ionization. We measured detection efficiencies and time constants as a function of the temperature of a hot rhenium surface. Compared to results on free K, Na, and Ba atoms we find practically no differences in the detection properties; apparently the helium host environment does not significantly influence the mechanism of surface ionization. In addition, data for Li, Ca, and Sr on detection probabilities and residence times of the ions on the hot rhenium surface will be presented for the first time. Time constants and desorption energies are extracted; for alkaline earth atoms the latter are found to be significantly higher compared to the desorption of the alkalis. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287750
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    Laser induced fluorescence measurements of dissolved oxygen concentration fields near air bubble surfaces (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3494-3501 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This article describes a laser-induced fluorescence (LIF) technique for measuring dissolved oxygen concentration gradients in water near the surface of an air bubble. Air bubbles are created at the tip of a needle in a rectangular bubble column filled with water that contains pyrenebutyric acid (PBA). The fluorescence of the PBA is induced by a planar pulse of nitrogen laser light. Oxygen transferring from the air bubble to the deoxygenated water quenches the fluorescence of the PBA. Images of the instantaneous and two-dimensional fluorescence field are obtained by a UV-intensified charge-coupled device (CCD) camera. Quenching of fluorescence intensity is determined at each pixel in the CCD image to measure dissolved oxygen concentration. Two-dimensional concentration fields are presented for a series of measurements of oxygen transfer from 1.6 mm bubbles suspended on the tip of a needle in a quiescent fluid. The images show the spatially varying concentration profiles, gradients, and boundary layer thicknesses at positions around the bubble surfaces. These direct and local measurements of concentration behavior within the mass transfer boundary layer show the potential of this LIF technique for the development of general and mechanistic models for oxygen transport across the air–water interface. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287341
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    An equipment for three-dimensional spatially resolved gas analysis (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3513-3521 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The apparatus described is able to measure three-dimensional temperature and partial pressure distributions in gas mixtures with a spatial resolution better than 0.5 mm. The measurements are performed in a well defined laminar gas flow in a duct of rectangular cross section. The gas mixture is sampled locally with a quartz tube orifice leak movable in three dimensions. Mass spectrometry is used for partial pressure measurements. The total pressure in the duct can be regulated in the range 50–760 Torr and the gas temperature can be varied between room temperature and 500 °C. The apparatus is primarily designed for studies of the distribution of reactants and products over catalytic surfaces. Because of the well defined gas flow in the duct the partial pressure distributions of reactants and products over the catalytic surface can be calculated with good accuracy. By comparing calculated pressure distributions to measured ones the local reaction rate on the catalytic surface as well as the pressures of reactants and products at the surface can be obtained. As an example it is shown how the hydrogen distribution over a platinum surface exposed to a mixture of hydrogen, oxygen, and argon can be used to calculate the local water formation rate on the platinum surface. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1287342
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    A newly developed low drift fast response salinity meter (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3539-3542 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Here a new conductivity probe, which is basically a stainless steel tube with a plastic plug with a hole, plugged in one end, is described. The tube is externally insulated and the other electrode is (usually earthed) a metallic slab fixed in the fluid. The electronic used is of a conventional type and uses a 1 kHz signal whose amplitude is modulated by the conductance across the probes terminals. The signal is amplified, rectified, and filtered. The probe is different from the conventional probes, in that the fluid is sucked through the small hole in the probe tip, and only through the fluid in the tip can an electric current flow. Hence, the output and the dynamic response depend, respectively, on the conductivity of the small volume of the fluid in the tip, and how fast it can be replaced. Tests on this and other types of probes, show that this probe has almost no drift and has a satisfactory dynamic response. Probes with different tip geometries have also been tested and show that the frequency response of the probe (typically 200 Hz) does not change significantly. Possible adaptation of such a probe for oceanographic measurements will be discussed. The author has successfully used such a system for laboratory study of turbulence in stratified fluids. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287620
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    A high-bandwidth electrical waveform generator based on an aperture-coupled stripline (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3559-3566 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An electrical waveform generator based on an aperture-coupled stripline is described. The device is a four-port electrical directional coupler consisting of two striplines coupled through an aperture in their common ground plane. Replacing the aperture layer of the device can produce arbitrarily shaped electrical waveforms with 100 ps structure over a pulse envelope of several nanoseconds. A numerical solution of the telegraph equations using the method of characteristics is used to model and design devices. Excellent agreement is obtained between the model and device performance. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288254
