bluuebunny/crossref_metadata_2025 huggingface dataset:
Conical geometry energy dispersive diffraction: First results
Authors: Häusermann Daniel , Itié Jean Paul
Published: July 2002

A new energy dispersive diffractometer has been developed. It consists of a solid tungsten carbide conical collimator and a large area annular detector. Diffracted intensities are increased by at least one order of magnitude. Developed for high-pressure studies and their microsamples, the instrument will improve the accuracy of intensity measurements by reducing crystallite statistics effects and the collection of a complete cone of diffraction will greatly facilitate high-pressure single-crystal studies. The results of the first test of the instrument are reported.
Azimuthal rotation of a continuously cooled UHV sample holder for surface physics investigations
Authors: Franzen W. , Kollias V. , El-Batanouny M.
Published: July 2002

We describe a novel design for a cryogenic sample manipulator to be used for angle-resolved surface investigations in an ultrahigh vacuum system. Azimuthal rotation of a sample in thermal contact with a closed-cycle helium refrigerator is achieved by rotation of the heat shield that surrounds the cold finger of the refrigerator.
A relatively simple way to produce THz bursts of optical pulses
Authors: MacFarlane D. L. , Narayan V.
Published: July 2002

We present the design, construction, and demonstration of a device to produce short, high-frequency bursts of ultrashort optical pulses. Specifically, we use a folded delay line structure called the optical rattler to produce a 600-GHz burst of 400-fs pulses.
A high-flux atomic oxygen source for the deposition of high T
c superconducting films
Authors: Yu-Jahnes L. S. , Brogan W. T. , Anderson Alfredo C. , Cima M. J.
Published: July 2002

A high-flux atomic oxygen source has been developed for the deposition of in situ superconducting high Tc films under conditions that require low chamber pressures (≤10−4 Torr). The source uses a remote microwave plasma to generate the atomic species and is capable of producing an atomic oxygen flux greater than 2×1016 cm−2 s−1. The O2 dissociation efficiency of the atomic oxygen source is measured to be approximately 25%–30% for an O2 flow of 5 sccm. This high efficiency is achieved by the combined effects of a boric acid surface treatment to minimize recombination on the quartz tube and the addition of N2 to the oxygen plasma to increase the atomic oxygen yield. We have developed a treatment for the quartz surface that gives reproducible atomic oxygen flux with no degradation of the surface coating with repeated usage.
A simple technique to prevent misfire arcing in discharge-pumped excimer lasers
Authors: Bashkansky M. , Wexler B. L.
Published: July 2002

A simple spark gap has been used to prevent arcing due to lack of preionization in a laboratory discharge-pumped excimer laser. Adjustment of the self-breakdown point of the gap can be made in place without allowing any damaging arcs.
Spin-polarized photoemission spectroscopy of magnetic surfaces using undulator radiation
Authors: Johnson P. D. , Brookes N. B. , Hulbert S. L. , Klaffky R. , Clarke A. , Sinković B. , Smith N. V. , Celotta R. , Kelly M. H. , Pierce D. T. , Scheinfein M. R. , Waclawski B. J. , Howells M. R.
Published: July 2002

A beamline has been established at the National Synchrotron Light Source to perform angle-resolved photoemission experiments on magnetic surfaces with spin sensitivity. The system has two novel features: it uses a miniature electron-spin polarization analyzer and it also uses synchrotron radiation from an undulator rather than a bending magnet.
Development of ultrasmall-angle scattering for studies of colloidal systemsa)
Authors: North A. N. , Rigden J. S. , Mackie A. R.
Published: July 2002

Ultrasmall-angle x-ray scattering (USAXS) using the Bonse–Hart twin-crystal diffractometer system1 on a synchrotron radiation source (SRS) is being developed as a technique for studying the structure of colloidal dispersions and other inhomogeneous materials with features in the size range 500 Å to 1 μm. The use of well-characterized colloidal samples in this range highlights the problems which must be resolved in order to obtain reliable data from the system. This paper addresses the specific problems of attenuation, absorption, detector dead time, and smearing for the USAXS configuration. The system has been used to study a variety of materials and some previously unobserved features have been found in the scattering profile of a colloidal latex. This serves to indicate the value of the improved system in the field of colloidal science.
Digitalized triple-probe system for the direct display of electron temperature in a time-varying plasma
Authors: Matsumura Shosaku , Berezin Alex A. , Chang Jen-Shih
Published: July 2002

A technique for instantaneous linear digitalization of plasma electron temperature display using a triple-probe method is presented. A digitalized feedback is introduced between the floating probe voltage and the voltage applied to the other probes which is proportional to the electron temperature. Transfer of digitalized data by a photocoupler is used to suppress the side current which causes serious error on a triple-probe method. The results show that the measured electron temperatures are in a fairly good agreement with a Langmuir single-probe data. Present system can be applied to most of a low-density plasma when the ratio (probe radius/Debye length) is less than 2 for a wide range ratios of (mean-free path/probe radius). Detail error estimation is conducted for the orbital motion limited conditions.
Fast timing signal sorter for multiple hit coincidence time-of-flight spectroscopy
Authors: Ben-Itzhak I. , Carnes K. D. , DePaola B. D.
Published: July 2002

