bluuebunny/crossref_metadata_2025 huggingface dataset:
Near-infrared high-gain strained layer InGaAs heterojunction phototransistors: Resonant periodic absorption
Authors: Bryan R. P. , Olbright G. R. , Fu W. S. , Brennan T. M. , Tsao J. Y.
Published: July 2002

We report high-gain phototransistors on GaAs substrates at wavelengths for which GaAs substrates are transparent, and hence, are promising for optoelectronic interconnect, optical-logic device, neural network, and lightwave communication applications. Using a new technique called resonant periodic absorption we have achieved high-optical gain at previously inaccessible wavelengths (≳925 nm). Resonant periodic absorption is achieved in an asymmetric microresonator consisting of a strained-layer InGaAs/GaAs heterojunction phototransistor sandwiched between distributed Bragg reflectors. By aligning the optical intensity maxima with the InGaAs quantum wells in the collector region of the phototransistor, we dramatically enhance the optical absorption.
Determination of the flexural modulus of thin films from measurement of the first arrival of the symmetric Lamb wave
Authors: Bobbin Sarah E. , Wagner J. W. , Cammarata R. C.
Published: July 2002

A technique is presented to measure the flexural modulus of free-standing thin metallic films from 1 to 25 μm thick. Lamb waves are excited in the film with a pulsed Nd:YAG laser, and detected using heterodyne interferometry. Variability in wave-form structure is observed as a function of experimental parameters and film thickness. The first arrival of the symmetric Lamb mode can be unambiguously identified regardless of wave-form shape, and is used to calculate the flexural modulus.
Surface structure of selenium-treated GaAs (001) studied by field ion scanning tunneling microscopy
Authors: Shigekawa H. , Hashizume T. , Oigawa H. , Motai K. , Mera Y. , Nannichi Y. , Sakurai T.
Published: July 2002

For a selenium-treated GaAs (001) surface followed by heat treatment at ∼530 °C, we have observed using field ion scanning tunneling microscopy ordered arrays with regular intervals of 4×periodicity in the [1̄10] direction (1.6 nm) to line up in the [110] direction. These ordered arrays are in good agreement with the 4×1 structure previously observed by other methods. In a closer view, the 4×structure was found to be formed by closely placed double rows.
Direct verification of energy back transfer from Yb 4f-shell to InP host
Authors: Taguchi Akihito , Taniguchi Moriyuki , Takahei Kenichiro
Published: July 2002

We report direct verification of energy back transfer from a Yb 4f-shell to an InP host, which has been proposed as a quenching mechanism for the intrinsic thermal quenching of intra-4f-shell luminescence. Photoluminescence time decay of the band-edge related luminescence for a Yb-doped InP sample was examined. In the temperature region from 100 to 120 K, it was observed that the luminescence time-decay curve is composed of two exponential decay components. The decay-time constant of the slower component in the band-edge related luminescence is the same as that in the Yb 4f-shell luminescence. This fact clearly shows that there is an energy transfer between the Yb 4f-shell electronic state and the InP host electronic state, and the energy back-transfer mechanism is the cause of the intrinsic thermal quenching of the Yb intra-4f-shell luminescence.
Differentiation of topographical and chemical structures using an interfacial force microscope
Authors: Joyce Stephen A. , Houston J. E. , Michalske T. A.
Published: July 2002

The forces between a tungsten tip and a self-assembled monolayer of hexadecylthiol (C16H33SH) on a thin gold film have been studied using a newly developed interfacial-force microscope. Imaging of the surface, combined with spatially resolved force versus separation measurements, allow for the distinction of topographical and chemical features of the surface. Several distinct regions are observed for this system. The first, characterized by a very weak interfacial interaction between tip and sample, is representative of the self-assembled monolayer. The other regions show relatively strong, long-range attractive forces, which are associated with gross defects in the film.
In situ optical characterization of GaAs surfaces under alternating supply of GaCl and AsH3
Authors: Nishi Kenichi , Usui Akira , Sakaki Hiroyuki
Published: July 2002

This letter describes the use of surface photoabsorption (SPA) measurements to characterize GaAs substrate surfaces under an alternating supply of GaCl and AsH3 in chloride atomic layer epitaxy (ALE). This characterization technique utilizes p-polarized light incident at the Brewster angle, which virtually eliminates the bulk contribution of the reflected light. It was found that the reflection intensity varied by several percent depending on the source gas supply sequence. This reflection intensity was constant during continuous GaCl supply, which corresponded to the self-limiting mechanism of chloride ALE. Optical reflection spectra were measured in the range of 300–800 nm during the flow of each source gas. The normalized spectra of reflection difference between GaCl and AsH3 supply depended on the incidence azimuth, which showed the existence of anisotropic surface bonds. By comparing these spectra to the reference data using triethylgallium as a Ga source, the GaAs surface under GaCl exposure was assumed to be a Ga-stabilized surface at 520 °C.
Control of surface particle density in pulsed laser deposition of superconducting YBa2Cu3O7 and diamondlike carbon thin films
Authors: Singh Rajiv K. , Bhattacharya D. , Narayan J.
Published: July 2002

