bluuebunny/crossref_metadata_2025 huggingface dataset:
Anomalous optically generated THz beams from metal/GaAs interfaces
Authors: Jin Y. , Ma X. F. , Wagoner G. A. , Alexander M. , Zhang X.-C.
Published: July 2002

We report the measurement of optically generated THz radiation from over ten different metal/GaAs interfaces. We observe an anomalous behavior in the THz beams emitted from these interfaces. In contrast to THz radiation generated at normal incidence where the amplitude of the THz signal decreases with increasing metal film thickness, at oblique incidence we observe increased THz emission with increasing metal thickness until reaching a maximum near 80 Å.
Lateral photovoltaic effect in porous silicon
Authors: Boeringer Daniel W. , Tsu Raphael
Published: July 2002

Porous silicon has received considerable attention for its potential as a silicon-based visible light emitter. In this letter we introduce the lateral photovoltaic effect in porous silicon and show its origin in amphoteric dangling bond traps at the porous silicon surface, which also play a role in the light-induced photoluminescence degradation. The use of the lateral photoeffect for a wide area position-sensitive visible light detector is demonstrated. The lateral photoeffect also provides a new electrical technique to study the atmospheric interactions of porous silicon, with possible applications for vapor detection.
Linewidths of phonon lines of natural and synthetic diamonds
Authors: Kirillov D. , Reynolds G. J.
Published: July 2002

Raman scattering has been used to measure phonon linewidths and frequencies of a number of high quality diamond crystals. It was found that the defect induced broadening produced a Lorentzian line shape. The smallest Lorentzian linewidth of 1.68 cm−1 at 300 K caused by anharmonicity and defects was obtained for the high pressure synthesized diamond. The linewidths of the diamonds grown by chemical vapor deposition varied, with the best sample having a linewidth of 2.31 cm−1, close to the values for natural diamonds. No measurable phonon frequency shift caused by defects was found.
Interface control in InAs/AlSb superlattices
Authors: Bennett Brian R. , Shanabrook B. V. , Glaser E. R.
Published: July 2002

The presence of two species of both cations and anions permits the construction of InAs/AlSb heterostructures with either AlAs- or InSb-like interfaces. Using migration-enhanced epitaxial techniques, we grew InAs/AlSb superlattices with both types of interfaces. The control of interfacial composition was confirmed by x-ray diffraction and Raman spectroscopy measurements. We demonstrate that superlattices displaying multiple x-ray diffraction satellites, distinct planar vibrational modes, and strong photoluminescence can be achieved with both InSb- and AlAs-bonded interfaces using appropriate buffer layers and growth temperatures.
Light emission in reverse bias operation from poly(3-octylthiophene)-based light emitting diodes
Authors: Garten F. , Schlatmann A. R. , Gill R. E. , Vrijmoeth J. , Klapwijk T. M. , Hadziioannou G.
Published: July 2002

We report light emission from light emitting diodes with poly(3-octylthiophene) (P3OT) as the active layer in both forward and reverse bias operation. The onset of electroluminescence (EL) of ITO/P3OT/Al devices occurs at current densities of 6.25×10−4 A/cm2 in both modes of operation; both cases show identical EL spectra. For a P3OT thickness of 100 nm the onset of electroluminescence and current occurs at 3 V in the forward bias mode, and at about 18 V in the reverse mode of operation, at which a completely different voltage dependence of the current is observed. In the reverse mode of operation, the data suggest that carrier injection is a tunneling process through a triangular barrier of 0.4 eV at the metal–polymer interface. In the forward bias a Schottky-like behavior is seen.
Room-temperature 2.78 μm AlGaAsSb/InGaAsSb quantum-well lasers
Authors: Lee H. , York P. K. , Menna R. J. , Martinelli R. U. , Garbuzov D. Z. , Narayan S. Y. , Connolly J. C.
Published: July 2002

We describe room-temperature 2.78 μm AlGaAsSb/InGaAsSb multiquantum well lasers. Pulsed laser operation was observed at 15 °C with a threshold current of 1.1 A (10 kA/cm2), and a maximum power output of 30 mW, and a maximum differential quantum efficiency of 9%. Lasers operated pulsed up to 60 °C with a characteristic temperature of 58 K over the range of 0–40 °C. To date, 2.78 μm is the longest emission wavelength for a room-temperature III–V laser.
Tunable mid-infrared generation by difference frequency mixing of diode laser wavelengths in intersubband InGaAs/AlAs quantum wells
Authors: Chui H. C. , Woods G. L. , Fejer M. M. , Martinet E. L. , Harris J. S.
Published: July 2002

We demonstrate difference frequency generation (DFG) of 8.66–11.34 μm wavelength light in intersubband InGaAs/AlAs quantum wells by mixing of 1.92 μm±25 nm and 2.39 μm±39 nm. The peak DFG second order nonlinear susceptibility χ(2) is measured to be 12±1 nm/V, more than 65 times that of GaAs, at a difference frequency output wavelength of 9.50 μm. The intersubband absorption for the 1–2 and 1–3 transitions is measured to be 9.3 and 2.1 μm, respectively. Second harmonic generation (SHG) of 4.76, 5.12, and 5.36 μm light with a CO2 laser is observed with a peak SHG χ(2) of 52±3 nm/V. Good agreement of experiment with theory is found for both the linear and nonlinear optical properties. This demonstration of mid-infrared DFG opens the possibility for monolithic diode laser pumps and compact waveguide frequency converters as tunable midinfrared sources.
Gain model for a microchannel plate operated in the reflection mode for detecting low-energy positive ions
Authors: Koshida Nobuyoshi , Ohno Takao
Published: July 2002

