bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-temperature calorimetry for small samples
Authors: DePuydt J. M. , Dahlberg E. D.
Published: July 2002

The construction and operation of a new calorimeter are described. The advantages of this calorimeter are its versatility, simplicity, and ease of operation. This calorimeter can be designed and constructed in less than one day and it allows for the measurement of heat capacities while either heating or cooling a sample through a temperature interval without the restriction that the sample temperature deviate only slightly from the reservoir temperature. The calorimeter described here has primarily been utilized in the temperature range from 0.4 to 10.0 K; however, the useful temperature range is not limited to this interval. Thus far heat capacities of approximately 5 μJ/K have been resolved, but estimates indicate that heat capacities on the order of 0.1 μJ/K could be measured with this type of calorimeter.
Discrepancies in accidental-coincidence corrections
Authors: DeVolpi A.
Published: July 2002

A new and improved correction for accidental coincidences has been devised. Comparison of results based on earlier formulations are provided. The differences between the new expression and the frequently used older formulations indicate possible systematically significant discrepancies in some reported experiments, for example, absolute determinations of the neutron yield in fission ν (252Cf) and in time-of-flight spectrum measurements.
A new system for LEED intensity measurements using a real-time digital video processor
Authors: Ogletree D. F. , Somorjai G. A. , Katz J. E.
Published: July 2002

A new system for low-energy electron diffraction (LEED) intensity measurements has been developed using a video camera and digital processing of the video signal. Complete two-dimensional LEED patterns are digitized in real time with high resolution using a commercial video processor. Intensity-voltage (I-V) data on all beams in complex LEED patterns are collected simultaneously. A microcomputer analysis program automatically tracks the diffraction beams as a function of energy and calculates beam position, size, and integrated intensity, including a local background correction. Using a video tape recorder for intermediate data storage, a complete set of I-V curves can be collected in less than 100 s.
Light-integrating cylinder for inertial confinement fusion light balance measurements in mirror illumination systems
Authors: Simpson J. D. , Drake D. J. , Speziale T.
Published: July 2002

This report describes the design and operation of a diagnostic instrument used for light balance measurements in inertial fusion experiments. The instrument is a light-integrating cylinder that uses the integrating principles of the Ulbricht sphere, but which was designed to operate in a reflective illumination environment. The cylinder has been used to make measurements with both high-absorption disk targets and low-absorption foil targets, illuminated with 20–80 J of green (527-nm) light. We have also modeled the cylinder to determine its theoretical integrating performance under a variety of operating conditions. Initial sensitivity was measured at 0.4 V/J and degraded over target shot number to about 0.25 V/J. The instrument has a measurement accuracy of 10% for scattered light and an absorption measurement accuracy of 10% for strongly absorbing targets, and 30%–70% for weakly absorbing targets.
Multichannel bolometer for radiation measurements on the TCA tokamak
Authors: Joye B. , Marmillod Ph. , Nowak S.
Published: July 2002

A multichannel radiation bolometer has been developed for the Tokamak Chauffage Alfvén (TCA) tokamak. It has 16 equally spaced chords that view the plasma through a narrow horizontal slit. Almost an entire vertical plasma cross section can be observed. The bolometer operates on the basis of a semiconducting element which serves as a temperature-dependent resistance. A new electronic circuit has been developed which takes advantage of the semiconductor characteristics of the detector by using feedback techniques. Measurements made with this instrument are discussed.
Charged fusion product analysis as diagnostics in high-energy deuterium beams
Authors: Bayetti P. , Bottiglioni F. , Martin G. , Paméla J.
Published: July 2002

The detection of protons (3 MeV) and tritons (1 MeV) originating from D–D fusion reactions are presented as a tool for inferring the main features of a powerful deuterium neutral beam. By an energy analysis, beam species content, neutralization, and power transmission efficiencies have been measured. Using a localization detector, a method for measuring beam profiles has been developed.
Electrical transport measurements in a gasketed diamond anvil cell up to 18 GPa
Authors: Gonzalez J. , Besson J. M. , Weill G.
Published: July 2002

A four-probe technique for electrical and photoelectrical measurements in a gasketed diamond anvil cell is presented. The special anvil profile and the method for the gasket preparation used in these experiments are described. Insulation and continuity of the electrical leads are shown to be satisfactory at least up to 18 GPa. As an example we report photoconductivity measurements in GaAs beyond crossover, under pressure, between direct and indirect band-gap configurations.
TEXT heavy ion beam probe system
Authors: Schoch P. M. , Forster J. C. , Jennings W. C. , Hickok R. L.
Published: July 2002

A good signal-to-noise ratio has been obtained during initial operation of the 500-keV TEXT heavy ion beam probe. A number of problems were identified during the start up phase and they have been or are being corrected. Present sensitivity for detecting changes in the space potential is 50 V, but it is expected that this can be reduced to 5 V when additional calibration and alignment procedures are completed.
JET soft x-ray diode array diagnostic
Authors: Edwards A. W. , Fahrbach H.-U. , Gill R. D. , Granetz R. , Oord E. , Schramm G. , Tsuji S. , Weller A. , Zasche D.
Published: July 2002

