bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of cavity size on lasting characteristics of a distributed Bragg reflector-surface emitting laser with buried heterostructure
Authors: Mori K. , Asaka T. , Iwano H. , Ogura M. , Fujii S. , Okada T. , Mukai S.
Published: July 2002

Transverse-mode characteristics of the distributed Bragg reflector-surface emitting laser diode with buried heterostructure were investigated as a function of the cavity size. Stable, fundamental transverse-mode operation was achieved for cavity openings of 4 μm in diameter and smaller. The effect of cavity size on threshold current and polarization characteristics is also discussed.
Optical absorption evidence of a quantum size effect in porous silicon
Authors: Sagnes I. , Halimaoui A. , Vincent G. , Badoz P. A.
Published: July 2002

This study presents optical transmission measurements performed on free-standing homogeneous porous silicon (PS) films of different porosities and substrate doping levels. The absorption coefficient curves deduced from these measurements, taking into account the total quantity of matter in the PS film, exhibit significant blue shift (up to 500 meV). These shifts, well correlated with the crystallite size variations with porosity and substrate doping observed by electron microscopy and gas adsorption experiments, are attributed to quantum size effects in the silicon microcrystallites.
Vapor transport growth of C60 crystals
Authors: Liu J. Z. , Dykes J. W. , Lan M. D. , Klavins P. , Shelton R. N. , Olmstead M. M.
Published: July 2002

A vapor transport technique has been used to produce large, high quality C60 single crystals. This technique, which uses an open tube method with a flowing helium gas carrier, eliminates the crystal size limitation found in the vacuum sublimation growth method.
In-plane epitaxial alignment of YBa2Cu3O7−x films grown on silver crystals and buffer layers
Authors: Budai J. D. , Young R. T. , Chao B. S.
Published: July 2002

Superconducting YBa2Cu3O7−x (YBCO) films were grown by laser ablation on Ag(001), Ag(110), and Ag(111) single-crystal surfaces. X-ray diffraction measurements showed that, in all cases, the films were aligned with specific in-plane epitaxial orientation with respect to the crystallographic axes of the substrate. The observed orientations were consistent with predictions of near-coincident site lattice models of the YBCO-Ag interface. This technique for achieving three-dimensional film alignment was extended to include a Ag epitaxial buffer layer on mica in place of a bulk Ag crystal. In-plane epitaxial alignment on metal substrates and buffer layers has important consequences in practical applications for inhibiting weak-link behavior caused by high-angle grain boundaries.
Fiber laser probe for near-field scanning optical microscopy
Authors: Betzig E. , Grubb S. G. , Chichester R. J. , DiGiovanni D. J. , Weiner J. S.
Published: July 2002

A hybrid near-field/fiber laser probe has been developed for high flux, reflection mode optical imaging of surfaces on a subwavelength scale. Spatial resolution of ∼100 nm (i.e., ∼λ/10 at λ=1060 nm) has been achieved simultaneously with signals of ∼1014–1015 photons/s, an improvement of ∼103–104 over earlier designs. The probe thus represents an important step in the development of advanced near-field transducers for high bandwidth applications such as high density data storage.
Difference-frequency generation and sum-frequency generation near the band gap of zincblende crystals
Authors: Zhang X.-C. , Jin Y. , Ware K. , Ma X. F. , Rice A. , Bliss D. , Larkin J. , Alexander M.
Published: July 2002

We present recent experimental results of difference-frequency generation (DFG) and sum-frequency generation (SFG) from zincblende materials. We measure the radiation field of difference-frequency generation and the radiation intensity of sum-frequency generation versus crystallographic orientation and fundamental photon energy. The simultaneous measurement of the angular dependence of polarized DFG and SFG is well characterized by the bulk second-order nonlinearity calculation. Pronounced resonant behaviors near the GaAs band gap for both radiations (DFG and SFG) are compared.
Charge transport in heavily B-doped polycrystalline diamond films
Authors: Werner M. , Dorsch O. , Baerwind H. U. , Obermeier E. , Haase L. , Seifert W. , Ringhandt A. , Johnston C. , Romani S. , Bishop H. , Chalker P. R.
Published: July 2002

