bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of the geometric disposition of the deflecting electrodes in HREELS spectrometers
Authors: Martel R. , McBreen P. H.
Published: July 2002

A new geometrical criterion is proposed for the optimization of high-resolution electron energy loss spectrometers based on spherical 180° SDA and cylindrical 127° CDA deflector anodes. This criterion concerns the relative geometrical configuration of the electrodes and its application should improve the energy resolution of tandem monochromator-analyzer spectrometers used in high-resolution electron energy loss spectroscopy (HREELS) studies of surfaces. Electron trajectory calculations for both spherical and cylindrical fields show that there exists a tandem configuration for which the electrons are perfectly refocused in position and in energy at the exit of the analyzer. On the contrary, the conventional tandem configuration used in HREELS results in a poorly defined image as a consequence of the optical aberrations of the deflectors. The correction of these aberrations is possible if a modification to the conventional configuration is applied. The new geometry may be achieved by a simple rotation of both the analyzer and the monochromator by 90° in the same sense with respect to the beam axis or by a 180° rotation of the monochromator from the conventional configuration. It is also shown that the adoption of these geometric configurations is consistent with the dispersion-compensation principle if the exit aperture of the monochromator and the entrance aperture of the analyzer are enlarged adequately.
Ion beam assisted deposition with a duoplasmatrona)
Authors: Ensinger W. , Barth M. , Martin H. , Schröer A. , Enders B. , Emmerich R. , Wolf G. K.
Published: July 2002

One of the recent applications of ion sources is their use for ion beam assisted deposition of thin films and coatings. This method combines a coating technique such as evaporation or sputtering with bombardment with ions in the keV energy range. The required ions with defined energy, flux, and impact angle are delivered from an ion source. An apparatus for ion beam assisted evaporation with a duoplasmatron ion source is described. The features of the duoplasmatron with respect to application for ion beam assisted deposition such as beam shape, uniformity and intensity, ion-to-neutral ratio, and focused and defocused mode are discussed.
An angle-resolved, wavelength-dispersive x-ray fluorescence spectrometer for depth profile analysis of ion-implanted semiconductors using synchrotron radiation
Authors: Schmitt W. , Hormes J. , Kuetgens U. , Gries W. H.
Published: July 2002

An apparatus for angle-resolved, wavelength-dispersive x-ray fluorescence spectroscopy with synchrotron radiation has been built and tested at the beam line BN2 of the Bonn electron stretcher and accelerator (ELSA). The apparatus is to be used for nondestructive depth profile analysis of ion-implanted semiconductors as part of the multinational Versailles Project of Advanced Materials and Standards (VAMAS) project on ion-implanted reference materials. In particular, the centroid depths of depth profiles of various implants is to be determined by use of the angle-resolved signal ratio technique. First results of measurements on implants of phosphorus (100 keV, 1016 cm−2) and sulfur (200 keV, 1014 cm−2) in silicon wafers using ‘‘white’’ synchrotron radiation are presented and suggest that it should be generally possible to measure the centroid depth of an implant at dose densities as low as 1014 cm−2. Some of the apparative and technical requirements are discussed which are peculiar to the use of synchrotron radiation in general and to the use of nonmonochromatized radiation in particular.
Time-resolved hard x-ray studies using third-generation synchrotron radiation sources (abstract)
Authors: Mills Dennis M.
Published: July 2002

The third-generation, high-brilliance, synchrotron radiation sources currently under construction will usher in a new era of x-ray research in the physical, chemical, and biological sciences. One of the most exciting areas of experimentation will be the extension of static x-ray scattering and diffraction techniques to the study of transient or time-evolving systems. The high repetition rate, short-pulse duration, high-brilliance, variable spectral bandwidth, and large particle beam energies of these sources make them ideal for hard x-ray, time-resolved studies. The primary focus of this presentation will be on the novel instrumentation required for time-resolved studies such as optics which can increase the flux on the sample or disperse the x-ray beam, detectors and electronics for parallel data collection, and methods for altering the natural time structure of the radiation. This work is supported by the U.S. Department of Energy, BES-Materials Science, under Contract No. W-31-109-ENG-38.
Improved atomic force microscope using a laser diode interferometer
Authors: Sarid Dror , Pax Paul , Yi Leon , Howells Sam , Gallagher Mark , Chen Ting , Elings Virgil , Bocek Dan
Published: July 2002

The performance of an atomic force microscope using a laser diode interferometer has been improved to the point where its resolution is comparable to that of laser beam deflection systems. We describe the structure of this microscope, present a model that takes into account the main parameters associated with its operation, and demonstrate its sensitivity by showing images of a small area scan with atomic resolution as well as a large area scan in a stand-alone configuration.
Variable-temperature ultrahigh vacuum scanning tunneling microscope: Mechanical and electronic instrumentation
Authors: Züger O. , Ott H. P. , Dürig U.
Published: July 2002