The arrays of silicon diodes recently installed on the Joint European Torus (JET) measure the plasma soft x-ray emission with high temporal and spatial resolution, allowing magnetohydrodynamic (MHD) effects to be investigated. The diagnostic consists of two ‘‘pinhole’’ cameras which view the same poloidal cross section in orthogonal directions. A data-acquisition system based upon three cascaded digital filters can convert the 200-kHz detector signal analog-to-digital converter (ADC) output to lower sampling rates of 10, 1, and 0.1 kHz. Initially, studies have concentrated on the sawtooth collapse. By means of a trigger system data on the sawtooth crash have regularly been recorded at a sampling frequency of 200 kHz. Using tomographic reconstruction techniques, the soft x-ray emissivity cross section during the crash has been reconstructed. First results during ion cyclotron radio frequency (ICRF) heating show no precursor activity prior to the sawtooth collapse, while during the crash, the hot central plasma is displaced off axis by about 30 cm on a time scale of 50–200 μs, after which a hollow soft x-ray profile forms.
High field nuclear magnetometer
Authors: Dutta April , Archie C. N.
Published: July 2002

A magnetometer capable of measuring changes in the nuclear magnetism of 3He in the presence of an 8-T magnetic field is described. A key component is a type II superconducting shield (NbTi) which stabilizes the external field. Short-term sensitivity is equivalent to detecting magnetic field changes of a few parts in 1010. In applications involving large pressure changes and 3He liquid–solid phase changes, additional problems arise. Sensitivity to physical distortion of the device in some applications can generally be corrected for or exploited for pressure detection.
Quantum yield of triethylamine and tripropylamine for the detection of VUV radiation up to 160 nm in ionization chambers
Authors: Goehlich A. , Terbeck W. , Döbele H. F.
Published: July 2002

Ionization efficiencies of tripropylamine (TPA) and triethylamine (TEA) as a function of wavelength are determined on the basis of the known values of NO. A TEA-filled ionization chamber is applied to record excimer continua of a very simple VUV source.
Improved circuit design for electrostatic self-resonating vibroscopes
Authors: Robinson H. , Wu H. F. , Ames M. , Schwartz P.
Published: July 2002

In this paper a new circuit design for automatic electrostatic vibroscopes is presented. Previously, the component which stabilized the self-oscillatory motion of the filament in the feedback loop of electrostatic vibroscopes was a negative temperature coefficient thermistor. In the present system this device is replaced with a programmable analog compander. This modification represents an improvement because response time is faster, the steady-state conditions are more stable, and the overall performance of the vibroscope is less susceptible to errors caused by changes in environmental conditions.
High spectral resolution, photon counting detector for Doppler temperature measurements in magnetically confined plasmas
Authors: Benjamin R. D. , Terry J. L. , Moos H. W.
Published: July 2002

This paper describes the design, construction, and performance of a single-stage microchannel-plate image intensifier used as a photon counting detector over the wavelength range from 1150 to ∼2000 Å. The intensifer incorporates three high strip current (∼300 μA) microchannel plates, constructed with 12-μ-diam channels and 15-μ center–center spacing, in a ‘‘Z’’ configuration. The use of high strip current MCPs requires gating the power supply to protect the plates from thermal runaway of the strip current. The output pulses are proximity focused onto a P-46 phosphor screen, which is fiber-optically coupled to a linear, self-scanning photodiode array. Maximum frame rates for the photodiode array are ∼ 125 000 frames/s, with maximum count rates of ∼25 000 photoevents/s. The detector was placed at the focal plane of a 1-m focal length Ebert–Fastie spectrometer and the performance characteristics of the spectrometer-detector system were evaluated using a hollow cathode Pt lamp. The linewidths measured during this evaluation demonstrate that the spatial resolution of the detector is better than 50 μ. The spectrometer-detector system was then used to determine ion temperatures from Doppler broadened impurity lines emitted from plasmas of the Alcator C tokamak. This detector demonstrated more than an order of magnitude increase in sensitivity compared to a photon-counting photomultiplier tube with a vibrating mirror previously used for these measurements with the same spectrometer. This permitted a determination of the central ion temperature of the Alcator C tokamak using the ‘‘forbidden’’ line of Fe xii at 1354.1 Å which was not detected with the previous system.
General purpose absorption cell for high-sensitivity spectrometry of liquid samples
Authors: Lunelli Bruno , Comelli Fabio
Published: July 2002

A priori requirements and compatible, optimized design considerations for a high-performance low-cost absorption cell for the spectrometry of liquid samples are discussed. A new cell model is presented.
New method for the measurement of wave potentials using varying emitted electron currents
Authors: Honzawa Tadao
Published: July 2002

A new method for the measurement of wave potentials using a low-impedance emissive probe is studied. In this method, a wave potential is estimated not from a floating potential change but from a time-varying emitted electron current from the probe. Results indicate that wave potentials observed in this way are usually considerably higher but more reliable than those obtained in a conventional high-impedance emissive probe technique.
Spherical void electrodynamic levitator
Authors: Arnold S. , Folan L. M.
Published: July 2002

We report a new design for an electrodynamic levitator for individual microparticles based on a spherical void. This configuration with its interior surface covered with a thin dielectric coating having high diffuse reflectivity is expected to prove ideal for the integration of inelastic scattered radiation such as fluorescence or Raman scattering.
Single-mode or controlled multimode microwave cavity applicators for precision materials processing
Authors: Asmussen J. , Lin H. H. , Manring B. , Fritz R.
Published: July 2002

