bluuebunny/crossref_metadata_2025 huggingface dataset:
Envelope-function theorem in the high-energy limit
Authors: Liboff Richard L. , Seidman Steven R.
Published: July 2002

The envel/pe-function theorem is considered in the ,imit that el%ctron energy far exceeds that of the characteristic height of the potgntial array which, in turn, is comprised of a slowly varying component and smaller amplitude rapidly varying component. Working in the nearly-free-electron model, it is found that ‘‘new’’ energies and wave functions at band edges are those related to the slowly varying component of the potential. Wave functions related to the rapidly varying potential component average to zero over a small function of a primitive cell. These properties comprise the envelope-function theorem relevant to high-energy charge carriers passing through a quantum well array.
Influence of cylindrical Langmuir probe diameter on ion branch of its I-V characteristic
Authors: Shun’ko E. V.
Published: July 2002

The expression connecting the plasma parameters with the current-voltage (I-V) characteristic of the attracting probe is obtained, and it is compared with the electron branches of the experimental probe I-V characteristics in the range of the probe potentials V≳0. The theoretical and experimental results are in a good agreement. Studies of the influence of a cylindrical Langmuir probe diameter on the ion branch of its I-V characteristic are described. The transition of the ion charges from the plasma to the measuring circuit of the probe leads to a decrease of the ion concentration in the near-probe region limited by the Debye length, as is shown. The relations given in the paper enable one to reconstruct the ion concentration by the experimental I-V characteristic disturbed by the probe.
Fast calculation of collection efficiency for optical emission spectroscopy of extended sources
Authors: Colgan M. J.
Published: July 2002

A simple method for estimating the collection efficiency of a nearly ideal optical system is described. Calculation of spatial response functions for the analysis and absolute calibration of optical emission data is emphasized. The simple geometric algorithm presented is several orders of magnitude faster than algorithms based on ray tracing. The method is applied to the case of a radially uniform cylindrical source between parallel plates and the results are in excellent agreement with ray tracing calculations.
A nanometer notch filter with high rejection and throughput
Authors: Carolan P. G. , Selden A. C. , Bunting C. A. , Nielson P.
Published: July 2002

The superior etendu available from a Fabry–Perot spectrometer is also accessible when used in reflective mode in producing a narrow bandwidth rejection, or ‘‘notch,’’ filter. We consider the instrumental defects and the practical effects involved in realizing a useful device. A simple figure of merit is obtained which allows the Fabry–Perot characteristics to be specified according to the desired performance of the rejection filter. A comparison is made between calculations and a prototype Fabry–Perot notch filter.
Measurements of the contributions from high-n dielectronic satellites to the Kα resonance line in heliumlike Fe24+
Authors: Beiersdorfer P. , Schneider M. B. , Bitter M. , von Goeler S.
Published: July 2002

Measurements are presented on the contributions from dielectronic satellite transitions from upper configurations 1s2lnl′, n≥3 to the characteristic x-ray emission of heliumlike Fe24+. The measurements were carried out on the electron beam ion trap at Livermore using high-resolution Bragg-crystal spectroscopy. By eliminating uncertainties in the location and magnitude of the satellite contributions inherent in theoretical predictions the measurements improve the use of the resonance line emission of heliumlike Fe24+ as a diagnostic of ion temperature and rotation velocity of high-temperature plasmas.
A multiframe soft x-ray camera with fast video capture for the LSX field reversed configuration (FRC) experiment
Authors: Crawford E. A.
Published: July 2002

Soft x-ray pinhole imaging has proven to be an exceptionally useful diagnostic for qualitative observation of impurity radiation from field reversed configuration plasmas. We used a four frame device, similar in design to those discussed in an earlier paper [E. A. Crawford, D. P. Taggart, and A. D. Bailey III, Rev. Sci. Instrum. 61, 2795 (1990)] as a routine diagnostic during the last six months of the Large s Experiment (LSX) program. Our camera is an improvement over earlier implementations in several significant aspects. It was designed and used from the onset of the LSX experiments with a video frame capture system so that an instant visual record of the shot was available to the machine operator as well as facilitating quantitative interpretation of intensity information recorded in the images. The camera was installed in the end region of the LSX on axis approximately 5.5 m from the plasma midplane. Experience with bolometers on LSX showed serious problems with ‘‘particle dumps’’ at the axial location at various times during the plasma discharge. Therefore, the initial implementation of the camera included an effective magnetic sweeper assembly. Overall performance of the camera, video capture system, and sweeper is discussed.
Two-dimensional electron density, temperature, and radial drift profiles of a laser plasma by 266 nm collective Thomson scattering (abstract)
Authors: Cameron S. M. , Tracy M. D. , Estabrook K. G. , DeGroot J. S.
Published: July 2002

Collective Thomson scattering measurements performed at 266 nm on an underdense, long scalelength laser-produced aluminum plasma (nc∼1021 cm−3, Z∼7, Te≥50 eV, L≥100 μm) under moderate irradiance conditions (1011 W/cm2) are used to obtain temporally integrated, spatially resolved (30 μm) electron temperature, density, and radial fluid velocity contours. For an ultraviolet diagnostic wavelength, the effects of inverse bremsstrahlung heating perturbations and refractive turning are significantly reduced, allowing high density coronal conditions in the vicinity of one-tenth critical to be investigated. Detailed knowledge of these plasma conditions are fundamental prerequisites for understanding the distributed absorption process within fusion plasmas and for validation of the modeling accuracy of hydrodynamic codes. Fluid equations with classical coefficients should accurately apply to the plasma in these experiments because electron thermal transport is in the Spitzer regime, and the authors report relatively good agreement between the experimental results and two-dimensional LASNEX simulations.
A multichannel interferometer for electron density measurements in COMPASS
Authors: Edlington Trevor , Wylde Richard
Published: July 2002