Temperature-dependent conductivity and Hall measurements have been carried out on heavily in situ B-doped polycrystalline diamond films in a temperature range from ∼100 to 750 K. The slope of the conductivity is clearly non-Arrhenius leading to a pronounced tail at low temperatures. Carrier transport at low temperatures is dominated by variable range hopping. The activation energy decreases with increasing doping concentration and the most heavily doped diamond films show metallic behavior above room temperature. Hole carrier concentrations up to 1.8×1021 cm−3 were measured in agreement with secondary-ion-mass spectroscopy investigations.
Refractive index of (AlxGa1−x)0.5In0.5P grown by metalorganic vapor phase epitaxy
Authors: Moser M. , Winterhoff R. , Geng C. , Queisser I. , Scholz F. , Dörnen A.
Published: July 2002

Ordered and disordered (AlxGa1−x)0.5In0.5P (x=0, 0.33, 0.66) layers have been grown on GaAs by metalorganic vapor phase epitaxy. The complex refractive index below and above the band edge has been determined by transmission experiments and ellipsometry. We have observed, that ordered and disordered samples only differ near the fundamental band gap with respect to these properties.
Surface study of YBa2Cu3O7−δ epitaxial films cleaned by an atomic oxygen beam
Authors: Terada N. , Ahn C. H. , Lew D. , Suzuki Y. , Kihlstrom K. E. , Do K. B. , Arnason S. B. , Geballe T. H. , Hammond R. H. , Beasley M. R.
Published: July 2002

An atomic oxygen beam generated by a microwave plasma source has been used to clean the surface of high-Tc superconducting a- and c-axis oriented YBa2Cu3O7−δ (YBCO) epitaxial thin films. The crystallinity and electronic structure of the cleaned films have been characterized in situ using reflection high energy electron diffraction, low energy electron diffraction (LEED), and ultraviolet and x-ray photoemission spectroscopies (UPS, XPS). Exposure of the surface at 350 °C to the atomic oxygen beam yields sharp LEED spots and a metallic feature at the Fermi level. For a-axis films, clear LEED patterns and a Fermi edge in UPS spectra of a recleaned surface are simultaneously observed. The contact resistance between a cleaned a-axis YBCO film and in situ deposited gold was found to be in the range of 10−10–10−9 Ω cm2.
Rough versus dilute interfaces in semiconductor heterostructures: The role of growth conditions
Authors: Grieshaber W. , Bodin C. , Cibert J. , Gaj J. , Merle d’Aubigné Y. , Wasiela A. , Feuillet G.
Published: July 2002

CdTe-CdMnTe interfaces grown by molecular beam epitaxy are studied using excitons confined in quantum wells. For increasing growth temperatures Zeeman splittings indicate an enhanced dilution of Mn ions at the interface while the optical linewidths evidence a decreasing roughness. These results directly illustrate the fact that the two methods are sensitive to different scales of interface broadening.
Near-field photoconductivity: Application to carrier transport in InGaAsP quantum well lasers
Authors: Buratto S. K. , Hsu J. W. P. , Betzig E. , Trautman J. K. , Bylsma R. B. , Bahr C. C. , Cardillo M. J.
Published: July 2002

A new contrast method in near-field scanning optical microscopy in which the near-field probe is used to excite photocurrent in a semiconductor sample is described and demonstrated. The use of near-field optics results in an order-of-magnitude improvement in spot size and a fivefold improvement in resolution over previous methods of photocurrent imaging. The application of this near-field photoconductivity technique to a multiquantum well laser provides direct visualization of carrier transport throughout the structure, yielding information on growth inhomogeneities, carrier leakage and isolation, and the overall quality of p-n junctions.
Anisotropy in diamond etching with molten cerium
Authors: Jin S. , Zhu W. , Siegrist T. , Tiefel T. H. , Kammlott G. W. , Graebner J. E. , McCormack M.
Published: July 2002