The detailed description, the experimental demonstration, and the design of single-mode microwave cavity applicators are presented. These microwave applicators utilize an internally tuned, single-mode (or selective multimode) cylindrical cavity to focus and match microwave energy into cylindrical rod, disk-, or slab-shaped material loads. The combination of mode focus control and variable, internal cavity matching allows the efficient coupling of microwave energy into a wide range of solid material loads. The experimental operation of these applicators is demonstrated for low loss to lossy materials, which include nylon, water, and semiconducting silicon wafers. Overall microwave coupling efficiencies of 70%–95% were measured and experiments demonstrated the ability to precisely control material heating. The single-mode fields can be used to heat and diagnose during processing, and on-line process diagnosis was experimentally demonstrated using cavity perturbation theory. When using these cavity applicators, many system variables such as tuning control, cavity electric field strength, input, and reflected power are available as potential process system feedback signals for automated intelligent processing. These applicators can be used to carefully study the fundamentals of electromagnetic interactions of many materials. Applications include the electromagnetic heating of foods, semiconducting and biological materials, and the heating and curing of epoxy and composite materials.
High-performance amplitude and phase digitizers at 60 MHz
Authors: Hobbs Philip C. D.
Published: July 2002

We describe high-performance successive approximation amplitude and phase digitizers capable of resolving 1 part in 4096 in amplitude and 0.1° in phase at a rate of 50 000 points per second. They communicate with a computer workstation by DMA over a GPIO bus. The phase digitizer exhibits negligible AM to PM conversion and an input amplitude range of 70 dB. Both digitizers reside on one thick 7×9-in. card module. The system is currently used in an electronically scanned laser microscope. We also describe a high-precision phase calibrator and associated calibration software.
Comment on ‘‘On the spatial and temporal resolution of ion temperature measurements based on neutral beam scattering’’ [Rev. Sci. Instrum. 5
8, 1320 (1987)]
Authors: van Heesch E. J. M.
Published: July 2002

The discrepancies found by Donné and Barbian [A. J. H. Donné and E. P. Barbian, Rev. Sci. Instrum. 58 (1987)] can be attributed principally to the choice of experimental and technical limits, basic assumptions, and definitions.
Simple cw NH3 laser operating in the 11–13-μm region
Authors: Chakrabarti A. , Reid J.
Published: July 2002

A simple and inexpensive method is described for extending the tuning range of a conventional cw CO2 laser into the 11–13-μm region. The technique consists of optically pumping a mixture of NH3 in Ar confined in a capillary waveguide. An output power as high as 1.9 W is attained in the 12-μm region from a pump power of only 8.8 W and a total of 12 laser transitions are observed in 15NH3. The construction of a compact line-tunable laser is described.
Compact pressure cell for light-scattering experiments
Authors: Bohidar H. , Berland T. , Jo/ssang T. , Feder J.
Published: July 2002

The design and construction of a unique and precision pressure cell suitable for use in light-scattering experiments has been described. The cell has been adapted to allow scattering experiments from liquid samples. The optics of the cell has been especially designed to obtain a higher signal-to-noise ratio. The cell has been designed to be small and compact with sample volume ∼40 mm3. However, it still has a large heat capacity (∼250 J/K) which ensures easy and stable temperature control of the sample. The cell can sustain hydrostatic pressure up to 1000 bar and temperature up to 150 °C. When operated in the constant temperature and pressure mode it offers long-time (∼16 h) temperature and pressure stability of ±2 mK and ±0.05%, respectively, in this entire range.
Eight-shot pneumatic pellet injection system for the tokamak fusion test reactor
Authors: Combs S. K. , Milora S. L. , Foust C. R. , Baylor L. R. , Barber G. C. , Burris R. D. , Fisher P. W. , Foster C. A. , Lunsford R. V. , Schmidt G. L. , Schuresko D. D. , Senko T. , Shanlever R. C. , Shipley W. D. , Sparks D. O. , Stewart K. A. , Wysor R. B.
Published: July 2002

An eight-shot pneumatic pellet injection system has been developed for plasma fueling of the tokamak fusion test reactor (TFTR). The active cryogenic mechanisms consist of a solid hydrogen extruder and a rotating pellet wheel that are cooled by flowing liquid-helium refrigerant. The extruder provides solid hydrogen for stepwise loading of eight holes located circumferentially around the pellet wheel. This design allows for three different pellet diameters: 3.0 mm (three pellets), 3.5 mm (three pellets), and 4.0 mm (two pellets) in the present configuration. Each of the eight pellets can be shot independently. Deuterium pellets are accelerated in 1.0-m-long gun barrels with compressed hydrogen gas (at pressures from 70 to 105 bar) to velocities in the range 1.0–1.5 km/s. The pellets are transported to the plasma in an injection line that incorporates two stages of guide tubes with intermediate vacuum pumping stations. A remote, stand-alone control and data-acquisition system is used for injector and vacuum system operation. The eight-shot injection system has been installed and operated on TFTR. The design features, operation, and performance characteristics of the system are described.
New concept in high-pressure sealing: Analysis and experiment
Authors: Lee Sam-Hyeon , Luszczynski K.
Published: July 2002