We have investigated the effects of target preparation and modification in controlling the particle density of films fabricated by the pulsed laser deposition (PLD) technique. YBa2Cu3O7 targets, prepared by unique processing conditions, were used to experimentally study the factors controlling surface morphology of PLD films. By varying the nature of the target processing conditions, the particle density can be considerably reduced in superconducting thin films and completely eliminated in diamondlike carbon thin films. Cold pressed and sintered bulk superconducting targets were subjected to controlled continuous wave (cw) CO2 laser irradiation for compacting and densifying the target. Another method employed was the incorporation of silver into the superconductor targets to improve its thermal conductivity, optical absorption coefficient, and bulk density. The particle density was found to significantly reduce for films deposited from cw CO2 laser processed YBa2Cu3O7 targets. The experimental results were in agreement with the subsurface superheating model which predicts that the particle density in PLD films can be considerably reduced by (i) increasing the absorption coefficient, (ii) thermal conductivity, and (iii) cohesion of the target grains. The first two factors decrease subsurface superheating effects while the third increases the barrier for particle removal.
Directionally alternating domain wall propagation in bistable amorphous wires
Authors: Gómez-Polo C. , Vázquez M. , Chen D.-X.
Published: July 2002

For iron-rich magnetostrictive bistable amorphous wires made by the in water quenching technique, the domain wall propagation changes direction after each magnetization reversal. This unique behavior suggests that the reverse-domain walls in the propagation rear end are pinned more tightly than those in the front end, which then becomes the starting end for the next magnetic reversal. The difference in the pinning strength between both ends is not ascribed to the aftereffect but may be due to different reverse domain structures therein.
Well resolved room-temperature photovoltage spectra of GaAs-GaInP quantum wells and superlattices
Authors: He Xiaoguang , Razeghi Manijeh
Published: July 2002

We report the first well resolved room-temperature photovoltage spectra due to the sublevel transitions in the GaInP-GaAs superlattices and multiquantum wells grown by low pressure metalorganic chemical vapor deposition. Sharp well resolved peaks attributed to exciton absorption of the electron-to-light hole and electron-to-heavy hole have been observed at room temperature. This indicates that GaAs-GaInP is a promising material for the application of the modulators, optical switches, and optical bistable divices. Satisfactory agreements between experimental measurements and theoretical results have been obtained. These results demonstrate that photovoltage spectroscopy is a simple, but very powerful tool to study quantum confinement structures.
First-order quasi-phase matched LiNbO3 waveguide periodically poled by applying an external field for efficient blue second-harmonic generation
Authors: Yamada M. , Nada N. , Saitoh M. , Watanabe K.
Published: July 2002

A novel method of fabricating a periodic domain structure with ideal laminar domains in LiNbO3 by applying an external field at room temperature is proposed. The method allows a high blue beam power of 20.7 mW and a high conversion efficiency of 600%/W cm2 to be obtained.
Polycrystalline silicon thin film transistors on Corning 7059 glass substrates using short time, low-temperature processing
Authors: Liu Gang , Fonash Stephen J.
Published: July 2002

A new fabrication process for polycrystalline silicon thin film transistors on 7059 glass substrates is reported. This unique fabrication process has the advantages of short processing time and low processing temperature (≤600 °C). The processing is based on the key step of using an ultrathin Pd layer, introduced to the surface of the glass prior to the deposition of an a-Si:H film, to reduce the crystallization time and temperature. It is also based on using an electron cyclotron resonance hydrogen plasma to reduced the passivation time. The n-channel TFTs produced by this new fabrication process have mobilities of 20 cm2/V s, and off-currents of 0.5 pA/μm.
Narrowing of the intersubband absorption spectrum by localization of continuum resonances in a strong electric field
Authors: Sirtori Carlo , Faist Jerome , Capasso Federico , Sivco Deborah L. , Cho Alfred Y.
Published: July 2002

Direct observation of strong localization of continuum resonances in the presence of an electric field is reported. Our structure consists of doped GaInAs quantum wells cladded by AlInAs/GaInAs quarter wave electron stacks and by AlInAs barriers. In a strong electric field of the appropriate polarity the first continuum resonance is strongly confined above the wells by the high reflectivity λ/4 stacks and by the field-induced triangular potential barrier, while the second continuum resonance becomes localized in the latter. This manifests itself in a strong narrowing of the intersubband absorption spectrum as a function of the electric field as a greater fraction of the oscillator strength is concentrated into a transition from the ground state of the well to a quasibound state in the continuum.
Additional transmission resonances in interband tunnel structures
Authors: Aversa Claudio , Sipe J. E.
Published: July 2002

We show that transmission resonances associated with heavy-hole states in InAs/GaSb based interband tunnel structures survive for vanishingly small crystal momentum parallel to the interface. These effects are expected to arise by several possible mechanisms including the material dependence of the zone-center Bloch functions. We find that one simple model can account for the diverse ways that such transmission resonances manifest themselves in this and other systems.
Mass selection of neutral clusters in Low-Energy Cluster Beam Deposition experiments: Is it realistic?
Authors: Roux J. F. , Cabaud B. , Fuchs G. , Guillot D. , Hoareau A. , Mélinon P.
Published: July 2002

The crucial problem in controlling and filtering the size of free neutral clusters generated by a cluster source is studied in the particular case of the Sattler source type. The present work shows that a velocity selector can be used to control the size of neutral clusters produced in the low-energy cluster beam deposition system. This velocity selector is also used to measure the kinetic energy of free Bi clusters. The experimental results obtained for Bi clusters are compared with previous theoretical predictions.
On the improvement of broadband stimulated Brillouin scattering reflectors
Authors: Perrone M. R. , Yao Y. B.
Published: July 2002

