bluuebunny/crossref_metadata_2025 huggingface dataset:
New time-of-flight mass spectrometer for improved mass resolution, versatility, and mass spectrometry/mass spectrometry studies
Authors: Pinkston J. David , Rabb Martin , Watson J. Throck , Allison John
Published: July 2002

Reported here is the design and experimental investigation of the performance characteristics of a new time-of-flight (TOF) mass spectrometer. The instrument combines the advantages of beam deflection for ion pulse formation with an electrostatic analyzer which reduces the energy spread of the ions admitted to the TOF region. The instrument is able to use ion sources which cannot be pulsed on a time scale suitable for conventional TOF analysis (e. g., chemical ionization sources). Improved mass resolution is demonstrated over a wide mass range such that all of the ions are in focus simultaneously. A resolution of 982 (full width at half-maximum) is achieved for the molecular ion peak of perfluorotributylamine at m/z 614. A preliminary investigation of a proposed technique for collecting information typically obtained by tandem mass spectrometry (MS/MS) has also been conducted using this instrument. This new method, named time-resolved ion kinetic energy spectrometry (TRIKES), combines time-of-flight (velocity) and kinetic energy analysis of undissociated parent ions and daughter ions which are products of decompositions occurring between the ion source and electrostatic analyzer. Unit resolution of the daughter ions produced upon metastable decomposition of the molecular ion of n-decane has been achieved in constant parent scans. The realization of rapid time-of-flight data collection rates in TRIKES may yield improved data collection rates in MS/MS.
Magnetic field homogeneity correction algorithm using pseudoinversion formula for NMR imaging
Authors: Ahn C. B. , Jo J. M. , Cho Z. H.
Published: July 2002

A systematic approach to passive shimming is proposed, and has been tested experimentally using a simultaneous gradient cancellation technique. In finding coil adjustments to correct gradients, the iterative application of the pseudoinverse (or generalized inverse) technique is used and a solution provided at each step. Each solution consists of a set of optimum values of adjustments. If the degree of freedom for adjustments is larger than the number of gradients to be corrected, the solution is the minimum norm solution. Through computer simulations, the algorithm is found to converge to a magnetic field homogeneous enough to allow nuclear-magnetic-resonance (NMR) imaging in only a few steps even in the presence of internal imperfections and misalignments as large as several 10 mm and an external asymmetric field affecting materials as near as a few meters. High homogeneity as well as fast convergence to a uniform magnetic field has been confirmed experimentally with the KAIS 1.5-kG magnet. By use of the proposed algorithm, we have experimentally obtained a field homogeneity of a 1.5-kG resistive magnet twice as homogeneous as that of the specified value with only a few iterations. Although it has been tested in the available low magnetic field, there are no restrictions in applying the technique to various magnets including superconductive magnets widely used in NMR imaging (in this case the algorithm is applied at the assembly stage).
Compact and reliable discharge-pumped XeCl laser with automatic preionization
Authors: Hiramatsu Mineo , Goto Toshio
Published: July 2002

A compact discharge-pumped XeCl laser is described with high efficiency and reliability at low operating pressures below 2 atm. Using 65.8% Ne, 30.0% Ar, 4.0% Xe, and 0.2% HCl mixture, the maximum total efficiency of 0.9% was obtained at the total gas pressure of 1.8 atm and the charging voltage of 18 kV. That efficiency was fairly high for the low operating pressure and the compact size of the laser chamber. The shot-to-shot reproducibility of the laser pulse was excellent, and the laser energy stability was within ±4%.
Inexpensive fine point pen system for H-P, Tektronix, and Wang plotters
Authors: Spielberg Johanan Isaac
Published: July 2002

The construction of a simple plotter pen holder that uses BIC fine and medium point pens is described.
Development of a reliable fast response laser-triggered dielectric switch
Authors: Kanabe T. , Yoshida K. , Kato Y. , Nakatsuka M. , Yamanaka C.
Published: July 2002

Detailed performances of a laser triggered dielectric switch (LTDS) are described. Thin polypropylene films of 25 or 35 μm in thickness were used for insulation of the spark gap. Maintenance-free operation was achieved by automatic winding of the film after each laser shot. A square optical pulse of 1 ns duration with a rise time of less than 350 ps was generated by using a fast Pockels cell driven by the LTDS with good reproducibility. The switching jitter was measured to be less than the detection limit of 100 ps. Using the LTDS, a single pulse was selected from a mode-locked pulse train with the success probability of better than 95%. Comparison of the performance of the LTDS with other switching devices are given.
Annealing furnace for III-V semiconductor devices
Authors: O’Connor J. M. , Hier H. S. , Ketchum R. M.
Published: July 2002

A furnace for annealing ion implantation damage in III-V semiconductors has been built and tested. Designed for research applications, the furnace can accommodate odd shapes of material up to 2 in. in diameter. Samples are loaded onto a novel cantilevered support and are not moved during the annealing operation, facilitating proximity annealing techniques. Both chambers of this dual chambered system are O-ring sealed for added safety during annealing in an arsine gas ambient. Electron mobilities between 4400 and 4600 cm2/V s at 300 K are routinely measured for 2×1017 cm−3 gallium arsenide material annealed in this sytem. The system has been used to anneal indium phosphide as well as gallium arsenide wafers.
ENDOR with polarization-modulated radio frequency fields
Authors: Forrer J. , Schweiger A.
Published: July 2002