We present several simple and reliable high-pressure fluid seals, both static and sliding, which have been tested up to 2 kbar. These Poulter-type seals are quite different in operation from the usual Amagat and Bridgman seals. Our analysis of the new sealing principle provides the basis for understanding the operation of Poulter seals as well as other previously poorly understood high-pressure seals. Poulter seals are shown to be in fact actuated by fluid pressure, like Bridgman’s unsupported area seals.
Single photon detection and timing system for a Lidar experiment
Authors: Viterbini Maurizio , Adriani Alberto , Di Donfrancesco Guido
Published: July 2002

An instrument for photon counting measurements in a Lidar experiment is described. Single events can be stored up to rates of 25 MHz and it is capable of 4096 data acquisitions for each measurement. Time information by two successive photons is achieved with an accuracy better than 14 ns. The system is interfaced with an HP 1000F series computer. A window discriminator/shaper for formatting the photomultiplier pulses is also described.
Reconstruction of plasma radiation features from projections measured with two bolometer arrays
Authors: Schivell J.
Published: July 2002

A specialized method has been developed to maximize the two-dimensional detail obtained from two perpendicular bolometer arrays. The technique relies on the assumption that poloidal variation exists only near the plasma surface. The cross section is divided into appropriate zones and the emittance is reconstructed by a numerical method. The position, intensity, and width of large features are clearly displayed. A marfe is tracked as it drifts around the plasma and evolves into a radiating shell detached from the limiter. A central peak, plus inner-wall radiating layer, plus a marfe appear in a high-density case reached by pellet injection.
Electrical resistance measurements on cryocrystals in a diamond-anvil cell to 70 GPa
Authors: Straaten Joop van , Silvera Isaac F.
Published: July 2002

A four-probe technique for measurement of electrical resistance and photoconductivity on cryocrystals in a diamond-anvil cell is described. The gasket and the method of fabrication of the electrical leads is discussed in detail. As an example, resistance and photoconductivity measurements on hydrogen iodide are presented.
Wideband spectrograph for free-electron laser experiments
Authors: Kulke B. , Burns M. J. , Orzechowski T. J.
Published: July 2002

We have designed, calibrated, and deployed an electron spectrograph to measure the effect of the free-electron laser interaction on the relativistic electron beam in an FEL. The spectrograph spans a wide energy range (ΔE/E∼1) and is designed for electron energies from 2 to 4 MeV. Calibration was achieved using a 2–6-keV proton beam, and the measured dispersion is in good agreement with the value predicted from ray tracing. The spectrograph has been used to estimate the extraction efficiency, and the results agree within 25% with the observed microwave power levels.
Characterization of a simple, high Reynolds number droplet generator for combustion studies
Authors: Peterson Richard B.
Published: July 2002

A new technique is described for generating droplets in the size range between 240 and 750 μm. The droplets are characterized by Reynolds numbers (in air at standard conditions) greater than 100, hence, with a liquid fuel as the droplet fluid, this technique has applicability in studies of convective droplet burning. The concept behind the technique is simple. A capillary tube is employed to deposit a droplet in the center of a flight tube. Gas flow through this tube detaches the droplet from the capillary, and the droplet accelerates down the tube. Droplets remain stable in the tube for tube diameters of 1.5 to 3 times the droplet diameter. Generation rate is dependent on the liquid flow rate through the capillary and can be varied sufficiently to produce droplets at a rate between 1 and 100 per second. Exit velocities are reported as a function of droplet size for a variety of flight tube lengths and diameters. Water was used in all experiments reported here, but no difficulty should arise in using the technique to produce liquid fuel droplets. The largest droplet generated was 750 μm with an exit velocity of 3.5 m/s yielding a Reynolds number of 175. The smallest droplet produced was 240 μm with an exit velocity of 11 m/s yielding a Reynolds number of 165. The highest Reynolds number achieved in this work, 371, was obtained with a droplet size of 390 μm and an exit velocity of 14.3 m/s. Decreasing the droplet size while increasing exit velocity should be possible.
Monochromator and beamline for soft x-ray studies in the photon energy range 500 eV–5 keV
Authors: MacDowell A. A. , West J. B. , Greaves G. N. , Van der Laan G.
Published: July 2002

The optical layout of a novel soft x-ray beamline at the Daresbury Synchrotron Radiation Source (SRS) is presented, together with the mechanical design of a precision-built soft x ray crystal monochromator. The mechanical and optical performance of the system are discussed, supported by data on the output flux and resolution of the monochromator. The flexibility of this optical arrangement for different kinds of experiments is examined.
Application of picosecond light pulses generated from an AlGaInP visible diode laser for photoluminescence decay measurement of GaAs/AlGaAs quantum wells
Authors: Yokoyama H. , Iwata H. , Onabe K. , Suzuki T.
Published: July 2002

