bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics measurement of the phase transformation in Ni2SiO4 under high pressure and temperature (abstract)
Authors: Yagi T. , Rubie D. C. , Tsuchida Y. , Utsumi W. , Kikegawa T. , Shimomura O.
Published: July 2002

The kinetics of the pressure-induced phase transformations in minerals are of considerable importance in affecting the dynamics of convection in the Earth. Because of the long exposure time of the high pressure in situ x-ray observations, however, it was very difficult to study the kinetics of such transformations. Combination of the synchrotron radiation and a large-volume high-pressure and high-temperature apparatus made it possible to perform such a study. The kinetics of the olivine-spinel transformation in Ni2SiO4 have been studied at conditions of 3.6–4.8 GPa and 765–980 °C. X-ray diffraction experiments were carried out using the MAX-80 high-pressure, high-temperature cubic-anvil apparatus at the National Laboratory for High Energy Physics, Japan. Synchrotron radiation was supplied by an accumulator ring operating at 6.5 GeV and between 15 and 5 mA. Ni2SiO4 olivine powder was hot pressed in the olivine stability field and then the pressure-temperature conditions were changed to initiate the transformation to spinel. Reaction progress was monitored by collecting x-ray diffraction patterns at intervals of either 30 or 100 s. The extent of transformation was estimated as a function of time and the data were analyzed on the basis of a nucleation and growth model. Pressure and temperature dependence of the transformation rate were determined from the present study.
Orbit distortion due to UVSOR wiggler
Authors: Yonehara H. , Kasuga T. , Hasumoto M. , Kinoshita T.
Published: July 2002

A three-pole wiggler with a maximum magnetic field of 4 T was installed in the UVSOR electron storage ring. The insertion effect on the tune and the closed orbit of the stored beam is not negligible. The measured tune shifts are in good agreement with the values estimated from results of the magnetic field measurement. Compensation of the vertical closed orbit distortion due to misalignment of coils of the wiggler was tried with a vertical steering magnet. However, compensation is not perfect at the maximum excitation level because the distance between the steering magnet and the wiggler is not sufficiently short.
A high-pressure cylindrical internal reflection cell for infrared spectroscopy
Authors: Sawamura Seiji , Kamaya Hiroshi , Ueda Issaku
Published: July 2002

A high-pressure cylindrical internal reflection cell is designed for use with water and aqueous solutions. The oil separator is a glass piston-cylinder type and is placed in the cell. The infrared absorption spectra of water are measured up to 30 MPa. This pressure is three times higher than the previously reported cell.
Novel method of measuring optical-intensity distributions of scintillations
Authors: Yamashita Mikio
Published: July 2002

A new method of measuring optical-intensity distributions of weak scintillations is described that uses the photon counting technique in combination with a variable optical attenuator. It is experimentally demonstrated that the proposed method permits the distributions to be determined from a set of integral data of count rates measured at different optical-attenuation factors. In addition to being almost insensitive to possible changes in PMT gain, the present method offers the advantage over the conventional one relying on pulse height analysis that it can provide virtually improved energy resolutions in measuring low-intensity scintillation energy spectra.
Electrically tunable coplanar transmission line resonators using YBa2Cu3O7−x/SrTiO3 bilayers
Authors: Findikoglu A. T. , Jia Q. X. , Campbell I. H. , Wu X. D. , Reagor D. , Mombourquette C. B. , McMurry D.
Published: July 2002

We have prepared electrically tunable microwave resonators incorporating superconducting YBa2Cu3O7−x (YBCO) and paraelectric SrTiO3 (STO) layers on LaAlO3 substrates. The top YBCO layer for each sample was patterned into a 8 mm long coplanar transmission line with a 40 μm gap and a 20 μm center line width. The microwave transmission through the coplanar transmission line exhibits resonances corresponding to standing microwaves along the coplanar transmission line. These resonances are modulated by applying a bias voltage between the center line and the ground planes. Samples with a 0.5 μm thick (2 μm thick) bottom STO layer show, for a resonance at around 8 GHz (5 GHz), a frequency modulation of about 4% (24%) and a quality factor Q of about 200 (50) under 100 V bias at 80 K.
Pyrometric temperature controller for million degree per second heating
Authors: Brauer S. , Ryan D. H. , Ström-Olsen J. O. , Sutton M. , Stephenson G. B.
Published: July 2002

A high-power proportional temperature controller, using a fast infrared pyrometer, has been developed to change and control the temperature of metallic ribbon samples with microsecond response. The apparatus provides uniform and controlled heating for time-resolved x-ray scattering studies of structural phase transitions. When high-power pulse heating is used, the system is capable of increasing the sample temperature at rates in excess of 106 K/s, without overshoot and with subsequent control to ±1 K at temperatures as low as 650 K.
Sensitive digital lock-in amplifier using a personal computer
Authors: Wang Xiaoyi
Published: July 2002

The low-frequency sensitivity limitation provided by internal 1/f amplifier noise is eliminated by employing lock-in detection. Since low frequency noise spectral analysis commonly uses digital processing and fast Fourier transform techniques, it is convenient to use digital lock-in detection as well. A simple digital lock-in amplifier based on an Apple IIe personal computer is capable of detecting signals many orders of magnitude below the internal l/f noise of a PAR (Princeton Applied Research) 113 amplifier.
Automated liquid-helium transfer tube lifting system
Authors: Kato Kiyonori , Suzui Mitsukazu
Published: July 2002