Design and construction of a broadband electron-nuclear double resonance (ENDOR) spectrometer with polarization-modulated radio frequency fields (PM-ENDOR) is reported. With this type of field configuration, each ENDOR resonance line is labeled by additional parameters so that the interpretation of complicated single-crystal ENDOR spectra may be considerably simplified. Details of the electronics and the X-band microwave cavity suitable to generate polarization-modulated rf fields in the frequency range 2–50 MHz are described. The quality of the PM field over the sample volume is investigated. Performance of the spectrometer is exemplified by applications on transition metal complexes.
Numerical simulation of electromigration-induced shape changes of voids in bamboo lines
Authors: Kraft O. , Arzt E.
Published: July 2002

Recently, it was found that electromigration-induced failure of metallic interconnects in integrated circuits occurs when rounded voids deform into narrow slitlike voids, which are often transgranular. The mechanism of this shape change is now examined by numerical simulation on the basis of electromigration-driven surface diffusion. As a result, it is found that shape change and motion of voids are competing processes. Large voids with respect to the linewidth are deformed by the electron wind whereas small voids move without any shape changes. Combining diffusional anisotropy with electron wind dynamics allows the experimentally observed faceting of even small voids to be reproduced in the simulation.
Design of a graphite element drop-tube reactor system for study of SO2 removal by injected limestone sorbents
Authors: Gullett Brian K. , Snow Gerry C. , Blom John A. , Kirchgessner David A.
Published: July 2002

The design and operation of a graphite element drop-tube reactor system for a study of the fundamental mechanisms and reaction rates of sulfur dioxide (SO2) removal by high-temperature injection of limestone-based sorbents is described. The reactor system is designed for laminar flow in an environment that allows for control of reaction temperature, sorbent particle residence time, and atmosphere composition. The sorbent injection system allows variable feed rates to as low as 1 mg/min for particles as small as 1 μm in diameter. The water-cooled sorbent collection system arrests the high-temperature reaction upon capture and allows analysis of the sorbent’s efficiency of SO2 capture and in situ particle-size distribution. The results presented show the reactivity of different types of sorbents at varying conditions of system operation.
Plasma diagnostics using an injected neutral helium beam
Authors: Levinton F. M.
Published: July 2002

A diagnostic for measurement of the internal magnetic field and the ion temperature is proposed which is applicable to the current generation of magnetic fusion devices. This technique involves the injection of a neutral helium beam into the plasma. The magnetic field can be determined from Zeeman spectroscopy of the neutral beam using laser-induced fluorescence or collisional excitation. Ion temperature measurements can be made from Doppler broadening of the charge exchange recombination radiation or elastic scattering of the beam particles. Details of the beam propagation through the plasma are solved numerically using a system of coupled rate equations. The diagnostic is suitable for a wide range of plasma and machine parameters. Results from computer simulations have been obtained for the S−1 spheromak and the tokamak fusion test reactor (TFTR) which show that ∼50% of a 20-keV beam can penetrate to the center of the plasma.
Acoustic microscopy applied to physical acoustics
Authors: Fossum J. O. , Cheeke J. D. N.
Published: July 2002

An acoustic microscope setup has been applied to determine Rayleigh wave velocities in crystals from acoustic materials signatures. The Rayleigh wave velocity close to and above the phase transition in SrTiO3 has been measured as a function of temperature. It has been shown that propane can be used as a coupling liquid between the acoustic lens and the sample enabling acoustic microscopy in the temperature region 85–220 K.
X-ray response of silicon surface-barrier diodes at 8 and 17.5 keV: Evidence that the x-ray sensitive depth is not generally the depletion depth
Authors: Wenzel Kevin W. , Petrasso Richard D.
Published: July 2002

The absolute x-ray response of 18 EG&G Ortec partially depleted silicon surface-barrier diodes (SBDs) has been measured at 8 and 17.5 keV. In addition we have examined the x-ray response of four Tennelec and two United Detector Technology partially depleted SBDs. The variation in response to 8 keV x rays, for which the optical depth is about 5, is comparatively slight (≲12%). The variation in response to 17.5-keV x rays, for which the optical depth is only ∼0.7, is comparatively large (∼100%). These variations are mainly attributable to differences in the SBD physical thicknesses, and thus to differences in optical depth. At both 8 and 17.5 keV the diodes respond linearly to large variations in incident flux (over three orders of magnitude). This linearity, and the diode x-ray response, in general, is insensitive to large changes in the detector bias voltage; thus the depletion depth, proportional to the square root of the bias voltage, does not play a critical role in determining the x-ray sensitive depth. It is important to emphasize that this finding is contrary to the commonly held belief that the x-ray sensitive depth is equivalent to the depletion depth. In addition, this result has a direct bearing on both SBD and p-i-n detectors intended for fully depleted operation, but used in an underbiased mode such that they are actually partially depleted. We conclude that SBDs have attractive features for quantitatively measuring x radiation from high-intensity sources for which hν≳10 keV.
Field inversion apparatus for gel electrophoresis
Authors: Kath Gary S. , Streicher Stanley L.
Published: July 2002

