bluuebunny/crossref_metadata_2025 huggingface dataset:
Broad beam high average current metal ion source
Authors: Xiaoji Zhang , Fengsheng Zhou , Huixing Zhang , Shenji Zhang , Qiang Li , Zhuen Han
Published: July 2002

For industrial application in material surface modification it is necessary to obtain higher average beam current for metal ion implantation. Two new versions of MEVVA ion source, MEVVA-II and MEVVA-IIA, in which the size of the extraction area is expanded to 60 mm in diameter have been developed, based on MEVVA-I being constructed early. The sources are operated in pulsed mode with a maximum beam duty cycle of 6%. A time average beam current of up to 10–30 mA has been extracted from a range of different cathode materials, such as C, Mg, Al, Ti, V, Cr, Fe, Ni, Cu, Zn, Y, Zr, Mo, Nb, Sn, Ta, W, and Pb. In the MEVVA-IIA, particularly, a movable cathode is used for compensating the consumption of the cathode material during the source operation, so that the running time may be extended, for example, it has been operated stably more than 16 h with a 10 mA beam current with a Ti cathode. In this paper, we will describe the source and some preliminary results.
Superconducting re-entrant cavity transducer for a resonant bar gravitational radiation antenna
Authors: Linthorne N. P. , Blair D. G.
Published: July 2002

A 10-GHz superconducting niobium re-entrant cavity parametric transducer was developed for use in a cryogenic 1.5-tonne Nb resonant bar gravitational radiation antenna. The transducer has a very high electrical Q (6×105 at 4.2 K), and was operated at high cavity fields without degrading the Q. A very high electromechanical coupling between the antenna and the transducer was therefore achieved. The highest coupling attained, constrained by the available pump power, was 0.11. If the transducer were to be operated in conjunction with a wideband impedance matching element, an antenna bandwidth comparable to the frequency of the antenna would be attained. The temperature dependence of the Q of the transducer was in good agreement with theory. At temperatures above about 6 K the Q was degraded by the increase in the BCS surface resistance, while at lower temperatures the Q was limited by radiative losses.
Response functions of the laser beam deflection probe for detection of spherical acoustic waves
Authors: Diaci Janez
Published: July 2002

Detection of spherical acoustic waves by the laser beam deflection probe is examined. The probe is modeled as a linear system transforming acoustic wave form into transient angular deflection of the probe beam. Transfer and step response functions are derived assuming thin Gaussian laser beam and small deflection angle. It is demonstrated that the probe behaves as a half-order differentiator when short acoustic transients are detected far from the source. Theoretical predictions are compared to the results of frequency analysis of optoacoustic signals detected by the deflection probe. Good agreement is found.
Langmuir and heat flux probes for RFX
Authors: Antoni V. , Bagatin M. , Desideri D. , Pomaro N. , Gadani G. , Gaggini P. , Monari M. , Parini A.
Published: July 2002

A movable limiter made of graphite and instrumented with an array of Langmuir and heat flux probes has been developed for the reversed field pinch experiment RFX. The limiter is mushroom shaped and designed to be exposed to the edge plasma for a discharge duration ≊250 ms. The distribution of the probes on the limiter surface allows simultaneous collection, in a single discharge, of edge parameters at different angles and radial positions. A bellows drive system with three degrees of freedom allows the instrumented limiter to be rotated and translated to investigate the spatial structure of the edge plasma. Cables and feedthroughs have been designed for 1-kV voltage and 5-A current. The power supply provides an output voltage ±100 V and a maximum current 4 A. Specific software has been developed for the automatic analysis of the Langmuir probes data.
A workstation based Langmuir probe system for low-pressure dc plasmas
Authors: Sudit Isaac D. , Woods R. Claude
Published: July 2002

A Langmuir probe measurement system suitable for characterization of extended, low-pressure dc or microwave plasmas has been developed around a VAXStation 3200 graphics workstation computer. Both planar and cylindrical probes have been constructed, but the latter has been deemed more satisfactory, and its design developed more fully. A novel interface circuit based on fast high voltage, transformer-coupled, isolation amplifiers has been constructed to permit probing of regions where the plasma potential is hundreds of volts away from ground, which are typically found in dc glow discharges. This circuit also incorporates a noise suppression feature, using feedback from a second identical probe (compensation probe), which has proven very useful. A great deal of high-resolution data can be collected quickly using the fast direct memory access (DMA) hardware. Many analysis capabilities and graphical display possibilities are implemented in the FORTRAN control program, but special emphasis has been placed on extracting plasma potentials, electron densities, and electron energy distribution functions (EEDFs) from the first and second derivatives of the probe I-V curve. These are obtained by numerical differentiation techniques that fully correct for ohmic voltage drops across the current sampling resistor. The capabilities of the system will be illustrated with several examples of probe data and EEDFs obtained in a large dc glow discharge system.
A simple conversion electron detector for Mössbauer source experiments
Authors: Liao L. X. , Ryan D. H. , Altounian Z.
Published: July 2002