An automatic liquid-helium transfer tube lifting system has been developed, in which the transfer tube can be raised or lowered very slowly by remote control. This system relieves the operator of considerable manual labor, and protects the O-ring seals from damage at low temperature.
High-speed single-flux-quantum circuit using planarized niobium-trilayer Josephson junction technology
Authors: Bunyk P. I. , Oliva A. , Semenov V. K. , Bhushan M. , Likharev K. K. , Lukens J. E. , Ketchen M. B. , Mallison W. H.
Published: July 2002

A simple test circuit of the rapid single-flux-quantum (RSFQ) logic family has been implemented in a planarized all-refractory technology using only two superconducting layers and small Nb/AlOx/Nb Josephson junctions (nominally 1.5×1.5 μm2) with critical current density jc≊6 kA/cm2. A special layout design of the integrated circuit (including a SFQ pulse generator, Josephson transmission line, and T flip–flop) was used to reduce 3D inductances resulting from absence of the ground plane. For samples with various junction parameters, the maximum frequency of the SFQ pulse train, which could be divided by 2 by the flip–flop, ranged from 200 to 370 GHz.
High-current ion beams of metallic elements
Authors: Torp B. , Nielsen B. R. , Rück D. M. , Emig H. , Spädtke P. , Wolf B. H.
Published: July 2002

The production of high-current ion beams of metallic elements has been undertaken using a modified version of the high-current ion source CHORDIS. The experiments were performed on both sites of GSI, Darmstadt and Danfysik, Jyllinge. Two different methods were tried: first, applying the sputtering technique to targets made by metallic elements, and second, using the chlorination technique. The sputtering technique proved to be far superior in that the metal beam obtained in this way was very stable and the lifetime of the source was long.
Superleak-tight cold valve testable at room temperature
Authors: Tsuda T. , Mori Y. , Satoh T.
Published: July 2002

In order to obtain a reliable cold valve (or low temperature valve) which can be tested at room temperature, several combinations of hard material for the valve stem tip and soft material for the valve seat were tested. The combination of Be-Cu and Ag gave satisfactory performance.
A new look at the Bitter method of magnetic imaging
Authors: Rice Paul , Moreland John
Published: July 2002

A scanning tunneling microscope (STM) was used in place of an optical microscope in the Bitter method to image the magnetic ferrofluid particles on the surface of a hard disk. The resolution obtainable with the usual Bitter method is limited by the optical viewing of the magnetic particles. Using the scanning tunneling microscope, we have obtained image resolution limited only by the ferrofluid particle size.
A method to increase the sensitivity of temperature measurements of current-carrying microelectronic components
Authors: Friedrich K. , Walther H. G. , von Geisau O. H.
Published: July 2002

The spatially resolved measurement of current-induced temperature changes in current-carrying microelectronic components is described theoretically and experimentally. A method to increase the sensitivity of such measurements in comparison with thermoreflectance is explained.
A multi-optical-fiber array with charge-coupled device image detection for parallel processing of light signals and spectra
Authors: Piccard Richard D. , Vo-Dinh Tuan
Published: July 2002

We describe a new two-dimensional multioptical-fiber array (MOFA) with 144 elements, its use with charge-coupled device (CCD) image detection to perform parallel processing for light intensity measurements, and its use with a concave aspherical grating and CCD image detection to perform parallel processing for spectrometry. Each 2-m fiber extending from the MOFA is individually sheathed in a flexible, opaque cover. The light signals can be measured simultaneously with cross-talk ranging from 0.4% to 0.03% of the peak signal, depending upon configuration. We characterize the instrument in both the intensity and the spectrometric configurations, and present techniques for optimizing performance.
Design, performance, and theory of long thermionic diodes
Authors: Herrmann P. P. , Schlumpf N. , Telegdi V. L. , Weis A.
Published: July 2002

We report experimental and theoretical investigations of the properties of thermionic diodes of novel design. The construction of long diodes (up to 30 cm) with indirectly heated cathodes, electrostatically shielded interaction volume, and large solid angle for ion collection is presented in detail. These diodes were designed with a high degree of symmetry in order to minimize both electric and magnetic fields in the interaction region. They are especially suited for ultraweak laser-induced transitions. We also present the first quantitative theory of the diode’s current versus voltage characteristic; it is shown to agree very well with the experimental results. From the calculated potential distributions and the measured ion trapping times we are able to estimate the diode gain. The (chopping) frequency dependence of the diode gain is described quite accurately by a simple schematizing model. We used two distinct methods to determine the diode gain experimentally and find an agreement with our estimate within a factor of 2. The behavior of the diode in axial magnetic fields was also investigated. The gross features can readily be explained on the basis of an extension of the theory. We have discovered an additional ‘‘fine structure’’ that is as yet not understood, but can however be exploited to measure magnetic fields down to ≊1 mGauss within the diode proper.
Two-wavelength laser interferometer based on the frequency-division-modulated laser diode sources
Authors: Chien Pie-Yau
Published: July 2002