A simplified model is presented to explain the gain characteristics of a microchannel plate (MCP) operated in the reflection mode for detecting low-energy positive ions. Analysis, taking into account an automatic preacceleration effect of the potential applied across a MCP on incident ions penetrating into the microchannels, can lead to high gain performance in this operation mode. The resultant calculated gain-applied potential and gain-incident ion energy curves fit well to the data reported previously. It is also shown that the gain is almost entirely determined by the transmissibility of incident ions through the microchannels toward the backplate.
Superconducting tests of beta=0.1 and beta=0.2 resonators
Authors: Storm D. W. , Amsbaugh J. F. , Corcoran D. T. , Howe M. A.
Published: July 2002

We have cooled down, multipactor conditioned, tested, helium conditioned, and retested several low beta (0.10) and two high beta (0.21) lead plated copper quarter-wave resonators. We discuss the choice of the quarter-wave resonator and of the lead plated copper technology. We describe the fabrication and present our techniques for conditioning the resonators. Performances are presented.
High-efficiency two-harmonics beam chopper
Authors: Xu G. S. , Qian Z. B. , Chen C. E.
Published: July 2002

A novel beam chopper with two-harmonics ( f and kf ) sweeping voltages is described. It is shown that beam utilization efficiency and the beam quality of the harmonic chopper are much better than that of the conventional sine-wave chopper. The beam utilization efficiency might be even higher than the square-wave chopper for low-velocity ions. In practice, a chopper with 1.5 and 13.5 MHz (k=9) was constructed with great convenience for the beam-pulsing system of a 4.5-MV Van de Graaff in Peking University. The bench tests indicated that the beam efficiency of the harmonic chopper was higher than a single-frequency chopper by about 47%, which agrees with the theory and the design.
High-performance acoustic microscope
Authors: Atalar Abdullah , Hoppe Martin
Published: July 2002

A commercial scanning acoustic microscope operating in the frequency range of 50–2000 MHz is described. It has a stable scan mechanism suitable for the high-frequency end to give high-resolution images and modes to allow for material characterization at the low-frequency end. The high-frequency electronics permitting a wideband operation with a variety of acoustic lenses are described. Microprocessors control many parts of the the instrument to release the user from the routine adjustments, resulting in a user-friendly interface. Images are presented to show the resolution and penetration abilities of the instrument at several frequencies, along with comparative optical images.
New instrument for measuring complex adiabatic compressibility and adiabatic pressure-induced temperature variation of liquids in the frequency range from 0.5 Hz to 2 kHz
Authors: Tanaka Hajime , Nishi Toshio , Wada Yasaku
Published: July 2002

A new instrument is presented for measuring complex adiabatic compressibility and adiabatic pressure-induced temperature variation (∂T/∂P)S of liquids in the low-frequency range from 0.5 Hz to 2 kHz. The relative accuracy of the measurement is of the order of 10−3–10−4. The velocity and absorption coefficient of sound in the low-frequency range give us information on slow relaxational phenomena. (∂T/∂P)S, which is directly related to the ratio of thermal expansion coefficient to specific heat, can be measured accurately by ac method. The measurement of these quantities provides us with new information on thermodynamic or low-frequency relaxational behavior of liquids, including critical liquids, liquid crystals near their phase transitions, and biological materials.
Current density monitor for intense relativistic electron beams
Authors: Fiorito Ralph B. , Raleigh Michael , Seltzer Stephen M.
Published: July 2002

We describe a new type of electric probe which is capable of measuring the time-resolved current density profile of a stable, reproducible, high-energy (>4-MeV) high-current (>1-kA) electron beam. The sensing element of this probe is an open-ended but capped-off 50-Ω coaxial line constructed of graphite. The graphite sensor is 4.3 mm in diameter, 6 cm long, and is range thin to the primary beam electrons. The probe produces a signal proportional to the intercepted beam current. When the sensor is scanned radially through the beam during repeated pulses, a curve of signal versus depth of insertion is produced from which the radial current density profile can be determined. Measurements are presented of the profile of the electron beam from the Experimental Test Accelerator (4.5 MeV, 10 kA) at Lawrence Livermore National Laboratory. Good agreement is shown between measurements made with this probe and the beam radius as predicted by transport codes. The advantage of the electric probe lies in its ruggedness, simplicity, inherent fast rise time, and low cost. In contrast to other systems it requires no radiation shielding, water cooling, or auxiliary support equipment to operate in an intense beam environment.
Collision-induced spectral measurements with a long path cell and a laser source
Authors: Dagg I. R. , Smith W. , Missio M. , Read L. A. A.
Published: July 2002

Laser measurements at 23.13 cm−1 of collision-induced absorption are described using absorption cells over 1500 cm in length and a liquid-helium-cooled bolometer. Also reported are a number of improvements over a previously described system operating at different laser frequencies. The improvements are related to the method of data collection and operation of the system which result in an increased accuracy of determination of the absorption coefficients of nonpolar condensed gases. Typical results are given for the cells used in the temperature range from 126 to 410 K at pressures up to 1500 psi.
Mass-sensitive ion energy analyzer for multispecies plasmas
Authors: Hairapetian G. , Stenzel R. L.
Published: July 2002