A compact seven channel interferometer has been designed and built to measure electron density profiles in the COMPASS (compact assembly) tokamak. Two far-infrared (FIR) laser cavities are optically pumped with a single continuous-wave CO2 laser, generating two similar beams at λ=433 μm with a small, tunable difference frequency (0.5–1.0 MHz). The COMPASS facility incorporates a complex set of poloidal field coils close to the vacuum vessel as well as a versatile set of close coupled ‘‘helical’’ resonant magnetic perturbation windings which severely restrict diagnostic access. As a result a novel approach to the optical circuit has been necessary. Wire grid polarizers are used to divide the laser power equally between channels and to overlay probing and local oscillator beams after the probe beams have made a double pass through the plasma. Gaussian beam-mode optics is used to minimize the size of the optical components.
Modulational sources, sideband correlations and nonstationary interference in waves scattered from random media (abstract)a)
Authors: Nazikian Raffi
Published: July 2002

For the small angle scattering of coherent plane waves from inhomogeneous random media, the three-dimensional mean square distribution of random fluctuations may be recovered from the interferometric detection of the nonstationary modulational structure of the scattered field. Modulational properties of coherent waves scattered from random media are related to nonlocal correlations in the double sideband structure of the scattered field. Such correlations may be expressed in terms of a suitably generalized spectral coherence function for analytic fields.
Radiochemistry measurements on Phebus laser
Authors: Garçonnet J-P. , Bayer C. , Juraszek D. , Schirmann D. , Bertin A. , Grenier G.
Published: July 2002

We have developed a silicon radiochemistry diagnostic to measure the glass pusher areal density <ρΔR≳ of D-T filled targets and irradiated with the two beams of the Phebus laser. We describe the experimental setup (debris automated retrieval and counting systems) and its performance. This diagnostic has been used to characterize the implosions performed in direct and indirect drive schemes. DT final densities as high as 100×DT liquid have been achieved.
Mechanized selection of fiber optic arrays for spectroscopy measurements
Authors: Paul S. F. , Cylinder D. , Durst R. D. , Fonck R. J.
Published: July 2002

A 400-fiber optic bundle has been installed as part of the beam emission spectroscopy diagnostic for measuring density fluctuations in Tokamak Fusion Test Reactor. One hundred bundles, each composed of four 1-mm-diam fibers, transmit Hα light 50 m away to 20 detectors located outside the radiation area. To shorten the time spent manually switching the bundles among the 20 detectors, a mechanized fiber selector was installed. The fiber bundles were separated into radial and poloidal groups of 220 and 180 fibers and coupled by a computer-controlled, motorized precision translation stage. The fibers were fastened to a plate and placed less than 0.003 in. from an identical plate that holds a similar array of fibers which transmits the light to the detectors. Holding the fiber spacing tolerance to 0.001 in., and using refractive index matching fluid, the highest measured loss was less than 0.5 dB, and generally was very small compared to the fiber’s insertion loss. The stages are actuated with precision encoded micrometers and controlled by the beam emission spectroscopy VAX-resident software via a RS-232/CAMAC interface allowing arbitrary selections of fibers between plasma discharges with a 5 min repetition rate.
Is it advantageous to use a commercial CCD for data acquisition in pulsed experiments? (abstract)
Authors: Failor B. H.
Published: July 2002

We found that a CCD compared favorably with the film currently used to record gated XUV camera images from plasma physics experiments. The CCD was 20 times as sensitive as the film, indicating that the CCD has an effective ISO of 40 000. The camera was successfully shielded from electromagnetic pulses with electric field strengths of 0.7–1 kV/m and pulse widths of 30–65 ns. The CCD also survived the γ-ray pulse, and no degradation in performance was seen after an accumulated dose of 10–20 rad. We also successfully acquired optical light images of a Z pinch using a commercial camcorder.
A high-resolution magnetic imaging system based on a SQUID magnetometer
Authors: Hibbs A. D. , Sager R. E. , Cox D. W. , Aukerman T. H. , Sage T. A. , Landis R. S.
Published: July 2002

We have recently developed a high-resolution magnetic imaging system based on an array of five superconducting pickup coils located within 1 mm of room temperature. The pickup coils are 1.70 mm in diameter and spaced 2.5 mm apart allowing spatial resolution of order 1 mm. They are each connected to an rf SQUID and have a magnetic field sensitivity of 3 pT/√Hz. The system includes a three axis nonmagnetic translation table for mounting the sample, a stage for temperature control, and complete computer control of all functions.
The Alcator C-Mod diagnostic complement (invited) (abstract)
Authors: Marmar E. S.
Published: July 2002