A two-wavelength interferometer based on the frequency-division-modulated laser diodes has been demonstrated. By employing this technique, the frequency difference between two laser diodes has been stabilized to less than 3.0×10−9 and the synthetic heterodyne signal is also generated for measuring the optical phase shift absolutely.
A new scheme for x-ray grazing incidence diffraction
Authors: Cui S. F. , Mai Z. H. , Wu L. S. , Wang C. Y. , Dai D. Y.
Published: July 2002

A new scheme for x-ray grazing incidence diffraction (GID) under total external reflection conditions is presented. This simple scheme allows the grazing angles and the scattering angles to be adjusted independently so that the structural and/or the chemical profiles of materials can be determined at controlled depths. As an example, Si1−xGex/Si superlattice materials were studied. Both commensurate and incommensurate growths between the two quantum wells in the strained-layer superlattice were observed by the GID technique.
Isolated ramping current sources for a cryogenic current comparator bridge
Authors: Elmquist Randolph E. , Dziuba Ronald F.
Published: July 2002

The design and performance of a pair of highly isolated ramping and reversing direct-current sources for use with a cryogenic current comparator resistance bridge and dc superconducting quantum interference device (SQUID) detector are described. The current sources are floating and isolated from one another, and are internally programmed to reverse the output current while maintaining the SQUID feedback control system in lock. The sources are designed to have low zero offset in order to limit the change of the current ratio in the reversal sequence. Sources have been constructed with full-scale current ranges from 0.65 to 100 mA and have been used in the comparisons of precision standard resistors at the 0.01 ppm level.
Contactless resistivity measurement with the high-frequency series resonance method
Authors: Mühlhaus V. , Kanh Y.
Published: July 2002

Resistivity of nonmagnetic metallic cylindrical samples is measured contactlessly with a high-frequency LC (inductance-capacitance) series resonance method by evaluating both frequency shift Δf and change of Q factor ΔQ due to the sample. By this method, sufficient accuracy can easily be achieved without any resistivity standards, although the size of the measuring coil as well as the value of the series capacitor (and hereby the operating frequency) are arbitrary and not part of the calculation. Results obtained for Cu, Al, Mg, Zn, Pd, Sn, Zr, and Bi are in agreement with the literature values.
Miniature TEA-CO2 laser with surface-wire-corona preionization
Authors: Sugii Masakatsu , Komatsu Katsuhiko , Hara Hiroshi
Published: July 2002

This paper describes an experimental study of a miniature, UV-preionized TEA-CO2 laser with a new type of surface-wire-corona preionizer. We have developed a surface-wire-corona preionizer consisting of segmented columnar SrTiO3 dielectric and a fine wire strained on the dielectric surface, we believe for the first time. By applying this preionizer to the TEA-CO2 laser, efficient laser operation at an overall efficiency of 8.9% with an output energy of 114 mJ has been achieved from a small discharge volume of 5.8 cm3 with active length of 14.5 cm. This efficiency is comparable to the maximum one obtained with miniature TEA-CO2 laser reported up to now.
Acoustic cavity method for phase boundary determinations: The critical temperature of CO2
Authors: Colgate S. O. , Sivaraman A. , Dejsupa C. , McGill K. C.
Published: July 2002

A versatile acoustic method for the determination of points on phase boundaries in a fluid system is shown to be not only precise, but also capable of producing numerous experimental points in a short time as compared to other methods. The present method using a spherical acoustic resonator assembly operating under microcomputer control is capable of detecting any kind of chemical or physical changes which take place in the constant volume system as the temperature is slowly varied. Results on its use to locate the critical point of CO2 are given.
Vibration isolation of distributed mechanical oscillators by mechanical suspensions with application to resonant-mass gravitational radiation antennae
Authors: Veitch P. J.
Published: July 2002

The use of mechanical suspensions to isolate resonant-mass gravitational radiation antennae from external vibrations is discussed. We investigate the optimization of several types of suspensions and illustrate the importance of ensuring that the internal resonances of both the flexible and massive components in the suspension occur at frequencies much higher than the antenna frequency. We present new techniques for estimating the Q limits imposed on the antenna by the suspension, and for determining the excitation of the antenna by ambient noise.
Use of a phase-sensitive detector for measuring magnetic hysteresis loops
Authors: Gömöry Fedor
Published: July 2002

A method for magnetic hysteresis loop measurement on small samples of high Tc superconductors is described, applicable to other types of magnetic materials as well. It is based on an unusual working regime of the phase-sensitive detector with a square wave mixer signal and controllable reference phase setting. The main advantages of the method are its sensitivity and the possibility of measuring in a wide frequency range. A drawback of the method is that it is fully correct only in the case of a symmetrical hysteresis loop.
An achromatic retarding mode for the Menzinger lens system
Authors: Jacobs Jason M. , McCorkle Richard A.
Published: July 2002

A novel mode of operation for the Menzinger retarding lens system, which first focuses and then abruptly decelerates the beam, is found to provide highly achromatic performance, robust operation, and selectable output beam profiles.
Waveform analysis with optical multichannel detectors: Applications for rapid-scan spectroscopic ellipsometry
Authors: An Ilsin , Collins R. W.
Published: July 2002

