bluuebunny/crossref_metadata_2025 huggingface dataset:
An extreme ultraviolet radiation source for the simulation of the ionosphere
Authors: Oyama K.-I. , Suzuki K. , Kawashima N. , Zalpuri K. S. , Teii S. , Nakamura Y.
Published: July 2002

An extreme ultraviolet (EUV) radiation source for space simulation of plasma and other related phenomena in the laboratory has been developed. A total of forty-eight small EUV lamps are put together to give a radiation diameter of more than 30 cm. The intensity of this lamp at the hydrogen Lyman-alpha line is more than twenty five times stronger than sunlight at the same wavelength and at a distance of about 30 cm from the source. The source is capable of emitting EUV radiations from 110 nm to the longer wavelengths, either continuously or in pulses, and has been used to produce a plasma of 105 els/cm3 when the pressure of NO gas in the chamber was 10−4 Torr. Since this plasma is extremely calm and fairly Maxwellian, it can be used to study the electron collection mechanism of a probe in a collision dominant medium. The source was also utilized to study the interaction between vibrationally excited nitrogen molecules and thermal electrons.
Microchannel water cooling of silicon x-ray monochromator crystals
Authors: Arthur J. , Tompkins W. H. , Troxel C. , Contolini R. J. , Schmitt E. , Bilderback D. H. , Henderson C. , White J. , Settersten T.
Published: July 2002

The use in silicon x-ray monochromator crystals of water cooling channels with dimensions optimized for efficient heat transfer from silicon to water has been investigated. Such channels are typically about 40 μm wide and 400 μm deep. Procedures have been found for reliably producing microchannel-cooled crystals with very small amounts of residual strain. These crystals have been tested at a high-power wiggler beam line at the Cornell High Energy Synchrotron Source, using an x-ray beam having total power in excess of 250 W and normal-incidence power density greater than 5 W/mm2. Under these conditions, the surface-temperature rise of a typical microchannel-cooled crystal was less than 5 °C, and degradation of the (111) rocking curve at 12 keV was very slight. The cooling efficiency is consistent with analytic calculations.
Spark source of carbon ions
Authors: Vasilyev A. A.
Published: July 2002

A spark carbon ion source (SIS) has been fabricated and tested with two systems of electric power supply. It was found that in the quasistationary spark (inductive energy storage scheme), and for a discharge current of ∼2 kA and timp∼100 μs, the ion charge state distribution is similar to the HF spark with a discharge current of 2 kA (1-MHz LC-circuit scheme). A total pulse carbon ion current of about 500 mA has been obtained from the quasistationary spark. The C+3 ion current was about 300 mA and the C+4 ion current ∼100 mA. The noise amplitude of the total ion current is no more than 10% in this mode of operation. The production of highly charged ions is explained by an increased potential drop in the discharge gap (60–100 V) for currents of 1.5–2.0 kA. It is shown that the quasistationary spark mode is accompanied by an occurrence of a stable anode spot while electrode evaporation increases and the vacuum spark is transformed into a high pressure spark discharge, leading to a shift of the ion spectral distribution to high charge states. The proposed spark ion source could find new applications in different accelerators along with PIG, ECR, etc.
Long-range scanning for scanning tunneling microscopy
Authors: Fu J. , Young R. D. , Vorburger T. V.
Published: July 2002

We report a scanning tunneling microscope (STM) with 500 μm×500 μm field of view. It departs from past designs in that a long-range X-Y stage carries the specimen and scans while the STM head is held stationary. The STM head is capable of scanning with a range of 8 μm. Combining the capability of tip scanning and X-Y stage scanning yields a wide dynamic range and has useful applications for measuring optical surfaces.
Simple procedure for improving the fidelity of holograms
Authors: Sharnoff Mark , Du Lei , Lin Hungyi
Published: July 2002

We demonstrate that the fidelity of a hologram is often impaired by multiple beam interference during the recording process. We describe a simple and widely adaptable procedure for eliminating such impairment, and we give a quantitative measure of the gain in fidelity that may ensue in the case of object waves recorded on silver halide emulsion at f/6.3.
Frequency monitoring a LIDAR transmitter for pulse-by-pulse analysis and control
Authors: Esproles Carlos
Published: July 2002

An electronic technique is described whereby the heterodyne mixing frequency of a pulsed LIDAR transmitter is displayed on a color-coded linear bar graph. The technique is of great utility for manually fine tuning the laser output frequency when the use of conventional frequency counters and spectrum analyzers is impractical in a rapidly firing system.
Hydrogen/deuterium negative ion scaling from a magnetic multipole ion source
Authors: McAdams R. , King R. F. , Newman A. F.
Published: July 2002

H−/D− current and emittance scaling is measured in a magnetic multipole negative ion source. The gas in the source is the only difference as no reoptimization of the source is carried out, thus giving a direct comparison of the performance for the two isotopes. It is found that the H− current is greater than the D− current by approximately a factor of 2 under the same discharge conditions. The extracted electron to ion ratio is commensurately higher in deuterium than in hydrogen. Finally, the emittance in deuterium at the higher arc currents is found to be lower than that in hydrogen. Some comments are made on the scaling within the context of the accepted model of negative ion production.
An alternative for gas dosing in ultrahigh vacuum adsorption studies
Authors: Glines Andrew M. , Carter Robert N. , Anton A. Brad
Published: July 2002

