ALBERT

Notes: We have developed a capacitance displacement sensor whose novel design greatly simplifies its construction and use. It is small, compact, extremely simple, and capable of angstrom resolution. It can be used with samples of any shape, size, or dielectric constant. One variant of the design allows its use at high temperatures, where such resolution has been unattainable until now. It may also be used to detect small changes in angle.

Notes: The metal coating on the surface of organic thin films has been examined to measure their surface profile by using a scanning stylus on them. The thickness of a Langmuir–Blodgett film has been successfully obtained by covering a sample with a platinum layer some nm thick. The network of the deposited overlayer is considered to be responsible for an increase in mechanical strength sufficient to endure a stylus load.

Notes: Two asymmetric double-probe configurations are presented. In each pair, one probe (antiprobe) has a surface area much larger than the other one (e probe). This asymmetry enables one to obtain the entire electron branch of the I-V characteristic and its second derivative. The e probe is axisymmetrically surrounded by the antiprobe and this geometrical arrangement leads to the removal of the influence of plasma potential fluctuations on the measurements. One of the configurations, owing to the supplement of another probe (ion probe or i probe), enables one to remove fluctuations of plasma density and thus to obtain the complete parameters of a turbulent plasma.

Notes: A simple new design for a high-pressure magnetic pump is described. The pump requires minimal machining, requires no lubricant or seals, and uses no special alloys, resins or polymer components, internally. The pump described could circulate supercritical carbon dioxide and methanol mixtures satisfactorily and could achieve pumping rates of 200-cm3/min water at atmospheric pressure and 30-cm water head. The pump is assembled primarily from commercially available parts at a total 1989 cost of approximately $300 plus the cost of the motor and drive.

Notes: A high-accuracy optical attenuator with transmission efficiencies variable in pseudobinary steps over a wide range is described that uses multilegged optical fiber lightguides and a set of optical shutters. It features excellent stability and reproducibility, and thus has proved particularly useful in some specific applications. Procedures for calibrating the relative light transmission efficiencies by the use of scintillations as a stable pulsed light source are also described in some detail.

Notes: A method for stabilizing the center frequency of a directly modulated semiconductor laser is described. The laser frequency is locked to a Fabry–Perot etalon by controlling both the injection current and temperature by a frequency error signal simultaneously. The square root of the Allan variance obtained here is 2.5×10−13〈σy(τ)〈4.0×10−13 for the sampling time 1 s〈τ〈1000 s.

Notes: In a typical reflection ellipsometry experiment, one characterizes the polarization state change that a polarized light beam undergoes upon reflection from a specular surface. This measurement provides ρ≡rp/rs, where rp and rs are the complex amplitude reflection coefficients of the surface for p- and s-polarized waves. Nearly 15 years have passed since the development of automatic ellipsometers along with the detailed calibration, error analysis, and data reduction procedures to be used with them. More specifically, these powerful instruments permit (1) determination of bulk dielectric functions and nondestructive depth profiling of static multilayered materials through measurements as a function of photon energy and (2) characterization of dynamic surfaces in adverse environments through measurements as a function of time at fixed photon energy. In the 15 intervening years, the major research thrusts in ellipsometry have been the exploitation of these instruments in materials and process characterization in diverse areas of materials science and electrochemistry. One of the simplest and most popular automatic ellipsometers is a photometric instrument in which one or more of the optical elements (polarizer, compensator, and/or analyzer) is designed to rotate continuously. In this article, the major developments in rotating element ellipsometry are reviewed since the first report of an automatic rotating analyzer instrument by Cahan and Spanier in 1969. The topics covered include rotating element configurations, calibration, characterization of errors and imperfections, absolute accuracy, data reduction, precision, and a review of the real-time applications accessible to these instruments. The sections on calibration, errors, and data reduction include new material and are written from a practical standpoint to assist in instrumentation setup and troubleshooting. The development and improvement of next-generation rotating element instruments that employ optical multichannel detectors to collect spectroscopic data on dynamic surfaces with time resolution as short as 5 ms now defines the forefront of research in this field.

Notes: A given uncertainty of the output current vector of the FDP leads to a corresponding uncertainty in the determination of the Stokes vector of incident light. Using an FDP instrument matrix measured free from imperfections in the calibration optics, and for a preset level of error for each current, the root-mean-square errors (RMSE) of the three normalized Stokes parameters (NSPs) are calculated as functions of the state of polarization of an assumed totally polarized incident beam. Experimental results are also presented that show the effect of reducing the power level of a light beam (from ∼0.2 mW to 〈60 nW, an attenuation range of 35 dBs) on the precision with which the NSPs are measured. The RMSE of each NSP is virtually independent of attenuation over an initial range of two decades and rises subsequently. However, it is the digitization (or quantization) error of the 12-bit analog-to-digital converter that sets the limit on precision in our FDP. The accuracy with which the NSPs are measured is also essentially independent of light level, provided that the adjusted operational-amplifier gains are correctly accounted for. The ability of our prototype FDP to resolve small changes of the state of polarization of light is tested directly by introducing known deliberate perturbations around several input states. Polarization states that are separated by 0.1° on the Poincaré sphere are found to be resolvable with an uncertainty of ∼0.03°.

Notes: We have designed and built a light scattering system that can detect scattered light in two spherical angles with scanning ranges more than 270° about the vertical axis and 100° about a horizontal axis. The detector and the sample holder are automated by high-precision stepping motors with a minimal angular increment 0.01° or 0.02°. A novel modular design in the detector allows the experimenter to examine the image of the scattering object and the direction of the scattered light while the detector is fixed at the measurement position. The angular resolution of the system is smaller than 0.19° in both azimuthal and polar directions. This setup has been successfully applied to study the static and dynamic properties of the ordered phases in colloidal solutions.

Notes: The design, construction, and evaluation of a combination spectrometer for measuring electronic absorption (EA), natural circular dichroism (CD), and magnetic circular dichroism (MCD) are described. Around the optical components of a JASCO ORD/UV-5 spectropolarimeter, a new EA/CD/MCD instrument was built with the realized intentions of increasing sensitivity and upgrading the analog tube type circuitry to a solid-state digitally, computer-controlled spectrophotometer. It is a flexible, dynamic, and user-controllable system, interfaced to an Apple II Plus computer, for studying instrument and signal parameters. The monochromator (M), photoelastic modulator (PEM), photomultiplier tube applied voltage (PMHV), and photomultiplier tube dc output current (PMdc) are under complete and independent software control. Our system has two unique aspects for obtaining the circular dichroism. First, the ac signal is measured with a voltage-to-frequency (V/f) converter; and, second, both the ac and the dc are independently recorded and their ratio is digitally calculated. This design has several advantages which include the elimination of voltage divider integrated circuits or division electronics, a wide dynamic range, a greater precision of ac values at low percentages of full scale, and the capability of continuous integration over long time periods. Also, both types of spectra, EA and CD or MCD, are obtained from the current output of the PM. This paper not only describes the design of the instrument for obtaining the two types of spectra but also compares four methods of obtaining the circular dichroism. Sensitivities of ∼1×10−7ΔA units are achievable as determined by measuring CD spectra of the well-known enantiomer (+)−[Co(en)3]3+.

Notes: A matrix method is introduced to invert the Poisson transformation that characterizes the effect of shot noise on optical measurements. This method offers the possibility of removing the effects of shot noise from these measurements. The theoretical limitations of the transformation and an algorithm for evaluation of the transformation matrix with maximal precision are discussed.