The photoluminescence decay of GaAs/AlGaAs quantum wells was successfully measured at room temperature by using 660-nm picosecond light pulses from an AlGaInP diode laser driven by short pulse current. Our experimental results reveal that picosecond light pulses from visible diode lasers may be widely applicable, in place of mode-locked gas, solid-state, or dye lasers, for studying the fast carrier recombination properties of many kinds of materials including GaAs and AlGaAs in the wavelength region of deep red to infrared.
Novel design for eucentric goniometer heads: A cap-in-socket tilt stage
Authors: Seul M.
Published: July 2002

A novel design for a biaxial goniometric stage is described. The two stacked mutually perpendicular arc sections of the conventional eucentric goniometer head are replaced by a single tilt platform. The principal feature is the motion of a spheroidal cap in a matching socket, permitting two-dimensional tilting action about a fixed center of rotation. This design has the advantage of a significant decrease in overall height of the goniometer head, providing additional space for a variety of attachments.
In situ monitoring of internal surface area during the growth of porous silicon
Authors: Peter L. M. , Riley D. J. , Wielgosz R. I.
Published: July 2002

A novel and convenient method of monitoring the internal surface area of a porous silicon layer formed on an n-type substrate has been developed. The technique has been employed during electrochemical growth and subsequent chemical leaching of porous silicon layers in hydrofluoric acid/ethanol. The method involves periodic interruption of the anodization current to allow in situ measurement of the interfacial capacitance under forward bias using a triangular voltage wave form. The observed evolution of the internal surface area is related to the development of photoluminescence.
Photo-thermoelastic mechanical beam chopper at a low frequency
Authors: Hane K. , Kanie T. , Hattori S.
Published: July 2002

A simple beam chopper advantageously using the thermoelastic bending due to photothermal effect is reported. The mechanical vibration for chopping is generated due to the modulated irradiation from a laser diode so that the chopper is remotely operated.
Origin of the 1.54 μm luminescence of erbium-implanted porous silicon
Authors: Shin Jung H. , Hoven G. N. van den , Polman A.
Published: July 2002

Photoluminescence of erbium-implanted porous silicon is investigated. Room temperature 1.54 μm Er3+ luminescence is observed after annealing. The luminescence spectrum, annealing characteristics, temperature quenching, and the luminescence lifetime suggest that the Er3+ luminescence is mediated by photocarriers in the amorphous silicon matrix in porous silicon, and not related to the presence of the crystal nanograins.
Personal computer based Fourier transform ion cyclotron resonance mass spectrometer
Authors: Guan Shenheng , Jones Patrick R.
Published: July 2002

An IBM PC AT compatible computer is used to host the interface of a Fourier transform ion cyclotron resonance mass spectrometer or FTMS. A common fast memory bank for both ion-excitation waveform and data acquisition is reserved in the computer’s system memory space. All the digital electronics circuitry is assembled on an IBM PC AT extension board. Neither an external frequency synthesizer nor a waveform digitizer is needed. Ion-excitation waveforms can be generated in either frequency-sweeping or inverse-Fourier transform modes. Both excitation and data acquisition can be carried out at eight megawords per second.
Factors determining dissociation fractions in atomic beams generated by ‘‘straight-through’’ microwave discharge sources
Authors: Spence David , Steingraber Orville J.
Published: July 2002

We have studied the parameters affecting the degree of dissociation in atomic beams produced by a source consisting of a quartz tube with an exit slit downstream from a microwave discharge, which is maintained by means of an Evenson cavity. These parameters include the effects of catalysts, discharge tube diameter, slit width, cavity-slit distance, discharge power, and tube material in producing atomic beams of hydrogen, oxygen, nitrogen, and the halogens. The achievable degree of dissociation is found to be quite sensitive to all those parameters except discharge power and tube material. Optimal values are presented.
Implementation and use of general-purpose interface bus interface in an automatic testing and measurement system of a magnet power supply
Authors: Jan G. J. , Law S. F.
Published: July 2002

A general-purpose interface bus (GPIB) interface card has been designed and installed on an IBM PC/XT microcomputer in order to make possible automated testing of a programmable dipole magnet power supply. This paper indicates how one can design and implement a GPIB interface and use it economically but effectively in testing and measuring the performance characteristics of the power supply. The overall system and associated software developed for the control and monitoring of the power supply are also described. The advantages of the system are stable operation, simplicity of hardware, the friendliness of software.
Development of a spectroscopically resolved multichannel image camera for a sounding rocket and satellite
Authors: Yokota Toshiaki , Sasaki Susumu , Kawashima Nobuki , Hoshi Masayuki , Teii Shinriki
Published: July 2002

An onboard model of a TV camera to detect spectroscopically resolved images has been developed. It has been able to detect several spectral pictures at the same time by using only one camera with no restriction against spectral selection between each picture. The wavelength of each picture has been selected electronically. The number of spectroscopically resolved pictures is dependent only on the memory size of the computer. This camera is equivalent to a standard TV camera in which 117 bandpass filters are installed. The favorable characteristics of this camera are that it does not cause a time difference between each picture and is able to display the physical parameters by numerical calculations and can change the spectral range even after launch. The principal purpose of this model is to assist in investigating the dynamic structure of the aurora and the atmospheric composition of planets.
A system for time-resolved laser fluorescence spectroscopy with multiple picosecond gating
Authors: Cubeddu R. , Docchio F. , Liu W. Q. , Ramponi R. , Taroni P.
Published: July 2002

