ALBERT

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Notes: Motional Stark effect measurements of internal field structure in low-field magnetic confinement configurations are considered for both magnitude and direction of the local magnetic field. The amplitude and phase delay of an oscillating spectral linewidth driven by a rotating polarizer provides a means of determining the magnitude and direction of the total field simultaneously while avoiding difficulties of neutral beam energy drift. Photon-noise limit estimates for a diagnostic beam on the low-field PEGASUS toroidal experiment indicate sensitivities of roughly 20 G and 0.2° for the magnitude and direction angle. These values are sufficient to provide significant constraints on magnetic equilibrium reconstructions. © 2001 American Institute of Physics.

Notes: A motional Stark effect (MSE) instrument to measure q(r) using the Torus Experiment for Technology (TEXT) neutral beam on the Alcator C-Mod tokamak has been designed and installed. The neutral beam is on the midplane, aimed radially, and designed to operate in hydrogen at 50 keV. The MSE optics view the outer half of the plasma −0.3〈(R−R0)/a〈1.05. This geometry results in a spatial resolution of 1 (edge)–3 (center) cm from a beam apertured horizontally to 2 cm. Estimates of the signal levels indicate for Hα that photoelectron statistical errors in the measurement of Bθ/Bφ can be less than 0.2% for ne0〈2.0×1014 cm−3 similar to other MSE instruments. The collection optics reside within the vacuum chamber reflecting and imaging the neutral beam through a vacuum window in the neutral beam port. The optics are designed so that beam emission spectroscopy can be carried out simultaneously with MSE measurements. Optical signals are transmitted to remote detectors by fiber optics. Low Verdet glass and dielectric mirrors are used to minimize polarization changes caused by the ambient fields. Polarization is measured by conventional techniques using photoelastic modulators, optical filters, and photomultipliers. © 2001 American Institute of Physics.

Notes: Charge exchange spectroscopy is one of the key ion diagnostics on the DIII-D tokamak. It allows measurement of impurity densities, toroidal and poloidal rotation speeds, ion temperatures, and the radial electric field. For the 2000 experimental campaign, we have replaced the intensified photodiode array detectors on the edge portion of the system with advanced charge-coupled device (CCD) detectors mounted on faster (f/4.7) Czerny–Turner spectrometers equipped with toroidal mirrors. The combination has improved the photoelectron signal level by about a factor of 20 and the signal to noise by a factor of 2–8, depending on the absolute signal level and readout mode. A major portion of the signal level improvement comes from the improved quantum efficiency of the back-illuminated, thinned CCD detector (70% to 85% quantum efficiency for the CCD versus 10% for the image intensifier) with the remainder coming from the faster spectrometer. The CCD camera also allows shorter minimum integration times: 0.33 ms while archiving to computer memory and 0.15 ms using temporary storage on the CCD chip. © 2001 American Institute of Physics.

Notes: The Alcator C-Mod divertor bypass has for the first time allowed in situ variations to the mechanical baffle design in a tokamak. The design utilizes small coils which interact with the ambient magnetic field inside the vessel to provide the torque required to control small flaps of a Venetian blind geometry. Plasma physics experiments with the bypass have revealed the importance of the divertor baffling to maintain high divertor gas pressures. These experiments have also indicated that the divertor baffling has only a limited effect on the main chamber pressure in C-Mod. © 2001 American Institute of Physics.

Notes: An electronics system has been installed and tested for the readout of avalanche photodiode (APD) detectors for the National Spherical Torus Experiment (NSTX) Thomson scattering system. Similar to previous designs, it features preamps with a fast and a slow output. The fast output uses pulse shaping to optimize sensitivity for the 8 ns scattered light pulse while rejecting noise in the intrinsic plasma background. A low readout noise of ∼25 photoelectrons is achieved at an APD gain of 75. The design incorporates a number of features to provide flexibility for various modes of calibration. © 2001 American Institute of Physics.

Notes: We are building a new Thomson scattering diagnostic system to measure electron temperature and density on the Madison Symmetric Torus (MST) reversed-field pinch experiment. This system has been designed to produce accurate single-shot measurements for 10 eV〈Te〈2 keV at electron densities ≥1018 m−3. Scattered light will be simultaneously recorded from 20 radial locations across the 50 cm minor radius of the plasma. Multipulse capability will be provided by two identical Nd:YAG pulsed lasers whose trigger timing can be independently varied. This will allow several combinations of input energy and pulse timing during an MST discharge, ranging from one 4 J pulse for increased accuracy during low density operation to 1 J pulses at 100 Hz for temporal evolution measurements. Scattered light will be collected by a custom deep-focus lens and coupled by optical fiber to 20 identical filter polychromators. These polychromators are being manufactured by General Atomics and use silicon avalanche photodiode detectors. Each polychromator contains three wavelength channels to allow determination of Te, plus one channel at the laser wavelength to allow calibration using Rayleigh scattering for measurement of ne. System control and data acquisition will be done with dedicated personal computers. © 2001 American Institute of Physics.

Notes: A collective Thomson scattering diagnostic is being developed for the measurement of confined fast ions in hot, dense plasmas. This includes such measurements as the ion tail in JT-60U and the alphas produced in a burning reactor or the upgraded Joint European Torus device. The diagnostic also has the capability of measuring the isotopic ratio of the core ions such as the D/T ratio (required in optimizing a burning plasma experiment). The advances under development for this diagnostic include improvements in the high power source laser, increased bandwidth and reduced noise in the receiver, and the development of an intermediate frequency electronic filter bank. Such improvements are designed to permit the temporal measurement of the fast ions and improve the accuracy in determining their velocity distribution. Modeling of the expected scattered signals produced by these improvements and the diagnostics capability to measure the velocity distribution and isotopic ratio are presented. © 2001 American Institute of Physics.