An orientation-dependent etching behavior has been observed during diffusional thinning of single crystal diamond by molten cerium. The etching rate at 920 °C was in the order of {111}≳{100}≳{110} with a relative ratio of about 5:2:1. This diamond etching anisotropy is tentatively attributed to the orientation-dependent difference in the energy required to break the bonds on each atomic plane. It is interesting to note that the easiest-etching plane found here, {111}, is the most difficult plane to polish mechanically, and the most difficult plane to etch, {110}, is the easiest plane for mechanical polishing.
Scintillator hodoscope system for a high intensity beam
Authors: De Palma M. , Macchia G. , Maggi G. , Nappi E. , Ranieri A. , Sacchetti A. , Selvaggi G. , Spinelli P.
Published: July 2002

In this paper the authors describe the construction and the operation of a scintillator hodoscope used in an intense beam. By using a fast scintillator (Pilot U), an XP1910 photomultiplier, and an appropriate electronic chain, a two-pulse separation of 6 ns per channel and a time resolution (σ) of 210 ps were obtained.
Fabrication of ultrathin drawn Pt wires by an extension of the Wollaston process
Authors: Sacharoff A. C. , Westervelt R. M. , Bevk J.
Published: July 2002

We have produced single ultrathin Pt wires with diameters as small as 80 Å, using an extension of the Wollaston composite drawing process. These wires were used in experiments to test the theory of quasi-one-dimensional electronic localization and interaction effects at liquid-helium temperatures. The procedures developed to draw composite wires and remove the outer jacket are described in detail.
Integrated noise measurement of a silicon avalanche diode detector using a CAMAC module
Authors: Drèze C. , Waksberg A.
Published: July 2002

This paper describes a detailed experimental study of the integrating noise of a silicon avalanche diode detector using a current integrating ADC CAMAC module. The dark current noise and shot noise measurements are discussed in relation to a previously described theoretical model. The results confirm that the model can be used to optimize the detector parameters in order to maximize the signal-to-noise ratio of the detection system.
Super-resolution through illumination by diffraction-born evanescent waves
Authors: Guerra John M.
Published: July 2002

A diffraction grating in silicon with 50 nm lines and spaces is illuminated with diffraction-born evanescent waves from its transparent replica. A rotation φ between the gratings results in a set of fringes with period λf that is larger than the period of the original gratings by a magnification factor M. These fringes are induced and observed with a photon tunneling microscope having an incident illumination of 650 nm in air. This super-resolution by what may be considered a form of optical heterodyning with evanescent waves is discussed.
Fiber-optic spectral-streak equalizer
Authors: Reedy Robert P. , Roeske Franklin , Smith Donald E.
Published: July 2002

A spectral-streak equalizer was developed for use with an electronic streak camera to correct for material dispersion in optical fibers. Material dispersion occurs because different wavelengths of light travel at different speeds through glass fibers; the resulting difference in transit times broadens light pulses, which can lead to errors in certain scientific applications. This new instrument combines optical equalization and streak equalization techniques; it uses an array of optical fibers, as in the optical equalization technique, to partially compensate for the dispersion and uses the streak camera dynamics, as in the streak equalization technique, to complete the compensation. This paper examines the principles of equalization and compares several techniques, enumerates general and specific design considerations, outlines the calibration procedure, details efficiency estimates, describes testing techniques, gives calibration data and test results for spectral-streak equalizers currently in use, and draws conclusions from recent experience with these devices.
Self-balanced bridge for automatic measurements of magnetic susceptibilities
Authors: Ocio M. , Hammann J.
Published: July 2002

An automatic bridge for low-temperature measurements of susceptibilities χ(0), χ′, and χ″ as a function of field and temperature is described. The system is based on a digitally controlled feedback loop which ensures continuous balanced operation, in phase as well as in quadrature. Several types of interchangeable mutual inductance equipment can be used, depending on the ranges of temperature and frequency. The electronic part fulfills the functions of null detection, amplification, digital integration and reading, and primary and feedback current generation. The null detection is performed by a SQUID system or by a voltmeter, according to the working frequency range. In ac operation, the amplification chain is made of two synchronous detectors, one in phase and the other in quadrature, followed by two digital integrators whose numerical outputs yield a measure of χ′ and χ″, and command two DAC multipliers generating the composite input voltage of the feedback current generator. All the digital functions are performed by a processing unit which also allows interfacing with a desktop computer via an IEEE bus. Measurements can be performed in the frequency range of 0–10 kHz, a temperature range of 12 mK–40 K, and a primary field range of 0.1–20 Oe. The resolution of the numerical part is 1 in 104. Sensitivities of the order of 6×10−7 emu for samples of 10−2 cm3 in a field of 0.4 Oe have been obtained using SQUID detection.
Device for measuring sound speeds in reactive liquids at high pressure and temperature
Authors: Shaw George H. , Caldwell D. A. ‘‘Buzz’’
Published: July 2002

