bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of an ITER compatible, thin foil Faraday collector as a lost alpha particle diagnostic for high yield D–T fusion plasmas
Authors: Loughlin M. J. , Cecil F. E. , Hone M. , Jarvis O. N. , Medley S. S. , Roquemore A. L. , Sadler G. J. , van Belle P. , Whitfield G.
Published: July 2002

We have examined the concept of a thin foil Faraday collector as a lost alpha particle detector capable of operating under ITER-like conditions. A prototype detector consisting of a single set of four 2.5 μm Ni foils was installed on the JET first wall and operated during a variety of deuterium plasma conditions during the 1995 JET run period. Although there was no significant production of alpha particles during these plasmas, the prototype demonstrated the expected resistance to the high temperature and x-ray backgrounds, as well as moderate neutron and gamma ray backgrounds characteristic of these plasmas. In addition, this prototype showed no significant response to neutral beam, rf, or lower hybrid plasma heating. The device did pick up a low level signal when neutral beams were injected simultaneously with heavy gas puffing. Strong intermittent correlations were seen with excursions in the Hα edge brightness signal. In addition, the detector produced a significant signal in response to a roughly 250 ms disruption precursor. A similar prototype detector was installed immediately outside the Tokamak Fusion Test Reactor vacuum vessel during the 1994 D–T run period to test the expected insensitivity to neutron backgrounds. No signal was seen above background during D–T plasmas for which the fast neutron production was in excess of 2×1018 n/s.
A thermal nondestructive evaluation system for detecting vertical cracks in unidirectional carbon fiber composites
Authors: Varis J. , Lehtiniemi R.
Published: July 2002

A thermal system for nondestructive detection of broken fibers in unidirectional carbon fiber composites is described. The sample is heated inductively so that a line-shaped coil is scanned in the direction of the fibers. Since the thermal conductivity along the fibers is much better than in the perpendicular direction, the heat generated flows mainly in the scanning direction. Thus, the broken fibers hinder the heat flow effectively. They can be detected by monitoring the thermal radiation from the sample surface using an infrared line scanner, the image line of which is synchronized with the heating line in order to record a two-dimensional thermal image. The effect of broken fibers on the surface temperature of unidirectional carbon fiber composites is evaluated numerically and the feasibility of the system is verified experimentally.
Microsphere electron multiplier applicability to picosecond time correlated single photon counting
Authors: Rosenwaks Y.
Published: July 2002

Electron transit-time spreads (TTS) measurements in the new microsphere plate electron multiplier is reported on. TTS’s of 120 and 150 ps were measured for a 0.7- and 1.4-mm-thick plates, respectively. The results are compared and discussed with regard to the widely used microchannel-plate multipliers.
Versatile scanning near-field optical microscope for material science applications
Authors: Gucciardi P. G. , Labardi M. , Gennai S. , Lazzeri F. , Allegrini M.
Published: July 2002

We describe an aperture emission mode scanning near-field optical microscope (SNOM), optimized for material surface science applications. This instrument can be operated in both transmission and reflection configurations, in order to investigate transparent as well as opaque samples. It employs optical shear-force detection for tip/sample distance control, designed to minimize interference with the probe light. The SNOM head has been fully integrated on a homemade atomic force microscope platform and is placed in a controlled atmosphere chamber for reduction of surface contaminants. Within the compactness and the versatility obtained in our instrument, we have been able to optically discriminate different materials with a λ/20 lateral resolution, and to distinguish polymeric aggregates, without damaging the surface, in spite of their rather poor optical contrast.
Theory of quasiequilibrium nonlinear optical absorption in semiconductor superlattices
Authors: Je K.-C. , Meier T. , Rossi F. , Koch S. W.
Published: July 2002

Quasiequilibrium nonlinear optical absorption spectra are computed for semiconductor superlattices. The theory generalizes the semiconductor Bloch equations to describe anisotropic structures. The equation for the interband polarization is solved numerically and the carrier-density dependent optical nonlinearities are computed. Starting from excitonic absorption, with increasing density exciton saturation and the development of gain is observed. The dependence of the gain spectra on structural parameters of the superlattice is discussed.
A new compact electron spin polarimeter with a high efficiency
Authors: Qiao S. , Kimura A. , Harasawa A. , Sawada M. , Chung J.-G. , Kakizaki A.
Published: July 2002

We have developed a new compact retarding-potential Mott spin polarimeter and achieved an efficiency of 1.9×10−4 for gold target operating in 25 keV. A novel design of the retarding field electron optics with 0.59 sr collection solid angle for scattered electrons was adopted based on Monte Carlo calculations for the spin-dependent electron scattering process and electron beam ray-tracing calculations. We have combined the new spin polarimeter with an angle-resolved photoelectron spectrometer and measured the spin- and angle-resolved photoelectron spectra and studied the spin-dependent electronic structure of Ni(110) along the Γ̄S̄ line of its surface Brilluoin zone.
Development of key components and technologies for a high repetition rate and high-power excimer laser
Authors: Goto Tatsumi , Takagi Shigeyuki , Kakizaki Kouji , Saton Saburoh , Kosugi Shinichiro , Ohishi Takashi , Kanazawa Yukio , Ishii Akira , Teranishi Tsuneharu , Yasuoka Koichi , Shinohe Takashi , Ohashi Hiromichi , Endo Fumihiko , Okamura Katsuya
Published: July 2002

