bluuebunny/crossref_metadata_2025 huggingface dataset:
High-temperature window seals for VUV experiments
Authors: Muller C. H. , Barrett M. W. , Lowenthal D. D.
Published: July 2002

A simple and reliable technique for sealing laser quality vacuum-ultraviolet grade windows to high-temperature, bakable vacuum systems has been developed. Both 7.5-cm-diam MgF2 and CaF2 windows were found to be He leak tight to temperatures exceeding 330 °C. Smaller 4-cm-diam windows seal at temperatures exceeding 400 °C. The seals do not appear to be adversely affected by temperature cycling and they do not distort the optical quality of the window. The sealing technique has been used without failures in a Hg vapor four-wave-mixing cell that is used to produce high-power 130-nm coherent radiation.
High-precision temperature controller based on phase-locked loop circuits
Authors: Rubio M. A. , Conde L. , Riande E.
Published: July 2002

We report a low-cost, high-performance analog electronic temperature controller based on an alternative technique to resistive bridges. The proposed device shows linearity around the working temperature, high resolution, and good transient behavior.
Vertical transition quantum cascade laser with Bragg confined excited state
Authors: Faist Jérôme , Capasso Federico , Sirtori Carlo , Sivco Deborah L. , Hutchinson Albert L. , Cho Alfred Y.
Published: July 2002

A new midinfrared (λ∼4.5 μm) intersubband quantum cascade laser based on a vertical transition is reported. A superlattice graded gap region was incorporated in the design to provide strong electron confinement in the upper state using a Bragg reflector. Pulsed operation at 100 K is reported with a threshold current density of Jth=3 kA/cm2 and a measured slope efficiency of 300 mW/A.
Reduced effective misfit in laterally limited structures such as epitaxial islands
Authors: Christiansen S. , Albrecht M. , Strunk H. P. , Hansson P. O. , Bauser E.
Published: July 2002

Numerical finite element calculations have been reported to determine a correction function Φ that describes the reduction of the misfit that occurs when laterally limited structures such as faceted islands or mesa structures are grown on a substrate. The reduction of the average strain energy density is calculated in these three-dimensional islands and compared to the constant strain energy density in a continuous layer. Ratios Φ are obtained from the calculation of different island geometries, i.e., different facet angles γ and different aspect ratios island width l to island height h. These discrete values are fitted by a function which can easily be applied to the full range of aspect ratios (l/h≳0) and facet angles (0°<γ<90°). Faceted Ge(Si) islands on Si(001) substrate, grown from the solution in the Stranski–Krastanov growth mode, serve as an example for the calculation. Experimental and theoretical values for the critical thickness of these islands agree well. This result demonstrates the drastic influence of islanding on misfit strain distribution in island and substrate as well and, consequently, on the strong increase of the critical thickness as determined by the mechanical equilibrium theory of Matthews and Blakeslee.
Plasma emission spectroscopy with an optical fiber probe
Authors: Jin Z. J. , Chan Chung , Whitaker Christopher
Published: July 2002

We have developed an optical fiber probe which is well suited for measuring localized light emission in plasmas. The plasma emission intensity distribution along the axis of a parallel-plate rf glow discharge has been used as an example for comparing measurements between the optical fiber probe and the standard lens-slit system.
A time-of-flight mass spectrometer for large molecular clusters produced in supersonic expansions
Authors: Conover C. W. S. , Twu Y. J. , Yang Y. A. , Bloomfield L. A.
Published: July 2002

Supersonic free jet expansions are often used to produce beams of cold molecules and clusters. They are an essential part of laser vaporization cluster sources, where small particles of a material are seeded within a helium carrier gas during the expansion. These sources accelerate the clusters to the thermal velocity of the helium gas used in the generation process. By tilting the acceleration grids in a time-of-flight spectrometer, the initial velocities of molecular clusters transverse to the flight path can be selectively reduced to zero, allowing for a less off-axis flight path and permitting detection of higher mass clusters than is possible with conventional post-acceleration deflection schemes. Mass-resolved spectra of ions larger than 27 000 amu have been obtained using this scheme.
Battery-powered current supply for superconductor measurements
Authors: Bray S. L. , Goodrich L. F. , Dube W. P.
Published: July 2002

To measure the critical current of superconductors, a high output current supply is required. In addition to high current capability, the supply should be designed to reduce ground loop problems, respond linearly to an input control signal, and minimize output noise. A current supply with these qualifications has been constructed and tested. Although the supply was originally designed for testing conventional superconductors at high current levels, it has also been successfully used in measurements on the high-critical-temperature ceramic superconductors where the maximum current output was less than 1 A. The supply can produce 1000 A output current with a noise level of approximately 0.05 A peak-to-peak. The specifics of the current supply’s design and performance are given.
Frequency tracking and filtering for a room-temperature resonant gravitational wave antenna
Authors: Frasca Sergio , Gabellieri Massimo
Published: July 2002