We describe the design, construction, calibration, and operation of a dosing system for controlled exposures of solid surfaces to gases in ultrahigh vacuum. The doser includes seven parallel tubes in a hexagonal pattern, sized to give nearly uniform flux over a 6-mm-diam circle on the sample, and arranged to compensate for an oblique incidence direction. This arrangement gives an enhancement in the ratio of total flux to diffuse flux from the background in excess of 10:1, in spite of a 15.5-mm distance between the doser and the sample.
Novel design of hot windows in saturated metal vapor absorption experiments
Authors: Tamir Y. , Shuker R.
Published: July 2002

We present a device which makes possible accurate determination of the absorption length of saturated metal vapors inside a long cylindrical absorption cell functioning in the heat-pipe regime. The device is simple to construct and to operate. The absorption length is determined by the spacing between two movable hot windows welded to inner pipes which are open ended in the cold part of the cell. In this configuration there is no differential pressure on the hot windows and thus can be used also in high-pressure studies. Moreover, thin windows can be used to minimize their effect on absorption measurements. A continuous independent adjustment of the absorption length and the vapor density can be achieved by simple adjustment of the hot windows spacing. This is accomplished by moving the inner pipes from outside the cell without opening it. A movable inner thermocouple is also added to control and measure the temperature and its distribution along the absorption region.
Spectrometer system and detector tests for the TFTR alpha-CHERS experiment
Authors: Thorson T. , McKee G. , Fonck R. J. , Stratton B.
Published: July 2002

An optical spectroscopy diagnostic has been designed to observe emissions from the nonthermal alpha particle population that will be generated during the D–T operation phase on TFTR. The system will observe spectral line emission near 469 nm from the slowing-down alpha population interacting with the heating neutral beams through charge exchange. The required spectrometer throughput and resolution are obtained by modification of a simple commercial spectrometer system, while a series of measurements indicate that a cooled CCD array is usable as a high-efficiency detector with photon-noise-limited accuracy to roughly a part in 104.
Application of high-resolution interferometry to plasma density measurements on TEXT-Upgrade
Authors: Brower D. L. , Jiang Y. , Peebles W. A. , Burns S. , Luhmann N. C.
Published: July 2002

High-resolution interferometry using far-infrared laser radiation is employed on TEXT-Upgrade to measure the spatial and temporal evolution of the electron density profile as well as small-scale perturbations. Perturbations to the electron density induced by naturally occurring sawtooth oscillations or externally imposed gas modulations can be used to ascertain the local particle flux and transport coefficients in the plasma interior. Density islands associated with Mirnov activity can also be resolved, providing detailed information on the density profile at island X and O points. Implementation of a second orthogonal view will allow accurate determination of the density profile in the various asymmetric plasma configurations of TEXT-Upgrade.
Cleaning of Thomson scattering window by a laser blow-off method
Authors: Narihara K. , Hirokura S.
Published: July 2002

Practicability of cleaning Thomson scattering windows by a laser blow-off method is demonstrated and discussed in terms of sweep speed and window damage probability. Optimum sweep speeds of ∼6 cm2/s are obtainable with a 30-Hz, 0.4-J/pulse Nd:YAG laser.
A sensitive He–Ne interferometer with passive beam power stabilization for low-density pulsed-plasma measurements
Authors: Chuvatin A. S. , Etlicher B. , Edison N. S. , Rouillé C.
Published: July 2002

A sensitive interferometer based on a Michelson scheme was constructed and applied to low-density pulsed-plasma measurements. Using a moderate power He–Ne laser and common photodetectors, a sensitivity as high as 1/1000 FWHM of an interference fringe was reached with a minimum line-integrated plasma density as low as 〈NeL〉min=8×1013 cm−2. This sensitivity was obtained in a real plasma experiment with space and time resolution of 1–2 mm and 120 ns, respectively. The time resolution for this technique is restricted mainly by the oscilloscope finite input capacitance and could be made higher but with a loss of sensitivity. In order to obtain such high a sensitivity, we used loads for the photocurrent registration higher than the 50-Ω matched load. The initial phase is not assumed to be optimized and is recorded separately during the operation of the interferometer. Suppression of electrical noise and of instabilities associated with the laser power requires a supplementary detector for background subtraction to improve the signal-to-noise ratio. A description of the high sensitivity interferometer with the passive beam power stabilization, analysis of the data treatment procedure, as well as measurements for an electron density distribution, are presented.
What do you measure when you measure the Hall effect?
Authors: Koon D. W. , Knickerbocker C. J.
Published: July 2002

A formalism for calculating the sensitivity of Hall measurements to local inhomogeneities of the sample material or the magnetic field is developed. This Hall weighting function g(x,y) is calculated for various placements of current and voltage probes on square and circular laminar samples. Unlike the resistivity weighting function, it is nonnegative throughout the entire sample, provided all probes lie at the edge of the sample. Singularities arise in the Hall weighting function near the current and voltage probes except in the case where these probes are located at the corners of a square. Implications of the results for cross, clover, and bridge samples, and the implications of our results for metal–insulator transition and quantum Hall studies are discussed.
Servopositioning with picometer resolution
Authors: Bergamin A. , Cavagnero G. , Mana G.
Published: July 2002

