bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurements of F*, CF, and CF2 formation and decay in pulsed fluorocarbon discharges
Authors: Hansen S. G. , Luckman G. , Colson Steven D.
Published: July 2002

The temporal population profiles of F*, CF, and CF2 in a sharp-edged, pulsed (500 μs), fluorocarbon discharge are examined. F* population rises and falls with the discharge current suggesting that electron impact of the parent fluorocarbon is the primary source of emitting fluorine atoms. Ground-state CF and CF2, monitored by laser-induced fluorescence, show noticeably slower formation and decay, but a simple kinetic model assuming that each arises from direct electron impact of the parent gas fits the data. It is shown that CF can be conveniently monitored by exciting the B̃(v′=2)−X̃(v″=0) transition with a 193 nm ArF excimer laser.
Determination of the local Al concentration in AlxGa1−xAs-GaAs quantum well structures using the (200) diffraction intensity obtained with a 10 Å electron beam
Authors: Ou H.-J. , Tsen S.-C. Y. , Tsen K. T. , Cowley J. M. , Chyi J. I. , Salvador A. , Morkoç H.
Published: July 2002

A novel method for determining the local concentration of Al in the AlxGa1−xAs layer of AlxGa1−xAs-GaAs multiple quantum well structures is reported. By scanning a 10 Å electron beam across the interface, the (200) dark-field scanning transmission electron microscopy (STEM) image shows the contrast of the AlxGa1−xAs-GaAs multilayer since the intensity of the (200) diffraction is sensitive to the Al concentration. The line scan intensity profile of the (200) diffraction, along a uniform specimen region of known thickness, shows the intensity variation of the (200) diffraction and reflects the local content of Al in each region. The simulation of the nanodiffraction patterns produces a chart of the (200) diffraction intensity versus the Al concentration for the determination of the local change of the Al concentration. A molecular beam epitaxy grown AlxGa1−xAs-GaAs specimen (x=0.57 as determined from Raman spectroscopy) is tested and the dark-field STEM studies show two thin layers of x=0.46 at the 1/3 and 2/3 height level within every AlxGa1−xAs layer.
Heteroepitaxial YBa2Cu3O7−x-SrTiO3-YBa2Cu3O7−x trilayers examined by transmission electron microscopy
Authors: Tidjani Mohammed E. , Gronsky Ronald , Kingston John J. , Wellstood Frederick C. , Clarke John
Published: July 2002

We report high-resolution transmission electron microscopy and electron diffraction studies of the heteroepitaxial superconductor-insulator-superconductor system YBa2Cu3O7−x-SrTiO3-YBa2Cu3O7−x deposited on polished (001)MgO substrates by in situ laser ablation. The resulting films grow epitaxially and consistently preserve a parallel orientation between the close-packed (001)YBa2Cu3O7−x planes and (001)SrTiO3 planes over the entire trilayer, even in the presence of ledges or steps along vicinal interfaces. Although the interface regions showed strain occasionally relieved by stacking faults, they were free of disorder and any evidence of impurity phases. The observed epitaxial growth is very likely responsible for the excellent electrical properties found in similarly constructed multilayer interconnects.
Generation of the pretilt angles in nematic liquid crystal (5CB) aligned on the rubbed polypyrrole films
Authors: Seo Dae-Shik , Kobayashi Shunsuke , Mochizuki Akihiro
Published: July 2002

We have investigated the pretilt angles generated in the nematic liquid crystal 5CB media, aligned on polypyrrole (PP) films through rubbing. It is shown that the PP films may be synthesized with two kinds of counter ionic atomic groups, i.e., rheonium oxide (ReO−4) which can generate about 5° pretilt angles and bromide (Br−) where no pretilt angle is observed.
Concentration profiles of CF in a CF4 radio frequency discharge via laser induced fluorescence and actinometry
Authors: Conner W. T. , Sawin H. H.
Published: July 2002

We have measured the steady state, axial concentration profiles of the CF radical in a symmetric, parallel plate, 13.56 MHz discharge in CF4 (with 5% Ar) using both laser induced fluorescence (LIF) and actinometry. The two lowest vibrational levels of the ground electronic state (X) of CF were probed with LIF and the two lowest vibrational levels of the B electronic state were observed in emission for actinometry. The LIF profiles, and thus, the X state concentration profiles, were both nearly flat in the bulk of the discharge. The B, v′=0 actinometric profile was sharply peaked, while the v′=1 was nearly flat. Therefore, spatially resolved actinometry works for the B,v′=1 level of CF but not for v′=0, under the discharge conditions studied.
Hydrogen assisted heat transfer during diamond growth using carbon and tantalum filaments
Authors: Yarbrough W. A. , Tankala K. , Mecray M. , DebRoy T.
Published: July 2002

Much of the previous work on the role of atomic hydrogen in diamond growth has been focused on its formation on various refractory metal filaments, its reaction in the gas phase and its role in the growth mechanism. In contrast, the effect of atomic hydrogen recombination on substrate heating is addressed in this letter. Experiments were conducted in vacuum, helium, and hydrogen environments. Tantalum and carbon filaments were used to vary atomic hydrogen generation rates. Furthermore, methane was added in some experiments to determine its effect on hydrogen assisted ‘‘chemical’’ heating of the substrate. The results indicate that when substantial amounts of atomic hydrogen are generated at the filament, reactions of atomic hydrogen at the diamond growth surface have a pronounced effect on the substrate temperature. Use of carbon filaments lead to significantly diminished atomic hydrogen generation rates and much lower substrate temperatures. Additions of small amounts of methane to hydrogen also resulted in reduced atomic hydrogen generation rates and, consequently, lower substrate temperatures.
Ion-induced fluorination in electron cyclotron resonance etching of silicon studied by x-ray photoelectron spectroscopy
Authors: Vender David , Haverlag Marco , Oehrlein Gottlieb S.
Published: July 2002