An apparatus is described which permits periodic inversion of the electric field during field inversion gel electrophoresis (FIGE) studies. The device is used in conjunction with a standard electrophoresis power supply and the gel electrophoresis cell. Adjustment of cycle period from 0.01 to 99.99 s and forward migration percent from 1% to 99% are accommodated either by local programming or from a personal computer via a RS-232C interface.
Low-cost 1-Hz resolution bandwidth spectrum analyzer in the 0.1–1000-MHz frequency range
Authors: Clays Koen , Strobbe Rik , Persoons Andre
Published: July 2002

We present a very effective, low-cost spectrum analyzer, built entirely from commercially available standard laboratory equipment. A broadband radio frequency synthesizer is used as the local oscillator input of a double-balanced diode mixer to convert the high-frequency input signal into the intermediate-frequency output of the mixer, a lower-frequency signal which is analyzed in an audio-frequency spectrum analyzer. The overall performance depends on the specifications of the frequency synthesizer, the mixer, and the spectrum analyzer. Our instrument has a resolution bandwidth of 1 Hz in the 0.1–1000-MHz frequency range with a −139-dBm sensitivity for the smallest bandwidth. Especially the single-hertz resolution bandwidth is an essential feature of our spectrum analyzer, not yet commercially available.
Optical carriage for laser-induced fluorescence in a magnetized plasma
Authors: Anderegg F. , Paris P. J. , Skiff F. , Good T. N. , Tran M. Q.
Published: July 2002

An ‘‘optical carriage’’ has been developed to improve plasma access for LIF diagnostics. Laser light inducing the fluorescence is transported through an optical fiber to the carriage. A telescope fixed on the carriage collects the plasma fluorescence light and sends it through a fiber bundle to an external PMT. The whole carriage is mounted on rails and can be scanned along and across the magnetic field.
Plasma density measurement using a simple microwave technique
Authors: Bora D. , Atrey P. K.
Published: July 2002

We describe a simple method of determining the plasma density unambiguously with the help of a microwave interferometer. The frequency of the Klystron source is modulated with the help of a staircase voltage pulse. The height of each staircase is adjusted in such a way that the corresponding phase shift is 90°. Signals proportional to the cosine and sine of the phase shift due to plasma are generated, and the plasma density is unambiguously measured. The advantages of the method are highlighted in the text.
Measurement of Zeff profiles from bremsstrahlung emission in the near infrared
Authors: Röhr H. , Steuer K. H. , Team the ASDEX
Published: July 2002

Local measurements of plasma radiation in the near infrared using the detection system of the ASDEX Thomson scattering device are reported. Comparison with hydrogen bremsstrahlung yields Zeff profiles. Good agreement with values from other diagnostics is obtained. Zeff behavior in a variety of ASDEX discharges is discussed.
High-resolution multichannel interferometric measurement of sawtooth density-pulse propagation (invited)
Authors: Kim Sung K. , Brower D. L. , Peebles W. A. , Luhmann N. C.
Published: July 2002

A unique high-resolution far-infrared multichannel interferometer system has been developed and successfully operated on the Texas Experimental Tokamak. Two sets of cylindrical parabolic mirrors are employed to expand both the local oscillator and probe beams in one dimension to cover the plasma cross section accessible through the vertical ports. A maximum of 29 mixers is configured on a linear array which provides a spatial resolution of 1.5 cm. The overall density resolution is ≤5×1010 cm−3 with a time response of 50 μs. The high resolution of the system permits detailed measurements of small-amplitude fine-structure density effects such as MHD activity during disruptions and sawteeth. Detailed observations of density-pulse propagation processes induced from sawtooth internal disruptions are described. Analysis of sawtooth density-pulse propagation measurements based on a diffusive model has led to a direct estimate of the internal electron particle diffusion coefficient.
Current response characteristics of microchannel plates x-ray detector using synchrotron radiation (0.6–2 keV and 5–20 keV)
Authors: Kondoh T. , Yamaguchi N. , Cho T. , Hirata M. , Miyoshi S. , Aoki S. , Maezawa H. , Nomura M.
Published: July 2002

The characteristics of microchannel plates (MCPs) for detection of x rays have been investigated using synchrotron radiation in the energy ranges from 0.6 to 2.0 keV and from 5 to 20 keV. Microchannel plates are operated under the condition of an unsaturated pulse-height distribution mode. The current response curve of MCPs is measured continuously with x-ray energy variation for the first time. The experimental result of some discontinuous jumps in the response is obtained at the energies corresponding to the absorption edge of the MCP materials. In the low-energy range (hν<2 keV), the dependence of the current response to the incident angle of x rays to the channel axis θ is measured to be proportional to cot θ, which is interpreted by the x-ray absorption near the surface of MCP channel wall. While, in the high-energy range (hν>5 keV), a weak dependence on θ is observed, and is attributed mainly to the penetration of x rays through multiple channels.
Diffusive trapping: An alternative to supersonic jet cooling for spectroscopic experiments?
Authors: Barnes J. A. , Gough T. E. , Stoer M.
Published: July 2002

A cell has been constructed which allows the observation of infrared spectra of nonequilibrium pressures of monomeric gaseous molecules cooled to cryogenic temperatures. Details of the performance of the cell are given, and it is suggested that this technique may be preferable to supersonic jet cooling for some applications.
A high-resolution low-energy electron diffraction instrument
Authors: Hwang Robert Q. , Williams Ellen D. , Park Robert L.
Published: July 2002