Alcator C-Mod is a high field, compact tokamak facility, which commenced operation in the fall of 1991. The device incorporates strong shaping and magnetic divertor capability, with high-power ICRF auxiliary heating and pellet fueling. Diagnosing the plasma properties of Alcator C-Mod poses numerous challenges. Detailed profile information will be required in order to understand the transport and confinement properties of the various regimes which will be explored. Diagnostic techniques which will be employed include laser scattering, interferometry, reflectometry, photon and particle spectroscopy, bolometry, and electric and magnetic probes. Parameters which will be measured include temperatures and densities (two-dimensional profiles in the confinement region), radiated power, Zeff , current density, fusion reactivity, MHD activity, and flux surface shape. Specific experiments to measure density and temperature fluctuations are also planned. Special emphasis has been placed on measurements of the properties of the edge plasma, with facilities to measure fueling and recycling fluxes, edge temperatures and densities (including neutrals), power flows, and impurity sources and transport in the limiter and divertor regions. This work is supported by U.S. Department of Energy Contract No. DE-AC02-78ET51013.
e-beam probe potential diagnostic in spherical electrostatic-inertial plasma confinement (SEIC) (abstract)
Authors: Gu Y. B. , Miley G. H. , Turner L.
Published: July 2002

A new e-beam probe is developed to study the potential structure inside a SEIC device [G. H. Miley et al., Fusion Technol. 19, 840 (1991)]. The device has a spherical grid negatively biased inside a spherical vacuum chamber. Ions oscillate through the highly transparent grid, forming a single potential well inside the cathode. The potential in turn attracts electrons from ionization of background gas. The measurement of this complex potential profile is the objective of this work. The e-beam probe offers advantages over the e-emitting probes and the laser heterodyne method. It minimizes perturbations (versus a physical probe) and detects smaller charge density variations than possible with laser techniques. The present e-beam probe utilizes a higher voltage and a modified focus compared to the earlier version used by Swanson [Swanson et al., Phys. Fluids 16, 1939 (1973)]. The characteristic e-beam deflection patterns observed are compared to predictions from an impulse approximation model.
Remotely controlled illumination system for TFTR in-vessel inspection
Authors: Medley S. S. , Johnson L. C.
Published: July 2002

Internal components of the Tokamak Fusion Test Reactor (TFTR) vacuum vessel are inspected routinely during nonoperational periods using in vacuo illumination probes in conjunction with a periscope/camera viewing system. The probes presently in use must be inserted manually by personnel in the test cell, and thus are not suitable during the DT operating phase of TFTR. A new probe concept was developed which is compact, mechanically robust, and remotely operated. Each probe consists of four 650 W tungsten–halogen lamps mounted on an inconel reflector and a rotatable, cylindrical shutter which protects the lamps from deposits during plasma operation. Six probes will be permanently mounted inside the vacuum vessel at top and bottom ports which are distributed to provide the most uniform illumination practicable. The probe design and results from prototype testing will be presented.
A global fitting code for multichordal neutral beam spectroscopic data
Authors: Seraydarian R. P. , Burrell K. H. , Groebner R. J.
Published: July 2002

Knowledge of the heat deposition profile is crucial to all transport analysis of beam heated discharges. The heat deposition profile can be inferred from the fast ion birth profile which, in turn, is directly related to the loss of neutral atoms from the beam. This loss can be measured spectroscopically by the decrease in amplitude of spectral emissions from the beam as it penetrates the plasma. The spectra are complicated by the motional Stark effect which produces a manifold of nine bright peaks for each of the three beam energy components. A code has been written to analyze these kinds of data. In the first phase of this work, spectra from tokamak shots are fit with a Stark splitting and Doppler shift model that ties together the geometry of several spatial positions when they are fit simultaneously. In the second phase, a relative position-to-position intensity calibration will be applied to these results to obtain the spectral amplitudes from which beam atom loss can be estimated. This paper reports on the computer code for the first phase. Sample fits to real tokamak spectral data are shown.
Enhanced spatial localization of collective scattering based on spatially varying electric fields (abstract)
Authors: Rettig C. L. , Doyle E. J. , Luhmann N. C. , Peebles W. A. , Philipona R. , Burrell K. H. , Groebner R. J.
Published: July 2002

Collective scattering measurements on DIII-D have been complicated by the large toroidal and polodial plasma rotation which results in a large spatially varying radial electric field, especially during neutral beam injection and H mode. This electric field produces a Doppler shift (via Er×B rotation) of the scattered spectra which usually dominates the measured phase velocity and depends strongly on plasma conditions and radial variations of the electric field. Measurements from charge exchange recombination spectroscopy allow the radial structure of Er to be independently determined. The strong variation of the radial electric field across the plasma has allowed unambiguous mapping of different frequency bands of the scattered spectra into different locations in the plasma. Thus, the characteristics of fluctuations originating from the plasma interior can be easily distinguished from the edge. Measurements of the radial variation of the turbulent fluctuations will be presented. This work is supported by the U.S. Department of Energy (DOE) under Grant No. DE-FG03-86-ER53225 and DOE Contract No. DE-AC03-89ER51114.
A multiple-beam, collective scattering technique for spatially resolved measurement of plasma turbulence (abstract)a)
Authors: Spivey B. A. , Sverdrup L. H. , Lin S. H. , Trissel R. G. , Peebles W. A.
Published: July 2002