Key components and technologies have been developed for an ultrahigh repetition rate XeCl excimer laser of 5 kHz to be used for industrial applications. A compact axial blower having a revolution rate of up to 10 000 min−1 and a maximum pressure of 16.2 kPa in air was made with a canned magnetic coupler to circulate a laser gas at a flow velocity of over 150 m/s in a discharge region. Materials constituting a laser chamber were tested to prevent discharge instability by gas contamination to enable long time operation. The dominant cause of the instability was investigated by a simple simulation. For a preionization, a novel sealed-off x-ray tube was developed to compare the suitability in a high repetition rate operation with that of conventional UV preionization. The gas due to the shock and acoustic waves generated by discharge pulses was measured to design the damper, which enabled the suppression of the gas turbulence by around a tenth. To simplify cumbersome laser maintenance, a new power supply provided by a novel fast switching semiconductor device was evaluated by operating the laser. The experimental laser apparatus integrating these key components and technologies was operated to confirm the practical availability for high repetition of up to 5 kHz. Many kinds of basic experiments have been performed to increase repetition rate, average power, and reliability. Though these experimental results have not yet been integrated and performed simultaneously, we have achieved operation up to an average output power of 0.56 kW at 5 kHz. Based on the results and empirical knowledge, the prospect for a practical high repetition rate excimer laser was discussed.
Microwave ion sources for material processing (invited)
Authors: Sakudo N.
Published: July 2002

Microwave ion sources were developed and used for material processing in industrial manufacture. Major applications of them were concentrated on semiconductor device fabrication, especially on modifying electrical properties of semiconductor material by ion implantation, as well as on processing submicron structures of semiconductor devices by so-called plasma etching. Most ion implanters for manufacturing silicon on insulator wafers exclusively adopt microwave ion sources because the sources work very stably for oxygen ions. Recently, the application of ion beams is extending to nonsemiconductor fields. Thus, ions are applied to surface modification of nonsemiconductor materials and to thin-film formation by ion beam deposition which is carried out with low energy of several tens of eV. The characteristics of films are very dependent on the beam energy values which are strictly determined by sum of the source bias voltage and the plasma potential with respect to the chamber. Microwave ion sources are very suitable to such applications of low-energy ion beams because the ions extracted from them have a very small energy dispersion. In this article, the features of microwave ion sources are specified and a variety of the sources are reviewed with respect to their applications.
Grid power loading in a multiaperture, multigrid negative ion accelerator
Authors: Hanada M. , Fujiwara Y. , Miyamoto K. , Miyamoto N. , Okumura Y. , Watanabe K.
Published: July 2002

Grid power loading in a multistage, multigrid accelerator was calorimetrically measured using the Japan Atomic Energy Institute 400 keV accelerator. This is the first result on the grid power loading in the multistage accelerator. It is turned out that the extracted electrons are effectively suppressed in an extractor. The leakage of the electrons extracted from the source plasma to the first acceleration grid, the second grid and the grounded grid were no more than 0.8%, 0.2%, and nearly zero of the extracted electron current, respectively. Under the optimum beam optics that gives the lowest beam divergence, the power loadings of the acceleration grids were dominated by acceleration of the stripped electrons. At a typical source operating pressure of 0.3 Pa, the power loadings of a first acceleration grid, a second acceleration grid, and a grounder grid were 3.4%, 5.0%, and 2.8% of the total beam power, respectively. From the comparison with the calculated grid power loading, it is found that the stripped electrons can be intercepted by intermediate acceleration grids before fully accelerated.
Results from energetic electron beam metal vapor vacuum arc and Z-discharge plasma metal vapor vacuum arc: Development of new sources of intense high charge state heavy-ion beams
Authors: Hershcovitch A. , Johnson B. M. , Liu F. , Anders A. , Brown I. G.
Published: July 2002

We are exploring a new approach for heavy-ion beam injection (e.g., into the relativistic heavy-ion collider at BNL), as well as new sources of intense high charge state ions to be mounted on a relatively low voltage platform for high energy ion implantation. While conventional metal vapor vacuum arc (Mevva) ion sources can produce up to hundreds of milliamps or more of several-times-ionized metal ions (e.g., U3+), the recent results from Batalin et al. indicate that the addition of an energetic electron beam may lead to considerably higher charge states. An alternative way to produce the electron beam is where a Z-discharge plasma is used to enhance multiple ionization. As the vacuum arc plasma plume expands into a magnetized drift region, a Z-discharge is triggered in the drifting metal plasma. The ions are then extracted and analyzed using a time-of-flight system. We report initial results using these schemes with applied discharge and electron beam voltages from 1 to 2 kV.
Ion charge state distributions of pulsed vacuum arc plasmas in strong magnetic fields
Authors: Anders André , Yushkov George , Oks Efim , Nikolaev Alexey , Brown Ian
Published: July 2002

