bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth conditions to optimize chemical order and magnetic properties in molecular-beam-epitaxy-grown CoPt/MgO(001) thin films
Authors: Ersen O. , Parasote V. , Pierron-Bohnes V. , Cadeville M. C. , Ulhaq-Bouillet C.
Published: March 2003

CoPt films grown on MgO(001) substrates by molecular-beam epitaxy are expected to develop a very large uniaxial magnetocrystalline anisotropy and a high coercivity when the [001] single variant L10 structure develops along the growth direction. The present study investigates the growth conditions that provide the best structural quality of the films and their related magnetic properties. The quality of the substrate surface, the thickness, and the texture of the Pt buffer layer, the presence or absence of a Cr seed layer, are found to be determinants for the fraction of well-oriented grains in the films, whereas the growth temperature mainly pilots the degree of L10 order η. The uniaxial magnetocrystalline anisotropy energy of the [001] grains (Ku001) is maximum at the stoichiometric composition and shows a linear increase with η. The coercive fields and the magnetic domain size are discussed in relation to the microstructure, the degree of L10 order and the magnetic microscopic constants of the films.
Suppression of Auger deexcitation and temperature quenching of the Er-related 1.54 μm emission with an ultrathin oxide interlayer in an Er/SiO2/Si structure
Authors: Kimura Tadamasa , Isshiki Hideo , Ide Sawa , Shimizu Takanori , Ishida Takeshi , Saito Riichiro
Published: March 2003

A strong enhancement of the Er3+-related 1.54 μm emission was obtained from Er-doped porous silicon (PSi), when host PSi was slightly oxidized before Er incorporation. Separate measurements of the energy transfer and the Auger deexcitation between carriers in Si crystallites of preoxidized PSi and Er3+ ions were measured as functions of the preoxidized time or the thickness of the SiO2 interlayer, and revealed that a 1 nm order thick SiO2 interlayer between Si crystallites and Er3+ ions suppressed the Auger energy backflow strongly with only a moderate decrease of the carrier mediated Er3+ excitation. A thin SiO2 interlayer was also effective at suppressing the phonon-assisted energy backtransfer at high temperatures, leading to a strong room temperature Er3+-related 1.54 μm emission.
Structure, high temperature transport, and thermal properties of Ba8GaxSi46−x (x=10 and 16) clathrates prepared by the arc melting method
Authors: Nataraj Devaraj , Nagao Jiro , Ferhat Marhoun , Ebinuma Takao
Published: March 2003

Ba 8 Ga 10 Si 36 and Ba8Ga16Si30 clathrates were prepared by the arc melting method and characterized for their structure, transport, and thermal properties by x-ray diffraction, electron probe microanalysis, electrical resistivity, and thermal conductivity measurements. The Rietveld refinement results gave the total occupancy of Ga/Si equal to 3.49/2.01, 0.99/14.01, and 5.51/17.99 for Ba8Ga10Si36 and 3.99/2.01, 1.99/14.01, and 10.01/13.99 for Ba8Ga16Si30, respectively, for 6c, 16i, and 24k sites. From the refined isotropic thermal displacement parameters, Debye temperature, average velocity of sound, lattice thermal conductivity, and Einstein temperature values were estimated. The calculated lattice thermal conductivity values were in agreement with room temperature experimental values of 1.128 and 1.071 W m−1 K−1, respectively, for two clathrates. The temperature variation of (300–850 K) electrical resistivity of Ba8Ga16Si30 showed metallic like behavior, whereas that of Ba8Ga10Si36 showed semiconducting behavior. The semiconducting nature was due to vacancies in the framework sites. High temperature thermal conductivity above Debye temperature was explained with anharmonic approximation.
Application of natural diamond detector to energetic neutral particle measurements on NSTX
Authors: Alekseyev A. G. , Darrow D. S. , Roquemore A. L. , Medley S. S. , Amosov V. N. , Krasilnikov A. V. , Prosvirin D. V. , Yu. Tsutskikh A.
Published: March 2003

Two natural diamond detectors have been installed on the National Spherical Torus Experiment (NSTX) to look at escaping neutrals at or near the neutral beam injection energy. Time resolved measurements have been obtained from these detectors at various tangency radii. The close proximity of the detector to the vessel required the development of a very fast low-noise preamplifier, which has been shown to be superior to similar commercial units. With this amplifier arrangement, electromagnetic pick-up noise was reduced to acceptable levels. However, radiation shielding was required to reduce the background levels from neutron-induced pulses in the detector. Calibration data along with the measured energy resolution is presented in the useful energy range for NSTX. Example data from plasma discharges is also presented.
Multiple film plane diagnostic for shocked lattice measurements (invited)
Authors: Kalantar Daniel H. , Bringa E. , Caturla M. , Colvin J. , Lorenz K. T. , Kumar M. , Stölken J. , Allen A. M. , Rosolankova K. , Wark J. S. , Meyers M. A. , Schneider M. , Boehly T. R.
Published: March 2003