A unique rapid-scanning ellipsometer employing a rotating polarizer optical configuration and a multichannel detector for a 1.5–4.5 eV spectral range, has been developed recently for real time studies of film growth and surfaces. This is a new application of the photodiode array-based optical multichannel detector that entails waveform analysis of the incident irradiance at each photon energy. For accurate ellipsometric spectra {ψ(hν),Δ(hν)}, the raw data in the form of photon counts, integrated over four or more equal sectors of polarizer rotation, must be corrected for systematic errors originating from the detection system. Simple procedures are described to characterize and correct for the most significant errors including detection system nonlinearity, image persistence, and scattered stray light in the spectrograph/detector enclosure.
Measurement of vaporized atom flux and velocity in a vacuum using a microbalance
Authors: Uetake Naohito , Asano Takashi , Suzuki Kazumichi
Published: July 2002

The flux and velocity of Cu and Ti vaporized by an electron beam were measured by a microbalance. A small disk was hung horizontally above the crucible and its weight change was measured by the microbalance. The flux was determined from the weight change due to vaporized atom deposition under the disk base. The total momentum of deposited atoms per unit time was determined from the weight change before and after the vapor was turned off by a shutter. The velocity could then be calculated from these two values. The velocity obtained for Cu depended slightly on the vaporization temperature and had reasonable agreement with the theoretical estimation obtained using an ideal gas treatment. The velocity of Ti was slightly higher than the theoretical result. Since Ti was excited to several metastable energy levels by electron beam heating, such an internal energy should be converted to kinetic energy following adiabatic expansion and would account for the velocity increase. The internal energy by excitation to the metastable energy levels must be taken into consideration in the case of high temperature heating, as with an electron beam evaporative source.
Rock property assessment using laser-generated acoustic waves
Authors: Hutchins D. A. , Young R. P.
Published: July 2002

A pulsed laser has been used to generate wide bandwidth acoustic pulses in a range of rock samples in the laboratory. A nonresonant piezoelectric transducer was used as the detector. This system can measure longitudinal and shear wave velocities simultaneously, from a single waveform, and can also be used to determine frequency-dependent attenuation in the MHz region. Values of a quality factor (Q) for longitudinal waves are evaluated.
Measuring laser-plasma x-ray emission using photodiode arrays
Authors: Marshall F. J. , Jernigan J. G. , Arens J. F. , Collins T. , Pien G.
Published: July 2002

The use of photodiode arrays (PDAs), as the detectors in laser-plasma x-ray diagnostics, is explored in this paper. Traditionally, in laser-fusion and laser-plasma research, film has been used in x-ray diagnostics to record the integrated x-ray flux. The advantages of film are its low cost and relative simplicity of use. Photodiode arrays, although more complex, offer the advantages of near instantaneous results, high sensitivity, stability of response, and in principle are easy to calibrate. A Hughes PDA has been used to image laser-plasma x rays by incorporating it into a pinhole camera. The readout electronics were developed at the Space Science Laboratory and experiments were performed on the University of Rochester’s OMEGA target chamber.
Measurement of x-ray laser beam divergence with CADIX, a time-resolved diagnostic tool using an insertable multilayer mirror
Authors: Reverdin C. , Bourgade J. L. , Bruneau J. , Charret M. , Desenne D. , Dulieu A. , Dumont H. , Louis-Jacquet M. , Sauneuf R. , Schirmann D. , Troussel P.
Published: July 2002

To study the x-ray laser beam deflection and divergence due to the refraction within the plasma, a specific diagnostic called CADIX has been developed at the Centre d’Etudes de Limeil-Valenton (CEL-V). When the beam refraction analysis is required a multilayer mirror is inserted on the x-ray laser output beam. It selects the lasing wavelengths and reflects them to an off-axis streak camera which records x rays as a function of time and angle. A detailed description of the instrument is presented including multilayer mirror calibration at the LURE (Laboratoire pour L’Utilisation du Rayonnement Synchrotron, Orsay, France). An experimental measurement on neon-like silver amplification is presented and analyzed with the response of the mirror. An important refraction effect is observed.
A simple method for overcoming spatial resolution limitations in soft x-ray spectrograph/detector systems
Authors: MacGowan B. J. , Koch J. A. , Mrowka S.
Published: July 2002

We describe a simple method for improving the spectral resolution of soft x-ray and extreme ultraviolet spectrographs which use electro-optical detector/intensifiers. In this method, the spectrometer is focused onto a narrow slit which is angled near 90° with respect to the dispersive axis and placed just in front of the detector. Proper choice of the width and angle of the slit is shown to have the effect of expanding the spectrum along the length of the slit to the point where the spatial resolution limitations of the detector are overcome.
The multichannel motional Stark effect diagnostic on TFTR
Authors: Levinton F. M.
Published: July 2002