A fast timing signal sorter for NIM standard electronics has been developed. This device sorts a sequence of fast timing signals arriving from one source to a series of outputs according to their time of arrival. Coincidence time-of-flight spectroscopy studies of molecular fragmentation in collisions with fast, highly charged ions are used to demonstrate the usefulness of this sorter.
A simple multifoil spectrometer for routine carbon and oxygen measurements
Authors: Hokin Sam , Fonck Ray , Martin Piero
Published: July 2002

A simple multifoil Ross filter spectrometer for monitoring principal (i.e., n=2−1) soft x-ray lines of H- and He-like carbon and oxygen has been installed on the Madison symmetric torus reversed-field pinch. It consists of four silicon surface barrier diodes, each covered by a different multilayer foil filter but viewing a common plasma volume. Each filter is composed of a combination of thin film absorbers with strategically located absorption edges, giving a peak transmission of around 10% at a wavelength of interest (C v 40.30 Å, C vi 33.74 Å, O vii 21.70 Å, O viii 18.90 Å) with good rejection of the others. A linear combination of these four lines is isolated by a given filter and a matrix inversion of the four simultaneous measurements produces the intensities of the individual lines. The time evolution of these lines shows evidence of radial shell structure and gives useful information of the dynamics of the electron temperature during sawtooth activity. This multifoil spectrometer provides a simple and inexpensive alternative to grazing incidence spectrometers as a monitor of C and O influx and radiated power in high temperature tokamaks, and may be especially applicable in a high neutron flux environment.
A five-channel, diamond photoconducting x-ray detector array for z-pinch experiments
Authors: Spielman Rick B.
Published: July 2002

We have built a five-channel, x-ray detector array based on diamond photoconducting detectors (PCDs). The diamond elements have dimensions of 3 mm × 1 mm × 1 mm (or 0.5 mm). We use diamond PCDs for their stability, flat spectral response, and low leakage currents. The good time response of diamond PCDs is due to the 100-ps electron/hole recombination time. Filters were designed to give information in the 1–10-keV spectral region. Calibration of the diamond PCDs showed sensitivities between 4 and 7 × 10−4 A/W for a bias of 100 V. We shall present data from z-pinch experiments on Saturn.
Fifteen chord FIR polarimetry system on MTX
Authors: Rice B. W.
Published: July 2002

A far-infrared polarimeter diagnostic has been added to an existing fifteen chord interferometer on the Microwave Tokamak Experiment (MTX). The polarimeter utilizes a new technique for determination of the Faraday rotation angle based on phase measurements of a rotating polarization ellipse. This technique allows the rotation angle to be determined even in the presence of signal amplitude variations caused by refraction. The implementation of this instrument requires no new detectors and minimal optics, making it quite inexpensive to add on to existing multichord interferometers. The MTX polarimeter has been operating for about a year and has achieved a resolution of ≤0.2° with a bandwidth of ≂1 kHz and a chord spacing of 1.5 cm. Typical Faraday rotation angles on MTX are in the range of 5°–15°. To obtain the poloidal field, the line-integrated density and Faraday rotation profiles are inverted in a manner consistent with the Grad–Shafranov equilibrium to first order in the inverse aspect-ratio expansion. Profile measurements during normal ohmic operation are presented.
Contact potential measurement: The preamplifier
Authors: Rossi Frank
Published: July 2002

The factors governing the choice of preamplifier type for the vibrating capacitive probe used in contact potential measurements are examined. Two types are compared: a high input impedance voltage amplifier and a current amplifier. The latter has been increasingly used in recent years due to its great advantages in dealing with parasitic input capacitance. We extend previous analyses, elucidating other advantages of the current amplifier. Particularly important are (i) the reduction of spurious microphonic signals, implying lower systematic error, and (ii) the white noise spectrum of its equivalent contact potential noise, which allows random error to be effectively reduced by increased averaging periods.
Pinhole detection in thin foils used in space plasma diagnostic instrumentation
Authors: Funsten H. O. , Barraclough B. L. , McComas D. J.
Published: July 2002

The efficiency of thin foils which are used for charge state modification, start/stop pulse triggering, and UV shielding in space plasma diagnostic instrumentation is highly sensitive to pinholes in the foil. In this study, we present a high resolution method to map pinhole locations and sizes in thin foils based on the different transmission properties of incident ions through holes and hole-free regions of the foil. Results are presented for 200-eV ions transmitted through 0.2-, 0.5-, and 1.0-μg/cm2 carbon foils. Acceleration of transmitted ions into the imaging detector increases both the imaging resolution and the contrast between holes and hole-free regions of the foil.
Amplitude modulation reflectometry for large fusion devices
Authors: Sánchez J. , Brañas B. , Estrada T. , de la Luna E. , Zhuravlev V.
Published: July 2002

One of the main problems which arises in density profile measurements by reflectometry is the need for continuous tracking of the phase delay; fast density fluctuations and strong modulation on the amplitude of the reflected signal can cause ‘‘fringe jumps’’ in the phase signal. Amplitude modulation reflectometry performs a time delay measurement by the determination of the phase delay of the modulating envelope of a millimeter wave reflected by the plasma. The phase delays involved are small, the measurement is not affected by the fluctuations and can be directly performed without complicated fringe counters; the method provides a promising possibility for real time determination of the plasma position and density profile. In the present paper the principles of the method are presented as well as the analysis on the effects of phase and amplitude fluctuations, dispersive effects, and accuracy requirements.
Status of the neutron diagnostic experiment for Alcator C-Mod
Authors: Fiore C. L. , Boivin R. , Granetz R. S. , Fuller T. , Kurz C.
Published: July 2002