A high-resolution LEED system with optimum operating parameters for use below 100 eV has been designed and tested. A field-emission-based electron gun with an angular divergence of  2 mrad, and a large sample detector distance of 150 mm provide the major improvements in resolution. Measured beam widths (Δk/2π FWHM) for both specular and nonspecular beams are approximately 0.002 Å−1 in the energy range of 50–100 eV.
Performance of a pneumatic hydrogen-pellet injection system on the Joint European Torus
Authors: Combs S. K. , Jernigan T. C. , Baylor L. R. , Milora S. L. , Foust C. R. , Kupschus P. , Gadeberg M. , Bailey W.
Published: July 2002

A pneumatic-based, hydrogen isotope pellet injector that was developed at the Oak Ridge National Laboratory (ORNL) has been used in recent plasma fueling experiments on the Joint European Torus (JET). The injector consists of three independent machine-gun-like mechanisms (nominal pellet sizes of 2.7, 4.0, and 6.0 mm in diameter) and features repetitive operation (1–5 Hz) for quasi-steady-state conditions (>10 s). An extensive set of injector diagnostics permits evaluation of parameters for each pellet shot, including speed, mass, and integrity. Pellet speeds range from 1.0 to 1.5 km/s. Over 3700 pellets have been fired with the equipment at JET, with about 1500 pellets shot for plasma fueling experiments. In recent experiments, the system performance has been outstanding, including excellent reproducibility in pellet speed and mass, and a reliability of >98% in delivery of pellets to the plasma.
Focusing properties of Bragg-Fresnel lens in white spectrum of synchrotron radiation (abstract)
Authors: Aristov V. V. , Basov Yu. A. , Kulipanov G. N. , Pindyurin V. F. , Snigirev A. A. , Sokolov A. S.
Published: July 2002

The investigation results on details of the imaging by Bragg-Fresnel lens (BFL) in white spectrum of synchrotron radiation are presented. BFL was fabricated on a silicon single crystal with the reflecting plane (III) by the methods of microlithography and plasma-chemical etching. The relief depth of the zone structure was 3 μm, the last zone was 0.5 μm in size, the total width of the zone plate was 200 μm. The superconducting wiggler installed at the storage ring VEPP-2M was used as a source of synchrotron radiation. The experimental results on the radiation focusing at different wavelengths (λ=1÷2.5 Å) were obtained. The results include the focusing both in- and outside the focal plane of the zone plate. The results are also presented on an observation of the focusing in antibragg diffraction geometry when the orientation of Fresnel zones coincides with the vertical section of initial incident beam of radiation. The obtained results are treated analytically.
Detection characteristics of microchannel plates and gold photocathodes for plasma x-ray diagnostics [near the absorption edges (2–8) keV)] (abstract)
Authors: Cho T. , Yamaguchi N. , Kondoh T. , Hirata M. , Miyoshi S. , Aoki S. , Maezawa H. , Nomura M.
Published: July 2002

Using undulator radiation from 2 to 8 keV, quantum efficiencies [QE(E)] of gold photocathodes, microchannel plates (MCP), and silicon surface barrier (SSB) detectors have been investigated. For the gold photocathodes, the detailed structure of QE(E) near the M absorption edges has been presented. Also, the secondary electron conversion efficiency of gold has been calculated using the mass absorption coefficient given by a relativistic Hartree–Slater model and by the semiempirical values of Henke et al., respectively. Extended x-ray absorption fine structure (EXAFS) has been observed in the secondary electron current of the gold photocathode as well as in the detection current responses of an MCP and of an SSB detector. Furthermore, the new findings adding to our recent paper1 have been summarized as follows: (i) EXAFS above the Si-K edge in the MCP response depends on photon incident angles, and (ii) a little upshift of the starting point energy of EXAFS in the MCP response is observed. These detailed characteristics and their interpretation are described in the following: (i) The current responses of the MCP are obtained as a function of the incident x-ray energy for θ=13° (the bias angle of the MCP), and 40° by using a gold-monitor current. Here, θ denotes the incident angle of the photons to the channel. The data for θ=40° show a smaller jump near the Si-K edge as compared with the data for θ=13°.

This is explained as follows: The incident photons for θ=13° are irradiated to and absorbed in the MCP ingredient of SiO2, while photons for θ=40° are incident to the electrode region. (The depth of the electrode coating is more than 10 μm from the MCP surface, while the photons are absorbed at less than 8 μm from the surface for θ=40°.) Thus, the data for θ=40° strongly reflect the characteristics of the electrode, but not of SiO2. The data for several values of θ consistently indicate that the height of this jump becomes smaller with increasing θ. (ii) The observed upshift of the starting point energy of EXAFS in the MCP response presents a contrast to EXAFS in the SSB detector response, in which upshift is not observed. This upshift is ascribed to the molecular structure of SiO2 (the chemical shift); that is, some valence electrons are removed from the Si atoms due to the oxidation (i.e., SiO2). Thus, the screening effects of the valence electrons on the core electron-nucleus attraction are reduced. This results in the shift of binding energy towards the higher-energy side. On the other hand, EXAFS in the SSB detector response reflects the characteristics of Si.
Complete characterization of a Si(Li) detector in the photon energy range 0.9–5 keV
Authors: Krumrey M. , Tegeler E. , Ulm G.
Published: July 2002