A room-temperature gravitational-wave antenna has been operated, almost continuously, for three years at Rome University. The data taken are the signal and noise near the first longitudinal mode νA of the cylinder. Some parameters of the antenna, like the transduction coefficient α and the resonance frequency νA, change with the external temperature. A method to track the frequency νA and to estimate the parameters is presented, and the matched filter is derived.
Transputer-based upgrading of a laser photon correlator
Authors: Brugè F. , San Biagio P. L. , Fornili S. L.
Published: July 2002

A powerful and cost-effective Transputer-based computer interfaced to a digital photon correlator provides high on-line data processing capabilities that improve the quality of the experimental data and makes efficient use of the experimental facilities, yielding access to parallel computing for more demanding computational needs. This upgrading approach can be profitably extended to other existing laboratory instruments.
A corona discharge probe system for measuring phase velocities in a dense suspension
Authors: Soo S. L. , Baker D. A. , Lucht T. R. , Zhu C.
Published: July 2002

Measurement of distribution of velocities of phases in pipe flow of a dense gas-solid suspension was facilitated by the use of an ion source in the form of a localized corona discharge and a downstream traversing electrostatic probe. The system utilizes the transient behavior of a corona discharge which provides a distinction of times of arrival of ions and solid particles of modified charges at a downstream probe. This probe system does not suffer the handicap of other available probe systems in a dense solid phase.
Videofluorometer for imaging tissue metabolism
Authors: Kelly Jeffrey J. , Rorvik Dawn A. , Richmond Keith N. , Barlow Clyde H.
Published: July 2002

A videofluorometer is described that directly acquires digital metabolic images of reduced nicotinamide adenine dinucleotide (NADH) fluorescence in tissue. NADH fluorescence provides an intrinsic indicator of the state of tissue mitochondrial oxidative metabolism. The device combines a computer-controlled fluorescence excitation system with digital image acquisition to quantify tissue bioenergetics in both spatial and time domains. Localized ischemia following coronary artery ligation in a perfused rat heart (model for a coronary artery occlusion heart attack) is used as an example to demonstrate the capabilities of the system. This videofluorometer permits monitoring changes in physiological state of organs and tissue without interfering with tissue metabolism. The digital nature of the acquired image allows detailed analysis of physiological features and their time dependence.
Digital rock-dust meter
Authors: Pinkerton John E. , Stine Daniel , Wagner David , Pillsbury Nathan , Roberts Thomas
Published: July 2002

This article describes the design of a digital rock-dust meter suitable for measuring the rock-dust content in coal-rock-dust mixtures in a mine environment. The work discusses the probe, digital circuitry, and equations used by the instrument. Data from several mines verifying the 2% accuracy of the device is also presented.
New photon correlator design based on Transputer array concurrency
Authors: Burgè F. , San Biagio P. L. , Fornili S. L.
Published: July 2002

A cost-effective five-Transputer photon correlator features samples times ranging from 4 μs to 130 ms, and up to 850 data channels, by emulating the operation of hardware correlators. The high concurrent computational power enables on-line processing of experimental data and real-time monitoring of the experiment. Operating speed and computing power can be easily enhanced by the addition of Transputer-based modules.
Digital parallel acquisition in frequency domain fluorimetry
Authors: Feddersen Brett A. , Piston David W. , Gratton Enrico
Published: July 2002

The analog electronics commonly found in frequency domain fluorometers are limited to collecting only a single frequency at a time, and can be a source of systematic errors. We have developed an instrument in which most of the analog electronics are replaced with a computer-controlled digital-acquisition system. The computer is used for the direct collection of multifrequency data; filtering and calculation of the phase and modulation ratio are done by the software. From these values, fluorescence lifetimes can be determined. This new approach reduces most of the systematic errors due to the analog electronics’ hardware and allows for reconfiguration of the instrument with only minor changes of the software. This digital-acquisition system is not a simple substitution of an analog element, but it provides a new function and new capabilities for frequency domain fluorometers. We have used this digital approach to build a ‘‘parallel’’ phase fluorometer which simultaneously collects and processes several modulation frequencies.
Operation of a normal-incidence transmission grating monochromator at ALLADIN (invited)
Authors: Tatchyn Roman , Källne Elisabeth , Toor Arthur , Cremer Theodore , Csonka Paul
Published: July 2002

A transmission grating (TrG) monochromator has been constructed and operated on the ALLADIN storage ring in Wisconsin in March–June of 1987. The x-ray source was a recently installed 30-period permanent magnet (PM) undulator with a 6.1-cm period. The monochromator configuration employed a single-bent focusing mirror between the source and the exit slit, with a gold transmission grating located between the mirror and the exit slit. The effective entrance slit was the circulating electron beam inside the ring. In this article, the performance of the monochromator in terms of its power loading capability is described.
A simple implementation of a power supply for constant phototube current in light modulation spectroscopy
Authors: Jellison G. E. , Modine F. A.
Published: July 2002

A simple implementation of a commercially available high-voltage power supply is described whereby the power supply can be used for voltage biasing of a photomultiplier tube operating either in a constant dynode voltage or in a constant output current mode. In the constant current mode, low frequency fluctuations in the current are suppressed without attenuation of a high frequency signal. Both the phototube output current and the dynode voltage can be set by external voltages in the range from −10 to +10 V, making computer control easy with standard digital-to-analog converters.
Long pulse CsI impregnated field emission cathodes
Authors: Kosai H. , Fisher A.
Published: July 2002