The Alcator C-Mod experiment is expected to produce neutrons at a rate of up to 1 × 1016 n/s during its highest performance operation. The global neutron detection system must provide accurate measurement of this production over the full operating regime of the experiment, 1011–1016 n/s. This is accomplished using a series of uranium fission detectors enriched in U235 of staggered sensitivity. These are distributed in two moderator assemblies. A BF3 detector is added to each moderator to cover the lowest operational range. Preliminary calibration of the system has been accomplished using a 65.4 μg Cf252 source placed inside the Alcator C-Mod vacuum vessel. The system design and calibration is discussed herein.
A two-crystal monochromator for the UVX ring of LNLS
Authors: Corrêa Mino C. , Tolentino Hélio , Craievich Aldo , Cusatis Cesar
Published: July 2002

A two-crystal x-ray monochromator was built at LNLS. It is based on the Golovchenko [J. A. Golovchenko, R. A. Levesque, and P. L. Cowan, Rev. Sci. Instrum. 52, 51 (1981)] geometry with one rotation and two translations in order to tune the wavelength and keep constant the position of the monochromatic beam, respectively. The Bragg angle can vary from 10° to 80° using a standard high precision external goniometer whose minimum step is 0.001°. The two translations are based on a leaf spring device, with a maximum wobbling of ±2 arcsec along 50 mm. Fine tuning between the two crystals and detuning for harmonic rejection are produced by elastic devices using the magnetic force between a permanent magnet and a solenoid acting on a weak link of the second crystal. The monochromator housing is vacuum compatible. The equipment was tested using a conventional x-ray source and a standard control system. It will be used associated with classical extended x-ray absorption fine structure (EXAFS) and the high precision x-ray optics experimental station.
Laue transmission x-ray spectrograph for inertial confinement fusion (ICF) diagnostics
Authors: Burek A. J.
Published: July 2002

An absolutely calibrated, focusing Laue transmission crystal spectrograph has been developed for inertial confinement fusion (ICF) diagnostics of high-energy x-ray continuum at NOVA. A single flat EddT 020 crystal, 500-μm thick, provides continuous energy coverage over the 5.5–25 keV energy range. The spectrograph is designed with low dispersion and low resolving power E/ΔE of between 10 and 50 for high sensitivity to continuum. Greater resolving power with lower continuum sensitivity is possible by increasing dispersion. The focusing design achieves very low background and provides a compact flat field for coupling to various position sensitive detectors including streak cameras. In addition to EddT, PET 020 has high efficiency in transmission in this energy range and used in the Cauchois geometry achieves high to moderate resolving power that is independent of ICF source size. Initial experiments with gold targets at NOVA with the EddT spectrograph show high sensitivity for single shot recording of continuum and gold L lines on Kodak DEF film. Factors affecting instrument design, resolving power, and sensitivity will be discussed.
The energy calibration of x-ray absorption spectra using multiple-beam diffraction
Authors: Hagelstein M. , Cunis S. , Frahm R. , Rabe P.
Published: July 2002

A new method for calibrating the energy scale of x-ray absorption spectra from an energy dispersive spectrometer has been developed. Distinct features in the diffracted intensity of the curved silicon crystal monochromator have been assigned to multiple-beam diffraction. The photon energies of these structures can be calculated if the precise spacing of the diffracting planes and the orientation of the crystal relative to the incident synchrotron radiation are known. The evaluation of Miller indices of operative reflections and the calculation of the corresponding photon energy is presented. The assignment of operative reflexes is simplified if the monochromator crystal can be rotated around the main diffracting vector H.
Optical design of GILDA, the Italian bending magnet beam line at ESRF
Authors: Pascarelli S. , Boscherini F. , Marcelli A. , Mobilio S.
Published: July 2002

In this paper we give a brief description of the optics for GILDA, the Italian CRG beam line at the ESRF. Ray-tracing simulations and simple calculations are used to discuss the effects which determine flux, resolution, and spot size.
Optical sources for pulse-position-modulation systems
Authors: Hausien H. H. , Martin J. D.
Published: July 2002

This article gives the results of an experimental and theoretical investigation into the use of a laser diode and an edge-emitting light-emitting diode for pulse-position modulation. Major factors affecting the maximum peak power are discussed, various aspects of the failure mechanisms occurring are reviewed, and experimental results are given. A model to calculate laser diode temperature under pulse conditions is presented.
A double-crystal monochromator for EXAFS at BSRL
Authors: Xie Yaning , Yang Hai , Shan Qiao , Xia Shaojian , Xian D.
Published: July 2002

The details of the double-crystal monochromator and its control system of the first monochromatic photon beam line for EXAFS studies 4W1B at Beijing Synchrotron Radiation Laboratory are described in this paper, the commissioning and the first experimental results obtained are also presented.
Miniature diamond anvil cell: Incorporating a new design for anvil alignment
Authors: Eremets M. I. , Timofeev Yu. A.
Published: July 2002