X-ray photoelectron spectroscopy has been used to investigate the effect of varying substrate bias when silicon is etched in a CF4 electron cyclotron resonance plasma. After etching, the silicon surface is found to be covered by a two layer structure consisting of damaged, fluorinated silicon and a fluorocarbon overlayer. The thickness of the fluorinated silicon layer depends on the self-bias voltage. Reduction of the ion energy leads to a thinner fluorinated layer as well as a lower etch rate, suggesting that damage and fluorination of the crystal lattice are important in the ion enhanced etching of silicon in fluorine containing plasmas.
Moving grating technique: A new method for the determination of electron and hole mobilities and their lifetime
Authors: Haken U. , Hundhausen M. , Ley L.
Published: July 2002

A new technique to determine the mobilities and lifetime of photogenerated electrons and holes in semiconductors relies on the short circuit current that is induced perpendicularly to a moving interference grating. Theoretical expressions for the short circuit current are derived that relate the carrier mobilities and their lifetime to the velocity and spatial period of the grating. The technique has been implemented and was successfully applied to a-Si:H.
Scanning tunneling microscopy of single-shell nanotubes of carbon
Authors: Ge Maohui , Sattler Klaus
Published: July 2002

Single-shell nanotubes of carbon were produced by vapor-phase condensation on highly oriented pyrolytic graphite (HOPG). Atomic-resolution images were obtained using a scanning tunneling microscope (STM). The nanotubes are 1 nm wide and up to 20 nm long. The atomic structure of a zigzag configured tube is identified. A C60 hemisphere with threefold symmetry could be the nucleation seed for its growth.
Fabricating nanoscale structures on Au surface with scanning tunneling microscope
Authors: Bessho K. , Hashimoto S.
Published: July 2002

Nanometer-scale pits and mounds were fabricated on Au surface with a scanning tunneling microscope (STM) by applying voltage pulses between the PtIr tip and the substrate. Applying a positive pulse to the substrate generated a pit on the surface with high probability, while a negative pulse formed a mound. The mechanism of structure formation is inferred to be field evaporation, and the polarity dependence is related to the high threshold value of the PtIr alloy tip for negative field evaporation. Furthermore, the fabricated mound could be removed by applying a positive pulse, suggesting that the STM voltage pulse method may be applied to rewritable ultrahigh density recording.
Stable hydrogenated amorphous silicon films deposited from silane and dichlorosilane by radio frequency plasma chemical vapor deposition
Authors: Osborne Ian S. , Hata Nobuhiro , Matsuda Akihisa
Published: July 2002

Hydrogenated amorphous silicon films have been grown by radio frequency (rf) plasma chemical vapor deposition with the addition of small amounts (up to 20%) of dichlorosilane to the silane. Results show that as the amount of dichlorosilane is increased, the films are more resilient to the creation of light induced defects. Under intense pulsed laser illumination (5 mJ/pulse, 10 ns, 10 Hz) the steady state defect density measured by the constant photocurrent method (CPM) is reduced by over one order of magnitude to 4×1016 cm−3 as compared to ∼5×1017 cm−3 for films grown under identical conditions with pure silane. Furthermore, there is a threefold increase in the deposition rate over the range of mixture ratios studied here.
Measurement of the wall radiation in soft x-ray region in PDX
Authors: Sesnic S. , Tenney F. H. , Bitter M. , Hill K. W. , von Goeler S.
Published: July 2002

A detector setup with three LN-cooled Si(Li) diodes is used to measure soft x-ray spectra (0.8–20 keV) emitted from the inside walls of the PDX vessel during the plasma discharge. The setup is part of a pulse-height-analysis system, which is used to measure the plasma and wall radiation simultaneously at five different radial positions. The wall and the plasma radiation are measured under different plasma conditions (e.g., OH and neutral beam heating). The wall radiation is very much increased during the neutral beam heating, with an enhancement factor of at least 10 over the OH wall radiation. Since we measure the plasma and the wall radiation at the same time, the measurements allow the conclusion that the wall radiation can be attributed essentially to fluorescence (line radiation, e.g., Ti-Kα) and scattering (continuum part of the wall radiation spectrum). The fluorescence and the scattering are both caused by soft x-ray radiation flux coming from the plasma. There seems to be no need to invoke other, more exotic causes for the wall radiation, for example, charge particle bombardment of the wall.
TFTR Mirnov loop system
Authors: Fredrickson E. , Colchin R. , McGuire K. , Morris W. , Sauthoff N.
Published: July 2002

Magnetic pick-up loops (Mirnov coils) located on the inner wall of the tokamak fusion test reactor (TFTR) vacuum vessel have been used to study magnetic fluctuations in the plasma. To study the high-frequency magnetic turbulence associated with beam injection, the signal from one coil is passed through a comb filter, which gives a measure of the frequency spectrum throughout the shot. To look for tearing modes, the signals from a poloidal array of 15 coils are summed in an analog system to give the amplitudes of the m=2, 3, and 4 coherent modes throughout the shot. Additionally, 20 coil signals are digitized individually at a rate of 100 kHz for 80 ms and at 10 kHz for 800 ms. These data may also be analyzed off line to get both the toroidal and poloidal mode numbers as well as the frequency spectrum for a limited portion of the discharge.
Soft x-ray tomography diagnostic for the Alcator C tokamak
Authors: Camacho J. F. , Granetz R. S.
Published: July 2002