Intense pulsed electron beams are produced by applying a voltage between an anode and a cathode in a vacuum diode. The average field can be as low as 10 kV/cm, depending on the cathode material. This field is much less than predicted by the Fowler–Nordheim equation for field emission. The source for the electrons is a plasma that forms on the cathode which has a zero or very low work function. This plasma propagates into the anode–cathode gap and as a result lowers the impedance and eventually shorts the diode. The impregnation of the cathode surface with CsI was found to delay the onset of the diode impedance collapse. The time behavior of the impedance of a diode driven by 400-kV, 1-μs pulse was investigated. Three cathode materials with and without CsI were evaluated.
A Fourier transform mass spectrometer for surface analysis by laser-induced thermal desorption of molecular adsorbates
Authors: Land Donald P. , Pettiette-Hall Claire L. , Sander Dirk , McIver Robert T. , Hemminger John C.
Published: July 2002

A Fourier transform mass spectrometer (FTMS) for ultrahigh-vacuum surface studies is described. The instrument incorporates standard surface analysis techniques such as Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and Ar ion sputtering, along with laser-induced thermal desorption (LITD) and thermal desorption spectroscopy (TDS) using FTMS detection, to perform surface analysis of metal samples. The manipulator allows temperature control of the samples between 110 and 1300 K. Using the LITD/FTMS surface reaction intermediates and kinetics are studied for the dehydrogenation of ethylene and cyclohexane on Pt(111). Relative sensitivities between AES and LITD/FTMS are discussed.
Comparison of H− and D− production in a magnetically filtered multicusp source
Authors: Inoue T. , Ackerman G. D. , Cooper W. S. , Hanada M. , Kwan J. W. , Ohara Y. , Okumura Y. , Seki M.
Published: July 2002

A JAERI (Japan Atomic Energy Research Institute)negative ion source was tested at LBL (Lawrence Berkeley Laboratory) as part of the U.S.–Japan Fusion Cooperation Program. By varying the strength of the magnetic filter from 450 to 930 G cm, we compared production, transport, and extraction of the negative ions. The maximum current densities, which were obtained at the corresponding optimum filter strength for each gas species, were 10.4 mA/cm2 for H− and 8.4 mA/cm2 for D− at arc discharges of 40 kW. The ratio of the ion current densities (JD−/JH−) is about 0.8, which is higher than 1/(2)1/2 . The electron to negative ion ratio was 13 for hydrogen and 38 for deuterium at the corresponding optimum filter strength. The higher ratio in deuterium is probably due to higher space potential of deuterium plasma by a few volts.
Recent results on negative ion production and extraction from the Culham Ion Source Test Stand
Authors: McAdams R. , King R. F. , Newman A. F. , Holmes A. J. T.
Published: July 2002

The plasma characteristics of a volume negative ion source are described. An indirect measurement of the negative ion current density in the source has been made. Beam extraction measurements are used to attempt to verify the measurement in the source. The two are found to be in proportion. The difference between the two is briefly discussed.
Apparatus for short time measurements in a fixed-bed gas/solid reactor
Authors: Gullett Brian K. , Bruce Kevin R. , Machilek Rudi M.
Published: July 2002

An apparatus for exposure of a solid to reactive process gas is described which makes possible short time (≥0.3 to 15 s) exposures in a fixed-bed reactor. Operating conditions for differential reaction with respect to the gas concentration and rapid quench for arresting high-temperature reactions are made possible by high gas flowrates through the sample bed. The residence time of solid exposure to the reactive gases is timed by a photosensor emitter/detector and oscilloscope. For times under 2 s, the standard deviation of the residence times is less than 10 ms. The ease of apparatus construction and operation, the operable temperature range (ambient to 850 °C), and the reproducibility of residence times down to 0.3 s makes the apparatus ideal for kinetic studies of rapid gas/solid reactions.
Simple vapor-pressure regulator with a diaphragm for maintaining cryogenic-bath temperatures
Authors: Ebisu Takeo , Watanabe Tadashi
Published: July 2002

We present a simple but useful vapor-pressure regulator for a liquid-helium bath. With the help of it, control within ±1 mK is readily achieved at temperatures from 4.2 down to 1.6 K.
An automatic molecular beam microwave Fourier transform spectrometer
Authors: Andresen U. , Dreizler H. , Grabow J.-U. , Stahl W.
Published: July 2002

We present hardware and software details of the pulsed molecular beam microwave Fourier transform (MB-MWFT) spectrometer used in the Kiel microwave group. We emphasize an automatic scanning facility which greatly increases the efficiency of MB-MWFT spectroscopy for the measurement of unassigned spectra.
Local mode spectroscopy of the carbon acceptor in GaAs: New experimental aspects
Authors: Alt H. Ch. , Dischler B.
Published: July 2002