A computer-controlled system for time-resolved fluorescence spectroscopy is described. The system provides the simultaneous acquisition of the fluorescence decay curve, of the time-integrated emission spectrum, and of two time-gated spectra. Gating within the fluorescence decay is provided by setting up windows in the output of the time-to-amplitude converter in single photon timing instrumentation. The gate parameters (position and width) are fully programmable. Depending on the laser source used, time resolutions between 45 and 150 ps are obtained. Therefore, in most situations no deconvolution procedures are required to elaborate the spectra. The system has been characterized with the aid of suitable test solutions. The results indicate that a correct choice of the gate parameters allows complementary information (in terms of both decay times and emission spectra) of the fluorescence parameters of molecular species in molecular systems.
Flash x-ray source excited by stacked Blumlein generators
Authors: Davanloo F. , Coogan J. J. , Bowen T. S. , Krause R. K. , Collins C. B.
Published: July 2002

Eight triaxial Blumleins have been stacked in series at one end while being synchronously commuted at the other end with a single hydrogen thyratron. Significant voltage gain has been maintained in the stack for periods of the order of 20 ns. Having no other switching elements, operation has been possible at repetition rates to 100 Hz. An x-ray diode has been matched to this pulse power source, making possible the emission of an average bremsstrahlung dose of 5.8 R/s from a sequence of 20-ns pulses. In less than 4 min of operation at 100 Hz, a dose of 1 kR could have been delivered to a target sample. When operated at 50-kV charging voltage, spectral measurements show the output to be a true continuum, peaking at intensities in excess of 2×108 keV/keV/shot and containing useful intensities of photons having energies of 150 keV.
Integrated automatic modular measuring system
Authors: Baikie I. D. , van der Werf K. O. , Hanekamp L. J.
Published: July 2002

This paper describes a versatile automatic measuring system composed of discrete modules. The modules can operate in both stand-alone and remote modes and are interconnected using an IEEE-488 bus, allowing utilization of standard measurement apparatus and peripherals. The system design allows user optimization of the measurement procedure, which can thus be tailored to meet specific experimental requirements. The flexibility of this system is demonstrated by its application in spectroscopic ellipsometry.
Absolute calibration of an atomic helium beam time-of-flight apparatus by flight path variation
Authors: Doak R. B. , Nguyen D. B.
Published: July 2002

Virtually all inelastic helium atom scattering experiments utilize time-of-flight (TOF) analysis to energy analyze the scattered beam. To date, the demands upon the accuracy of these TOF measurements have not been particularly great (typically a few percent), and rather rudimentary calibration techniques have sufficed. For certain experiments, e.g., for time-resolved measurements of specular scattering to determine surface-bound states of helium or to observe surface-step interference, this is no longer the case. We describe an in situ calibration technique based upon a variation of the TOF flight path that allows us to calibrate our path length and time origin to within a few millimeters and microseconds, respectively (<2×10−3). A comparison with ‘‘zero flight time’’ laser timing measurements shows that finite drawout/transit times through the beam detector can introduce nonnegligible systematic errors into the laser calibration technique, even in the present favorable instance (light beam mass, drawout along the beam axis). We demonstrate the utility of surface diffraction as either a consistency check or to accurately determine unknown reciprocal lattice vectors.
Soft-x-ray Bragg spectrograph with an intensified framing camera
Authors: Koenig Z. M.
Published: July 2002

A Bragg x-ray spectrograph was developed for pulsed diagnostics. It covers the wavelength region 2–100 Å and accommodates two convex crystals and a time-resolving x-ray intensifier. The x-ray detector is a gated intensified camera incorporating a custom-designed microchannel plate (MCP) built into a microwave circuit for fast pulsing of four or seven separate images. Various photocathodes (Au, Ni, CsI, and MgF2) have been deposited directly onto the microchannel plate to form the strip lines. The MCP is mounted above a high-quality phosphor screen coated on top of a fiber-optic faceplate. Time resolution is obtained by sequentially gating the independent strip electrodes on the MCP for subnanosecond electrical gating. A one-dimensional time-resolved spectral image can be obtained.
Neutron emission time measurements for ICF targets
Authors: Lerche R. A. , Kania D. R. , Lane S. M. , Tietbohl G. L. , Bennett C. K. , Baltzer G. P.
Published: July 2002

The neutron emission time for laser-driven inertial confinement fusion targets is determined from data recorded with fast neutron and optical detector systems. Two types of neutron detectors are used. Radiation-induced conductivity devices have a 130-ps FWHM response and are sensitive to targets with yields greater than 5×1010 DT neutrons. They measure the average neutron emission time with a precision of ±50 ps and are fast enough to measure the neutron production rate within a target core as a function of time. Plastic scintillators coupled to microchannel-plate photomultiplier tubes have a 1.2-ns FWHM response and measure the average neutron emission time with a precision of ±75 ps for targets with yields greater than 106 neutrons. Streak cameras record the incident laser power. Optical fiducial signals that are injected into each detector are used to cross time between the detector systems. Measurements made on 1-mm-diam spherical targets irradiated with 23 kJ of 0.35-μm light delivered in a temporally square 1.1-ns pulse and yielding 1013 neutrons show a burn duration greater than 300 ps and an average neutron emission time of about 850 ps.
Frequency dependencies of precision resistors
Authors: Cutkosky Robert D.
Published: July 2002