A variable-temperature ultrahigh vacuum scanning tunneling microscope is described which was specifically designed for the study of Ga surfaces close to the bulk melting point (Tm=29.8 °C). Since the temperature must be controlled with great accuracy the sample stage and the rest of the microscope are in thermal equilibrium. The instrument also incorporates a novel approach to vibration isolation that is based on a lossy acoustic waveguide. Analog electronics form an integral part of the microscope since a dynamic range of 120 dB must be reached. Interconnection techniques are discussed in this context and a circuit of a high-voltage amplifier is shown that provides a voltage swing of ±400 V with less than 1 mVpp noise over a bandwidth of 10 kHz. Results are presented which confirm the design concepts applied to this instrument.
Analysis techniques for directly and indirectly driven hydrodynamic experiments on Nova
Authors: Glendinning S. G. , Remington B. A. , Haan S. W. , Munro D. H. , Weber S. V.
Published: July 2002

Over the past five years we have performed an extensive series of experiments on hydrodynamic (Rayleigh–Taylor) instabilities. Typically such experiments involve the time-resolved radiography of an accelerated foil (planar geometry) with the line-of-sight of the radiograph along the direction of motion. In comparing experimental data to simulations, the simplest approach is to extract the modulation in exposure level of such a radiograph versus time and compare the inferred growth rate (assumed to be exponential) with the growth rate in column density (Δρz) from a simulation. We have found that this gives unsatisfactory results. We will discuss the techniques for experimental analysis and post processing of simulations which we use for a more direct comparison of the data with the simulation, including the extraction of Fourier components versus time from the data, the effect of backlighter spectra, emission from sources other than the backlighter, and the nonlinear effects of instrument response.
A swept two-frequency microwave reflectometer for edge density profile measurements on TFTR
Authors: Hanson G. R. , Wilgen J. B. , Bigelow T. S. , Collazo I. , Thomas C. E.
Published: July 2002

The edge density profile can play a significant role in determining the plasma confinement and the coupling of the ion cyclotron resonance frequency (ICRF) heating power to the plasma. To experimentally measure the edge density profile in the Tokamak Fusion Test Facility (TFTR), a two-frequency microwave reflectometer is being built. This reflectometer will operate in a swept two-frequency configuration between 91 and 118 GHz using the extraordinary mode. The frequency separation between the two microwave signals will be held constant while the signals are swept across the frequency band. By measuring the differential phase delay between these two signals, the density profile can be reconstructed. Two-frequency profile reflectometry is discussed and results of modeling of this type of reflectometer measurement for TFTR are shown. Finally, the design of the TFTR edge profile reflectometer microwave system is described.
Computer-controlled system designed to measure photodegradation of photochromic compounds
Authors: Dubest R. , Levoir P. , Meyer J. J. , Aubard J. , Baillet G. , Giusti G. , Guglielmetti R.
Published: July 2002

In this paper, we describe a new, entirely computer-controlled apparatus designed for degradation studies of photochromic compounds. Photodegradation can be performed in three different ways using, in addition to the usual flash mode, the cyclic and continuous modes which more closely simulate daylight exposure conditions. In each mode, the ‘‘fatigue resistance’’ parameter is computed. Moreover, the spectrokinetic parameters of photomerocyanine species can be obtained from the kinetic mode. Due particularly to the fully computer-controlled experimental setup, the between-day reproducibility of the initial absorbance and fatigue resistance determinations are better than 4% and 6%, respectively. Owing to the modular design of the menu-driven software, written in C language, the apparatus is very flexible and easy to use.
Hydrogen and deuterium ion species mix and injected neutral beam power fractions of the TEXTOR–PINIs for 20–60 kV determined by Doppler shift spectroscopy
Authors: Uhlemann R. , Hemsworth R. S. , Wang G. , Euringer H.
Published: July 2002

The ion species fractions of the multimegawatt neutral beam ion sources for Torus Experiment for Technological Oriented Research (TEXTOR) were determined by Hα/Dα-light Doppler shift spectroscopy. The ion sources are modified Joint European Torus (JET) plug in neutral injectors (PINIs) with a three-grid acceleration system and a magnetic field in the plasma box produced by permanent magnets in checkerboard arrangement. The ion species mix of the extracted beam was measured for energies of 20–60 keV and beam currents of 13–100 A of hydrogen and deuterium produced by the two ion sources (PINI) mounted on the neutral beam injectors of TEXTOR. The maximum H+/D+ fraction at full power operation is 66%–69%. No significant difference between the two ion sources was found. The results of the hydrogen ion species mix are in good agreement with prior optical and momentum analysis made on the NI-Testbed. The additionally measured dependence of the extracted species mix from the source gas pressure is small in the pressure range above 3 μbar where the ion sources are usually operated. Measurements over the beam pulse length from 0.1 to 3 s show no change in the species mix. For calculating the deuterium ion species mix at low energies, several cross sections for Hα-light excitation, charge exchange, and dissociation available from the literature were extrapolated to about 3 keV per nucleon.