Stimulated Brillouin scattering (SBS) of unmodified XeCl laser radiation in n-hexane was investigated for building phase-conjugating mirrors. It was found that the SBS mirror reflectivity could be improved by setting a holographic grating in front of the SBS mirror and by using the first order beam reflected by the grating to pump the Brillouin medium. Maximum energy and power reflectivities of 45% and 80%, respectively, were measured. The SBS mirror energy reflectivity was reduced by 45% by removing the grating. The phase conjugation fidelity of the backscattered radiation was close to one, with or without the grating.
Coulomb blockade in a silicon tunnel junction device
Authors: Ali D. , Ahmed H.
Published: July 2002

Single electron tunnel junctions have been formed in ultrathin silicon-on-insulator material by electron beam lithography and dry etching. Clear Coulomb blockade effects have been observed at 300 mK in the current-voltage characteristics as a function of the voltage applied to a control sidegate. The effects are not smeared out by thermal fluctuations until temperatures greater than 4 K are reached.
New formation mechanism of electric field domain due to Γ-X sequential tunneling in GaAs/AlAs superlattices
Authors: Zhang Yaohui , Yang Xiaoping , Liu Wei , Zhang Penghua , Jiang Desheng
Published: July 2002

We have studied the sequential tunneling of doped weakly coupled GaAs/AlAs superlattices (SLs), whose ground state of the X valley in AlAs layers is designed to be located between the ground state (EΓ1) and the first excited state (EΓ2) of the Γ valley in GaAs wells. The experimental results demonstrate that the high electric field domain in these SLs is attributed to the Γ-X sequential tunneling instead of the usual sequential resonant tunneling between subbands in adjacent wells. Within this kind of high field domain, electrons from the ground state in the GaAs well tunnel to the ground state of the X valley in the nearest AlAs layer, then through very rapid real-space transfer relax from the X valley in the AlAs layer to the ground state of the Γ valley of the next GaAs well.
Focused ion beam direct deposition of superconductive thin film
Authors: Nagamachi Shinji , Yamakage Yasuhiro , Ueda Masahiro , Maruno Hiromasa , Shinada Kei , Fujiyama Yoichi , Asari Masatoshi , Ishikawa Junzo
Published: July 2002

Focused ion beam direct deposition of niobium has been developed as a technique for fabricating superconductive thin films. A Nb2+ ion beam extracted from a Nb10–Au50–Cu40 liquid metal ion source was accelerated to 40 keV, focused, deflected and finally decelerated to 50–1000 eV. The beam current density was 0.4–2 mA/cm2 and the minimum deposited linewidth was about 0.5 μm. The sticking probability of the Nb2+ ion beam and the critical temperature of deposited niobium films were measured. The deposition at different deposition rates and different residual gas pressure were performed. A clear relation was obtained between the critical temperature and the concentration of contaminations. This relation is consistent with the published relation for bulk niobium if it is assumed that the sticking probability of residual gas is 0.2. However, dependence of the critical temperature on ion energy was not observed.
Transverse mode behavior in native-oxide-defined low threshold vertical-cavity lasers
Authors: Huffaker D. L. , Deppe D. G. , Rogers T. J.
Published: July 2002

Data are presented characterizing the transverse mode behavior of AlAs/GaAs/InGaAs vertical-cavity surface-emitting lasers fabricated using a native-oxide process. The native-oxide process results in laser diodes with active regions defined to be 10, 8, and 4 μm squares. We show that the transverse lasing mode is influenced by mirror reflectivity, with significant mode changes occurring with drive current for 8–10 μm devices in the ranges of one to four times threshold. In smaller devices of 4 μm square dimension, the transverse mode at threshold appears as a lowest order mode.
Pulsed laser deposition and characterization of epitaxial Cu/TiN/Si(100) heterostructures
Authors: Vispute R. D. , Chowdhury R. , Tiwari P. , Narayan J.
Published: July 2002

Three-dimensional epitaxial Cu/TiN/Si(100) heterostructures have been grown by pulsed laser deposition using a single chamber, in situ processing method. The epitaxial TiN layers on Si(100) were grown at 600 °C and epitaxial Cu layers on TiN/Si(100) in the temperature range 200–600 °C using optimized laser parameters. These structures were characterized using three-axis x-ray diffraction (Θ, Φ, Ψ scans) technique and high-resolution transmission electron microscopy. The results clearly indicate cube-on-cube epitaxial alignment along the three axes, i.e., 〈100〉Cu∥〈100〉TiN∥〈100〉Si. The Cu/TiN and TiN/Si interfaces were found to be quite sharp without any indication of interfacial reaction. The growth mechanism of copper on TiN was found to be three dimensional, with the size of island varying from 0.3 to 1.5 μm. We discuss domain matching epitaxy as a mechanism of growth in these large lattice mismatch systems, where three lattice constants of Si(5.43 Å) match with four of TiN(4.24 Å) and seven units of Cu(3.62 Å) match with six of the TiN. The implications of these results in the fabrication of advanced microelectronic devices are discussed.
Hydrogen passivation of dislocations in InP on GaAs heterostructures
Authors: Chatterjee B. , Ringel S. A. , Sieg R. , Hoffman R. , Weinberg I.
Published: July 2002