The temperature dependence of the local mode absorption of CAs at 580 cm−1 is reexamined using high-resolution Fourier transform spectroscopy. A new carbon-related line is detected at room temperature on the low-energy side of the main carbon peak at 576.6 cm−1. It follows that the integrated absorption of the whole band is independent of temperature in the temperature range between 77 and 300 K. Calibration factors are given for 77 and 300 K, providing a consistent interpretation of previous data.
Intense metal-ion-beam production using an impregnated-electrode-type liquid-metal ion source
Authors: Ishikawa Junzo , Tsuji Hiroshi , Aoyama Yuji , Takagi Toshinori
Published: July 2002

The properties of liquid-metal ion sources are very sensitive to their tip structure. Because the impregnated-electrode-type liquid-metal ion source has a porous tip, it generates more than 300-μA ion currents of various metals including relatively high vapor-pressure metals such as Li, Cu, Ga, Ge, Ag, In, and Au, from which ions can be stably extracted. The large beam divergence, a common disadvantage in liquid-metal ion sources, can be overcome by designing new lens systems to efficiently transport the ion beam for both high- and low-energy applications. In addition, the ion beam current can be multiplied by using multiple emission cusps; thus, a germanium ion current of 1.3 mA was obtained by a three-point emission source. Therefore, the impregnated-electrode-type liquid-metal ion source can be utilized as a metal ion source for general applications.
A time-of-flight spectrometer for detection of low-energy hydrogen atoms
Authors: van Toledo W. , de Bree A. R. , van Buuren R. , de Kluiver H. , Donné A. J. H.
Published: July 2002

This article deals with an application of the technique of converting hydrogen atoms into negative ions on a low-work-function surface, which is similar to the method nowadays utilized in H− surface sources. This conversion technique is the basis for a time-of-flight spectrometer, for which a proof of principle has recently been established. The conversion takes place on a tungsten (110) crystal target that is covered with cesium. By mounting this target in the detector part of the spectrometer, this apparatus is made sensitive to hydrogen atoms that have energy in the range 10–1000 eV. This feature makes the spectrometer a very powerful and unique tool for detection of low-energy hydrogen atoms. It is, for instance, capable of detecting low-energy hydrogen atoms that are emitted from the edge of a tokamak plasma, and therefore it can yield information on the hydrogen recycling inside the tokamak and hence on the energy balance of the plasma. In the paper we discuss the principle of the detection method, along with a presentation of some time-of-flight spectra that have been obtained from a tokamak plasma.
Using a fast lens to collect the signal in a VISAR system
Authors: Sweatt William C. , Crump O. B.
Published: July 2002

VISAR (velocity interferometer system for any reflector) systems are used to measure the Doppler shift of a backscattered laser beam incident on a target, from whence the target’s velocity can be calculated. In the past, slow lenses (F/4 or slower) have been used to collect the scattered light. As a result, the relationship between the velocity and the Doppler shift was precisely known, but in many applications a multiwatt laser was required to give an adequate signal. We are using faster lenses and lower-powered lasers. A faster lens will collect more power and a wider spectrum of Doppler-shifted signal. The average Doppler shift is reduced slightly because of the larger range of signal-collecting angles, but it is essentially a linear function of velocity. The wider Doppler spectrum also reduces the fringe contrast slightly, but it is only significant for very fast lenses and large numbers of fringes.
A vibrating fiber microbalance for measuring layer-by-layer adsorption on graphite
Authors: Bruschi L. , Torzo G.
Published: July 2002

This article describes an improved version of the graphite fiber microbalance, a device that was recently proved to be a useful tool for investigating adsorption phenomena. Hydrodynamic effects, that may yield large errors in the calculation of the adsorbed mass, if not properly evaluated, are carefully accounted for. An accurate measurement of the film coverage is obtained by using a correction to Stokes equations in the region of semiballistic regime that is much simpler than the slip theory used by other authors.
Frequency stabilization of a diode laser using simultaneous optical feedback from a diffraction grating and a narrowband Fabry–Perot cavity
Authors: Patrick H. , Wieman C. E.
Published: July 2002

We present a system which uses optical feedback from a diffraction grating to provide primary control over the frequency tuning of a diode laser, and employs simultaneous optical feedback from a narrowband Fabry–Perot cavity to reduce the linewidth. The frequencies of the optical feedback from the diffraction grating and narrowband cavity are electronically locked using a novel technique. The reduction in the linewidth is measured as a reduction in the frequency noise seen on the side of a Cs-saturated absorption line. The presence of optical feedback from the narrowband cavity reduces the frequency noise by a factor of 3 compared to the frequency noise obtained using the grating feedback alone.
Improving the accuracy of a quartz crystal microbalance with automatic determination of acoustic impedance ratio
Authors: Wajid Abdul
Published: July 2002

A new method for automatic determination of acoustic impedance ratio, or z ratio, of a thin solid film deposited upon an AT-cut quartz crystal is described. The method uses frequency information from two piezoelectrically excitable resonant modes which are not harmonically related. This results in an improvement of accuracy for the quartz crystal microbalance (QCM) technique, requiring no prior knowledge of a material’s z ratio. The method is quite general and requires no adjustable parameter specific to a particular quartz crystal design. Results of extensive testing on wide ranging materials including metals, dielectrics, codeposited alloys, and sequential layers is presented. Excellent agreement is found between the predicted values and the gravimetrically measured mass of deposited films.
A differentially pumped electron-energy-loss spectrometer with multichannel detector for time-resolved studies at intermediate ambient pressures
Authors: Lorraine P. W. , Thoms B. D. , Ho W.
Published: July 2002