Notes: We have developed two high-efficiency, all-solid-state exciters for pumping TEA CO2 lasers, and experimentally proved their energy scalability, high-efficiency operation, and high repetition rate operation. The small-scale all-solid-state exciter of the two-stage magnetic pulse compressor was operated with an output transfer energy of 8.8 J/pulse and energy transfer efficiency of 78%, and the average CO2 laser power of 117 W was obtained at 250 pps using this exciter. The larger all-solid-state exciter of three-stage magnetic pulse compressor is ten times as large as the small one, and operated with an output transfer energy of 95 J/pulse and an energy transfer efficiency of 84%. With the larger exciter, a CO2 laser output of 9.1 J/pulse was obtained with a total laser efficiency of 8.1%. As a result, the scalability of the exciter for the CO2 laser has been demonstrated.

Notes: We have developed a constant current supply and a temperature control circuit that can be used for frequency-stable operation of laser diodes. These instruments can stabilize laser diode injection current and temperature to better than ±1 μA and ±0.3 mK, respectively, over time periods exceeding 1 h. We have excited the Li(2S↔2P) transition with a red-light-emitting laser diode and find that our instrumentation stabilizes the laser frequency to within ±10 MHz over a period exceeding 1 h.

Notes: A combined microwave cavity and photographic diagnostic for high-speed projectiles has been developed. The diagnostic allows consistent determination of projectile mass and shape and serves as one fiducial mark for a speed measurement. The 3.219-GHz cavity has been used for experiments with both frozen deuterium and plastic pellets traveling at speeds from 1500–4500 m/s.

Notes: An interrupted field time-of-flight (IFTOF) technique that enables displacement-current-free measurement of the photocurrent in the conventional transient photoconductivity experiment is described and implemented. During the drift of the photoinjected charge carriers across the sample, the applied field is removed at time T1 and reapplied at time T2=T1+ti, where ti is the interruption time. During the interruption period ti, the charge carriers interact with the deep traps so that the recovered photocurrent when the field is reapplied at T2 = T1 + ti indicates the concentration of carriers remaining in the transport band. Although the IFTOF technique has a number of distinct advantages for studying charge trapping and release processes in high-resistivity solids, it has generally not been adopted as a convenient experiment since the sample capacitance results in large displacement currents at switching.The present paper describes a Schering-type bridge network that is excited by a switchable floating high-voltage supply. Recently available high-voltage complementary TMOS transistors were used to switch voltages as high as 500 V. Trigger signals to initiate the various IFTOF events were simply and economically generated from TTL logic gates and IC timers while the required time delays were obtained via clocked digital countdown techniques. The IFTOF method was successfully applied to the examination of hole trapping processes in chlorinated a-Se:0.3%As xeroradiographic-type films for which the conventional TOF measurement indicated essentially trap-free photocurrent. Using the IFTOF technique, it is shown that over a time scale far exceeding the conventional TOF transit time, the photoinjected hole concentration under low field conditions decays almost exponentially with a well-defined trapping time τ. Furthermore, by interrupting the electric field while the photoinjected charge packet is at different locations in the film, it is shown that the IFTOF technique may be used to examine the dependence of the trapping time on the distance into the film. IFTOF is therefore a valuable technique for studying trapping inhomogeneities in amorphous semiconductor films. It is expected that the simple displacement-current-free IFTOF technique described in this paper, with further improvements, may be applied to study charge carrier trapping and release kinetics in a wide variety of high-resistivity solids.

Notes: A method has been developed to significantly suppress the effects of statistically distributed reference pulses on the gain of a stabilized scintillation spectrometer. A modified analog stabilization scheme equipped with a pulse derandomizer is proposed for this purpose. Using this method the energy resolution of the reference peak for reference pulse rate 10 s−1 improved nearly twice, namely from 7.9% to 4%.

Notes: A modified Mach–Zehnder interferometer has been built for measuring the electro-optic properties of crystals. The system is capable of resolving an optical path length change of 5×10−3 A(ring). The electro-optic R33 coefficient of the LiNbO3 crystal has been measured; the result is in excellent agreement with the previously reported values.

Notes: A new far-infrared spectrometer design is described that utilizes double polarization modulation. Based on the Martin–Puplett interferometer, this new design has high sensitivity in the region between 5 and 200 cm−1 and eliminates problems due to fluctuations in the source, interferometer drift, and reduced dynamic range in studies with small sample absorption. The new spectrometer allows, for the first time, the extension of reflection-absorption spectroscopy of ultrathin films and surface coatings into the far infrared. We present far infrared reflection-absorption data of ultrathin potassium iodide films and submicron thick polyethylene oxide films. Use of the spectrometer for far infrared dichroism studies of thin polymer films and dielectric crystals and polarization-dependent normal incidence reflectance measurements is also described.

Notes: We have constructed a high-resolution x-ray image intensifier (XRII) for use in atomic physics. The XRII consists of an alkali halide scintillator crystal coupled by a fiber optic to a proximity focused microchannel plate stack with a bialkali photocathode and wedge and strip readout. The useful area of the detector is 12 cm2. We have measured full width half maximum spatial resolutions at 22 keV of 300 μm and at 122 keV of 600 μm with 0.5-mm-thick and 1.6-mm-thick CsI(Na) crystals, respectively. With NaI(Tl) crystals, x-ray arrival times can be determined with sub-100 ns resolution. In this paper we present the detailed performance of the XRII as well as a brief discussion of the theory of photoelectron limited fast timing.

Notes: A cell has been constructed which allows the electrochemical interphase on electrode surfaces to be studied ex situ using glancing angle x-ray and gas phase electron yield detection. The various components of the cell are described. The electrode and interphase are emersed using the thin strip emersion technique, and the x-ray beam is totally reflected from the vertical electrode surface above the horizontal electrolyte thin strip. Examples of Au L3 edge and XAFS spectra of an anodically oxidized gold electrode at θ=4 mrad show the technique to be very surface sensitive.

Notes: A simple solenoid-valve pulsed halogen atom source for the measurement of heterogeneous reaction kinetics in a very low pressure reactor (VLPR) is described. The source leads to injection of 300 μs–300 ms pulses of halogen atoms into a Knudsen cell, where their number density can be monitored in real time by means of resonance enhanced multiphoton ionization (REMPI). The operation of the source does not interfere with the detection technique. The performance of the source has also been verified using effusive molecular beam mass spectrometric analysis of the effluents of the Knudsen cell. The source is expected to find application in a variety of studies related to fundamental questions regarding etching and deposition reactions, as well as in fundamental chemical kinetic studies involving atoms and stable free radicals.

Notes: A numerical analysis of a four-electrode electron mirror is presented. It is shown that this system can have adjustable aberration coefficients, opposite to the aberrations of conventional electron optical systems. Therefore, it is possible to use such an electron mirror as an aberration corrector to further improve resolutions in electron microscopes.

Notes: A reflection electron microscope for ultrashort-time imaging of laser-induced processes on surfaces was developed. The instrument is based on a conventional transmission electron microscope modified for high-energy electron reflection, and, in addition, equipped with a laser-pulsed high-brightness electron gun, an interaction chamber, and a tilting unit. Images with exposure times of ≤20 ns of transient surface processes can be obtained. The spatial resolution depends on the exposure time and is limited by a compromise between shot noise in the electron image, chromatic aberration of the objective lens, and radiation damage due to the illuminating electron beam. The performance of the microscope is demonstrated by short exposure time images of laser pulse treated bulk GaAs and Au films on Si showing evaporation, flow, and capillary waves, proceeding within 10–500 ns.