Vacuum arc plasmas with discharge currents of 300 A and duration 250 μs have been produced in strong magnetic fields up to 4 T. Ion charge state distributions have been measured for C, Al, Ag, Ta, Pt, Ho, and Er with a time-of-flight charge-mass-spectrometer. Our previous measurements have been confirmed which show that ion charge states can be considerably enhanced when increasing the magnetic field up to about 1 T. The new measurements address the question of whether or not the additional increase continues at even higher magnetic field strength. It has been found that the increase becomes insignificant for field strengths greater than 1 T. Ion charge state distributions are almost constant for magnetic field strengths between 2 and 4 T. The results are explained by comparing the free expansion length with the freezing length. The most significant changes of charge state distributions are observed when these lengths are similar.
Digital cross-correlation technique for fluorescence-lifetime measurement using a radionuclide-scintillation excitation source
Authors: Burden Daniel L. , Hieftje Gary M.
Published: July 2002

We describe a digital cross-correlation instrument that employs a radio-frequency mixer and a radionuclide-scintillation light source to measure fluorescence lifetimes. The digital approach provides single-photon sensitivity and accurate lifetime analysis even at low sample concentrations. The unique characteristics of the scintillation excitation source, coupled with the simplicity of mixer-based signal processing, give this approach particular appeal over traditional instrumentation used for excited-state decay measurements. We discuss the system design and evaluate its performance using two optical configurations. The close-packed configuration provides an indication of the general fluorescence detection limits which can be expected from measurements made with scintillation-based light sources. After applying a procedure to correct for systematic error caused by the mixer diode-bias potential, the results from the digital system demonstrate lifetime accuracy over a range of sample concentrations (nM–mM). Finally, we develop a modified detection sensitivity parameter and calculate its value to be 1×10−3 s photon−1 pathlength−1 for our experiments. This new parameter can assist in the design of other scintillation-based lifetime measuring devices.
Theoretical and experimental studies of vibrations of optical fiber cantilevers for atomic force microscopy
Authors: Zhu Rong
Published: July 2002

Optical fiber cantilevers with uniform diameters are fabricated using an etching method. Resonant frequencies of the optical fiber cantilevers with different lengths and diameters are calculated with the flexural wave theory of elastic beams. An experimental system is built for measuring the spectrum of the resonant frequencies of the optical fiber cantilever. Two optical fiber cantilevers with diameters of 8.8 and 11 μm and lengths of 568 and 776 μm, are examined separately with the system. The measurements agree well with theory. The experiments show that the higher vibrational modes of the optical fiber cantilever can be excited with high amplitude, which is well suited for sensing purposes.
A programmable prescaler for minimizing counting errors with PC-based data acquisition cards
Authors: McCabe P. R. , Utz A. L.
Published: July 2002

Many commonly used PC-based data acquisition counter boards are specified to count regularly occurring events at rates up to 7 MHz. Boards with this frequency limit begin to systematically and significantly underestimate the rate of randomly occurring events occurring at average frequencies much lower than the specified 7 MHz rate due to the dead time of the counter. This report highlights the origin of this error and describes an easily constructed prescaler circuit that permits accurate event counting at rates up to, and even exceeding, the nominal speed of the counter.
Development of the Los Alamos solid-state optical refrigerator
Authors: Edwards Bradley C. , Buchwald Melvin I. , Epstein Richard I.
Published: July 2002

Laser-induced cooling of a solid by net anti-Stokes fluorescence, first experimentally demonstrated in 1995, can be the basis of a new type of cryocooler, an optical refrigerator. This article describes the physics and design issues of a practical optical refrigerator for operation at 77 K. In particular, the Los Alamos Solid-State Optical Refrigerator (LASSOR) which we are developing would have an operating efficiency comparable to commercial small cryocoolers, be completely vibration-free and operate for years without maintenance.
Eddy current damping of high Q pendulums in gravitational wave detection experiments
Authors: Cagnoli G. , Gammaitoni L. , Kovalik J. , Marchesoni F. , Punturo M.
Published: July 2002

The test masses of a large interferometric gravity wave detector (VIRGO project) will be controlled by actuators consisting of magnets attached to the masses and solenoids attached to an auxilliary and potentially electrically conductive reference mass. A brief analytic model of the damping produced by the eddy currents induced by the magnets’ motion relative to the reference mass is presented. The results of a series of experimental tests to verify this model are also given. They demonstrate that a conducting reference mass should not degrade the Q of the pendulum sufficiently to affect the sensitivity of the VIRGO detector.
Background measurement with constant detector geometry in positronium three quanta annihilation experiments
Authors: Consolati G.
Published: July 2002

In experiments on positronium annihilation in three photons, the background rate of triple-coincident events is usually measured by performing a separate counting run, in which one of the detectors is moved out of the three quanta annihilation plane. A thorough analysis shows that this approach can entail systematic errors and we suggest an alternative procedure. By employing a few auxiliary coincidence modules, the new approach avoids the necessity of a further dedicated counting run with modified detector geometry. Experimental results confirm the viability and accuracy of the method.
Nonresonant four-wave mixing in photorefractive CdTe crystals using a picosecond parametric generator
Authors: Jarašiūnas Kestutis , Gudelis Vytautas , Delaye Philippe , Roosen Gerald
Published: July 2002