The effects of hydrogenation on the properties of Zn-doped InP/GaAs heterostructures grown by metalorganic chemical vapor deposition were studied by current-voltage (I-V), deep level transient spectroscopy (DLTS), and photoluminescence. Significant improvements in leakage current and breakdown voltage in InP diodes on GaAs were observed after a 2 h hydrogen plasma exposure at 250 °C. DLTS indicated a corresponding reduction in total trap concentration from ∼6×1014 to ∼3×1012 cm−3 at a depth of ∼1.5 μm below the surface. The Zn dopants were completely reactivated by a subsequent 5 min 400 °C anneal without degradation of the reverse current or reactivation of the deep levels. Anneals in excess of 580 °C were necessary to reactivate the deep levels and degrade the leakage current to their original values, indicating the passivation of threading dislocations by hydrogen, and the existence of a wide temperature window for post-passivation processing.
Diffusion of phosphorus in arsenic and boron doped silicon
Authors: Wittel Fred , Dunham Scott
Published: July 2002

The diffusivity of phosphorus is measured in silicon with nearly uniform arsenic or boron background doping no>(0.1<n/ni<30) at temperatures of 915, 1015, and 1105 °C. It is found that diffusion via neutral and single negatively charged point defects are sufficient to account for the experimental data, with no need to include diffusion via double negatively charged point defects. Greatly reduced diffusivity is observed in the boron-doped samples, which is consistent with the formation of immobile donor–acceptor pairs. Activated diffusion and pairing coefficients are calculated based on this work and combined with experimental results previously reported in the literature.
Lattice sites of ion implanted Li in diamond
Authors: Restle M. , Bharuth-Ram K. , Quintel H. , Ronning C. , Hofsäss H. , Jahn S. G. ,   ISOLDE-Collaboration, Wahl U.
Published: July 2002

Radioactive Li ions were implanted into natural IIa diamonds at temperatures between 100 and 900 K. Emission channeling patterns of α-particles emitted in the nuclear decay of 8Li(t1/2=838 ms) were measured and, from a comparison with calculated emission channeling and blocking effects from Monte Carlo simulations, the lattice sites taken up by the Li ions were quantitatively determined. A fraction of 40(5)% of the implanted Li ions were found to be located on tetrahedral interstitial lattice sites, and 17(5)% on substitutional sites. The fractions of implanted Li on the two lattice sites showed no change with temperature, indicating that Li diffusion does not take place within the time window of our measurements.
Enhancement of Coulomb blockade in semiconductor tunnel junctions
Authors: Nakazato Kazuo , Ahmed Haroon
Published: July 2002

The Coulomb blockade region was measured directly in an experimental single-electron memory device. The device was constructed with multiple-tunnel junctions (MTJ) formed by making a sidegated constriction in δ-doped GaAs. The Coulomb blockade region is defined by electron transfer rates of less than 10 electrons per second. At low values of sidegate voltages in the MTJ an enhancement of the Coulomb blockade is observed and explained by the formation of a nonuniform electrostatic potential in the semiconductor tunnel junctions.
Si-induced island formation and surface ordering on GaAs(001)-c(4×4)
Authors: Avery A. R. , Sudijono J. , Holmes D. M. , Jones T. S. , Joyce B. A.
Published: July 2002

Scanning tunneling microscopy (STM) has been used to study the deposition of Si at 400 °C onto the c(4×4) surface reconstruction of GaAs(001) surfaces grown in situ by molecular beam epitaxy (MBE). Emphasis is placed on the nucleation, island formation, and surface ordering, as a consequence of adsorption onto the c(4×4) surface. With increasing Si coverage, a series of anisotropic ‘‘needlelike’’ islands is formed. A site exchange model is proposed in which the deposited Si atoms displace the top layer As atoms of the c(4×4) structure, with the displaced As atoms forming dimers in a new top layer.
Improved transient response of thermocouple sensors
Authors: Dantzig J. A.
Published: July 2002

A procedure is described for improving the fidelity of the transient response of thermocouple sensors. The procedure entails calibration of the sensor, followed by signal processing to reconstruct the original temperature history which produced a recorded signal. An example is given, demonstrating calibration and a three- to four-fold improvement in transient response.
An all solid-state magnetic switching exciter for pumping excimer lasers
Authors: Shimada Tsutomu , Obara Minoru , Noguchi Akira
Published: July 2002

A thyristor, silicon controlled rectifier (SCR), switched multistage magnetic pulse compressor has been successfully developed for KrF excimer laser excitation. Being composed entirely of solid-state elements, this exciter will provide the extremely long lifetime at high repetition rate operation that cannot be realized by a conventional power supply with a discharge switch.
Laser-induced holographic surface relief gratings on nonlinear optical polymer films
Authors: Kim D. Y. , Tripathy S. K. , Li Lian , Kumar J.
Published: July 2002

We report observation of holographic surface relief gratings with relatively large amplitude on a second order nonlinear optical polymeric material. Surface relief gratings on these polymer films were created upon exposure to polarized Ar+ laser beams at 488 nm without any subsequent processing steps. The surface structure of the relief gratings was investigated by atomic force microscopy. The depth of the surface relief in a typical case was 120 nm which is approximately 20% of the original film thickness. The diffraction efficiency of gold-coated gratings was investigated as a function of wavelength and capability of recording orthogonal gratings on the same film was demonstrated.
Laboratory-oriented data-acquisition and distribution system
Authors: Rebaglia B. I. , Birello G.
Published: July 2002