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    Highly accurate smoothing filter (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3570-3578 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An iterative filter for the smoothing of degraded line shapes with Gaussian noise, and a signal to noise ratio defined in a wide interval 20–∞ is presented. The smoothed line shape shows errors below 2% in its height and width parameters with regard to the true values used in the simulation. The filter reduces the Gaussian noise to less than a half. In the tests carried out with a PC computer, the new filter proved that the original line shape for a linewidth of 5–30 is better recovered than the Savitsky–Golay filter. The application of the procedure only involves the use of the linewidth parameter of the degraded peak which simplifies the smoothing process. The filter follows two basic operations: first, an oversmoothing is applied to the degraded line and second, an iterative enhancement on the oversmoothing spectrum is made. The resulting spectrum of these two operations is compared with the degraded line by a least squares fitting method. When the filter is used in a simplified version, it is useful not only to determine very overlapped lines in a degraded spectrum, but also to calculate the background in an experimental spectrum. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287040
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    Ultrasonic imaging, particle detection, and V(z) measurements in molten zinc using focused clad buffer rods (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3579-3586 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Ultrasonic imaging, particle detection, and V(z) measurements have been performed using focused clad buffer rods in molten zinc at temperature more than 600 °C. The focused ultrasonic waves are generated by a spherical or cylindrical acoustic lens which is fabricated at the end of the clad buffer rod. In order to evaluate its focusing ability, several experiments are carried out at 10 MHz in a pulse-echo mode. The lateral resolution at the focus of the spherical acoustic lens in molten zinc is quantitatively examined and compared with that in water using a thin stainless wire with a diameter of 380 μm. High resolution ultrasonic imaging is carried out by the common C-scan technique. The signal-to-noise ratio of the reflected signals from the flat sample surface at the focus is better than 35 dB. Ultrasonic images are obtained from the amplitude and time delay variations of the reflected signals. An attempt has also been made to detect particles suspended in molten zinc. Backscattered signals from particles are clearly visible at the focal region of the lens. For quantitative materials evaluation, V(z) curve measurements are performed using both spherical and cylindrical surface lenses and the leaky surface acoustic wave velocity of a ceramic (SiC) plate immersed in molten zinc is successfully determined. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287041
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    The use of pressure controlled Fabry-Pérot interferometer with linear scanning of data for Brillouin-type experiments (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2988-2991 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The article presents results from work with Fabry-Pérot interferometers in Brillouin laser light scattering experiments, where optical signals of very low level intensity are observed. The information presented here can be useful in other types of optical experiments where scanning in the Fabry-Pérot interferometer spectral range has to be used. In such situations the shape of spectral lines as well as their relative distances can be detected. The key to the solution presented here is the use of a silicon-membrane pressure sensor coupled to a pressure chamber. It makes it possible to view spectral lines equally spaced after nonlinear flow of air from a chamber where the Fabry-Pérot interferometer is placed. Linear scanning in the spectral range equal to a frequency of about 150 GHz is possible. The method can be applied to Fabry-Pérot's etalons, very frequently produced some years ago. Now it should find new fields of application, in a simple and cost effective way, in student laboratories as well as in other research institutions. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1304872
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    dc and ac optical nulling bridges for sensitive transmittance measurements (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2995-3003 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present a formal comparison between dc and ac nulling optical bridges. We consider their performance in monitoring over long periods of time (several minutes), small and slow (in a time scale of seconds) changes in transmittance of an optical component. We consider two fundamentally different ac optical bridges (OB), an amplitude modulated optical bridge (AM-OB), and a switching optical bridge (Sw-OB). For each OB, we derive a general expression for the minimum detectable change in transmittance (|ΔT|min), taking into account all the important noises. It is found that under optimum conditions the dc- and AM-OB have similar detection limits imposed by the 1/f noise of the photodetectors. It is shown that the Sw-OB can in principle overcome the 1/f noise of the detector and approach the shot-noise limit; however, it is sensitive to switching device imperfections (to first order in smallness), which could easily prevent achieving a detection limit below the 1/f noise. It is also shown that the Sw-OB has intrinsic advantages over the dc- and AM-OB for its use in remote sensors. It can eliminate more efficiently noise induced along the propagation of light from the sensing point to the photodetector. We conclude that when using low power optics (P≤1 mW) and considering a bench instrument, the dc- and AM-OB can be used for a target resolution down to |ΔT|min(approximate)10−5–10−6. The Sw-OB optical bridges should be chosen if |ΔT|min(approximate)10−6–10−8 is to be attempted. In any case, strict conditions are to be met before considering approaching the detection limits imposed by electronic noises. These conditions are discussed in detail. In particular, atmospheric isolation will be needed in general below |ΔT|min(approximate)10−4. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1305509