A vibration-free conversion electron detector has been constructed for Mössbauer source experiments with extremely low doping levels (∼1 ppm) of cobalt-57. While the overall efficiency is somewhat less than that of microfoil systems, the design is greatly simplified and it still yields more than a sixfold enhancement in signal-to-noise ratio over standard transmission methods. The lightweight detector (∼25 g) may be mounted directly on a conventional transducer without limiting the performance. This allows low-temperature source measurements to be made by moving the detector and fixing the sample/source in a cryostat. The overall linewidth (HWHM) of the detector is 0.16 mm/s with the broadening being due to saturation effects in the enriched foil.
Mechanical loss in fibers for low noise pendulums
Authors: Kovalik Joseph , Saulson Peter R.
Published: July 2002

We describe measurements of the quality factors of resonances in fibers made of tungsten, silicon, sapphire, and fused quartz. The silicon and sapphire samples exhibited losses consistent with thermoelastic damping. Our fused quartz samples showed excess loss at some frequencies. The tungsten fibers had quality factors much lower than the thermoelastic prediction at all frequencies that we measured. We calculate the expected Brownian motion of pendulums made with similar fibers.
High repetition rate operation of a rotating dielectric spark gap
Authors: Nilaya J. Padma , Biswas D. J. , Narayan B. S. , Chatterjee U. K.
Published: July 2002

The reliable operation of a spark gap at 300 Hz pulse repetition frequency by rotating a suitably configured dielectric plate between its electrodes is reported. The triggering of the spark gap has been achieved by the use of an optical sensor.
A scanning tunneling microscope suitable for biological applications
Authors: Cricenti Antonio , Generosi Renato , Selci Stefano
Published: July 2002

We have designed and built a scanning tunneling microscope (STM) suitable for biological applications. A sound-isolated chamber contains the STM unit; the chamber can be evacuated or filled with inert gas, after the sample and tip are loaded, in order to reduce contamination on sample and tip. The STM unit is mounted inside two separable cylindrical supports. The lower cylinder contains the sample holder mounted on top of a step-motor controlled x-y-z stage, while the upper one contains the piezoelectric tip scanner. An I/V converter preamplifier mounted inside the x-y-z stage and a completely digitized feedback circuit, together with a full software package in UNIX X-window environment and data processing, allow fast sample–tip approach and reduced acquisition time. Atomic resolution images of highly oriented pyrolytic graphite (HOPG) in air and reproducible large scan on a platinum grating are routinely obtained. Images of human liver ferritin deposited on an activated gold substrate have also been obtained.
Low-energy ion beam extraction and transport: Experiment–computer comparison
Authors: Spädtke Peter , Brown Ian , Fojas Paul
Published: July 2002

Ion beam formation at low energy (∼1 keV or so) is more difficult to accomplish than at high energy because of beam blowup by space-charge forces in the uncompensated region within the extractor, an effect which is yet more pronounced for heavy ions and for high beam current density. For the same reasons, the extracted ion beam is more strongly subject to space charge blowup than higher energy beams if it is not space-charge neutralized to a high degree. A version of vacuum arc ion source with an extractor that produces low-energy metal ion beams at relatively high current (∼0.5–10 kV at up to ∼100 mA) using a multi-aperture, accel–decel extractor configuration has been created. The experimentally observed beam extraction characteristics of this source is compared with those predicted using the axcel−inp code, and the implied downstream beam transport with theoretical expectations. It is concluded that the low-energy extractor performance is in reasonable agreement with the code, and that good downstream space charge neutralization is obtained. Here, the code and the experimental results are described, and the features that contribute to good low-energy performance are discussed.
A versatile Czochralski crystal growth system with automatic diameter control
Authors: Aggarwal M. D. , Metzl R. , Wang W. S. , Choi J.
Published: July 2002

A versatile Czochralski crystal pulling system with automatic diameter control for the growth of nonlinear optical oxide crystals is discussed. Pure and doped bulk single crystals of bismuth silicon oxide (Bi12SiO20) have been successfully grown using this system. The system consists of a regular Czochralski type pulling system with provision for continuous weighing of the growing crystal to provide feedback for power control.
Ultraminiature high pressure cell for angularly dependent transport measurements at high magnetic field and low temperature
Authors: Danner G. M. , Chaikin P. M.
Published: July 2002

A miniature cell for studies of transport and thermodynamic properties of materials to pressures to 10 kbar at 0.5 K has been developed. This is an improvement upon previous designs because its extremely small size (0.3 in. diam.×0.5 in.; 0.762 cm diam.×1.27 cm) allows it to be used in a confined space. In addition we have developed a highly precise mechanism for rotation that permits 360° rotation of this cell and particularly for low temperature rotations in a narrow bore, high field magnet.
The use of scanning conduction microscopy to probe abrasion of insulating thin films
Authors: Dickinson J. T. , Jensen L. C. , Siek K. H. , Hipps K. W.
Published: July 2002

The use of scanning force microscopy (SFM) to probe wear processes at interfaces is of considerable interest. A simple modification of the SFM which allows one to make highly spatially resolved measurements of conductivity changes produced by abrasion of thin insulating films on metal substrates is presented here. The technique is demonstrated on fluorocarbon polymer thin films deposited on stainless-steel substrates.
Electro-optical modulators in particle detectors
Authors: Tsang T. , Radeka V.
Published: July 2002