A macroscopic one-axis movement with picometer resolution was made possible by a feedback loop driving a piezoelectric element locking an elastic guide to a reference value, or to a reference path. The guide displacement has been measured by a high-resolution optical interferometer. Not only were prompt and accurate positionings obtained, but disturbances due to seismic noise were also compensated for. In contrast to conventional positioning, driver linearity and stability, antivibration support, and maximum displacement are not subjected to strict conditions. The performances of an x-ray interferometer were greatly improved by this feedback: the positioning with 1-pm resolution over 30-Hz bandwidth and 0.1-mm maximum displacement was made possible.
Calibration of micron-size thermocouples for measurements of surface temperature
Authors: Schreck Erhard , Hiller Bernhard , Singh Gurinder P.
Published: July 2002

Imbedded thin-film thermocouples can be used for the measurement of transient surface temperatures with high spatial resolution and sensitivity. To minimize environmental effects it is desirable to have close proximity between the reference junction and the sensor junction. In this article, we present and compare two calibration techniques for such thermocouples. The first technique is a steady-state technique and uses a focused laser beam with a diameter of 3 μm as a point heat source. This technique consists of two steps. The first step is an absolute, but spatially averaged temperature measurement with a resistive temperature sensor. In the second step, the uncalibrated thermocouple junction is translated to resolve the spatial temperature profile generated by the laser spot. Both measurements are then combined to provide an absolute calibration which is independent of the thermal properties of the imbedding material and of the absorbed laser power. We used a simple sensor design which consists of a Ni resistive stripe, and the thermocouple junctions it forms with Ta/Au/Ta electrical leads. The second calibration technique is based on a dynamic measurement. To implement this technique we fabricated a small electrical heating element close to one of the junctions. With the dynamic calibration, the time-resolved response of the thermocouple to a short heat pulse is recorded. A least-squares fit of a simple model of heat diffusion to the measured response yields both the temperature calibration of the thermocouple and the heat diffusivity of the imbedding medium. The temperature calibration of the thermocouple obtained with the dynamic technique is in good agreement with the steady-state calibration.
Transit detector for intermediate monitoring in time-of-flight mass analyzers
Authors: Drechsler G. , Bässmann C. , Fraunberg W.-D. v. , Boesl U. , Schlag E. W.
Published: July 2002

We present a particle detector for intermediate monitoring of beams of ion bunches (e.g., in time-of-flight mass analyzers). Its principle is secondary electron emission from a thin wire whose cross section is small (i.e., <5%) compared with the cross section of the primary ion beam. By means of a special experimental setup, anionic, cationic, or neutral particle beams can be formed; in addition, a tandem arrangement of our transit detector and a second detector at the end of the ion flight region allows us to test this transit detector. The influence on mass resolution, reliability of ion peak heights, dependence on kinetic energy and charge of the primary particles, and linearity have been investigated. This new detector may be useful for tandem mass spectrometric experiments, e.g., in time-of-flight analyzers with secondary excitation by collisions or photon absorption.
Magnetic force microscopy using electron-beam fabricated tips
Authors: Rührig M. , Porthun S. , Lodder J. C.
Published: July 2002

We used a new concept of tip preparation for magnetic force microscopy (MFM) proposed recently based on coating electron beam deposited carbon needles with appropriate magnetic thin film materials. In combining the advantages of electron beam fabricated needles with those of already widely used thin film tips, high resolution MFM tips can be prepared routinely and reproducibly on all type of cantilevers. Due to the fabrication procedure, which is described in detail, the effective magnetic tip volume is formed by a homogeneous, magnetically isolated, high aspect ratio thin film element favoring a single domain tip behavior. To reinforce the inherent shape anisotropy an additional uniaxial anisotropy is induced along the tip axis by applying an external field during the deposition of the ferromagnetic alloy. Because of the parallel side walls and the rounded tip end, most of the stray field will emanate from the apex region, resulting in a high field density and only little influence on the magnetization within the sample of interest. By using a material with high saturation magnetization, the thickness of the magnetic layer can be drastically reduced, leading to an increased resolution. To demonstrate the potential of the new concept various MFM observations on different types of materials for magnetic storage technology have been performed without changing the presented basic preparation parameters.
Long pulse 250 keV electron gun for high-pressure gas lasers
Authors: Ustinovskii N. N. , Peters P. J. M. , Gielkens S. W. A. , Witteman W. J.
Published: July 2002

The design and performance of a secondary emission electron gun with a wire ionized plasma as an ion source is discussed. An electron beam current density of up to 100 mA/cm2 is obtained over an area of 55×5 cm2 at a cathode voltage of 250 kV in pulses with a duration of about 20 μs. The current distribution over the beam area is uniform to better than 25%. The achieved combination of pulse duration, beam current, and electron energy is attractive to excite high-pressure gas laser media. Preliminary results with the utilization of the gun in an electron beam sustained discharge excited atomic Xe laser show an output energy of 1 J/ℓ at a wavelength of λ=1.73 μm.
Measurement of plasma diamagnetism by a coil located inside a conducting wall
Authors: Li X. B. , Cross R. C.
Published: July 2002