A new diagnostic tool has been developed that can discriminate between ions in a multispecies plasma of intermediate densities (107<ni<1012 cm−3) and temperatures (0<kTi<100 eV) and measure their local densities (to within 5%) and temperatures (to within 1 eV) using time-of-flight techniques. The probe consists of an exciter in line with a movable retarding-grid ion energy analyzer (detector), and has a spatial and temporal resolution of ∼0.4×4 cm and ∼200 ns, respectively. The exciter structure is composed of three mesh grids, an accelerator, and two shields (diameter 4 cm, separation 2 mm). A+80 V fast rising pulse (30-ns rise time, 2-μs width) is applied to the center grid which excites ion bursts that are detected by the ion energy analyzer. The charge-to-mass ratio of Ar+, Ar++, Ne+, He+, H+ is determined to within 10%, and the relative densities and temperatures of Ar+, Ne+, and H+ are measured.
Ion signal calibration in the imaging atom-probe with an external, time-gated image intensifier
Authors: Kellogg G. L.
Published: July 2002

A commercial, external image intensifier unit has been adapted to an imaging atom-probe mass spectrometer. The image intensifier can be operated in a pulsed mode to obtain time-gated (i.e., species specific) images while simultaneously recording time-of-flight mass spectra. This capability was used to calibrate the amplitudes of rhodium, tungsten, and neon ion signals which appear in imaging atom-probe mass spectra. The signal amplitudes were found to be directly proportional to the number of imaged ions over a range of amplitudes covering three orders of magnitude. The proportionality constant was found to be nearly the same for doubly charged rhodium and triply charged tungsten ions, but significantly different for neon ions. The constant was not sensitive to variations of ∼30% in the applied voltage (i.e., ion energy).
Varactor resonator calibration for dielectric measurements
Authors: Migliuolo M. , Deri R. J.
Published: July 2002

A new calibration procedure of the superconducting helical resonator using a varactor diode is presented. This method improves the accuracy with which resonator parameters can be measured and reduces the overall measurement time needed for the calibration.
Efficient stator/rotor assembly for magic-angle spinning NMR
Authors: Jiang Y. J. , Woolfenden W. R. , Alderman D. W. , Mayne C. L. , Pugmire R. J. , Grant D. M.
Published: July 2002

A newly designed stator assembly for cylindrical spinners used in magic-angle spinning nuclear-magnetic-resonance experiments is described. Separate driving and bearing gas chambers allow variable and stable spinning speeds, and this design permits easy starting and stopping of the rotor. Isolation of the chambers is achieved with the application of pressure screws rather than O rings or glue lines to avoid leakage at high gas pressures. The overall dimensions are optimal to facilitate easy assembly. Some significant modifications have been made to an earlier spinner design. These improvements give better efficiency and concentricity of the spinner. Applications are illustrated with carbon-13 cross polarization/magic angle spinning (CP/MAS) spectra carried out at different rotor spinning rates.
Cylindrical Pierce gun for high-intensity bremsstrahlung isochromat spectroscopy
Authors: Hillebrecht F. U. , Keppels J. , Otto R.
Published: July 2002

We describe an electron gun suitable for bremsstrahlung isochromat spectroscopy (BIS). The design is based on the Pierce geometry and especially adapted to fit a large solid angle (0.07 sr) toroidal x-ray monochromator consisting of 54 quartz single crystals. Performance parameters, as well as some examples of BIS spectra, are presented.
Generation and propagation of high-brightness electron beams from a magnetically crowbarred injector
Authors: Humphries S. , Len L. K. , Allen C. B.
Published: July 2002

Tests of a 300-keV electrostatic electron beam injector with a magnetic crowbar switch are described. The saturable ferrite core switch allows generation of a constant voltage, 80-ns pulse directly from a Marx generator. Inductive isolation in the switch permits direct access to the high-voltage electrode for thermionic or active plasma cathode experiments. The pulse modulator can drive a 1.5-kA load. A high brightness 290-A beam from a felt plasma-emission cathode was extracted and propagated in vacuum. Because of the reliability of the magnetic crowbar switch, more than 500 shots were accumulated on the cathode at over 1 kA/cm2 with no degradation of the output. The output beam had a normalized brightness of 2.6×108 A/(m rad)2. A solenoidal lens was used to match the space-charge-dominated beam into a 1-m-long periodic focusing system with 25 reversing solenoidal coils. A beam current of 150 A was successfully transported through the 1.7-cm radius tube.
Measurement of the complex dielectric constant of lossy fibers and rods at microwave frequencies
Authors: Lind Arthur C. , Wenger Terry R.
Published: July 2002

Three related waveguide devices are described for measuring the dielectric constants of fibers and rods. In each device the sample is located one-quarter guide wavelength from the shorted end of the waveguide. A slot in the side or end of the guide permits easy insertion and removal of a fiber sample without having to thread it through holes in the waveguide. The dielectric constant along the length of the fibers can be measured as they are rapidly pulled through the device. The technique allows accurate measurement of samples having a wide range of diameters and dielectric constants. Measurements of carbon, nickel alloy, and alumina samples are described, and the experimental sources of error are analyzed.
Noncontacting optical probe
Authors: Jing Fang-Sheng , Hartman A. W. , Hocken R. J.
Published: July 2002