Results of an investigation to minimize the local electronics in particle detectors using electro-optical intensity modulators are reported. The electrical charge signals from a particle detector are first applied to a low noise electronic charge-sensitive preamplifier and the resulting signal charges are converted into optical signals using an integrated Ti:LiNbO3 Mach–Zehnder interferometric optical modulator. By driving the optical modulator with a low noise diode-pumped Nd:YAG laser at a wavelength of 1.3 μm and detecting the output signals using a fast pulse shaping technique, the charge output of a particle detector can be measured at high rates with high accuracy up to 3 decades of dynamic range. The performance characteristics of such a detector signal transfer scheme, using first a single channel optical modulator and then a 16-channel integrated optical modulator array, is reported. Using the charge output from a multiwire proportional chamber, this electrical charge to optical signal transfer scheme is compared to the conventional particle detection technique. Effects of radiation dose on the optical modulator are also presented. Finally, the implication of using such an optical technique is discussed.
Measurements of beam geometry fluctuations of typical argon-ion and Nd:YAG lasers with relevance to laser interferometer gravitational wave detectors
Authors: Skeldon K. , Hough J.
Published: July 2002

The best sensitivity of a laser interferometric gravitational wave detector can only be achieved after considerable reduction is made in fluctuations of the geometry of the laser beam. Beam geometry fluctuations can be divided into four main types; lateral beam movement, tilt of the beam, variations in the beam width, and fluctuations in the beam curvature. Here we describe new techniques of measurement. The results for two types of laser beam geometry fluctuation—lateral movement and width fluctuation—for an argon-ion laser and for a diode pumped monolithic ring Nd:YAG laser are presented.
Generation of 24.0 T at 4.2 K and 23.4 T at 27 K with a high-temperature superconductor coil in a 22.54 T background field
Authors: Ohkura K. , Sato K. , Ueyama M. , Fujikami Jun , Iwasa Y.
Published: July 2002

The 4.2 K and 27 K current-carrying performance of a high-temperature superconducting (HTS) coil was measured in background fields up to 22.54 T generated by a hybrid magnet (Hybrid III) at the MIT Francis Bitter National Magnet Laboratory. The coil, 40 mm winding i.d., 108 mm winding o.d., and 113 mm high, consists of 17 double pancakes, each wound with silver-sheathed BSCCO-2223 tapes. Each pancake is the product of a react-and-wind method. In total, the test coil contains ∼1200 m of BSCCO-2223 conductor weighing ∼7 kg. Prior to the measurements in Hybrid III, the coil was tested in zero background field in the temperature range from 4.2 to 77 K. It was coupled to a Gifford–McMahon type cryocooler and at 15 K generated a peak field of 2.1 T; at 18 K, it generated 1.9 T, operating continuously for ∼50 h. In a 22.54 T background field of Hybrid III, the coil reached critical currents of 116.5 A ([Jc]sc, critical current density based on the BSCCO cross-sectional area only, of 261 A/mm) at 4.2 K and 67 A ([Jc]sc=150 A/mm) at 27 K, establishing record net fields at respective temperatures of 24.0 and 23.4 T for HTS magnets. These currents correspond to overall winding current densities of 47 and 27 A/mm. High-field critical current data for short samples of the tape of the same formulation at 4.2 and 27 K are also presented. Although a [J]sc of 261 A/mm at 24 T and 4.2 K for the test coil is significantly less than ∼600 A/mm for the short samples at the same operating point, if factors such as length, bending, and even differences in defining critical current are considered, the coil and short samples have nearly the same critical current performance. Electromagnetic stresses do not seem to have any negative effects on coil performance. Record fields of 24.0 and 23.4 T were achieved after the test coil had experienced, over a period of 15 months, 20 thermal cycles between room temperature and cryogenic temperatures.
Optimization of spherical grating monochromators operating with variable included angle for different applications
Authors: Melpignano P. , Di Fonzo S. , Bianco A. , Jark W.
Published: July 2002

The concept of variation of the angle of deflection in a spherical grating monochromator allows to keep the defocus aberration at zero while keeping the entrance and the exit slit distances fixed. This report presents the optimization of this concept for different applications in which one would always like to work with maximum resolving power and photon flux while keeping the exit slit at a fixed position. Three designs are presented for medium resolution (E/ΔE = 3000) soft x-ray microscopy studies in the photon energy range 200–1200 eV and 20–300 eV and for high-resolution spectroscopy (E/ΔE≳10 000) in the larger range 20–800 eV.
Phase-sensitive interferometry with ultrashort optical pulses
Authors: Kop Rik H. J. , Sprik Rudolf
Published: July 2002

Reliable phase-sensitive time-resolved interferometry with ultrashort pulsed lasers is performed with the use of a closed scanning Michelson interferometer in combination with a fixed Mach–Zehnder interferometer at the front end. The technique is based on measuring the full phase and frequency properties of the pulse distortion of an ultrashort optical pulse introduced by linear or nonlinear interaction with a sample. The necessary stability and reproducibility to perform an interferometric measurement is provided by a commercially available Fourier transform spectrometer enabling time-resolved measurements from the IR well into the visible part of the optical spectrum. The feasibility of the technique is demonstrated by measuring the distortion introduced by an etalon and a surface-plasmon polariton.
Correlation radiometry of electron cyclotron radiation in TEXT-U (invited)
Authors: Cima G. , Watts C. , Gandy R. F.
Published: July 2002