A general purpose parallel interface links a large number of composite I/O channels to a small calculator.
Approaches to the diagnostics of alpha particles in tokamaks (invited)
Authors: Zweben S. J.
Published: July 2002

Alpha particles from D/T reactions are expected to be produced at a power level of about 5 MW in Q≂1 beam heated experiments in the tokamak fusion test reactor (TFTR) and will become the dominant heating mechanism in future tokamak ignition devices. Although alphas should be well confined according to neoclassical orbit theory, the effects of plasma instabilities on alpha confinement and the effect of alphas on plasma confinement and heating remain to be seen. This paper describes the physical context for alpha particle measurements in tokamaks and reviews the status of recent approaches to their diagnosis.
Neutron spectroscopy on Nova
Authors: Cable M. D. , Lane S. M. , Lerche R. A. , Prussin S. G. , Vieira R. G.
Published: July 2002

Some fundamental properties of inertial confinement fusion implosions can be measured using diagnostics based on neutron spectroscopy. An instrument that will measure neutron spectra using time-of-flight techniques with an array of ‘‘single-hit’’ detectors is being developed for use on Nova. Its initial application will be measurement of ion temperature. Potential other applications, such as measurement of fuel 〈 ρR〉 will also be discussed.
Optimum design of a polarimeter for visible light
Authors: Daniels J. M.
Published: July 2002

The principles for the design of a polarimeter to analyze visible light are deduced and a design is suggested. This design provides maximum accuracy in the determination of the Stokes parameters, the procedure for analysis is simple, and it is easily adapted to automatic operation.
Development and applications of monochromatic x-ray imaging
Authors: Ridgeley A.
Published: July 2002

An ideal plasma diagnostics device would resolve in five dimensions, three spatial, one time, and one energy. Traditional x-ray plasma diagnostics devices resolve in only one or two dimensions. It is possible to devise diagnostic equipment to resolve three parameters simultaneously. The means by which this can be achieved using techniques involving multilayer mirrors, concave spherically curved crystals, and crystals cut to special planes are discussed. Results are presented for monochromatic imaging using multilayer mirrors and possible applications of the technique are outlined.
Effective Kα x-ray excitation rates for plasma impurity measurements
Authors: Hill K. W. , Bitter M. , von Goeler S. , Hiroe S. , Hulse R. , Ramsey A. T. , Sesnic S. , Shimada M. , Stratton B. C.
Published: July 2002

Metal impurity concentrations are measured by the pulse-height-analyzer (PHA) diagnostic from Kα x-ray peak intensities by use of an averaged excitation rate 〈σv〉. Low-Z impurity concentrations are inferred from the continuum enhancement (relative to a pure plasma) minus the enhancement due to metals. Since the PHA does not resolve lines from different charge states, 〈σv〉 is a weighted sum of rates; coronal equilibrium is usually assumed. The 〈σv〉 used earlier omitted the intercombination and forbidden lines from the dominant heliumlike state. The result was an overestimate of metals and an underestimate of low-Z impurities in cases where metals were significant. Improved values of 〈σv〉 using recent calculations for H-, He-, and Li-like Fe range from 10% to 50% larger than the earlier rates and yield metal concentrations in better agreement with those from vacuum ultraviolet (VUV) spectroscopy.
Electron temperature measurements from line ratios of He- and H-like argon in the Alcator C tokamak
Authors: Rice J. E. , Marmar E. S. , Källne E. , Källne J.
Published: July 2002

Line ratios of certain transitions in H- and He-like Ar are quite sensitive to electron temperature. In particular, the 1s2–1s4p transition in Ar16+ (λ=3.200 Å) lies very close to the 1s–3p transition in Ar17+ (λ=3.151 Å). The intensity ratio of these two lines is a sensitive function of electron temperature, through the changing ionization balance, at least over the range 1200 eV<Te<2500 eV. This has been exploited with a compact, high-resolution x-ray spectrometer to obtain time histories of central electron temperature in Alcator C tokamak plasmas. Time resolution of 20 ms has been achieved.
Studies of x-ray switching and shuttering techniques
Authors: Wark J. S. , Hauer A. , Kilkenny J. D.
Published: July 2002

Experimental studies have been conducted on the changes in x-ray diffraction properties of crystals under intense subnanosecond laser heating. One beam of the PHOENIX laser system was used to create an intense source of x-ray line radiation. This radiation was, in turn, diffracted from a silicon crystal that was heated with the other beam of the laser. The diffracted radiation was temporally resolved with an x-ray streak camera. The diffracted lines are observed to broaden on a subnanosecond time scale. From the temporal structure of the diffracted radiation, information is derived on the nature of the laser heating process. We show that such interruption of the diffracting process is a potentially useful mechanism for x-ray switching and shuttering. Considerations for the design and construction of such devices are discussed.
Spectral measurements from laser-produced plasma in OMEGA
Authors: Burkhalter P. G. , Newman D. A. , Rosen D. L. , Hudson K. , Richardson M. , Audebert P.
Published: July 2002