A soft x-ray tomography diagnostic has been built and operated on the Alcator C tokamak with the use of an 80-channel array of detectors. The detector system consists of miniature PIN photodiodes which are located around the periphery of the plasma at one toroidal location (top and bottom ports) in order to image the poloidal cross section of the plasma’s soft x-ray emissivity. The compact size and inexpensive cost of these detectors allow for the large number of views required to avoid any assumptions about plasma rotation, position, or symmetry in the reconstruction algorithm. The use of logarithmic amplifiers in the electronic circuitry makes it possible to record conveniently data from a wide range of plasma operating parameters. This diagnostic has been used to study plasma position and shape, magnetohydrodynamic (MHD) phenomena, and the effects of impurities. Data from a pellet-fueled discharge exhibiting large-scale MHD activity are presented. The system has recently been expanded to 128 detectors with the addition of an array on a side port in order to improve its coverage of the plasma and the resolution of the reconstructions.
Estimation of impulse-response signals through empirically derived digital matched filter smoothing
Authors: Bialkowski Stephen E.
Published: July 2002

A real-time digital filter is described which may be most useful for optimal determination of the magnitude of impulse-response functions found in pulsed, repetitive experiments of low duty cycle. This filter is based on a matched filter but employs an interference orthogonalization step. This results in a signal magnitude estimate which is independent of coherent interference. The filter updates the signal magnitude estimate upon each repetition of the experimental cycle. Comparisons to signal estimation using gated sampling devices are given.
Two-dimensional interferometry
Authors: Blümich B.
Published: July 2002

A two-dimensional cross-correlation technique is described, which allows time-resolved pump-and-probe experiments to be performed with two continuous broadband excitations. The progress of a rate process stimulated by one excitation is investigated by the second. Within the linear response limit the technique is characterized by low excitation power and high response energy. Potential applications are in the study of dynamic mechanical and electrical material properties by spectroscopic methods such as nuclear-magnetic resonance or Fourier transform infrared spectroscopy, and in optical T1 measurements with a time resolution on the order of the inverse bandwidths of the excitations. A two-dimensional digital interferometer capable of microsecond resolution is described and used to illustrate the principle of the method with an investigation of a two-input electronic circuit.
High-temperature thin-film Pt–Ir thermocouple with fast time response
Authors: Tong H. M. , Arjavalingam G. , Haynes R. D. , Hyer G. N. , Ritsko J. J.
Published: July 2002

We have developed a thin-film Pt–Ir thermocouple which exhibits bulklike thermoelectric behavior up to 790 °C, the highest temperature observed with thin-film pure-element thermocouples. Using a Q-switched Nd:YAG laser and a signal averaging oscilloscope, its thermal response time was measured to be 60 ns. The ease of implementation in electronic devices coupled with the reproducibility over a wide temperature range make this thin-film thermocouple well suited for monitoring instantaneous temperatures during device processing.
EPR automatic frequency control circuit with field effect transistor (FET) microwave amplification
Authors: Hyde James S. , Gajdzinski Jerzy
Published: July 2002

An electron-paramagnetic-resonance (EPR) reference-arm microwave bridge is described that incorporates a FET microwave amplifier and a balanced quadrature mixer. An automatic frequency control (AFC) circuit is described that employs 70-kHz frequency modulation of the oscillator. AFC feedback is based on formation of the sum of squares of the I and Q outputs of the mixer using analog devices. The resulting AFC circuit is independent of the phase angle α of the reference-arm microwave voltage with respect to the signal-arm microwave voltage at the mixer. An L-band bridge is described that incorporates the circuit. Good AFC lock was obtained from 1 μW to 100 mW of incident power independent of α using a loop-gap resonator of Q=500.
Automatic system for the control of batch-produced 11CO2 for continuous labeling experiments
Authors: McKinney C. J. , Fares Y. , Magnuson C. E. , Jaeger C. H. , Goeschl J. D. , Need J. L.
Published: July 2002

A system for storage and continuous dispensing of constant activity 11CO2 from batch production is described. The system has been used successfully to maintain constant activity levels for 2-h plant tracer kinetic experiments. This development now allows any existing cyclotron facility to supply a radioisotope stream continuously from a short batch irradiation. It requires no modification for use with other isotopes such as N-13 or O-15 in gaseous form and can be used in other biological and clinical investigations as well as the plant physiology investigations for which it was developed.
Calibration scheme for Allen–Bradley resistors, 4.2–100 K
Authors: Lawless W. N. , Hampton S. K. , Clark C. F.
Published: July 2002

Based on measured R–T data for ten tempered Allen–Bradley resistors (BB, (1)/(8)  W, 1 kΩ), a four-point-calibration scheme is described that yields ΔT/T≤0.5% (≤0.8%, 55–65 K) in the range 4.2–100 K. The procedure involves three successive approximations to the equation log R=A+BT−P.
Computer simulation of a 360° field-of-view ‘‘top-hat’’ electrostatic analyzer
Authors: Sablik M. J. , Golimowski D. , Sharber J. R. , Winningham J. D.
Published: July 2002