Notes: By using a microwave heterodyne interferometer assisted by microwave scattering techniques, computer tomographic images of spatial distributions of plasma density can be obtained. Two 9.5 GHz Gunn diodes, whose frequencies are offset by 35 MHz, are used in a heterodyne branch. In front of the detection horn antenna, multiple diodes are lined up, which scatter the microwave power with modulation frequency of 5 kHz, and the whole spatial information in one direction can be obtained by a pair of launcher-detector systems assisted by these diodes. This system is a simple and low-cost means to get images compared with popularly known multichannel interferometer techniques; still, precise, spatial resolution in the images has been observed.

Notes: The Fraunhofer diffraction measurements from a tandem mirror plasma are reported. The successful use of a new multichannel detector array permits a detailed study of k−ω spectra of long-wavelength waves with a few plasma shots. The observed dispersion relations are in good agreement with those of drift wave including a Doppler shift due to E×B rotation velocity.

Notes: A novel technique was developed to measure the current distribution of an electric arc foot on the electrodes of a plasma torch. The method is based on the induced voltage generated by the passage of the arc over the measuring probe. The technique is suitable for long operation times in plasma torches. Examples of measurements are given for arcs in pure Ar and in Ar+0.3% CO, moving at 9 m/s at 100 and 140 A, respectively. The peaks in the linear current density were 7.6 and 4.2×104 A/m for Ar and Ar+0.3% CO, respectively. The current density was estimated to be around 104 A/cm2 for Ar and 2×103 A/cm2 for Ar+0.3% CO.

Notes: A simple technique has been developed for the high resolution measurement of small changes in capacitors which have one grounded electrode. The capacitor is arranged to be the tuning element in a series resonant LC tank circuit that is driven by a transistor emitter follower. Signal information is provided by observing the phase shift in the transistor collector current that results from any small change in the capacitor value. Implementation is simple, readily analyzable, provides good diagnostics, is easily multiplexed into arrays, and has potential applications in a number of areas including high resolution proximity sensing, capacitive topography, atomic force microscopy, and capacitor microphones.

Notes: Several circuits are proposed which store energy in an inductor and which, upon command, efficiently and rapidly transfer that energy to another inductor. In one of the proposals, a device is described that employs three capacitors to create, with the inductors, a doubly tuned circuit. The capacitors isolate the inductors insofar as direct current is concerned, and remove the need for "floating'' switches. To transfer energy, the current through the primary inductor is simply switched off, and the current is then "picked up'' in the secondary inductor a half cycle of oscillation later. Validation of this concept is provided by an instrument that switches 20 A between 350 μH inductors in 75 μs, the limitation on speed/current being the 400 V limit of the circuit employed. Loss of 5% of the current is ascribed totally to the resistance of the circuit during the half cycle switching period.

Notes: A drop calorimetric apparatus is described. The receiving calorimeter is isoperibolic and quasi-isodiabatic (an almost constant heat flow is maintained during the measurement by means of a fixed temperature difference ΔT between the calorimeter and the surrounding metallic block). The incremental ΔH of a sample dropping from the furnace into the calorimeter (at room temperature) is obtained by ΔH=ΔE1+ΔE2 where the energy ΔE1 is evaluated electrically, and ΔE2 (which should be zero if the calorimeter were perfectly isodiabatic) is computed by integration of the small ΔT perturbations. ΔE2 is about 1% of the total energy involved. Results of preliminary tests and examples of applications in metallurgical thermochemistry are reported.

Notes: A miniature high-pressure cell for electrical and galvanomagnetic measurements down to 2 K has been designed and fabricated. The Bridgman anvils are made of either tungsten carbide, or reinforced alumina, for pressures up to 8 and 4 GPa, respectively. This cell is calibrated both at high pressures and at low temperatures. The pressure clamped at room temperature is not found to vary significantly when cooled down to liquid helium temperatures.

Notes: A personal computer controlled CAMAC analyzer for time resolved spectroscopy and the design of a specially interfaced CAMAC module for routing data are described. The system is intended for spectroscopic data acquisition of slowing-down-time or time-of-flight neutron spectrometers. Its maximum throughput rate is 140 kHz and can be increased up to 250 kHz.

Notes: A fast scanning tunneling microscope (FSTM) is developed using a new method of compensating for the probe tip servo error in constant current mode. The compensation value is derived from the ratio of tunnel current fluctuation to tunnel current (ΔI/I) in a differential tunnel current equation. Dynamic video images of Si(111) adatomic structures taken using the FSTM prove that this method is effective for fast scanning.

Notes: A self-crowbar switch for a gas-puff z-pinch, driven by a pulsed power generator with output voltage 600 kV, pulse width 70 ns, and characteristic impedance of 3 Ω, has been built and tested successfully. Discharges with pulsed gas injection are placed into four groups dependent on the delay between the pulsed power generator trigger time and the gas-puff trigger time. For short delay times (〈2.8 ms), vacuum discharge occurs. For moderate delay times (2.8–3.8 ms), a z-pinch plasma is produced without using the self-crowbar switch, and the plasma exists for a much longer time than the voltage pulse, that is, 700 ns compared to 70 ns. For relatively longer delay times (3.8–6 ms), the self-crowbar switch operates, and the decay time of the current becomes approximately 2.5 μs. Moreover, a z-pinch occurs after self-crowbarring. For long delay times (〉6 ms), a z-pinch does not occur. The self-crowbar switch is believed to operate by photoionization of puffed gas which has reached the switch region.

Notes: We describe a new technique for picosecond synchronization on a 80-MHz mode-locked laser. An implementation of such technique is described, and experimental results are presented. Better than 30-ps FWHM synchronization jitter is demonstrated, with an optical pulse amplitude fluctuation of a decade. Such results confirm that single-photon-timing experiments with picosecond resolution are possible by using high-repetition-rate light pulses (i.e., without any cavity dumper).

Notes: An optical configuration, utilizing a two wavelength source is presented. Its use as both a normal heterodyne-interferometric sensor yielding nanometer resolution, and as a subcarrier system with a much enhanced unambiguous range, but reduced resolution, are discussed. A major attribute of this system is that heterodyne signal processing has been achieved without the use of a frequency or phase shifter. Preliminary results indicate the resolution of the first configuration is comparable to that achievable in interferometric systems, while the latter shows a displacement resolution of greater than 1 mm, and vibration amplitude resolution of greater than 10 μm, over a 22-cm dynamic range.

Notes: A special purpose vibrating orifice droplet generator is described possessing improved short-term monodispersity (instantaneous diameter fluctuations of 2×10−5 and a differential drift of 10−5/min.). We demonstrate that this is sufficient to allow cw laser excitation of specific morphology-dependent resonances (MDRs). Improved performance results from (1) the liquid sample being direct pressure fed to the vibrating orifice from a closed pressure reservoir rather than by a conventional gear driven syringe pump, and (2) the vibrating orifice is driven by a periodic square wave voltage source having a frequency which is four orders of magnitude more constant (1 part in 108 per day) than sources normally used. A novel variational size spectroscopy is also described that is made possible by programmed frequency ramping of the voltage source driving the vibrating orifice. By monitoring elastic scattering during ramped size changes we have been able to infer precise values of droplet index of refraction (to ±0.001) and size (to ±3 parts in 104) at any orifice operating frequency by comparison of the resulting experimental pattern to Lorentz–Mie calculations. This aerosol source permits the next generation of optical experiments (e.g., double resonance, fluorescence rate inhibition and enhancement, cw nonlinear optical, accurate chemical speciation, etc.) to be performed on droplets with diameters of 10–80 μm.