Curved- and flat-diffraction crystal spectrographs were developed to collect x-ray spectra from high-atomic-number elements (cadmium–rare earths) in the 5–17-Å region. The plasma source was generated by the 24-beam, frequency-tripled light of the OMEGA laser system. The spectral patterns were identified with the aid of atomic structure calculations and from Moseley plots of isoelectronic sequences. The Ne-like (third-order diffraction) and Na-like ionization stages were observed in the Cd and Sn spectra. The rare-earth spectra were predominantly 3d-4p, 4f transitions over a range of ionization stages involving the M shell. Calibration spectra were obtained with L-series transitions from Fe and Cu targets and K lines from Si plasma excited in the glass supporting stalk.
Absorption spectroscopy of a laser-produced plasma
Authors: Kilkenny J. D. , Lee R. W. , Kolbe G. , Estabrook K. , Landen O. , Bailey J. , Lewis C. L. S.
Published: July 2002

P i n plasma sources are used as x-ray backlights for an Al plasma produced by focusing 1.06-μm laser light to irradiances of 1012 W/cm−2. Spatially resolved absorption features of the helium- like states of ionization of the plasma allow ground-state densities of the helium and hydrogenlike stages to be measured. Comparison with simulations indicates the need for realistic opacity effects to produce a high enough state of ionization for the plasma temperature. Work performed under the auspices of the U.S. DOE by the Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.
Diagnostic system for measurement of particle balance in TMX-U
Authors: Allen S. L. , Correll D. L. , Hill D. N. , Wood R. D. , Brown M. D.
Published: July 2002

Several diagnostics measure the particle sources and losses in the Tandem Mirror Experiment-Upgrade (TMX-U) plasma. An absolutely calibrated high-speed (0.5 ms per frame) filtered (6561 Å) video camera measures the total ionization source as a function of radius. An axial view of the plasma automatically integrates the axial variations within the depth of field of the system. Another camera, viewing the plasma radially, measures the axial source variations near the deuterium fueling source. Axial ion losses are measured by an array of Faraday cups that are equipped with grids for repelling electrons and are mounted at each end of the experiment. Unequal ion and electron (nonambipolar) radial losses are inferred from net current measurements on an array of grounded plates at each end. Any differences between the measured particle losses and sources may be attributed to ambipolar radial losses and/or azimuthal asymmetries in the particle-loss profiles. Methods of system calibration, along with details of computer data acquisition and processing of this relatively large set of data, are also presented.
Development of gyrotrons for plasma diagnostics (invited)
Authors: Woskoboinikow P.
Published: July 2002

Recent advances in high-frequency (>100 GHz) gyrotron technology are reviewed and application to millimeter/submillimeter wave plasma diagnostics is discussed. Gyrotrons have useful capabilities of high-power (>1 kW), long pulse/cw operation, narrow linewidth (<100 kHz), and good spatial mode quality with efficient (∼90%) mode converters. These capabilities could be used to significantly improve collective Thomson scattering diagnostics for the study of instabilities, plasma waves, turbulence, and thermal ion fluctuations. Imaging applications with many detector arrays of plasma density, field direction, and microinstabilities may be possible with gyrotons. In a high-field compact ignition tokamak experiment a possible millimeter wave diagnostics window could be exploited by a gyrotron to measure a number of parameters, including alpha particle density and velocity distribution.
Study of optically thin electron cyclotron emission from TFTR using a Michelson interferometer
Authors: Stauffer F. J. , Boyd D. A.
Published: July 2002

The tokamak fusion test reactor (TFTR) Michelson interferometer, which is used as an electron-temperature diagnostic, has a spectral range of 75–540 GHz. This range is adequate for measuring at least the first three cyclotron harmonics, and it spans both optically thick and thin portions of the electron cyclotron emission (ECE) spectrum. During the most recent opening of the TFTR vacuum vessel, a concave, carbon reflector was installed on the back wall of the vessel, opposite the light-collecting optic of the Michelson system. The reflector is designed to prevent the observation of optically thin ECE that originates from a location that is outside the field of view of the light collecting optic. If this is achieved, it should be possible to derive the electron-density profile from measurements of either the extraordinary mode third harmonic or the ordinary mode second harmonic. An analysis of ECE spectra that have been measured before and after installation of the reflector will be presented. This work was supported by U.S. DOE Contract No. DE-AC02-76-CHO-3073.
Spectroscopic diagnostics on JET (invited)
Authors: Behringer K.
Published: July 2002

The present spectroscopic diagnostics on Joint European Torus (JET) consist of bolometry, fiber- and close-coupled visible spectroscopy (200–700 nm), as well as survey (10–170 nm) and spatial scan VUV spectroscopy (10–250 nm). Visible bremsstrahlung is used routinely for Zeff measurements. Hydrogen and impurity influxes from walls, limiters, and rf antennas are derived from visible spectral lines. Visible charge-exchange spectroscopy, utilizing part of the JET heating beams, yields ion temperatures, rotation velocities, and impurity concentrations in the plasma. VUV spectroscopy is employed for measuring the impurity content in the bulk plasma using an impurity transport code. Spatial scan spectrometers allow verification of the transport models by means of recorded emission shells. A 20-m-high resolution crystal spectrometer yields ion temperatures and rotation velocities from the He- and H-like resonance lines, as well as other plasma parameters. A pulse-height analysis system covers the energy range of metal and Cl-K lines and can be used for electron temperature measurements. In the near future XUV (0.7–35 nm) and double-crystal spectrometers (0.1–2 nm), one of them providing a spatial scan, will be available, enabling studies of H- and He-like light impurities, as well as Ne-, He-, and H-like metals. Bolometry, visible spectroscopy, and two crystal instruments will be the only diagnostics left during the JET active phase. By then, models and methods must have been established for assessing the behavior of the important impurities C, O (,Be), and Ni with these diagnostics.
Spectroscopy of plasmas with a multifiber commutator
Authors: Bunting C. A. , Carolan P. G. , Field A. R. , Forrest M. J.
Published: July 2002