Via computer simulation, we have studied the characteristics of the ‘‘top-hat’’ electrostatic analyzer, which has in principle a 360° field of view in the acceptance plane. Explicit details are given on how the simulation calculations were done. A finite-difference method employing a polar mesh was used for the computation of the electrostatic field inside the analyzer. A three-dimensional ray-tracing technique was used for computation of the particle trajectories. The analyzer was found to have the following properties: (1) the exit angular response is extremely sharp (±1°) and can be made sharper by truncating the turn angle of the analyzer to an angle ≂90°θ0/2, where θ0 is the half-angle subtended by the top-hot; (2) there is no energy-angle skewing for particle beams parallel to the acceptance plane; (3) transmission can be maximized for normal incidence with respect to the analyzer axis; (4) the exit velocity distribution is peaked fairly sharply in one direction and can be made sharper by imposing an entrance mask; (5) the analyzer has a large geometric factor.
Heavy-ion beam probe for the Advanced Toroidal Facility
Authors: Carnevali A. , Connor K. A. , Aceto S. C. , Lewis J. F. , Glowienka J. C. , Shipley D. , Eberle C.
Published: July 2002

Neoclassical theory predicts that radial electric fields develop in plasmas confined in nonaxisymmetric tori and that they strongly influence the confinement in such devices. A heavy-ion beam probe has been planned for the ATF torsatron at Oak Ridge National Laboratory with the primary goal of providing direct measurements of the plasma potential radial profile and thus of the radial electric field. The complex ATF geometry and magnetic field structure present a diagnostic environment more challenging than that found on previous beam probe systems which have operated on tokamaks, mirrors, and bumpy tori. Particular attention has been given to system alignment and control capabilities. Since the probing ion trajectories remain essentially the same with or without the plasma, an in situ calibration scheme using suitable ionization targets is possible. Installation of the complete diagnostic system is planned for 1988.
Transport of negative ions produced at a barium surface located within a multicusp ion source
Authors: van Os C. F. A. , Kleyn A. W. , Lea L. M. , Holmes A. J. T. , van Amersfoort P. W.
Published: July 2002

An experimental study on the production of negative ions at a pure barium surface mounted in a multicusp bucket source is presented. The conversion efficiency, i.e., the ratio of the extracted negative-ion current and the positive-ion current incident on the surface, for deuterium and for hydrogen, have been measured as a function of source pressure, converter bias, and distance between conversion surface and extraction aperture. The conversion efficiency for deuterium is somewhat larger when compared to hydrogen. The conversion efficiencies obtained agree with a model, taking into account the concentration of hydrogen in the barium surface layers. The cross sections which were measured for the stripping of negative ions by neutral gas agreed well with values from literature. The experimentally determined divergence of the surface-produced beam was 4.5° for hydrogen and 3.6° for deuterium at an energy of 100 eV. At a source pressure of 5 mTorr, the volume-produced negative-ion current could be enhanced by 10%; for 1 mTorr this enhancement was of the order of 25%.
Characterization and active stabilization of a harmonically modulated continuous-wave Nd:LiYF4 laser
Authors: Vanherzeele Herman
Published: July 2002

A continuous-wave harmonically modulated Nd:LiYF4 laser has been built, which offers a high degree of mechanical, electrical, and optical stability. Different operating regimes of this system are outlined. For reliable operation, the cavity length has to be accurately matched to the frequency of the mode-locker driver, much more so than for a fundamentally modulated system. For this purpose, a computer-controlled length-stabilization system is developed. This active stabilization scheme, which compensates thermal and mechanical drifts of the resonator and eliminates the warm-up time of the laser, ensures a stable optical pulse train at the fundamental axial mode spacing of the resonator. The stabilization system is fully compatible with other more commonly implemented analog feedback mechanisms. It should find applications in most harmonically modulated solid-state lasers, and possibly also in fundamentally modulated ones. Compared to the latter, the actively stabilized harmonically modulated laser generates pulses that are shorter and have less jitter.
Capacitor-charging power supply for laser pulsers using a boost circuit
Authors: Bhadani P. K.
Published: July 2002

A capacitor-charging circuit providing high-voltage gain, inherent command-charge capability, and high efficiency is proposed. It can be used in high average-power laser pulsers as well as in thyratron trigger-generator circuits at low-power levels. It offers simple and compact means of varying the charging voltage on a capacitor. Unlike conventional command-resonant chargers, where the cathode of the switch is floated at high potential, a high-voltage switch is not required in the charging path in the proposed scheme. Operation of this circuit is described at 5 kHz with a voltage gain of 20.
Implementation of an image intensifier coupled with a linear position-sensitive detector for measurements of absorption and emission spectra from the nanosecond to millisecond time regime
Authors: Ushida K. , Nakayama T. , Nakazawa T. , Hamanoue K. , Nagamura T. , Mugishima A. , Sakimukai S.
Published: July 2002

Combining a nanosecond ruby laser with a detection system (a polychromator, an image intensifier and a linear position-sensitive detector) controlled by a microcomputer, a convenient laser photolysis system has been constructed. Operating the image intensifier in gated or continuous mode, the time-resolved absorption and emission spectra from the nanosecond to millisecond time regime can be recorded very easily by one or two excitation laser shots. The spectral resolution is 2.5 nm, while the shortest temporal resolution is 10 ns. Also, by simply turning a mirror in the polychromator, the multiple-component decays of transient absorptions, fluorescences, and phosphorescences can be analyzed by means of a combination of a photomultiplier with an oscilloscope controlled by a microcomputer.
Photothermal deflection spectroscopy at 77 K
Authors: Nonomura S. , Hayashi H. , Nitta S.
Published: July 2002