Very low level plasma density and temperature fluctuations can be responsible for anomalous transport in thermonuclear magnetic traps. Measuring these fluctuations by detecting plasma electron cyclotron emission (ECE) might indicate where, in ω−k space, the most dangerous instabilities are located. The most attractive feature of ECE is the good localization of the source, unique to this range of frequencies among plasma radiation. However, to maintain spatial resolution, only a small number of radiation modes should be detected. The consequent poor statistics of the ECE measurement allows one to measure only the average value for the temperature fluctuation amplitude via correlation analysis of two ECE signals with suitable correlation properties. Initial measurements of this kind have been performed successfully. But, results have only been partially conclusive as to the relevance of electrostatic turbulence to heat transport, due to still too limited poloidal spatial resolution and the inability to correlate the measured signals with corresponding potential fluctuations. Suggestions of how to extend the present results to correct for these drawbacks are discussed.
Moiré deflectometry diagnostic for transient plasma, using a multipulse N2 laser
Authors: Moosman B. , Bystritskii V. M. , Boswell C. J. , Wessel F. J.
Published: July 2002

We have designed a multipulse laser system to measure nanosecond time scale, plasma-density gradients by moiré deflectometry. The complete system consists of four, transverse-excited, atmospheric pressure (TEA) N2 laser oscillators and two low-pressure N2 laser amplifiers; two oscillator pulses are injected into a single amplifier. The amplified pulses are less than 1 ns in duration, with a variable, interpulse time of 4–10 ns. As described here, two TEA oscillators and a single amplifier were used to image air-density gradients in an expanding, air-shock wave produced by a spark discharge.
Particle simulation of the potential formation across the magnetic filter
Authors: Naitou Hiroshi , Fukumasa Osamu , Sakachou Kouji
Published: July 2002

The potential formation across the magnetic filter (MF) is studied by the two-and-one- half-dimensional (two configuration and three velocity spaces) electrostatic particle simulation. The strength of the MF is selected to influence only electron dynamics; ions move freely across the MF. The MF divides the plasma into the main plasma and the diffused plasma. The density and temperature of the main plasma is controlled, while there is no artificial treatment for the diffused plasma. It is found that the (collisionless) anomalous diffusion of electrons plays an important role in determining the potential structure in which the potential of the main plasma is higher than that of the diffused plasma. It is also found that by changing the potential of the wall adjacent to the diffused plasma, the plasma potential of the diffused plasma can be controlled without affecting the main plasma.
Growth of AlN by metalorganic molecular beam epitaxy
Authors: MacKenzie J. D. , Abernathy C. R. , Pearton S. J. , Krishnamoorthy V. , Bharatan S. , Jones K. S. , Wilson R. G.
Published: July 2002

Thin film AlN has been grown on Al2O3 and GaAs substrates by metalorganic molecular beam epitaxy using amine bonded alane precursors and either tertiarybutylamine or nitrogen from a compact electron cyclotron resonance (ECR) plasma source operating at 2.45 GHz. Typical growth pressures were in the 0.5–1×10−4 Torr range. The growth rates, impurity backgrounds, and surface morphologies were examined for both nitrogen sources and both the solid and liquid alanes. In general, growth efficiencies were good for both alane precursors, allowing for deposition of the low temperature, ∼400 °C, AlN buffers needed for subsequent growth of GaN and InGaAlN alloys. Low growth temperatures could not be obtained using tertiarybutylamine, presumably due to poor decomposition efficiency of the source at low temperatures. The structural quality of material grown at high temperatures from the ECR plasma was measured by atomic force microscopy, high resolution x-ray diffraction, and transmission electron microscopy, indicating single crystal material with a surface roughness of ∼8 Å and an x-ray full width half-maximum of 430 arcsec. This ECR plasma-derived material was of sufficient quality to allow for the growth of multiple quantum well InGaAlN structures.
A computer-controlled apparatus for performing high-resolution adsorption isotherms
Authors: Mursic Z. , Lee M. Y. M. , Johnson D. E. , Larese J. Z.
Published: July 2002

A high precision, computer-controlled adsorption isotherm apparatus has been constructed and used to investigate a variety of physisorbed systems. Suitable for absolute measurements, this apparatus features good vapor pressure resolution and outstanding temperature stability. The hallmark of the apparatus, however, is the graphical computer interface, written using the popular LABVIEW package, which offers a flexibility and ease-of-use not achieved in previous automated systems. This article will demonstrate the quality of data obtainable with this system, as well as the simplicity of operation afforded by the graphical interface.
Microwave plasma continuous emissions monitor for trace-metals in furnace exhaust
Authors: Woskov P. P. , Rhee D. Y. , Thomas P. , Cohn D. R. , Surma J. E. , Titus C. H.
Published: July 2002

A microwave plasma continuous emissions monitor has been successfully demonstrated for sensitive (<1 ppb), real time measurements of trace metals in furnace exhaust. The instrument uses a robust, up to 1.5 kW, 2.45 GHz microwave plasma sustained in a portion of the undiluted furnace exhaust flow for atomic emission spectroscopy. The waveguide device is constructed of refractory materials compatible with high-temperature environments (≳500 °C) and is flange mountable into the inside of the furnace exhaust duct. Fused quartz fiber optics in close proximity to the plasma flame transmit the UV through visible emission (190–690 nm) to three spectrometers for simultaneous monitoring of several metals. This instrument has been used for continuous monitoring for a 49 h period with 0.5 s time resolution on a dc graphite electrode arc furnace during a soil vitrification test. Results are presented for chromium, manganese, and iron emissions during soil loading operations.
Ultrahigh vacuum scanning force microscope with fiber-optic deflection sensor
Authors: Kracke B. , Damaschke B.
Published: July 2002