We have designed a device for measuring sound speeds in reactive liquids at high pressure and temperature. It has been tested in experiments on liquid-potassium metal at pressures up to 0.7 GPa and temperatures up to 423 K. The limitations on pressure and temperature were imposed by auxiliary instrumentation rather than the properties of the device, and it seems likely that it would be suitable for more extreme conditions. The data on potassium agree well with precise room-temperature data. The sound velocities measured as a function of pressure at various temperatures can be used to calculate equation-of-state parameters such as the bulk modulus and its pressure derivatives. The experiments on potassium indicate that bulk modulus can be determined to ±1%, its first pressure derivative to about ±5%, and second pressure derivative to about ±50% (the last for a run with a 0.7-GPa pressure range). The device should permit sound velocity measurements in a variety of liquids which are reactive, corrosive, and/or miscible with pressure media.
Two-color x-ray generator for detection of aluminum by differential absorption
Authors: Eversole J. D. , Gamble R. C.
Published: July 2002

Development and calibration of a high-intensity, ‘‘two-color’’ x-ray source for application to differential absorption measurements of aluminum is described. The output intensity from this source is predominantly in two atomic emission lines: the aluminum and silicon Kα lines at 1.49 and 1.74 keV, respectively. Anode fabrication techniques and modifications to a commercial rotating anode x-ray generator necessary to achieve this unique source are detailed. Measurements made with an ionization chamber suggest that the output intensity of the aluminum Kα line is 1.1×109 photons/s mm2 at a distance of 60 mm from anode center when operated at 20 kV and 10 mA. The aluminum line intensity was about 50% of the silicon line. These same techniques can be readily adapted to produce a variety of selected atomic line spectra for differential absorption diagnostics of other species of interest.
Surface enhanced Raman scattering on silver grating: Optimized antennalike gain of the stokes signal of 104
Authors: Baltog I. , Primeau N. , Reinisch R. , Coutaz J. L.
Published: July 2002

Using a silver grating of variable groove depth overcoated by a thin film of copper phthalocyanine, we measured an increase of the Raman efficiency of 104 as compared to the flat case (copper phthalocyanine on a flat silver surface). This effect is due to the resonant excitation of delocalized surface plasmons. The value of 104 corresponds to an optimum groove depth of the grating which acts as a high gain directive antenna when surface plasmons resonance is achieved at the Stokes frequency.
Magnetically driven, acoustically tracked, translating-ball rheometer for small, opaque samples
Authors: Tran-Son-Tay R. , Beaty B. B. , Acker D. N. , Hochmuth R. M.
Published: July 2002

A new rheometer has been designed to measure the rheological properties at low Reynolds number of microliter quantities of opaque suspensions. The rheometer uses a falling-ball technique to measure steady-state viscosity and a vertically oscillating, magnetically driven ball for viscoelastic measurements. The motion of the ball is tracked by ultrasound echo location, in which sound waves are transmitted and received by an ultrasound transducer mounted at the base of the tube. Concentrated suspensions of red blood cells are used as opaque test samples. The results obtained are in good agreement with those reported in the literature. The data confirm the fact that a concentrated suspension of red blood cells behaves as a shear thinning material and that the energy stored by the suspension during an oscillatory cycle increases with frequency. Testing of the rheometer is also made by using a Newtonian silicone oil. Viscosity measurements obtained with both the falling- and oscillating-ball methods are consistent and are within 2% of the value of 47.3±0.5 cP given by the Cannon-Fenske viscometer. However, it is found that the oscillating-ball technique gives the largest standard deviation, 6%, as opposed to 2% for the falling-ball technique.
Compact friction and wear machine
Authors: Hannigan James W. , Schwarz Ricardo B.
Published: July 2002