Notes: Collective light scattering measurement is a powerful tool for investigating fluctuations and their relation with anomalous transport since it allows a direct, discriminating analysis of the turbulent scales. This high scale resolution has a counterpart in a poor spatial resolution, but some localization can be recovered allowing us to discriminate edge from core turbulence behavior and to determine turbulence profiles. More information about localization can be obtained using temporal dynamics of the scattered signal when the fluctuation velocity in the poloidal plane is sheared. Making use of the consequently separated Doppler shifts, different technics are used to extract localized information from frequency spectra and from the signal phase derivative. Capabilities of the diagnostic are illustrated by recent results obtained on Tore Supra in different regimes. © 2001 American Institute of Physics.

Notes: The Chandra X-ray telescope has four separate detectors, two charge coupled devices, and two microchannel plates, behind a set of four highly polished, nested mirrors. The on-orbit performance of the imaging system is 〈1 arcsec, a dramatic improvement from the 5–8 arcsec previously available. In addition, two transmission gratings can be placed in the system, which for point sources can reach resolutions of 300–1000+ over the range λ∼1.5–160 Å. The entire system was calibrated prelaunch at NASA/MSFC in Huntsville, Alabama. The results have been dramatic: the first light image of the supernova remnant Cas A showed a never-before-seen point source near the center of the remnant that may be the neutron star left over after the explosion. Even the calibration image of a distant quasar (taken for focusing purposes) showed an x-ray emitting jet extending out from the nucleus for more than 20 kpc, which challenges current theories about jet propagation. The grating observations done by Chandra take x-ray astrophysics out of the photometry era into the spectroscopic age. Astrophysical plasmas reach conditions far out of the reach of any terrestrial laboratory, and astronomers are just beginning to understand the diagnostics of these plasmas; Chandra observations may even someday provide the best measurements of certain atomic rates. However, before that point is reached the astronomical community must gain a much better understanding of the existing and ongoing work in x-ray diagnostics from other fields. The general state of x-ray diagnostics for astronomical plasmas will also be discussed. © 2001 American Institute of Physics.

Notes: A fully calibrated multilayer mirror (MLM) based soft x-ray spectrometer has been developed and installed on the Compact Helical System (CHS). This MLM based spectrometer is a new approach to devising a soft x-ray spectrometer with medium time and energy resolutions. The spectrometer mainly consists of a MLM as the dispersive element and a 20-channel (p-i-n) pin diode array for the detection of the soft x-rays. Both the MLM and the pin diodes have been calibrated at the KEK (High Energy Accelerator Research Organization) Photon Factory for an energy range of 300–1200 eV. The reflectivity of the mirror was found to increase from 3% (photon energy of 335 eV) to 25% (photon energy of 1050 eV). The pin diodes were found to have almost 100% efficiency for creating electron-hole pairs in the calibrated energy range. The spectrometer was installed on the CHS with the aim of fast electron temperature measurement and study of fast magneto-hydrodynamic (MHD) events occurring in plasmas. The experiments show that in the energy range of measurement, the electron "temperature" determined from the slope of the soft x-ray spectrum is much lower than that measured by the Thomson scattering diagnostic. Analysis showed that the soft x-ray spectrum is highly contaminated by impurity emission. Therefore it may be possible to measure electron temperature with this diagnostic if we choose another energy range where we can measure the continuous spectrum. The present time resolution of the system is of the order ∼0.1 ms, which made it possible to study the behavior of the plasma during fast MHD events. Modulations in the soft x-ray intensity were observed during MHD events in CHS plasmas. Analysis of these shows that these may be due to modulations in the temperature or the impurity concentration. © 2001 American Institute of Physics.

Notes: Laser–plasma instabilities that produce an unacceptably high level of hot electrons are potentially dangerous for both direct-drive and indirect-drive inertial confinement laser fusion. The hot electrons preheat the fuel and prevent compression of the capsule to the requisite conditions for ignition. Fast electron generation and preheat can be inferred from the hard x-ray radiation generated by the interaction of the hot electrons with the target. On the University of Rochester's OMEGA laser system, time-resolved hard x-ray detectors have been operating in an energy range from 10 to 500 keV. In this article we will present initial results for the yield and spectrum of the hard x-ray radiation. The concept used on OMEGA can be easily extended to infer the amount of laser energy coupled to suprathermal electrons and to the target for both direct- and indirect-drive implosions on the upcoming National Ignition Facility, as well as to measure the conversion efficiency in high-x-ray-yield experiments. © 2001 American Institute of Physics.

Notes: Recent development of the JT-60U charge exchange recombination spectroscopy (CXRS) diagnostic system is reported. The measurements of the radial profiles of the ion temperatures, the toroidal and poloidal rotation velocities, and the impurity density are based on CXR spectra of fully stripped carbon ions induced by neutral beam injection. Measurements are made simultaneously at 59 spatial points (23 toroidal and 36 poloidal) with a time resolution of 1/60 s throughout the full discharge pulse of 15 s. Considerable effort has been expended to ensure the automatic provision of reliable profile data, where the mechanical components of the system must cope with both a baked tokamak vessel (∼300 °C) and an expected disruption-induced acceleration of up to 60 g, where g denotes the gravitational acceleration, i.e., 9.8 m2/s. © 2001 American Institute of Physics.

Notes: A set of experiments on neutron and x-ray generation was performed on the S-300 facility for the last few months. The S-300 facility is a pulse generator with electric current achieving 3.5 MA, voltage 400–500 kV, and rise time ∼100 ns. (Chernenko et al., Proc. of the 11th International Conference of Power Particle Beams, Prague, 1966, p. 154). It is designed as van eight-module machine transmitting electromagnetic power to the low-inductive load through the vacuum line with self-magnetic isolation. Diagnostic techniques and methods on S-300 used are described in this article. Ten-channel polychromator is used for the soft x-ray and vacuum ultraviolet bands (50–500 eV) measurements with spectral resolution of 5%–20% and time resolution less than 2.5 ns. Radiated power measurements in the region of 0.1–10 keV are performed by vacuum x-ray diodes and semiconductor detectors equipped with different filters. Curved crystal x-ray spectrography is intended for plasma density, electron, and ion temperature evaluation. Visible and x-ray radiation image converter tubes and a streak camera reproduce plasma dynamics. Laser shadow and schlieren probing are used to investigate rare periphery plasma motion. Time-of-flight and activation technique is designed for total neutron yield determination. © 2001 American Institute of Physics.