The correction factors used for calculating the ion species fraction from the ratio of the relevant integrated Doppler shift light peaks are given as a function of the gas target density in the neutralizer and of the energy per nucleon. The optical spectrometers specially designed and constructed for neutral beam Hα-light Doppler shift spectroscopy give a sufficient resolution of 1 Å and enough light intensity also at smaller beam energies and currents. The subsequent injected neutral beam power fractions H0(E), H0(E/2), and H0(E/3) and the molecular fractions H02(E) and H02(2/3E) are given as a function of acceleration voltage considering the beam line transmission and 90% of equilibrium gas target density. The injected full energy neutral beam component at 55 keV is for hydrogen 48% or 0.7 MW and 66% or 1.1 MW for deuterium.
A computer program to analyze x-ray diffraction films
Authors: Nguyen Jeffrey H. , Jeanloz Raymond
Published: July 2002

We have developed a Macintosh computer program to analyze Debye–Scherrer x-ray powder diffraction films digitized with a conventional scanner. The program uses a fast derivatives-free procedure to fit distorted ellipses corresponding to the diffraction rings on the film. These ellipses are collapsed into a one-dimensional plot of intensity versus scattering angle, from which one can extract information about the diffraction pattern that would have been lost in visual reading. Moreover, uncertainties are decreased by a factor of ∼30 over visual reading, and the analysis of diffraction films is reduced to a matter of minutes.
Cryogenic scanning tunneling microscope with a magnetic coarse approach
Authors: Davydov D. N. , Deltour R. , Horii N. , Timofeev V. A. , Grokholski A. S.
Published: July 2002

A compact, rigid, and reliable cryogenic scanning tunneling microscope (CSTM) with a vertical electromagnetic coarse approach system was developed. This device can be used for topographic and local tunneling spectroscopy studies at liquid nitrogen and helium temperatures. Minimal step sizes of 28 nm for the electromagnetic translation device were achieved. The additional possibility of a coarse approach operation in the inertial slip-stick mode, without electromagnets, was successfully tested, making this STM compatible with external magnetic fields. A simple technique for characterizing the STM rigidity has been developed. Preliminary data, taken with this instrument are presented, demonstrating the achievement, at liquid helium temperature, of atomic resolution for topographic studies, and also the possibility of measuring simultaneously superconducting energy gap spectra.
Low-temperature scanning tunneling microscope with a reliable piezoelectrical coarse approach mechanism
Authors: Altfeder I. B. , Volodin A. P.
Published: July 2002

The design of a compact low-temperature scanning tunneling microscope (STM) with a reliably operated piezoelectrical coarse approach system is described. The tip translation device is based on a new principle of sequential and parallel longitudinal step motions of the balanced frictional supports of the STM tip. The instrument was successfully tested in a temperature range from 0.4 to 300 K. The design is well suited for low-temperature applications.
Thermal anemometry for mass flow measurement in oscillating cryogenic gas flows
Authors: Rawlins Wayne , Radebaugh Ray , Timmerhaus Klaus D.
Published: July 2002

Constant temperature anemometers and resistance temperature detectors have been adapted to measure the instantaneous mass flow rates and temperatures in oscillating gas flows at frequencies up to 30 Hz and temperatures down to 70 K. These devices were used to study the behavior of the oscillating working fluid (helium) in a regenerative refrigerator called an orifice pulse tube refrigerator with little intrusion in the system. The probes have proved to be very robust with no probe breakage even under the severe operating conditions imposed by the oscillating mass flow. Calibration procedures are presented for correcting the anemometer output associated with the oscillating temperatures and pressures in such systems. Under these conditions the sensors appear to have an uncertainty of less than 1.6%. Typical results obtained with these sensors are presented in this paper. These sensors could be used in many other applications for studies of oscillating systems where instantaneous mass flow rates and temperatures are required.
Dynamics of piezoelectric tube scanners for scanning probe microscopy
Authors: Taylor M. E.
Published: July 2002

This article considers the equations of motion of piezoelectric tubes used as transducers in scanning tunneling microscopy and other scanning probe microscopies. Solutions for the dynamics responses of the tube are obtained for both extension and bending. The lowest frequency resonances are found for some common designs of tube scanner, and the results compared with available experimental data. It is shown that the response is determined by the load carried by the tube, as well as by its material properties and geometry.
Constant-fraction circuits for picosecond photon timing with microchannel plate photomultipliers
Authors: Cova S. , Ghioni M. , Zappa F. , Lacaita A.
Published: July 2002

Since single-photon pulses of photomultiplier tubes (PMTs) have statistically fluctuating amplitude, constant-fraction trigger circuits (CFTs) are normally employed for accurate timing. However, with the subnanosecond signals of microchannel-plate types (MCPs) nonideal CFT behavior is observed. A residual amplitude-dependent time walk sets the ultimate resolution in time-correlated photon counting (TCPC). We present a quantitative analysis of the problem and discuss published results. We assess the effect of pulse shaping filters and derive criteria for selecting the fast preamplifier. For MCP models with 40-ps intrinsic resolution, we show that by changing the pulse delay and attenuation ratio in the available CFTs, with minor circuit modifications, the residual time walk is strongly reduced and the detector performance can be fully exploited. For faster MCP types, with 20-ps resolution or better, the improvement is also remarkable, but we show that there is margin for further improvement and we point out criteria for designing new CFTs.
Nonaerodynamic sabot stripper for research gas gun
Authors: Mock W. , Holt W. H.
Published: July 2002