A miniature diamond anvil cell (DAC) of overall dimensions φ10×24 mm made of nonmagnetic NiCrAl alloy is described. A new design permits the alignment of anvil flats as perfectly as in traditional DACs. A lever-arm assembly and a fiber-optical system for the cell are described. Two example of experimental results obtained with the cell are given, namely the pressure dependence of the refractive index of diamond and the pressure-induced shifts in the photoluminescence peaks of a quantum well sample. A maximum pressure of 110 GPa was reached with beveled anvils.
Low-energy conversion electron Mössbauer spectroscopy using a chevron microchannel plate detector
Authors: Sinor T. W. , Standifird J. D. , Taylor K. N. , Hong C. , Carroll J. J. , Collins C. B.
Published: July 2002

A detection system for conversion electron Mössbauer spectroscopy is described. A chevron microchannel plate assembly attached to a two-stage electrostatic lens is used to preferentially detect electrons with energies ≤15 eV. Mössbauer spectra collected with these electrons can provide information about a variety of solid-state surface phenomena.
Holographic pattern photobleaching apparatus for the measurement of lateral transport processes at interfaces—Design and performance
Authors: Miehlich Rainer , Gaub Herman E.
Published: July 2002

A new instrument was developed which allows the detection and characterization of lateral transport processes at the fluid–solid interface. It is based on holographic photobleaching combined with a laterally resolved fluorescence detection by a photon-counting camera. The geometry of the holographic pattern was chosen such that by ‘‘on-chip’’ integration of photoelectrons in the liquid-nitrogen-cooled camera the images are integrated along the symmetry axis of the pattern and subsequently stored on the chip. Time-dependent changes in the pattern caused by directed motion or by diffusion are then qualified by Fourier analysis. Lateral diffusion coefficients between 10−12 and 10−6 cm2/s and velocities between 10−10 and 10−4 m/s are measurable. In order to discriminate processes at the surface and in the volume, evanescent field illumination can be chosen. The penetration depth of the evanescent field can be varied from 96 to 800 nm. The performance of the instrument is demonstrated on selected examples.
Using a free-standing thermistor array to measure VUV emission from a tokamak plasma
Authors: Paul S. F. , Fonck R. J. , MacAulay A. K.
Published: July 2002

A compact 15-channel bolometer array composed of discrete thermistors has been installed on the Princeton Beta Experiment tokamak. The response time, fastest for detectors with low thermal capacities, has been optimized by using ‘‘free-standing’’ detectors. The detector is supported only by thin electrical leads and no thermal substrate is employed. Overheating due to limited heat dissipation is controlled with careful detector biasing. The sensitivity is limited by the systematic errors in the model of the heat transfer from the detector to the electrodes and leads. A two-pole cooling model was found to characterize the detector’s thermal decay far better than a simple exponential and resulted in an NEP≊3×10−7 W/√Hz with a 300-Hz bandwidth.
A low-temperature ultrahigh vacuum scanning tunneling microscope system and tunneling spectra of the Bi2212 superconductor
Authors: Ikeda Kazuto , Takamuku Kenshi , Kubota Hiroshi , Itti Rittaporn , Koshizuka Naoki
Published: July 2002

We designed and constructed an ultrahigh vacuum scanning tunneling microscope (UHV-STM) which is available for the measurement of tunneling spectra at low temperature. The sample holder is cooled by thermal conduction to the stage that thermally connects with the refrigerator head. We cleaved Bi2Sr2CaCu2Oy (Bi2212 high Tc superconductor) single crystals under ultrahigh vacuum conditions, and measured tunneling spectra of the Bi–O surface at 35 K. The spectra were smeared due to the fact that the STM tip was at high temperature (≳100 K).
Uncertainty intervals for polarized beam scattering asymmetry statistics
Authors: Coakley Kevin J. , McClelland Jabez J. , Kelley Michael H. , Celotta Robert J.
Published: July 2002

In many scattering experiments, the quantity of most direct physical interest is a measure of the difference between two closely related scattering signals, each generated by a Poisson scattering process. This difference is often expressed in terms of an asymmetry statistic, that is, the difference normalized to the sum of the two signals, corrected for an additive background contribution. Typically, a propagation of errors approach is used to compute confidence intervals for asymmetry. However, these confidence intervals are not reliable in general. In this work, generally accurate confidence intervals for asymmetry are obtained using a parametric bootstrap approach. Based on the observed data, data are simulated using a Monte Carlo resampling scheme. The resampled data sets satisfy a constraint that ensures that background-corrected count rates are not negative.
Noncontacting microwave coupling to a cryogenic gravitational radiation antenna
Authors: Ivanov E. N. , Tobar M. E. , Turner P. J. , Blair D. G.
Published: July 2002

Gravitational radiation detectors must detect extremely small displacements, and thus require elaborate vibration isolation systems to attenuate the surrounding environmental noise. Contacting electrical leads can provide a direct path that will short circuit the vibration isolation, and degrade the antenna Q factor. Noncontacting microstrip transceivers provide a practical means of electromagnetically coupling to a resonant bar gravitational antenna when a microwave transducer is used as a signal readout system. Two microwave patch antennas now operate as transceivers on the University of Western Australia’s 1.5 tonne niobium bar gravitational radiation antenna and are described in detail in this paper. This system allows improved vibration isolation without degradation of the acoustic Q factor of the niobium bar. Combined with a cryogenic amplifier, this system should achieve a reduction of 57 dB in the series noise power. This corresponds to a factor of 700 reduction in the effective displacement noise when referred to the transducer, from 2×10−16 to 3×10−19 m/√Hz.
Flexible thermomechanical analysis of polymeric fibers
Authors: Sikorski M. E. , Buckley C. P. , Hearle J. W. S. , Mukhopadhyay S. K.
Published: July 2002