Notes: We report the development of techniques to diagnose plasmas produced by x-ray photoionization of thin foils placed near the Z-pinch on the Sandia Z Machine. The development of 100+ TW x-ray sources enables access to novel plasma regimes, such as the photoionization equilibrium. To diagnose these plasmas one must simultaneously characterize both the foil and the driving pinch. The desired photoionized plasma equilibrium is only reached transiently for a 2-ns window, placing stringent requirements on diagnostic synchronization. We have adapted existing Sandia diagnostics and fielded an additional gated three-crystal Johann spectrometer with dual lines of sight to meet these requirements. We present sample data from experiments using 1-cm, 180-eV tungsten pinches to photoionize foils made of 200 Å Fe and 300 Å NaF co-mixed and sandwiched between 1000 Å layers of Lexan (C16H14O3), and discuss the application of this work to benchmarking astrophysical models. © 2001 American Institute of Physics.

Notes: A modular, low-cost, digital signal processor (DSP)-based lock-in card is described for measuring optical attenuation. By transferring the lock-in operation from the analog domain to the digital domain, the nonlinearities gain, and offset errors and drifts are virtually eliminated. The dual phase lock-in operation has been implemented on the low-cost DSP56002 evaluation module (DSP56002EVM) of Motorola that is widely used in audio signal processing. This evaluation board contains a 24 bit DSP56002 DSP and a stereo CD-quality audio codec that makes the board ideal for implementing signal processing algorithms. Due to the maximum sampling rate of the codec embedded on the DSP56002EVM, the frequencies of the processed signals must be below 20 kHz. This specification is enough for the most common applications in the field of optics, where low or very low frequency (〈1 kHz) references are frequent. The software algorithm implementing the lock-in amplifier can be particularized by the user on the basis of the needed performances. The effects of finite word length in the digital filter implementation are analyzed. This analysis reveals that a 24 bit word length is not enough to ensure the filter stability and the required frequency response. To overcome this problem, the double precision multiply mode must be used. When the DSP56002 enters this mode, double precision 48 bit by 48 bit multiplication can be performed. The lock-in performance has been tested. The measured amplitude variations of the reference sine signal are about 0.003%, which do not affect the signal measurement. The lock-in behaves like a band-pass filter centered on the reference frequency whose bandwidth is related to the low-pass filter cutoff frequency. The measured frequency response shows that the lock-in performs as theoretically predicted. The DSP56002EVM can be used as a lock-in for electrical signals in stand-alone operation. Besides, we have designed a card that interconnects to the DSP56002EVM and allows the ensemble to act as an optical attenuation detector that measures optical losses over 70 dB. This range is similar to that achievable by commercially available optical loss testers and makes it suitable for optical return loss measurements of all kinds of commercially available optical connectors. © 2001 American Institute of Physics.

Notes: Electron cyclotron emission (ECE) has been employed as a standard electron temperature profile diagnostic on many tokamaks and stellarators, but most magnetically confined plasma devices cannot take advantage of standard ECE diagnostics to measure temperature. They are either "overdense," operating at high density relative to the magnetic field (e.g., ωpe(very-much-greater-than)Ωce in a spherical torus) or they have insufficient density and temperature to reach the blackbody condition (τ〉2). Electron Bernstein waves (EBWs) are electrostatic waves that can propagate in overdense plasmas and have a high optical thickness at the electron cyclotron resonance layers as a result of their large kperp. In this article we report on measurements of EBW emission on the CDX-U spherical torus, where B0∼2 kG, 〈ne〉∼1013 cm−3 and Te(approximate)10–200 eV. Results are presented for electromagnetic measurements of EBW emission, mode converted near the plasma edge. The EBW emission was absolutely calibrated and compared to the electron temperature profile measured by a multipoint Thomson scattering diagnostic. Depending on the plasma conditions, the mode-converted EBW radiation temperature was found to be ≤Te and the emission source was determined to be radially localized at the electron cyclotron resonance layer. A Langmuir triple probe and a 140 GHz interferometer were employed to measure changes in the edge density profile in the vicinity of the upper hybrid resonance where the mode conversion of the EBWs is expected to occur. Initial results suggest EBW emission and EBW heating are viable concepts for plasmas where ωpe(very-much-greater-than)Ωce. © 2001 American Institute of Physics.

Notes: A heavy ion beam diagnostic is being developed for the tokamak ISTTOK (R=0.46 m, a=0.085 m, Bt≅0.5 T, Ip=6–9 kA), based on multiple cell array detectors, aimed at the study of the time variation of the plasma density, electron temperature, poloidal magnetic field, and plasma potential radial profiles. In this article we describe an alternative method to the traditional electrostatic energy analyzers for measurements of the plasma potential based on the time-of-flight technique. The initial results of the measurements of the changes on the average plasma potential during tokamak discharges with minor disruptions are also presented. These results have been obtained measuring the time-of-flight of the ions of a pulsed primary beam from the electrostatic plates of the ion gun to the primary detector. © 2001 American Institute of Physics.

Notes: A direct calibration technique for the heavy ion beam probe system using the mesh probe is established. The mesh probe makes it possible to calibrate the diagnostic system with the same condition as a real plasma measurement. The location of the sample volume could be determined with the spatial resolution of about 7.5 mm. It shows good agreement with this expected result by the trajectory code with an accuracy of about 1%. © 2001 American Institute of Physics.