A diamagnetic loop is installed inside the vacuum vessel of the Tortus tokamak. It consists of a ten turn diamagnetic coil and a graphite limiter. The low influence of the eddy currents in the vessel wall and relatively lower stray coupling on the diamagnetic signal make the measurement feasible. The experimental results, when plasma current ramped down, have shown that the plasma is paramagnetic for plasma current Ip≳9 kA and diamagnetic for plasma current Ip<9 kA. The measurement method, detail of the experiment system, and illustrative results are presented.
Low-temperature growth of Bi4Ti3O12 epitaxial films on SrTiO3(001) and Bi2Sr2CaCu2O8(001) single crystals by laser molecular beam epitaxy
Authors: Choopun Supab , Matsumoto Takuya , Kawai Tomoji
Published: July 2002

Epitaxial thin films of bismuth titanate Bi4Ti3O12 have been grown by laser molecular beam epitaxy on SrTiO3(001) and Bi2Sr2CaCu2O8(001) single crystal at low processing temperature. X-ray diffraction patterns exhibit that c-axis oriented Bi4Ti3O12 thin films can be grown at a substrate temperature as low as 450 °C with good crystallinity and no presence of secondary phases. RHEED patterns evidence the flat surface of the films and the layer-by-layer growth mode.
300 ps ruby laser using stimulated Brillouin scattering pulse compression
Authors: Nizienko Yu. , Mamin A. , Nielsen P. , Brown B.
Published: July 2002

Using the stimulated Brillouin scattering phase conjugation and pulse compression technique, a conventional long pulse ruby laser was successfully converted to give 300 ps pulses at 1 J energy level. The technique allows the use of smaller amplifiers than required in a conventional short pulse laser which in turn leads to operation at increased repetition rate. The completed laser when operated at 1.5 Hz produces stable output parameters. Each laser pulse is characterized by a sharp rise and a measured pre-pulse level of less than 10−6 of the main pulse, making it suitable for LIDAR Thomson scattering measurements.
Magnetic pulse compressor for prepulse discharge in spiker-sustainer excitation technique for XeCl lasers
Authors: Giordano G. , Letardi T. , Muzzi F. , Zheng C. E.
Published: July 2002

A high-voltage pulse output modulator using a step-up transformer with two stages of magnetic pulse compression circuits has been developed as a spiker for the purpose of obtaining the breakdown of the gas mixture when using the spiker-sustainer excitation technique for pumping XeCl discharge lasers. When the transformer input is fed by a current pulse with a peak value and a full width of 1.16 kA and 1.6 μs, respectively, formed by a discharge of an initially charged 19-kV, 57-nF capacitance in series in the transformer primary loop, the 2.7-nF output capacitor bank (Cp) of the spiker can be charged up to 67 kV with a (10%–90%) rise time of 59 ns. The modulator has been tested at a repetition rate of up to 600 Hz in burst mode using a resistor in parallel with Cp as the load.
MEVVA ion source for the ITEP synchrotron
Authors: Katz M. M. , Kondratiev L. N. , Pomelov N. N. , Rogal A. D.
Published: July 2002

A MEVVA (metal vapor vacuum arc) ion source has been made and tested at the Institute of Theoretical and Experimental Physics (ITEP), Moscow. The ions are created in the plasma formed from the cathode metal vapor of a vacuum arc discharge. An ion beam current of about 200–400 mA in repetitively triggered pulses of width 0.1 ms has been obtained. The ion charge state distributions have been measured for seven elements (Be,C,Al,Fe,Cu,Zr,W) and they are in reasonable agreement with results of other workers. The MEVVA ion source is simple to operate and has a reliability acceptable for use as an ion source for ITEP synchrotron injection.
Low-cost, high-performance array detector for spectroscopy based on a charge-coupled photodiode
Authors: Johnson J. Bruce , Edwards Glenn , Mendenhall Marcus
Published: July 2002

We describe a nitrogen-cooled array detector system based on the Thomson TH 7832A charge-coupled photodiode. Performance comparisons are made between this system and others based on two-dimensional CCDs. The TH 7832A compares favorably in resolution, spectral range, and readout speed. Analysis of read and shot noise contributions identifies classes of experiments for which the larger read noise of the TH 7832A is inconsequential.
Detection of a 10−4 helium peak in a deuterium atmosphere using a modified high-resolution quadrupole mass spectrometer
Authors: Hiroki S. , Abe T. , Murakami Y.
Published: July 2002

This paper describes how a small helium (4He) peak can be separated from a large adjacent deuterium (D2) peak using a modified quadrupole mass spectrometer (QMS). This QMS utilized a condition of the second stability zone (zone II) in the Mathieu diagram. The minimum detectable peak ratio of 4He to D2 was 10−4 when a mass scan line was set close to the upper tip, and was 10−3 when the scan line was adjusted to the lower tip. The ion transmission rates simulating the peaks were calculated for the upper and lower zone conditions. It was found that a longer peak tail occurs when an unstable orbit has mainly a cosh function. From the experimental and theoretical data, it is concluded that the upper zone condition is the most suitable for realizing a high-resolution peak.
Enclosed flow tube injector system for low temperature kinetic studies
Authors: Henry Bruce , Fried Alan , Fox Jack , Calvert Jack G. , Mozurkewich Michael
Published: July 2002