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    Design of a scanning atom probe with improved mass resolution (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3016-3023 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A design for a high mass resolution scanning atom probe is described, which utilizes a two-conductor microelectrode held at 10–100 μm from the specimen. Field evaporation pulses are applied to the part of the counter-electrode closest to the specimen, while the output is maintained at ground. If the gap between the two conductors is small, field evaporated ions pass through the microelectrode while the pulse voltage is essentially constant, and thus the resultant spread in ion energies is small and the mass resolution in time-of-flight mass spectrometry is correspondingly improved. Initial results indicate improvements of 4–5 times over the mass resolution obtained with a simple counter electrode. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1304877
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    Direct imaging of highly charged ions in an electron beam ion trap (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3050-3058 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have directly observed the ion cloud distribution in an electron beam ion trap using visible and ultraviolet fluorescence from lines in the ground term of Ar13+, Xe31+ and Xe32+ ions. Using a gated intensified charge coupled device camera, we have the capability to measure both static and dynamic ion cloud distributions. The images provide information about the trapped highly charged ions which is difficult to obtain by other methods. To demonstrate the usefulness of the technique, we took images of static ion clouds under different conditions and compared the distributions to a simple model. We also recorded time resolved images which show that we can monitor the relaxation of the ion cloud toward equilibrium when the trapping conditions are suddenly changed. The information provided by such measurements can be used to improve models of ion cloud dynamics and, combined with modeling, these techniques can help improve measurements of atomic data using electron beam ion traps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1305521
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    Spectral resolution for a five-element, filtered, x-ray detector array using the method of Backus and Gilbert (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3072-3079 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The generalized method of Backus and Gilbert (BG) is described and applied to the inverse problem of obtaining the spectrum from a five-channel, filtered array of x-ray detectors. This diagnostic is routinely fielded on the Z facility at Sandia National Laboratories to study soft x-ray photons (∼100–2300 eV), emitted by high density Z-pinch plasmas. The BG method defines spectral resolution limits on the system of response functions that are in good agreement with a classical unfold method, based on a histogram representation of the source spectrum. The resolution so defined is independent of the source spectrum. For noise-free, simulated data the BG approximating function is also in reasonable agreement with the source spectrum (150 eV blackbody) and the unfolded spectrum. This function may be used as an initial trial function for iterative methods or a regularization model.© 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1304869
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    Correlation-based phase noise measurements (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3085-3091 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In the characterization of the phase noise of a component, it is common practice to measure the cross-spectrum density at the output of two phase detectors that simultaneously compare the component output signal to a common reference. This technique, which is based on correlation and averaging, allows the rejection of the phase detector noise. On the other hand, it is known that the interferometer exhibits lower noise floor and higher conversion gain than other phase detectors suitable to radio-frequency and microwave bands. Thus, we experimented on an improved instrument in which the phase noise of a component is measured by correlating and averaging the output of two interferometers. The measurement sensitivity, given in terms of noise floor, turns out to be limited by the temperature uniformity of the instrument, instead of the absolute temperature T. This feature makes the instrument suitable to investigate the spectrum Scursive-phi(f) of phase fluctuations below kBT/Po, i.e., the thermal energy kBT referred to the carrier power Po. The described method is suitable to the implementation of instruments in a wide frequency range, from some 100 kHz to 40 GHz and beyond. In principle, this method can also be exploited for the measurement of amplitude noise. Theory and experimental proof are given. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1304871
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    Microscope system for use in high magnetic fields (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3108-3110 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe a microscope system, with video output, that operates within the confines and the high magnetic field of the 195 mm wide bore, 20 T resistive magnet at the National High Magnetic Field Laboratory. The accessibility of this system allows the user to vary the field of view and focus in situ and to produce images with up to 10 micron resolution. It allows for temperature regulation of samples to within 1 °C and in situ sample manipulation. Images of a biological specimen, Xenopus laevis embryos, in high magnetic field are presented. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1304880
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    Reflection surface x-ray diffraction patterns: k-space images (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3132-3137 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: For the past two decades, x-ray diffraction has been utilized for surface structural determination. Unlike reflection high-energy electron diffraction (RHEED) which is a complicated dynamical scattering process, x-ray surface analysis is simple and straightforward due to the kinematic nature of x rays. Using high brilliance x rays from an undulator beamline and a highly sensitive charge coupled device detector, we successfully observed RHEED-like x-ray diffraction patterns. The patterns were recorded during the preparation of Si(111)-(7×7), transformation to Ge/Si(111)-(5×5) and Ge growth. Also, simultaneous measurements of x-ray reflectivity and crystal truncation rods are shown feasible with this technique. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1305512