Notes: The MEDUSA array is a multielement, scintillator-based neutron time-of-flight spectrometer designed primarily to measure primary and secondary neutron production from indirect drive DD and DT capsule implosions at the Omega Laser in Rochester, NY. The array consists of 824 identical scintillator-photomultiplier tube detectors coupled to analog signal discriminators and high resolution, multihit time-to-digital converters, and is located 19.4 m from the center of the Omega target chamber. It is possible to accurately measure the neutron energy spectrum by simply measuring an adequate sample of neutron flight times to the array (the burn time width is negligible). However it is essential to understand the response of the array detectors to the fusion neutrons before an energy spectrum can be deduced from the data. This array response function is generally given in terms of a calibration constant that relates the expected number of detector hits in the array to the number of source neutrons. The calibration constant is a function of the individual detector gains, the thresholds of the discriminators, and the amount of neutron attenuating material between the array and the target. After gain matching the detectors, a calibration constant can be generated by comparing the array response against a known yield of neutrons (this requires dozens of implosions) or from a first principles measurement of the individual detector efficiencies. In this article, we report on the results of both calibrations of the MEDUSA array. In particular, we will focus on the issues and errors associated with the very different measurements required and discuss a new technique being considered for rapid in situ future calibrations. © 2001 American Institute of Physics.

Notes: A pinhole soft x-ray imaging camera is being developed for use on the Caltech solar prominence simulation experiment and also the Caltech spheromak experiment. The camera is based upon a commercial gated intensifier which produces an image on a phosphor screen. Moderate signal level, excellent time resolution, and reasonable imaging have been obtained, but there has not been any determination of the x-ray energy spectrum. An estimation of the spectrum is now underway using filtered AXUV diodes and it is expected that knowledge of the x-ray energy will enable further optimization of the camera.© 2001 American Institute of Physics.

Notes: In the reversed field experiment the electron temperature and density at the edge are measured from the intensity ratio of selected lines emitted by an atomic helium beam injected into the plasma. Helium is injected through a single microtube 30 mm long and with 150 μm of internal diameter. Four beam splitters allow three interference filters, coupled to linear array cameras or alternatively to photomultipliers, and a charge coupled device camera to observe the same beam volume. The application of photomultipliers as detectors has recently increased the time resolution of the diagnostic. This allows following the time evolution of edge density and temperature during nonstationary processes. Moreover, the enhanced time resolution increases the capability of the diagnostic to measure the edge electron temperature and density fluctuations, which are relevant to the edge electrostatic transport studies. © 2001 American Institute of Physics.

Notes: Optical fibers are used to couple light into fast time-resolved spectrometers for many applications. Here several issues arise that can seriously limit the temporal resolution, such as the wavelength dependent group delay, and intermodal dispersion. These issues are investigated in 10 m length fibers using either a 400 μm core step index or graded index fiber. A unique broadband (400–700 nm) short pulse (∼1 ps) light source is used to measure the fiber group delay with a time-resolved spectrometer. Intermodal dispersion is also studied in these fibers using a narrow-band 1 ps pulse that is injected into the fiber with various coupling schemes, and a novel technique is employed to record the time-dependent angular mode structure. Finally, a conceptual design using ∼100 μm core graded-index fibers is proposed for multichannel streaked optical spectroscopy on the National Ignition Facility. Designs appropriate for a low spectral resolution instrument (stimulated Raman backscattering) and a high spectral resolution instrument (stimulated Brillouin backscattering) are presented. The fiber dispersion issues are discussed in the design of these diagnostics. © 2001 American Institute of Physics.

Notes: A wavelet-transform-based spectral analysis is examined for application to beam emission spectroscopy (BES) data to extract poloidal rotation velocity fluctuations from the density turbulence data. Frequency transfer functions for a wavelet cross-phase extraction method are calculated. Numerical noise is reduced by shifting the data to give an average zero time delay, and the applicable frequency range is extended by numerical oversampling of the measured density fluctuations. This approach offers potential for direct measurements of turbulent transport and detection of zonal flows in tokamak plasma turbulence. © 2001 American Institute of Physics.

Notes: A thermoelectric power generation system using reciprocating flow combustion in a porous thermoelectric conversion element has been developed and examined in its performance. Mn- (n-type) and Co- (p-type) doped FeSi2 powders were molded into the cylindrical element via a spark plasma sintering process, in which Mn- and Co-doped parts were separated by a thin insulator sheet exclusive of a terminus. The porous element consisted of two semicylindrical p/n couples, arranged electrically in series but thermally in parallel. A thermopower of 1.0–1.2 mV/K at 295–624 K and an apparent internal resistivity of 1.6×10−1 Ω cm at 556–624 K have been obtained for the element. A power generation system was then made using a pair of the elements, which were arranged lengthwise in a cylindrical combustion chamber. A reciprocatory flow of dilute fuel gas was introduced into the element, and it was ignited between the element. A steep temperature gradient of about 200 K/cm was formed lengthwise in both elements. The energy density has reached as much as 7 kW/m3 (excluding combustion chamber and mounting clamp) by the reciprocating flow combustion with a dilute fuel gas which may not even be normally flammable. © 2001 American Institute of Physics.

Notes: The multichannel far-infrared (FIR) heterodyne polarimeter-interferometer system on the Madison Symmetric Torus (MST) is now operational. The combined system consists of 11 channels with variable radial and toroidal spacing. Poloidal magnetic field is determined by measuring the Faraday rotation of the FIR laser beam after propagation through the plasma by use of a phase technique. The polarimeter has 3 mrad rms noise level and 1 ms temporal resolution while the interferometer resolution is nedl=1×1012 cm−2 with time response of 1 μs. Absolute calibration of the polarimeter system is achieved by use of a rotating quartz half-wave plate. The first 11-channel polarimeter measurements from MST indicate a Faraday rotation profile in good agreement with expectations from the MSTFIT equilibrium code. Future plans to reduce the polarimeter time response from 1 ms to 10 μs will allow direct measurement of magnetic fluctuations associated with global resistive tearing modes on MST. The effect of these modes on density is already clearly resolved and provides insight into the dynamics of these structures. Improving the time response will also result in lower phase noise for both the polarimeter and interferometer. © 2001 American Institute of Physics.