Photothermal deflection spectroscopy (PDS) at 77 K is described. The sample is immersed in liquid nitrogen with the liquid nitrogen acting as both the cooling and the deflecting medium. The experimentally obtained thermal diffusion length and relative change of refractive index of liquid nitrogen are compared with those of carbon tetrachloride. The construction of the liquid-nitrogen cryostat is the key factor in reducing the noise. A sensitivity of αd=10−4 is obtained for the present system. This technique enables the sensitive measurement of PDS at low temperatures.
An adhesion tester for thin oxide films on a metal
Authors: McCoy R. E. , Green G. L. , Williams Richard
Published: July 2002

We have developed an instrument to measure the relative adherence of oxide films on sheet steel. It is based on the observation that, when a sheet metal substrate is bent, a surface film may adhere for a gentle bend, but peel off under a sharp bend. The instrument bends the sample around a conical mandrel, allowing us to observe the adherence as a continuous function of the radius of curvature of the bend. We show the usefulness of the instrument in ranking a series of samples, quantitatively, according to the adherence of the film. The bending method should be useful for characterizing other films on metal substrates.
Second-generation combined CARS-LDV instrument for simultaneous temperature and velocity measurements in combusting flows
Authors: Goss L. P. , Trump D. D. , Lynn W. F. , Chen T. H. , Schmoll W. J. , Roquemore W. M.
Published: July 2002

This article describes the design and operation of a second-generation combined CARS-LDV instrument capable of measuring temperature and two velocity components in a turbulent combusting flowfield. Improvements to the instrument over the first-generation system include multiple acquisition modes ranging from independent to 4-μs time coincidence, more extensive automation of the data acquisition and burner controls, and improved procedures for analysis and display of raw data. Measurements made on a propane–air diffusion flame are discussed.
ATF neutral particle analysis system
Authors: Wade M. R. , Colchin R. J. , Lyon J. F. , Morris R. N. , Thomas C. E. , Roquemore A. L.
Published: July 2002

A two-dimensional scanning neutral particle analyzer has been installed on the Advanced Toroidal Facility (ATF). This TFTR-type E∥B spectrometer provides an extended energy range, mass resolution, and flexibility in viewing orientation. Characteristics of the E∥B analyzer and the associated data acquisition and control systems are discussed. Data representative of those taken during neutral beam injection and ion cyclotron heating on ATF are presented to illustrate the analyzer capabilities.
Performance of the fusion gamma diagnostic on TFTR
Authors: Medley S. S. , Scott S. D. , Roquemore A. L. , Cecil F. E.
Published: July 2002

A gamma-ray spectrometer has been implemented on TFTR which features a count rate capability in excess of 10 MHz. The detector consists of a fast NE226 scintillator (∼2 ns decay time) and a Thorn-EMI 9791-KA photomultiplier tube (∼1.5 ns rise time) which is nested in shielding structures appropriate for suppression of magnetic pickup, rf noise, and the neutron/gamma radiation background. Gamma spectra are obtained on Δt≤1 ms time scales by linear fanout of the photomultiplier signal to 15 single-channel analyzers consisting of Phillips Scientific NIM Model 730 threshold/ΔE-window discriminators. Planned applications of the fusion gamma diagnostic include measurement of the ∼17 MeV prompt gamma emission from both the d(3He,γ)5Li and the p(7Li,γ)8Be reactions during ICRF minority heating of the 3He and proton species, respectively.
Gated neutron streak camera with a uranium cathode (abstract)
Authors: Miyanaga N. , Oida H. , Yamanaka M. , Yamanaka T. , Nakai S. , Yamamoto T. , Iida T. , Araki T. , Ohga T. , Miyake C.
Published: July 2002

A gated neutron streak camera with a uranium oxide cathode has been developed for laser fusion experiments. The energy spectrum of secondary electrons was improved by coating the uranium oxide cathode with thin cesium iodine. The tube design was carried out by computer calculation of electron trajectories. The newly developed streak tube showed a temporal resolution of about 70 ps. This streak camera can be applicable to a neutron yield greater than 1012 with a reasonable signal-to-noise ratio by gating a microchannel plate electron multiplier.
Ion temperature measurements in the ATF torsatron using titanium forbidden lines (abstract)
Authors: Crume E. C. , Horton L. D. , Isler R. C. , Morita S.
Published: July 2002

Several forbidden lines of titanium have recently become strong enough to be identified in ATF plasmas in the ultraviolet and in the visible. The increase in intensity has resulted from gettering of the vacuum vessel with titanium both to suppress light impurities and to control hydrogen recycling. Three orders of the forbidden Ti xiv line at 2117.1 Å have been observed in vacuum, and the second and third orders have been observed in air using two different Czerny–Turner spectrometers. Doppler broadening of this line has been used to infer ion temperatures in the interior of ATF plasmas. These data supplement ion temperature measurements employing lines from carbon, nitrogen, and oxygen reported earlier [R. C. Isler et al., Nucl. Fusion 29, 1391 (1989)]. Tentative identifications of other forbidden lines such as Ti vii at 1938.4 Å, Ti xv at 2544.8 Å, Ti xvii at 3370.8 Å and 3834.4 Å, and Ti xviii at 1778.1 Å have also been made. Research was sponsored by the Office of Fusion Energy, U.S. Department of Energy, under contract DE-AC05-84OR21400 with Martin Marietta Energy Systems, Inc.
Energy deposition and hydrodynamic response of PBFA-II targets (abstract)
Authors: Perry F. C. , Noack D. D.
Published: July 2002