We built a scanning force microscope working in ultrahigh vacuum. The lever deflection is measured by a fiber-optic interferometer. To detect large lever deflections the distance between the fiber end and the cantilever backside is controllable by a piezoelectric device. With this technique force–distance curves can be acquired even over large distances. We implemented a stepper motor with gear reduction system for coarse approach in our microscope. First measurements of thin gold films grown on mica obtained in situ at 10−8 Pa are presented.
High-resolution absorption spectra of water vapor and acetylene detected by temperature tuning of laser diodes
Authors: Li Daqun , Baker John G.
Published: July 2002

A newly developed 0.78 μm single-mode laser diode spectrometer tuned by scanning the laser temperature with a resolution of better than 0.005 cm−1 is used to detect weak overtone spectra of water vapor and acetylene. A total of 3.65 nm continuous tuning range can be recovered from mode hops by operating two laser diodes alternately in different temperature regions at different injection current settings. The sensitivity of this spectrometer is demonstrated by its capability of detecting a weaker water vapor spectral line with an absolute intensity of 1.45×10−25 cm2/cm per molecule at 296 K using a 2.8 m single pass absorption cell by means of frequency-modulation spectroscopy.
The JET soft x-ray diagnostic systems
Authors: Alper B. , Dillon S. , Edwards A. W. , Gill R. D. , Robins R. , Wilson D. J.
Published: July 2002

A new multicamera soft x-ray detector system has been constructed for the pumped divertor phase of JET to provide improved spatial and temporal resolution. It is based on 12 compact pinhole cameras each of which uses a 35 element PIN photodiode array. The cameras are housed in a secondary vacuum and view the plasma through beryllium windows 250-μm-thick which absorb x rays with energies below ∼2 keV. The front-end electronics, located up to 10 m away from the detectors, sample data at 250 kHz, with a 100 kHz passband. The diodes are operated at zero bias voltage. The system ran successfully during the 1995 phase of JET operation with poloidal mode numbers up to m=5 being successfully reconstructed. Detector noise levels (<1 nA) were small compared to signal statistical noise. Some deterioration in diode performance was observed after exposure to an integrated neutron fluence of ∼1013 n. cm−2. Tests have shown that operating with 3 V reverse bias can offset much of the fall in performance from radiation damage. Using a similar 16 element PIN photodiode, a windowless camera has been developed for installation in the JET primary vacuum, to investigate fast XUV/x-ray events which develop at lower energies near the plasma edge or in the divertor. Finally, a radiation hardened system is being developed for D-T operation.
Visible spectroscopy in the DIII–D divertor
Authors: Brooks N. H. , Fehling D. , Hillis D. L. , Klepper C. C. , Naumenko N. N. , Tugarinov S. N. , Whyte D. G.
Published: July 2002

Spectroscopy measurements in the DIII–D divertor have been carried out with a survey spectrometer that provides simultaneous registration of the visible spectrum over the region 400–900 nm with a resolution of 0.25 nm. Broad spectral coverage is achieved through the use of a fiberoptic transformer assembly to map the curved focal plane of a fast (f/3) Rowland-circle spectrograph [Tugarinov et al., Rev. Sci. Instrum. 66, 603 (1995)] into a rastered format on the rectangular sensor area of a two-dimensional charge-coupled device (CCD) camera. Vertical grouping of pixels during CCD readout integrates the signal intensity over the height of each spectral segment in the rastered image, minimizing readout time. For the full visible spectrum, readout time is 50 ms. Faster response time (<10 ms) may be obtained by selecting for readout just a small number of the 20 spectral segments in the image on the CCD. Simultaneous recording of low charge states of carbon, oxygen, and injected impurities has yielded information about gas recycling and impurity behavior at the divertor strike points. Transport of lithium to the divertor region during lithium pellet injection has been studied, as well as cumulative deposition of lithium on the divertor targets from pellet injection over many successive discharges.
Multichannel far-infrared polarimeter system on TEXT-Upgrade
Authors: Brower D. L. , Zeng L. , Jiang Y.
Published: July 2002

A far-infrared polarimeter diagnostic has been added to the UCLA multichord heterodyne interferometer system on TEXT-Upgrade. The polarimeter utilizes the phase technique of Rice [Rev. Sci. Instrum. 63, 5002 (1992)] in order to measure the Faraday rotation angle of the incident laser beam upon transmission through the plasma. From these data one derives information on the poloidal magnetic field, current density, and safety factor profiles. Due to the excellent port access and the polarimeter/interferometer scanning capability, the Faraday rotation profile can be measured across the entire plasma cross section.
A fast charge coupled device detector for charge exchange recombination spectroscopy on the DIII-D Tokamak
Authors: Thomas D. M. , Burrell K. H. , Groebner R. J. , Gohil P. , Kaplan D. , Makariou C. , Seraydarian R. P.
Published: July 2002