Collective Thomson scattering has long been utilized to study electrostatic turbulence in magnetic confinement fusion plasmas with a view to demonstrating a causal link to the observed anomolous transport of heat and particles. However, this goal has been severly hampered by the relatively poor spatial resolution available at the dominant turbulence wave numbers using standard experimental techniques. Good spatial resolution is necessary if adequate comparison of theory and experiment is to occur. The present paper describes the basic principles of a new technique utilizing simultaneous, multiple input beams, a detector array, and coherent tomographic inversion algorithm, which can substantially improve the available spatial resolution for these important measurements. The proposed multiple beam scattering diagnostic offers a spatial resolution of ∼10 cm at a fluctuation wave number of 5 cm−1 when the angular envelope of the beams is 0.1 rad. Optical designs suitable for implementing the multiple beam diagnostic on a large tokamak have been developed.
Performance evaluation of the TFTR gyrotron CTS diagnostic for alpha particles
Authors: Rhee D. Y. , Cohn D. R. , Machuzak J. S. , Woskov P. , Bretz N. , Budny R. , Efthimion P. C. , Park H. K.
Published: July 2002

A large-angle, 60-GHz collective Thomson scattering (CTS) diagnostic system for localized measurements of DT alpha-particle velocity distribution and fraction is being implemented on TFTR. Calculations of expected CTS spectra, signal-to-noise ratio per receiver channel, and estimated error in determining the temperature and fraction of alpha particles are being carried out. The experimental spectra are simulated by adding noise to the theoretical calculation by a Monte Carlo technique. Error analysis is then performed by using a relative intensity calibrated nonlinear curve fitting code to calculate the desired plasma parameters (Ti, Tα, nα/ni). Simulation results indicate that expected background emission of 20 eV during Supershot in TFTR poses no problem to the experiment. Also short integration times (<10 ms) can be used to resolve the energetic ion features, thus offering a possibility for the study of temporal evolution of energetic ion velocity distribution during a single plasma shot.
Reflectometry as a fluctuation diagnostic: A one-dimensional simulation
Authors: Chou A. E. , Luhmann N. C. , Peebles W. A. , Rhodes T. L.
Published: July 2002

Reflectometry is currently employed to characterize turbulence in fusion plasmas worldwide and is expected to be a major diagnostic on the next generation of machines (e.g., ITER). Until recently, little was known about the response of a reflectometer to fluctuations (degree of localization of the signal, sensitivity to fluctuation wave number, dependence on density scale length, etc.). To elucidate these properties, we have been modeling reflectometer behavior with a code based on solution of a one-dimensional full wave equation. The code models an infinite plane plasma with density gradient in the x direction and solves the full wave equation to find the electric field of the reflectometer’s electromagnetic wave. It can simulate stationary and moving density perturbations with arbitrary waveforms and wave numbers in plasmas with arbitrary density profiles. We present results of test cases comparing computational results to known analytic solutions for linear and 1−α2/x2 plasma density profiles, which show very good agreement.
A narrow line high average power CO2 laser for pumping far-infrared laser media
Authors: Watterson Reich
Published: July 2002

A 10 MW peak power, 1000 pps transverse discharge CO2 laser is under construction. This device will be employed to optically pump a far-infrared medium, NH3 for example, and comprise the submillimeter master oscillator of an alpha Thomson scattering diagnostic for fusion plasmas. Transverse laser discharge stability will be maintained by a compact flow recirculation flow loop which is contained within a compact (1 m diam ×1.5 m long) cylindrical pressure vessel. Magnetic pulse compression techniques will also be employed to efficiently generate the laser discharge. System details and current fabrication status will be presented.
Absolute calibration of the JT-60U neutron monitor using a 252Cf neutron source (abstract)a)
Authors: Nishitani T. , Takeuchi H. , Kondoh T. , Itoh T. , Kuriyama M. , Ikeda Y. , Iguchi T. , Barnes Cris W.
Published: July 2002

Absolutely calibrated measurements of the neutron yield are important for the evaluation of the plasma performance such as the fusion gain Q in D-D operating tokamaks. The time-resolved neutron yield is measured with 235U and 238U fission chambers and 3He proportional counters in the JT-60U tokamak. The in situ calibration was performed by moving the 252Cf neutron source toroidally through the JT-60 vacuum vessel. Detection efficiencies of three 235U and two 3He detectors were measured for 92 locations of the neutron point source in toroidal scans at two different major radii. The total detection efficiency for the torus neutron source was obtained by the averaging the point efficiencies over the whole toroidal angle. The uncertainty of the resulting detection efficiency for the plasma neutrons is estimated to be ±11%.
Diagnostic needs for fluctuation and transport studies (invited)
Authors: Carreras B. A.
Published: July 2002

The identification of fundamental transport mechanisms in magnetically confined plasmas is a critical issue for the magnetic fusion program. Recent progress in understanding fluctuations and transport is well correlated with the development and use of new diagnostics, but a great deal of information is still missing. Some of the required measurements are well beyond our present diagnostic capabilities, but some are within reach and could answer critical questions in this area of research. Some of these critical issues are discussed.
Spontaneous nuclear polarization of atomic hydrogen at low magnetic field
Authors: Luppov V. G. , Roser T.
Published: July 2002

The known spin-exchange rates of atomic hydrogen lead to fast spontaneous buildup of high nuclear polarization at low magnetic field. We propose to use the nuclear polarized atomic hydrogen gas to produce an intense ultracold nuclear polarized beam of atomic hydrogen.
Bent crystal, bent multilayer optics on a multipole wiggler line for an x-ray diffractometer with an imaging plate detector
Authors: Fourme R. , Dhez P. , Benoit J. P. , Kahn R. , Dubuisson J. M. , Besson P. , Frouin J.
Published: July 2002