We are developing at PBFA II a laser-reflection-holographic-interferometer technique to measure the time- and space-resolved hydrodynamic response of planar targets to intense light-ion-beam energy deposition. The interpretation of these experiments will lead to an improved understanding of ion beam divergence. A linear analysis of thermoelastic response indicates that ion beam spatial and temporal profiles (including filamentation), as well as properties of the high-temperature ablation plasma, can be obtained from such experiments. For PBFA II we have used the hydrodynamic code TITAN to design the experiments. Single crystals of Al2O3 will be employed initially as targets, since their high Hugoniot elastic limit of ∼200 kbar will permit an elastic wave analysis. Single crystals of LiF will be used at energy deposition levels corresponding to megabar pressures. We will discuss the theory, previous electron beam, and planar plate impact experiments which have employed the diagnostic technique, advantages of arranging the Al2O3 and LiF as shock wave window materials, possible limitations on the technique, and PBFA-II results. This work was supported by U.S. DOE contract No. DE-AC04-76DP00789.
Neutron measurements on ZFX
Authors: Gerber K. A. , Sethian J. D.
Published: July 2002

The NRL ZFX Facility is being used to form dense Z pinches from single fibers composed of cryogenically frozen deuterium (D2) or deuterated polyethylene (CD2). Fiber diameters range from 40 to 125 μm. Maximum current through all these pinches has been about 1 MA with a rise time of 670 ns. Total neutron yields per shot are measured with a pair of rhodium foil activation counters mounted coaxial and perpendicular to the fiber axis. In order to include the effects of external scattering and absorption these detectors are calibrated in situ using a 252Cf neutron source at the pinch location. Total neutron yields have also been determined using bubble detector dosimeters. This is believed to be the first application of these detectors on a pulsed plasma source. Neutron energy spectroscopy and production time are determined with either a pair of scintillator/photomultiplier detectors located at two different perpendicular distances from the pinch axis or a single microchannel plate photomultiplier (μcp-pmt) detector. Both x-ray shielding and neutron flux collimation are required on these detectors. Typically the detected neutrons (up to 2×109 per shot) were emitted in two to four distinct but overlapping 150–200 ns wide bursts starting 300–400 ns after the current initiation.
A proposed diagnostic for time-resolved 14 MeV neutron measurements on TFTR
Authors: Ku L. P. , Nazikian R. , Prorvitch V.
Published: July 2002

A novel method for time-resolved measurements of the 14 MeV neutron flux in an intense 2.5 MeV neutron and γ-ray background has been developed. Discrimination against the background 2.5 MeV neutron and γ-ray flux is achieved by the use of polyethylene and lead shielding. A high detection efficiency of DT neutrons is obtained by the use of large volume plastic scintillators and photomultiplier tube designed for operating in high magnetic field environments. Design computations for such a detector system on TFTR show that an absolute detection efficiency of ∼10−8 counts per DT neutron may be obtained. A source strength of 1013 DT n/s may readily be detected by this method using both count mode and current mode operation with a resolution of ∼10 ms within a statistical accuracy of ∼5%.
Fast alpha diagnostics using carbon pellet injection
Authors: Fisher R. K. , McChesney J. M. , Howald A. M. , Parks P. B. , Thomas D. M. , McCool S. C. , Rowan W. L.
Published: July 2002

Charge exchange interactions of alpha particles with the ablation cloud surrounding an injected carbon pellet can be used to measure the energy spectrum of the incident fast confined alpha particles in a fusion plasma. Measurement of helium neutrals from He2++C4+→He0+C6+ interactions appears to be the most attractive option. This paper describes progress on developing this diagnostic including measurements during pellet injection into the TEXT tokamak.
Bremsstrahlung measurements in the near infrared on ASDEX
Authors: Steuer K.-H. , Röhr H. , Kurzan B.
Published: July 2002

In the ASDEX Thomson scattering system the scattered light of a Nd:YAG laser beam (λ=1064 nm) is measured to obtain electron density and temperature profiles every 16 ms. The same system is continuously used to measure bremsstrahlung in the near infrared, allowing determination of radial Zeff profiles. Some characteristic examples of radiation and Zeff profiles are given. The time resolution of the detection system (≤50 kHz) is sufficiently high to observe fast MHD phenomena such as sawtooth instabilities around the q=1 surface and density fluctuations in the plasma edge. Furthermore, the diagnostic can also be used for real time control of the electron density. This applies in particular in cases where large sawteeth and pellet injection generate counting errors in the interferometer signal. The relation between the line density n and the central chord bremsstrahlung signal Ub was investigated for different heating scenarios in a wide density range.
Z
eff behavior following Li and C pellet injection into TFTR
Authors: Howell R. B. , Terry J. , Marmar E. S. , Hill K. W. , Hulse R. , Janos A. , Park H. , Ramsey A. T. , Taylor G.
Published: July 2002

Injection of both Li and C pellets into TFTR discharges has provided a variety of almost instantaneous changes to the normal equilibrium profiles. The profile measurements of visible bremsstrahlung intensity, electron density, and temperature were used to deduce Zeff profiles versus time. The evolution Zeff is examined in L mode and supershot cases. A comparison is made to the soft x-ray profile behavior for these same conditions.
Pellet ablation profile measurements on the JT-60 tokamak
Authors: Nishitani T. , Nagashima K. , Kondoh T. , Nishino N. , Yoshino R. , Hirayama T. , Takeuchi H.
Published: July 2002