We demonstrate that a parametrically pumped picosecond laser has enough coherence and energy to write transient phase gratings at nonresonant interaction, thus allowing a study of time-resolved carrier transport in CdTe crystals to be made. Autocorrelation trace of light diffraction efficiency on transient grating allowed us to measure a coherence length of the parametric generator. Carrier diffusion, recombination, and drift in light-created internal space-charge (SC) electric fields have been studied in vanadium or germanium doped semi-insulating CdTe crystals by nonresonant four-wave mixing technique at 940 nm wavelength. It was found that modification of the deep level charge state in CdTe:V by As codoping has changed the sign of majority carriers, responsible for the creation of SC field. Dynamics of free carrier grating decay in CdTe:Ge revealed an electron-governed very fast initial grating decay which develops with time into the double-exponential hole-governed grating decay. Time-resolved transient grating technique described in this article provides a powerful tool for investigation of the role of deep traps in photorefractive semiconductors and optimization of their photoelectric properties in a required temporal and spectral range.
A precision capacitance cell for measurement of thin film out-of-plane expansion. I. Thermal expansion
Authors: Snyder Chad R. , Mopsik Frederick I.
Published: July 2002

A high sensitivity technique based on a three-terminal parallel plate capacitor for the measurement of the out-of-plane expansion of thin films is presented. The necessary assembly protocols and data reduction techniques for the proper use of this capacitance cell are presented. To demonstrate the ability of the technique to produce correct results for the thermal expansion of materials, the results on 〈0001〉 single crystal Al2O3 are shown and compared to the literature. Also, results for a thin polymeric film designed for use as an interlayer dielectric are shown to display the utility of the technique to resolve the measurement of displacement in thin films.
High-performance autofocus circuit for biological microscopy
Authors: Bravo-Zanoguera Miguel , v. Massenbach Benedikt , Kellner Albert L. , Price Jeffrey H.
Published: July 2002

An autofocus circuit, based on measurement of the high spatial frequency image components, was designed for automated microscopic scanning of biological specimens. By careful consideration of the system transfer function, elimination of video end-of-line filter artifacts, correction for illumination instability, and incorporation of autogain, the focus measurement circuit attained the sensitivity and dynamic range necessary for robust operation even at the extremes of biological specimen detail encountered in exhaustive raster scans of thousands of fields. This new circuit exhibited a 25-fold improvement in dynamic range over a previous analog implementation, matched real-time digital performance at an order of magnitude lower cost, resulted in autofocus precision of 56 nm (or 10-fold better than the depth of field of the objective) in scanning experiments comprising over 10 000 microscope fields, and tracked focus at scanning speeds of up to 3.45 fields/s. Focus was correctly maintained in these scanning experiments without additional compensation for low-detail images. This circuit makes possible the widespread inclusion of high-performance autofocus as a low cost option in video microscopy systems.
Enhancement of the transverse Kerr magneto-optic effect by multiple reflections
Authors: Tejedor M. , Fernández A. , Cerdeira M. A.
Published: July 2002

Enhancement of the transverse Kerr magneto-optic effect is attained by means of multiple reflections. A polarized and stabilized laser beam is used to observe the transverse Kerr magneto-optic effect. The beam is reflected several times on a cobalt thin film obtaining an important improvement on the effect-signal ratio if we compare it with the results for only one reflection.
Application of x-ray imaging to current profile measurements in the PEGASUS experiment
Authors: Tritz K. , Fonck R. , Thorson T.
Published: July 2002

For low-aspect ratio toroidal devices, flux shape information can be used as a constraint for reconstruction of the plasma current profile and q profile. A model current profile was used to compare the sensitivity of the equilibrium reconstruction using soft x-ray (SXR) image constraints to motional Stark effect (MSE) constraints. The deviation in the χ2 of the fit versus current profile was similar in both cases, showing that the SXR data is as good a constraint on the equilibrium as MSE information. There are two soft x-ray imaging systems under consideration to determine the shape of the internal flux surfaces on PEGASUS. One diagnostic consists of a series of vertically spaced, tangentially viewing linear detector arrays. Another design using a two-dimensional pinhole camera for a soft x-ray image of the plasma is also being evaluated.
A rotating coil probe for the magnetic field measurement on a long pulsed tokamak
Authors: Fujita J. , Matsuura K. , Kawahata K. , Fujiwaka S. , Itoh S. , Sato K. N. , Nakamura K. , Zushi H. , Sakamoto M. , Hanada K. , Jotaki E. , Makino K.
Published: July 2002

In order to determine the magnitude and the position of the plasma current in a long pulsed tokamak such as the International Thermonuclear Experimental Reactor (ITER), it is urged to establish a reliable method which is free from the zero-level drift of the integrator as well as the radiation damage for the steady-state magnetic field measurement. For this purpose, we have developed a hybrid system, a combination of a conventional magnetic probe for the measurement of fast varying magnetic field and a rotating coil magnetic probe for that of slowly varying field. The rotating coil is energized by an air turbine to avoid electromagnetic interference and the induce signal with a constant rotation frequency is picked up through a transformer to eliminate mechanical contacts. An automatic gain control circuit is also designed for the compensation of rotation speed fluctuation. The system is proved to achieve a flat frequency response with a proper choice of cross over frequency for high- and low-frequency systems. The rotating coil probe is tested for over 170 h without any trouble. The probe was applied to the poloidal magnetic field measurement on the TRIAM-1M long pulsed tokamak, and proved to work satisfactorily.
Charge-exchange neutral particle measurements on electron cyclotron resonance heating experiments in hot-ion-mode plasmas of the GAMMA 10 tandem mirror
Authors: Nakashima Y. , Hasegawa Y. , Shoji M. , Kobayashi S. , Saito T. , Kiwamoto Y. , Cho T. , Mase A. , Ichimura M. , Itakura A. , Hirata M. , Kohagura J. , Islam K. Md. , Oishi M. , Yoshikawa M. , Tamano T. , Yatsu K.
Published: July 2002