Notes: A CO2 laser (λ=10.6 μm) imaging interferometer is designed for electron density profile and electron density fluctuation measurements on large helical device (LHD). The purposes of this diagnostic are reliable electron density monitor in high density operation (especially in pellet injection discharge), precise measurement of electron density profiles and observations of density fluctuations. By using a CO2 laser, refraction effect becomes negligible, and the interferometer promises to be free from fringe jumps at high density. We plan to get 5 mm spatial resolution, (56 ch for each of two 280 mm slab beams, 50 ch for one 250 mm and 16 ch for 80 mm crossed beam), 3×10−3 rad phase resolution and 200 kHz frequency response for the above purpose. And fluctuation will be studied within the wave number range of 7×10−3≤k≤0.6 mm−1. © 2001 American Institute of Physics.

Notes: A new type of shearing interferometer using an air wedge is described. This interferometer is based on a beam splitter constructed using two 90-degree prisms. A small air gap, which varies in spacing from top-to-bottom, separates the second prism from the first and forms the air wedge. The single incident laser beam is focused near the gap, and the two primary reflections from the long sides of each prism form the two coherent virtual sources necessary for interferometry. The shift between the two images of the object at the detector, as well as the orientation and frequency of the fringes, can be independently adjusted by altering the air gap thickness and angle, as well as the position of the laser focus in the gap. This interferometry scheme is inexpensive and easily aligned, and has been successfully and reliably used in exploding wire experiments. © 2001 American Institute of Physics.

Notes: A new type of digital phase linearizer has been developed for real-time electron density measurement using a multichannel far-infrared (FIR) interferometer. The phase linearizer can measure phase shifts up to 640 fringes. The size of internal memory is 16 bits-2 Mwords and the sampling frequency of the waveform data is up to 1 MHz. The internal clock for the counter is selectable to 100 or 200 MHz and the frequencies of the input signals, i.e., the reference signal and the probe one, are around 1 MHz. In the performance test the resolution of the phase components is achieved at 1/100 fringes, which corresponds to the line integrated density of 9.0×1016 m−2. For real-time measurements the phase linearizer has digital-to-analog converter (DAC) output. The resolution of DAC output is 12 bits and the amplitude is ± 5 V. The density feedback system on the large helical device has been utilized. © 2001 American Institute of Physics.

Notes: We have developed a YAG Thomson scattering (TS) system for the measurements of electron temperature and density profiles on the large helical device (LHD). The LHD-TS has four YAG lasers, and flexible operational modes are possible by using them. For example, (1) high-energy mode: The pulse energy can be increased up to four times by firing the four lasers simultaneously. In this mode, the data quality can be improved for low-density plasmas. (2) High repetition mode: When firing the lasers at intervals of 5 ms, the lasers work as a 200 Hz laser. The laser beams are guided to the LHD by seven steering mirrors. The first mirror is real-time feedback controlled for precise beam transport. The beam pointing stability is improved successfully from 200 μrad to below 4 μrad with the feedback-control system. We describe the details of the laser system for the LHD-TS. © 2001 American Institute of Physics.

Notes: In this article, the recently installed high resolution multiposition Thomson scattering (TS) system of the TEXTOR tokamak is presented. Light from a pulsed ruby laser is scattered by the free electrons of the plasma and transmitted by fiber optics to a polychromator for spectral analysis. The Doppler broadened spectrum of the scattered light is analyzed with a Littrow spectrometer, detected with an image intensifier, and recorded with two intensified charge coupled device cameras. Values of the electron temperature (Te) in the range of 50 eV up to 4 keV can be measured at 450 spatial elements of 2 mm along a chord of 900 mm, with a resolution of 8 mm. The observational error on Te was found to be 〈3% at an electron density (ne) of 3.5×1019 m−3 using a laser energy of ∼8 J. These features make—to our knowledge—the multiposition TS system of TEXTOR to be the one with the highest spatial and spectral resolution in the world. In this article the first results of this powerful diagnostic will be presented. © 2001 American Institute of Physics.

Notes: The two-dimensional (2D) structure of plasma density turbulence in a magnetically confined plasma can potentially be measured using a Thomson scattering system made from components of the Nova laser of Lawrence Livermore National Laboratory. For a plasma such as the National Spherical Torus Experiment at the Princeton Plasma Physics Laboratory, the laser would form an (approximate)10-cm-wide plane sheet beam passing vertically through the chamber across the magnetic field. The scattered light would be imaged by a charge coupled device camera viewing along the direction of the magnetic field. The laser energy required to make 2D images of density turbulence is in the range 1–3 kJ, which can potentially be obtained from a set of frequency-doubled Nd:glass amplifiers with diameters in the range of 208–315 mm. A laser pulse width of ≤100 ns would be short enough to capture the highest frequency components of the expected density fluctuations. © 2001 American Institute of Physics.

Notes: A multipass intracavity laser probing system operating in a burst mode has been tested for the Torus Experiment for Technology Oriented Research Thomson scattering diagnostics. The parameters tested were the probing pulse energy and power as well as pulse repetition frequency. The system is to be applied for the dynamic study of fast plasma phenomena (e.g., transport barrier formation and filaments) requiring both high time and spatial resolutions of the electron temperature measurements. © 2001 American Institute of Physics.

Notes: The 100 ns, 20 MA pinch-driver Z is surrounded by an extensive set of diagnostics. There are nine radial lines of sight set at 12° above horizontal and each of these may be equipped with up to five diagnostic ports. Instruments routinely fielded viewing the pinch from the side with these ports include x-ray diode arrays, photoconducting detector arrays, bolometers, transmission grating spectrometers, time-resolved x-ray pinhole cameras, x-ray crystal spectrometers, calorimeters, silicon photodiodes, and neutron detectors. A diagnostic package fielded on axis for viewing internal pinch radiation consists of nine lines of sight. This package accommodates virtually the same diagnostics as the radial ports. Other diagnostics not fielded on the axial or radial ports include current B-dot monitors, filtered x-ray scintillators coupled by fiber optics to streak cameras, streaked visible spectroscopy, velocity interferometric system for any reflector, bremsstrahlung cameras, and active shock breakout measurement of hohlraum temperature. The data acquisition system is capable of recording up to 500 channels and the data from each shot is available on the Internet. A major new diagnostic presently under construction is the BEAMLET backlighter. We will briefly describe each of these diagnostics and present some of the highest-quality data from them. © 2001 American Institute of Physics.