Four hydrogen pellets, two of 3 mm■×3 mml pellets and two of 4 mmF/×4 mml pellets, with the velocity of ∼2.3 km/s, were injected to OH and NB heated plasmas by a four-barrel pneumatic injector on the JT-60 tokamak. The pellet ablation profile was estimated by the measurement of the Hα emissions originating from the ablation cloud using a fiber optics array combined with the Hα -filtered multichannel photodiode. The fiber optics array consisting of ten channel bundles views the pellet pass in the vacuum vessel. The optical fiber was developed to tolerate baking up to 300 °C. The measured ablation profiles were compared with the calculated one by the neutral gas shielding model with a self-limiting effect. A good agreement was obtained between measured and calculated ablation profiles in OH plasmas; however, the fast-ion-induced ablation needed to be taken into account in the calculation for NB-heated plasmas.
Neutral particle diagnostics for ALCATOR C-Mod
Authors: Kurz C. , Fiore C. L.
Published: July 2002

The ALCATOR C-Mod experiment will be equipped with two PPPL charge exchange neutral particle analyzers (CENAs), one of which views the plasma tangentially (Rtan/R0=1.05), whereas the second has a horizontally scannable sight line (0≤Rtan/R0≤0.51). The perpendicularly viewing CENA will be capable of analyzing neutrals up to 600 keV amu for up to three separate species simultaneously. Thus high-energy tails can be observed together with the bulk ion temperature. The operation of both analyzers will allow simultaneous measurements from both the perpendicular and tangential chords. The CENAs will be used to study the effect of ICRF heating on the ion energy distribution with emphasis on the high-energy tail. A Fokker–Planck code (FPPRF) [Hammett, Ph.D. thesis, Princeton (1986)] is used to assess the appropriate operating regime of the analyzer (n≤4×1020 m−3 for Ti=2 keV, for Maxwellian ion energy distribution). The experimental design and computer simulations will be detailed.
Results of beam characterization measurements on PBFA II (abstract)
Authors: Derzon M. S. , Bailey J. E. , Chandler G. A. , Johnson D. J. , Maenchen J. , Matzen M. K. , McGuire E. J. , Mehlhorn T. A. , Nelson W. E. , Pantuso J. A. , Rockett P. D. , Ruiz C. L. , Schmidlapp A. , Smith T. , Stygar W. A. , Torres J. A. , Wiemann D. K.
Published: July 2002

Recent experiments were performed at PBFA II to characterize the ion beam on-axis. The targets were comprised of two parts. One was a conical gold foil whose beam-induced fluorescence was used to obtain a beam footprint and a measurement of beam voltage. The gold also served as a Rutherford scattering source for an ion pinhole camera. The other part was an on-axis Li cylinder, contained within the gold cone, whose gamma output was used as a beam calorimeter. We present the results of this data.
Pellet imaging techniques in the ASDEX tokamak (abstract)
Authors: Wurden G. A. , Büchl K. , Hofmann J. , Lang R. , Loch R. , Rudyj A. , Sandmann W.
Published: July 2002

As part of a USDOE/ASDEX collaboration, a detailed examination of pellet ablation in ASDEX with a variety of diagnostics has allowed a better understanding of a number of features of hydrogen ice pellet ablation in a plasma. In particular, fast-gated photos with an intensified Xybion CCD video camera allow in situ velocity measurements of the pellet as it penetrates the plasma. With time resolution of typically 100 ns and exposures every 50 μs, the evolution of each pellet in a multipellet ASDEX tokamak plasma discharge can be followed. When the pellet cloud track has striations, the light intensity profile through the cloud is hollow (dark near the pellet), whereas at the beginning or near the end of the pellet trajectory the track is typically smooth (without striations) and has a gaussian-peaked light emission profile. New, single pellet Stark broadened Dα, Dβ, and Dγ spectra, obtained with a tangentially viewing scanning mirror/spectrometer with Reticon array readout, are consistent with cloud densities of 2×1017 cm−3 or higher in the regions of strongest light emission. A spatially resolved array of Dα detectors shows that the light variations during the pellet ablation are not caused solely by a modulation of the incoming energy flux as the pellet crosses rational q surfaces, but instead are a result of dynamic, nonstationary, ablation process.
Low-frequency MHD diagnostics on TFTR
Authors: Fredrickson E. D. , McGuire K. , Janos A.
Published: July 2002

A set of four saddle coils has been added to TFTR. In addition, the TFTR Mirnov loop system has been enhanced through the addition of low drift analog integrators allowing direct, local measurement of the poloidal field. The upper frequency response of these systems is limited by the optical isolation electronics to 5 kHz. These new diagnostics are used for the detection and identification of low-frequency (or locked) MHD modes. Additionally, the integrated Mirnov coil signals can be used in the determination of the global equilibrium.
Broadband homodyne reflectometer devoted to density fluctuation measurements
Authors: Estrada T. , Sánchez J. , Brañas B. , Navarro A. P.
Published: July 2002