A new enclosed injector system for low temperature kinetic studies is described. This system offers a number of advantages over more conventional designs of moveable inlet injectors. The enclosed injector prevents the introduction of contaminants into the flow reactor. In conventional designs, ambient contaminants adsorbed onto the outside of the injector could be transported into the flow reactor. The enclosed injector exposes the reactant gas to the same length of inlet tubing at a uniform temperature regardless of the injector position. In addition, the enclosed injector minimizes temperature gradients in the flow reactor caused by heat transfer along the injector. This is a particular problem when the flow reactor is operated near atmospheric pressure at reduced temperatures. Finally, this design is significantly more compact than conventional injector designs. This system has been successfully employed in studies of the heterogeneous reaction of N2O5 with sulfuric acid aerosols over the temperature range 225–293 K.
A PC-based instrument of a modified differential normal pulse voltammetry with background current correction technique
Authors: Liao B. Y. , Young M. S. , Wang C. Y.
Published: July 2002

Instead of the fixed pulse durations in conventional differential normal pulse voltammetry, a PC-based instrument using adaptable pulse duration vectors for background current correction has been proposed and implemented. With this PC-based instrument, a sequence of pulse duration vectors is determined in an initial blank solution voltammetry by assigning a decay percentage constant to the charging current. These vectors are then used in the subsequent test solution in order to obtain a pure oxidation current response in a resulting voltammogram with its corresponding features. Experimental results are presented to show the effectiveness and advantages of the PC-based instrument for the measurements of dopamine in a phosphate buffered solution.
A static gas phase cell for optical spectroscopy in the 300–700 K range
Authors: Westerfield Wayne , Davis Wendy , Rodriguez Juan
Published: July 2002

A static cell has been developed for routine gas phase spectroscopy under high vacuum conditions. Its design provides both reusability and convenience using parts readily available from commercial vendors at an economical price. The cell features a warm-up cycle that keeps the windows free of condensation and an operating range of 300–700 K that offers good uniformity of temperature throughout the cell for extended periods of time. The operation of the cell is illustrated with absorption spectra of a zinc metalloporphyrin in the gas phase.
A study of non-ideal focus properties of 30° parallel plate energy analyzers
Authors: Fujisawa A. , Iguchi H. , Hamada Y.
Published: July 2002

A succinct model is proposed to describe non-ideal characteristics owing to electric field penetration into the drift region in actual parallel plate energy analyzers. A good agreement has been obtained between the theoretically expected and experimentally observed focus properties of the 30° parallel plate analyzer.
Vacuum arc ion source with filtered plasma for macroparticle-free implantation
Authors: Anders Simone , Anders André , Brown Ian G. , MacGill Robert A. , Dickinson Michael R.
Published: July 2002

An inherent feature of the vacuum arc discharge is that small droplets of micrometer size (macroparticles) are produced along with the plasma in the cathode spots. Droplet contamination of the substrate can occur when implanting metal ions using a vacuum arc ion source. The contamination can be significant for some cathode materials such as lead and other low melting point metals, which for some ion implantation applications such as for semiconductor doping and metallic corrosion inhibition can be a detriment. We have developed a vacuum arc ion source in which the plasma is filtered before the ions are extracted. By guiding the arc-produced plasma through a 60° bent magnetic duct, macroparticles are completely removed from the plasma. No additional power supply for the guiding magnetic field is required since the pulsed arc current itself is used to drive the magnetic solenoid. Tests have shown that macroparticle-free metal ion implantation can be done while maintaining the high ion beam current typical of vacuum arc ion sources.
Development of high power negative-ion sources for fusion research at JAERI
Authors: Ohara Y. , Hanada M. , Inoue T. , Maeno S. , Miyamoto K. , Mizuno M. , Okumura Y. , Tanaka M. , Watanabe K.
Published: July 2002

Recent progress regarding high power negative-ion source development for fusion research at JAERI is described. Using the cesium-seeded volume production-type negative-ion sources with an electrostatic acceleration system, a stable production of multiampere negative hydrogen/deuterium ion beams and a high energy acceleration of negative hydrogen ions of 0.2 A up to 350 keV have been demonstrated. On the basis of this recent progress, the construction of a 500 keV, 22 A, deuterium negative-ion source for a neutral beam injection system for the JT-60 tokamak was initiated. Additionally, a 1 MeV, 1 A Cockcroft–Walton-type test facility has been prepared in order to demonstrate high current negative ion acceleration up to 1 MeV. Through these research and development activities, the high power negative-ion source technology sufficient for the realization of a neutral beam injection system for a fusion experimental reactor such as the International Thermonuclear Experimental Reactor, is in the planning stages.
Photorefractive p-i-n diode quantum well spatial light modulators
Authors: Lahiri I. , Kwolek K. M. , Nolte D. D. , Melloch M. R.
Published: July 2002