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    Miniature rotatable vacuum cell for low-temperature thermal measurements in high magnetic field (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3148-3150 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe a miniature vacuum cell allowing thermal measurements in liquid He medium. The small size of the cell allows rotation in the limited space of high field magnets. A useful accessory for cell evacuation is also described. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1305507
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    Characterization of coatings on magnetic metal using the swept-frequency eddy current method (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3161-3167 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A measurement technique using the swept-frequency eddy current (SFEC) method for determining the thickness, conductivity, and permeability of metallic coatings on metal substrates for the case when either coating, substrate, or both are magnetic was developed. This technique involved using the empirically determined permeability of the metals as input to the model calculation. This technique is demonstrated for nickel layers (25–200 μm) over copper substrates, copper layers (25–200 μm) over nickel substrates, and zinc layers (50–400 μm) over steel substrates. The electrical impedance was measured for air-core coils in the presence and absence of the layer using a 4194A Hewlett–Packard impedance analyzer. An analytic closed-form solution for calculating the impedance of a cylindrical air-core probe over a layered metallic half-space is presented. The determination of coating thickness and conductivity and permeability of the metals is based on the comparison of the data taken with air-core coils and theoretical calculation that using the closed-form solution developed. Most of the cases studied show experiment and theory agreeing fairly well, within 10%, with no adjustable parameters. The physical phenomena of eddy currents interaction with the coated magnetic metals are also discussed. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1304862
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    Precision microwave dielectric and magnetic susceptibility measurements of correlated electronic materials using superconducting cavities (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3151-3160 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We analyze microwave cavity perturbation methods, and show that the technique is an excellent, precision method to study the dynamic magnetic and dielectric response in the GHz frequency range. Using superconducting cavities, we obtain exceptionally high precision and sensitivity for measurements of relative changes. A dynamic electromagnetic susceptibility ζ˜(T)=ζ′+iζ″ is introduced, which is obtained from the measured parameters: the shift of cavity resonant frequency δf and quality factor Q. We focus on the case of a spherical sample placed at the center of a cylindrical cavity resonant in the TE011 mode. Depending on the sample characteristics, the magnetic permeability μ˜, the dielectric permittivity ε˜=ε′+iε″, and the complex conductivity σ˜=σ′+iσ″ can be extracted from ζ˜H. A full spherical wave analysis of the cavity perturbation indicates that: (i) In highly insulating samples with dielectric constant ε′∼1, the measured ζ˜H∼χ˜M, enabling direct measurement of the magnetic susceptibility. The sensitivity of the method equals or surpasses that of dc superconducting quantum interference device measurements for the relative changes in magnetic susceptibility. (ii) For moderate ε˜ and conductivity σ˜, ζ˜H∝ε˜+iωσ˜/ε0−1, thus enabling direct measurement of the sample dielectric constant ε˜, even though the sample is placed in a microwave magnetic field. (iii) For large σ we recover the surface impedance limit. (iv) Expressions are provided for the general case of a lossy dielectric represented by ε˜+iωσ˜/ε0. We show that an inversion procedure can be used to obtain ε˜+iωσ˜/ε0 in a wide range of parameter values. This analysis has led to the observation of new phenomena in novel low-dimensional materials. We discuss results on magneto dynamics of the three-dimensional (3D) antiferromagnetic state of the spin chain compound Sr2CuO3. In dielectric susceptibility measurements in Sr14Cu24O41, we directly observe a dielectric loss peak. Dimensional resonances in the paraelectric material SrTiO3 are shown to occur due to the rapid increase of dielectric constant with decreasing temperature. The cavity perturbation methods are thus an extremely sensitive probe of charge and spin dynamics in electronic materials. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1305519
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    The construction of a gas aggregation source for the preparation of size-selected nanoscale transition metal clusters (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3178-3183 
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    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The design and operation of a gas aggregation source is described. The source combines the attributes of high-temperature operation (enabling preparation of transition metal clusters), mass selection, ultrahigh vacuum compatibility, and transportability. This makes it ideally suited to in situ studies such as scanning tunneling microscope or synchrotron radiation experiments. Data are presented to illustrate the performance of the source; recent results obtained in synchrotron radiation studies are highlighted. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1304868