We have developed a compact ring-on-ring wear machine that measures the friction coefficient between large area surfaces as a function of time, normal stress, and sliding velocity. The machine measures the temperature of the sliding surfaces and collects the wear debris.
Numerical linearization of a silicon intensified target vidicon response
Authors: Basak Soumen , Ferrone Frank A.
Published: July 2002

We have linearized the output of a silicon intensified target vidicon as a function of input illumination by use of a cubic polynomial with coefficients which vary according to spatial position. The need for this procedure and its effectiveness are described.
X-ray response of silicon surface-barrier diodes at 8 and 17.5 keV: Evidence that the x-ray sensitive depth is not generally the depletion depth (abstract)
Authors: Wenzel Kevin W. , Petrasso Richard D.
Published: July 2002

The absolute x-ray response of 18 EG&G Ortec partially depleted silicon surface-barrier diodes (SBDs) have been measured at 8 and 17.5 keV. In addition we have examined the x-ray response of four Tennelec and two United Detector Technology partially depleted SBDs. The variation in response to 8 keV x rays, for which the optical depth is about five, is comparatively slight (≲12%). The variation in response to 17.5 keV x rays, for which the optical depth is only ∼0.7, is comparatively large (∼100%). These variations are mainly attributable to differences in the SBD physical thicknesses, and thus to differences in optical depth. At both 8 and 17.5 keV the diodes respond linearly to large variations in incident flux (over three orders of magnitude). This linearity, and the diode x-ray response in general, is insensitive to large changes in the detector bias voltage; thus the depletion depth, proportional to the square root of the bias voltage, does not play a critical role in determining the x-ray sensitive depth. It is important to emphasize that this finding is contrary to the commonly held belief that the x-ray sensitive depth is equivalent to the depletion depth. In addition this result has a direct bearing on both SBD and PIN detectors intended for fully depleted operation, but used in an underbiased mode such that they are actually partially depleted. We conclude that SBDs have attractive features for quantitatively measuring x radiation from high-intensity sources for which hν≳10 keV.
Gated x-ray pinhole camera for time-resolved 2-D images of laser-driven targets (abstract)
Authors: Turner R. E. , Powers G. , Bell P. , Kilkenny J. D.
Published: July 2002

We describe the operation of a multiframe x-ray pinhole camera with time resolutions on the order of 200 ps. This diagnostic provides complementary information to that obtained with a conventional x-ray streak camera. We will describe the characterization of the instrument, obtained optically and electronically, and show x-ray data obtained from laser fusion experiments. This work was performed under the auspices of the U. S. DOE by the Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.
Soft x-ray radiation from laser plasma (abstract)
Authors: Sato S. , Kobayashi I. , Yasojima Y. , Murai Y.
Published: July 2002

Laser-target interaction was studied to make an efficient soft-x-ray source with a table-top laser system. A 1-J, 20-ns ruby laser was focused on various planar targets (Z=6 to 82). The laser power intensity on the targets was about 1011–1012 W/cm2. Spectra (2–35 nm) and intensities of soft x-ray radiation from target plasma were measured by using a 2-m grazing incidence spectrometer and a x-ray diode. Even at this low laser power intensity, high-energy radiation of 0.5–3 keV was obtained. Spectra from low-Z materials show strong line radiations over a weak continuum and those from high-Z materials consist of a continuum predominantly. The target Z-number dependence of the intensity of 0.5–3-keV radiation has a periodic structure and relates to atomic shell structures. In this experiment the maximum x-ray conversion efficiency was obtained from a 22Ti target.
Measurements of radial profiles of the ion temperature and the plasma rotation velocity with the TFTR vertical x-ray crystal spectrometer (abstract)
Authors: Bitter M. , Hsuan H. , Rice J. E. , Hill K. W. , Diesso M. , Grek B. , Hulse R. , Johnson D. W. , Johnson L. C. , von Goeler S.
Published: July 2002