A variety of ac and dc resistors were examined for frequency dependence from dc to 400 Hz. It is concluded that several choices are available for use as standards in resistance thermometry.
Pulsed molecular-beam, diode-laser spectrometry using rapid scanning techniques
Authors: De Piante A. , Campbell E. J. , Buelow S. J.
Published: July 2002

We describe a diode-laser spectrometer for obtaining direct absorption, rovibrational spectra of monomers and/or weakly bound, molecular complexes which are found in supersonic expansions. The spectrometer incorporates a tunable, semiconductor diode-laser source and a pulsed-gas slit nozzle. White cell optics are used in the vacuum chamber to increase effective path length, and a Fabry–Perot etalon is used for relative frequency calibration. Stabilization of the source output is accomplished by locking onto a zero crossing of the etalon fringe-spacing pattern with a gated integrator. The diode laser is scanned rapidly (∼0.2 cm−1/ms) to modulate absorption signals at frequencies which can be electronically filtered from source noise. For 2000 scans, absorbances as small as 1.3×10−5 (0.003% absorption) can be detected. Amplitude fluctuations in the detected signal due to interference effects in the optics and gain variations in the diode laser are eliminated by recording data with and without gas flow from the nozzle, then performing the appropriate subtractions. Because source drift and multiple crossing-angle effects contribute ≤0.0005 cm−1, observed linewidths (0.003 cm−1) were determined to be laser limited. Data obtained on the van der Waals molecule (Ar⋅Co) are presented and discussed.
Microstructure collimator for soft x-ray spectroscopy
Authors: Bier W. , Schubert K. , Röhr H. , Schumacher U.
Published: July 2002

Novel microstructures manufactured with high precision and reproducibility are proposed for high-resolution collimators in flat crystal soft x-ray monochromators for plasma spectroscopy. The newly developed technique for this type of collimator is based on surface structuring of foils using profiled microdiamonds. Results of x-ray tests of a microstructure collimator demonstrate that the predicted angular resolution of 5000 at a transmission of about 0.3 can be obtained.
A study of the seizure problem with high-current filament feedthroughs in plasma generators
Authors: Hemsworth R. S. , Altman H. , Hurford D.
Published: July 2002

Large diameter (1–2.5 mm) Tungsten filaments are now commonly found in plasma sources used on high-power neutral injectors. In many cases problems have arisen in trying to remove or replace the filaments as the component parts of the filament chuck are found to diffusion bond together. This can cause severe difficulties in the necessary routine replacement of such filaments. This paper describes a series of tests carried out with systems used in the plasma sources of the JET neutral injectors in order to find methods of eliminating this problem. A design of filament stem and connector, both elegant and simple, is described which completely avoids the problem. Also, it is shown that the use of dissimilar metals and/or antiseizure agents are effective in preventing the diffusion bonding of the filament chuck components.
Triggering of a vacuum spark source by impact of a low-energy laser beam on the cathode
Authors: Damany H. , Laporte P.
Published: July 2002

It is shown that the triggering of a vacuum spark source is easily obtained by focusing onto the cathode a pulsed laser beam of short duration and rather low energy per pulse. The main advantages of this kind of triggering are discussed in comparing with the previous designs based on an auxiliary sliding spark.
Intensity dependence of high-order autocorrelation functions in fluorescence correlation spectroscopy
Authors: Palmer Arthur G. , Thompson Nancy L.
Published: July 2002

This paper describes several instrumental contributions to experimentally obtained high-order photoelectron fluctuation autocorrelation functions in single-photon counting fluorescence correlation spectroscopy. As shown, the high-order functions are intensity-dependent for at least three reasons: the presence of background light; the stochastic nature of photon collection and detection; and the temporal response of the photoelectron pulse counter. Theoretical expressions that describe the effects are derived and experimentally confirmed, and methods of determining the high-order fluorescence fluctuation autocorrelation functions of interest from experimentally obtained photoelectron fluctuation autocorrelation functions are outlined.
Low-temperature bolometer array
Authors: Boninsegni M. , Boragno C. , Ottonello P. , Valbusa U.
Published: July 2002

The implementation of a 16-channel, low-temperature bolometer linear detector array is described. The detectors are silicon samples, whose surfaces are doped with phosphorus by the technique of ionic implantation. A single digital processor implemented on a common PC both provides the scanning of the array and performs synchronous signal detection from the different bolometers. The actual system has been tested with a broad infrared source, and some possible improvements are indicated.
Jig for tapered high-temperature superconductor tubes used as electron beam lenses (Supertrons)
Authors: Osada T. , Tohyama A. , Chino Y. , Matsuzawa H.
Published: July 2002

The structure of a jig is reported, which is useful to form gently tapered high-temperature superconductor tubes.
Dripping faucet apparatus with temperature and high-resolution timing and flow rate controls
Authors: Wu Xiaomao , Tekle Ephrem , Schelly Z. A.
Published: July 2002