A description is given of an optical probe, consisting of an optical microscope with modified internal illumination, a dual chopper with its two edges straddling the image plane, and a dual area sensor mounted behind the chopper. An analysis shows that the sensitivity of this proximity probe is essentially the same as that of the Simon probe, while its linearity is much better. Also, its construction is much simpler. A prototype has shown resolution of 0.02 μm and linearity errors of 0.5 μm (at 100-μm range), respectively.
Use of thermal desorption modulators in gas chromatograph/mass spectrometer
Authors: Mitra Somenath , Phillips John B.
Published: July 2002

A thermal desorption modulator is comprised of a short length of tubing with some adsorbent or chromatographic stationary phase inside. A flowing stream containing a sample can be introduced into an instrument such as a gas chromatograph through a modulator. The concentration of samples in the flowing stream can be effectively modulated by modulating the temperature of the modulator. The purpose of this study is to demonstrate the application of a thermal desorption modulator in GC/MS.
In situ dye laser calibration for Thomson scattering diagnostics
Authors: Rasmussen D. A. , Kindsfather R. R. , Thomas C. E. , Gormley R. P. , Painter S. L.
Published: July 2002

The standard laser Thomson scattering calibration technique involves the convolving of density and wavelength response calibrations. This usually includes an in situ Rayleigh scattering from neutral gas for an absolute density calibration at the laser wavelength. In addition, a spectral calibration (i.e., a National Bureau of Standards traceable lamp and white reflective plate) is required to determine the relative wavelength channel responses for the combination of collection optics, spectrometers, and associated detectors. This technique involves a considerable amount of time and effort in two-dimensional scattering systems because of the number of spectrometers/detectors and the large range of scattering and collection angles. An alternative technique employing a nominal 40-mJ, small-divergence tunable dye laser substituted into the Thomson scattering laser beam path is proposed. Rayleigh scattering (from ∼10-Torr H2) measurements are made at a high repetition rate (1–10 Hz) while the dye laser output wavelength is scanned. This includes in one step the in situ density and channel response calibrations.
Narrow-band velocity selector for neutral particles
Authors: Miers R. E. , York R. W. , Pickett P. T. , Taylor W. L.
Published: July 2002

A velocity selector wheel of novel spiral groove design was constructed and successfully tested. The wheel can be used to select a narrow band (∼±1.2%) of velocities from a molecular beam while presenting an effective open time of 38%. No velocity sidebands are transmitted and alignment is relatively simple. Experimental measurements verified performance essentially as predicted.
In-situ monitoring of redeposited carbon in the vicinity of a plasma–graphite interacting region (abstract)
Authors: Hsu Wen L.
Published: July 2002

The interaction of the plasma with graphite limiters in fusion devices has been observed to lead to the formation of carbon film deposits. This occurs from the erosion of the graphite tiles in a high-flux region and subsequent redeposition of the carbon atoms onto a low-flux surface. The redeposition of carbon has strong ramifications on the in-vessel tritium inventory. A commercially available quartz crystal monitor has been tested in a plasma simulator device to measure the flux of eroded carbon. The test was done with the intent of mounting such a detector in TFTR. The monitor measures the deposited film thickness as a change in the resonance frequency of the crystal. The plasma simulator is a Penning discharge operated with graphite electrodes. Initial tests show the crystal monitor has high sensitivity and can detect film thickness changes of a few angstroms. Thermal shock problems, however, may limit time resolution of the measurement and can provide only an integrated deposited thickness within a discharge. This work was supported by the U. S. DOE.
Characterization of a high-magnification x-ray microscope on Nova (abstract)
Authors: Glendinning S. G. , Phillion D. W. , Kilkenny J. D.
Published: July 2002

We have implemented a Wolter-type x-ray optic in a high- (22×) magnification microscope on Nova. We report on the on-line characterization of this system and show results from the several types of experiments performed. The point spread function, contrast transfer function at selected spatial frequencies, x-ray throughput, alignment accuracy, and field of view have all been measured as configured for Nova experiments. Such characterization may be used to remove the degradation introduced by the instrument. This work was performed under the auspices of the U.S. DOE by the Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.
Measurements of the ion temperature and plasma rotation from Kα emission with the TFTR horizontal x-ray crystal spectrometer (abstract)
Authors: Hsuan H. , Bitter M. , Rice J. E. , Hill K. W. , Johnson L. , Liew S. L. , Scott S. D. , von Goeler S.
Published: July 2002

The TFTR horizontal x-ray crystal spectrometer has been improved by installation of γ and neutron shielding and is now operating in the TFTR Test Cell up to the presently maximum neutron production rates of 2×1016 neutrons/s. Further optimization by using a modified detector may assure operation of the spectrometer during the DT phase when TFTR is covered by an igloo. The instrument is set up for simultaneous observation of the entire satellite spectrum of Ni xxvii, and it provides data on the time evolution of the central ion temperature and the central plasma rotation velocity. Ion temperatures of 20–30 keV have been measured under ‘‘supershot’’ conditions. The highest rotation velocity observed with unidirectional injection was 1.1×106 m/s.
Plasma fluctuation signal analysis tool
Authors: Hong J. Y. , Ritz Ch. P. , Powers E. J. , Kim S. B.
Published: July 2002