A setup for diffraction and diffuse scattering studies on biological crystals, in the wavelength range 1.5–0.9 Å, is operating on the superconducting wiggler line of the storage ring DCI at LURE. Double focusing and rejection of harmonic contribution are achieved by combining two Bragg reflectors with elliptical curvature, respectively, a Si or Ge single crystal and a large W/Si interferential reflector (layered synthetic microstructure). Area detectors include photographic films and an imaging plate scanner device.
A data collection program for x-ray diffractometry
Authors: Brennan Sean
Published: July 2002

A computer program for controlling diffractometers is described. At present it is capable of controlling a four-circle diffractometer in a variety of calculation modes, a two-circle diffractometer, and also a z-axis diffractometer. The program includes on-screen plotting of both the current scan and previous scans. There is a separate program which consists of the plotting subset of the commands so that while one user is collecting data other users can be analyzing old data simultaneously. Extensive on-line help is provided. The program is written in fortran, runs on the VMS operating system, and is primarily dependent on CAMAC for data collection.
Digital measurement of resistance fluctuations
Authors: Moon J. S. , Mohamedulla Arshia F. , Birge Norman O.
Published: July 2002

We describe a digital technique for measuring the spectral density of resistance fluctuations with simultaneous background subtraction. The technique implements either of two equivalent ac bridge techniques that rely on extremely good orthogonality between the two channels of a dual-phase lock-in amplifier. We use a digital signal processor (DSP) chip and a personal computer in place of both the lock-in amplifier and spectrum analyzer. The digital system can measure sample 1/f noise that is 100 times smaller than the experimental background noise; this performance equals or surpasses that of any analog system. The system is low cost, very flexible, and can function as a stand-alone digital lock-in amplifier or low-frequency spectrum analyzer.
Two time-dependent, focus-dependent experiments using the energy-dispersive spectrometer at LURE
Authors: Fontaine A. , Baudelet F. , Dartyge E. , Guay D. , Itié J. P. , Polian A. , Tolentino H. , Tourillon G.
Published: July 2002

Rather than a brief review of what has been achieved at LURE [A. Fontaine, E. Dartyge, J. P. Itié, A. Polian, H. Tolentino, and G. Tourillon, Topics in Current Chemistry 151, (Springer, Berlin, 1989), Vol. 151] since 1985 with the fully dedicated, energy dispersive x-ray absorption fine structure beam line, we will present two classes of experiments plus a discussion on the present ultimate source of noise of our mechanical movement-free spectrometer. Moreover, the readers interested in this field, can find two other studies with the new born ports at Hamburg [M. Hagelstein, S. Cunis, R. Frahm, W. Niemann, and P. Rabe, Phys. B 158, 324 (1989)] and Daresbury [G. Baker, C. Richard, A. Catlow, J. Couves, A. J. Dent, G. Derbyshire, G. N. Greaves, and J. M. Thomas, XAFS VI York 1990]. Related to this field are the quick extended x-ray absorption fine structure spectrometers developed initially at Hamburg under R. Frahm [R. Frahm, Nucl. Instrum. Methods A 270, 578 (1988)] and at LURE under P. Lagarde and C. Prietto [P. Lagarde, M. Lemonnier, and H. Dexpert, Physica B 158, 337 (1989)], which have been able in these two years to open new routes in a wide variety of science.
Microcomputer-based Peltier thermostat for precision optical radiation measurements
Authors: Zhu Xiaosong , Krochmann Eike , Chen Jiashu
Published: July 2002

We have developed a microcomputer-based thermostat for a light measuring head in precision optical radiation measurements. This thermostat consists of a single-chip microcomputer, a digital-to-analog converter, a liquid crystal display, a power operational amplifier, and a Peltier element (thermoelectric cooler). The Peltier element keeps the temperature of the photometer head at 20±0.1 °C in the ambient temperature range from −20 to 60 °C. A control algorithm which combines the ‘‘Bang-Bang’’ mode and proportional-plus-integral-plus-derivative mode is used to achieve fast and smooth thermostatic performance. This thermostat is effective, inexpensive, and easy to adjust. Several applications of the Peltier thermostat are mentioned.
Improvement of the temperature distribution on the surface of Si monochromator heated by synchrotron radiation
Authors: Hrdy J. , Wolf P.
Published: July 2002

From the preliminary finite difference calculations it follows that by making the suitable notches (grooves) to the surface of the crystal monochromator heated by synchrotron radiation, it is possible to reduce the temperature variation across the surface of the crystal. The role of the notches is to reduce that component of the heat flow which is parallel with the surface of the crystal.
Gas pump with a magnetically coupled piston
Authors: Shelton D. P. , Donley E. A.
Published: July 2002

A simple pump has been constructed which is useful for stirring gas in a sample cell for gas-phase nonlinear optics experiments. It uses a piston and has been operated at gas pressures from 0 to 200 atm, and at temperatures from room temperature to 200 °C.
X-ray generation from a gas-puff z-pinch driven by a pulsed power generator with a self-crowbar switch
Authors: Takasugi K. , Akiyama H. , Shimomura N. , Sato M. , Tazima T.
Published: July 2002