A new microcomputer-controlled instrument has been developed for making measurements of thermomechanical behavior of polymeric fibers and yarns under conditions relevant to high-speed industrial fiber processing. The instrument can apply extension and/or twist, and rapid heating or cooling in the temperature range 20–300 °C, while tension and torque are measured. Particular novel features are: a temperature control device providing heating or cooling at rates up to 103 K/s; a new form of high-sensitivity torque transducer with resolution of 10−9 Nm; and computer integration of extension, twist, and temperature. The instrument provides an unprecedented degree of flexibility in the design of thermomechanical tests. It is suitable not only as a versatile research tool for material property measurements relevant to processes such as spinning, heat setting, and thermobonding of fibers, but also as a convenient tester for use in quality control on fibers and yarns.
Transient one-dimensional heat flow technique for measuring thermal conductivity of solids
Authors: Log T.
Published: July 2002

A transient one-dimensional heat-flow technique for absolute determination of thermal conductivity of solids has been developed. A commercial thermistor, pressed into contact with the front surface of a bar-shaped test specimen typically 5–20 mm long, is used simultaneously as a constant heat source and as a sensor of the temperature increase. The measurement time is typically 5–10 s. Measurements on stainless-steel and graphite standards from NIST indicate that the technique is accurate to within 3% in the thermal conductivity range 10–100 W m−1 K−1 at room temperature.
A new apparatus for the measurement of physical adsorption of gas mixtures at elevated pressures
Authors: Malbrunot P. , Vidal D. , Vermesse J.
Published: July 2002

The new apparatus described enables making simultaneously absolute measurements of physisorption, bulk density, and adsorption kinetics of multicomponent gas mixtures as a function of pressure up to 30 MPa. The method which combines the dynamic and the gravimetric methods is self-sufficient because it does not require complementary data. An in-line high-pressure chromatographic device directly measures the time evolution of the effluent flow composition (breakthrough curves). Results of adsorption, density, and adsorption kinetics at high pressures of the equimolar Ar-CH4 mixture on activated carbon are reported.
Simple apparatus for the liquefaction of neon directly into a research Dewar
Authors: Francavilla T. L. , Soulen R. J. , Claassen J. H.
Published: July 2002

A simple apparatus for liquefying neon is described for use in experiments that require a stable thermal environment at 27 K. This apparatus makes use of a closed-cycle refrigerator attached to an insulated cold finger inserted into a conventional stainless steel Dewar to liquefy a quantity of neon gas stored previously in a tank. The system is inexpensive and easy to use. Furthermore, the neon is recovered for subsequent reuse upon completion of the experiment. Starting with a Dewar holding a small coil that had not been precooled, and using a refrigerator with rated cooling capacity of 15 W at 26 K, approximately 0.5 ℓ of liquid neon was condensed into the Dewar in ∼4 h. The apparatus has been used to measure the critical currents of high Tc oxide tape coils both with and without the application of an external magnetic field.
Arc-heated magnetically trapped expanding plasma jet generator
Authors: Akatsuka Hiroshi , Suzuki Masaaki
Published: July 2002

For the purpose of new applications of thermal and recombining plasma, an apparatus is developed which continuously produces ‘‘arc-heated and magnetically trapped expanding plasma jet.’’ In this apparatus, arc-heated thermal helium plasma of atmospheric pressure is spouted from a nozzle of 1.2 mm inner diameter into a rarefied gas wind tunnel of about 3–20 Pa with a parallel magnetic field of 0.025–0.16 T. Investigations about the plasma are carried out and stationary inverted populations are observed downstream along this plasma jet. The magnetic field establishes stable arc discharge. Electron temperature Te, ion temperature Ti, and electron density ne of the plasma are about 0.1–1, 0.1–0.8 eV, and 1×1012–2×1013 cm−3, respectively. Two examples of applications of this apparatus are discussed. One is a potential active laser medium, and the other is a cluster preparer.
A spontaneous desorption-based polyatomic ion source
Authors: Yau A. Y. , Park M. A. , Kaercher R. G. , Schweikert E. A.
Published: July 2002

We describe an ion source based on the spontaneous desorption process. The production, acceleration, and separation processes allow for the production of keV energy polyatomic ions while maintaining a high signal-to-background ratio. Both atomic and polyatomic ions with up to 37 keV energy were generated. Because the spontaneous desorption process is naturally pulsed, the ion source was attached to a dual time-of-flight mass spectrometer for secondary ion mass spectrometry experiments. In this article, we describe the design of both the polyatomic ion source and the mass spectrometer.
Effect of trapped ions in a gated time-of-flight apparatus
Authors: Martus K. E. , Orient O. J. , Chutjian A.
Published: July 2002