Charge-exchange (C–X) neutral particle measurements have been carried out in hot-ion-mode plasmas of the GAMMA 10 tandem mirror. In the present experiment, a microwave power of 40 kW in 28 GHz is injected toward a second harmonic ECR layer located in the vicinity of the ICR layer at the central region and the radial profiles of ion temperatures determined from the energy spectrum of the C–X neutrals by using a neutral particle energy analyzer (NPA) are investigated from the viewpoint of ion energy balance. At the onset of the ECRH pulse, a remarkable increase of C–X neutral flux with high energy (few keV to few tens keV) is observed with NPA and the resultant ion temperature on the plasma axis is found to increase from 2.5 to 5.0 keV at the electron line density of 3×1013 cm−2. Based on the measured plasma parameters, radial profiles of ion-energy losses due to classical processes are evaluated and ECRH in the central region is confirmed to reduce the energy loss due to electron drag significantly in the core-plasma region.
Spectroscopic measurement of impurity ion behavior in the GAMMA10 tandem mirror
Authors: Ikeda K. , Nagayama Y. , Itoh T. , Kawamori E. , Okamoto Y. , Tamano T. , Yamaguchi N. , Yatsu K. , Yoshikawa M.
Published: July 2002

Behavior of impurity ions has been investigated using visible spectroscopy in the GAMMA10 tandem mirror. A 40 channel visible spectrometer system has been developed for measurements of the ion temperature and ion flow velocity. The spectrometer consists of a 100 cm monochromator, a 40 channel optical fiber array and an image intensifier tube coupled with a charge coupled device TV camera. The spectra from low ionization states of oxygen and carbon are measured in ion cyclotron range of frequency heated plasmas. High ion temperatures (3–10 keV) of O4+ are observed in the anchor region, where the minimum B mirror field is produced by baseball coils. The O4+ ion is heated by the fourth harmonic frequency of O4+, which is most likely due to the cyclotron higher harmonic damping.
Effect of reflection on Hα emissions in Alcator C-MOD
Authors: Karney C. F. F. , Stotler D. P. , Skinner C. H. , Terry J. L. , Pappas D. A.
Published: July 2002

In order to explain anomalous intensity ratios which have been observed in Alcator C-MOD, the Hα emissions in that experiment have been modeled with the DEGAS 2 code including the effects of wall reflection. By assuming that the first wall has different reflection coefficients for the two polarizations, we have qualitatively reproduced the observed anomaly.
System for temperature and power flux measurements on the RFX first wall
Authors: Pasqualotto R. , Pugno R. , Sonato P. , Valisa M. , Zaccaria P.
Published: July 2002

A thermal imaging system has been installed on the RFX at Consorzio RFX to investigate the phenomenology of the plasma wall interactions. The infrared camera, model Amber AE4128, is based on a 128×128 InSb focal plane array detector and operates in the range of 4.5–5 μm with an acquisition rate of 217 Hz and 12 bit of dynamic range. The system, absolutely calibrated, is sensitive from room temperature up to 3000 °C, with different setups. The experimental data are compared with the numerical results obtained by means of transient thermal analyses carried out on analytical and finite element models of a graphite tile.
Toroidal cartography of the high-m magnetic islands in tokamak plasma
Authors: Savrukhin P. V. , Tsaun S. V. , Grashin S. V. , Khimchenko L. N. , Kislov D. A. , Klimanov I. V. , Semenov I. B. , Sushkov A. V.
Published: July 2002

A toroidally viewing soft x-ray imaging system and an orthogonal matrix array of soft x-ray diodes are designed for identification of the small-scale plasma perturbations in the T-10 tokamak. Numerical modeling of the helical perturbations with high longitudinal wave numbers (m=5–30) is used for specification of the basic design of the system (optimal position of the diagnostic, field of view, and spatial and mode resolutions) in the T-10 tokamak. A system of external windings is designed for controllable excitation of the low-m magnetic islands and for studies of their effect on small-scale modes.
Interactive optical design and realization of an optimized charge coupled device Thomson scattering system for the spherical tokamak START
Authors: Walsh M. J. , Conway N. J. , Dunstan M. , Forrest M. J. , Huxford R. B.
Published: July 2002

A high resolution, multipoint Thomson scattering system has been successfully implemented on the START tokamak. It incorporates a low-divergence, 10–15 J Q-switched ruby laser system with a gated (GaAs) image intensifier (II) and a charge coupled device as the detection elements. It is designed to measure temperatures between 25 eV and 4 keV and densities from 3×1018 m−3 with high accuracy (∼2.5%). The spatial resolution is approximately 1.5 cm. An interactive design of the optics train has been used to ensure matching of the optics from light collection to light detection. Use of coherent fiber bundles allows a resolution down to about 2 mm.
Neutron spectrometry of radio-frequency heated deuterium–tritium plasmas
Authors: Tardocchi M. , Ballabio L. , Conroy S. , Ericsson G. , Frenje J. , Gorini G. , Guadagno C. , Källne J. , Prandoni P. , Traneus E.
Published: July 2002