Laser-based shock experiments have been conducted in thin Si and Cu crystals at pressures above the Hugoniot elastic limit. In these experiments, static film and x-ray streak cameras recorded x rays diffracted from lattice planes both parallel and perpendicular to the shock direction. These data showed uniaxial compression of Si(100) along the shock direction and three-dimensional compression of Cu(100). In the case of the Si diffraction, there was a multiple wave structure observed, which may be due to a one-dimensional phase transition or a time variation in the shock pressure. A new film-based detector has been developed for these in situ dynamic diffraction experiments. This large-angle detector consists of three film cassettes that are positioned to record x rays diffracted from a shocked crystal anywhere within a full π steradian. It records x rays that are diffracted from multiple lattice planes both parallel and at oblique angles with respect to the shock direction. It is a time-integrating measurement, but time-resolved data may be recorded using a short duration laser pulse to create the diffraction source x rays. This new instrument has been fielded at the OMEGA and Janus lasers to study single-crystal materials shock compressed by direct laser irradiation. In these experiments, a multiple wave structure was observed on many different lattice planes in Si. These data provide information on the structure under compression.
JET beamline with integrated x-ray, VUV, and visible spectrometers, for burning plasma experiments
Authors: Barnsley R. , Coffey I. , Lucock R. , Stamp M. F. ,   Contributors to the EFDA-JET Work Programme
Published: March 2003

We report several developments to the JET Tokamak survey spectroscopy beamline, which now supports a suite of x-ray, VUV, and visible instruments, located in a radiation-shielded bunker outside the torus hall. The instruments have vacuum systems that are integrated into the tritium circuit, and are available for D–T experiments. The x-ray and VUV diagnostics have real-time data reduction. The proposed plasma impurity monitor for ITER is based on these developments.
Integrated impurity diagnostic package for magnetic fusion experiments
Authors: Stutman D. , Finkenthal M. , Moos H. W. , Fournier K. B. , Kaita R. , Johnson D. , Roquemore L.
Published: March 2003

We develop an integrated instrumental and computational package for the diagnosis of impurity content, Zeff profile, particle transport, and magnetohydrodynamics activity in magnetic fusion experiment plasmas. The package includes broadband filtered arrays of absolute (AXUV) photodiodes, a transmission grating imaging spectrometer measuring up to 20 chords across the discharge and having a few angstrom spectral resolution, together with an atomic physics database coupled with an impurity transport code. The atomic physics database is based on ab initio computations with the Hebrew University Lawrence Livermore atomic code. The package is designed for the diagnostic of sub-keV plasmas having predominantly low-Z impurities (C, B, and O) together with trace metals. A preliminary version is being tested on the National Spherical Torus Experiment spherical torus at the Princeton Plasma Physics Laboratory, using the ultrasoft x-ray imaging system and a grazing incidence spectrometer. Representative results from non-H-mode discharges are presented.
Imaging transmission grating spectrometer for magnetic fusion experiments
Authors: Blagojević B. , Stutman D. , Finkenthal M. , Moos H. W. , Kaita R. , Majeski R.
Published: March 2003

The Johns Hopkins Plasma Spectroscopy Group is developing a transmission grating based imaging spectrometer for the ultrasoft x-ray [(USXR), 10–300 Å] range. The spectrometer will be integrated into an impurity diagnostic package for magnetic fusion experiments, which provides time and space resolved information about radiation losses, Zeff profiles, and particle transport. The spectrometer has a simple layout, consisting of collimating and space resolving slits, a transmission grating, and a two-dimensional imaging USXR detector. We tested two types of detectors, a CsI coated multichannel plate and a phosphor P45 coated fiber optic plate, both with intensified charge-coupled-device image readout. The performance of the 5000 1/mm, 3:1 bar to open area ratio transmission grating has been evaluated in the laboratory using Kα lines from a Manson source and the emission from a Penning discharge. A prototype spectrometer equiped with the first type detector and optimized for 6 Å spectral resolution has been tested successfully on the CDX-U tokamak at the Princeton Plasma Physics Laboratory. A spectrometer using the second detector version has been developed for the NSTX spherical torus at Princeton. Spatially resolved spectra have been recorded with 25–250 ms time integration with both spectrometers. In both experiments, spectra are dominated by low-Z impurities, C, N, and O.
First measurement of hard x-ray spectrum emitted from high-energy electrons in electron cyclotron heated plasma of LHD
Authors: Muto S. , Morita S. , Kubo S. , Shimozuma T. , Idei H. , Yoshimura Y.
Published: March 2003

Hard x-ray spectrum up to 200 keV has been successfully observed for the first time from electron cyclotron heated plasmas with an x-ray pulse-height analyzer installed on a horizontal port of Large Helical Device. A solid-state germanium detector viewing the plasma center is used as a detector. The data-acquisition system is basically operated with a high counting rate (∼64 kHz). The apparatus is equipped with a collimator and filters. The detector is supported by vibration dumpers and covered by an electrically isolated shield to avoid mechanical vibration and electromagnetic noise. The obtained hard x-ray spectrum indicates a non-Maxwellian distribution. The density of the high-energy electrons is estimated to be two orders less than the bulk electrons.
Energy and pitch angle-resolved measurements of escaping helically trapped energetic ions at the small major radius side of the compact helical system
Authors: Isobe M. , Darrow D. S. , Kotani J. , Shimizu A. , Suzuki C. , Yoshimura Y. , Minami T. , Takahashi C. , Nagaoka K. , Nishimura S. , Toi K. , Matsuoka K. , Okamura, and the S. ,   CHS group
Published: March 2003