A plasma fluctuation signal analysis software package is described that surmounts common difficulties by using an information-hiding method and a layered structure.This approach leads to portability and easy customization for experimentalists who are not necessarily experts in signal analysis. The software contents and examples of applications to actual experimental data will be discussed.
ATF data management
Authors: Kannan K. L. , Baylor L. R.
Published: July 2002

Data management for the Advanced Toroidal Facility (ATF), a stellarator located at Oak Ridge National Laboratory, is provided by DMG, a locally developed, VAX-based software system. DMG is a data storage and retrieval software system that provides the user interface to ATF raw and analyzed data. Data are described in terms of data models and data types and are organized as signals into files, which are internally documented. The system was designed with user accessibility, software maintainability, and extensibility as primary goals. Extensibility features include compatibility with ATF as it moves from pulsed to steady-state operation and capability for use of the DMG system with experiments other than ATF. DMG is implemented as a run-time library of routines available as a shareable image. General-purpose and specialized data acquisition and analysis applications have been developed using the DMG system. This article describes the DMG system and the interfaces to it.
Polarimeter design for measurement of the poloidal field in a tokamak (abstract)
Authors: Levinton F. M.
Published: July 2002

A polarimeter has been designed and built to measure the direction of linearly polarized light. The device will be installed on the PBX-M tokamak to view visible light from collisional excitation of a diagnostic neutral beam operated with helium. Due to the Zeeman effect the π-component of the emitted radiation from the helium beam will be linearly polarized parallel to the direction of the local magnetic field, when viewed perpendicular to the plane of the magnetic field components. A Fabry–Perot interferometer will be used, because of its high resolution and throughput, to transmit only the π component of the Zeeman triplet. A photoelastic modulator1 (PEM) is used to modulate the polarization angle of the light. Depending on the orientation of the PEM it can measure the sine or cosine of the angle of polarization. A test setup consisting of two PEMs to measure both the sine and cosine of the polarization angle has demonstrated a resolution of <0.1°. This work was supported by U.S. DOE Contract No. DE-AC03-86ER80409.
Neutral probe beam q-profile measurements in PDX and PBX-M
Authors: Kugel H. W. , Gammel G. M. , Kaita R. , Reusch M. F. , Roberts D. W.
Published: July 2002

Using the fast ion diagnostic experiment technique, a neutral probe beam (NPB) can be aimed to inject tangent to a magnetic surface. The resultant ion orbit shifts, due to conservation of canonical toroidal angular momentum, can be measured with a multi-sight-line charge exchange analyzer to yield direct measurements of radial magnetic flux profiles, current-density profiles, the radial position of the magnetic axis, flux surface inner and outer edges, q profiles, and central-q time dependencies. An extensive error analysis was performed on previous PDX q measurements in circular plasmas and the resulting estimated contributions of various systematic effects are discussed. Preliminary results of fast ion orbit shift measurements at early times in indented PBX-M plasmas are given. Methods for increasing the absolute experimental precision of similar measurements in progress on PBX-M are discussed.
Detection of plasma equilibrium shifts with fiber-optic sensing of image currents
Authors: Forman P. R. , Jahoda F. C. , Miller G.
Published: July 2002

Plasma shifts generate opposite-polarity net shell image currents at diametrically opposed shell locations. In theory these image currents can be detected by Faraday rotation fiber-optic current sensors wound around the shell sections. In practice the validity of the measurement depends on the extent of suppression of the linear birefringence induced by the fiber coil bending and lateral pressure. Circular birefringence bias twist of 60 turns/m of 125-μm o.d. single-mode fiber is sufficient for 2-in. radii of curvature bends, in agreement with theory, while 100 turns/m of 80-μm o.d. fiber have not been successful with 1-in. radii of curvature, contrary to calculations. Different means for further suppression of linear birefringence are discussed.
Simple ion temperature diagnostics for a short tokamak discharge
Authors: Zurro B. , García-Castañer B. , Hidalgo C. , Pérez S. , Pallás L.
Published: July 2002

A simple experimental procedure used in the TJ-I tokamak, for simultaneously measuring the ion temperature is described. Two monochannel systems (neutral and optical) are scanned at a preprogrammed time of the tokamak discharge, where the signals are stationary. System performances are illustrated with results obtained in the TJ-I tokamak.
Radiative and diffusional effects to the population densities of the excited-state atoms in hydrogen plasma
Authors: Cho K. Y. , Eddy T. L.
Published: July 2002

Collisional–radiative (C–R) calculations based on the generalized multithermal equilibrium (GMTE) model are used to find the effects of radiative transfer and diffusion on excited-state populations in a hydrogen plasma. Radiation absorption factors are introduced to study the nonlocal aspects of radiative transfer. Unlike escape factors, the absorption factor can represent the absorption of more radiation than that emitted, and hence provides C–R analysis in strong gradients such as the outer edge of arcs or plasma jets. The Boltzmann temperatures of excited atoms are found not necessarily equal to the electron kinetic temperature, contrary to the usual assumption.
A trapezoidal function voltage generator for electrochemical applications
Authors: Holze Rudolf
Published: July 2002