Spectrometry of the neutron emission has been used to probe the nonthermal features of the fuel ion velocity distributions in tokamak plasmas, especially, those arising from auxiliary heating. The first time resolved measurements are reported from the use of the new magnetic proton recoil (MPR) spectrometer in observations of deuterium–tritium plasmas at JET with strong ion cyclotron resonance heating. Results from preliminary analysis data are presented and compared with simulated neutron emission spectra based on the assumptions of a thermal plasma (a single Maxwellian ion distribution) or anisotropic Maxwellians with parallel and perpendicular temperatures, beside their relative amplitudes. The diagnostic results attained are also used to assess the diagnostic capabilities and the potential for use of MPR based diagnostics on burning plasma tokamaks.
Preliminary electron density profile and fluctuation measurements on GAMMA 10 using ultrashort-pulse reflectometry
Authors: Kubota S. , Onuma T. , Kato M. , Mase A. , Tokuzawa T. , Oyama N. , Itakura A. , Hojo H. , Bruskin L. G. , Tamano T. , Yatsu K. , Domier C. W. , Luhmann N. C.
Published: July 2002

The use of ultrashort pulses (full width at half-maximum=1–100 ps) as a source of broadband, time-resolved radiation has high potential for application in microwave diagnostics for fusion plasmas. Here we report on the ultrashort-pulse reflectometry system developed for electron density profile and fluctuation measurements on the GAMMA 10 tandem mirror. The four-channel system (selectable frequencies of 8–17 GHz at 1 GHz intervals) measures the double-pass time-of-flight from the vacuum window to the cutoff layer. The hardware has an uncertainty of ±40 ps and can be operated at a repetition rate of 400 kHz. The system is operational, however, data from plasma experiments is unavailable at the moment. Results from a single-channel O-mode system show time-of-flight measurements consistent with values calculated from profiles obtained by a scannable single-channel interferometer. Fluctuation measurements are also consistent with results from a Fraunhofer diffraction diagnostic. These results suggest that with further refinements, ultrashort- pulse reflectometry will yield a simple yet reliable diagnostic for fusion devices.
Optimized instrumentation for edge Te and ne measurements on COMPASS-D tokamak from He I line intensity ratios
Authors: Field A. R. , Carolan P. G. , Conway N. J. , O’Mullane M. G.
Published: July 2002

Instrumentation has been developed for the measurement of electron temperature and density profiles at the boundary of COMPASS-D tokamak plasmas from He I line intensities. The technique is applicable to measurements of ne and Te over the relevant ranges of 1017–1020 m−3 and 10–500 eV. Spectra from eight viewing chords viewing a thermal helium jet are recorded on a CCD sensor with ≈1 ms time resolution. A 0.6 m Czerny-Turner spectrometer, corrected for astigmatism using an internal, cylindrical lens optimizes throughput by availing of a 110×110 mm2, 300 l/mm grating. ne and Te profile measurements from L-mode (low) and quiescent H-mode (high) confinement plasmas are presented.
X-ray crystal spectrometer for the HANBIT mirror machine
Authors: Lee S. G. , Hwang S. M. , Bitter M.
Published: July 2002

Design study of an x-ray crystal spectrometer for the HANBIT mirror machine is presented. The x-ray emissivity of HANBIT plasmas is rather low as a result of the low values of the electron temperature and density. The design difficulty from the low x-ray emissivity can be overcome by utilizing a vacuum spectrometer sightline parallel to the long axial length of HANBIT and using an x-ray sensitive vacuum charge-coupled device camera as a detector.
Newly developed matrix-type semiconductor detector for temporally and spatially resolved x-ray analyses ranging down to a few tens eV using a single plasma shot
Authors: Kohagura J. , Cho T. , Hirata M. , Minami R. , Numakura T. , Okamura T. , Sakamoto Y. , Tamano T. , Yatsu K. , Miyoshi S. , Tanaka S. , Sato K. , Inoue M. , Saitoh Y. , Yamamoto S.
Published: July 2002

For the purpose of the measurements of temporally and spatially resolved electron temperatures (Te) during a single plasma shot alone, we propose and fabricate a new matrix-type semiconductor x-ray detector. This detector is fabricated using the precise formation of thin dead layers (SiO2) with six different thicknesses (from 10 to 5000 Å) aligned in line on its surface compactly. Each “row” has seven channels for the measurements of plasma x-ray radial profiles so as to make x-ray tomographic reconstructions; namely, the compact-sized matrix detector having six rows and seven columns with a 5×5 mm2 active area for each matrix unit. These various SiO2 layers are proposed to be utilized as ultrathin “x-ray absorption filters” with different thicknesses, which are never obtained as “self-supporting material absorbers” because of their ultrathin properties. This novel idea enables us to analyze x-ray tomography data including in the Te region down to a few tens eV. The simultaneous comparison of each tomographically reconstructed data from each detector row provides the temporal evolution of energy-resolved x-ray or Te profiles using “the absorption method.” The first application of this newly developed matrix detector is made to obtain Te profiles in the GAMMA 10 tandem mirror.
Comparison of digital correlation techniques in time-resolved fluorometry using a radionuclide-scintillation excitation source
Authors: Burden Daniel L. , Hieftje Gary M.
Published: July 2002