We have developed and installed a new, second escaping fast ion probe for the small major radius side of the compact helical system. This is a Tokamak Fusion Test Reactor type scintillator-based probe and is intended to detect unconfined helically trapped fast ions whose orbits largely deviate from magnetic flux surfaces. We observed a localized light spot on the scintillator screen in neutral beam-heated discharges and it was confirmed to be a true fast ion signal. The analysis suggests that the probe detects partially thermalized, pitch angle scattered beam ions.
Improvements in off-center focusing in an x-ray streak camera
Authors: McDonald J. W. , Weber F. , Piston K. W. , De Dios E. O. Vergel , Holder J. P. , Bell P. M.
Published: March 2003

Due to the planar construction of present x-ray streak tubes, significant off-center defocusing is observed in both static and dynamic images taken with one-dimensional resolution slits. Based on the streak tube geometry, curved photocathodes with radii of curvature ranging from 3.5 to 18 in. have been fabricated. We report initial off-center focusing performance data on the evaluation of these “improved” photocathodes in an x-ray streak camera.
Designing and building an integrated target chamber system for high intensity short-pulse laser-target interaction experiments
Authors: Yasuike Kazuhito , Orimo Satoshi , Nishiuchi Mamiko , Suzuki Masayuki , Matsukado Kouji , Daido Hiroyuki , Arisawa Takashi , Kimura Toyoaki , Tajima Toshiki
Published: March 2003

We have recently designed and are building a plasma experiment chamber system for a high intensity short pulse Ti:sapphire 100 TW laser (λ=800 nm, 2 J, 20 fs) at the Advanced Photon Research Center, JAERI. The expected primary use of the chamber is for high intensity (up to 1020 W cm−2) laser solid target experiments for hot electron, ion, and x-ray production. In order to achieve these intensity levels, the focal spot size on the target needs to be much smaller (⩽φ10 μm) than those used in relatively high laser energy experiments using ⩾100 fs laser pulse widths. The system consists of a target monitor system, a target insertion device (manipulator shuttle), a target stage assembly, and an on-target beam profiler all integrated together. We used calibrated apertures, hereafter called “zero pinholes,” placed at the focal point to assess the on-target energy accurately within a defined spot area. It is intended for general experiments rather than specifically configured ones, e.g., time-diffraction kind of experiments. However, great care was taken to have the capability to accommodate these types of experiments in the future.
Linear alignment of GaN quantum dots on AlN grown on vicinal SiC substrates
Authors: Brault J. , Tanaka S. , Sarigiannidou E. , Rouvière J.-L. , Daudin B. , Feuillet G. , Nakagawa H.
Published: March 2003

We demonstrate linear alignment of self-assembled GaN quantum dots (QDs) grown by molecular beam epitaxy on AlN using vicinal SiC substrates. Under specific surface preparation, such substrates can present well-ordered steps. We also show that stepped AlN layers can be grown on such SiC substrates, the height and width of AlN step depending on growth parameters. Such steps induce a heterogeneous nucleation of QDs and promote an alignment along their edges. We demonstrate, by atomic force microscopy, the possibility of controlling the island spatial distribution and point out a lateral ordering of the dots.
Evaluation of the incident angle of the beam into 30° electrostatic energy analyzer directly during HIBP operation in plasma experiments
Authors: Nedzelskiy I. S. , Malaquias A. , Gonçalves B. , Varandas C. A. F. , Cabral J. A. C. , Dreval N. B. , Khrebtov S. M. , Komarov A. D. , Kozachok A. L. , Krupnik L. I.
Published: March 2003

The resolution of the plasma potential measurements by a 30° electrostatic energy analyzer of a heavy-ion beam probe (HIBP) is strongly related to the accuracy of knowledge of the incident angle of the beam (θ). Initially it is determined by the calculations of the beam trajectories in the confining magnetic field of the plasma device. However, because the magnetic-field simulation codes are not exact, an uncertainty in θ always exists. A common practice to reduce the influence of this uncertainty consists in tuning the analyzer geometry parameters in such a way as to minimize the dependence on the variation of θ that results from a scan of the beam across the plasma. Still, the attachment of the energy analyzer to the diagnostic port cannot be controlled with enough precision and, therefore, an unknown shift out from the chosen optimal range of θ is predictable. This article proposes a method for the direct evaluation of the incident angles during operation of HIBP in plasma experiments. It is based on the addition of a second split-plate detector along a 30° exit axis of the analyzer, and on the comparison of the respective normalized beam currents. The experimental verification of the method on a test facility has shown that an accuracy better than Δθ=0.1° can be attained.
Improved 20 keV injection system for the heavy-ion-beam diagnostic of the tokamak ISTTOK
Authors: Cabral J. A. C. , Nedzelskiy I. S. , Malaquias A. J. , Gonçalves B. , Varandas C. A. F. , Bondarenko I. S. , Khrebtov S. M. , Komarov A. D. , Kozachok A. L. , Krupnik L. I.
Published: March 2003