Although the q profile plays a key role in theories of instabilities and plasma equilibrium, it has been quite difficult to measure until the recent development of the motional Stark effect (MSE) diagnostic. A multichannel motional Stark effect polarimeter system has recently been installed on the Tokamak Fusion Test Reactor (TFTR). The diagnostic can measure the magnetic field pitch angle [γp=tan−1(Bp/BT)] at ten radial locations. The doppler shifted Dα radiation from a TFTR heating beam is viewed near tangential to the toroidal magnetic field via a re-entrant front surface reflecting mirror. The field of view covers from inboard of the magnetic axis to near the outboard edge of the plasma with a radial spatial resolution of 3–5 cm. A high throughput f/2 optics system results in an uncertainty for γp of ∼0.1°–0.2° with a time resolution of ∼5–10 ms. Initial pitch angle profiles from TFTR have been obtained. The MSE data is consistent with the estimated magnetic axis position from external magnetic measurements and the q=1 radius is in good agreement with the inversion radius from the electron cyclotron emission temperature measurements.
Measurements of edge electron densities on TEXT using a low-energy neutral lithium beam (abstract)
Authors: McChesney J. M. , West W. P. , Howald A. M.
Published: July 2002

Collisionally excited fluorescence from a low-energy (20–30 keV) neutral lithium beam can be used to determine edge electron densities in fusion devices. A lithium beam with an equivalent neutral particle current of 2 mA has been installed on TEXT. This system can be used to measure edge density profiles, and to measure edge density fluctuations with time resolution of ∼2 μs and spatial resolution ∼0.5 cm. The observed fluorescence is not directly proportional to the underlying electron density due to the effects of beam attenuation and the finite lifetime of the radiating state. An algorithm to unfold the electron density profile, including spatial fluctuations, from the observed fluorescence signal has been developed. Results from the initial operation of the lithium beam on TEXT will be presented, and compared with data from the TEXT HIBP and IR scattering diagnostics. This work supported by U.S. Department of Energy Contract DE-AC03-89ER53277.
Density profile measurement using a multichannel difluoromethane laser interferometer system on ATF
Authors: Ma C. H. , Baylor L. R. , Hutchinson D. P. , Murakami M. , Wilgen J. B.
Published: July 2002

Recent results of the electron density profile measurement on the Advanced Toroidal Facility are presented. A multichannel difluoromethane laser interferometer system has been routinely employed to study density evolution in electron cyclotron heated as well as neutral-beam-heated plasma discharges with gas fueling and pellet injection. A chordal inversion code has been developed, and has been used successfully to reconstruct the asymmetric density profiles. Cross-correlation of density profiles measurements among far-infrared interferometer, Thomson scattering, the heavy-ion beam probe, and the fast reciprocating Langmuir probe has been achieved. Radial density profiles measured by the four diagnostics are generally in good agreement and are hollow profiles under most experimental conditions.
Diagnostics of high density plasma reactors used in the processing of electronic and photonic materials (invited) (abstract)
Authors: Gottscho Richard A. , Nakano Toshiki , Sadeghi Nader , Trevor Dennis J. , Lee T. C.
Published: July 2002

High-density plasmas are being used in the manufacture of electronic devices and systems because they provide high throughput at low pressure and low ion energy. Low pressure is desirable for maximizing process uniformity over large substrates while low ion energy is desirable for minimizing process-induced damage. However, the optimal design for a high density plasma reactor is unclear and the technology has largely developed empirically: many alternatives for magnetic and geometric design are offered for the same processing applications. In this talk we discuss diagnostic measurements of high density plasma reactors and how they can be used in developing improved reactor designs and in providing insight into materials processing. Laser-induced fluorescence measurements of metastable ion velocity distributions are made in both Ar and Cl2 electron cyclotron resonance and helicon plasmas. The effects of magnetic field configuration, power, and pressure on the energy and angular distributions of the ions will be described along with electron density measurements made by microwave interferometry. Where appropriate, comparisons will be made with the recent theoretical results of Graves and Porteous [D. B. Graves and R. K. Porteous, American Vacuum Society National Symposium, Seattle, WA, November (1991)].
The determination of wave fields from perturbed particle orbits (abstract)
Authors: Skiff Frederick N.
Published: July 2002

Propagation of wave fields in plasma is influenced by the particle motions through charge densities and currents. Likewise, the dynamics of particle motion is influenced by the wave fields. A family of techniques for determining wave fields given time-resolved measurements of the particle distribution function will be presented. Essential aspects of the theory behind these techniques will be outlined. Because the plasma dielectric response is nonlocal in space and time, a measurement of the particle velocity distribution which is resolved in space and time may indicate the wavelength as well as phase and amplitude of a wave. Data from laboratory experiments will be presented. This research was supported by an Alfred P. Sloan Research Fellowship and a National Science Foundation PYI award.
A fully programmable data acquisition system for the TJ-I and TJ-IU devices
Authors: Pacios L. , Guasp J. , Vega J.
Published: July 2002

A new data acquisition system has been developed for the TJ-I tokamak and the TJ-IU torsatron. This system is based on the VME standard and it is controlled by an MC68020 microprocessor. This scheme is similar to the ones existing at CERN and used in high-energy physics experiments. [On-line Computing Group, Valet-Plus Operation Guide, Data handling, CERN DD Division OC Group]. The data acquisition system consists of 60 independent, fully programmable channels. Each channel has its own analog-to-digital converter (ADC) with a resolution of ten bits and a RAM memory of 128 kbytes (kB). A digital-to-analog converter is also included for providing an analog output in order to display the stored signal on oscilloscopes. The maximum sampling rate achievable with the ADC used is 500 Ksamples/s, which is equivalent to a sampling period of 2 μs. Each channel is programmed to have its own sampling period (in 400-ns steps), and to use the amount of storage required according to the sampling period and the pulse length, up to a maximum of 128 kB. The system controls not only the 7680 kB corresponding to the memory of the 60 channels, but a RAM buffer of 4 MB as well. The system is linked to a local ETHERNET network in order to send the recorded data to the disks of a VAX/VMS computer, where the data are available for analysis.
Measurements of rf emission and transmission in the 5–500 MHz range in TFTR (abstract)
Authors: Greene G. J.
Published: July 2002