A nonaerodynamic sabot stripper has been designed and implemented for use with a 40.00-mm smooth bore research gas gun. The stripper consists of several metal parts to stop and contain the sabot while allowing the carried object to pass unhindered through it. The single-piece sabot is stopped by impacting replaceable layers of 19-mm-thick aluminum and steel plates and 3.2-mm-thick rubber sheets. The metal plates and rubber sheets have 25.4- and 31.8-mm diam holes, respectively, for passage of the carried object. The sabot stripper is located 230 mm from the muzzle of the gas gun and is aligned before each shot using a special metal fixture that is inserted into the gun muzzle. Cubes measuring 12.7 mm have been launched in a flat-faced orientation. Targets consisting of 76.2 mm×76.2 mm plates of various thicknesses are positioned in an assembly that attaches to the sabot stripper and is located 57 mm behind it. The velocity range for the experiments was from 0.61 to 0.94 km/s.
Three-dimensional probe reconstruction for atomic force microscopy
Authors: Vesenka James , Miller Richard , Henderson Eric
Published: July 2002

Colloidal gold particles are used as hard, spherical imaging targets to assist in the three-dimensional reconstruction of the atomic force probe apex. Probe reconstructions are shown to be accurate to 1 nm resolution and dynamically change as the sample is scanned, emphasizing the utility of colloidal gold particles as in situ calibration standards for image reconstruction of a coadsorbed specimen.
Atomic velocity distributions in a hydrogen beam effusing out of a radio frequency discharge dissociator
Authors: Jaduszliwer Bernardo , Chan Yat C.
Published: July 2002

We have measured atomic hydrogen velocity distributions in an effusive beam coming out of a rf discharge dissociator by using a magnetic deflection technique. Dissociator pressures varied between 0.028 and 0.340 Torr. At low dissociator pressures the measured atomic velocity distributions were narrower than the expected beam Maxwellians; at higher pressures they were indistinguishable from beam Maxwellians at the dissociator wall temperature, indicating full thermalization of the atoms prior to exiting the dissociator. Monte Carlo simulations of the thermalization process within the dissociator reproduce these results, and point out the important role of vibrational excitation of the background hydrogen molecules as an energy loss mechanism. Our results are significant when designing magnetic state selectors for spin- or hyperfine-polarized atomic hydrogen beams.
Compact substrate heater for use in an oxidizing atmosphere
Authors: Jones T. E. , McGinnis W. C. , Briggs J. S.
Published: July 2002

A compact heater, designed for the deposition of thin films at high temperatures in an oxidizing atmosphere or in vacuum, is described. The heater, including an oxygen-resistant case and the attached substrate, can be loaded into a vacuum deposition chamber through a small-diameter load-lock port, and will operate in 0–1 atm of oxygen at temperatures up to at least 800 °C. Heat is generated resistively, and the substrates are heated directly by thermal conduction. The heater was built specifically to heat substrates during the growth of high-temperature superconducting thin films.
Micromachined 1–3 composites for ultrasonic air transducers
Authors: Haller M. I. , Khuri-Yakub B. T.
Published: July 2002

Airborne ultrasound has many applications, such as robotic sensing, NDE, and gas flow measurements. Coupling of ultrasound into air from plane piston piezoelectric transducers is inefficient because of the large impedance mismatch between the piezoelectric and air, and the lack of appropriate matching materials. Standard design practice requires the use of a matching layer material with an acoustic impedance of approximately 0.02 MRayls and a thickness of a quarter-wavelength. Such materials are not readily available. A method to manufacture low impedance materials using micromachining techniques for matching piezoelectrics into air are presented here. These materials are capped 1–3 composites of air and Kapton(R). The acoustic effect of the cap is significant and necessitates a modified design technique. This technique involves the use of two matching layers with inverted acoustic impedances. Using the new fabrication technology and the new design technique, an 860-kHz transducer was fabricated with a one-way insertion loss of 17 dB and a fractional 3 dB bandwidth of 6%. It is believed that, using this technology, a transducer with a one-way insertion loss of 10 dB and a fractional bandwidth of 10% is possible.
Some observations of the effect of magnetic field and arc current on the vacuum arc ion charge state distribution
Authors: Paoloni Frank J. , Brown Ian G.
Published: July 2002

The charge state distribution of ions produced in a vacuum arc plasma has been investigated for cathode materials Ti, Sn, and Pt as a function of arc current and magnetic field strength in which the arc is located. A vacuum arc ion source was used in combination with a time-of-flight charge state diagnostic. It was found that the arc impedance and the ion charge states increase substantially with magnetic field strength. While there was effectively no variation of charge state distribution with arc current for the case of zero applied field, there was a significant increase in the charge states with arc current when the applied magnetic field was 1 kG.
Synchrotron-radiation plane-wave GID topography (abstract)
Authors: Novikov D. V. , Gog T. , Griebenow M. , Materlik G.
Published: July 2002