We demonstrate the performance of all-semiconductor photorefractive p-i-n diodes operating in the longitudinal quantum-confined Stark geometry. Low-temperature-grown shallow quantum wells provide high-mobility vertical transport, and potential steps incorporated into the semiconductor buffer layers increase the transit time across the buffer and therefore increase the quantum efficiency for trapping of charge before it is swept out to the doped p-type and n-type contacts. The buffer design and the doped contacts both make all-semiconductor photorefractive devices possible, with peak transient output diffraction efficiencies approaching 3%, but without the need for dielectric insulating layers. We also redefine device speed by making a distinction between transient rise times and frequency response, showing that in these p-i-n devices the update rate is an order of magnitude slower than the inverse rise time.
A new electrochemical cell for atomic force microscopy
Authors: Wanless E. J. , Senden T. J. , Hyde A. M. , Sawkins T. J. , Heath G. A.
Published: July 2002

Described is the design for a new electrochemical cell for in situ studies with the atomic force microscope. Improvements over presently used cells include an axially symmetric electrode geometry, large counter electrode, and the ability to incorporate a standard reference electrode close to the working electrode.
Assortment of optimal conditions for running the impulse diode thermometer
Authors: Iskrenovic P. S. , Mitic D. B.
Published: July 2002

In the algorithm for iterative evaluation of temperature measured by the p-n junction in the impulse regime two voltages appear as parameters. Their values are limited only by the operating characteristics of the impulse diode thermometer, i.e., both values must fall within the interval determined by the hardware normal operating conditions. The choice of these values within the allowed interval seems to be arbitrary; however, analysis of the expression for relative measurement errors leads to the criterion for the optimal choice of these parameters that allow the impulse diode thermometer to operate with the maximal resolution and minimal error.
A simple and effective method for improving the accuracy of selective audio-frequency voltage measurements
Authors: Mirko Obradovic , Ranko Rodic , Vojislav Arandjelovic
Published: July 2002

An examination of the results of the accuracy measurements of a bench top audio-frequency selective voltmeter, based on the superheterodyne principle, showed that an accuracy of the order of only 10% of measured values could be achieved if no internal error correction procedure in the measurements had been used. The temperature variations of the parameters of the quartz band-pass filter have been identified as the main source of the measurement error. An application of the internal reference signal from a relatively simple and inexpensive source improved the overall accuracy up to the order of 3%. Finally, it was shown that by combining the wide band and selective measurements of the signals from the built-in tracking generator further improved the overall accuracy to better than 1% and eliminated altogether the need for using any separate source of internal reference signals.
High-speed digitizer/averager data-acquisition system for Fourier transform electron paramagnetic resonance spectroscopy
Authors: Pohida Thomas J. , Fredrickson Hal A. , Tschudin Rolf G. , Fessler Joseph F. , Krishna Murali C. , Bourg John , Harrington Frank , Subramanian Sankaran
Published: July 2002

A high-speed digitizer/averager data-acquisition system designed and built as part of a 300-MHz Fourier transform electron paramagnetic resonance spectrometer is described. There are two key features of the system: (1) the maximum digitizing rate is 300 Msamples/s and (2) a 256-point free-induction-decay signal running summation can be updated in less than 3 μs. At the maximum digitizing rate, the system can sum 65 536 FIDs in 220 ms. The system consists of an analog-to-digital converter/adder unit (ADCA) and an IBM compatible personal computer. The ADCA is comprised of a digitizer, high-speed sample buffers, high-speed adders/memory, and control hardware. Design techniques, such as parallel processing, utilized to meet the high-speed performance requirements are described. Trigger and timing signals for the system are derived from the spectrometer. System efficiency, synchronization, and time base stability are demonstrated in the spectrometer at a sampling frequency of 200 MHz. Signal-to-noise ratio enhancements are shown using a lithium phthalocyanine test sample.
Negative-ion production probability in rf plasma sputter-type heavy negative-ion sourcea)
Authors: Tsuji Hiroshi , Ishikawa Junzo , Kawabata Yasuyuki , Gotoh Yasuhito
Published: July 2002

We have constructed a rf plasma sputter-type heavy negative ion source, which can deliver high current negative ion beams such as Cu− of 12.1 mA, Si− of 3.8 mA, and B−2 of 1 mA in dc operation mode. In our source, the estimated negative ion production probability of Cu was much more than the value obtained by the conventional negative ionization probability equation with an exponential dependence on velocity. We measured heavy negative ion production probabilities by Xe+ sputtering on various cesiated metals. The probabilities were strongly affected by the cesiated surface condition which was determined by a flux of neutral cesium supply to the surface and a target surface temperature. The measured maximum probabilities at the optimal conditions were considerably high, and they were about 10% or more for Cu, C, Si, Ge, and W targets and about 1% for Ta and Mo targets. The probability for very low velocity particles such as sputtered heavy metal atoms might be affected by a surface ionization process with a high local surface temperature.
Noninvasive measurement system for human respiratory condition and body temperature
Authors: Toba Eiji , Sekiguchi Sadamu , Nishimatsu Toyonori
Published: July 2002