A self-crowbar switch was operated on the pulsed power generator LIMAY-I and applied to a gas-puff z-pinch load. The radial collapse of the plasma is demonstrated to occur with the aid of the self-crowbar switch after the applied power pulse has turned off. X-ray emission was observed to coincide with radial collapse of the plasma, and the pinched plasma was visually observed by an x-ray pinhole photograph. The x-ray intensity increased with decrease of the puffed gas density.
A device for generation and accumulation of plasma with relativistic electron temperature by means of the gyromagnetic autoresonance
Authors: Colunga-Sánchez S. , Andreev B. B. , Golovanisky K. S.
Published: July 2002

Results of an experimental study of a relativistic plasma generated by means of the gyromagnetic autoresonance in the plasma synchrotron accumulator called GYRAC-D are presented. The use of a new heating scheme in the regime of a train of pulses with the further accumulation of the generated plasma in a mirror magnetic configuration and improvement of vacuum conditions owing to a system of external injection make it possible to obtain a plasma with the following parameters: Te≊200 keV, ne≊1×109 cm−3, and lifetime approximately 1 s. No major obstacles to further increase the density are observed.
A high-stability quartz crystal microbalance electrode for simultaneous solution-phase electrochemistry/microgravitometry
Authors: Komplin Glenn C. , Schleifer Fred , Pietro William J.
Published: July 2002

A quartz crystal microbalance (QCM) oscillator circuit is described which incorporates a high-gain feedback amplifier controlled by an automatic gain network. Signal level in the oscillator feedback loop is automatically optimized to provide sufficient gain necessary to sustain stable oscillation, but not so much gain as to induce waveform clipping, which would detriment frequency stability. The crystal is driven and loaded by a low-impedance network, and one side of the crystal is held at low impedance to ground. In this way, the microbalance crystal may be used in place of a working electrode in an electrochemical apparatus. Gravitometric studies at the surface of the electrode may be combined simultaneously with cyclic voltammetry, chronocoulometry, chronoamperometry, or any other electrochemical experiment in aqueous and nonaqueous solutions. The QCM signal is heterodyned with a reference signal to produce a difference frequency on the order of a few hundred Hertz. An optional frequency-to-voltage converter is also described so that the beat frequency can be monitored in real time on a chart recorder. The results of a simultaneous electrochemical/microgravitometry experiment involving the growth and redox cycling of a Prussian blue film on the surface of the QCM are presented.
A new device for electrical resistivity measurements as a function of temperature (86–700 K) under controlled atmosphere by the four-probe method
Authors: Kokabi H. R. , Provost J. , Desgardin G.
Published: July 2002

A device for measuring electrical resistivity as a function of temperature using unsoldered, sharp, and independent contacts has been developed. The probes are fixed on fine ceramic tubes, which are actuated by pressure-sensitive springs. The ceramic tubes are guided by metallic struts that also serve as thermal screens. The device is placed in an enclosure where a primary vacuum is established and introduce a neutral, reducing, or oxidizing gas. Measurement can be performed continually between 86 and 700 K. Materials having resistivities in the 10−8–106 Ω m range have been characterized even when they present resistivity jumps of many orders of magnitude.
Modeling of surface charge distributions in electret ionization chambers
Authors: Fallone B. G. , MacDonald B. A.
Published: July 2002

Computer modeling of the change of electret surface-charge distribution within electret ionization chambers (EIC) during the electret charging and discharging processes are described. Assuming a uniform and constant rate of ion generation, the theory of ion recombination in air is applied to Laplace’s equation to develop a description of the rate of charge accumulation and surface charge distribution. It is shown that distortions of electric fields within the air gap of the EIC control the distribution of charge accumulation, while saturation conditions, that determine the level of recombination of charges within the air gap of the EIC, control the maximum potential that can be deposited onto the electret surface. Results of modeling are compared with measured data, and suggestions for refinement in the model are discussed.
Quantum transport in sputtered, epitaxial Si/Si1−xGex heterostructures
Authors: Sutter P. , Groten D. , Müller E. , Lenz M. , von Känel H.
Published: July 2002

Radio–frequency magnetron sputter epitaxy was employed for the synthesis of n–type modulation doped Si/Si1−xGex heterostructures. Si channels were grown coherently on sputtered, compositionally graded Si1−xGex buffers of low defect density, and remotely doped with phosphorus by plasma assisted gas phase doping. Magnetotransport measurements on these films revealed Shubnikov–de Haas oscillations in the longitudinal and the integer quantum Hall effect in the transverse magnetoresistance, demonstrating the presence of a two–dimensional electron gas. At T=1.6 K and sheet densities of 1012 cm−2, electron mobilities as high as 15 800 cm2/V s give evidence of the excellent structural and electronic properties achievable by the sputter growth technique.
Enhancement of the superconducting properties of TlBa2CaCu2O7+δ thin films via postannealing
Authors: Siegal M. P. , Venturini E. L. , Newcomer P. P. , Morosin B. , Overmyer D. L. , Dominguez F. , Dunn R.
Published: July 2002

The superconducting properties of TlBa2CaCu2O7+δ(Tl-1212) films are greatly enhanced by annealing in unreactive ambients such as nitrogen at temperatures ranging from Ta=250–600 °C. The transition temperature, Tc, of these Tl-1212 films as-grown in oxygen is 70 K. Annealing for 1 h at 250 °C elevates Tc above 90 K. Tc further increases and sharpens for Ta=600 °C. In addition, subtle changes occur in the microstructure correlating with improved critical current density. These results indicate that Tl-1212 films may be of greater relevance for electronics applications than previously believed.
A 50 MW pulse-forming network with a voltage stability within 0.03%
Authors: Meddens B. J. H. , Delmee P. F. M. , Van Amersfoort P. W.
Published: July 2002