The response function of a Si(Li) detector has been measured in the photon energy range 0.9–5 keV using monochromatized synchrotron radiation at a double crystal monochromator. The response is described by a hypermet function and the spectral dependence of its parameters is presented. The quantum detection efficiency of the detector is determined from measurements in the undispersed synchrotron radiation of the electron storage ring BESSY, which is a primary radiometric standard.
Calibration of semiconductor photodiodes as soft x-ray detectors
Authors: Krumrey M. , Tegeler E. , Thornagel R. , Ulm G.
Published: July 2002

A new procedure for the calibration of photon detectors is presented, based on the electron storage ring BESSY as a calculable radiometric standard source and an energy dispersive Si(Li) detector. The quantum detection efficiency of the Si(Li) detector is determined in the undispersed synchrotron radiation of BESSY, and the detector to be calibrated is compared to the Si(Li) detector in monochromatic radiation. The procedure is applied in the photon energy range from 800 to 3500 eV to calibrate semiconductor photodiodes which are promising as transfer standard detectors due to their high quantum efficiency, excellent stability in intense radiation, and insensitiveness to surface contaminations.
Higher order contributions in the synchrotron radiation spectrum of a toroidal grating monochromator determined by the use of a transmission grating
Authors: Kühne M. , Müller P.
Published: July 2002

The synchrotron radiation spectra of toroidal grating monochromators (TGM) working in the short wavelength VUV are often contaminated by significant amounts of higher orders. Even by the use of suitable filters they cannot completely be suppressed. Using a transmission grating behind the exit slit of the monochromator the exit beam can be dispersed and the contributions of the different orders analyzed. For the 162° TGM at the radiometric laboratory of PTB at BESSY the higher-order distributions have been quantitatively determined for two gratings of line densities of 200 and 600 ℓ/mm at electron beam energies of 337 and 756 MeV. It is shown that at the energy of 337 MeV and the wavelength region between 5 and 45 nm the contributions of the higher orders to the detector signal are restricted to less than 10% even without the use of filters. At the energy of 756 MeV the same result can be achieved by inserting suitable filters.
Estimations of Touschek effect and ion clearing by the decay rate plot method
Authors: Tomimasu Takio , Noguchi Tsutomu , Sugiyama Suguru , Yamazaki Tetsuo , Mikado Tomohisa , Chiwaki Mitsukuni , Nakamura Takeshi , Suzuki Ryoichi
Published: July 2002

It is demonstrated that the decay-rate plot method is a good means for estimating Touschek effect and ion clearing. The computer-processed decay-rate plot against stored current I is very useful for indicating the decay mode (I or II) changing with local pressure conditions of a storage ring and to evaluate the 1/e lifetime of the stored beam current. At decay mode I, the decay rate is roughly proportional to I2 and at decay mode II the decay rate is proportional to I. Generally speaking, the ion clearing can reduce the decay rate and longer lifetime can be achieved at the higher beam current. However, when a local- and current-independent high-pressure gas is present in a storage ring, the experimental results show that the decay mode is changed from I to II at low currents below a threshold current by ion clearing and that threshold current depends on a level of local pressure.
Surface temperature and distortion of optical elements exposed to high power synchrotron radiation beams (invited)
Authors: Mourikis S. , Jark W. , Koch E. E. , Saile V.
Published: July 2002

Mirrors made of various materials have been investigated under surface power densities of approximately 1–2 W/mm2 emitted by a powerful hybrid wiggler installed in the 5.3-GeV DORIS storage ring. Thermal inhomogeneities and deformations at surfaces with a height resolution of 50 nm have been determined quantitatively. The only material withstanding these power levels without a significant deformation is SiC. Conventional cooling geometries are found to be useless for a reduction of the surface distortion.
Synchrotron radiation focusing by a Bragg–Fresnel lens (invited)
Authors: Aristov V. V. , Basov Yu. A. , Snigirev A. A.
Published: July 2002

Since the discovery of x rays and until the present time the possibilities of their controlling and focusing have been widely discussed. In the hard spectrum region (λ∼1 Å) the main focusing schemes are the following: geometrical focusing based on incoherent interaction of wave packets reflected by different regions of bending crystals and coherent (dynamic) focusing performed at the cost of the effect of refraction index angular dispersion near the exact Bragg angle value −θB. A main disadvantage of geometrical focusing is low spatial resolution (∼0.1 mm) and temperature stability. In the case of coherent focusing a main disadvantage is a narrow angular aperture (∼10 sec. of arc) at spatial resolution (∼1–10 μm). Recently, advances in the development of diffraction physics and microstructuring technology open up possibilities for fabricating effective focusing x-ray optical elements—Bragg–Fresnel lenses (BFL)—with high spatial resolution (∼0.1 μm) at a wide angular aperture and high temperature stability. The present paper describes the main principles of Bragg–Fresnel optics (BFO). It presents the results on the synchrotron experiment and on observation of focusing. In this work the peculiarities of BFL diffraction contrast formation are investigated and image transmission using a BFL is performed. Possibilities of developing x-ray optical schemes of ultrahigh resolution on the basis of BFL elements are also discussed.
High-voltage, full-floating 10-MHz square-wave generator with phase control
Authors: Bernius Mark T. , Chutjian Ara
Published: July 2002