The initial injection system of the heavy-ion-beam diagnostic (HIBD) of the tokamak ISTTOK provides a 2 mm diameter and 3.6 mrad divergence beam of Cs+ or Xe+ ions, after extraction from a plasma ion source and acceleration up to 20 keV by a gap lens and diameter definition by a set of apertures. However, the beam current is significantly reduced to 1.5 μA, therefore, complicating the HIBD measurements of the plasma parameters. Creation of the beam with a higher current and the same, or close, geometrical parameters requires a significant improvement of the ion optics of the injection system. This article describes an injection system built in the acceleration tube, and presents results of test experiments with a solid-state thermionic source (SSTS) and a monocusp plasma ion source (MPIS). The improved injection system is characterized by a good match to both ion sources. The use of the long focus ion optics of the acceleration tube allows one to obtain an output beam current up to 11 μA of Cs+ ions with SSTS and 39 μA of Xe+ ions with MPIS, and dimension preservation at the focus point. Operating on the tokamak ISTTOK, the injection system significantly increased the signal-to-noise ratio and improved the measurements of the plasma parameters.
Lithium beam probe for edge density profile measurements on the large helical device
Authors: Morisaki T. , Komori A. , Motojima O. ,   LHD Experimental Group
Published: March 2003

A 30 keV lithium beam probe system to measure edge density and its fluctuation has been developed on the large helical device (LHD) and has just started its operation. On a test setup relevant to LHD conditions, the equivalent beam current ∼0.1 mA was obtained without the unfavorable beam divergence, in spite of a long distance more than 6 m from the injector. In the preliminary experiments in LHD, it was found that the beam penetrates up to ρ∼0.8 (ρ:normalized minor radius). By using the electrostatic deflection plates coupled with an in situ beam position monitor, the probe system operation is available, without the magnetic field shield, under the flexible experimental conditions with various magnetic field configurations.
Comparison of ion temperature diagnostics on the Madison symmetric torus reversed-field pinch
Authors: Reardon J. C. , Craig D. , Den Hartog D. J. , Fiksel G. , Prager S. C.
Published: March 2003

There have been three ion temperature diagnostics operating on the Madison symmetric torus (MST) for the past two years: (i) Charge-exchange recombination spectroscopy (CHERS), which measures the temperature of fully stripped impurity (C6+) ions, and has a spatial resolution of ±1 cm and a time resolution of 3 ms; (ii) Rutherford scattering (RS), which measures the temperature of the bulk majority (D+) ions, and has a spatial resolution of roughly ±7 cm and a time resolution of 30 μs; and (iii) the ion dynamics spectrometer (IDS), which measures a chordal average of the temperature of partially stripped impurity (C4+) ions, with a time resolution of 10 μs. The first two diagnostics use neutral beams, while the third is passive. The classical ion energy equilibration time τii<1 ms between all ion species, so we naively expect that all ion temperature measurements should agree in steady state. Here we present simultaneous measurements of: CHERS and RS profiles in high-current burst-free pulsed poloidal current drive (PPCD) discharges; CHERS and RS profiles in standard high-current discharges; and IDS and RS profiles in standard low-current discharges. Measurements in standard discharges are made a long time before and after magnetic reconnection events, during which there is believed to be a large, nonclassical input of energy to the ions. RS and CHERS measurements consistently agree; IDS measurements are consistently less than RS measurements, due to the effect of the C4+ emission profile on the IDS measurements.
Impact of bulk non-Maxwellian electrons on electron temperature measurements (invited)
Authors: de la Luna E. , Krivenski V. , Giruzzi G. , Gowers C. , Prentice R. , Travere J. M. , Zerbini M.
Published: March 2003

In neutral beam injection and ion cyclotron resonance frequency (NBI+ICRF) heated high-temperature Joint European Torus (JET) plasmas, electron cyclotron emission (ECE) spectra measured by the Michelson interferometer are inconsistent with the electron bulk distribution being Maxwellian. This conclusion follows from new, accurate modeling of the ECE spectra over the full measured frequency range, covering the first four harmonics of the cyclotron frequency. A model distribution function obtained by fitting a measured ECE spectrum reveals a distortion of the Maxwellian that is sharply localized at ∼1.5×thermal momentum. A consequence deduced from this distribution is that the electron temperature measured by JET’s Thomson scattering diagnostic, which weighs the bulk electrons differently, should be lower than the ECE one in the spatial region where this distortion exists. This prediction appears to be confirmed by temperature profile comparisons showing that core Thomson scattering electron temperatures on JET are up to 20% lower than ECE values for plasmas with strong NBI+ICRF heating. The possibility of addressing experimentally the question of whether the plasma has a Maxwellian bulk is also discussed. This goal can be accomplished by observing the emission at different angles with respect to the magnetic field (oblique ECE). Simulations of oblique ECE spectra using the model distribution function obtained previously show an angular variation of the emission that is characteristic of the distorted bulk.
Measurements of density fluctuations in reflectometry of cylindrical plasmas
Authors: Bruskin L. G. , Oyama N. , Shinohara K. , Miura Y. , Kogi Y. , Mase A. , Hasegawa M. , Hanada K.
Published: March 2003

An analytical model of fluctuation reflectometry is developed, which is capable of handling the plasma profiles of arbitrary shape and curvature. The experimental profiles are piece-wise approximated by the functions, which allow for the integration of the full-wave O-mode equation. The model is applied to the reflectometry of the JT-60U tokamak plasma to provide a preliminary estimation of the fluctuation amplitude and spectral width.
On the use of the analytic signal to retrieve the phase from broadband reflectometry signals
Authors: Figueiredo António C. A. , Bizarro João P. S.
Published: March 2003