A three-mesh gate is used in a time-of-flight (TOF) apparatus to analyze the velocity of positive ions. Test results and a theoretical description are presented of an effect arising from trapping ions between meshes of a two-gate TOF velocity analyzer. The entrapped ions produce a side peak in the TOF spectra corresponding to faster ions. The onset and relative height of the side peak is dependent on the gating voltage and risetime of the pulsing electronics, while the relative intensity depends upon the velocity being sampled and the ratio of the gate width to duration.
A new approach for mapping x-ray rocking curves
Authors: Gao Dachao , Davis Tim J. , Wilkins Stephen W. , Pogany Andrew P.
Published: July 2002

A new experimental geometry for simultaneously mapping the rocking curves of a sample over a one- or two-dimensional array of points on the sample has been developed. The 422 asymmetric diffraction of Cu Kα1 radiation with a monolithic channel-cut silicon crystal angularly collimates and spatially expands the x-ray beam. A cooled Reticon linear photodiode array with 25-μm spatial resolution was used for the one-dimensional detector. Compared with the commonly used double-crystal diffractometer method, more information can be obtained from the present method, for example, characterization of the minute local misorientation of subgrains and the precise determination of the curvature of a crystal. The uniformity of the crystal quality and the local variation of the curvature of the crystal planes over a sample can also be revealed from the contour map of the rocking curves. Maps of the rocking curves of several samples have been collected using this method.
Ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometer
Authors: Alber George M. , Marshall Alan G. , Hill Nicholas C. , Schweikhard Lutz , Ricca Tom L.
Published: July 2002

A new Fourier transform ion cyclotron resonance mass spectrometer is described in three sections: magnet, vacuum system, and electronics/data system. Each component is described in detail (e.g., manufacturer’s part numbers, drawings, circuit schematics, etc.). Of special interest is the high-frequency signal generation and processing required to extend the lower-mass limit for singly charged ions to 1 u. In particular, two new multiple heterodyne techniques for high-frequency measurements are described, as well as a method for producing a long-duration electron beam, and the implementation of z-axis ejection for selective removal of unwanted ions of various mass-to-charge ratios.
High-speed circuits for TE discharge lasers and high-voltage applications
Authors: Houtman H. , Cheuck A. , Elezzabi A. Y. , Ford J. E. , Laberge M. , Liese W. , Meyer J. , Stuart G. C. , Zhu Y.
Published: July 2002

Pulsed transverse electric (TE) glow discharges used to produce population inversions in gas lasers at 1–20 atm require high-speed, high-voltage, high-current capacitor banks. In this article we first review and compare the circuits in common use to produce the required fast, self-sustained glow discharges in CO2, excimer, and N2 lasers. The parameters and circuit types given will be useful to future designers of pulsed gas lasers to design and to optimize any proposed circuit in order to yield any desired operating conditions and parameters. The n-stage circuit types presented are capacitor-transfer (C-C), L-C inversion, Marx bank, and fourfold L-C inversion, with their double-sided counterparts, and also their transmission-line counterparts, such as the Blumlein circuit. A one-parameter differential equation is developed which describes the general series C-L-R circuit. Electrical pulses measured on various lasers are compared with the differential equation solutions for various bank impedances and load resistances. We then present the design and measurements of a new automatically preionized, double-sided, L-C inversion circuit for an 800-mJ, TE CO2 laser, and compare it to previous systems. Methods to lengthen the discharge pulse, and some novel active mode locking techniques are discussed. We compare the L-C inversion circuit, the fourfold L-C inversion circuit, the conventional Marx bank, and the ‘‘double Marx bank’’ for lasers and other applications, such as pulsed particle accelerators. Finally, we discuss capacitor bank interconnections, electro-optic probe systems, and various triggering methods.
Far-infrared ellipsometer
Authors: Barth K.-L. , Keilmann F.
Published: July 2002

A far-infrared rotating-analyzer ellipsometer which uses a step-tunable, optically pumped gas laser as its light source is described herein. As polarizers novel metal grids with 10 000:1 polarization contrast were used. The instrument determines the complex dielectric function in the spectral range between 10 and 150 cm−1. A cryostat allows both reflection and transmission measurements from 10 to 330 K. Measurements of the birefringence of crystalline quartz, of both the carrier density and the scattering frequency of doped semiconductors, and of the low energy excitations of high-TC YBaCuO ceramics are presented herein.
4.8-keV x-ray backlight framing method for observing images of soft-x-ray-driven fusion capsules
Authors: Katayama M. , Shiraga H. , Nakai M. , Kobayashi T. , Kato Y.
Published: July 2002

We report on a diagnostic method for observing the implosion asymmetry of soft-x-ray-driven fusion capsules. The method consists of an x-ray backlight source using a 4.8-keV quasi-monochromatic titanium x-ray source and a fast multiframe x-ray imaging system. With the proper combination of spectral filters and photocathode to reduce intense background x rays from a gold cavity plasma, x-ray backlighting images of the fusion capsules have been successively obtained with spatial and temporal resolutions of 20 μm and 80 ps, respectively. These images are used to study the implosion velocity and the lower-mode distortion caused by x-ray irradiation nonuniformity on the imploding fusion capsule.
Tunnel diode oscillator application to high sensitivity de Haas–van Alphen and superconducting critical field studies of anisotropic organic conductors
Authors: Athas G. J. , Brooks J. S. , Klepper S. J. , Uji S. , Tokumoto M.
Published: July 2002