Notes: An integrated flat-flame/ microprobe sampling quadrupole mass spectrometer system, complemented by optical spectrometry based on optical fibers, is presented. The short microprobe sampling line (total 25 cm) is directly connected to an open ion source closely flanked by two nude cryopumps (900 l/s) yielding a background pressure of 10−9 Torr and a sampling pressure of about 10−5 Torr. Due to this improved microprobe system, mass spectrometry can be used for analysis of stable species (including fuel, O2, H2O, CO2, CO, and Ar) with less disturbance of the sample than with a conventional microprobe with a back pressure of about 1 Torr. Optical spectrometry is used for the study of emission from important radical species (such as C2, CH, and OH). The system is proposed as a complement to more conventional flat-flame/MBMS systems in which the sampling cone can effect the experimental system. Details are provided concerning the configuration of the whole system ranging from gas delivery to data evaluation. Test data are presented for a 16% methanol/68% oxygen/16% argon flame studied at a pressure of 40 Torr, to elucidate the special features of this system.

Notes: A new excitation/detection scheme for Fourier-transform–ion-cyclotron-resonance (FT-ICR) studies is described. The ions are created in the center of a hyperbolic Penning trap and excited to a large magnetron radius. Parametric-mode excitation is used to drive the cyclotron motion. The ions are detected in the conventional dipole-mode detection scheme by use of a segmented ring electrode. Since the resonance frequencies of excitation (ν+−ν−) and detection (ν+, the reduced cyclotron frequency) differ by the magnetron frequency (ν−), this method allows the simultaneous excitation and detection of the ion motion.

Notes: In this work we present an alternate concept of a fast-pulsed valve which is convenient for molecular-beam spectroscopy and gas puffing in plasma assemblies. The valve operates at repetition rates up to 100 Hz with repetitive high-intensity 100-μs FWHM pulses. Its efficient closed magnetic circuit with low power consumption permits a high-repetition-rate operation. The very light mass-spring assembly allows for rather narrow repetitive pulses. The valve has a small size and is self-sealed for use with corrosive gases. A fast PVDF pyroelectric detector was used for diagnosis.

Notes: The design and operating characteristics of a fully differential pressure transducer are described. The device is intended for use with He II heat transfer experiments where it operates in vacuum and at low temperatures (T〈4.2 K). A movable electrode is attached to two sets of miniature bellows such that the electrode position is determined by the differential pressure across the device. The movable electrode is located between two fixed electrodes, thus forming a pair of variable capacitors. A dedicated charge amplifier is used to convert the pressure induced capacitance change to an ac output voltage. The sensitivity is roughly 5 μV/Pa. For the present application, the capacitor and electronics have acceptable performance, with a mean noise level of ±5 Pa.

Notes: Direct measurement of the transfer function of hot-wire anemometers is needed whenever any turbulence frequencies approach the hot-wire frequency response. In particular, in high-speed applications it is not possible to obtain hot-wire frequency response sufficient to capture all of the turbulent kinetic energy. With knowledge of the hot-wire response, either an estimate of the turbulent integral scale or an approximation of the high-frequency part of the turbulent spectrum may be sufficient to correct measurements by post-detection frequency compensation. Described in this article are simple electronic circuits and a technique for obtaining sine-wave test frequency response of a hot-wire anemometer in a very short time without prohibitively high sampling rates.

Notes: An analysis is presented to calculate scalar permittivity and tensor permeability for ferrite materials from waveguide transmission cavity data. A correct measurement of the permittivity of ferrites and other high dielectric constant materials, requires an extension of current techniques to a second-order perturbational analysis. This second-order correction offsets an apparent frequency dependent dielectric behavior measured during a multimode cavity measurement. The analysis implies that dimensions of ferrite samples to be used in various waveguides (X-Ka bands) must be reduced to a near 0.015-in. cross-sections to eliminate a coupling of permittivity and permeability measurements.

Notes: A new version of a corona triode setup, allowing charging dielectric foils with a constant current, was developed. The charging current is kept constant by controlling the grid voltage. We show that the sample surface potential can be inferred from the grid voltage and present results of the uniformity of charge deposition during the charging procedure. Sample charging currents could be varied from 1 to 300 nA/cm2 and the foils could be charged up to ±6 kV. The method was applied to measure the potential buildup on Teflon FEP and PVDF samples and these results are discussed. They showed that the method can be successfully applied to study the polarization buildup of β-PVDF foils under corona charging.

Notes: The principle common to mechanical integraphs in general is reviewed, with regard to many of those previously published. In addition, two novel integraph mechanisms are described in detail.

Notes: The stepwise expansion method for the measurement of compressibility isotherms of gases, developed recently in this laboratory, has been modified in order to measure those gases for which only low-pressure fiducial density data are available. The modified method has been tested with CH4 as a measuring gas at 298.15 K and up to 9.9 kbar.

Notes: We describe the design of a modified split-ring resonator, especially suited to low-temperature experiments, which enables cavities with dimensions of order 1 cm to resonate at frequencies as low as a few hundred megahertz.

Notes: Generation of picosecond and nanosecond time-scale time delays in a pump-probe laser system has been implemented without the use of an optical delay line, by rf-phase shifting of the mode-locking rf-signal. The system consists of dual picosecond dye lasers pumped by synchronized mode-locked, Q-switched, cw Nd:YAG lasers. The phase shifter operates with better than 10-ps precision and generates time delays from 0 to 26 ns.

Notes: A completely stand-alone multichannel scaler system which can be easily built using commercially available integrated circuits is described. The multichannel scaler is interfaced to an 8-bit Intel-8085 based microcomputer through a peripheral interface adapter (PIA) Intel 8255. The inherent data latching property of PIA is made use of in the present study. The multiscaler interface system developed has decided advantages: it displays 1024 channels simultaneously, needs no attention of the microprocessor during data acquisition, has less hardware complexity, irrespective of the kind of microprocessor chosen, and has a minimal dead time (approximately 2%) and triple precision storage. Further, the method of Mössbauer data acquisition described in our note results in a higher rate of collection and subsequent lower rate of processing.

Notes: The gain of a secondary electron multiplier has been measured in the magnetic field perpendicular to ring-shaped continuous dynodes. It has the maximum value at the magnetic flux density of about 80 G.

Notes: A simple and safe way is presented to protect power meters when dealing with moderate waist and high peak-power pulsed laser beams, such as Nd:YAG laser beams.

Notes: A bellow-pump allows to circulate high-purity gas at high pressure without contaminating the sample. Its main features are low cost, simple design, easy operation, all-metal construction, and adjustable flow rate.

Notes: An instrument has been constructed for generating the complex scanning and data-collection sequences required for scanning tunneling microscopy. The instrument is controlled by and returns data to a laboratory computer over an IEEE 488-bus. A very high data-collection speed was achieved through the use of a digital signal-processing microprocessor coupled to a 16-bit I/O processor.

Notes: The foil-induced dissociation of molecular ions can provide a direct image of the stereochemical structures of small molecules. Such experiments require high-resolution measurements of the relative momenta of all dissociation fragments. In order to improve and extend previous studies of this type to a larger variety of molecules and clusters, we have developed a new type of low-pressure multiwire proportional counter. The novel feature of this large-area (25×50 cm2 ) multiparticle detector is that all the signals are recorded from a single two-level printed circuit board which serves as the anode. This segmented anode consists of three families of nonintersecting "wires'' which are interwoven on the rear surface of the board. By redundantly determining positions and arrival times, the new segmented anode multiparticle detector provides good time resolution (100–200 ps) and high spatial resolution (0.2 mm) for detecting as many as six simultaneous particles.