Charge exchange recombination (CER) spectroscopy has become a standard diagnostic for Tokamaks. CER measurements have been used to determine spatially and temporally resolved ion temperature, toroidal and poloidal ion rotation speed, impurity density, and radial electric field. Knowledge of the spatial profile and temporal evolution of the electric field shear in the plasma edge is crucial to understanding the physics of the L to H transition. High speed CER measurements are also valuable for edge localized mode studies. Since the 0.52 ms minimum time resolution of our present system is barely adequate to study the time evolution of these phenomena, we have developed a new charge coupled device (CCD) detector system with about a factor of 2 better time resolution. In addition, our existing system detects sufficient photons to utilize the shortest time resolution only under exceptional conditions. The new CCD detector has a quantum efficiency of about 0.65, which is a factor of 7 better than our previous image intensifier-silicon photodiode detector systems. We have also equipped the new system with spectrometers of lower f/number. This combination should allow more routine operation at the minimum integration time, as well as improving data quality for measurements in the divertor-relevant region outside of the separatrix. Construction details, benchmark data, and initial Tokamak measurements for the new system will be presented.
Performance and operation of a beam chopping system for a cyclotron with multiturn extraction
Authors: Yokota W. , Fukuda M. , Okumura S. , Arakawa K. , Nakamura Y. , Nara T. , Agematsu T. , Ishibori I.
Published: July 2002

A beam chopping system for a cyclotron is in operation at the JAERI cyclotron facility. A combination of a pulse voltage chopper in the injection line and a sinusoidal voltage chopper after the exit of the cyclotron is adopted to produce beam pulses spaced at 1 μs–1 ms intervals from natural cyclotron beams. The chopping system was designed according to a simple formulation of the chopping process in which the multiturn extraction was taken into account. Performance of the chopping system was experimentally proved to satisfy requirements of the design. In actual operation to produce beam pulses at long intervals, however, the number of the multiturn extraction is usually larger than the assumed value in the design because of a large phase acceptance of the cyclotron. Careful tuning of the acceleration phase width or the base magnetic field of the cyclotron is necessary to reduce it. It is essential to strictly define the acceleration phase of injected beams in the central region of the cyclotron to improve this situation.
Sapphire resonator for the measurement of surface impedance of high-temperature superconducting thin films
Authors: Ormeno R. J. , Morgan D. C. , Broun D. M. , Lee S F. , Waldram J. R.
Published: July 2002

A technique using cavity perturbation of a cooled sapphire disk resonator has been developed to measure the surface impedance Zs=Rs+iXs of high-temperature superconducting thin films. The resonator is excited in the TE011 mode at 14.4 GHz and induces a-b plane screening currents in the sample. The resonator and its enclosure are maintained at 4.2 K while the sample is heated independently on a movable sapphire rod. The thermal isolation of the sample and resonator leaves the measurement virtually free of systematic error and permits the use of a superconducting niobium shield. The combination of low dielectric loss sapphire and a superconducting enclosure results in typical unloaded quality factors (Q) of several million. The ability to move the sample makes the sensitivity variable, allowing surface resistance values from 5 μΩ to several Ω to be measured. Background loss can also be accurately determined at the time of experiment by withdrawing the sample from the influence of the resonator. In addition, sensitive measurements of the penetration depth can be made by spring-loading the film onto quartz spheres glued to the resonator surface; this technique is shown to be free of systematic error up to a temperature of 60 K.
High repetition rate compact source of nanosecond pulses of 5–100 keV x-ray photons
Authors: Khacef A. , Viladrosa R. , Cachoncinlle C. , Robert E. , Pouvesle J. M.
Published: July 2002

A powerful, compact, and repetitive flash x-ray system based on a cable transformer technology powered by ceramic capacitors in a Blumlein-like configuration has been developed. Open circuit voltages in excess of 100 kV can be achieved while commutation occurs at low voltage (<20 kV). The x-ray emission from a low impedance x-ray diode with a hollow cathode configuration was observed under a wide range of experimental conditions. The critical parameters limiting the flash x-ray performances are mainly the pressure in the x-ray diode and the anode–cathode space. This true table top device is able to produce doses up to 1 R per shot, measured at the output window, of x-rays between 5 and 100 keV. The pulse widths were about 20 ns and the maximum repetition rate was about 60 Hz. Operation is possible in air or in other gases (He, Ne, Ar, Kr, Xe, H2, N2) at pressures varying from 10−3 mbar for xenon to about 1 mbar for helium.
Cantilever magnetometry in pulsed magnetic fields
Authors: Naughton M. J. , Ulmet J. P. , Narjis A. , Askenazy S. , Chaparala M. V. , Hope A. P.
Published: July 2002

The technique of cantilever magnetometry is shown to be functional in pulsed magnetic fields. Employing micromachined single crystal silicon cantilevers and capacitance detection, we demonstrated a utilizable sensitivity to magnetic moment of 2.5×10−12 Am2 in magnetic fields to 36 T, representing an improvement of more than a factor of 10 over competing technologies. Torque magnetization measurements on microcrystals of anisotropic superconductors are presented as evidence of the feasibility of the technique in long pulse magnets of pulse duration ∼0.1–1 s.
A digital control system for the iodine stabilized He–Ne laser
Authors: Ahola Tom , Hu Jianpei , Ikonen Erkki
Published: July 2002

A digital control system has been developed for the iodine stabilized He–Ne laser. The system is based on a digital signal processor and a general purpose microprocessor. The hardware is briefly described. The algorithms used for laser frequency locking are presented and new methods which are made possible by this system are discussed. An improved way of locking the laser to the fifth or seventh harmonic of the modulation frequency has been implemented digitally.
High-speed multishot pellet injector prototype for the Frascati Tokamak Upgrade
Authors: Frattolillo A. , Migliori S. , Scaramuzzi F. , Angelone G. , Baldarelli M. , Capobianchi M. , Cardoni P. , Domma C. , Mori L. , Ronci G.
Published: July 2002