Active and passive measurements using an array of broadband rf magnetic probes in TFTR have suggested several diagnostic applications. Swept, fast wave propagation experiments using one probe as a launching antenna have revealed absorption peaks from the dominant minority species (hydrogen and helium-3) in ohmic plasmas. A new synchronous modulation/detection system has been installed to allow operation during beam heated plasmas, where spontaneous emission is significant. Proposed experiments will investigate the localization of the absorption and evaluate the utility of this measurement as a diagnostic for tritium. The signal processing system for the probe array has also been recently modified to permit fast gating during ICRF heating pulses. This change allows measurement of the rf emission spectrum immediately following a heating pulse and will be used to look for features arising from slowing down of the high-temperature minority tail. The experiment, by analogy, may give an indication of the spectral signature that will result from alpha particles during future DT operation. This work was supported by U.S. Department of Energy Contract No. DE-AC02-76-CHO-3073.
Electron temperature fluctuation measurement from ECE on TEXT-U
Authors: Kwon M. , Gandy R. F. , Thomas C. E. , Lim W. K.
Published: July 2002

The conceptual design and theory of diagnostics to measure electron temperature and density fluctuations using electron cyclotron emission (ECE) was proposed and a new, single-sightline ECE system with the heterodyne radiometer has been built for TEXT-U. This ECE system was designed to employ auto- and cross-correlation techniques. Calculations indicate that fluctuations as small as 0.2% in amplitude can be achieved from auto-correlation of the ECE signal. The cross-correlation technique, however, must be used to resolve the fluctuations in frequency. Auto- and cross-correlation between optically thick ECE channels will be used for our initial approach to electron temperature fluctuation measurement with the single-sightline ECE system. A description of the TEXT-U ECE system, investigation of the feasibility of this measurement, and the initial results of test, calibration, and operation are presented.
Localized magnetic field pitch angle measurements by collective Thomson scattering
Authors: Woskov P. , Rhee D. Y.
Published: July 2002

A novel new method is proposed to measure the internal magnetic field pitch angle in tokamaks by measuring the frequency of the lower hybrid resonance in the collective Thomson scattered spectrum. The resonance frequency has a dependence of 1.2 and 2.0 GHz/deg pitch angle for ITER and C-MOD-like plasma parameters, respectively, using a submillimeter-wave diagnostic source. Sensitivity to other plasma parameters such as electron density, temperature, energetic ion fraction, and magnetic field is shown to be weak.
Precision of ion temperature and impurity fractional density measurement using the JET collective Thomson scattering diagnostic
Authors: Orsitto F.
Published: July 2002

In this work some calculations are reported about the possibility of a simultaneous determination of the temperatures and densities of several different plasma ions using the JET gyrotron collective scattering diagnostic. It should be possible to determine the ion temperatures with a 20% error and the ion densities with ∼50% error, because of the high S/N (signal-to-noise ratio) that can be obtained in this experiment. These figures are obtained assuming 400 kW of incident power, a short integration time (10 ms), the central frequencies and the bandwidths of a 14 channels filter bank of the detection system, and a global (ECE background+detection system) noise temperature of ∼600 eV. The results are obtained using a multiparameter fit of an ‘‘experimental spectrum’’ obtained averaging the calculated form factor in each channel of the filter bank and associating an error to this number calculated using the heterodyne S/N signal-to-noise ratio. The model function used in the fit is a known function of ion temperatures and densities. A deuterium plasma has been considered with hydrogen, carbon, and beryllium impurities. Te and ne are assumed to be known from other diagnostics. These conclusions are confirmed using a Monte Carlo code, which takes into account the statistics of the scattered signal.
Broadband heterodyne reflectometry on the W7-AS stellarator (abstract)
Authors: Hartfuss H. J. , Sánchez J. , Estrada T.
Published: July 2002

A broadband heterodyne reflectometer, operating in the frequency range 75–110 GHz, has been installed and operated at the W7-AS Stellarator in Garching for the study of density fluctuations and fast density profile determination. Both local (LO) and signal (rf) oscillators can be swept over the whole frequency range. Due to the balanced detection scheme, all drifts, as well as the broadband noise of the BWO (rf and LO) oscillators, are canceled at the different downconversion stages. After installation on W7-AS, first results reproduced the original findings of the former homodyne system [J. Sanchez, H. J. Hartfuss, E. Anabitarte, A. P. Navarro, et al. Nucl. Fusion 30, 2383 (1990)] as well as new results on the radial distribution of density fluctuations have been obtained. A phase drift due to asymmetries in the spectrum around the last IF has been observed; this phenomenon is strongly dependent on the plasma conditions and could be caused by plasma rotation. It is presently under study. The system offers broadband operation together with the possibility to decouple phase and amplitude oscillations of the reflected beam. The high dynamic range (up to 80 dB) is able to overcome the large amplitude oscillations of the reflected beam. The reflectometer described offers a good basis for further developments on large devices, which will require a very high sensitivity due to the long waveguide runs, together with the advantage of the operation in a continuous frequency range and fast sweeping capability.
Radial distribution of turbulence correlation lengths obtained by reflectometry in the TJ-I tokamak (abstract)
Authors: Sanchez J. , Brañas B. , de la Luna E. , Estrada T.
Published: July 2002