A microwave reflectometer has been used in the TJ-I tomakak (R=0.30 m, a=0.10 m, IpIp< 50 kA, Bt < 1.5 T) to monitor density fluctuations in the plasma bulk. Experiments were made in the range 33–50 GHz, x mode. The system uses a single antenna for launching and receiving the microwave beam. Since broadband operation usually requires homodyne detection, different techniques were used to overcome the limitations due to this detection scheme. Radial profiles of the density turbulence were taken and the behavior of the spectra analyzed. A slow frequency sweeping has been performed to provide a method to normalize the signals reflected from different radial positions. In addition this technique can be used to obtain information on the absolute value of the phase oscillation amplitude. Spectra of the edge density fluctuations obtained by reflectometry and by Langmuir probes are compared. By the use of two reflectometers in the same antenna, radial correlation experiments can be performed. Some discussions on the ability of homodyne reflectometry to determine coherence lengths are also presented. A slow sweeping of the frequency is proposed to overcome the lack on the information given by the homodyne system.
Scintillation measurement of density fluctuations in a tokamak plasma (abstract)
Authors: Howard J. , Nazikian R. M. , Sharp L. E. , Hamberger S. M.
Published: July 2002

Recent theoretical results for line integrated measurements of phase and amplitude perturbations introduced on a laser beam probing a randomly fluctuating plasma are compared with phase scintillation data obtained on the LT-4 tokamak. It is shown that an estimate of the transverse velocity profile along the line-of-sight can be obtained from single shot measurements of the phase perturbations.
A feasibility study of an XUV spectroscopic measurement of electron density and temperature fluctuations in tokamak plasma center (abstract)
Authors: Huang L. K. , Finkenthal M. , Regan S. , Moos H. W.
Published: July 2002

With the advent of layered synthetic microstructure (LSM) technology, high-reflectivity narrow-band XUV filters, and LSM coated gratings become available, thus making possible normal-incidence high-throughput devices in the 10–200 Å range. Therefore it may become feasible to measure rapid (τ∼10−6 s) fluctuations of the electron density and temperature in the hot central region of the tokamak plasma, by measuring fluctuations on the L-shell charge-state line emissions. We present and discuss the linear dependence of correlated line intensity fluctuations on local T̃e and ñe. Various configurations for the proposed measurements are presented and evaluated.
Autocorrelation and crossed-sightline correlation of ECE for measurement of electron temperature and density fluctuations on ATF and TEXT (abstract)
Authors: Thomas C. E. , Gandy R. F.
Published: July 2002

The great stumbling block in the quest for fusion power using magnetic confinement devices is anomalous transport. It is conjectured that turbulent plasma fluctuations may be responsible for the degraded energy confinement observed in experiments. There exists a clear need for more detailed experimental studies of plasma microturbulence. A conceptual design is presented for a diagnostic to measure electron temperature and density fluctuations using electron cylotron emission (ECE). The proposed ECE systems will employ autocorrelation and cross-correlation techniques to measure radiation from the Advanced Toroidal Facility (ATF) at Oak Ridge National Laboratory (ORNL) and also from the Texas Experimental Tokamak (TEXT) at the University of Texas. This set of experiments on a stellarator and a tokamak will allow a unique comparative study of the fluctuation physics in the two different magnetic configurations. The paper presents the theoretical basis and conceptual design of the diagnostic.
Time-resolved, simultaneous density, temperature, and absorption measurements in dense laser-produced plasmas (abstract)
Authors: Kearney K. J. , Mostovych A. N. , Stamper J. A.
Published: July 2002

We describe an optical diagnostic setup which permits simultaneous spatially and temporally resolved measurements of temperature and density from cold, dense laser-produced plasmas. Such information is necessary to investigate the physics of strongly coupled plasmas. The plasma is created in a slab geometry such that the transverse slab dimension is approximately one optical depth of the probing radiation in thickness. To perform the measurements the 2nd harmonic (λ=0.527 μm) of a mode-locked Nd:glass laser (τpulse=300–500 ps) is split into two orthogonally polarized beams. One of the beams measures plasma electron density using polarization wave front interferometry. The other beam uses a set of fast (τ=350 ps) photodiodes to measure single-frequency optical absorption. Plasma electron temperature is determined from time-resolved absolute emission measurements combined with the optical absorption measurements via Kirchoff’s law. This technique avoids the difficulties involved in spectroscopic temperature measurements, where the spectral intensities and line profiles are affected by the physics of the cold, dense plasma. A set of timing fiducials allows the entire set of diagnostics to be synchronized in time, while an accurate, self-referenced alignment system assures that all diagnostics sample the same region of plasma volume.
Fluctuation measurements in the DIII-D and TEXT tokamaks via collective scattering and reflectometry (abstract)
Authors: Peebles W. A. , Baang S. , Brower D. L. , Burrell K. , Doyle E. J. , Groebner R. J. , Lehecka T. , Luhmann N. C. , Matsumoto H. , Philipona R. , Rettig C. , Rhodes T. L. , Yu C. X.
Published: July 2002

Anomalous transport in fusion plasmas remains an enigma requiring explanation. A predictive capability is highly desirable if confinement enhancement regimes such as H-mode or super shots are to be extrapolated to the next phase in development of the International Fusion program, epitomized, for example, in ITER. Therefore, identification of the role that electrostatic turbulence plays in confinement is a critical issue requiring detailed experimental data capable of testing and challenging existing theoretical models. This paper presents microturbulence measurements obtained on the DIII-D and TEXT tokamaks utilizing heterodyne, far-infrared collective scattering and reflectometry techniques. The experimental systems are described on both machines and emphasis placed on results obtained during the L–H transition, ELM activity, and saturated ohmic operation where ion temperature gradient driven (ITGD) turbulence is theoretically predicted to exist. This work was supported by the U.S. Department of Energy under contract Nos. DE-FG03-86ER53225, DE-AC05-78ET53043, and DE-AC03-89ER51114.