A comparison is carried out between the phase derivative of broadband reflectometry signals, which are cosine signals calculated from a given electron-density profile according to the model that underlies the functioning of broadband reflectometers, and the phase derivative of the corresponding analytic signals. A class of density profiles commonly employed to model high-temperature plasmas is considered, for which it is shown that the two phase derivatives agree well, except for some oscillatory behavior at the beginning and ending of the signals. Gibbs’ phenomenon, associated with the practical calculation of the analytic signal is identified as the cause of this effect. The reconstructed density profiles are shown to be practically unaffected by the oscillations, which are averaged out upon integration, leading to good agreement with the original density profiles.
Laser-based diagnostic for tracing magnetic-field lines in spheromaks and other self-organized magnetically confined plasmas
Authors: McLean H. S. , Hill D. N. , Ryutov D. D. , Chen H.
Published: March 2003

We are in the process of testing a technique for measuring the magnetic-field line topology in magnetically confined plasmas. The basic idea is to use a high-powerful short-pulse laser to launch a burst of energetic (∼100 keV) electrons from a target passing through the plasma of interest; these electrons then generally follow field lines until they strike a solid surface, where a burst of x rays is produced and then detected. The field line connection length can be determined from the time delay between the laser pulse and the burst of x rays. The topology of the field lines can be inferred by measuring the connection length as a function of initial target location inside the plasma. Measuring the spatial distribution of the x-ray production will provide further information on the field topology, including the effects of magnetic-field fluctuations and stochasticity. The work will eventually include testing the appropriate x-ray detectors, measuring the background x-ray emission in a spheromak plasma, measuring the energetic electron production by a short-pulse high-power laser, and making preliminary measurements of the edge field line topology in the Sustained Spheromak Physics Experiment using a pulsed electron-beam source as a prototype for a laser-based source. This technique may have broad application to a variety of plasma configurations and provide physics data applicable to a wide range of plasma physics problems.
High-spatial resolution edge electrostatic probe system for RFX
Authors: Serianni G. , Baker W. , Dal Bello S.
Published: March 2003

The RFX reversed field pinch (RFP) is undergoing major modifications of the load assembly and will be equipped with a large number of external coils for active magnetohydrodynamics mode control. The investigation of plasma parameters is then of paramount importance to study the effects on the plasma of both the new passive structure and the action of the external active coils. The study of turbulence is also very important because of its influence on plasma transport. A system of electrostatic probes is needed, fulfilling very challenging requirements in terms of spatial and temporal resolution, which are characteristic features of RFP plasmas. This system should also be integrated with other in-vessel sensors (magnetic and calorimetrical probes) and with other diagnostics placed outside the vessel. A description of the diagnostic system is presented. The global layout of the probes along the first wall is shown: The system allows a two-dimensional investigation of the plasma; both single and triple electrostatic probes have been constructed. Each sensor is embedded in the graphite tiles which completely cover the vessel. The design of the probes is displayed, describing the original solutions adopted to cope with several technological issues. In particular, due to the high number of signals and to limited space available within the vessel, the probe dimensions were minimized. Since RFX possesses no iron core, care has been devoted to avoid pick-up of stray time-varying magnetic fields. Under particularly high thermal loads onto the wall, due to the absence of limiters and to phase-locked magnetic modes, thermal requirements are provided by a suitable choice of materials, at the same time meeting the necessary standards of electrical insulation. Mechanical tests on the carbon tiles modified for inserting the probes were also needed; thermal and electrical tests on prototypes were performed.
Development of a multichannel far-infrared tangential interferometer/polarimeter for the National Spherical Torus Experiment
Authors: Deng B. H. , Chen H. C. , Domier C. W. , Johnson M. , Lee K. C. , Luhmann N. C. , Nathan B. R. , Park H.
Published: March 2003

Completion of a multichannel far-infrared (FIR) tangential interferometer/polarimeter is under way for the National Spherical Torus Experiment, for the measurement of plasma electron density and toroidal magnetic-field distributions. The system is based on the three-wavelength configuration, which was first developed by Rommers and Howard in the RTP tokamak [Plasma Phys. Controlled Fusion 38, 1805 (1996)]. The probe beams enter the plasma through the windows on the midplane in Bay-K, and are reflected back to the detectors by retro-reflectors. The three FIR beams with a wavelength of 119 μm are produced by three Methanol lasers optically pumped by a CO2 laser tuned to 9.7 μm. The entire system is designed to have a full remote control capability using the LABVIEW program and fiber links. The technical details of the system development will be presented together with preliminary experimental result.
Studies of resonantly produced plasmas in the H-1NF heliac using a far-infrared scanning interferometer
Authors: Collis S. M. , Howard J. , Warr G. B. , Michael C. A. , Harris J. H. , Blackwell B. D. , Pretty D. G.
Published: March 2003

The H-1NF heliac regularly operates using the ion cyclotron range of frequencies at 0.5 T to produce plasmas with a mixture of hydrogen and helium gases. Due to the complex three-dimensional structure of the magnetic flux surfaces, these plasmas require sophisticated diagnostic systems, with good spatial coverage, to extract meaningful physical information. This article presents a study of the dependence of the plasma density profile on resonant heating conditions and magnetic configuration, using a far-infrared scanning interferometer. Recent modifications to the system and data that illustrate the performance of the interferometer will be discussed.
Phase contrast imaging interferometer for edge density fluctuation measurements on LHD
Authors: Tanaka K. , Vyacheslavov L. N. , Akiyama T. , Sanin A. , Kawahata K. , Tokuzawa T. , Ito Y. , Tsuji-Iio S. , Okajma S.
Published: March 2003