We directly compare two digitally based correlation techniques for measuring the fluorescence-decay kinetics of sample solutions excited by a radionuclide-scintillation light source. Time-correlated single-photon counting and digital cross correlation exhibit markedly different results under identical experimental conditions. However, both digital-processing techniques allow analysis even with the low-light intensities provided by the relatively weak scintillation source. The light source is unique among those used for time-resolved fluorescence measurements because it is compact, power free, inexpensive, portable, easy to maintain, and delivers a stochastic excitation sequence. The random nature of the pulse train can introduce severe systematic errors if the lifetime measurements are conducted in the wrong manner. In comparing the two digital correlation techniques, we illustrate the behavior of both systems under various conditions of radionuclide activity and light intensity. We find that over a wide range of conditions, digital cross correlation gives superior accuracy, shorter analysis times, and is generally the better approach. However, we also discuss analytical situations where the use of time-correlated single-photon counting might be preferred.
Simultaneous observation of Barkhausen pulses and jumps in resistance fluctuations in ferromagnetic materials
Authors: Lopez R. J.
Published: July 2002

An experimental setup which simultaneously registers induced Barkhausen pulses and short time variations in electrical resistance has been developed. The skin effect associated with the use of an alternating current of 100 kHz reduces the volume of the sample which is sensitive to the passing of the current, making it possible to detect the rapid modifications in resistance in a standard Ni thermocouple wire subjected to a slowly varying magnetic field. The combination of both techniques clearly shows the association between jumps in resistance and the dynamics of some magnetic domains.
Holey-plate plasma source using a partial-coaxial microwave cavity
Authors: Yoshida Yoshikazu
Published: July 2002

High-density microwave plasma created and sustained by evanescent waves emitted from a holey plate has been studied. This source is called a holey-plate plasma source. Microwave power at 2.45 GHz is supplied from a coaxial cavity and then converted into an evanescent mode through the use of a holey plate. The plate is made from a 0.5 mm thick, 54 mm diam stainless steel sheet with 2.5 mm diam, 3.6 mm pitch holes, thus allowing high-density plasma to be generated near the surface of the plate. An evanescent electric field is produced from the cavity resonator to a plasma production chamber that is 54 mm in diameter. A detailed description of the plasma source and the plasma characteristics are presented in this article. The plasma density is 6.5×1011 cm−3 with an electron temperature of 3 eV at an argon gas pressure of 2 Pa.
In situ sample temperature measurement in plasma immersion ion implantation
Authors: Tian Xiubo , Fan Zhineng , Zeng Xuchu , Zeng Zhaoming , Tang Baoyin , Chu Paul K.
Published: July 2002

Plasma immersion ion implantation (PIII) is an excellent surface modification technique because it is not restricted by the line-of-sight limitation that plagues conventional beamline ion implantation. However, the lack of in situ monitoring has hampered wider acceptance of the technique in industry. It is known that the implantation temperature has a large influence on the surface properties of the treated specimens in addition to the more obvious parameters such as implantation voltage, pulse duration, pulsing frequency, and so on. Direct measurement of the target temperature is complicated by the sample high voltage as well as by interference from the electromagnetic field and plasma. In this article, we present a novel interference-free, in situ temperature measurement technique employing a shielded thermocouple directly attached to the sample stage. Our experiments show that the setup can monitor the target temperature in real time, even under severe arcing conditions. Our results also indicate that in a hot filament glow discharge radiation heating is quite small, and sample heating is primarily caused by ion bombardment during the PIII cycles. The new design will open up other possibilities such as in situ dose monitoring if, for example, the thermocouple is replaced by a Faraday cup.
A new and sophisticated electrochemical scanning tunneling microscope design for the investigation of potentiodynamic processes
Authors: Wilms M. , Kruft M. , Bermes G. , Wandelt K.
Published: July 2002

One of the main topics in electrochemistry is the investigation of the potential controlled solid/liquid interface. As a local probe technique electrochemical scanning tunneling microscopy becomes more and more important for the analysis of atomic structures and local structuring effects. The described microscope is optimized for potentiodynamic imaging, i.e., the sample potential can be varied in a wide range during the scan of an image. In combination with cyclic voltammetry potential induced phase transitions on the surface can be imaged and directly correlated to distinctive profiles in the simultaneously recorded voltammogram. The new design grew out of the parallel development of the tunneling unit and the electrochemical periphery. This guarantees the best adaptation of tunneling microscopy to electrochemistry and vice versa. Low drift, high resolution, flexibility, reliability, and ease of handling are the characteristics of the new instrument.
X-ray focusing test and x-ray imaging test by a microcapillary x-ray lens at an undulator beamline
Authors: Kohmura Yoshiki , Awaji Mitsuhiro , Suzuki Yoshio , Ishikawa Tetsuya , Dudchik Yu. I. , Kolchevsky N. N. , Komarov F. F.
Published: July 2002