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    A scanning dual-capillary-tube viscometer (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3188-3192 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The present study introduces the concept of a new scanning dual-capillary-tube viscometer (SDCV) for viscosity measurements of both Newtonian and non-Newtonian fluids, including whole blood, over a wide range of shear rates. The flow rate and pressure drop measurements that are usually required for the operation of a capillary-tube viscometer are replaced with two measurements of liquid-height variation with time. Using a charge-coupled device sensor array, one could measure the variation of fluid levels at each riser tube, h1(t) and h2(t), from which the test fluid viscosity was calculated. The feasibility and accuracy of the SDCV technique has been demonstrated for a standard-viscosity oil and for bovine blood by comparing results against established viscosity measurement techniques. A power-law viscosity model was used to correlate the data for the latter. The dual-capillary-tube viscometer extends the shear rate range as low as 0.1 s−1 for both the viscosity of mineral oil (9.9 cP at 25 °C) and bovine blood with 3% ethylenediaminetetraacetic acid at room temperature. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1305513
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    A medium-frequency interferometer for studying auroral radio emissions (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3200-3206 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An interferometer for use between 2.5 and 3.0 MHz has recently been developed for the purpose of studying auroral radio emissions. The instrument consists of an array of 17 antennas, associated electronics for amplitude and phase measurements, and computer hardware for instrument control and data recording. In its standard operational mode, the instrument sweeps from 2.5 to 3.0 MHz in 1 kHz steps every 1.5 s. The intensity of the received signal and the phase at each antenna is measured for each 1-kHz-wide bin. These data can be used to produce spectrograms showing the intensity of the received signal versus frequency and time and for determining the direction of arrival for any signal in the instrument bandwidth. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1305518
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    Adjustable resonant cavity for measuring the complex permittivity of dielectric materials (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3207-3209 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An adjustable resonance cavity was developed to measure the complex permittivity of dielectric materials. The cavity has an inner diameter of 16.400 cm and an inner height of 2.54 cm. The aluminum stationary wall holder was positioned about 10.8 cm above the top of the cavity. It was fixed into place by three 1.27-cm-diam linear shafts. By suspending from the wall holder, the movable wall moved vertically by sliding on 1.27 cm bore-closed ball bushings. By turning a 1 in.-12 nut, the movable wall could be positioned so that the cavity height equaled the height of the sample. Therefore, this enables the measurement of the permittivity of samples with heights between 0.88 and 1.91 cm and radius between 1.27 and 3.18 cm. The complex permittivity of the sample was calculated based upon the sample dimensions, central frequency of TMono modes, and Q factor of the resonance curve using an exact solution. The complex permittivity was measured at the three lowest modes, where the frequency span is 1–4 GHz. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1304865
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    Six-degree-of-freedom displacement measurement system using a diffraction grating (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3214-3219 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Six-degree-of-freedom displacement measurement systems are applicable in many fields: precision machine control, precision assembly, vibration analysis, and so on. This article presents a new six-degree-of-freedom displacement measurement system utilizing typical features of a diffraction grating. It is composed of a laser source, three position sensitive detectors, a diffraction grating target, and several optical components. Six-degree-of-freedom displacement is calculated from the coordinates of diffracted rays on the detectors. A forward and an inverse problem were solved to compute the full pose of an object through kinematic analysis. The experimental results show that the measurement system had a maximum error of ±10 μm for translation and ±0.012° for rotation. The repeatability is about 10 μm for translation and 0.01° for rotation. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1305816
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    Femtoampere current reference stable over atmospheric temperatures (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3231-3232 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Calibration of ultralow current ammeters deployed in atmospheric ion counters requires stable current references operating at high source impedance. Using standard precision components, this current reference generates equal bipolar currents of nominally ±500 fA, cyclically for 32 s each. The currents were found to be stable to 2 fA over the temperature range −20 to 20 °C, typical of atmospheric conditions. The output current is delivered via a capacitor, and by arranging for the capacitor to be guarded at ground potential when the system is not generating a current, the reference can be permanently connected to an electrometer with minimal leakage. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1304859
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    Current mode Schmitt trigger for a phototransistor/resistor detector (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3233-3233 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A current mode Schmitt trigger for a phototransistor/resistor detector is presented. It can be successfully operated with a 1.5 V power supply. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1304860