X-ray-diffraction topography is a traditional tool for investigating the real structure of crystals and provides high sensitivity to lattice constant variations with good space resolution. However, recent advances in technology and the growing importance of surface regions of single-crystal and multilayer systems require new approaches to this method, which are made possible by the high brightness and wide tunability of synchrotron radiation. In this work the SR plane-wave grazing-incidence diffraction (GID) topography is discussed as an effective tool for depth-resolved investigations of near-surface defect structures in single crystals and epitaxial layers. The favorable properties of synchrotron radiation enable one to avoid the usual limitations on applicability of this diffraction geometry and investigate all classes of defects in real materials. The experiments were performed at the beamlines ROEMO1 and CEMO of HASYLAB, using double-crystal Ge/asymmetric Si monochromators. The image formation of near-surface dislocations and the effects of refraction on rough surfaces were investigated. Oblique diffraction planes were used to compare the topography in skew incoplanar and coplanar geometries. The latter is shown to be more effective, as it utilizes the wavelength tunability of SR and allows one to vary the diffraction conditions in a wide range from usual highly asymmetric to grazing incidence below the critical angle of total external reflection (and the penetration depth from hundreds to tens of nanometers) without off-plane rotations and provides pictures free of complicated geometrical distortions.

The dislocation images at different diffraction conditions proved to be qualitatively the same for near-surface defects, while the structure distortions, produced by the defects in the underlying layers, become invisible at grazing incidence, due to both depth resolution of the method and inevitable loss of lattice-parameter resolution. This might be a substantial advantage for characterization of films on substrates with a low perfection. Thus SR based plane-wave GID topography provides all the features of usual asymmetric topography and has substantial advantages for surface defect analysis.
A spin rotator for detecting all three magnetization vector components by spin-polarized scanning electron microscopy
Authors: Kohashi Teruo , Matsuyama Hideo , Koike Kazuyuki
Published: July 2002

A spin rotator for observing magnetic domains with all three magnetization components of a sample surface by spin-polarized scanning electron microscopy (spin SEM) has been developed. The spin rotator is placed between the sample and the spin detector in a spin SEM, and can rotate the polarization vector of secondary electrons by π/2. Although the spin detector itself can detect only two independent polarization components, the rotation of polarization makes third-component detection possible. The conventional spin rotator, which is a well-known energy filter named a Wien filter, has been much improved to have a large focusing area by using hyperbolic cylindrical pole pieces as a magnet and several auxiliary electrodes. As a result, all the secondary electrons emitted from the area of a surface as large as 1 mm in diameter can pass the spin rotator with uniform spin rotation, and the distribution of all three magnetization components can be imaged successfully by spin SEM.
Measurement of 14 MeV neutrons at TFTR with Si-diode detectors
Authors: Ruskov E. , Heidbrink W. W. , Duong H. H. , Roquemore A. L. , Strachan J. D.
Published: July 2002

A detector system based on partially depleted silicon surface barrier detectors and fast front-end electronics has been built and cross calibrated to a set of absolutely calibrated 4He recoil detectors. The cross-calibration factor for the channel with the widest dynamic range is 2.5×10−13 counts per 14 MeV source neutron. These data agree well with the independent neutron activation data. The new detector system covers a large dynamic range (corresponding to 1013–1018 neutrons/s). The response is linear, except at the highest count rates where the detector dead time (∼200 ns) causes departure from linearity. The noise discrimination against 2.5 MeV neutrons and γ pileup is excellent. Measurements of D-T neutrons from a tritium gas puff experiment as well as from a high-power D-T discharge in the TFTR tokamak are presented.
Review of drive symmetry measurement and control experiments on the Nova laser system (invited)
Authors: Hauer A. , Delamater N. , Ress D. , Hsing W. , Suter L. , Powers L. , Landen O. , Harris D. , Thiessen R. , Magelssen G. , Lindman E. , Phillion D. , Amendt P. , Watt R. , Hammel B.
Published: July 2002

Good radiation drive symmetry is crucial for achieving ignition in laboratory inertial fusion experiments. X-ray drive symmetry in hohlraums has been the subject of investigation for more than four years and a great deal of progress has been made. Over the last two to three years, a concerted series of (indirect) drive symmetry experiments has been performed on the Nova laser system and is the subject of the present paper. The goals of this work have been to develop measurement techniques and to apply them to symmetry variation and control experiments. The principal diagnostic has utilized the symmetry signature impressed on the dense core of a target imploded by the hohlraum x-ray environment. The core is distorted by drive asymmetries and x-ray imaging of this core provides a mapping that can be compared with theoretical modeling and thus related to specific amounts of drive asymmetry. We will describe the instruments and measurement techniques used in these experiments and present representative data analysis.
Optical distance meter using a short pulse width laser diode and a fast avalanche photodiode
Authors: Araki Tsutomu
Published: July 2002

An accurate optical distance meter that features a pulsed laser diode as a light source and two avalanche photodiodes as detectors, is reported. A cascade connection of avalanche transistors drives the laser diode to emit a periodic output pulse of 0.8 ns rise time. The photodiode rise time was found to increase whenever the incident intensity decreased below a certain threshold. Measurement errors caused by this effect were corrected by numerical processing. The optical distance meter yielded a calibration error of 0.5 mm for a white paper target placed 1 m from the laser source. The distance meter was also utilized to profile the bottom of a plastic waterpipe.
Calibration and correction of distortions in two-dimensional detector systems (abstract)a)
Authors: Hammersley A. P. , Svensson S. O. , Thompson A. , Graafsma H. , Kvick Å. , Moy J. P.
Published: July 2002