A phase contrast interferometer employing a CO2 laser (wavelength λi=10.6 μm) is designed and installed in order to study density fluctuations on a large helical device. A 250×50 mm slab beam passes the edge of the plasma, where ρ=r/a>0.65, and provides observations of edge density fluctuations. A spatial image of the integrated fluctuations is measured by a multichannel detector array, of which the effective spacing is 5 mm in the plasma. Measured wave number components are dominated by radial components, and within the range of 7.2×10−2⩽k⩽0.63 mm−1 and within the frequency range of 5–125 kHz. A clear difference in the fluctuation levels and peak wave numbers are observed between different discharges, which differ in the energy confinement.
Raman calibration of the LHD YAG Thomson scattering for electron-density measurements
Authors: Yamada I. , Narihara K. , Hayashi H. ,   LHD Experimental Group
Published: March 2003

We have calibrated the LHD yttrium aluminum garnet (YAG) Thomson scattering system by using anti-Stokes rotational Raman scattering from air for the measurements of absolute electron-density profiles of LHD plasmas. The air Raman calibration was carried out at near atmospheric pressure and room temperature. Total uncertainty in measured electron densities is estimated to be ±15% or less. Electron densities obtained with the calibrated YAG Thomson scattering show good agreements with those measured by the LHD millimeter-wave interferometer.
Charged particle-induced gamma excitation as a possible diagnostic technique for escaping MeV ions on ITER
Authors: Bonheure G. , Van Wassenhove G.
Published: March 2003

The knowledge of the flux of energetic ions to the first wall and their energy and pitch angle distributions are important for ITER. We study the possibility of using charged particle-induced activation which provides an attractive, simple, and robust technique to measure escaping million electron volt ions. For time resolved measurements, prompt gamma rays emitted by the target are directly viewed with a spectrometer. In this preliminary study we assess the possibility to fulfill the requirements necessary for the ITER alpha loss detectors. Test experiments are under preparation and simulations with the Monte Carlo MCNP4C code are used to assess the performance (signal-to-noise ratio) of the detectors.
Diagnostics plan for the national compact stellarator experiment
Authors: Johnson D. , Brown T. , Neilson H. , Schilling G. , Takahashi H. , Zarnstorff M. , Cole M. , Lazarus E. , Fenstermacher M.
Published: March 2003

The National Compact Stellarator Experiment (NCSX) is a stellarator-tokamak hybrid seeking to combine the good confinement, high beta, and moderate aspect ratio of the tokamak with the quasi-steady-state operation and good stability properties of the stellarator. A preliminary list of measurement requirements, intended to satisfy the needs of the phased research plan, provides the basis for a full complement of plasma diagnostics. It is important to consider this full set, even at this early stage, to assess the adequacy of the stellarator design for diagnostic port access. The three-dimensional nature of the plasma is a measurement challenge, as is the necessity for high-spatial resolution to assess the quality of magnetic surfaces. Other diagnostic requirements include the need for re-entrant views that penetrate the cryostat, for a convenient e-beam probe for field line mapping, and for a diagnostic neutral beam for active spectroscopy.
Data processing in fusion experiments with remote participation
Authors: Barrera E. , Ruiz M. , López S. , Vega J. , Sánchez E.
Published: March 2003

Remote participation in fusion experiments is becoming more and more widespread. From the point of view of the data processing that each experiment generates, remote participation increases the present needs of existing systems. On the one hand, these systems must be able to acquire the data from each discharge (with hundreds of channels and high-sample frequencies) and, on the other hand, they must be able to compress, analyze, and process data in as short period of time as possible. This would mean a decrease in network bandwidth use when sending results to remote investigators, a considerable saving of space in the local database, and a reduction of computation time in the server. Furthermore, in remote participation experiments, the system would allow each user to configure their own measures and analyses (downloading their own high-level programs in the system—writing in 4GL languages, for example in LABVIEW—and receiving the processed data as soon as possible). What is proposed as a solution for data processing in experiments with remote participation (that will be applied in the stellarator type device (TJ-II) of the Research Center for Energy, Environment, and Technology (CIEMAT), of Madrid Spain, is a distributed system that guarantees noise immunity and electromagnetic shielding (for example, based on several PCI (peripheral component interconnect) extensions for instrumentation (PXI) chassis with several digitizer boards in each one). It is not possible to process all data from the system’s own controller. Therefore, the following alternative will be presented: The design of the development of a processing board, that works in a peripheral PXI slot (nonsystem slot), running a real-time operating system (WNT+RTX, RT-LINUX,…), that communicates by PXI bus with the controller. In this way, the needs of data processing in remote participation experiments can be fulfilled.
Electron temperature determination and subsequent analysis of short time-scale variation of plasma parameters in ISTTOK discharges
Authors: Plyusnin V. V. , Cabral J. A. C. , Figueiredo H. , Varandas C. A. F.
Published: March 2003