Notes: We have developed a low-cost, robust, multifoil-filtered spectrometer to provide absolute measurements of low-Z impurity concentrations in the Madison Symmetric Torus reversed-field pinch. The spectrometer utilizes an array of six thin-film coated soft x-ray diodes. Each multilayered coating is specifically tailored to isolate the K-shell emission lines of H- and He-like oxygen, carbon, and aluminum. With calibrations obtained via a synchrotron source, absolute measurements of photon flux have been made. We address the technical aspects of this diagnostic and present impurity data from both standard and high-confinement plasma discharges. © 2001 American Institute of Physics.

Notes: A National Ignition Facility (NIF) core diagnostic instrument has been designed and will be fabricated to record x-ray spectra in the 1.2–20 keV energy range. The high-energy electronic x-ray instrument has four reflection crystals with overlapping coverage of 1.2–10.9 keV and one transmission crystal covering 8.6–20 keV. The spectral resolving power varies from approximately 1000 at low energies to 315 at 20 keV. The spectrum produced by each crystal is recorded by a modified commercial dental x-ray charge coupled device (CCD) detector. The scintillators on the CCD detectors are optimized for the energy ranges. A one-channel x-ray spectrometer, using one transmission crystal covering 12–60 keV, will be fabricated for the OMEGA laser facility. The transmission crystal spectrometers are based on instruments originally designed at National Institute for Standards and Technology for the purpose of characterizing the x-ray flux from medical radiography sources. Utilizing one of those instruments and a commercial dental x-ray CCD detector, x-ray images were recorded using a single pulse from a laboratory x-ray source with a peak charging voltage of 200 kV. A resolving power of 300 was demonstrated by recording on film the Kα1 and Kα2 characteristic x-ray lines near 17 keV from a molybdenum anode. The continuum radiation from a tungsten anode was recorded in the 20–50 keV energy range. The transmission crystal spectrometer has sufficient spectral resolution and sensitivity to record the line and continuum radiation from high-Z targets irradiated by the NIF laser and the OMEGA laser.

Notes: The radiation field in a hohlraum (4 mm diameter×4 mm length) with a ∼10 TW x-ray input has been simultaneously measured by two independent techniques. An active shock breakout measurement of radiation-driven shock velocity in aluminum indicates a peak radiation field with incident flux equivalent to a Planckian distribution with a temperature of 147±3 eV. In the same experiment, a time- and spatially resolved measurement of x-ray re-emission from the gold hohlraum wall indicates re-emission flux equivalent to a Planckian brightness temperature of 145±5 eV. © 2001 American Institute of Physics.

Notes: Three x-ray spectrometers, each with a transmission grating dispersion element, are routinely used at the Z soft x-ray facility to measure the spectrum and temporal history of the absolute soft x-ray power emitted from z-pinch and hohlraum radiation sources. Our goal is to make these measurements within an accuracy of ±10%. We periodically characterize the efficiency of the gratings used in the spectrometers by using an electron-impact soft x-ray source, a monochromator, grazing-incidence mirrors, thin filters, and an x-ray charge-coupled device (CCD) detector. We measure the transmission efficiency of the gratings at many photon energies for several grating orders. For each grating, we calculate efficiency as a function of photon energy using published optical constants of gold and multiple-slit Fraunhofer diffraction theory and fit the calculation to the measurements using the physical parameters of the grating as variables. This article describes the measurement apparatus and calibration techniques, discusses the grating efficiency calculation and fitting procedure, and presents recent results.

Notes: X-ray powers on the order of 10 TW over an area of 4.5 mm2 are produced in the axial direction from the compression of a low-density foam target centered within a z-pinch on the Z generator.1 The x rays from this source are used for high-energy–density physics experiments, including the heating of hohlraums for inertial confinements fusion studies.2 In this article, detailed characteristics of this radiation source measured using an upgraded axial-radiation-diagnostic suite3 together with other on- and off-axis diagnostics are summarized and discussed in terms of Eulerian and Lagrangian radiation–magnetohydrodynamic code simulations. The source, characterized here, employs a nested array of 10-mm-long tungsten wires, at radii of 20 and 10 mm, having a total masses of 2 and 1 mg, and wire numbers of 240 and 120, respectively. The target is a 14 mg/cc CH2 foam cylinder of 5 mm diameter. The codes take into account the development of the Rayleigh–Taylor instability in the r–z plane, and provide integrated calculations of the implosion together with the x-ray generation. The radiation exiting the imploding target through the 4.5 mm2 aperture is measured primarily by the axial diagnostic suite that now includes diagnostics at an angle of ∼30° to the z axis. The near on-axis diagnostics include: (1) a seven-element filtered silicon-diode array,4 (2) a five-element filtered x-ray diffraction (XRD) array,5 (3) a six-element filtered PCD array,6 (4) a three-element bolometer,7 (5) time-resolved and time-integrating crystal spectrometers, and (6) two fast-framing x-ray pinhole cameras having 11 frames each. The filtered silicon diodes, XRDs, and PCDs are sensitive to 1–200, 140–2300, and 1000–4000 eV x rays, respectively. They (1) establish the magnitude of the prepluse generated during the run in of the imploding wire arrays, (2) measure the Planckian nature of the dominant thermal, and (3) nonthermal component of the emission. The bolometers and XRDs mounted on the near-normal and 30° LOS (line-of-sight) measure the total power and check the Lambertian nature of the emission. Additionally, a suite of filtered fast-framing x-ray pinhole cameras and silicon-diode arrays behind a transmission grating, mounted on LOSs nearly normal to the z axis, quantify the plasma plume exiting the aperture. The hard bremsstrahlung generated is estimated with both on- and off-axis shielded scintillator photomultiplier diagnostics. © 2001 American Institute of Physics.