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    Elliptical x-ray microprobe mirrors by differential deposition (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2635-2639 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A differential coating method is described for fabricating high-performance x-ray microfocusing mirrors. With this method, the figure of ultrasmooth spherical mirrors can be modified to produce elliptical surfaces with low roughness and low figure errors. Submicron focusing is demonstrated with prototype mirrors. The differential deposition method creates stiff monolithic mirrors which are compact, robust, and easy to cool and align. Prototype mirrors have demonstrated gains of more than 104 in beam intensity while maintaining submilliradian divergence on the sample. This method of producing elliptical mirrors is well matched to the requirements of an x-ray microdiffraction Kirkpatrick–Baez focusing system. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150668
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    A simple microbeam profiling technique for x-ray optics (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2640-2643 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Enhancement of the quality of images or maps obtained using micro x-ray fluorescence spectrometry requires knowledge of the flux distribution profile of the primary x-ray beam. A simple procedure based on a wire scan was developed for the determination of an x-ray microbeam profile. This technique is simple and can be used for a given excitation/detection geometry without any change in spectrometer configuration. However, the result of such a scan is a convolution of the beam profile with the shape of the wire. To restore the actual distribution of photon flux density, a nonlinear least-squares procedure was adapted to model the profile using a parametric function to describe the flux distribution. Among the algorithms tested, a sigmoid function was found to be the best for describing the beam profile. The results of calculations were verified by measurements using a charge coupled device camera. Reasonably good agreement was obtained between the two different techniques. The results of this work confirmed that a wire scan combined with a mathematical restoration procedure is useful for describing the actual profile of an x-ray microbeam created using a pinhole collimator. An advantage is that the microbeam profile is calculated at the location of the measured samples. The results indicated that the χ2 value could be used to select the optimum function to describe the microbeam profile. The procedure can also be used to evaluate the quality of a pinhole collimator. We plan to use measured microbeam profiles in combination with mathematical procedures to improve the spatial resolution of linear scans of patterned samples. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150669
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    Doppler-free modulation transfer spectroscopy of rubidium 52S1/2–62P1/2 transitions using a frequency-doubled diode laser blue-light source (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2655-2662 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A frequency-doubled diode laser spectrometer in the blue-wavelength region with a continuous-frequency tuning range of up to ∼7 GHz has been developed, comprising a powerful fundamental light source based on a master/slave laser combination coupled with a KNbO3 crystal for second-harmonic generation in a power-enhancement cavity. It has been employed for the observation of saturated absorption spectra in 52S1/2–62P1/2 hyperfine transitions of atomic rubidium with the aid of a modulation transfer spectroscopic technique, and also the frequency stabilization to one of them has been demonstrated, suggesting the possibility of the establishment of a precision optical frequency marker in the blue range. A relative stability of better than 2.8×10−10 is estimated based on the locked error signal in the preliminary stabilization. With a further study of the frequency instability and uncertainty, in addition to supplementary improvements of apparatus, one may expect a realization of a stabilized laser in the blue-spectral domain. Details of the developed blue-light source are described and the demonstrated results of the rubidium spectroscopy are also described and discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150672
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    Michelson interferometry with 10 pm accuracy (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2669-2676 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We demonstrate a new heterodyne Michelson interferometer design for displacement measurements capable of fringe interpolation accuracy of one part in 36 000. Key to this level of accuracy are the use of two acousto-optic modulators for heterodyne frequency generation and digital signal processing demodulation electronics. We make a direct comparison of our interferometer to a commercial interferometer based on a Zeeman-stabilized laser, and show that the residual periodic errors in ours are two orders of magnitude lower than those in the commercial unit. We discuss electronically induced optical cross talk and optical feedback as sources of periodic error. Our new interferometer is simple, robust, and readily implemented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150715
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    Ultrasmall volume refractive index detection using microinterferometry (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2684-2692 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A microinterferometric backscatter detector (MIBD) has been developed to perform subnanoliter volume refractive index measurements using a simple, folded optical train based on the interaction of a laser beam and a fused silica capillary tube. Positional changes of the interference pattern extrema (fringes) allow for the determination of Δn at the 10−7 level, corresponding to 5.3 pmole or 0.48 ng of solute, when thermal noise is controlled at 8×10−3 °C. MIBD is relatively path-length insensitive for capillaries ranging in inner diameter from 75 to 775 μm, allowing a large range of detection volumes, from 350 pL to 40 nL, to be produced. A theoretical model of the microinterferometric backscatter detector has also been developed and evaluated and has been found to be in agreement with experimental data. This model indicates increased sensitivity of the instrument as the wavelength of the probe beam and the wall thickness of the capillary tube are reduced. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150675