Wherein a fast (50 ns) rise-time high-frequency square-wave generator capable of switching between arbitrary voltages of high potential difference (1000 V or more) is described utilizing solid-state circuitry of low power consumption. Power field effect transistors are used as the active switching element, which afford compact size and simplified circuit construction. With the addition of monostable multivibrators, high-voltage square-wave pulse trains of controllable phase are produced. The generator should find application in a wide variety of situations where fast switching between high voltages is required, such as in time-of-flight, coincidence, and beams-modulation experiments.
Instrumentation for millisecond-resolution scattering studies (invited)
Authors: Stephenson G. B. , Ludwig K. F. , Jordan-Sweet J. L. , Brauer S. , Mainville J. , Yang Y. S. , Sutton M.
Published: July 2002

Time-resolved x-ray scattering studies of phase transition kinetics have been carried out using the wide-bandpass monochromator and fast linear position-sensitive detector system at the IBM/MIT beamline X-20C at the National Synchrotron Light Source (NSLS). We report here on the instrumentation that has been developed for these studies, and in particular on the methods used to measure, change, and control sample temperature with millisecond resolution.
A low cost, high performance imaging system for scanning tunneling microscopy
Authors: Brown A. , Cline R. W.
Published: July 2002

A low-cost, high-performance image acquisition and display system for scanning tunneling microscopy, based on a PC/AT compatible computer and a video frame grabber is described. The imaging system allows the use of fast scan rates and provides for viewing of the image as it is acquired. The imaging system could be used in any application involving single frame image acquisition at a rate at or below the standard video rate of 30 s−1.
Simple electromechanically operated optical shutter
Authors: Ye Mao-fu , Jiang De-yi , Wong C. S.
Published: July 2002

This note illustrates the operation of a simple optical shutter with an opening time of fractions of a millisecond. The shutter can be used to produce a square light pulse from a cw laser such as the He-Ne laser or tunable dye laser.
Real-time digital control, data acquisition, and analysis system for the DIII-D multipulse Thomson scattering diagnostic
Authors: Greenfield C. M. , Campbell G. L. , Carlstrom T. N. , DeBoo J. C. , Hsieh C.-L. , Snider R. T. , Trost P. K.
Published: July 2002

A VME-based real-time computer system for laser control, data acquisition, and analysis for the DIII-D multipulse Thomson scattering diagnostic is described. The laser control task requires precise timing of up to eight Nd:YAG lasers, each with an average firing rate of 20 Hz. A cpu module in a real-time multiprocessing computer system will operate the lasers with evenly staggered laser pulses or in a ‘‘burst mode,’’ where all available (fully charged) lasers can be fired at 50–100 μs intervals upon receipt of an external event trigger signal. One or more cpu modules, along with a LeCroy FERA (fast encoding and readout ADC) system, will perform real-time data acquisition and analysis. Partial electron temperature and density profiles will be available for plasma feedback control within 1 ms following each laser pulse. The VME-based computer system consists of two or more target processor modules (25 MHz Motorola 68030) running the VMEexec real-time operating system connected to a Unix-based host system (also a 68030). All real-time software is fully interrupt driven to maximize system efficiency. Operator interaction and (non-real-time) data analysis takes place on a MicroVAX 3400 connected via DECnet.
MDS-Plus data acquisition engine
Authors: Flor G. , Cazzaro F. , Fregonese G. , Stangherlin S.
Published: July 2002

MDS-Plus, a model driven data acquisition system being jointly developed at Istituto Gas Ionizzati, MIT Plasma Fusion Center, and Los Alamos National Laboratory, is based on the concept of an experiment model. The model contains descriptions of experiment data, devices, and actions to be performed. The data acquisition engine, i.e., the part of the system which actually executes the acquisition process, is driven by the contents of the model itself and implemented as a set of independent processes. A scheduler keeps the data acquisition engine in step with a state machine reflecting the operation of the actual experiment; a dispatcher takes care of the appropriate sequencing of the operations associated with each state of the experiment; various servers actually execute actions on behalf of the dispatcher.
Real-time digital filtering, event triggering, and tomographic reconstruction of JET soft x-ray data (abstract)
Authors: Edwards A. W. , Blackler K. , Gill R. D. , van der Goot E. , Holm J.
Published: July 2002

Based upon the experience gained with the present soft x-ray data acquisition system, new techniques are being developed which make extensive use of digital signal processors (DSPs). Digital filters make 13 further frequencies available in real time from the input sampling frequency of 200 kHz. In parallel, various algorithms running on further DSPs generate triggers in response to a range of events in the plasma. The sawtooth crash can be detected, for example, with a delay of only 50 μs from the onset of the collapse. The trigger processor interacts with the digital filter boards to ensure data of the appropriate frequency is recorded throughout a plasma discharge. An independent link is used to pass 780 and 24 Hz filtered data to a network of transputers. A full tomographic inversion and display of the 24 Hz data is carried out in real time using this 15 transputer array. The 780 Hz data are stored for immediate detailed playback following the pulse. Such a system could considerably improve the quality of present plasma diagnostic data which is, in general, sampled at one fixed frequency throughout a discharge. Further, it should provide valuable information towards designing diagnostic data acquisition systems for future long pulse operation machines when a high degree of real-time processing will be required, while retaining the ability to detect, record, and analyze events of interest within such long plasma discharges.
Recent developments in optically pumped far-infrared lasers for plasma diagnostics (abstract)
Authors: Jiang Y. , Rettig C. L. , Burns S. , Lee J. H. , Luhmann N. C. , Peebles W. A.
Published: July 2002