The Frascati Tokamak Upgrade (FTU) may require multiple high-speed pellet injection in order to achieve quasi-steady-state conditions. A research and development program was thus being pursued at ENEA Frascati, aimed at developing a multishot two-stage pellet injector (MPI), featuring eight “pipe gun” barrels and eight small two-stage pneumatic guns. According to FTU requirements, the final goal is to simultaneously produce up to eight D2 pellets, and then deliver them during a plasma pulse (1 s) with any time schedule, at speeds in the 1–2.5 km/s range. A prototype was constructed and tested to demonstrate the feasibility of the concept, and optimize pellet formation and firing sequences. This laboratory facility was automatically operated by means of a programmable logic controller (PLC), and had a full eight-shot capability. However, it was equipped as a first approach with only four two-stage guns. In this article we will describe in detail the guidelines of the MPI prototype design, which were strongly influenced by some external constraints. We will also report on the results of the experimental campaign, during which the feasibility of such a two-stage MPI was demonstrated. Sequences of four intact D2 pellets in the 1.2–1.6 mm size range, fired at time intervals of a few tens up to a few hundreds of ms, were routinely delivered in a laboratory experiment at injection speeds above 2.5 km/s, with good reproducibility and satisfactory aiming dispersion. Some preliminary effort to address the problem of propellant gas handling, based on an innovative approach, gave encouraging results, and work is in progress to carry out an experiment to definitely test the feasibility of this concept.
Self-optimizing and adaptive digital signal processor based algorithms in scanning tunneling microscopy
Authors: Scheuring J. , Clauss W. , Kern D. P.
Published: July 2002

A self-optimizing proportional integral differential feedback loop and an adaptive scan generator have been implemented in a digital signal processor board EVM56k from Motorola for the control of a scanning tunneling microscope. The self-optimizing feedback loop uses an evolutionary algorithm to optimize the step response of the system. The variation of the target step response strongly determines the results of the optimizing process and allows to optimize either for highest scan speed or best signal-to-noise ratio. In combination with the improved adaptive scan generator, the adjustment of the scan velocity to the local topography of the sample increases image contrast and quality considerably.
A new interferometer to measure preheat in laser targets
Authors: Kyrala George A. , Johnson Randall P. , Hurry Tom
Published: July 2002

Many interferometer designs exist to measure the distance change through a fringe displacement. Different interferometers were used to measure the movement of the backside of a heated foil in laser plasma interactions. However, when a laser heated target sits in the middle of a target chamber with noise from pumps and other sources of vibrations, the fringes become difficult to observe and align. We have built a differential interferometer where the light paths in each arm of the interferometer retrace each other, hence making the fringes much less sensitive to vibrations than a regular interferometer. This allows the main part of the interferometer to sit outside the vacuum chamber, where it is easy to align. The final focusing element resides close to the target and collects a significant amount of the scattered light. In this investigation we will use the interferometer to measure the expansion of the backside of a preheated target in the TRIDENT chamber. Using the coefficient of linear expansion, the heat capacity of the material, and the expansion distance, we estimate a time dependent preheat temperature of the target.
Apparatus for vortex dynamics studies in high Tc samples using close cycle refrigerator and rf oscillators
Authors: Patnaik S. , Singh Kanwaljeet , Budhani R. C.
Published: July 2002

The design, fabrication, and performance of an apparatus for measurements of rf penetration depth in superconducting samples are described. The instrument makes use of a close-cycle helium refrigerator and is capable of measuring vortex dynamics in superconducting sample of volume as small as 1×10−3 cm3 with a signal-to-noise ratio of 1400. The system has been tested for a tunnel diode oscillator and an IC 74LS04 oscillator in the 3–5 MHz frequency range. Both magnetic field magnitude and angular variations to the resolution of 1 G and 0.05°, respectively, are possible with the apparatus. The system performance is evaluated by measuring the dynamical behavior of vortices in platelet samples of Bi2Sr2CaCu2O8 and (Bi-Pb)2Sr2Ca2Cu3O10 superconductors.
Compact THz-radiation source consisting of a bulk semiconductor, a mode-locked fiber laser, and a 2 T permanent magnet
Authors: Ono Shingo , Tsukamoto Takeyo , Sakai Masahiro , Liu Zhenlin , Ohtake Hideyuki , Sarukura Nobuhiko , Nishizawa Seizi , Nakanishi Akio , Yoshida Makoto
Published: July 2002

A compact THz-radiation source using an InAs semiconductor is demonstrated with a turn-key femtosecond fiber laser as an excitation source and a newly designed 2 T permanent magnet. By using a newly designed magnetic circuit, a compact permanent magnet which can exceed the remanence magnetic field was obtained. This compact source is sufficiently intense for absorption spectroscopy.
Deformation of sapphire induced by a spherical indentation on the (101̄0) plane
Authors: Nowak R. , Sekino T. , Maruno S. , Niihara K.
Published: July 2002