Notes: Nutating a Cassegrain telescope's secondary mirror is a convenient method of steering the telescope beam through a small angle. Using this principle we have constructed a high performance beam switch for a millimeter wave telescope. A low mass, graphite-epoxy laminate secondary mirror is driven by linear electric motors operated in a frequency compensated control loop. By design, the nutator exerts little net oscillating torque on the telescope structure, resulting in virtually vibration free operation. The inherent versatility of beam switching by subreflector nutation allowed us to test a variety of switching waveforms without making any hardware changes. To reduce the peak stresses on the mechanical linkage between the mirror and the motors and to attain a minimum transition time between mirror positions, we use a digitally generated driving waveform tailored to the system's transfer function. The nutator can shift the telescope beam by 10 arcminutes, a 1.25° rotation of the 75-cm-diam secondary mirror, in an interval of 8 ms and it can sustain a switching frequency of 10 Hz.

Notes: A time-of-flight positron emission tomograph (TOF-PET) was recently developed for the purpose of clinical medical study and brain research. It provides high-quality positron images with a spatial resolution of 8 mm full width at half-maximum (FWHM) which is obtained by the use of time-of-flight (TOF) location techniques and small 10×18-mm BaF2 detectors to detect the positron-electron annihilation γ-rays. The time-of-flight resolving time was 623 ps (FWHM) in the system, which has improved the S/N ratio for positron images. This new TOF-PET has been designed to digitally record the arriving time of γ-rays at the detectors using the system clock. With this method, the architecture of hard and software for taking TOF sinograms and reconstructing TOF images is simplified compared to that of other TOF-PET systems. The details of this system are described here.

Notes: The operational characteristics of a metal vapor vacuum arc ion source have been studied. The beam current has been measured as a function of ion source extraction voltage (5–80 kV), arc current (50–250 A), metal-ion species (Ti, Ta, and Pb), and extractor grid spacing (0.89 and 0.38 cm). The measured beam current ranged up to 700 mA. The parametric variation of beam current is compared to that expected from the Child–Langmuir equation and excellent agreement is found.

Notes: In this paper a dual laser acousto-optical diffraction technique is described that provides an absolute calibration of a CO2 laser coherent scattering apparatus and other heterodyne receivers. Rather than directly detecting the sound pressure of the acoustic field or the power diffracted from the CO2 laser beam, the sound pressure is measured with the heterodyne detection of acousto-optical diffraction from a He-Ne laser beam. Noise equivalent power (NEP) measurement of the heterodyne receiver for the CO2 laser scattering apparatus and the studies of the detector bias and local oscillator power dependence of NEP values are performed by this technique. The measured minimum NEP value (6.8×10−20 W/Hz) is very close to the quantum noise limit.

Notes: This article evaluates a photoreflectance apparatus in which unwanted photoluminescence and laser light are separated from the signal by a monochromator placed in front of the detector as compared to separation by the more commonly used glass filters. We present results from the application of both techniques to the study of the 3.4- and 4.3-eV structures in both bulk silicon and silicon films on sapphire, the 1.4-eV structure in GaAs, and the 1.8-eV structure of Al0.33Ga0.77As. The replacement of glass filters with a second monochromator, in addition to allowing a better rejection of spurious light, extends the range of wavelengths in which a satisfactory photoreflectance signal can be obtained and permits observation of a signal closer to the modulating laser line. On the other hand the use of glass filters can be preferable for high laser power, for weak signals in regions of low grating efficiency, or merely for economical reasons.

Notes: A high-throughput von Hámos-type Bragg crystal spectrometer is described that is operated with the Livermore electron beam ion trap. The spectrometer is employed to measure high-resolution x-ray spectra from highly charged heliumlike and neonlike ions. Data from heliumlike Ti20+ and Fe24+ and from neonlike Au69+ are presented to demonstrate the utility of the new instrument.

Notes: We describe the design and performance of a 10-GHz harmonic-content frequency-domain fluorometer. The modulated excitation is provided by the harmonic content of a train of ps pulses. High-speed and/or high-frequency detection was attained with a triode-type microchannel plate photomultiplier tube (MCP PMT) from Hamamatsu, R-2566-6, with 6 μm channels. To minimize the cost of the electronic components, and to minimize the noise due to these components, the detection circuits consists of two frequency ranges, 10 MHz–2 GHz and 2–10 GHz. The upper frequency limit of 10 GHz is determined by the current MCP PMT, so the usual configuration includes a low-noise 2–10-GHz amplifier. This amplifier is easily replaced with a 2–18-GHz amplifier to allow operation to 18 GHz and the use of faster PMTs, should they become available in the future. Measurement of known optical delays demonstrates the accuracy of the instrument. For instance, a 1.69 ps optical delay was measured as 1.7±0.4 ps from 0.5 to 10 GHz, and 1.7±0.2 ps from 2 to 8 GHz, where the uncertainty indicates the maximum deviation from the expected value. The data were shown to be free of systematic errors by measurements on fluorophores with single exponential decays, with decay times ranging from 61 ps to 1.24 ns. Measurement of anisotropy decays with correlation times of 24 ps are shown and it is predicted that correlation times as short as 1 ps could be measured with this instrument. And finally, the sensitivity of the instrumentation was demonstrated by measurements of the very weak intrinsic tryptophan emission of deoxyhemoglobin, which displays decay times ranging from 2 to 820 ps.

Notes: The construction and the fundamental studies of a repetitive flash x-ray generator having a simple diode with an energy-selective function are described. This generator consisted of the following components: a constant high-voltage power supply, a high-voltage pulser, a repetitive high-energy impulse switching system, a turbo molecular pump, and a flash x-ray tube. The circuit of this pulser employed a modified two-stage surge Marx generator with a capacity during main discharge of 425pF. The x-ray tube was of the demountable-diode type which was connected to the turbo molecular pump and consisted of the following major devices: a rod-shaped anode tip made of tungsten, a disk cathode made of graphite, an aluminum filter, and a tube body made of glass. Two condensers inside of the pulser were charged from 40 to 60 kV, and the output voltage was about 1.9 times the charging voltage. The peak tube voltage was primarily determined by the anode-cathode (A-C) space, and the peak tube current was less than 0.6 kA. The peak tube voltage slightly increased when the charging voltage was increased, but the amount of change rate was small. Thus, the maximum photon energy could be easily controlled by varying the A-C space. The pulse width ranged from 40 to 100 ns, and the x-ray intensity was less than 1.0 μC/kg at 0.3 m per pulse. The repetitive frequency was less than 50 Hz, and the effective focal spot size was determined by the diameter of the anode tip and ranged from 0.5 to 3.0 mm in diameter.

Notes: An eight bit digital phase shifter is described which is suitable for multiple pulse NMR of solids in terms of settling time ((approximately-equal-to)2 μs) and phase resolution (1.406°). The unit incorporates an 8-bit Merrimac digital phase shifter model PSDW-84-1, and an amplification-damping-pulse shaping circuit to solve the problem of variable attenuation as a function of phase setting. Results of multiple quantum spin counting and homonuclear dipolar decoupling experiments on ensembles of strongly dipolar coupled spin 1/2 systems are used to demonstrate the capability of the unit.