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    High-energy neutral particle measurement system in the large helical device (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2698-2703 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The development of a high-energy neutral particle measurement system for ion temperature measurements and high-energy particle confinement analysis during neutral beam injection and ion cyclotron resonance frequency heating experiments in the large helical device (LHD) is described here. We have been improving the time-of-flight neutral particle analyzer for the LHD which had been developed in ENEA Frascati. The control and data acquisition systems were designed to be suitable for long discharges in the LHD. The horizontal and vertical movable stage is prepared to investigate pitch-angle distribution and loss cone. We have resolved many difficulties at installation, for example, the strong leakage magnetic field from the LHD and the limitations of magnetized materials near the LHD, the quench of the superconducting magnetic field, the narrow viewing port, and the fully remote control system. The preliminary results in plasma experiments are also described here. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150677
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    Detection efficiency of a channel electron multiplier for low energy incident noble gas ions (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2704-2709 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The absolute detection efficiency of a continuous channel electron multiplier (DeTech 407-EIC) has been measured for the noble gas ions He+, Ar+, and Xe+, with energies up to 4.9 keV. For all ions, the detection efficiency initially rises linearly as a function of velocity. Our results and a reanalysis of literature data show that the threshold velocity below which a multiplier does not respond to impinging ions cannot be regarded as independent of the ion's atomic number, Z, as previously reported. Instead, the threshold velocity is proportional to Z−c. The experimentally obtained efficiency-versus-velocity curves for our detector have been analyzed in the region of linear increase. The resulting expression for the detector efficiency, cursive-epsilon, is a function of the ion's atomic number and velocity, v, and can be written as cursive-epsilon(v,Z)=a(v−b/Zc)Zn, with a, b, c, and n being constants. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150678
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    A sensitive dispersion interferometer with high temporal resolution for electron density measurements (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2710-2715 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A dispersion interferometer with a sensitivity of up to 10−4 fringe shifts and a time resolution of about 1 ns was developed. This time resolution exceeds previous systems by three orders. The operation of the dispersion interferometer and its characteristic properties are discussed and the experimental setup of the installation is explained in detail. The stability of the interferometer was tested and it was shown that its operation point drifts less than 0.25 rad/h. The interferometer was used to investigate the high power ion diodes at the pulse generator KALIF, where focused proton beams with power densities of up to 1 TW/cm2 are generated. For the very first time the electron line density inside the diode gap, where the protons are accelerated, could be directly measured. The line density was on the order of several 1013 cm−2. A straightforward estimation of the line density using a simplified diode model proved to be in excellent agreement with the results. The dispersion interferometer can be used for sensitive electron density measurements on nanosecond time scales. Further developments to improve the sensitivity are discussed. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150679
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    Simple microwave preionization source for ohmic plasmas (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2728-2732 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A simple economical 2.45 GHz microwave system has been developed and utilized for preionization on the Korea Advanced Institute of Science and Technology (KAIST)-TOKAMAK. The magnetron microwave source was obtained from a widely used, household microwave oven. Since ac operation of the magnetron is not suitable for tokamak application, the magnetron cathode bias circuit was modified to obtain continuous and stable operation of the magnetron for several hundred milliseconds. Application of the developed microwave system to KAIST-TOKAMAK resulted in a reduction of ohmic flux consumption. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150682
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    Ion dynamics in the sheath in multicomponent plasma with negative ions (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2733-2736 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Observations on steady state ion-rich sheath around a negatively biased grid in a double plasma device have been made in multicomponent plasma with negative ions. A hump in the potential profile is found to occur at the sheath edge. The characteristics of the hump depend on the grid voltage, source biasing voltage, density difference in the two chambers, and the negative to positive ion concentration ratio. It is argued that resonance which is coupled with the beam ions and background ions is associated in the excitation mechanism to create the nonsymmetrical structures in the plasma potential profile. Below the critical concentration ratio, the hump grows in height and above the critical ratio, the width of the hump increases but the height decreases and ultimately it vanishes. The variation in the hump potential profile due to the injection of negative ions can be explained by the ion momentum exchange and by their dynamics. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150683