We report the first application of a tunnel diode circuit to investigate the de Haas–van Alphen effect and superconducting critical field values in small single crystal organic conductors. The materials of interest are in the family of charge transfer salts (BEDT-TTF)2X, where X is one of a number of anion structures. Small (≤1 mm3) oriented single crystal samples were placed inside the inductance coil of the LC tank circuit of the oscillator, and measurements were carried out at low temperatures and in high magnetic fields. We observe a marked improvement over previous magnetic methods for the determination of both de Haas–val Alphen signals and for critical field studies. The method is applicable where such information is required for very small samples.
Vertical high-precision Michelson wavemeter
Authors: Morales A. , de Urquijo J. , Mendoza A.
Published: July 2002

We have designed and tested a traveling, Michelson-type vertical wavemeter for the wavelength measurement of tunable continuous-wave lasers in the visible part of the spectrum. The interferometer has two movable corner cubes, suspending vertically from a driving setup resembling Atwood’s machine. To reduce the fraction-of-fringe error, a vernier-type coincidence circuit was used. Although simple, this wavemeter has a relative precision of 3.2 parts in 109 for an overall fringe count of about 7×106.
High-pressure stopped-flow nuclear magnetic resonance apparatus for the study of fast reactions in solution
Authors: Funahashi Shigenobu , Ishihara Koji , Aizawa Sen-ichi , Sugata Takashi , Ishii Masao , Inada Yasuhiro , Tanaka Motoharu
Published: July 2002

A high-pressure proton nuclear magnetic resonance (NMR) probe for a stopped-flow method has been developed, which enables us to follow fast reactions at various pressures up to 200 MPa. The high-pressure stopped-flow NMR (HP-SF-NMR) method has been applied to the study of several reactions at high pressures: the reaction of tetramethyltin with iodine in chloroform and the solvent exchange reaction on aluminum(III) ion in N, N-dimethylformamide. The volumes of activation for the iodomerization of tin and the solvent exchange reaction on aluminum(III) were determined to be −24.9±3.8 cm3 mol−1 and −2.2±0.8 cm3 mol−1, respectively. The apparatus permits measurement of activation volumes for reactions with half lives longer than a few seconds if the nuclear relaxation time of the measured proton is short enough. Several requirements for the applicability of HP-SF-NMR are discussed.
Characterization of a velocity-modulation atomizer
Authors: Takahashi Fumiaki , Schmoll W. John , Dressler John L.
Published: July 2002

A novel liquid droplet generator, or atomizer, capable of generating either monodisperse droplet streams or a polydisperse spray, has been characterized using phase-Doppler anemometry and two visualization techniques. The atomizer consists of a piezoelectric driver in a circular housing with an orifice plate across the end of the housing. Unlike conventional droplet generators or atomizers, this device directly induces a high-amplitude velocity perturbation of the liquid jet. Orifice plates with a circular hole (diameter: 34 or 98 μm) or a rectangular hole (527×31 μm2) were used. In the low-power mode, the atomizer with a circular orifice generated a stream of monodisperse water droplets with a diameter 1.5 to 3.4 times the jet diameter and a separation 2.3 to 26 times the jet diameter at 10 to 68 kHz. Droplets smaller than the minimum size predicted by Rayleigh’s criterion can be generated with an increased modulation power. The droplet velocity can be adjusted in a wide range (4 to 26 m/s), and a high Reynolds number (∼250) can be attained. In the high-power mode, the atomizer produced a polydisperse water spray with a Sauter mean diameter less than half the jet (equivalent) diameter. The rectangular orifice required significantly less driving power to generate a spray. This atomizer is suitable for both fundamental studies and practical applications.
Plane grating monochromator beamline for VUV radiometry
Authors: Scholze F. , Krumrey M. , Müller P. , Fuchs D.
Published: July 2002

A new beamline for radiometric applications (e.g., detector calibration and reflectometry) has been installed and characterized at the laboratory of the Physikalisch-Technische Bundesanstalt at the electron storage ring BESSY. The beamline is equipped with a SX700 type plane grating monochromator and a toroidal mirror behind the exit slit of the monochromator for collimating the radiation to allow angle resolved reflectometry. A divergence of 0.1 mrad has been achieved. The beamline has been optimized for high spectral purity of the radiation. Within the photon energy range from 40 to about 1500 eV the total amount of stray light and higher order radiation stays below 1%. A photon flux of up to 1011 s−1 has been measured in the focal point of the toroidal mirror. It corresponds to a radiant power of a few μW and thus allows use of a cryogenic radiometer for detector calibration. The details of the beamline layout and the results of the performance characterization are presented.
Correction of geometrical distortions in scanning tunneling and atomic force microscopes caused by piezo hysteresis and nonlinear feedback
Authors: Stoll Erich P.
Published: July 2002

Geometrical distortions of scanning tunneling or atomic force microscope pictures can be caused by delayed response of the piezo-ceramics and errors of the nonlinear feedback system. The images are adversely affected mostly at the boundaries where the tip motion is reversed and also at surface steps. Assuming logarithmic corrections for the time dependence of the piezo response and for the feedback nonlinearity, it is shown how these errors can be eliminated. The procedure is applied to three test samples: well-ordered clean single-crystal gold and copper surfaces, for which the correction parameters are determined as a function of temperature, scan velocity, and the place where the tips move into the scanned area. Gathering this information from various test samples, a data base can be built up that can be used to correct other samples recorded under the same conditions.
Time-resolved fluorescence using synchrotron radiation excitation: A powered fourth-harmonic cavity improves pulse stability
Authors: Polewski Krzysztof , Kramer Stephen L. , Kolber Zbigniew S. , Trunk John G. , Monteleone Denise C. , Sutherland John C.
Published: July 2002