An analog circuit based on standard operational amplifiers is described, which generates a trapezoidal voltage signal with rise and fall times as well as holding times variable over a wide range. Application of the circuit in spectroelectrochemistry is described, its properties are compared to currently available electrochemical instrumentation providing similar voltage functions.
Helium-filled proportional counter for low-temperature operation (1.75–4.2 K) and its application to cryogenic resonance-electron Mössbauer spectroscopy II
Authors: Isozumi Yasuhito , Ito Shin , Fujii Tatuo , Katano Rintaro
Published: July 2002

The operation of the helium-filled proportional counter (HFPC) has been investigated at low temperatures below liquid-helium temperature, 4.2 K. It has been found that the gas gain as a function of the anode voltage is not appreciably changed by the temperature of the filling gas, but continuous electric discharges are induced at lower anode voltages as the gas temperature is decreased. The present counter technique has been applied to resonance-electron Mössbauer spectroscopy in the temperature region below 4.2 K.
Generation of various polarization states from insertion devices: A review
Authors: Elleaume Pascal
Published: July 2002

Most insertion devices (IDs) which have been built so far are planar with the field in the vertical plane. They are the easiest to design, and they fit well to the narrow vertical aperture available on storage rings. As bending magnets, these IDs generate essentially horizontally polarized radiation. Recently, several new proposals and prototypes have been produced in order to generate different polarization states. The Stokes decomposition of the radiation from these devices is given versus photo energy. This discussion is illustrated by taking the European Synchrotron Radiation Facility (ESRF) conditions in the hard x-ray range.
Elastic constants and Poisson ratio in the system AlAs–GaAs
Authors: Krieger M. , Sigg H. , Herres N. , Bachem K. , Köhler K.
Published: July 2002

Near infrared Brillouin scattering was used to determine all three elastic constants, and hence Poisson’s ratio ν=C12/(C11+C12) of epitaxial AlxGa1−xAs layers on GaAs. The AlxGa1−xAs layers were grown by metalorganic chemical vapor deposition and molecular beam epitaxy. We found evidence for a slight bowing in all elastic constants versus Al composition x. The elastic constants of AlAs were determined to be C11=119.9 GPa±1.2 GPa, C12=57.5 GPa±1.3 GPa, and C44=56.6 GPa±0.7 GPa. From x-ray measurements and the Poisson ratio ν=0.324±0.004 the relaxed (cubic) AlAs lattice constant is found to be aAlAs=5.661 72 Å±0.000 08 Å.
A photoelectronic source for electron avalanche measurements
Authors: Mahajan S. M. , Sudarshan T. S.
Published: July 2002

A photoelectronic source described by Borghesani et al. [Rev. Sci. Instrum. 57, 2234 (1986)] employed a Xenon flash lamp to obtain relatively large electronic current pulses of microsecond duration. A theoretical analysis and a subsequent rule of thumb indicated that a minimum thickness of 50 Å is needed for obtaining maximum electron yield through such a device. In this note, we report the fabrication details of a similar but a much faster response (∼1 ns) electrode system to produce an electron burst. The film thickness corresponding to maximum photoemission yield was estimated by using a crystal oscillator. Optimum thickness was found to be ∼100 Å which is in general agreement with the earlier device having microsecond duration pulse.
Superconductive radiation detector with large sensitive area (series-connected STJ detector)
Authors: Kurakado Masahiko , Matsumura Atsuki , Takahashi Toru , Ito Shin , Katano Rintaro , Isozumi Yasuhito
Published: July 2002

One of the serious problems in the development of particle detectors with superconducting tunnel junctions (STJ) is the difficulty in devising a large area that is sensitive to nuclear radiations. The problem has been solved by using an assembly of micro STJs connected in series (series-connected STJ detector), which is designed for detecting nonthermal phonons created by irradiating the rear substrate (sapphire) with nuclear radiations. The present detector is sensitive not only to ionizing events but also to nonionizing events, providing us with a new method to detect nuclear radiations. Some features of the series-connected STJ detector are described in this article.
Generation of a focused proton beam with a self-magnetically BΘ-insulated ion diode
Authors: Schimassek Walter , Bauer Walter , Stoltz Otto
Published: July 2002

A self-magnetically BΘ -insulated ion diode was investigated and optimized at the pulsed power line KALIF (2 MV, 50 ns, 2 Ω) to produce a focused and pulsed high-intensity proton beam for generation of high-power density in matter. This diode is characterized by an azimuthal insulating magnetic field that is generated by the diode current. The beam is neutralized by electrons from the cathode vanes, so that neither a gas filled drift space nor foils are needed. The beam therefore propagates in vacuum and repeated shots are possible without changing parts. The protons had energies up to 1.8 MeV and the proton content in the ion beam was about 50%. The maximum total diode current was about 800 kA and its efficiency was as high as 70%. The beam microdivergence was determined to be 1.1°. The radial dependence of the proton current density was measured and is proportional to r−1.74. This result was confirmed by 2D quasistatic particle-in-cell simulations. The focus was optimized by adjusting the anode shape and the gap geometry and by decreasing the beam divergence. The FWHM diameter of the focus at a distance of 300 mm was about 10 mm and the resulting focused power density was 0.13 TW/cm2. The effect of the gap distance on focusing and impedance was investigated and it was found necessary to adjust the gap to better than 0.1 mm over the total 30-cm-diam anode to obtain the best performance. The electron loss and the corresponding erosion at the posts that hold the anode was reduced. The lifetime is now limited by the plastic anode insert to 10–15 pulses. Based on these results a ‘‘small BΘ diode’’ is suggested for which a power density increase of a factor of 3 is estimated.
Dual diode preamplifier for detection of laser Doppler interference photons
Authors: Olkkonen H.
Published: July 2002