Notes: Measurements of the hohlraum wall temperature in Z-pinch driven hohlraum experiments require looking through small (2–4 mm diameter) diagnostic holes that undergo some degree of hole closure. The existing soft x-ray diagnostics on Z measure the total flux exiting this diagnostic hole and are therefore affected by this hole closure. To avoid having to measure the effective diagnostic hole area we have designed and constructed an imaging diode array (IDA) that incorporates pinhole imaging and an array of filtered silicon diodes to measure the absolute x-ray intensity from a spatially resolved region of a target. The instrument uses silicon diodes with subnanosecond time response that are sensitive to soft x rays in the range 100–3000 eV. An image of the target area is projected onto the silicon diodes using pinholes. Between each pinhole and it's respective diode is a soft x-ray filter. The material and thickness of the filter are selected to allow unfolding of spectral information in the 100–3000 eV spectral region. We plan to insert a set of grazing-incidence mirrors between each of the filter/diode pairs in a future version of this instrument to better define the spectral bandpass of each diode channel. Radiation from the target region is monitored by a gated microchannel-plate-intensified image recording device that is located immediately behind the diode array. A small shadow in the recorded image corresponds to the specific area of the target that is imaged onto each silicon diode. We are presently fielding this instrument in experiments on the Z facility located at Sandia National Laboratories in Albuquerque, NM. The instrument is located on the same line-of-sight and measures the same spatial region as a filtered fast-framing x-ray pinhole camera and a transmission grating spectrometer. This article describes the design of the IDA diagnostic and presents the results of measurements obtained in hohlraum experiments conducted on Z. © 2001 American Institute of Physics.

Notes: Characterization of hot electron production from an ultraintense laser–solid target plasma interaction by using a buried molybdenum K-shell fluor layer technique has been reported. Laser energy was typically 400 J and its intensity was from 2×1018 up to 3×1020 W cm−2 at 20 TW to 1 PW laser power by changing pulse duration from 20 ps down to 0.5 ps. X-ray background noise level was significantly greater, i.e., gamma flash, in the shorter pulse experiments. Data analysis procedures for the experiments were developed. The conversion efficiency from the laser energy into the energy, carried by hot electrons, has been estimated to be ∼50% at 3×1020 W cm−2 laser intensity, higher than ∼18% at 1019 W cm−2 and ∼12% at 2×1018 W cm−2 intensity. © 2001 American Institute of Physics.

Notes: A high vacuum x-ray crystal spectrometer was fabricated utilizing a large spherically bent mica crystal (2 cm×7 cm) and a x-ray sensitive charge coupled device camera to observe heliumlike neon spectra in the wavelength range from 13.4474 to 13.6980 A and heliumlike spectra of other low-Z elements, such as Mg and Al. The spectrometer was specifically designed for use at a low x-ray intensity magnetic mirror machine. The x-ray imaging characteristics of the large spherically bent mica crystal have been tested in the laboratory with an x-ray source, using the bremsstrahlung continuum. The results of these calibration measurements will be presented. © 2001 American Institute of Physics.

Notes: We have mounted 1 μm thick aluminized polyimide windows onto the position sensitive proportional counters employed by the wide-band flat crystal spectrometers at the Lawrence Livermore National Laboratory electron beam ion trap experiment. The aluminized polyimide, supported by thin wires across the short axis of the window, is used to isolate the detection chamber of the proportional counters, which operate at a pressure of 760 Torr, from the vacuum chamber of the spectrometer. The windows are modified versions of those developed for the proportional counters which were used during ground calibration of the Chandra X-ray Observatory. The transmission properties of these windows are, therefore, well known. The increased transmission efficiency of the polyimide windows relative to the 4 μm thick polypropylene window material previously employed by our proportional counters has extended the useful range of the spectrometer from roughly 20 to 30 Å at energies below the carbon edge, as well as increasing detection efficiency at wavelengths beyond the carbon edge. Using an octadecyl hydrogen maleate crystal with 2d=63.5 Å, we demonstrate the increased wavelength coverage by measuring the resonance, intercombination, and forbidden lines in helium-like N VII in two different density regimes. The thin polyimide windows have also increased the efficiency of the spectrometers entire wavelength range. To demonstrate the increased efficiency we compare the Fe XVII spectrum in the 15–17 Å band measured with the 1 μm aluminized polyimide windows to the 4 μm aluminized polypropylene windows. The comparison shows an average increase in efficiency of ∼40%. The polyimide windows have a significantly lower leak rate than the polypropylene windows making it possible to achieve approximately an order of magnitude lower pressure in the spectrometer vacuum chamber which reduces the gas load on the trap region. © 2001 American Institute of Physics.

Notes: The neutral beam (NB) shine-through profile is routinely monitored on the Large Helical Device (LHD) both to calibrate the port-through power of the NB and to evaluate the NB-deposition power to LHD plasmas. The profile is measured with a calorimeter (CM) array on an armor plate of the NB counter wall inside the LHD vacuum vessel. An infrared camera is also used to check the beam profile where CMs are not located, and measures a temperature increase of the armor plate due to the NB heat load. The measured beam profile is compared to the calculated NB profile at the armor plate. The measurement indicates that the beam is not uniform at the exit of the ion source and that the steering angle of the beam in the horizontal direction is not the same as the designed value. It is found that the monitoring of the NB shine-through profile is important to estimate the NB port-through power and the NB deposition power, especially when the neutral beam injector (NBI) is based on a large negative-hydrogen ion source. © 2001 American Institute of Physics.

Notes: He and Li beams have been installed and set into operation at the TJ-II stellarator with the aim of measuring electron temperature and density profiles in the edge and scrape-off layer regions of the plasma. The effusive thermal Li beam penetrates up to a normalized effective radius of ρ=0.6–0.7 in typical electron cyclotron heated plasmas. Density profiles deduced from the Li beam are wider than those obtained from extrapolation of the profile measured by Thomson scattering. The He beam is a pulsed supersonic one. Simultaneous detection of three emission lines (667.2, 706.5, and 728.1 nm) is made with a set of three photomultipliers. First He beam measurements of ne and Te in TJ-II are presented and the agreement among results of different plasma edge diagnostics is discussed. © 2001 American Institute of Physics.