Notes: A device for the measurement of thermal properties of phase change materials and, in general, of medium thermal conductivity materials, is described. The measuring cell is a modified version of the guarded hot plate technique, here designed for about 8-cm-diam samples. A well-known difficulty arises in such a device: its limitation when the sample cross section becomes too small with respect to its thickness. A finite-element model is used to study the shape of isotherms in a thick sample (10 cm) for different configurations of the measuring device. This analysis has led to the selection of the optimum design. It shows that the instrument is able to handle samples with a diameter to thickness ratio of about 1 so far as the heat transfer coefficient remains beneath some limits (here 100 W/m2 K). The control system is also described and some typical results are presented.

Notes: A scheme for reducing vibration that occurs during precise positioning control is discussed. The positioning drive mechanism used in ULSI manufacturing is composed of many mechanical parts: a rotational dc motor, a ballscrew, etc. Such a mechanism causes vibration while the positioning stage approaches a desired position. Therefore, this article proposes ways to diminish this vibration. The control system currently in use utilizes the output from a tachogenerator (TG) attached to the DC motor as a damping loop. However, the TG cannot detect the positioning stage velocity but only the dc motor velocity. The vibration reduction scheme proposed in this article is to use the damping loop of the directly measured stage velocity. The stage velocity is calculated from the stage positions which are detected by a laser interferometer. A new control scheme has been designed after modeling the positioning drive mechanism and the control system currently in use. The validity of the proposed control scheme has been confirmed by computer simulations and experiments. As a result of diminishing a vibration of about 85 Hz by the proposed control scheme, the positioning time was decreased from 105 ms to 64 ms for a 20-μm positioning stroke.

Notes: We report on a study of the error fields of a set of layer-wound short solenoids of the type used in high-current electron linear-induction accelerators. These error fields are mainly caused by the azimuthal variation of the winding pitch angle. The conventional winding pattern design tends to concentrate the error fields in a dipole component perpendicular to the solenoid axis. Compounding the problem are smaller contributions due to the asymmetric coil feeds and conductor crossovers from one layer to the next. We have constructed and tested a prototype quadrufilar solenoidal magnet which utilizes symmetry to cancel the effects of current leads and crossovers and which, in the absence of winding errors, should have an intrinsically straight magnetic axis. This design tends to concentrate the error field in the much less harmful octapole component. Measurements of the dipole error field yield a value of the order of one milliradian for the quadrufilar magnet as compared with about six milliradians for the conventional ETA-II magnets and twelve milliradians for the ATA magnets. Several approaches for improvement are suggested. The improved cooling of the quadrufilar design allows dc operation at fields almost three times higher than the conventional magnets.

Notes: We report on the estimation of the variance of a narrowband stationary random process in the presence of wideband observation noise. The aim is to reduce the measurement time required to obtain accurate estimates. We discuss the solution based on the Wiener-Kolmogoroff optimum filter and propose a simple suboptimal technique using an analog differentiator. Computer simulations as well as experimental results on the Brownian motion of a cryogenic gravitational wave detector with high quality factor confirm the theoretical prediction that the variance of a narrowband process can be determined in a time smaller than the correlation time of the process.

Notes: We have investigated the inert gases Ar, Xe, and He for suitability as pressure media in a diamond anvil cell at liquid-helium temperature, from 0 to 30 kbar, and compared these with a 4:1 methanol/ethanol mixture. Xe gives severe nonhydrostaticity and is of no value as a low-temperature medium. Ar gives much less nonhydrostaticity, but little improvement over the 4:1 methanol/ethanol mixture. He gives no observable nonhydrostaticity even when the pressure is changed at low temperature. A technique for loading with He is presented.

Notes: We present the specifications for a computer-controlled, low-noise, bipolar current source for use with superconducting electronics. Our instrument, which contains two such sources, operates in the 10−7–10−3 A range and has a bipolar output in which the null output is not a unique point on the operating curve. This device has been used successfully with superconducting electronics to measure current-voltage characteristics of superconducting thin films.

Notes: We describe a high-gain (∼107) amplifier for use with large-area silicon photodiodes for monitoring the intensity of plasma light from fusion experiments. To achieve the necessary gain without saturating the output signal, the amplifier design incorporates a bootstrap technique and capacitive coupling between amplifier stages. This design eliminates voltage offset at the amplifier output due to detector leakage, while retaining desirable low-frequency response characteristics.

Notes: We have developed an apparatus for easy and consistent etching of small tips suitable for use with a scanning tunneling microscope. Its unique features are free access to the etching region and a continuous supply of electrolyte for the production of many tips in succession.

Notes: We have designed and implemented a rugged, simple double-ribbon buncher grid that has greatly increased the mean time between failure over wire mesh designs. This grid is used to prebunch several microamperes of beams of heavy ions such as 127I or 79Br at 200 keV, for injection into a MP Tandem Accelerator, itself the injector for the Chalk River Superconducting Cyclotron.

Notes: A high-power, lumped-elements, interdigital bandpass filter is described which has been used to improve the isolation between decouple and observe channels of NMR spectrometers, and to "clean'' the transmitter signals. With no calculations, and with the help of a sweeper or a spectrum analyzer, filters of this type can be easily assembled and tuned over the 90–400 MHz range, typical of the proton decoupling frequencies.

Notes: The calculation of lead-placement errors for resistivity and Hall signals is extended to the family of cross-shaped samples. Empirical expressions for errors [Δρ/ρ=− 1/2 (2d/D)2n and ΔRH/RH=− 1/2 (2d/D)n] are given in the limit of large contact displacement (d/D→ 1/2 ). For crosses, the exponent n was found to increase as n ∝ (l/D)−1.42 as the ratio of leg width to overall size, l/D, was reduced. For square and circular cloverleafs, n is less sensitive to the increase of the slit length, giving power laws with exponents of 0.8 and 0.6, respectively, in terms of the parameter λ=2r/D.

Notes: An optical configuration for a current sensor utilizing the Faraday effect is described. A common path optical fiber heterodyne interferometer is used to greatly reduce noise produced by environmental effects. A miniature sensing element at the distal end of the fiber allows remote magnetic field or current measurements to be made. Solenoid generated magnetic fields over the range 0.7 to 10 μT, corresponding to solenoid currents from 10 to 150 mA, have been detected over a frequency range from 25 to 125 Hz with a linear response.

Notes: We report on the design, characterization, and operation of a low-noise FET-input differential amplifier, which is used as second stage for a dc SQUID in the electronic instrumentation of the gravitational wave detector of the Rome group at CERN. The 3-dB bandwidth of the amplifier is from 10 kHz to 1.5 MHz. At the SQUID modulation frequency of 70 kHz the voltage noise is 0.5 nV/(Hz)1/2, the current noise is 35 fA/(Hz)1/2.

Notes: A proportional magnetic valve has been developed that permits continuous flow of cryogenic fluids and gases. The proportional valve (PV) may be electrically controlled in the manual mode (open loop current drive) or in the automatic mode (closed loop current drive). A complete control system for liquid-nitrogen (LN) flow control applications is described. The system includes alarm and automatic supply tank switching features.