This work clarifies the origin of the characteristic discontinuities registered during the deformation of the (101̄0) plane of sapphire, by means of depth sensing indentation experiments with a spherical indenter. The sudden increase of the plasticity of the crystal was found to be caused by a twinning process. The calculation and analysis of the distribution of resolved shear stresses under a spherical indenter predicted the features of the surface deformation. The high resolution microscopic examination of the residual impressions confirmed the theoretical prediction.
Comparison of quasi-phase-matching geometries for second-harmonic generation in poled polymer channel waveguides at 1.5 μm
Authors: Jäger M. , Stegeman G. I. , Brinker W. , Yilmaz S. , Bauer S. , Horsthuis W. H. G. , Möhlmann G. R.
Published: July 2002

We have investigated three different quasi-phase-matching approaches to second-harmonic generation (SHG) in DANS (4-dimethylamino-4′-nitrostilbene) poled polymer channel waveguides at 1.5 μm. Periodic photobleaching and periodically poled electrodes deposited directly on the film produced unacceptably high propagation losses. However, periodic electrodes on the substrate gave low losses and useful SHG.
Near-field optical spectroscopy of single quantum wires
Authors: Harris T. D. , Gershoni D. , Grober R. D. , Pfeiffer L. , West K. , Chand N.
Published: July 2002

Low temperature near-field scanning optical microscopy is used for spectroscopic studies of single, nanometer dimension, cleaved edge overgrown quantum wires. A direct experimental comparison between a two dimensional system and a single genuinely one dimensional quantum wire system, inaccessible to conventional far field optical spectroscopy, is enabled by the enhanced spatial resolution. We show that the photoluminescence of a single quantum wire is easily distinguished from that of the surrounding quantum well. Emission from localized centers is shown to dominate the photoluminescence from both wires and wells at low temperatures. A factor of 3 absorption enhancement for these wires compared to the wells is concluded from the photoluminescence excitation data.
Crystallization-resistant photorefractive polymer composite with high diffraction efficiency and reproducibility
Authors: Cox A. M. , Blackburn R. D. , West D. P. , King T. A. , Wade F. A. , Leigh D. A.
Published: July 2002

We report on a high optical quality, long-life guest-host photorefractive polymer composite which exhibits a 60% device steady-state diffraction efficiency and 120 cm−1 two-beam coupling gain, well in excess of its absorption of 3.5 cm−1, at a wavelength of 676 nm. In contrast to alternative composite materials of comparable high dye content, this performance has been achieved without unacceptably compromising device lifetime or ease of fabrication and storage. This is an efficient, easily prepared and comparatively stable polymer composite with device lifetimes under storage conditions already exceeding eight months and no indication of sample degradation with repeated holographic read–write cycles.
Novel electro-optic effect associated with a homeotropic to twisted–planar transition in nematic liquid crystals
Authors: Suh Seong-Woo , Shin Sung Tae , Lee Sin-Doo
Published: July 2002

A homeotropic to twisted-planar (HTP) structural transition is demonstrated in a homeotropically aligned nematic liquid crystal with negative dielectric anisotropy. This HTP transition results in a novel electro-optic effect useful for extremely high contrast, wide viewing, and achromatic display applications. The HTP architecture is found to be a promising candidate for use in the active addressing scheme. The role of the surface anchoring and molecular chirality on the HTP transition is also discussed.
Efficient, fast response light-emitting electrochemical cells: Electroluminescent and solid electrolyte polymers with interpenetrating network morphology
Authors: Cao Yong , Yu Gang , Heeger Alan J. , Yang C. Y.
Published: July 2002

The device performance of light-emitting electrochemical cells is improved by adding a bifunctional liquid additive into the light-emitting layer. Because of the surfactant-like character of the additive, the light-emitting layer exhibits a high surface area bicontinuous three-dimensional network morphology. The semiconducting polymer forms a continuous network phase enabling electronic transport of injected electron and holes: the electrolyte forms a continuous network phase enabling fast ion transport; the nm length scale of the phase separated network enables rapid, effective transport of the ions into the conducting polymer during electrochemical doping.
Quasi-phase-matched second harmonic generation in a polymer waveguide with a periodic poled structure
Authors: Tomaru Satoru , Watanabe Toshio , Hikita Makoto , Amano Michiyuki , Shuto Yoshito , Yokohoma Itaru , Kaino Toshikuni , Asobe Masaki
Published: July 2002

Quasi-phase-matched (QPM) second harmonic generation in a poled polymer waveguide has been realized. A waveguide with a periodic structure was fabricated by conventional photolithography and reactive ion etching. The waveguide with a QPM structure was composed of poled polymer and UV cured epoxy resin. Phase-matched second harmonic generation was observed, using laser light with a fundamental wavelength 1.48–1.65 μm. This phase matched condition was dependent on the periodic length. The waveguide had a typical second harmonic generation efficiency of about 4×10−1% W−1 cm−2 around a wavelength of 1.55 μm.
In situ wafer bonding of an InP/InGaAs epitaxial wafer with a Si wafer in an ultrahigh vacuum chamber
Authors: Kagawa Toshiaki , Matsuoka Yutaka
Published: July 2002

An InP/InGaAs epitaxial wafer prepared by gas source molecular beam epitaxy was directly bonded with a Si wafer in an ultrahigh vacuum chamber without exposure to the air. The photoluminescence of an InGaAs quantum well layer does not deteriorate even if it is located 100 nm from the bonding interface. In a pin structure fabricated by bonding, carriers injected to the intrinsic region by forward bias reach the interface and recombine through the recombination centers at the interface.