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    Subresolution axial distance measurements in far-field fluorescence microscopy with precision of 1 nanometer (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2742-2745 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Fluorescent objects closer than the diffraction resolution limit can be distinguished in far-field microscopy provided they feature different emission spectra. Utilizing the superior axial resolution of 4Pi-confocal microscopy of 100–150 nm, we investigate the precision with which fluorescence objects with subdiffraction axial distance can be measured in the far field. At a wavelength of 820 nm distances on the order of 60 nm between beads and a monomolecular Langmuir–Blodgett layer were determined with a precision of 1.2 nm within 3.2 s. The reduced spatial extent of the 4Pi-confocal point-spread-function improves the precision of colocalization measurements in double stained specimens and opens up the prospect on far-field fluorescence profilometry with (sub) nanometer height resolution. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150685
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    Quantitative imaging of dielectric permittivity and tunability with a near-field scanning microwave microscope (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2751-2758 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe the use of a near-field scanning microwave microscope to image the permittivity and tunability of bulk and thin film dielectric samples on a length scale of about 1 μm. The microscope is sensitive to the linear permittivity, as well as to nonlinear dielectric terms, which can be measured as a function of an applied electric field. We introduce a versatile finite element model for the system, which allows quantitative results to be obtained. We demonstrate use of the microscope at 7.2 GHz with a 370 nm thick Ba0.6Sr0.4TiO3 thin film on a LaAlO3 substrate. This technique is nondestructive and has broadband (0.1–50 GHz) capability. The sensitivity of the microscope to changes in permittivity is Δεr=2 at εr=500, while the nonlinear dielectric tunability sensitivity is Δε113=10−3 (kV/cm)−1. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150687
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    Imaging of liquid crystals using a new scanning near-field optical microscope with microfabricated tips and shear force detection (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2759-2764 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We report results obtained with a scanning near-field optical microscope which was developed, recently. The scanning head of the device is mounted on an inverted polarizing microscope. The sample is illuminated through a microfabricated tip which is mounted on a single-mode optical wave-guiding fiber. The light transmitted through the sample is collected in the far field by a microscope lens. The distance between the tip and the sample is controlled by shear force detection, using a nonconventional setup. We applied this new equipment successfully in order to investigate birefringent and dichroic liquid crystal films, using polarization modulation or fluorescence detection, respectively. An optical resolution down to (approximate)200 nm was obtained on the sample of a cholesteric liquid crystal for a wavelength of 488 nm. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150688
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    Fundamental limits to force detection using quartz tuning forks (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2776-2780 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This paper explores the fundamental limits of the use of quartz tuning forks as force detectors in scanned probe microscopy. It is demonstrated that at room temperature, pressure, and atmosphere these force sensors have a noise floor of 0.62 pN/Hz and exhibit a root mean square Brownian motion of only 0.32 pm. When operated as a shear force sensor both dissipative and reactive forces are detected on approach to the sample. These forces are sufficient to reduce the amplitude of motion of the probe nearly to zero without physically contacting the surface. It is also demonstrated that conventional proportional-integral feedback control yields closed loop responses at least 40 times faster than their open loop response. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150691
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    Ultrahigh pressure cell for materials synthesis (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2784-2790 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe here an apparatus for generating ultrahigh pressures and temperatures for materials synthesis. The system uses a spherically shaped explosive charge to radially compress various materials contained within the sample cavity. The results show the system is completely reproducible and, because of the geometry of the loading system, the workpiece that holds the precursor material is in excellent postshock condition. Samples are subjected to a pressure pulse of approximately 230 GPa for a period of 4 μs. Using this system, C60 has been compressed using a variety of quenching materials to attempt to generate diamond. Two organic precursors have also been tested to determine if the high stress conditions are suitable to synthesize β-carbon nitride. In this article, the design of the system, the numerical modeling using Dyna East Finite Element Lagrangian and CTH hydrocodes, and the results of the synthesis experiments will be presented. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150693
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    An automated apparatus for measuring the tensile strength and compressibility of fine cohesive powders (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2791-2795 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This paper describes an apparatus based on a novel use of a powder bed, whereby the relationship between consolidation stress, tensile strength, and free volume of fine powder is measured. The powder to be tested is first initialized to a reproducible state. The initialized powder is next consolidated either beyond its own weight or below its own weight by means of a controlled flow of gas. An ultrasonic device measures the height of the bed, thus providing an average value of the powder free volume. Next the consolidated bed of powder is subjected to a slowly increasing gas flow, so directed as to put the powder under tension. The overpressure causing the powder to break provides a measure of the tensile strength of the powder, which in turn is a function of the consolidation and free volume. The relationship between consolidation stress, tensile strength, and free volume is related to powder flowability. © 2000 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.1150694
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