Measurements of the electron temperature using standard diagnostics, like electron cyclotron emission or soft x-ray diagnostics, tend to be inadequate due to the natural limitations of these methods at low-toroidal magnetic field (B0⩽0.5 T) and plasma density [ne∼(1–5)×1018 m−3] in the typical discharges of the ISTTOK tokamak. On the other hand, the presence of a noticeable population of the suprathermal (runaway) electrons often causes a significant discrepancy between the values of the electron temperature yielded by different diagnostics. A numerical code was developed for the determination of the electron temperature from the measured macroscopic plasma parameters in discharges with and without runaway electrons. Simultaneous reconstruction of the time variation of the electron temperature and the runaway electron characteristics was carried out self-consistently using plasma power-energy balance calculations with the inclusion of the runaway process. Runaway electron instability caused the short-time relaxations of the plasma parameters detected by the ISTTOK data acquisition system. Analysis of the plasma parameters evolution during relaxations was used for the verification of the reconstruction procedure. The developed algorithm of the experimental data analysis was investigated in relation to its possible use for modeling of the runaway generation during a thermal quench in large-scale tokamak disruptions.
Comparative study design of a heavy ion and neutral beam diagnostic for the International Tokamak Experiment Reactor
Authors: Malaquias A. , Nedzelsky I. , Gonçalves B. , Varandas C. A. F. , Cabral J. A. C. , Melnikov A. , Eliseev L. , Perfilov S. , Yudina O. , Krupnik L.
Published: March 2003

In this article, we address the major physics principles and the engineering issues associated with the implementation of a heavy ion beam diagnostic for the International Tokamak Experiment Reactor (ITER) for the edge measurements of the plasma electric and poloidal magnetic fields. Two different diagnostic configurations are discussed. The ions’ trajectories and attenuations were calculated by dedicated simulation codes using the relevant ITER equilibrium parameters. Estimations of measurement accuracy are presented for a chosen configuration.
Relationship between copper concentration and stress during electromigration in an Al(0.25 at. % Cu) conductor line
Authors: Kao H.-K. , Cargill G. S. , Giuliani F. , Hu C.-K.
Published: March 2003

Synchrotron-based x-ray microbeam fluorescence and diffraction have been used for in situ measurements of Cu concentration and biaxial stress in a 200-μm-long, 10-μm-wide Al(0.25 at. % Cu) conductor line with 1.5-μm-thick SiO2 passivation during electromigration. Measurements over 48 h with T=300 °C and j=1.5×105 A/cm2 show that a stress gradient of 3 MPa/μm develops over the upstream 130 μm of line length where Cu concentration drops below 0.15 at. %, and a 10-μm-long void develops at the cathode end of the line, but little change in stress occurs over the downstream 70 μm of line length where Cu concentration remains above 0.15 at. %. These experimental results have been reproduced by a finite element model in which the downstream Cu transport is accompanied by a counter flow of Al in the upstream direction, and downstream Al motion is blocked where the local Cu concentration is above ∼0.15 at. %. Defect mediated coupling between Al and Cu diffusive flows, e.g., Cu–vacancy binding, is proposed as the cause for the counterflow of Al when the Cu concentration is above the critical concentration, and as the mechanism by which Cu reduces the rate of electromigration damage in Al(Cu) conductor lines.
An analytical expression for quantum-well tunneling lifetimes
Authors: Ng W. H. , Chan K. S.
Published: March 2003

An analytical expression is presented for the tunneling-escape lifetime of an electron occupying a quantum state localized in a quantum well in a heterostructure, using the perturbation approach. In the present derivation, an orthogonal basis set of wave functions is used, and all the terms in the perturbation expansion are included. The present formulation is exact and free from the inconsistencies in the transfer Hamiltonian method found recently by Fransson et al. [Phys. Rev. B 64, 153403 (2001)]. The tunneling lifetimes obtained by the present formulation agree with those obtained by the complex energy method. The analytical expression is useful in modeling tunneling devices in the sequential tunneling picture. We find that coupling of quantum states outside the quantum well to excited states localized in the quantum well is very important, and including these terms changes the tunneling lifetime by about six orders of magnitude.
Multipeak pulse x-ray diffraction study of shocked single crystals
Authors: Zaretsky E.
Published: March 2003

The geometry of a pulse x-ray diffraction survey is suggested to obtain a multipeak x-ray diffraction pattern from a single crystal sample in planar impact experiments. This geometry allows simultaneous recording of x-ray reflections from different crystal planes. The corresponding mathematical expressions for screen (detector) positions of the reflections produced by both strained and unstrained crystals are developed. In the case of the reflections from (200) and (220) crystal planes, the expressions enable the strain tensor components to be extracted from the relative shifts of diffraction peaks. The expressions were applied to interpret the multipeak diffraction patterns obtained from NaCl single crystals both shock-compressed and unloaded after the shock compression. The lattice strain alterations observed may be explained within the framework of dislocation theory of plastic deformation.
Metastable behavior of anion-site donors in InAs
Authors: Risse M. , Vianden R.
Published: March 2003