Requirements on electron energy stability are extremely tight for operation of a free-electron laser. In case a radio-frequency field is used to accelerate the electrons, this leads to stringent requirements on the stability of the klystron output power and, hence, on the stability of the source producing the cathode voltage. A pulse-forming network (PFN) capable of delivering a 19 kV pulse with a stability of 0.03%, during 20 μs, is presented. The PFN consists of four parallel lines, each containing 19 cells of a 20 nF capacitor and a 20 μH solenoid. The solenoids are equipped with taps and a plunge tuner. An innovative line switch is used, namely a stack of 32 thyristors in series. Numerical simulations of the pulse shape show that, in order to obtain the best possible pulse flatness, it is essential to arrange the capacitors such that the difference between adjacent capacitances is minimized.
A single photon timing instrument that covers a broad temporal range in the reversed timing configuration
Authors: Bowman Lawrence E. , Berglund Kris A. , Nocera Daniel G.
Published: July 2002

A versatile single-photon timing instrument based on the reversed timing configuration has been constructed. Unlike similar instruments, the apparatus described here is capable of recording a broad range of excited-state decay times owing to a switched fiber optic delay. This allows the user to readily collect time-resolved luminescence data over a variable time window in the reversed-timing configuration. With proper adjustment of the appropriate components, one can acquire a luminescence decay over a variable time range from less than 1 ns to nearly 1 μs. The full width at half-maximum of the instrument response function is 42 ps. The utility of a switched fiber optic delay is discussed and the device’s construction is described.
A high-temperature pulsed supersonic nozzle
Authors: Fink M. , Häger J. , Glatzer D. , Walther H.
Published: July 2002

A pulsed supersonic nozzle is presented which can be heated to 1300 K and cooled to 4 K. The whole system is composed of quartz to prevent the decomposition of the molecules at a high temperature. The nozzle has produced gas pulses at a rate of 10 Hz and pulse lengths of 5 ms. The performance of the system is demonstrated by the flight time and the rotational temperature of NO molecules as a function of the stagnation pressure and the nozzle temperature.
Modeling of spatial distortions in a high-speed image converter camera
Authors: Patrie Bryan J. , Seitzman Jerry M. , Hanson Ronald K.
Published: July 2002

A computer model for correcting the spatial distortion in images acquired with a high-speed image converter camera is described. The distortion is caused by electrodynamic interaction of the photoelectric currents within the image converter camera, and appears as an inward bowing of the individual high-speed images. The model is implemented in a postprocessing algorithm, using the pixel values in an image to infer the interacting photoelectric currents and thus allow computation of the distorting force acting on each pixel. The force is converted into a corrective translation using three system parameters which are determined by analyzing images for which the predistortion geometry is known. Measurements on a variety of test images show the model removes up to 85% of the image converter distortion.
Tester for granular superconductors
Authors: Stankowski Jan , Czyżak Borysl/aw
Published: July 2002

A device meant as a supplement to a standard electron paramagnetic resonance spectrometer, permitting easy and accurate determination of the Tc-onset critical temperature superconductors, has been designed and constructed. The method of tracing microwave absorption changes permits detecting even very small amounts of the superconducting phase and determining the Tc-onset critical temperature with an accuracy of an order of 0.1 K.
A small rugged nitrogen laser for instrumentation
Authors: Rodrigues Silvana Vianna , Baumann Wolfram
Published: July 2002

A novel small and rugged type of a free running atmospheric pressure nitrogen laser is presented and its behavior is studied in detail. Pulse half-widths are between 800 ps for 60 mm active channel length, and 1.1 ns with pulse energies of 150 μJ for 170 mm active length, both at 2.4 mm laser gap. The maximum pulse energy is found at a field strength-to-pressure ratio around 110 V/(cm Torr), in agreement with what is reported in literature for nitrogen lasers. Preionization by ultraviolet light from the free running spark gap could be ruled out while corona discharge over the capacitor foil surface between the laser electrodes could not be excluded.
Theoretical consideration of intensity of an x-ray microbeam formed by a hollow glass pipe
Authors: Furuta K. , Nakayama Y. , Shoji M. , Kaigawa R. , Hanamoto K. , Nakano H. , Hosokawa Y.
Published: July 2002

Intensities of x-ray microbeams formed by the 250-mm-long hollow glass pipes of inner diameters of 27.4, 23.0, and 18.8 μm have been theoretically investigated, by taking account of the slope distribution of microprojections (surface roughness) on the pipe inner wall, using the Monte Carlo method. The intensities for all the pipes calculated on the supposition that each pipe inner wall is perfect (i.e., zero rms of the slope distribution) have been much greater than the experimental values in the x-ray energy region from 6.93 to 19.6 keV. Assuming the slope rms from 2.5×10−4 rad to 3.3×10−3 rad, the calculated results have agreed with the experimental values. Discussions on the results for all the pipes are given in relation to the x-ray anomalous dispersion, the penetration of x rays, the intensity distribution on the x-ray sources used, undulation of the pipes, and the presence of microdust in the pipes.
Bipolar treatment of the electrically detected photocarrier grating method
Authors: Hundhausen M. , Ley L.
Published: July 2002