The design, construction, and operation of a high-resolution electron-energy-loss spectrometer featuring a position-sensitive resistive anode detector and differential pumping are described. The position-sensitive detector provides a 66-fold increase in acquisition speed over a single-channel spectrometer. The differential pumping provides pressure isolation of 105 between the spectrometer elements, except the lenses, and the sample region. An optically isolated multicomputer-based control and data acquisition system provides complete spectrometer control and automated sample cleaning and characterization. The spectrometer, together with a differentially pumped supersonic molecular beamline, permits in situ measurements of the interaction of a wide range of gas molecules with solid surfaces.
A new apparatus for the detection of phase equilibria in polymer solvent systems by light scattering
Authors: Szydlowski Jerzy , Rebelo Luis P. , Van Hook W. Alexander
Published: July 2002

New equipment designed to measure the effect of pressure and isotopic substitution on liquid/liquid equilibria in polymer/solvent systems is described. The phase separation is detected by monitoring low-angle forward scattered light, together with simultaneous loss in transmitted light, from an He–Ne laser shining through the sample. Phase transitions can be induced by varying temperature/time and/or pressure/time profiles or by a combination of such changes. The system operates at high precision (±0.001 K, ±0.002 MPa), and over wide temperature and pressure ranges (240≤T/K≤600, 0.01≤P/Mpa≤35). The temperature, pressure, and transmitted and scattered light intensities are digitally recorded, and the rate of change of the temperature and/or pressure used to induce the phase transition is under computer control. The system is being used to study the temperature, pressure, polymer molecular weight, and molecular weight distribution, and H/D dependences of phase equilibria for polystyrene (PS)/(CH3)2CO and PS/(CD3)2CO solutions. Sample results are reported. The pressure and molecular weight dependences of the coexistence curve, and their isotope effects, are large.
Design and construction of a simple UHV-compatible high-pressure reaction cell
Authors: Wang Yarw-Nan , McAllister Robert , Herman Richard G. , Simmons Gary W. , Klier Kamil
Published: July 2002

The design of a high pressure reaction cell, internal to a commercial ultrahigh vacuum (UHV) system that provides for high-pressure catalytic reaction studies with UHV surface science capabilities, is described in detail. This reaction cell is comprised of the following two elements: (a) a sample-holding flange that extends from the central manipulator and (b) a self-contained sealing ‘‘cup’’ that is attached to an existing 6-in. flange. This reaction cell operates hydraulically and features a small cell volume (∼45 ml) that can be pressurized up to 5 atm, sample heating and cooling capabilities, continuous gas flow or static batch modes, relatively rapid sample transfer (1–2 min) between high- and low-pressure conditions, and gas product analysis. The principle advantage of the present design over the previous ones is its compatibility with commercial UHV systems, without the requirement of bell jar reinforcement. Results of methane activation studies on a Pd(679) single crystal that exemplify the bridging of the pressure gap using this reaction cell are also briefly presented.
A two color multichord infrared interferometer for RFX
Authors: Innocente P. , Martini S.
Published: July 2002

A multichord interferometer designed for the Reversed Field experiment (RFX) (R=2 m, a=0.5 m, I=2 MA) is presented. The high density expected and the rather limited diagnostic access to the plasma motivated the choice of a two-color CO2/CO laser (10.6/5.4 μm) interferometer. Due to the time-varying magnetic fields ≥0.1 T around the torus entailed by the operation of the machine, the system has been mounted on a 3 ton graphite C-shaped optical table supported by a stainless steel structure on pneumatic vibration isolators. This led to long term stability of alignment and a very low level of mechanical vibrations. The interferometer can be moved in and out of the torus with ease by a carriage-rail system for maintenance both of the diagnostic and of the machine. The design foresees eight vertical chords spanning the arms of the C-shaped table and includes more additional measurements using a horizontal port and mirrors mounted inside the vacuum chamber. The expected accuracy in line density units is ≤1×1018 m−2, and the overall concept is that of a reliable system for high density and large size magnetic confinement plasmas.
Position-sensitive time-of-flight mass spectrometer using a fast optical imaging technique
Authors: Kinugawa Tohru , Arikawa Tatsuo
Published: July 2002

A simple position-sensitive time-of-flight mass spectrometer has been developed with an aid of a gatable image intensifier. This spectrometer is a display-type analyzer allowing simultaneous measurements of the mass, speed, and angular distributions. The apparatus demonstrates a time resolution of 30 ns, a mass resolution over 125, and a spatial resolution over 60 in a multiphoton ionization experiment of NO molecules. The single-ion counting technique employed can detect a low-energy (∼100 meV) photofragment distribution without suffering from Coulombic repulsion.
The fabrication of quantum wire structures through application of CCl4 towards lateral growth rate control of GaAs on patterned GaAs substrates
Authors: Kim Yong , Park Yang Keun , Kim Moo-Sung , Kang Joon-Mo , Kim Seong-Il , Hwang Seong-Min , Min Suk-Ki
Published: July 2002