A method for determination of radial correlation lengths of the electrostatic turbulence has been developed and applied to the TJ-I tokamak [T. Estrada, J. Sanchez, B. Brañas, and A. P. Navarro, Rev. Sci. Instrum. 61, 3034 (1990)]. The method uses homodyne detection and is based on the slow sweeping of one oscillator while the other remains at fixed frequency. The decay of the coherence can be observed as the distance between the two probing points increases. By the operation in the Q band (33–50 GHz) extraordinary mode, the system reaches most of the plasma radius. Correlation lengths obtained at the edge are compared with those measured at the plasma center. A critical issue for this comparison is the detailed knowledge of the local density gradient. The proposed method can provide the density profile information, avoiding the effect of lost fringes, even in the presence of turbulence. This fact can be used to determine the local density gradient which is needed to evaluate the separation between both reflecting points. Initial experimental results and a discussion on its degree of accuracy is presented.
Development of a far-infrared ring laser for plasma diagnostic applications
Authors: Lee J. H. , Rettig C. L. , Luhmann N. C. , Peebles W. A.
Published: July 2002

Linear cavity optically pumped far-infrared (FIR) lasers have been used extensively for plasma diagnostic measurements. However, recent experiments have suffered from frequency pulling induced by feedback of FIR radiation. The application of a ring cavity to FIR lasers is investigated as a means of improving frequency stability, particularly in the presence of strong feedback. Unidirectional traveling wave laser operation is observed, and so feedback radiation does not interact directly with the dominant cavity mode. The resultant frequency pulling is observed to be minimal (∼5 kHz) in comparison with a linear cavity (Δf∼100 kHz) when a feedback power of Δf∼2% is studied. In addition, the ring laser eliminates the two-photon light shift, and, therefore, significantly (a factor of 10) improves the absolute frequency stability near the absorption line center.
New calibration procedure for an inverse photoemission spectrograph
Authors: Vavassori P. , Puppin E.
Published: July 2002

A new calibration procedure for determining the instrumental efficiency of a grating-based inverse photoemission spectrograph is described. Our results are in good agreement with those obtained by following another procedure previously adopted by other authors. The new procedure is particularly convenient for inverse photoemission experiments conducted in the so-called ‘‘isochromat’’ mode.
High-pressure instrumentation at CHESS
Authors: Brister Keith
Published: July 2002

Diamond anvil cells have been used to generate a wide range of pressures, from 0.1 to over 400 GPa (for reference, the center of Earth is about 360 GPa). Samples are squeezed between two diamond anvils and studied using infrared, visible, and x-ray probes. Recently a bending magnet station at CHESS has become available for the general user for diamond anvil cell work using x rays. This has opened up new areas of research as the experimenters need only to bring a sample in a diamond anvil cell and can leave with the x-ray data mostly analyzed. Although most of the work has been with energy dispersive x-ray diffraction, some Laue work has been performed as well. Performing Laue diffraction studies with a station equipped for energy dispersive diffraction has the advantage that, with the addition of a rotation stage, the energy of a Laue diffracted spot can be analyzed.
An ion trap storage/time-of-flight mass spectrometer
Authors: Michael Steven M. , Chien Mingta , Lubman David M.
Published: July 2002

An ion trap/time-of-flight (TOF) mass spectrometer combination has been developed in order to combine the storage capabilities of an ion trap with the speed and resolution of a time-of-flight device. The ion trap is an rf quadrupole trap which operates in the total storage mode, i.e., with the dc voltage=0 on the end caps and rf voltage on the ring electrode. The trap has an ion storage time of ≥2 s at an rf potential of 310 Vpp. The stored ions are ejected into the time-of-flight device using a −150 V dc pulse on the exit end cap which causes the ion trajectories in the trap to become unstable. The ions are mass analyzed using either a linear or reflectron TOF. In the linear mode the resolution is 240 while in the reflectron mode a resolution of 1300 at m/z 93 is achieved. The storage capabilities of this device may have important applications towards enhancing sensitivity, the study of very slow metastable decay, and photodissociation mass spectrometry and spectroscopy.
Measuring longitudinal displacements using laser beam diffraction changes near the focal point
Authors: Yamashita Tadaoki , Nakashima Hirotaka , Nagashima Michiyoshi , Nishiuchi Kenichi
Published: July 2002