The TFTR vertical x-ray crystal spectrometer has now been operating with three crystals and position-sensitive detectors according to the original design specifications. The observed spectra of heliumlike Ti xxi, Cr xxiii, Fe xxv, and Ni xxvii have permitted a detailed comparison with the predictions from atomic theories, and they have provided data on the radial profiles of the ion temperature and toroidal rotation velocity, as well as the radial ion charge-state distribution in TFTR discharges. Central ion temperatures of 20 keV and central plasma rotation velocities of 5×105 m/s have been recorded from plasmas with auxiliary neutral beam heating. These experimental results are presented. Also discussed are further instrumental improvements, such as the installation of two additional crystals and detectors and the installation of γ and neutron shielding, which will make it possible to measure under full DD and DT operation with 27 MW of neutral beam injection where neutron production rates of 1019 neutrons/s are expected.
E×B Wien analyzers (abstract)
Authors: Leal-Quiros E. , Prelas M. A.
Published: July 2002

The Wien filter is an E×B deflecting analyzer with the electrostatic field perpendicular to the magnetostatic field. The twofold functions of the Wien filter are as an energy analyzer as well as a mass analyzer. It has very high resolution for paraxial charged particle beams with V=E/B, the Wien velocity. Two Wien filters were built and tested for electrons up to 3.5 keV and protons beams of 200 eV. The performance of the two is compared and appears to have features useful for high-temperature plasma diagnostics including simultaneous measurement of energy and mass spectra and high resolution.
LOCUS database system
Authors: Murphy J. A. , Wieland R. M.
Published: July 2002

LOCUS is a database system for creating, manipulating, and interactively investigating databases. LOCUS was written in response to the need to study the data from the experimental devices at the Princeton Plasma Physics Laboratory and is now also used extensively at other fusion laboratories. An example of its use is the determination of scaling laws for tokamak plasmas. To do this, LOCUS allows the user to enter and modify data, define subsidiary variables as arbitrary functions of original data, plot and fit such variables, and perform multiple linear regression analysis. Through a flexible interactive interface the program is easy to learn and largely self-documenting. There are two implementations of LOCUS: one that manipulates data in VAX/VMS ISAM files and another that manipulates data in the commercial relational database management system INGRES.
Integrated, multivendor distributed data-acquisition system
Authors: Butner David N. , Drlik Marena , Meyer William H. , Moller Jeffrey M. , Preckshot George G.
Published: July 2002

A distributed data-acquisition system that used various computer hardware and software is being developed to support magnetic fusion experiments at Lawrence Livermore National Laboratory (LLNL). The experimental sequence of operations is controlled by a supervisory program, which coordinates software running on Digital Equipment Corporation (DEC) VAX computers, Hewlett–Packard (HP) UNIX-based workstations, and HP basic desktop computers. An interprocess communication system (IPCS) allows programs to communicate with one another in a standard manner regardless of program location in the network or of operating system and hardware differences. We discuss the design and implementation of this data-acquisition system with particular emphasis on the coordination model and the IPCS.
Role of superconducting electronics in advancing science and technology (invited) (abstract)
Authors: Faris S. M.
Published: July 2002

The promises of the ultrahigh-performance properties of superconductivity and Josephson junction technologies have been known for quite some time. This presentation describes the first superconducting electronics and measurement system and its important role as a major tool to advance microwave and millimeter wave technologies. This breakthrough tool is a sampling oscilloscope with 5-ps rise time, 50-μV sensitivity, and a time domain reflectometer with 8-ps rise time. In order to achieve these performance goals, several technological hurdles had to be overcome including perfecting a manufacturing process for building Josephson junction IC chips, developing an innovative cooling technique, developing interfaces and interconnections with bandwidths in excess of 70 GHz, and developing the room-temperature hardware and software necessary to make the instruments convenient, easy to use, easy to learn, in addition to making available functions and features users have come to expect from sophisticated digital test instrumentation. These technological developments are stepping stones leading to the realization of more sophisticated and complex electronic systems satisfying the needs of scientists, technologists, and engineers. The unprecedented speed and sensitivity make it possible to attack new frontiers.
Spectroscopic measurement of the poloidal field profile in the TEXT
Authors: Wróblewski D. , Huang L. K. , Moos H. W. , Phillips P. E.
Published: July 2002