Notes: A new type of fast neutral particle analyzer using Si diode cooled by Peltier module has been designed and developed. It is known that leak current in a solid-state detector is reduced by its use in low temperature. It is shown in this article that Peltier effect provides a very handy way of cooling the detector as long as a temperature around 0 °C is aimed at. The detector was easily cooled down to −1.6 °C and the performance of the detector was studied by the use of x/γ rays from 241Am. The leak current was remarkably reduced as the detector is cooled improving energy resolution from 9.2 keV at room temperature to 4.3 keV at −1.6 °C. In addition, the lower detectable energy limit was expanded from 25 keV to 14 keV. A Si detector is also sensitive to visible light and x ray. Therefore, the detector of our "reference design" is furnished with an evaporated 1000-Å-thick aluminum layer to reduce the visible light and with a lead collimator to reduce the x ray. The detector was finally installed on the Compact Helical System device for a test of overall performance and an energy spectrum from a diagnostic neutral beam was successfully measured. This test was conducted without an Al layer and this result suggests a possibility of eliminating it. © 2001 American Institute of Physics.

Notes: X-ray backlighting is a powerful tool for diagnosing a large variety of high-density phenomena. Traditional area backlighting techniques used at Nova and Omega cannot be extended efficiently to National Ignition Facility scale. New, more efficient backlighting sources and techniques are required and have begun to show promising results. These include a backlit-pinhole point-projection technique, pinhole and slit arrays, distributed polychromatic sources, and picket-fence backlighters. In parallel, there have been developments in improving the data signal-to-noise and, hence, quality by switching from film to charge-coupled-device-based recording media and by removing the fixed-pattern noise of microchannel-plate-based cameras. © 2001 American Institute of Physics.

Notes: We report on the application of the polarized 3He gas spin filter technique for the measurement of spin-polarized diffuse neutron reflectivity with spin analysis. The spin filter together with a one-dimensional position-sensitive detector enables the simultaneous investigation of sections in reciprocal space while exploiting spin sensitivity. An example of diffuse neutron scattering from a Fe/Cr superlattice demonstrates the potential of the method. In addition we present a first step towards the interpretation of diffuse scattering from magnetic multilayers by exploiting the supermatrix formalism. © 2001 American Institute of Physics.

Notes: Measurements of electroreflectance and surface photovoltage spectroscopy of semiconductor structures are described using a transparent indium–tin–oxide-coated glass electrode in soft contact mode on the semiconductor surface. This improvisation (simplification) reduces the magnitude of the ac modulation voltage necessary for the electroreflectance measurement to less than a volt from about a kV (∼103 V) as required in the conventional contactless setup. This soft contact mode also enhances the sensitivity of the surface photovoltage signal by three orders of magnitude. We also formulate an analytical criterion to extract the transition energies of a quantum well from the surface photovoltage spectrum. © 2001 American Institute of Physics.

Notes: In this article we describe apparatus for the study of the microwave-driven growth of particles in solution by in situ small angle neutron scattering (SANS). This apparatus has enabled the first preliminary experiments using microwave-activated in situ diffraction. We take iron oxide as the prototype system, but the technique may be extended to a wide variety of chemical reactions that deposit solids from solution. The key features of the apparatus are a microwave cavity with a modular construction that may be adapted to the geometric constraints of the diffractometer, and a computer-controlled microwave generator that may be set to maintain either constant pressure or temperature in the reaction vessel. In this particular piece of equipment the reaction vessel is adapted so that part of the sample fills a cell of identical construction to those commonly used in SANS measurements for optimal transmission of the neutron beam. © 2001 American Institute of Physics.

Notes: A reflectometer based on a conventional sealed x-ray source for the study of molecular organic surface films (such as Langmuir monolayers) has been devised, which outperforms similar instruments using rotating anode generators and approaches even most advanced experimental stations attached to third generation synchrotron sources. Reflectivities of ∼5×10−9 are thus becoming available while the measurement of a full reflectivity curve takes approximately 4 h to complete. The instrument is operated under full digital control, permitting the automated recording of measurement programs. In an example of its performance we demonstrate that dipalmitoylphosphatidylglycerol monolayers on electrolytic subphases may be characterized to a level of detail which until recently was not even available at synchrotron sources. While conventional box models of lipid monolayers are inadequate for modeling experimental data at the high momentum transfer that has become accessible with the new instrument, a recently developed modeling technique based on volume-restricted distribution functions [Schalke et al., Biochim. Biophys. Acta 1464, 113 (2000)] enables studies of ion binding to the phospholipid in submolecular detail. © 2001 American Institute of Physics.

Notes: A novel methodology for simultaneous strain and temperature measurements by means of an ac powered electrical resistance strain gauge connected to a strain conditioner using thermocouple wires is proposed and validated. To this aim a specific device has been designed and implemented; the characteristics of the electronic circuit for signal conditioning have then been tested in order to determine the overall performances in temperature and strain measurements. The field verification of the method is conducted by imposing strain fields in the range from 0 to about 700 μm/m and temperature variations in the range from −10 to 100 °C. The difference between the strain measured by the proposed device and the one evaluated by a conventional digital strain meter was always less than 4 μm/m while the mean temperature discrepancy was 0.5 °C with respect to the reference temperature measured with a K-type thermocouple. Finally, compensation of temperature effects on the actual strain value has been performed while the temperature ranges from ambient to 100 °C with a residual error value of 1.4±1 μm/m. © 2001 American Institute of Physics.

Notes: A wide band electro-optic modulator is presented which allows the frequency calibration of Brillouin spectra over the frequency range from a few MHz up to (approximate)40 GHz, a range spanning Brillouin light scattering from condensed matter. Measurements of both frequency and the linewidth of Brillouin peaks relative to longitudinal acoustic modes of water using the electro-optic modulator as a frequency reference are presented. © 2001 American Institute of Physics.