For the investigation of the chaotic dynamics of drop detachment from an orifice, a novel dripping faucet apparatus was constructed, and its design and use are described. It is equipped with high-resolution timing (1 μs) and flow rate control (0.05%), and can be operated at different temperatures, and at constant as well as continuously varying flow rates. The last feature allows for the direct recording of the ‘‘dripping spectrum’’ (drop period versus flow rate) in a single run. Examples of results not obtainable with previous instruments are presented.
Anode foil changer for high-current relativistic electron beam diode systems
Authors: Fine T. A. , Rhee M. J.
Published: July 2002

An anode foil changer for pulsed, high-current, relativistic electron beam diode systems is described. This device allows multiple shots to be taken with a foil-anode diode system while maintaining a continuous vacuum. Shot-to-shot reproducibility is greatly improved, while at the same time a significant time savings is realized. Also, various diagnostics and options are added to the basic design which further increase its utility and flexibility.
Calibrated soft x-ray spectroscopy using transmission grating, pinhole and film
Authors: Chaker M. , Bareau V. , Kieffer J. C. , Pépin H. , Johnston T. W.
Published: July 2002

The combination of transmission diffraction grating (free-standing gold bars), pinhole and film can be used for quantitative measurements of the x-ray spectra in the 0.1–1.5-keV region by adopting the procedures described. The steps consist of film calibration and deconvolution of overlapping contributions from different spectral orders. In addition, spatial resolution is available in the direction perpendicular to the dispersion axis for each x-ray energy. The working example presented is the characterization of an x-ray source created by a laser-target interaction, for possible use in x-ray microscopy or x-ray lithography.
Improved low-energy diffuse scattering electron-spin polarization analyzer
Authors: Scheinfein M. R. , Pierce D. T. , Unguris J. , McClelland J. J. , Celotta R. J. , Kelley M. H.
Published: July 2002

An improved low-energy diffuse scattering electron-spin polarization analyzer is described. It is based on the low-energy (150 eV) diffuse scattering of polarized electrons from polycrystalline evaporated Au targets. By collecting large solid angles and efficiently energy filtering the scattered electrons, a maximum figure of merit, FOM=S2I/I0=2.3×10−4 is achieved. Maximum measured values of the Sherman function were S=0.15. Further, the instrumental (false) asymmetry due to changes in the trajectory of the incident electron beam has been minimized by balancing the angular and displacement asymmetries. A total residual scan asymmetry as low as 0.0035/mm has been measured over 4-mm scan fields at the Au target in the detector. This instrumental asymmetry would produce a maximum error in the polarization in a SEMPA experiment of less than 0.3% for a 100-μm full-field scan. Details of the design and performance of the new detector are given.
Passivated uranium as an electron-spin analyzing target
Authors: Pappas D. P. , Hopster H.
Published: July 2002

A passivated uranium surface has been tested as an electron-spin analyzing target in a retarding potential Mott detector. The effective Sherman function and yield were measured for electron energies of 15–34 keV at energy-loss acceptance windows of 500 and 1000 eV. The figure of merit was found to be ≊1×10−5. The uranium target had a higher Sherman function than either gold or thorium at 20-keV and 500-eV energy loss. The passivated surface is also extremely stable, thus proving to be an acceptable target for electron-spin analysis.
High q-resolution electron gun for low energy electron diffraction
Authors: Cao Yijian , Conrad Edward H.
Published: July 2002

We present a new unipotential electron gun design for low energy electron diffraction. The gun has excellent spatial resolution. With a 170-mm gun-to-detector working distance, it produces a spot between 50 and 114 μm in diameter for energies between 500 and 100 eV, respectively. These specifications make it ideal for high q-resolution studies of surface defects. The unipotential design offers independent beam energy and current control without refocusing, and operates at beam currents as high as 25 nA (near the space-charge limit). The operating current of this gun is 10–40 times higher than existing guns with similar spatial properties.
New powder diffractometer at HASYLAB/DESY
Authors: Arnold H. , Bartl H. , Fuess H. , Ihringer J. , Kosten K. , Löchner U. , Pennartz P. U. , Prandl W. , Wroblewski T.
Published: July 2002

The new powder diffractometer installed on the beamline B2 at HASYLAB/DESY is described. It features a new design with a blocked double circle plus a third single circle which can be translated towards one another. The wide space between the two circle units conveniently holds complicated and spacious attachments and makes the instrument especially suitable for measurements under controlled environment conditions.
Feasibility study into the use of mechanical choppers to alter the natural time structure of the APS
Authors: Mills D. M.
Published: July 2002

In standard operating mode, the Advanced Photon Source (APS) is projected to be with 20 equally spaced bunches of positrons separated by 177 ns. This time structure may not be optimal for all experiments, particularly those experiments that require long periods (microseconds to milliseconds) of darkness preceding and/or succeeding the x-ray burst. As a result, an ongoing study is being made into the possibility of altering the natural time structure of the x-ray bursts from the APS. One possibility is through the use of fast kicker magnets (wobblers). A more passive approach is through the use of high-speed mechanical choppers. Using choppers rotating between 18 000 and 20 000 rpm (typical rotational speeds for currently operational neutron choppers), a single burst of x rays can be passed while blocking the surrounding bursts. Interpulse periods are adjustable from approximately 3 to 300 μs depending on the slit configuration of the chopper wheels. Even longer periods of darkness can be achieved by using phased choppers and/or mechanical shutters.