We have observed the remarkable increase of GaAs lateral growth rate in the presence of CCl4 during metalorganic chemical vapor deposition (MOCVD) on patterned GaAs substrates. The lateral growth rate shows a linear dependence on CCl4 flow rate. On the other hand, the GaAs vertical growth rate is relatively insensitive to the CCl4 flow rate. The maximum ratio of lateral to vertical growth rate is about 14. Using these characteristics, we have fabricated CCl4-doped quantum wires (QWRs) on V-groove structures. The QWR structures show thickness enhancement factors, defined as the ratio of QWR thickness in the center region to the quantum well thickness in the nonpatterned region, as high as 5.6.
Recent developments of diagnostics at JET (invited)
Authors: Stott P. E.
Published: July 2002

Since the first operation of JET in 1983, there has been a considerable program of diagnostic development to keep pace with the requirements of the experimental program. Many diagnostic systems have been upgraded and several new ones have been added. New diagnostics are being built and others modified for the pumped divertor which will come into operation at the end of 1993. A few months ago JET carried out a preliminary experiment with tritium which produced the first significant fusion power (over 1.5 MW) and provided the first real test of diagnostics in a high radiation environment. A more extensive experimental program in tritium is planned for 1995 and 1996.
Rotational soft x-ray tomography of noncircular tokamak plasmas
Authors: Nagayama Y. , Edwards A. W.
Published: July 2002

A rotational tomography technique for noncircular tokamak plasmas has been developed. Using a linear transformation from an elliptic coordinate system to the circular one, and compensating for the Shafranov shift, the elliptic plasma shape is transformed to the concentric circular shape. Fitting the data of a quarter rotation to the Fourier–Bessel expansions, the tomography is performed. This technique is applied to the snake oscillation, to the slow sawtooth crash, and to the post-cursor oscillations of noncircular plasmas on JET.
Design and calibration of a fast-time resolution charge exchange analyzer
Authors: Scime Earl , Hokin Samuel
Published: July 2002

A five channel, fast time resolution, scanning charge exchange analyzer has been developed for the Madison Symmetric Torus (MST). The analyzer consists of an iron vacuum vessel, a gas stripping cell, an electrostatic bending field, and five continuous electron multiplier detectors. The incident neutral flux and operation of the detectors in current mode limits the time resolution of the analyzer to 10 μs. The analyzer was absolutely calibrated over the energy range of interest (500–2000 eV) with a H+ beam, so that the charge exchange power loss could also be measured. The analyzer can be swiveled on a shot-to-shot basis for measurements of Ti(r), where 0.3<r/a<0.7. The mechanical design was driven by the need for a low cost, expandable ion temperature diagnostic.
Time-resolved temperature measurements during pulsed laser irradiation using thin film metal thermometers
Authors: Brunco D. P. , Kittl J. A. , Otis C. E. , Goodwin P. M. , Thompson Michael O. , Aziz M. J.
Published: July 2002

In this article, we describe a technique using NiSi and Pt thin film metal thermometers to provide accurate temperature information on a nanosecond time scale during pulsed laser processing of materials. A surface layer of interest is deposited onto the thermometer layer, and temperatures are determined from temperature dependent changes in the metal film’s resistance. Details concerning the design and fabrication of the device structure and experimental considerations in making nanosecond resolved resistance measurements are discussed. Simple analytical estimates are presented to extract quantities such as incident laser energy stored in the sample. Finally, transient temperature data in the thermometer film, in combination with heat flow calculations, allow temperature determination as a function of time and depth into the sample and, additionally, can provide information about material properties of the surface layer.
Fabrication of Ge–Au film thermometers using interfacial atomic diffusion
Authors: Zhu Da-Ming , Lin Fengqi
Published: July 2002

We describe a new method which utilizes an interfacial atomic diffusion mechanism to fabricate Ge–Au film thermometers. The thermometers were made of multiple Ge/Au layers. In situ resistance measurements during the fabrication process indicate that Au and Ge atoms were diffused into neighboring layers. When the deposited Au layer thickness in a multilayer film is between 8 and 10 Å, the resistance of the film shows a power law behavior over a wide temperature range. As the Au layer thickness increases to beyond 10 Å, the resistance of the film becomes less sensitive to temperature. Both the temperature dependence and the magnitude of the film resistance are consistent with results obtained in Ge–Au alloys.
A transmission geometry electrochemical cell for in situ x-ray diffraction
Authors: Robinson K. M. , O’Grady W. E.
Published: July 2002

High intensity synchrotron x-ray radiation has increased the feasibility of studying the solid–liquid interface in situ. Recent work on the structure of Au single crystal electrodes has shown the need to merge appropriate electrochemical cell designs to work on standard four-circle diffractometers. In this report, a new electrochemical cell is described for use in in situ structure determination. The cell provides excellent electrochemical control of the electrode surface, as determined by the cyclic voltammagram, in conjunction with the x-ray studies.
Capillary soldering system for the material property characterization of solder joints
Authors: Stromswold E. I. , Pratt R. E. , Quesnel D. J.
Published: July 2002