Optically pumped far-infrared (FIR) lasers are widely utilized in the diagnosis of fusion plasmas. Applications such as interferometry, polarimetry, and collective scattering all rely heavily on the characteristics of such lasers. In particular, the stability, available power, and wavelength of the FIR laser are extremely important in establishing system performance. This describes recent development work at UCLA directed at improving the above laser characteristics. Stability improvement is investigated via the use of a FIR ring cavity which automatically eliminates the feedback effects of CO2 pump radiation. Modifications in the optical design of both CO2 and FIR laser cavities have led to increased FIR output power. Finally, the use of a novel FIR output coupler and increased pump power has increased the number of high-power FIR wavelengths available for plasma diagnostic applications. This work was supported by U.S. DOE contract No. DE-FG03-86ER-53225.
Impact of radiation measurements on hardening of TFTR diagnostics
Authors: Johnson L. C. , Hill K. W. , Gilbert J. D. , Jassby D.
Published: July 2002

Contrary to previous plans for the preparation of diagnostic systems for D-T break-even experiments in the Tokamak Fusion Test Reactor (TFTR), it now appears that a limited Q∼1 demonstration can be carried out without constructing a close-fitting igloo radiation shield around the tokamak. In order to assess the impact of D-T operation of TFTR without an igloo shield, particularly with regard to hardening of diagonstic systems, we have mapped neutron and gamma fluxes inside the test cell and test cell basement, using a variety of radiation measurements. The measurements are sufficiently detailed to resolve massive hardware components, such as neutral beams and shielded diagnostic systems, and can be used to predict local fluxes. By comparing the measurements with transport code calculations for the case of a bare tokamak, we conclude that the models have substantially overestimated fluxes both inside and outside the TFTR shield walls. It may be possible to eliminate an igloo shield, by taking credit for the shielding effectiveness of massive hardware around the tokamak. However, this will increase the need for local diagnostic shielding.
Spectroscopic diagnostic for measurement of plasma rotation in the Texas Experimental Tokamak (TEXT)
Authors: Meigs A. G. , Rowan William L. , Woodward N. W.
Published: July 2002

Plasma rotational velocity measurements may be applied to the test of plasma theory, to the assessment of the effects of plasma perturbations, and as substitutes for electric field measurements. For these applications, we developed a plasma rotation diagnostic based on the measurement of the Doppler shift of impurity spectra. In ohmic plasmas, the measurement is complicated by the small size of the velocity induced line shift compared with the line width. To overcome this problem, our diagnostic system is configured to observe each of two plasma regions at several times during a single shot using a single array detector. This procedure can eliminate the need for a separate absolute wavelength calibration if the regions are properly chosen and can minimize the effects of detector noise and shot-to-shot plasma variation. The two chords selected for observation can be changed from shot to shot. The details of the novel optical system are described. As an example of the technique, rotational velocity profiles for ohmic plasmas perturbed by a radial, resonant magnetic field are presented.
Development of a multipoint Thomson scattering system for a large reversed field pinch experiment
Authors: Bassan M. , Pasqualotto R. , Sardella A. , Giudicotti L.
Published: July 2002

A multipoint Thomson scattering system is under development for the measurement of Te and ne spatial profiles in RFX, a large (a=0.48 m, R=2 m, I≤2 MA) reversed field pinch experiment. In this system, the beam from a low divergence ruby laser (E=15 J, Δt=30 ns) is focused to cross the plasma in the equatorial plane. The scattering signal from 30 locations along a plasma diameter is collected by means of high transmission fiber optic bundles. An effective viewing dump was obtained by engraving sharp poloidal grooves in the first wall graphite tiles. The scattering light spectra are analyzed by means of three spectrometers, each including an F/3.4, aberration corrected, holographic grating and a 40-mm-diam MCP photomultiplier with a 10×10 anode array. These detectors use a high strip current, V-plate, electron multiplier with 105 electron gain and have a recovery time of less than 30 μs. In the 300-channel data acquisition electronics, the plasma light background may be sampled 100 ns before the scattering pulse. The system is designed in order to achieve a spatial resolution of 2.5 cm, useful to study small-scale correlation phenomena, and will also measure fast, submillisecond fluctuations of Te and ne by exploiting the two-pulse capability of the laser.
X-ray technique for continuous time- and space-resolved observation of hot spots
Authors: Choi P. , Aliaga R.
Published: July 2002

A time- and space-resolved technique to record the evolution of hot spots, local dense hot regions in plasma pinches is presented. Based on a modified form of the ADRRM 2-D x-ray streak technique reported previously, the new method allows the presence of hot spots to be recorded conclusively. The basics of the technique are described and the limitations of the system discussed. The technique has been applied to study the evolution of hot spots in a plasma focus operating with a mixture of Kr and D2. The results demonstrate that the presence and evolution of the hot spots can be recorded with spatial and temporal resolution in the range of mm and ns, respectively.
High precision powder x-ray diffraction measurements at high pressures
Authors: Meade Charles , Jeanloz Raymond
Published: July 2002