A modular system of techniques and software has been developed for the calibration and correction of intensity linearity, uniformity of response, spatial distortion, and image plate decay. With calibration the Molecular DynamicsTM Imaging Plate scanner system has been shown to give comparable results to the MarResearchTM scanner. The ESRF x-ray image intensifier/charge-coupled device detectors inherently cause large spatial and uniformity of response distortions, and successful data analysis depends on calibration and correction. Results of synchrotron radiation experiments are presented.
A one-dimensional numerical study of ultrashort-pulse reflectometrya)
Authors: Cohen Bruce I. , Afeyan Bedros B. , Chou A. E. , Luhmann Neville C.
Published: July 2002

This article presents a first analysis elucidating theoretical aspects of ultrashort-pulse reflectometry. It is studied by means of the numerical integration of a one-dimensional full-wave equation for ordinary modes propagating in a plasma. The numerical calculations illustrate the potential of using the reflection of ultrashort-pulse microwaves as an effective probe even in the presence of significant density fluctuations. The difference in time delays of differing frequency components of the microwaves can be used to deduce the density profile. The modification of the reflected pulses in the presence of density fluctuations is examined and can be understood based on considerations of Bragg resonance. A simple and effective profile-reconstruction algorithm using the zero crossings of the reflected pulse and subsequent Abel inversion is demonstrated. The robustness of the profile reconstruction algorithm in the presence of a sufficiently small amplitude density perturbation is assessed.
A combined thermal dissociation and electron impact ionization source for radioactive ion beam generationa)
Authors: Alton G. D. , Williams C.
Published: July 2002

The probability for simultaneously dissociating and efficiently ionizing the individual atomic constituents of molecular feed materials with conventional, hot-cathode, electron-impact ion sources is low and consequently, the ion beams from these sources often appear as mixtures of several molecular sideband beams. This fragmentation process leads to dilution of the intensity of the species of interest for radioactive ion beam (RIB) applications where beam intensity is at a premium. We have conceived an ion source that combines the excellent molecular dissociation properties of a thermal dissociator and the high ionization efficiency characteristics of an electron impact ionization source that will, in principle, overcome this handicap. The source concept will be evaluated as a potential candidate for use for RIB generation at the Holifield Radioactive Ion Beam Facility, now under construction at the Oak Ridge National Laboratory. The design features and principles of operation of the source are described in this article.
Time resolved side scatter diagnostics at NOVA
Authors: Kyrala George A. , Evans Scott , Jimerson Johnny , Fernandez Juan
Published: July 2002

Side scattering of radiation during the interaction of a laser beam with the long scale length plasma in a hohlraum is a difficult problem that is relevant to the viability of inertial confinement fusion. It is important to measure the absolute amount of laser side scatter as well as the angular distribution of that scatter. The oblique scatter array (OSA) diagnostics have been implemented on NOVA to measure these quantities. We have used a fiber-optically coupled streak camera to measure the temporally and angularly resolved side scatter radiation at 351 nm at nine different angles. Filtered PIN diodes were positioned at 31 various angles in the E-field plane and B-field plane of the incident probe beam to sample and measure the scattered radiation at the 351 nm wavelength of the probe. The diode data was used to calibrate the Brillouin power received by the nine strategically located fiber optic channels. This presentation describes the OSA and associated diagnostics.
Design and simulation of a broadband, high speed quasioptical beam switch array for moderate pulse reflectometry
Authors: Jiang F. , Zhang W.-M. , Chen Z.-T. , Domier C. W. , Luhmann, Jr. N. C.
Published: July 2002

High speed, high on-off contrast ratio switches utilizing beam control grid array technology are under development for use in moderate pulse reflectometry. This approach, which utilizes arrays consisting of hundreds of Shottky varactor diodes embedded within an overmoded wave guide, is expected to generate switching times in the 100–500 ps range with high power handling capabilities. The switches are designed for initial wideband operation in V band (50–75 GHz) operation although they can be operated both at lower and higher frequencies, and are intended for use in a moderate pulse reflectometry system such as used on the RTP tokamak.
Upgrade of the RFX CO2 interferometer using in-vessel optics for extended edge resolution
Authors: Innocente P. , Martini S. , Canton A. , Tasinato L.
Published: July 2002

The extension to 16 chords of the eight-chord two-color MIR interferometer of the RFX reversed field pinch experiment (R=2 m, a=0.46 m) is presented. The new measurements are done through a 100 mm equatorial port with beams which are reflected back by corner cube metal mirrors mounted inside the vacuum vessel. Moreover, for four of the new chords, the beams are also steered by copper mirrors mounted inside the access pipe, whose edges are at 20–30 mm from the plasma surface. In this way measurements along lines of sight that are at a mean distance of 67 and 21 mm from the vessel first wall are possible. This results in a significant improvement of the density profile reconstruction towards the plasma edge. All the optics inside the vacuum vessel are fixed and the beam layout and focusing have been optimised to take in the misalignments due to the vacuum vessel thermal deformations. The system proved to work well despite mechanical vibrations as large as ≈1.5 mm at frequencies of ≈200 Hz. Stability of alignment and survival of the optics in the proximity of the plasma is also satisfactory.
Mode number identification with a soft x-ray array
Authors: Kaita R. , Sesnic S.
Published: July 2002