A first focusing test of the undulator radiation at SPring-8 has been done using two types of x-ray refractive lenses in thin glass capillaries. One (lens No. 1) contained bubbles in a glue whereas the other (lens No. 2) contained bubbles in glycerol. The capillaries had inner diameters of 0.2 and 0.8 mm, respectively. Using x rays of 17–18 keV, the undulator source image was investigated at the focal plane. The spherical aberrations and the field distortions were carefully examined by taking the images of a gold mesh. Lens No. 1 had an advantage of high transmissivity in the hard x-ray region (18% at 18 keV) and high tolerance to severe radiation damage, e.g., ∼5×1012 photons/s/0.03 mm2 of the 18 keV x rays for an exposure time of 1 h. On the other hand, lens No. 2 had an advantage of a large aperture, 0.8 mm, and a small field distortion, e.g., less than 10% inside a diameter of 300 μm.
Initial long-pulse plasma heating at reduced power with negative-ion-based neutral beam injector in large helical device
Authors: Takeiri Y. , Noda N. , Nakamura Y. , Oka Y. , Osakabe M. , Kawahata K. , Kaneko O. , Tsumori K. , Sato M. , Mutoh T. , Goto M. , Ida K. , Inagaki S. , Kado S. , Masuzaki S. , Morita S. , Nagayama Y. , Peterson B. J. , Sagara A. , Sakakibara S. , Sato K. , Tanaka K. , Sudo S. , Ohyabu N. , Motojima O.
Published: July 2002

We have achieved long-pulse plasma heating using a negative-ion-based neutral beam injector (NBI) in the large helical device (LHD), where the confinement magnetic field is generated by only external superconducting coils. In the initial long-pulse experiments at lower power than that in short-pulse experiments, 80 keV–1.1 MW NBI heating lasted for 10 s with a little increase in the plasma density at the pulse end. Almost steady-state plasma heating was achieved for 21 s with 66 keV–0.6 MW NB injection. Plasma relaxation oscillation phenomena at a period of 1–2 s were also observed for 20 s. Above 1 keV plasma was easily sustained with a long-pulse NBI heating in LHD, without the current drive nor the disruption in tokamaks. Negative ion source operation was stable and the cooling water temperature rise of beam accelerator grids was nearly saturated with a temperature rise below 10 °C. For a higher power injection, the pulse duration is determined by the beam blocking, where the reionization loss is exponentially increased together with an increase in outgas in the injection port. The port conditioning by a careful repetition of injection is effective to the extension of the injection duration and the plasma maintenance duration. The initial long-pulse NBI heating at the reduced power has demonstrated an ability of steady-state operation in superconducting LHD.
Estimation method for electron-hole pair density in plasma columns
Authors: Kanno I.
Published: July 2002

A simple method to estimate the electron-hole pair density in plasma columns created by heavy ions is described. The volume of plasma column is described in a ratio to the one of cone with the same range and bottom radius of the plasma column. The volume ratio is expressed by second polynomials of the energy per unit mass of the heavy ion. With three parameters of the second polynomials, the range and the bottom radius of the cone, the volume of the corresponding plasma column, and consequently, the electron-hole pair density inside it are easily estimated.
Spectroscopic gas-flow imaging through an infrared optical fiber bundle
Authors: Saito Mitsunori , Kikuchi Katsuhiro , Tanaka Chinari , Sone Hiroshi , Morimoto Shozo , Yamashita Toshiharu , Nishii Junji
Published: July 2002

Spectroscopic imaging was achieved in the midinfrared region by using a PtSi charge coupled device camera and band-pass filters. A coherent bundle of chalcogenide glass fibers was used as an infrared image guide to realize the remote observation of inaccessible objects. Infrared images taken at 1/60 s intervals represented transient distributions of molecules that absorb the probe infrared light. Real-time observation of bursting CH4 and CO2 gases was successfully demonstrated.
Peltier-effect module for highly localized temperature manipulations
Authors: Huang Lei , Wang Wanjun , Murphy Michael C.
Published: July 2002

A Peltier-effect module suitable for applications that require manipulation of the temperature (cooling or heating) of microsized subjects or at a highly localized spot was developed. The module was constructed from a commercial electronic refrigeration device based on the Peltier effect with an array of microprobes attached to its top surface. The microprobes were fabricated using the LIGA (German acronym for lithographie, galvanoformung, abformung) process—one of the microelectromechanical systems technologies. The 1000-μm-tall microprobes were fabricated on a titanium plate and then bonded onto the top surface of a commercial Peltier device. When an electrical current was supplied to the Peltier device, the top surface (with microprobes) of the device was cooled and the other side was heated. Heat was conducted from a microsample on the tip of microprobe to the top surface of the Peltier device. A dynamic model of the module was developed and numerical simulation studies were conducted. The prototype module was tested and the experimental results matched well with those predicted by the numerical simulations. The maximum difference between the temperature of a microsample and that at the surface of the Peltier device was approximately 1 °C.
High energy operation of the Tokyo-electron beam ion trap/present status
Authors: Kuramoto Hideharu , Shimizu Hiroshi , Nakamura Nobuyuki , Currell Fredric J. , Kato Daiji , Kinugawa Tohru , Tong Xiao M. , Watanabe Hirofumi , Fukami Tsunemitsu , Li Yueming , Ohtani Shunsuke , Sokell Emma J. , Yamada Chikashi , Hirayama Takato , Motohashi Kenji , Tsurubuchi Seiji , Okazaki Kiyohiko , Sakurai Makoto , Tarbutt Michael R. , Silver Joshua D.
Published: July 2002

We are using the Tokyo electron beam ion trap (Tokyo-EBIT) to study a wide range of the physics of highly charged ions. Transition wavelengths have been investigated using visible and x-ray spectroscopy. The charge-state distributions of the extracted ions from the trap are shown for the different experimental conditions. Ionization cross sections are measured by observing the time dependence of the charge state evolution in the extracted ions. A brief introduction of the recent studies is given.