We describe a new technique for averaging two-dimensional powder diffraction patterns to form a single profile of the diffracted intensity at different values of the scattering angle 2θ, I(2θ). This approach significantly improves the precision with which d spacings and diffracted intensity can be measured relative to conventional techniques of powder diffraction at high pressures. By analyzing the diffraction patterns from samples inside the high-pressure diamond cell we find that scattering angles, 2θ, can be determined with an uncertainty of ±0.0068° and the relative intensities of different (hkl) diffraction lines are obtained to within ±0.9%. Combining the measurements of 2θ and intensity we have determined the equation of state and the Debye–Waller (B) factor of gold to 15.4 GPa. These are the highest pressures to which B has been measured to date, and we find that the results are in good agreement with thermodynamic measurements at low pressures.
A high intensity cluster ion source for fast beam experiments
Authors: Bae Y. K. , Cosby P. C. , Nicholson M. , Olson W.
Published: July 2002

A high intensity cluster ion source that can be used for various fast beam spectroscopic studies has been constructed and demonstrated. The cluster ions are grown around seed ions that are generated by electron impact ionization of gas very near the exit of the nozzle (∼1 nozzle diameter distance). The generated cluster ions are coaxially focused and extracted from the pulsed (10 Hz, 200 μs pulse) supersonic expansion through a skimmer by applying a weak (∼1 V/cm) electric field, and injected into a photofragment spectrometer. With the source we have successfully generated well-collimated intense beams of various positive and negative cluster ions, such as H+n, H3O+■ (H2)n, (CO)+n, (N2)+n, (CO2)+n, (NO)+n, He+n, Ar+n, Xe+n, and (CO2)−n, with peaks currents of ∼500 pA at cluster size n=10. Preliminary photofragmentation studies of selected cluster ions have been performed to demonstrate the capability of the source.
Tokamak T-10 soft x-ray imaging diagnostic
Authors: Bobrovskij G. A. , Kislov D. A. , Lyadina E. S. , Savrukhin P. V.
Published: July 2002

Three arrays of silicon surface-barrier diodes were recently installed on T-10 (R=1.5 m, a=0.3 m). The detectors view the plasma cross section along 58 chords spaced in the poloidal direction at one toroidal location. The tomographic reconstruction technique allows one to obtain the time evolution of the two-dimensional soft x-ray intensity profiles in the energy range of 2.5–15 keV. The field of view covered the main part of the plasma (r/a<0.7) with a spatial resolution as small as 2 cm, which is consistent with the scale of the processes under study. The signals are digitized at rates up to 100 kHz and stored in 464K (total) memory (8K per channel). The measured soft x-ray emission was applicable for investigation of the magnetohydrodynamic instabilities, heat and particle transport, and plasma position control. Studies of the evolution of soft x-ray perturbations were made in ohmically and ECRH heated plasmas. It was shown that the effect of ECRH on the plasma parameters (transport coefficients, sawtooth activity, modification of the electron temperature profiles) depends on the position of the EC resonance zone within the plasma cross section. The tomographic reconstruction revealed the different mechanisms of sawtooth crashes in the T-10 plasma.
Flexible instrument for time-correlated single-photon counting
Authors: Becker W. , Stiel H. , Klose E.
Published: July 2002

A single-photon counting instrument is described that is capable of recording single decay curves, time-resolved spectra, and sequences of fluorescence decay curves with the emission wavelength, the time from the start of the experiment, or other externally variable values as parameters. The instrument contains an internal microcomputer for experiment and measurement system control, data processing, and data management. It can be operated at pulse repetition rates ranging from 10 to 200 MHz and allows a photon count rate of up to 106/s. The FWHM of the instrument response is 94 ps with a photomultiplier tube of type 18 ELU-FM.
The Surrey STM: Construction, development, and evaluation of a scanning tunneling microscope
Authors: Hammiche A. , Wei Yu , Wilson I. H. , Webb R. P.
Published: July 2002

A scanning tunneling microscope has been built together with the necessary controlling electronics. Currently this is used at atmospheric pressure but is capable of use under vacuum with minor modifications. Trials of the system, and subsequent adjustments, have taken place using highly oriented pyrolitic graphite and gold evaporated on silicon samples. Good and versatile control of tunneling current was achieved. We report on the design, development, construction, and evaluation of the instrument. Preliminary results illustrating reproducible topographical images are presented and discussed. Gap-versus-bias voltage and gap-versus-tunneling current characteristics are also presented and discussed.
Millimeter-wave phase-imaging interferometer for the GAMMA 10 tandem mirror
Authors: Hattori K. , Mase A. , Itakura A. , Inutake M. , Miyoshi S. , Uehara K. , Yonekura T. , Nishimura H. , Miyashita K. , Mizuno K.
Published: July 2002

A millimeter-wave phase-imaging interferometer has been developed for the study of density profiles of the GAMMA 10 tandem mirror. The interferometer uses a 70-GHz klystron oscillator and a quasi-optical transmission system. The probe beam is expanded so as to fill an orthogonal view of a plasma cross section. The view is imaged onto a detector array. The detector array consists of beam-lead GaAs Schottky barrier diodes bonded to antennas fabricated using photolithographic techniques on a fused-quartz substrate. Two types of antennas, bow-tie and Yagi–Uda antennas have been used in order to provide an effective matching to millimeter-wave beams, and compared for the performance of an imaging system. The interferometers have been applied to the central-cell and plug-cell plasmas of GAMMA 10.