A five-stage capillary soldering system that can emulate commercial soldering processes in a laboratory environment has been designed, constructed, and tested using Sn-Pb and Sn-Ag solders. The system is comprised of a loading stage, a preheat stage, a soldering stage, a primary cool down stage, and a secondary cool down stage. The thermal history of a given sample is controlled by selecting the temperature of each stage and the sample hold time at each stage of the process. A temperature controller maintains the temperature of each heated stage of the device within ±3 °C of the target temperature, providing excellent control over the heating and cooling rates and the maximum process temperature of each sample produced. The maximum attainable process temperature of the system is 280 °C allowing for the use of a wide range of solder chemistries. A specially designed sample holder and associated measurement techniques allow for joint thickness control to within 0.0010 in. The process control provided by this system has been found to produce high-quality, reproducible solder joint specimens that are suitable for material property characterization.
Soft x-ray tomography diagnostic at the RTP tokamak
Authors: da Cruz D. F. , Donné A. J. H.
Published: July 2002

An 80-channel soft x-ray tomography system has been constructed for diagnosing the RTP (Rijnhuizen Tokamak Project) tokamak plasma. Five pinhole cameras, each with arrays of 16 detectors are distributed more or less homogeneously around a poloidal plasma cross section. The cameras are positioned close to the plasma edge to enable viewing angles which could not be reached otherwise. The system can be used for making tomographic reconstructions of the soft x-ray emissivity with a relatively high poloidal mode number (up to both components of m=4), which is an improvement with respect to other plasma tomography systems presented in literature. The temporal resolution of the system is 5 μs. Apart from a description of the hardware and geometrical layout of the system, the paper will focus on two important issues, namely the calibration of the detectors and the positioning of the cameras in the vacuum vessel of the tokamak. A dedicated x-ray source has been designed for the relative calibration of the detectors of each individual camera. Misalignment causes several artifacts in tomographic reconstructions obtained with multicamera systems. Therefore, two new methods are proposed which make use of the plasma itself for improving the knowledge about the positions of the cameras.
Simple analytical model of gain saturation in microchannel plate devices
Authors: Giudicotti L. , Bassan M. , Pasqualotto R. , Sardella A.
Published: July 2002

We derive, discuss, and test against experimental data an analytical model of the gain saturation in microchannel plate (MCP) devices. By introducing a simple recharging circuit for each dynode, we extend the well-known, unsaturated gain model of Eberhardt to a microchannel operating in condition of gain saturation and show that the amplification of a current pulse and the voltage drop along the channel can be described by a pair of coupled differential equations. Solutions of these equations are given in various conditions, including an approximate solution, valid in the case of weak saturation and a general solution in implicit form. The behavior of a microchannel operating in current mode is studied by finding the transient and steady-state solutions obtained with an input step current wave form. Exact solutions are given for the charge gain of pulses with a short duration, compared to the dynode recharging time, and for the gain recovery of a microchannel after the amplification of a short pulse. The single channel saturation model is then extended to multistage MCP assemblies by taking into account the statistical distribution of the photoelectrons at the input and the spread of the multiplied electron cloud in the interplate gaps. The expressions found in this way are used for the best fit of experimental data from a Z-stack MCP photomultiplier operated in single and double pulse mode. Satisfactory agreement between the model and experimental data is obtained in the case of single pulse measurements, finding a reduced chi squared χ2=4.67. Less satisfactory agreement is found for double pulse data, giving χ2=7.46 and a clear indication that the model may be significantly improved by taking into account the charge redistribution among the dynodes during the recharging process, neglected in the present formulation.
A high-pressure NMR probehead for measurements at 400 MHz
Authors: Zahl Achim , Neubrand Anton , Aygen Sitke , van Eldik Rudi
Published: July 2002

A new high-pressure NMR probehead designed for a 400 MHz widebore NMR spectrometer is described. For the first time, the electrical leads of the rf circuit, the tubes for the thermostating liquid and the high-pressure fluid, as well as the wires of the Pt-100 resistor for temperature control, are all fitted at the bottom of the high-pressure vessel. The sample can easily be removed through a top plug, which allows a relatively fast exchange of the sample. A rather simple design leads to a low-cost construction. The high-pressure vessel and the rf circuit are placed inside a standard probehead jacket, such that the high-pressure probehead can be fitted into the superconducting magnet in the same way as a commercial probehead.
Performance of the Superconducting Super Collider H−rf volume ion source and Linac injector
Authors: Saadatmand K. , Hebert J. E. , Okay N. C.
Published: July 2002