Spatially resolved spectra have been obtained, during a single discharge, with one spectrometer using an optical multifiber commutator (OMC). We report results from this device which can be preprogrammed to select up to nine viewing chords, via high transmission optical fibers. This arrangement has been incorporated with a multichannel (OMA) spectrometer, where the fiber-to-fiber switching time matches the basic video scan of the detector (16 ms). The spectrometer can be operated in medium resolution mode (0.3 Å) with a conventional grating or with high resolution (0.05 Å) by substituting an echelle grating. The apparatus has been used for the evaluation of ion temperatures in the source and extraction regions of the Culham negative ion source. It is presently employed in JET for the study of the relative impurity influxes from the wall, the limiters, and the rf antennas.
High-intensity lithium beam for Zeeman spectroscopy
Authors: Weber P. G. , Masamune S.
Published: July 2002

The Zeeman splitting of neutral lithium introduced to a hot plasma as a beam may be used to determine both the magnitude and direction of the local magnetic field. Dye lasers can improve the sensitivity of the method, either by resonance fluorescence or by intracavity absorption. A limit on the applicability of this diagnostic is set by the lithium density in the plasma. A high density, 80-kV lithium beam has been developed to access plasmas of larger dimension and/or higher densities, or to permit measurements with better time resolution than with previous beams. The beam utilizes a high density lithium ion source. Diagnostics include 2-D ion beam profiling, Faraday cup, magnetic analyzer, and a ‘‘pepperpot’’ probe for measurements of beam intensity, composition, and divergence. Beam currents can exceed 10 mA in a ≤2-cm-diameter beam with a divergence of several milliradians.
TFTR CAMAC data-acquisition system
Authors: Rauch W. A.
Published: July 2002

Diagnostic data acquisition on Princeton’s tokamak fusion test reactor (TFTR) is accomplished via CAMAC (computer automated measurement and control system). This paper describes the capabilities of this instrumentation technique as applied to TFTR diagnostics and presents the family of CAMAC modules and equipment necessary for TFTR data acquisition and process control. These modules provide system configurations that range from meeting the basic requirements of digital and analog input/output to the requirements of transient digitizers, scalars, histogramming memory controller (each with add-on memory storage), timing and sequencing and timed gate units, function generators, and microprocessor interface units. The applications and guidelines that have evolved from our experience with TFTR CAMAC are presented.
Personal computer applications in DIII-D neutral beam operation
Authors: Glad A. S.
Published: July 2002

An IBM PC AT has been implemented to improve operation of the DIII-D neutral beams. The PC system provides centralization of all beam data with reasonable access for on-line shot-to-shot control and analysis. The PC hardware was configured to interface all four neutral beam host minicomputers, support multitasking, and provide storage for approximately one month’s accumulation of beam data. The PC software is composed of commercial packages used for performance and statistical analysis (i.e., LOTUS 123, PC PLOT, etc.), host communications software (i.e., PCLink, KERMIT, etc.), and applications developed software utilizing fortran and basic. The objectives of this paper are to describe the implementation of the PC system, the methods of integrating the various software packages, and the scenario for on-line control and analysis.
Data structure for the description of tokamak diagnostics
Authors: Hertweck F. R. , Maier J.
Published: July 2002

A novel open-ended file structure has been designed to describe ‘‘shot files’’ of a tokamak experiment. Elements of a shot file are data structures, called objects, that describe various aspects of the experiment. A general overview of the data analysis system AMOS/D is presented first, and then a detailed description of the shot file structure and the access procedures to shot data are given.
Diagnostic control, data acquisition, and data processing at MFTF-B (invited)
Authors: Preckshot George G.
Published: July 2002

Diagnostic instruments at the Mirror Fusion Test Facility (MFTF-B) are operated by a distributed computer system which provides an integrated control, data acquisition, and data processing interface to the experimentalist. Instrument control settings, operator inputs, and lists of data to be acquired are combined with data acquired by instrument data recorders to be used downstream by data processing codes; data processing programs are automatically informed of operator control and setpoint actions without operator intervention. The MFTF-B distributed computing environment permits us to take advantage of several kinds of computing equipment and commercial software. The combined diagnostic control and results presentation interface is presented to experimentalist users by a network of high-resolution graphics workstations. Control coordination, data processing, and data base management are handled by a shared-memory network of 32-bit super minicomputers. Direct instrument control, data acquisition, data packaging, and instrument status monitoring are performed by a network of dedicated local control microcomputers. A description of this system and our experiences in implementing the first MFTF-B diagnostic instrument, the magnetic field alignment diagnostic (MFA), are reported here.
CHERS software system—A microVAX-based diagnostic
Authors: Lagin L. , Schneider U. , Arnold N. , Fonck R. , Jaehnig K. , Roney P. , Davis W. , Christianson G.
Published: July 2002