A preamplifier circuit using two parallelly placed p-i-n diodes was constructed to detect the coherent light scattered from the moving object in the laser Doppler velocimeter. The preamplifier effectively eliminates the common mode light, noise due to laser mode variation, and 50-Hz pickup. The amplifier can be applied in various velocity measurements, e.g., determination of skin blood flow.
Temperature measurements with micrometer spatial resolution
Authors: Izaguirre F. , Csanky G. , Hawkins G. F.
Published: July 2002

A novel technique has been developed to measure temperatures with a spatial resolution less than 10 μm. This method uses the temperature-sensitive time decay fluorescence of a phosphor as a surface sensor. The spatial resolution is obtained by using an electron beam to excite individual phosphor grains deposited on the surface of interest. The phosphor selected for its dynamic range and chemical stability is the inorganic compound magnesium fluorogermanate activated with manganese. The time decay constant of its fluorescence decreases monotonically with temperature between −200 °C to 450 °C. This method was verified on a cross-sectioned Zener diode. A description of the technique and a temperature map of the sectioned area of an operating diode are presented.
A tunneling instrument for angle resolved tunneling spectroscopy
Authors: Suzuki M. , Fujii T. , Miyashita M. , Onuki T. , Enomoto H. , Ozaki H.
Published: July 2002

A new tunneling instrument has been developed to observe the anisotropy of the Fermi surface. This instrument has two advantageous mechanisms over the conventional scanning tunneling microscope (STM); a tilt mechanism to keep two crystals parallel to each other and a rotation mechanism of the proven crystal over the sample crystal. We have evaluated its performance.
A spring-guided micropositioner with linearized subnanometer resolution
Authors: Nishimura Kunitoshi
Published: July 2002

A micropositioner consisting of flexure pivoted levers with a displacement amplifying mode to enhance displacement sensor sensitivity and a displacement reducing mode to achieve high resolution is described. The micropositioner is actuated by a piezoelectric driving element controlled by a closed-loop servocircuit, and provides fast response and high repeatability. A successful application to STM is also described.
A compact interferometer using moire effect for the phase compensation
Authors: Watanabe S. , Hane K. , Goto T.
Published: July 2002

A compact interferometer using a grating beamsplitter is reported. The phase of the interference signal was adjusted by using the moire effect of the gratings, so that a small optical path difference was compensated precisely by the magnified displacement of the grating. The optical system was analyzed theoretically on the basis of the Fourier optics. For the interferometric measurement in the microscopic region, a compact optical system was assembled from the microscopic objective and the 25-μm gratings. The characteristics of the proposed interferometer were investigated in the measurements of film thickness, piezoelectric vibration, and photoacoustic effect.
Surface tensiometer utilizing laser-beam reflection at cylindrical liquid menisci
Authors: Ishida Kenji , Kinoshita Shinji , Mori Yasuhiko H.
Published: July 2002

A surface tensiometer has been devised which is based on the mathematical solution, as a function of the surface tension of a liquid, of the profile of a cylindrical meniscus formed against a flat plate brought into contact with the free surface of a quiescent pool of the liquid. Only the angles of inclination of the meniscus at two arbitrary points are to be actually measured; the angle at each point is known accurately by observing the angle of reflection of a laser beam vertically irradiated onto the point. No knowledge of the contact angle on the plate is required. The tensiometer is suitable for the study of surface adsorption or of insoluble monolayers just the same as in the Wilhelmy plate method, but it is still superior to the Wilhelmy plate tensiometers and other conventional surface balances in its applicability to the measurements in an atmosphere completely insulated from the laboratory air. An apparatus is demonstrated that has been constructed primarily for the measurements of surface tensions of aqueous lithium bromide (LiBr) solutions with higher alcohol additives, i.e., working fluids of absorption heat pumps, under reduced pressures and elevated temperatures.
Fiber-optic based analog signal delivery system with automatic remote control
Authors: Mendieta Francisco Javier , Martinez Juan Paulo , Arvizu Arturo
Published: July 2002

The design and development of equipment for remote transducer output signal delivery is described which is based on a fiber-optic transmission-reception system employing subcarrier angular modulation for true direct current coupling, high linearity, and low noise behavior. Also, a fiber-based digital uplink for controlling the remote transmitter is presented which provides gain/attenuation programming, calibration signal insertion, battery test, and turn on/stand-by, both manual and automatically using and embedded computer controller. Performance measurements are given.
Imaging band-pass analyzer using double 90° spherical analyzers
Authors: Kim Changyoung , King Paul L. , Pianetta Piero , Kelly Michael A. , Bryson Charles A.
Published: July 2002

The design and testing of an imaging band-pass analyzer (BPA) consisting of two 90° spherical sectors operating in a magnetic-field-free region is described. Image electrons injected nearly parallel to one another and perpendicular to the first 90° sector are focused into an energy plane where electrons of desired energy are band-pass filtered. A second 90° sector is used to recover the energy-filtered image. With a 1-mm aperture, energy resolution of 1% and spatial resolution of 0.01% of the main path radius are calculated and agree well with the test results over an image size of 12×12 mm2. The addition of this analyzer to our magnetic projection photoelectron microscope poses an additional technological problem in that the electrons are required to pass from a relatively high-field area to a field-free region without disruption of the image. Design considerations for a structure that abruptly terminates a magnetic field yet is transparent to image electrons are described.
Dynamic method for measuring the velocity variation of ultrasound in piezoelectric ceramics with an alternating electric field
Authors: Cho Yasuo , Matsuno Fumihiko
Published: July 2002