Notes: The spatial resolution of a SQUID magnetometer is known to be determined by the size of the magnetometer pickup coil and the distance of this coil from the source of the magnetic field. With the advent of spatial-filtering techniques for converting magnetic field maps to current density images, it is clear that the quality and spatial resolution of the current image is also affected by the detailed characteristics of the transfer function between the current sources and the pickup coil. We show that the quality of a current image can be improved over that obtained with conventional pickup coils by using a multiturn pickup coil whose interturn spacing is adjusted to provide a source-coil transfer function with specific characteristics. This process is functionally equivalent to apodization techniques applied in optical image processing, in which the aperture function of the telescope is adjusted to improve spatial resolution. In coil design, the process of apodization involves designing a magnetometer coil whose transfer function has its first zero at a relatively large spatial frequency. Using apodization, we can decrease coil size and increase the number of turns without a large increase in coil inductance. Our model calculations demonstrate that apodization allows us to optimize the ability of a coil design to image a current distribution, subject to the constraints of signal-to-noise ratio, spatial resolution, and coil inductance.

Notes: A new controller, especially suited for phase-locked loops, is discussed. The controller, composed of RC-circuit electronics, has a gain with a slope of −30 dB/decade over a wide bandwidth. It is shown that in certain systems the present controller (PI3/2 controller) provides a much higher feedback gain than an ordinary proportional-integrator controller (PI controller). As applications, the superconducting quantum interference device (SQUID) and an electrically adjustable point contact used in surface microscopy or spectroscopy are discussed in some detail. The operation of the controller in a piezo-driven point contact was studied experimentally.

Notes: A 19-channel grating polychromator is developed to measure the temporal evolution of the electron cyclotron emission spectrum in the second and third harmonics in MTX tokamak with an aim to determine the electron temperature in ohmically heated thermal plasmas as well as the electron energy distribution function in gyrotron and free-electron laser-pumped nonthermal plasmas. The spectrometer can cover a spectral range of about 0.3 to 1.4 mm and deliver a maximum spatial resolution of about 1 cm radially. A combination of a 90° off-axis paraboloidal mirror as the collimating element and a toroidal mirror to focus the diffracted beam yields images on the exit slits with a modest astigmatic distortion. Liquid-helium-cooled InSb detectors are installed in nine channels and associated electronics are optimized for a very low noise and fast response time ( ∼ 2 μs). A faster detector element, with response 〈 100 ns, is envisioned for the remaining ten channels.

Notes: A broadband reflectometric system in O-mode operation has been developed for the density profile determination, MHD and turbulent fluctuation measurement, and evaluation of the particle diffusion coefficient in the JT-60 tokamak. For the profile determination, full Ka-Q band frequencies of BWOs have been swept in 750 μs, in order to minimize the effect of doppler shift due to the fluctuation of reflection layers. The heterodyne fixed-frequency reflectometer has unveiled its effectiveness to probe MHD activities, diagnosing the m=1 tearing mode oscillations. It has also enabled the observation of the dramatic suppression of edge plasma density fluctuations at the L- to H-mode transition in the LHCD limiter plasma. Furthermore, the propagation delay of density pulses has been observed by different fixed-frequency channels during a series of sawteeth, from which the particle diffusion coefficient was evaluated, with a newly proposed method applicable to fully diffusive plasmas.

Notes: High-power, large-angle ((approximately-greater-than)10°), collective Thomson scattering diagnostics can provide localized density and velocity distribution data of confined alpha particles, ICRH simulated alpha particles, and ions related to ICRH and neutral beam energy deposition. Millimeter-wave gyrotron systems are under development for TFTR and JET. Scattering with a submillimeter gyrotron is being investigated for Alcator C-Mod. Major design issues include plasma accessibility, scattering angle, orientation to magnetic field, spectra of non-Maxwellian velocity distributions, signal-to-noise ratio, refraction, electron cyclotron emission, and beam and viewing dumps.

Notes: Motional Stark effect produces large net linear polarization of Hα emission from neutral beams in tokamaks. Measurement of the polarization direction permits determination of the local magnetic field pitch angle. Design of a single point, spatially scannable, high-sensitivity polarimeter installed on DIII-D is described. Excellent signal-to-noise ratio with good temporal and spatial resolution was obtained in preliminary measurements of magnetic field pitch angle.

Notes: The DIII-D tokamak is being upgraded to allow for divertor biasing, baffling, and pumping experiments. This paper gives an overview of the new diagnostics added to DIII-D as part of this advanced divertor program. They include tile current monitors, fast reciprocating Langmuir probes, a fixed probe array in the divertor, fast neutral pressure gauges, and Hα measurements with TV cameras and fiber optics coupled to a high-resolution spectrometer.

Notes: Six infrared cameras measure temperature changes on the protective graphite armor inside the DIII-D vacuum vessel. Simultaneous time-dependent temperature measurements are made on armor tiles located on the centerpost and divertor regions, and on both outboard limiters. The nearly complete poloidal coverage is useful in measuring both the plasma heat flux distributions inside the vessel and the plasma power balance. Spatial resolution of each camera system is (approximately-less-than)1 cm, while the minimum resolvable time is 125 μs. Data from the IR TV systems are recorded on video tape, and are post-processed serially, using an image processor with an AT-compatible microcomputer. The processing system controls all VCRs, interprets DIII-D timing pulses, digitizes video data in the predetermined regions of interest, averages digitized signals to reduce noise, and constructs data files which are then stored as part of the permanent shot record.

Notes: Since June 1986 the DIII-D tokamak has had over 16 000 discharges accumulating more than 250 Gbytes of raw data (currently over 30 Mbytes per discharge). The centralized DIII-D databases and the associated support software described earlier provide the means to extract, analyze, store, and display reduced sets of data for specific physics issues. The confinement, stability, transition, and cleanliness databases consist of more than 7500 records of basic reduced diagnostic data datasets. Each database record corresponds to a specific snapshot in time for a selected discharge. Recently some profile datasets have been implemented. Diagnostic data are fit by a cubic spline or a parabola by the in-house energy code to provide density, temperature, radiated power, effective charge (Zeff), and rotation velocity profiles. These fits are stored in the profile datasets which are inputs for the onetwo code which computes transport data.

Notes: The PBX-M Thomson scattering system is reviewed after its first 9 months of operation. The system measures Te(R) and ne(R) at 55 radial points on the horizontal midplane with a spatial resolution of ≤1.1 cm. The scattered light is collected by a Bouwers concentric mirror system and imaged onto 12-m-long fiber bundles. A composite entrance slit is used to optimize the system performance. The synchronization between the scattered light and detector gate is done via a laser-triggered spark gap. A penetration in the indentation coil allows the (ruby) laser beam to be dumped away from the plasma chamber. Other aspects of the system will be discussed.

Notes: A continuously operable low-temperature (10–20 K) sample mount for a solid-state inelastic electron scattering spectrometer is described. The cooling is achieved by a closed-cycle gas phase He refrigerator. Because the entire sample chamber is at a potential of 300 kV, it must be isolated from ground, requiring computer automation for positioning, and insulating plumbing for the helium. The motion control has a detachable coupling that allows for complete thermal isolation from room temperature. Details and problems encountered in the design are described.

Notes: With the recent advances in layered synthetic microstructure (LSM) technology, it is now possible to build a simple, high-throughput, near-normal incidence soft x-ray spectrometer as a diagnostic for magnetically confined plasmas. Such spectrometers could be used for radiative power loss measurements from intrinsic impurities, an impurity concentration monitor, or ion temperature measurements from Doppler broadening of high charge-state metallic impurities. LSMs have been developed as either flat or curved multilayer mirrors (MLMs) or as coatings for conventional gratings. Flat multilayer mirrors can have near-normal incidence reflectivities greater than 50% throughout the entire soft x-ray region with bandpasses that can be less than 4 A(ring). Coated gratings are being developed that will combine the high soft x-ray reflectivity of the LSM with the high resolution of the grating. Specific applications of LSMs as dispersive elements will be discussed. As an example, LSM-based low-resolution spectra of both a laboratory and tokamak plasma will be presented.