A special chromel (C) and alumel wire (A) thermopile has been developed which can measure the human respiratory condition and body temperature without directly contacting a sensor to the human body. The measurement system enables high speed, real time, noninvasive, and simultaneous measurement of respiratory rates and body temperature with the same sensor. The special CA thermopile, with each sensing junction of approximately 25 μm, was constructed by using spot welded thermopile junctions. The thermoelectric power of 17 pairs of special CA thermopile is 0.7 mV/ °C. The special CA thermopile provides high sensitivity and fine frequency characteristics, of which the gain is flat to approximately 10 Hz.
Photon correlation system for fluorescence lifetime measurements
Authors: Morgan C. G. , Murray J. G. , Mitchell A. C.
Published: July 2002

The construction and testing of a dual-channel photon correlator is reported for the frequency domain imaging of fluorescence lifetimes using photon-counting detection. A light source modulated at radio frequency excites fluorescence, which is detected using an imaging single-photon detector. After discrimination, single-photon events are processed in parallel by the correlation circuit, the purpose of which is to allow both the mean phase delay and the demodulation of fluorescence to be calculated relative to a reference signal derived from the modulated excitation source. Outputs from the correlator are integrated in a computer, resulting in accumulation of images which have been statistically filtered by sine and cosine transforms, and which can be manipulated within the computer to generate a resultant image where contrast depends on fluorescence lifetime rather than fluorescence intensity.
Apparatus for simultaneous observation of the electro-optic response and small angle x-ray scattering in liquid crystals
Authors: Gleeson H. F. , Carboni C. , Morse A. S.
Published: July 2002

A novel apparatus allowing the simultaneous observation of small angle x-ray scattering and time dependent birefringence changes of a dynamic system is described. The apparatus incorporates a monochromatic light source, polarizers, a fast photodiode detector, and electric field generating equipment, such that electro-optic response times between 10 μs and 100 s may be measured. The electro-optic apparatus is incorporated in an x-ray camera sited at the Synchrotron Radiation Source at Daresbury Laboratory, UK. The x-ray apparatus allows the study of structures ∼30 Å in dimension and the detector is time resolved with a minimum response time of 10 μs. A hot stage and temperature controller are also incorporated into the apparatus, allowing the study of smectic liquid crystal devices. Results from the simultaneous acquisition of time resolved x-ray scattering data and electro-optic measurements from a thin film of smectic-A liquid crystal are presented.
Beam focusing of low-energy ion source by aperture displacement
Authors: Ueda Yoshio , Yoshikawa Takafumi , Nishikawa Masahiro , Goto Seiichi
Published: July 2002

For low-energy plasma ion source (<1 keV), the narrow acceleration gap and application of high accel–decel voltage ratio are useful for obtaining high brightness ion beam. This paper describes these effects in a triode multiaperture extraction system on the characteristics of geometrical focusing by aperture displacement experimentally. Beam parameters such as focal length and beam divergence were estimated from a two-dimensional (axial and radial) power density profile by a Gaussian beamlet model. It is found that this model agrees very well with the beam power density profile. The relation of focal length with aperture displacement roughly agrees with the analytical model derived by Conrad. However, the effective gap width for the model is not simply determined from the aperture geometry.
Window transmission monitoring and cleaning schemes used with the Light Detection and Ranging Thomson scattering diagnostic on the JET tokamak
Authors: Brown B. W. , Gowers C. W. , Nielsen P. , Schunke B.
Published: July 2002

The Light Detection and Ranging Thomson scattering diagnostic on the JET tokamak makes routine measurements of the plasma electron temperature and density profiles. During JET operations the windows used for scattered light collection gradually become coated with deposits due to the plasma erosion of the wall. The consequent loss in transmission can affect the electron density and also the electron temperature measurement. This paper describes both the method adopted to monitor the change in transmission due to the gradual build up of deposits and the application of laser window cleaning to counteract it.
Performance of a diamond-anvil high-pressure x-ray diffractometer in the Guinier geometry
Authors: Sahu P. Ch. , Yousuf Mohammad , Shekar N. V. Chandra , Subramanian N. , Rajan K. Govinda
Published: July 2002

In this paper, the performance of a novel high-pressure diamond-anvil powder x-ray diffractometer in Guinier geometry is reported. The diffractometer is a combination of a curved quartz-crystal monochromator, a Mao–Bell-type diamond-anvil cell, a flat position sensitive detector, and a Huber goniometer with compound stages to realize this geometry. The incident x-ray beam is from a rotating anode x-ray generator. It is shown that the above experimental arrangement results in an enhanced S/N ratio, improvement in resolution, and reduction of the data-acquisition time. Test results on UAl2 are presented to demonstrate the advantages of the setup in the study of phase transitions at high pressure.
Monofilament drawing device for in situ x-ray scattering studies of orientation development in polymeric fibers
Authors: Nolan S. J. , Broomall C. F. , Bubeck R. A. , Radler M. J. , Landes B. G.
Published: July 2002