In tokamak plasmas, a key element in the understanding of magnetohydrodynamic (MHD) instabilities is the determination of their toroidal and poloidal mode numbers. This is usually accomplished by correlating measurements of radiation, particles, or magnetic oscillations at separate positions toroidally and poloidally around the torus. It is possible, however, to obtain the same information with arrays of soft x-ray detectors viewing the horizontal midplane and the poloidal cross section of the tokamak from a single location. The perturbation due to an MHD mode on a toroidal shell will modulate the soft x-ray emission along sightlines intersecting it. The number of maxima, and the angular separation between the channels detecting them, have a straightforward geometrical relationship to the mode number. This approach thus avoids the need for complex inversion of line-integrated signals. The method has already been used to determine poloidal mode numbers on the Princeton beta experiment-modification tokamak, and the results will be presented.
Time-dependent electron temperature diagnostics for high-power, aluminum z-pinch plasmas
Authors: Sanford T. W. L. , Nash T. J. , Mock R. C. , Spielman R. B. , Seamen J. F. , McGurn J. S. , Jobe D. , Gilliland T. L. , Vargas M. , Whitney K. G. , Thornhill J. W. , Pulsifer P. E. , Apruzese J. P.
Published: July 2002

Time-resolved x-ray pinhole photographs and time-integrated radially resolved x-ray crystal-spectrometer measurements of azimuthally symmetric aluminum-wire implosions suggest that the densest phase of the pinch is composed of a hot plasma core surrounded by a cooler plasma halo. The slope of the free-bound x-ray continuum, provides a time-resolved, model-independent diagnostic of the core electron temperature. A simultaneous measurement of the time-resolved K-shell line spectra provides the electron temperature of the spatially averaged plasma. Together, the two diagnostics support a one-dimensional radiation–hydrodynamic model prediction of a plasma whose thermalization on axis produces steep radial gradients in temperature, from temperatures in excess of 1 kV in the core to below 1 kV in the surrounding plasma halo.
One- and two-dimensional simulations of ultra-short-pulse reflectometry
Authors: Cohen Bruce I. , Kaiser Thomas B. , Garrison John C.
Published: July 2002

Ultra-short-pulse reflectometry is studied by means of the numerical integration of one- and two-dimensional full-wave equations for ordinary and extraordinary modes propagating in a plasma. The numerical calculations illustrate the use of the reflection of ultra-short-pulse microwaves as an effective probe of the density or magnetic profile in the presence of density or magnetic fluctuations in the plasma. Bragg resonance effects can be identified in the reflected signals, which give information on fluctuations. It is also demonstrated that ultra-short-pulse reflectometry can be used to perform correlation reflectometry measurements in which correlation lengths for density fluctuations are deduced from the observed cross-correlation function of phase shifts as a function of frequency.
Dynamic pulsed plasma reactor for chemical vapor deposition of advanced materials
Authors: Sanner Mark A. , Park Jin Y.
Published: July 2002

A dynamic pulsed plasma reactor (DPPR) capable of chemical vapor deposition of advanced materials on substrates located in a supersonic expansion nozzle is described. The DPPR combines plasma, shock tube, and supersonic expansion nozzle techniques in obtaining vapor phase quenching rates of 107–108 K/s for nanometric particle size formation. Deposition of Ti(s) and TiN(s) from Ar–TiCl4, Ar–H2–TiCl4, and N2–H2–TiCl4 reactants were experimentally investigated with deposition products characterized by scanning electron microscopy, atomic force microscopy, and energy dispersive x-ray analytical techniques. Theoretical gas dynamics describing wave motion and propagation of reactants in the DPPR are presented and resulted in identifying deposition mechanisms of homogeneous and heterogeneous nucleation for Ti(s) and TiN(s) on Pyrex substrates, respectively. This article describes reactor design, operating characteristics, and theoretical wave dynamics in the experimental system.
Thermal conductivity measurement of microgram whiskers
Authors: Verebelyi D. T.
Published: July 2002

A method of measuring the thermal conductivity of 25 μm wire and of single crystals with dimensions less than 1000×100×10 μm3 is described using the classic longitudinal steady-state method. Data from a Pb-doped Bi2Sr2Ca1Cu2Ox (Bi-2212) whisker is verified with Nb, Pt, and Au standards. Careful application of temperature matching shielding and microthermocouples have produced an absolute measurement with an error less than 25% over the temperature range 30–200 K. A complete accounting of significant errors is reported.
Transfer function analysis of the constant voltage anemometer
Authors: Sarma Garimella R.
Published: July 2002