Notes: The development of intense x-ray sources and sensitive gated detectors is needed for the diagnosis of ICF implosions. A laser plasma x-ray source, with an instantaneous power of 200–500 MW in the range 2.7–3 keV, was used to evaluate a specific detector configuration. The detector, consisting of a PET crystal and a MCP framing camera, was used to obtain radiographs of NaCl-doped targets. Applications are currently signal limited, indicating the need for brighter x-ray sources and/or more sensitive detection systems.

Notes: The efficiency of plasma current drive with lower hybrid waves is reflected in the distribution of suprathermal electrons formed during this process. Past measurements of the bremsstrahlung radiation from these electrons depended on arrays of hard x-ray detectors at different toroidal and poloidal locations around tokamaks [Nucl. Fusion 25, 1515 (1985)]. To avoid the space requirements and the complex correlation and inversion procedures associated with such systems, a single 23-cm-diam hard x-ray image intensifier tube is being installed for two-dimensional imaging on PBX-M. It will be optically coupled to an image processor already in place for a soft x-ray pinhole camera [Rev. Sci. Instrum. 59, 1831 (1988)], and analysis algorithms similar to those already developed for this diagnostic will be used.

Notes: Photoconductive detectors (PCDs) fabricated from natural IIa diamonds have been used to measure the x-ray power emitted from laser-produced plasmas. The detector was operated without any absorbing filters which distort the x-ray power measurement. The 5.5 eV band gap of the detector material practically eliminates its sensitivity to scattered laser radiation thus permitting filterless operation. Excellent agreement was achieved between a diamond PCD and a multichannel photoemissive diode array in the measurement of radiated x-ray power and energy.

Notes: Soft x-ray pinhole imaging has recently become established as a valuable diagnostic for visualization of field reversed configuration (FRC) plasmas in the TRX-2, FRX-C/LSM devices. Gated MCP image converter devices with CsI cathodes and Be filters with a peak response around 11 nm wavelength are used for exposure durations ranging from a few tenths up to several microseconds. Results of experiments with single and Chevron channel plates are discussed along with estimates of linear exposure limitations with both film and CCD cameras as recording media. Plans for multiframe devices on the FRX-C/LSM and the LSX devices are also discussed.

Notes: Two separate crystal spectrometers are being developed for high-energy x-ray continuum measurements at Aurora and NOVA for ICF diagnostics. Both spectrometers are required to record hard x-ray continuum over the wide energy range of 5–35 keV. Continuous spectral coverage is required with low-energy resolution E/ΔE of the order of 10 to 20. The spectrograph for NOVA will use a Laue transmission geometry while the Aurora spectrograph will use a de Broglie curved crystal geometry. The instrumentation for Aurora will also include two discrete, time-resolved, high-energy channels for recording integrated continuum in the 40–60 keV and 60–90 keV bands. Individual component and end-to-end system calibration and alignment for both spectrographs will be done using the high-energy x-ray calibration facilities at KMS. We describe these spectrograph designs and discuss and compare the factors that affect their performance.

Notes: The x-ray pulse height analysis diagnostic designed and built for the RFX reversed field pinch experiment is presented. The system is designed so as to be sensitive over a wide range of RFX operational conditions (100 eV ≤Te ≤ 2 keV). An array of three liquid N2 cooled Si(Li) detectors looks at the plasma through an equatorial port of the torus and can be tilted ±20° off the plane in order to scan over the central half of the minor diameter on a shot-to-shot basis. A second windowless single detector views the plasma along a fixed chord through a second equatorial port and is sensitive to x-ray energies as low as 500 eV. Commercial electronics are mostly used. The throughput is limited only by the shaping amplifier and pulse pileup rejector. Software simulation of the x-ray flux, including the pulse pileup rejection procedure of the electronic chain, was used to dimension the diagnostic, i.e., number of detectors, size of the apertures, and filter combinations. Preliminary tests indicate 20 ms as a realistic target for the electron temperature time resolution, reducible to 5 ms when all of the four detectors are addressed to the same properly chosen x-ray energy region.

Notes: In continuation of the collaborative work between the Institute of Laser Engineering, Osaka and Max–Planck-Institut für Quantenoptik, Garching on x-ray confining cavities, we have performed a new series of experiments using the GEKKO-XII laser facility (4 kJ, 0.9 ns, λ=0.35 μm). The results from two experimental objectives will be presented. The first objective was the direct observation of the x-ray confinement effect in a cavity. A special design target allowed the simultaneous measurement of the x-ray flux emanating from a "closed'' cavity and an "open'' cavity. The second objective was the study of radiation transport mechanism in high- and low-Z materials. Thin foils of Au and Al were used as windows on diagnostic holes of x-ray confining cavities and their emission was compared to that of an open hole. A summary of the main results will be presented.

Notes: X-ray pinhole images are formed on microchannel plate striplines to time-resolve Z-pinch emissions. Applications include a study of Z-pinch linearity necessary for x-ray lasers, the evolution of hot spots, and a study of Z-pinch heating mechanisms. In particular, multiple pinholes per strip with different filters allow the spatial and temporal variation of different temperature regions to be studied.

Notes: New diagnostic techniques have provided measurement of relatively gradient-free x-ray spectra from high-powered laser-produced plasmas. Simultaneously space- and time-resolved x-ray spectra were measured from a variety of microdot plasmas using an array of multiframe, imaging, electronically gated x-ray crystal spectrometers with 100 ps time resolution. A multiframed, multicolored gated x-ray pinhole camera provided measurement of the plasma uniformity. A four-frame holographic interferometer was used to measure the electron density profile. Conventional x-ray streaked crystal spectrographs, spatially resolved x-ray (film) spectrometer, and pinhole cameras supplemented these new diagnostics. The instruments allow detailed studies of both the population kinetics of highly charged ions in dense plasmas and the hydrodynamics of laser-produced plasmas for the first time. The new diagnostics are described including data from ongoing experiments. Work was performed in part under the auspices of the U.S. Dept. of Energy by LLNL under Contract No. W-7405-Eng-48.

Notes: A seven channel polychromator, utilizing high performance interference filters (transmission (approximately-greater-than)80%, rejection at laser wavelength〉105), has been tested for use in the multi-Nd:YAG laser Thomson scattering system for the DIII-D tokamak. Unique features of this polychromator are the combination of high throughput, easy alignment, flexibility, compact size, and low cost when compared with other alternatives. Light is introduced to the polychromator (f/1.75) via a fiber optic bundle which permits the use of small (3.0 cm diam) optics and leads to a compact (44×24×8 cm) design, an important design consideration for multiple polychromator systems. The light is cascaded through a series of different bandpass interference filters and relay lenses which are mounted on two precision parallel rails in such a way that alignment is trivial. The relay lenses are positioned directly in front of the filters so that light reflected from the filter passes through the lens twice. This leads to an efficient, compact design and reduces the angle of incidence (4 °) and the cone angle of light (4.5 °) seen by the filter, an important factor for narrowband (3.0 nm) filters. The transmission (average 70%) was optimized for 700–1100 nm by using broadband coatings throughout. The output images of each channel (2.3 mm. diam) can be directly coupled to large format (3 mm diam) RCA silicon avalanche photodiode detectors, avoiding the losses caused by fiber optic coupling.