The physical properties of polymer fibers are directly related to the development of orientation in the draw zone under extensional conditions. Although the final properties and microstructure of fibers can be evaluated after processing is completed, it is desirable to understand the development of orientation during drawing independently from the effects superimposed by subsequent unit operations. In situ x-ray scattering measurements of the extrudate in the draw zone provide an ideal means of accomplishing this goal. Depending on the polymeric system to be studied, rotating anode or synchrotron-based x-ray sources may be required, making portability of the fiber drawing device highly desirable. This paper describes an easily transportable in situ x-ray filament drawing device, and discusses typical data obtained using the device to produce filaments from a liquid crystalline nematic solution of poly(cis-benzoxazole) in polyphosphoric acid.
Vacuum tests of a beamline front-end mock-up at the Advanced Photon Sourcea)
Authors: Liu C. , Nielsen R. W. , Kruy T. L. , Shu D. , Kuzay T. M.
Published: July 2002

A mock-up has been constructed to test the functioning and performance of the Advanced Photon Source (APS) front ends. The mock-up consists of all components of the APS insertion-device beamline front end with a differential pumping system. Primary vacuum tests have been performed and compared with finite element vacuum calculations. Pressure distribution measurements using controlled leaks demonstrate a better than four decades of pressure difference between the two ends of the mock-up. The measured pressure profiles are consistent with results of finite element analyses of the system. The safety-control systems are also being tested. A closing time of ∼20 ms for the photon shutter and ∼7 ms for the fast closing valve have been obtained. Experiments on vacuum protection systems indicate that the front end is well protected in case of a vacuum breach.
Beamline optimization and phase space transformationa)
Authors: Bahrdt J. , Flechsig U. , Senf F.
Published: July 2002

The transformation of ray coordinates through a complete beamline is described via a single matrix. This transformation matrix can be used either for conventional ray tracing or for phase space transformation. The matrix elements represent the optical aberrations of the complete system. An optimization program is described that minimizes a weighted sum of the matrix elements.
An integrated instrumentation for light-scattering and time-resolved fluorescence measurements
Authors: Musolino M. , Cubeddu R. , Pifferi A. , Taroni P. , Lago P. , Rovati L. , Corti M.
Published: July 2002

An integrated instrumentation which combines in the same system static and dynamic laser light scattering and time-resolved fluorescence spectroscopy is described. The two types of measurements can be performed simultaneously on the same sample contained in a thermostated cuvette. The light scattering allows measurements of molecular weights and hydrodynamic radii in the range of 20 Å to a few micrometers. The overall time resolution of fluorescence measurements is around 50 ps. The system provides the simultaneous acquisition of the fluorescence decay curve, of the time integrated emission spectrum, and of two time-gated spectra. The light-scattering technique gives information on the global structure of the aggregates, while fluorescence measurements are sensitive to the local interactions of a fluorescence probe with the surroundings. The contemporary use of these two complementary techniques can be quite valuable mostly for biological samples for which stability and reproducibility with time can sometimes be a problem. As an example, combined measurements of the dimension of dimyristoylphosphatidylcholine vesicles around their temperature transition and of fluorescence lifetimes of the diphenylhexatriene probe incorporated in the vesicles is shown.
Spectrometer for high resolution resonant inelastic x-ray scatteringa)
Authors: Schülke W. , Kaprolat A. , Fischer Th. , Höppner K. , Wohlert F.
Published: July 2002

The requirements on the radiation source, the monochromator/mirror, the diffractometer, and the crystal dispersive analyzer for an optimum instrumentation dedicated to high resolution resonant inelastic scattering experiments are formulated. The possibility for the application of dispersion compensation is stressed. A provisional instrumentation at the HARWI–Compton beamline is described and test measurements of the resonant inelastic scattering cross section of Cu for incident photon energies scanning across the K threshold and for scattered photon energies near the Kα1 line are reported. By means of model calculation the important role of correct absorption correction of resonant inelastic scattering data is emphasized.
Scanning tunneling microscope with three-dimensional interferometer for surface roughness measurement
Authors: Fujii Toru , Yamaguchi Masataka , Suzuki Masatoshi
Published: July 2002

The scanning tunneling microscope (STM) has been known for its high lateral resolution, but its unreliable vertical accuracy has prevented it from being widely used as a profiler for roughness and step height measurements. An STM equipped with an optical interferometer to calibrate STM tip feedback controlled motion in the Z direction along with interferometers for monitoring X and Y raster scanning has been developed. The resolution of the interferometer was 0.12 nm rms. Maximum line scanning distance is 250 μm and the motion in this direction is secured by a parallel spring mechanism. Step height and pitch measurements on a surface topography standard agree in nanometer scale with the certified value of the standard. The result of high accuracy roughness measurement with the STM supports the common observation that STM measurement gives larger roughness than interferometric measurement.
The soft x-ray transmission properties of thin polyimide windows and their application to future detectors
Authors: Bavdaz M. , Peacock A. , Fuchs D. , Lederer T. , Müller P. , Scholze F. , Ulm G. , Vittanen V.-P. , Mutikainen R.
Published: July 2002

The x-ray transmission properties of a very thin polyimide window in the range 7–310 Å have been investigated. The window is nominally 0.24 μm thick and is supported by a hexagonal polyimide grid. Transmission of over 60% and 80% at the oxygen Kα and carbon Kα lines, respectively, have been achieved. The use of such windows as the entrance window of a gas scintillation counter (GSPC) operating as a broadband spectrometer at XUV wavelengths is discussed. Overall detector efficiencies of greater than 10% for wavelengths less than 150 Å are possible to achieve.