The development and application of a new dynamic measuring method of velocity variation of piezoelectric materials, especially of lead zirconate titanate (PZT) ceramics, with an alternating electric field is presented. This method has the following advantages over the conventional static method. (1) The velocity variation due to nonlinear effect is separable from the velocity variation due to temperature change. (2) The adiabatic nonlinear coefficients are obtainable. (3) In spite of the dynamic nature of the method, it fixes the sign of the nonlinear coefficient. (4) Separating the orders of the velocity variation as a function of the applied electric field, each order of coefficients is determinable.
Construction and performance of a bent crystal x-ray monochromator
Authors: Stephens Peter W. , Eng Peter J. , Tse Teddy
Published: July 2002

We describe an x-ray monochromator which uses a sagittally bent crystal to focus 5.7 mrad of horizontal divergence. Complete construction details are given, enabling the reader to duplicate the device. The rocking curve width and diffraction efficiency differ insignificantly between the bent (focusing) and flat crystal geometries. The unit has been operated successfully at energies up to 18 keV, providing a seventyfold increase in x-ray flux over unfocused radiation.
A new photometric detector in the visible spectral range based on a silicon photodiode
Authors: Bergbauer R. , Bremer C. , Grell E.
Published: July 2002

From the equivalent circuit of a photodiode it is shown that the light-induced current of the photodiode is expected to be characterized by a linear function of the light intensity in a range of eight decades. The electrical circuit of the detector based on a silicon photodiode (S1722-02; Hamamatsu) in combination with an operation amplifier used as a current-voltage converter and its realization is specified. It exhibits 10%–90% rise times between 200 ns and 5 μs depending on the internal amplification selected out of five stages. The wavelength dependence of the signal-to-noise ratio of this photodiode system is determined and compared with that of a detector based on a photomultiplier (1P28; RCA, Lancaster). At wavelengths above 580 nm the photodiode system exhibits a signal-to-noise ratio up to 20 times better than the photomultiplier system. Employing a HeNe laser as light source, a signal-to-noise ratio as high as 2×104 is found with a time resolution of 1 μs.
Generation of synchronized trains of picosecond laser pulses at two wavelengths in a single-cavity synchronously mode-locked dye laser
Authors: Buccafusca O. , Rocca J. J. , Marconi M. C. , Menoni C. S.
Published: July 2002

Synchronized trains of 5 ps pulses at two wavelengths were generated in a single-cavity synchronously pumped dye laser containing a mixture of two dyes in a single jet and intracavity spatial masking for frequency selection. The utilization of this dual wavelength dye laser to monitor the relaxation of photoexcited carriers in multiple quantum wells was demonstrated.
A simple and efficient pulsed-heating atomic beam source for resonance ionization spectroscopy
Authors: Katsuragawa Hidetsugu , Kubota Masashi , Minowa Tatsuya , Komatsu Haruko
Published: July 2002

A simple and low-cost pulsed atomizer for resonance ionization spectroscopy of Mo has been produced. The atomizer has made it possible to measure the isotope shift of Mo with a 200 μg sample in resonance ionization spectroscopy.
Optimum capacitor ratio in a transversely excited atmospheric CO2 laser
Authors: Tou T. Y. , Low K. S.
Published: July 2002

The performance of a pulsed CO2 laser using the capacitor transfer circuit is generally known to improve with an optimum peaking-to-storage capacitor ratio Cp/Cs which varies from around 0.1 to almost 0.5. There has been no reported attempt to account for precisely the origin of this optimum ratio and the large difference amongst them with different experimental setups. In this paper, the optimum capacitor ratio is shown to depend uniquely on the distributed circuit inductances. This may be understood from a simple consideration of the impedance matching for achieving an optimum power transfer at a quasiconstant E/N ratio into the main discharge.
A static high-pressure apparatus based on an internal force produced by constraining thermal expansion
Authors: Kawashima Yasushi
Published: July 2002

A static high-pressure apparatus based on an internal force produced by constraining thermal expansion is devised. This apparatus does not require a large hydraulic press and is not accompanied by frictional force because it does not have a sliding part. As an example, in case of using lithium fluoride as a pressure source, the high pressures created in the apparatus are measured using pressure dependences of melting points of lead and aluminum. By the measurements, it is demonstrated that the apparatus creates pressures of 1.65 and 2.85 GPa at 440 and 842 °C, respectively. These measured values are in good agreement with the values calculated by using the finite-element method.
High-resolution deposition rate monitor
Authors: Jiang Y. M. , Torre J.-P. , Wang K. , Pesty F. , Garoche P.
Published: July 2002

A 16-MHz piezoelectric quartz resonator has been used to build up a high-resolution deposition rate monitor. A direct counting allows a resolution of 1 ng/cm2 at a rate of one reading per second. Direct computer interface and increase in the voltage excitation above the plasma noise level have been successfully used to monitor the deposition rate in a dc sputtering apparatus.