The metastability of the well-known EL2 and DX centers in III–V compound semiconductors are now understood theoretically to be due to the same basic mechanism, namely, the different possibilities of sp hybridization. Analogous theoretical considerations suggest that group VI and VII impurities on a group V site could exhibit similar properties. In the present study, the perturbed angular correlation technique was employed to study the behavior of the radioactive halogen Br77−which decays to Se77−after implantation into InAs depending on the annealing procedure and the predoping of the base material. A strong correlation of the final lattice site with the position of the Fermi level was found, and a detailed description of the possible lattice surrounding of the Br77(77Se) probe is given.
Size effects of optical and magneto-optical properties of epitaxial CrPt3 films
Authors: Broschwitz M. , Knetsch S. , Borgschulte A. , Bizdoaca L. , Schoenes J.
Published: March 2003

The magneto-optical polar Kerr effect and the optical functions of epitaxial films of CrPt3 have been studied as a function of film thickness. For this purpose, a wedge-shaped film was grown with film thickness ranging from 0 to 100 nm. A Kerr rotation of about 0.25° and -0.5° has been found in the near-ultraviolet and near-infrared spectral range, respectively, for the thicker films, decreasing rapidly with decreasing film thickness. In contrast, the shapes of the Kerr rotation and ellipticity spectra remain nearly unchanged. The optical functions are found to be strongly affected by the film morphology, which was studied by reflection high-energy electron diffraction and atomic force microscopy. The results are in good agreement with effective-medium calculations.
Decay of space charge in conjugated polymers measured using pyroelectric current transients
Authors: Feller F. , Geschke D. , Monkman A. P.
Published: March 2003

The decay of space charge in conjugated polymers due to detrapping from deep traps after the turn-off of an external bias has been investigated. We present an experiment for measuring time-resolved laser intensity modulation method spectrum with a resolution of about 1 s. For this pyroelectric current transients have been recorded at different temperatures from 220 to 360 K. The data have been analyzed, assuming detrapping of charge carriers from single energy trap levels to a Gaussian distribution of transport levels to be the predominating process of the space-charge decay. In poly[2-methoxy, 5-(2’-ethyl-hexyloxy)-p-phenylene-vinylene], we find hole trapping with a trap depth of Et=0.6 eV and a trap density Nt>2×1021 m−3. In poly(2,5-pyridinediyl) both electron and hole trapping are observed, and the analysis of the decays yield Et=0.55 eV and Nt>1021 m−3. No deep trapping could be observed in poly(9,9-dioctylfluorene), confirming the high chemical purity of this polymer.
Micro-Raman and ultraviolet ellipsometry studies on μc-Si:H films prepared by H2 dilution to the Ar-assisted SiH4 plasma in radio frequency glow discharge
Authors: Das Debajyoti
Published: March 2003

Micro-Raman and ultraviolet ellipsometry studies have been performed on μc-Si:H films prepared by increasing the H2 dilution to the Ar-assisted SiH4 plasma in rf glow discharge. Combining the results obtained from the Bruggeman effective medium approximation fitting to the ellipsometry data and the Gaussian deconvolution of Raman spectra, it has been observed that the overall crystallinity improves along with the lowering in the incubation layer thickness, elimination of the amorphous component from the bulk, and the reduction of void fraction in the bulk as well as in the growth zone and surface layer. However, at very high H2/Ar ratio in the plasma a lowering in the crystallinity has been recorded along with an associated increase in the voids and an appearance of a small amorphous component in the bulk of the material. An increase in the voids arising at the grain boundary zone causes the hindrance to the crystallization in the network and is the result of higher H2 dilution, beyond a certain level, to the Ar-assisted SiH4 plasma, in the formation of a Si:H network. A correlation has been established between the data obtained from micro-Raman and ellipsometry in the structural characterization of a silicon–hydrogen system.
Superelasticity in high-temperature Ni–Mn–Ga alloys
Authors: Chernenko V. A. , L’vov V. , Pons J. , Cesari E.
Published: March 2003

The stress–strain behavior of two single crystalline Ni–Mn–Ga alloys with martensitic transformation temperatures above the Curie temperature has been studied during uniaxial compression along the [001] and [110] axes. The superelastic effect associated to the reversible stress-induced martensitic transformation has been obtained in these high-temperature shape memory alloys. The experimental values of the critical stress to induce the martensitic transformation, σc, depend linearly on the test temperature. This dependence is described well by the thermodynamics of the stress-induced martensitic transformation through a Clausius–Clapeyron-type equation. However, the experimental values of slopes dσc/dT obtained in the two compression directions can only be interpreted well if it is assumed that different martensitic phases are formed for each compression axis. Good agreement with the thermodynamic model exists if tetragonal martensites with c/a<1 and >1 are induced in the [001] and [110] axes, respectively.
Linear birefringence measurement at 157 nm
Authors: Wang Baoliang
Published: March 2003

The author describes a linear birefringence measurement instrument designed for the new optical lithography wavelength—157 nm. This instrument contains a deuterium lamp with magnesium fluoride window, a monochromator, a polarizer-photoelastic modulator (PEM) combination, a PEM-polarizer combination, and a photomultiplier tube. The sample is placed between the two PEMs. For measuring linear retardation, the signals carried on the first harmonics of the two PEMs are analyzed using lock-in amplifiers. A computer program calculates and displays both the retardation magnitude and angle of fast axis. The instrument reported here is a special polarimeter designed for measuring linear retardation in high quality optical components at 157 nm and other deep-ultraviolet wavelengths. It provides a retardation sensitivity of 0.01 nm at 157 nm.