A nanometer displacement probe is created by using a knife edge, a two-part-divided photodiode, and high quality lenses. The laser beam, of wavelength 780 nm, is focused on the sample surface, where the image formed of the beam is read by the photodiode through the same optical path. The displacement signal is found to originate from the diffracted image change at the surface. A dynamic range of 2 μm and a minimal resolution of 1 nm for a lens of f=3.6 mm are obtained. The difference current, when normalized by the summation current, becomes a function of displacement and is independent of the sample surface reflectivity. As an application, a piezoceramic piece having a mean roughness of 1.03 μm was used. The frequency characteristics measured by this mechanical displacement method and the conventional electric oscillation measurement method were compared and found to be in good agreement.
Stabilization of the output power of a 20-MW klystron to within 0.1%
Authors: Meddens B. J. H. , Delmee P. F. M. , Van der Geer C. A. J. , Manintveld P. , Van Der Meer A. F. G. , Van Amersfoort P. W.
Published: July 2002

For operation of a free electron laser, requirements on electron energy stability are extremely tight. When a radio frequency field is used to accelerate the electrons, this leads to stringent requirements on the stability of the klystron output power. We present results obtained with a 20-MW klystron which is energized by a pulse-forming network. The achieved stability of the klystron power is better than 0.1% during 20 μs.
Charge synchronization for a piezoelectric droplet generator
Authors: Warnica W. D. , Van Reenen M. , Renksizbulut M. , Strong A. B.
Published: July 2002

Improvements to an existing piezoelectric droplet generator are reported. This instrument produces monosize droplets from the periodic breakup of a liquid jet. Droplets tend to be closely spaced because of the method of generation, so increased separation is obtained by selectively charging and deflecting some of the droplets from the main stream to a drain. A phase-shifting circuit is used to synchronize the charging signal with droplet formation so that droplets are properly charged or discharged, as required. Originally, charge synchronization was obtained by controlling the amplitude of the piezoelectric transducer voltage and thus, altering the breakup length of the jet which was observed to lead to the production of satellite droplets or loss of control at large amplitudes. The present circuit avoids these problems.
Application of a bridge circuit for an inductive critical current density measurement of superconducting thin films
Authors: Lee S.-P. , Jung C. U. , Kim Y. K. , Jo W. , Noh T. W.
Published: July 2002

Recently, a new contactless Jc measurement technique by monitoring nonlinear responses from a coil mounted in the proximity of a superconducting film was reported by Classen et al. [Rev. Sci. Instrum. 62, 996 (1991)]. An improved method to measure the nonlinear inductive response is developed using an inductance bridge circuit, which discriminates the third-harmonic signal due to the nonlinearity from those of other origins. Moreover, in this technique, the phase of the third-harmonic signal can be used to determine the critical current.
Tunable repetition rate optical spectroscopy with high-power visible diode lasers
Authors: Tatum J. A. , MacFarlane D. L. , Serreze H. B.
Published: July 2002

The methodology and apparatus are described to perform tunable repetition rate optical spectroscopic measurements using high-power visible diode lasers. Here, a train of picosecond pulses interrogates a material, a sample, or a device under test. The response of the sample or device varies as the pulse repetition frequency changes. Using an rf modulated high-power AlGaInP 670-nm diode laser, the pulse train repetition frequency may be smoothly varied from the kHz range up to the GHz range. The power and the pulse width may be kept constant by adjusting the rf power and the dc injection current. This procedure is automated through computer control. Here we describe the details of our particular setup and present examples of the technique.
A new instrument for spatially resolved laser desorption/laser multiphoton ionization mass spectrometry
Authors: Voumard Pierre , Zhan Qiao , Zenobi Renato
Published: July 2002

A new reflectron time-of-flight mass spectrometer using a pulsed CO2 laser for desorption of neutral molecules, followed by a pulsed, tunable UV laser for resonant multiphoton postionization is described. The innovative features of this instrument are the following: spatially resolved desorption in the μm range, a simple and efficient ion extraction geometry, and several improvements in sample loading, positioning, and observation. Excellent sensitivity in the attomole range and a mass resolution of M/ΔM≊2000 are demonstrated. Primary applications include spatially resolved organic trace analysis and the detection of selected chemical compounds in complex mixtures.
Photothermal displacement technique: A method to determine the variation of thermal conductivity versus temperature in silicon
Authors: Benedetto G. , Spagnolo R. , Boarino L.
Published: July 2002

A method to determine the variation of thermal conductivity as a function of temperature in silicon is described. The method is based on the application of a photothermal displacement technique in the temperature range 30–300 K. The results obtained on samples with different types and dopant concentrations are shown to be in good agreement with those reported in the literature.
Effect of Coulomb interaction on time of flight of cold antiprotons launched from an ion trap
Authors: Camp J. B. , Witteborn F. C.
Published: July 2002

Time-of-flight spectra for Maxwell–Boltzman (MB) distributions of antiprotons initially held in an ion trap and detected after being launched through a 50-cm-long shielding drift tube have been calculated. The distributions used are of temperature 0.4–40 K, cubic length 0.003–3.0 cm, and number 10–100 particles. The mutual Coulomb repulsion of the particles causes a reduction in the number of late arrival particles expected from the MB velocity distribution. The Coulomb energy is not equally divided among the particles during the expansion. The energy is transferred preferentially to the outer particles so that the reduction in the number of slow particles is not necessarily large. The reduction factor is found to be greater than unity when the potential energy of the trapped ions is greater than ∼5% of the ions’ kinetic energy and is ∼2 for the launch parameters of the Los Alamos antiproton gravity experiment.