The electrically detected transient grating technique was introduced recently to determine ambipolar diffusion constant Damb and lifetime τR of photocarriers in semiconductors. These material parameters are extracted from the transient current perpendicular to an intensity grating formed by coherent laser beams after that grating is switched on and off. We describe the bipolar treatment to calculate the time-dependent photocurrent by solving the rate equations for electrons and holes with Poisson’s equation. The shape of the transient signal depends critically on the dielectric-relaxation time (τdiel) in addition to Damb and τR. A satisfying fit of experimental data for amorphous hydrogenated silicon is obtained when τdiel is adjusted appropriately.
A new technique of measuring the complex dielectric permittivity of liquids at microwave frequencies
Authors: Subramanian V. , Bellubbi B. S. , Sobhanadri J.
Published: July 2002

A new technique, based on the cavity resonance, of measuring the complex dielectric permittivity of liquid samples is described in detail. The errors in the measurement of the real and imaginary parts of the complex dielectric permittivity are ∼±1% and ±3%, respectively. The complex dielectric permittivity values measured using this method for some standard liquids are also presented. A comparison is made between the present values and the values obtained using standard techniques.
Pulse charging of capacitors for reduction of voltage stress
Authors: Lee S. , Kumar Suresh , Chia T. C. , Serban A. , Springham S. V.
Published: July 2002

The advantages of on-demand pulse charging of high-voltage (HV) capacitors are discussed, highlighted by use of the technique to reduce the pulse width of a nitrogen laser to subnanosecond. Pulse charging reduces the HV stress on the capacitor dielectric resulting in a more compact laser reducing the discharge time of the laser strip-line capacitor. The HV pulse for charging is produced by switching a low-voltage capacitor via a step-up coil into the HV strip-line capacitor which is then immediately discharged. The system reduces the on-charge duty cycle to below 0.001.
All metal bakeable piezoelectric valve
Authors: Marescaux Dan
Published: July 2002

An ultrahigh vacuum leak valve is described, which can be baked up to 450 °C. The throughput can be adjusted between 1×10−10 and 5×10−6 Pa m3 s−1. The actuator is a piezoelectric stack which can be easily removed and set back. The baking temperature with the actuator in place is limited by the thermal specifications of the piezoelectric material. The inner surfaces, which are solely stainless-steel and gold, allow an almost unlimited choice of working gases.
Nd3+:ethylene glycol amplifier and its stimulated emission cross section
Authors: Han K. G. , Kong H. J. , Kim H. S. , Um G. Y.
Published: July 2002

We demonstrate that Nd3+:ethylene glycol can be used as an amplifier gain medium for a Nd3+:YLF laser. It has been known that Nd3+:liquid is hard to use as a gain medium due to fluorescence quenching. However, we could use Nd3+:ethylene glycol as a gain medium by using a new amplification system, and we also measured the stimulated emission cross section of Nd3+:ethylene glycol. A maximum gain of ∼2 was obtained in our experimental setup, and the stimulated emission cross section of Nd3+:ethylene glycol was measured to be 1.5(±0.5) ×10−19 cm2.
A simple method for prolonging the effective pathlength in laser kinetic spectroscopy
Authors: Haggquist Gregory W. , Razi Naqvi K.
Published: July 2002

A multipass cell, which offers more than tenfold gain in sensitivity in ordinary and kinetic absorption spectroscopic measurements, is constructed by depositing aluminum mirrors on the flat walls of a standard fluorimetric cell, and its performance is demonstrated.
Extra interface state generation enhanced by fluorine in tungsten-polycided metal-oxide-semiconductor devices with nitrided oxide gate dielectric
Authors: Chen C. W. , Fang Y. K. , Lee G. Y. , Hsieh J. C. , Liang M. S.
Published: July 2002

Interface state generation in oxynitride gate dielectric devices with tungsten-polycide (W-polycide) and polycrystalline silicon (poly-Si) gate structures were investigated. A significant amount of fluorine-induced interface states were detected in W-polycide gate device with nitridation of thermal gate oxide by both the charge pumping technique and capacitance/gate voltage (C/V) measurement. Re-oxidation of oxynitride gate oxide results in partial annealing of these interface states. A model of the fluorine induced strain gradient between silicon dioxide and silicon (SiO2/Si) interface was proposed to explain the extra interface state generation mechanism.
Radiation processing of Cr-GaAs contacts
Authors: Breza J. , Kadlečíková M. , Konakova R. V. , Lyapin V. G. , Milenin V. V. , Statov V. A. , Tkhorik Yu. A. , Filatov M. Yu.
Published: July 2002

We report on the influence of 60Co gamma-radiation upon the properties of Cr-GaAs diode structures. Auger depth profiling proved that while a low dose of radiation made the transition region wider, higher doses caused its narrowing. Radiation treatment affected the Schottky barrier height and ideality factor favourably.
Electrochemically induced changes in the surface diffusion in polycrystalline platinum electrodes
Authors: Hidalgo M. , Marcos M. L. , González Velasco J.
Published: July 2002

Surface diffusion coefficients, DS, of platinum adatoms were measured in situ on polycrystalline platinum electrodes inmersed in 1 M HClO4, 1 M H3PO4 and 0.5 M H2SO4 electrolytic solutions at different potential values. The change in the DS values observed, as well as the rate of change of DS with the potential value, confirm an adsorbate induced relaxation of Pt electrode surfaces.