The Superconducting Super Collider (SSC) ion source is required to provide a 30 mA H− beam at 35 keV with a normalized rms emittance (εn-rms) of less than 0.18 π mm mrad. An rf-driven volume source was chosen for the commissioning of the SSC linear accelerator (Linac). The divergent ion source output beam is matched into the radio frequency quadrupole accelerator (RFQ) by an electrostatic low-energy beam transport (LEBT). The SSC Linac injector (consisting of ion source, LEBT, and RFQ) is required to provide 25 mA of H− beam (pulse width of 9.6–35 μs at 10 Hz repetition rate) at 2.5 MeV with transverse normalized rms emittance (εt-n-rms) of less than 0.2 π mm mrad and longitudinal normalized rms emittance (εl) of less than 0.82×10−6 eV s. The performance of our rf volume source and initial experimental results from the SSC injector are discussed.
A tunable microwave plasma source for space plasma simulation experiments
Authors: Walker David N. , Duncan Dwight , Stracka John A. , Bowles Jeffrey H. , Siefring Carl L. , Baumback Mark M. , Rodriguez Paul
Published: July 2002

In laboratory experiments related to space plasma physics it is often desirable to produce plasmas with characteristics as close as possible to various naturally occurring plasma regimes. In the near-earth region space plasma densities typically vary from 103–107 cm−3 and temperatures range from a few tenths of an eV to the order of 1 eV. The plasma parameters of electron density, electron temperature, and ion species are primary variables which are often not easy to reproduce in a chamber environment which is dependent upon conventional gas discharge or arc sources for plasma production. A simple microwave discharge device was developed which is easily tunable and capable of producing the moderate range of electron densities without an external magnetic field. The Asmussen-type microwave plasma source described here covers and exceeds the parameter ranges required, is relatively easy to construct, and is inexpensive. The device makes use of an air dielectric coaxial coupler to couple magnetron output to a resonant cavity. Estimates of effective electric fields and source densities and temperatures suggest that similar devices can easily be constructed and fashioned to produce these parameters, depending upon requirements, over a wide range of values. The use of widely available commercial magnetrons manufactured for microwave ovens allows a certain ease in the construction of these devices in that available cavity Q’s can range to lower levels and therefore resonant lengths can be adjusted more easily. The design is discussed relative to desired experimental parameter ranges and some discussion is given of expected source current densities, electric fields, and temperature ranges.
Single-crystal magnetic metal films on GaAs grown by electrodeposition
Authors: Hart R. , Midgley P. A. , Wilkinson A. , Schwarzacher W.
Published: July 2002

Large area (0.8 cm2) single-crystal films ∼1 μm thick of Ni–Cu alloy have been electrodeposited directly onto (100) n-type GaAs. The epitaxial relationship was found to be (001) Ni–Cu parallel to (001) GaAs and [110] Ni–Cu parallel to [100] GaAs. Magnetic measurements show the films to be ferromagnetic.
Simple, high-resolution interferometer for the measurement of frequency-dependent complex piezoelectric responses in ferroelectric ceramics
Authors: Li Jie-Fang , Moses P. , Viehland D.
Published: July 2002

In this paper, we report the development of a simple but precise piezoelectric spectrometer using a Michelson–Morley interferometer. The measurement system has been developed to study the frequency and temperature dependence of the complex piezoelectric and electrostriction coefficients of ferroelectric materials. The spectral data are collected by computer and has significantly wider frequency range and lower noise than other such systems. Results are reported for a quartz sample, a La-modified lead zirconate titanate ferroelectric, and a lead zirconate titanate sol-gel derived ferroelectric thin film.
Multiple-pass laser beam deflection probe for detection of acoustic and weak shock waves in fluids
Authors: Diaci Janez , Možina Janez
Published: July 2002

We examine a novel laser beam deflection arrangement for detection of acoustic and weak shock waves in fluids. Novelty of the arrangement is folding of the probe beam by two parallel plane mirrors in such a way that the probe beam passes the wave propagation region several times before it reaches the deflection-detecting photodetector. In this way the probed wave interacts with several segments of the probing beam in sequence. A single oscilloscope trace of the photodetector output thus gives us the possibility to study the evolution of the probed wave at several distances from the source. To demonstrate the potentials of the arrangement we present wave forms of spherical blast waves detected in air during laser ablation of solid samples. We also discuss a simple theoretical model that qualitatively explains the most characteristic features of this arrangement.
Active millimeter-wave pyrometer
Authors: Woskov P. P. , Cohn D. R. , Rhee D. Y. , Thomas P. , Titus C. H. , Surma J. E.
Published: July 2002

A 135 GHz heterodyne receiver with a rotatable graphite waveguide/mirror system has been implemented on a waste remediation direct-current arc furnace for internal surface temperature measurements. The linear temperature measurement range extends from <1° to approximately 15,000 °C relative to ambient with a simultaneous capability to monitor surface reflectivity with the local oscillator leakage. Reliable and robust operation on a continuous 24 h basis in a smoky, dirty furnace environment is demonstrated for a total of five furnace runs reaching a maximum temperature of 2200 °C. Complete temperature profile measurements with approximately 5 cm spatial resolution clearly documented thermal gradients on the slag melt surface and refractory walls and ceiling for all operating regimes of the furnace. The unique active probing capability of this instrument provided additional real-time information on melt surface turbulence, changing furnace wall emissivity, and millimeter-wave optic losses inside the furnace.