The pulsed nature or ‘‘time structure’’ of synchrotron radiation from electron storage rings is used to measure the kinetics of the decay of electronically excited states and is particularly useful because the wavelength of excitation can be chosen at will. However, changes in the length of the pulses of radiation from a storage ring resulting from the gradual decrease of current circulating in the ring during the course of a ‘‘fill’’ limit the duration of data collection, and hence photometric sensitivity. A fourth-harmonic cavity that was recently added to the vacuum ultraviolet (VUV) storage ring at the National Synchrotron Light Source slows the loss of current during a fill, and thus increases the total number of photons produced. When operated in a passive (unpowered) mode, however, the fourth-harmonic cavity increases both the average width of the photon pulses and the changes in width that occur during a fill, thus reducing the usefulness of the VUV ring in timing experiments. We demonstrate that operating the fourth-harmonic cavity in an active (powered) mode, while further increasing pulse duration, can stabilize pulse width, thereby restoring timing capabilities.
Broadband heterodyne reflectometer at the W7-AS stellarator
Authors: Hartfuss H. J. , Estrada T. , Hirsch M. , Geist T. , Sanchez J.
Published: July 2002

A broadband heterodyne reflectometer, operating in the frequency range 75–110 GHz in extraordinary mode polarization, has been installed and operated at the Wendelstein 7-AS stellarator for the study of density fluctuations and density profile determination. At 2.5 T it covers the density range between 5×1018 and 5×1019 m−3. The system differs from the usual setup as it combines the advantages of heterodyne detection with broadband capability avoiding the limitations of phase-locked sources and permits the unambiguous determination of the phase delay independent of amplitude fluctuations in the reflected beam. After a first downconversion to an intermediate frequency of about 6 GHz, two additional mixing steps lead to an intermediate frequency of 60 MHz, which carries the phase delay from the plasma as a phase modulation. The phase information is yielded numerically from sin/cos detection at 60 MHz. Due to the balanced detection scheme, the drift as well as the broadband noise of the signal and local oscillators are canceled. The system has a dynamic range of about 60 dB and is within this range almost insensitive to amplitude fluctuations of the reflected beam. Examples are given demonstrating the potential of the system installed.
Corrosion-resistant pulsed solenoid valve
Authors: Wright Scott A. , McDonald J. Douglas
Published: July 2002

We present a novel pulsed valve design that is especially suited for use with severely corrosive gases. The design is unique in that the stem seals the gas inlet, rather than the outlet. All parts in contact with the high-pressure gas flow are constructed of ceramic and fluoroplastics.
Extremely low-noise amplifier for interfacing active devices to instruments for spectral analysis
Authors: Manfredi P. F. , Speziali V. , Svelto F.
Published: July 2002

An analog interface has been developed in order to perform very accurate noise spectral analysis with currently available instrumentation. It employs the device under test as a front-end element, whose input-referred noise voltage is amplified by a feedback loop which adds an extremely small noise contribution, followed by two cascaded low-noise amplifiers. The interface is suitable for spectral analysis in the 100 mHz–100 kHz frequency range. Its intrinsic noise contribution is estimated around 1 nV/√Hz at 100 mHz and 50 pV/√Hz at frequencies beyond 1 kHz.
The role of film re-emission and gas scattering processes on the stoichiometry of laser deposited films
Authors: Gonzalo J. , Afonso C. N. , Perrière J.
Published: July 2002

Laser ablation of a BiSrCaCuO target is performed both in vacuum and in an oxygen pressure of 0.1 mbar. Two substrates are located in the chamber in order to study the role of re-emission processes from the growing film and/or the scattering of the ablated species by an oxygen atmosphere. The results indicate that re-emission processes from the growing film are very weak (they may affect up to 1% of the deposited material at most) and are not related to the re-sputtering of the growing film. Films grown in vacuum are found to have the correct cation composition, whereas those grown in an oxygen environment show significant variations which are clearly related to gas scattering processes.
Doppler-limited spectroscopy at cryogenic temperatures: Application of collisional cooling
Authors: Newnham D. , Ballard J. , Page M.
Published: July 2002

A coolable gas cell for the measurement of mid-infrared spectra of gases at cryogenic temperatures as low as 77 K is described. The design of the cell allows it to be operated in collisional cooling (or diffusive trapping) mode to generate significant nonequilibrium pressures of monomer vapor for gases which would normally have vanishingly small vapor pressure at low temperatures. Fourier transform infrared spectra of carbon dioxide (CO2), nitrogen dioxide (NO2), and methyl silane (CH3SiH3) vapors cooled by collisions with helium gas at 77 K are reported. Sufficiently high concentrations of monomer gas may be produced at low total pressure conditions (<10 h Pa) to allow spectra to be recorded at the Doppler resolution limit. The resulting spectroscopic simplification indicates that efficient collisional cooling of the vibrational, as well as rotational, degrees of freedom occurs.