The charge exchange recombination spectroscopy (CHERS) diagnostic is the first tokamak fusion test reactor (TFTR) diagnostic to utilize a microVAX II computer for device control, data acquisition, analysis, and event-driven processing. The CHERS system is controlled from a single interactive menu-driven process, enabling the diagnostic physicist to perform interactive device control and monitoring, calibration and control file editing, and to control automatic device setup, data acquisition and display, and postshot analysis. All software is written in fortran. Device control is accomplished using the (ORNL) VAX CAMAC and TAU real-time image processing system (RTIPS) fortran subroutines. Standard VAX system services are utilized, including the use of event flags, global sections, logical names, security services, process control, and spawning of subprocesses.
Neutron streak tube
Authors: Wang C. L. , Lerche R. A. , Medecki H. , Phillips G. E. , Singh M. S.
Published: July 2002

We present the design and construction of a simple neutron streak tube. The cathode is a 10-μm-thick U238 strip, 25 mm wide and 1.5 mm high, vacuum deposited on a stainless-steel substrate which replaces the cathode of a Lawrence Livermore National Laboratory (LLNL) model 3 x-ray streak camera. Accompanying a fission fragment, about 200 low-energy secondary electrons are emitted from the cathode. The streak tube was tested at a rotating target neutron source and at the Nova laser which produced 1013 neutrons from the fusion target. Preliminary results are presented.
Neutron calorimeter as a fusion diagnostic
Authors: Proctor A. E. , Nieschmidt E. B.
Published: July 2002

A calorimeter is described which is applicable as a fusion neutron diagnostic. The device has the following distinct advantages: low sensitivity to thermal neutrons, large dynamic range, small mass resulting in fair time resolution, small physical size, independent calibration, little shielding required, no heat loss to surroundings, and low cost. The heat generation is provided by neutron induced fissions in a foil of 235U or 238U. The effects, advantages, and disadvantages of these target materials are discussed. The expected time resolution and dynamic range are estimated for both target materials.
Double parallel-plate electrostatic analyzer for Tara end-loss studies
Authors: Sullivan James D. , Casey J. A. , Irby J. H. , Smith D. K. , Sevillano E.
Published: July 2002

An endloss spectrograph has been designed and is being fabricated for the Tara tandem mirror. This spectrograph is a double parallel-plate electrostatic analyzer about 60 cm in length with a 30° entrance angle; the high-voltage plate is a transparent wire cloth grid which allows higher energy particles to pass through for detection on a symmetric ground plane. The analyzer has three detection planes: first, the normal focal plane for low-energy detection at high resolution (0.1–4 keV); second, the entrance grounded plate for mid energies (4–6 keV); and third, the symmetric ground plane for coarse resolution at higher energies (8–20 keV). The analyzer is defocusing on the symmetric plane. This spectrograph will be able to measure simultaneously the endloss potential cutoff and ions from the neutral beams; in conjunction with a loss cone neutral beam source the resolution is sufficient (60 eV) to measure the plasma potential.
Microjet burners for molecular-beam sources and combustion studies
Authors: Groeger Wolfgang , Fenn John B.
Published: July 2002

A novel microjet burner is described in which combustion is stabilized by a hot wall. The scale is so small that the entire burner flow can be passed through a nozzle only 0.2 mm or less in diameter into an evacuated chamber to form a supersonic free jet with expansion so rapid that all collisional processes in the jet gas are frozen in a microsecond or less. This burner can be used to provide high-temperature source gas for free jet expansion to produce intense beams of internally hot molecules. A more immediate use would seem to be in the analysis of combustion products and perhaps intermediates by various kinds of spectroscopies without some of the perturbation effects encountered in probe sampling of flames and other types of combustion devices. As an example of the latter application of this new tool, we present infrared emission spectra for jet gas obtained from the combustion of oxygen–hydrocarbon mixtures both fuel-rich and fuel-lean operation. In addition, we show results obtained by mass spectrometric analysis of the combustion products.
Closed feedback system on the vertical beam position
Authors: Koyama Atsushi , Sasaki Satoshi , Ishikawa Tetsuya
Published: July 2002

We have developed two feedback systems to keep constant the vertical position of the incident beam on a sample. They are systems enclosed within the experimental station and independent of the storage ring. The first system adjusts the sample height by translating an apparatus in the case where the shortest response speed of feedback was about 0.5 s. The variation of the beam height was stabilized within about 5 μm. The other system changes the distance between two crystals of a double-crystal monochromator. The height of the exit beam was stabilized within 10 μm against any fluctuation of the incident beam.
Construction of a multiundulator, Revolver No. 19, at the Photon Factory
Authors: Isoyama G. , Yamamoto S. , Shioya T. , Ohkuma H. , Sasaki S. , Mitsuhashi T. , Yamakawa T. , Kitamura H.
Published: July 2002

A multiundulator, Revolver No. 19, was constructed and installed at the straight section (B 18-B19) of the 2.5-GeV Photon Factory storage ring. The mechanical structure of Revolver No. 19 consists of a main frame and two rotatable beams with four base plates, on which undulator magnets with four different lengths of period are mounted. A pair of undulator magnets with a desired period length can be selected by revolving the rotatable beams. The energy range of the radiation covered by fundamental peaks from the undulator magnets is from 7.8 to 1150 eV.