The transfer function for the constant voltage anemometer (CVA) circuit has been derived in terms of circuit and hot-wire parameters and the expressions for the natural frequency and damping ratio have been obtained. Bandwidth in each case was determined from the plot of the normalized transfer function. The theoretical bandwidth behavior calculated from the transfer function plots for the prototype agrees with independent tests of the prototype using laser radiation heating of the hot wire in an air jet. The near constant value of the bandwidth of the CVA with the variation in the hot-wire overheat and its Reynolds number that were observed with the laser tests have been substantiated with the theoretical values from the transfer function. Bandwidth testing with sine wave injection, in situ time constant measurement for proper compensation setting, method to optimize the design to have nearly a constant bandwidth even with different compensation time constants and the operational advantages of CVA are also discussed.
A scanning transmission x-ray microscope for materials science spectromicroscopy at the advanced light source
Authors: Warwick T. , Franck K. , Kortright J. B. , Meigs G. , Moronne M. , Myneni S. , Rotenberg E. , Seal S. , Steele W. F. , Ade H. , Garcia A. , Cerasari S. , Denlinger J. , Hayakawa S. , Hitchcock A. P. , Tyliszczak T. , Kikuma J. , Rightor E. G. , Shin H.-J. , Tonner B. P.
Published: July 2002

Design and performance of a scanning transmission x-ray microscope (STXM) at the Advanced Light Source is described. This instrument makes use of a high brightness undulator beamline and extends the STXM technique to new areas of research. After 2.5 years of development it is now an operational tool for research in polymer science, environmental chemistry, and magnetic materials.
Characterization of an x-ray radiographic system used for laser-driven planar target experiments
Authors: Smalyuk V. A. , Boehly T. R. , Bradley D. K. , Knauer J. P. , Meyerhofer D. D.
Published: July 2002

We have characterized the sensitivity, resolution, and noise of an x-ray radiographic system. Using this information we have formulated a Wiener filter that reduces noise, compensates for detector resolution, and facilitates measurement of perturbations in laser-driven targets.
Interfacing a transient digitizer to a step-scan Fourier transform spectrometer for nanosecond time resolved spectroscopy
Authors: Letendre Laura T. , Dai Hai-Lung , McLaren Ian A. , Johnson Timothy J.
Published: July 2002

A new signal processing and data acquisition system has been developed that allows a Fourier transform spectrometer to be interfaced to external transient digitizers for time-resolved spectroscopy. Time resolution is limited only by the transient digitizer and detection system response time. For the present system it is about 1 ns. The capabilities of this system are demonstrated with visible Fourier transform spectra of both scattered laser light and fluorescence from electronically excited NO2 gas.
Improved performance of the Thomson scattering system in RFX
Authors: Pasqualotto R. , Sardella A. , Intravaia A. , Marrelli L.
Published: July 2002

A Thomson scattering diagnostic is used in the RFX reversed field pinch experiment to measure single pulse, multipoint electron temperature (Te) profiles. Recent significant improvements have provided reliable and routine operation of the diagnostic. Custom developed CAMAC charge analog-to-digital converters have been introduced, which sample the plasma light 170 ns after the laser light and have greater sensitivity. The spectrometer configuration and the calibration procedure have been optimized. These upgrades have finally led to better fitted scattering spectra and more regular estimates of Te profiles, allowing the measurement of temperatures as low as 20 eV. The introduction of a second spectrometer has recently added a further ten positions to the original ten point profile, resolving the often steep Te edge gradient. On axis values are in good agreement with other Te measurements from SXR diagnostics (either SiLi and double filter method). Te profiles are typically rather flat, but some dependence on the plasma parameters, like density and pinch parameter, has been drawn. Significant Te profile modifications have been observed during transient events like pulsed poloidal current drive and pellet injection. The diagnostic will be completed soon, allowing production of 27 point profiles, with the introduction of the third spectrometer. Double pulse operation of the laser is in progress.
Fast beam photofragment apparatus for studies of electronic and nuclear dynamics
Authors: Pedersen H. B. , Jensen M. J. , Safvan C. P. , Urbain X. , Andersen L. H.
Published: July 2002

A new fast beam photofragment apparatus for studies of electronic and nuclear dynamics is described. The experimental setup involves a chopped ion beam crossed at 90° by a pulsed laser beam. Photofragments are extracted parallel to the ion beam direction and imaged on a multisphere plate (MSP) detector. The time of flight of a photofragment from the interaction point to the MSP detector is determined by a coincidence technique. The setup allows determination of the photofragment energy and the direction of emission for each event of photofragmentation. In photoelectron spectrometry the energy resolution is tunable down to the meV region. For testing, the apparatus has been applied to photodetachment of Li−(1S) at 1064 nm.
Photoemission electron microscope for the study of magnetic materials
Authors: Anders Simone , Padmore Howard A. , Duarte Robert M. , Renner Timothy , Stammler Thomas , Scholl Andreas , Scheinfein Michael R. , Stöhr Joachim , Séve Laurent , Sinkovic Boris
Published: July 2002

The design of a high resolution photoemission electron microscope (PEEM) for the study of magnetic materials is described. PEEM is based on imaging the photoemitted (secondary) electrons from a sample irradiated by x rays. This microscope is permanently installed at the Advanced Light Source at a bending magnet that delivers linearly polarized, and left and right circularly polarized radiation in the soft x-ray range. The microscope can utilize several contrast mechanisms to study the surface and subsurface properties of materials. A wide range of contrast mechanisms can be utilized with this instrument to form topographical, elemental, chemical, magnetic circular and linear dichroism, and polarization contrast high resolution images. The electron optical properties of the microscope are described, and some first results are presented.