The poloidal field profile in the Texas Experimental Tokamak is determined from the analysis of circular polarization of the forbidden (magnetic dipole) line Ti xvii 3834 Å. A high-sensitivity polarimeter measures the difference between right- and left-hand circularly polarized line profiles, a quantity which is directly proportional to the magnitude of the magnetic field component in the direction of observation. The fractional circular polarization smaller than 10−2 can be detected, which allows determining the poloidal magnetic field in the center of the plasma with uncertainty as small as 50 G. The instrumentation is relatively simple and inexpensive. Description of the polarimeter and results of measurement of the poloidal field profile and the safety factor on the tokamak axis are presented.
Detection of trapped magnetic fields in a theta pinch using a relativistic electron beam
Authors: Leemans W. P. , Clayton C. E. , Joshi C.
Published: July 2002

A novel nonperturbative diagnostic is used to infer the existence of trapped magnetic fields in a θ-pinch plasma. A thin beam of 1.5-MeV electrons from a 9-GHz, X-band linear accelerator is injected along the axis of a θ pinch with a period of 6 μs. The electron pulse duration is approximately 1 μs. Without any fill gas, when the θ pinch is fired, only those electrons within ±50 ns of the second Bext =0 are transmitted. The rest of the electrons are deflected by the solenoidal field, which acts as a strong lens. When the plasma is present even these transmitted electrons at Bext=0 are deflected because the plasma can trap some of the field lines. The magnitude and the scale length of these trapped fields can be estimated from the extent of the deflection.
Recent developments in millimeter wave diagnostics at JET (invited) (abstract)
Authors: Costley A. E.
Published: July 2002

There are presently two substantial millimeter wave diagnostic systems on JET in different stages of development: an established, comprehensive electron cyclotron emission (ECE) system and a recently installed multichannel reflectometer. The ECE system comprises a ten-channel antenna array in the vacuum vessel, an oversized waveguide transmission system, and an assembly of ECE instrumentation—Michelson and Fabry Perot interferometers, grating polychromator, and heterodyne radiometer. From measurements made with the Michelson interferometers the time and spatial dependencies of the electron temperature in the poloidal cross section are determined with resolutions of ∼15 cm and 15 ms, respectively. From measurements made with the other instruments, the time dependence of the temperature at specific locations is determined with resolutions ≳2 cm and ≳100 μs. The sensitivity is such that changes in temperature down to approximately a few eV can be clearly resolved. The multichannel reflectometer will probe the plasma in the ordinary mode at 12 frequencies in the range 18–80 GHz. It will have two modes of operation: narrow-band swept and fixed frequency. In the swept mode the spatial profile of the electron density will be measured with a time resolution ≳200 μs and a spatial resolution ∼1 cm, while in the fixed frequency mode of operation movements in the different density layers will be measured with a sensitivity approximately a few mm and bandwidth ≳100 kHz. In addition, a possible collective Thomson scattering diagnostic for measuring the velocity distribution of the confined α particles in the DT phase of JET operation is currently being studied. This system would use a high-power millimeter wave (140 GHz) gyrotron and heterodyne detection.
Reactive ion-beam deposition and cleaning system
Authors: Yamada Hiroshi
Published: July 2002

A reactive ion-beam deposition (RIBD) and cleaning (RIBC) system using low-temperature crystalline film growth and substrate cleaning is described. The RIBD and RIBC methods use low-energy-controlled ionized species produced from electron-cyclotron-resonance (ECR) plasma of reactive gases. The basic system comprises an ECR-type ion source allowing precise energy control of ionized species in the region of less than 500 eV and a high-vacuum cleaning and growth chamber evacuated at less than 3×10−7 Pa. Employing this system, Si substrate cleaning and high-crystalline-quality homoepitaxial film growth with superstructures on the substrates can be reliably performed at the low temperature of 650 °C.
Direct memory access digital events analyzer
Authors: Basano L. , Ottonello P.
Published: July 2002

We present a random-point-process multifunction analyzer in which a long sequence of interpulse intervals are recorded in the RAM bank of a personal computer, through a suitably designed front end attached to a commercial DMA interface. Laser light scattered by ground-glass disks and by aqueous suspensions of polystyrene latex spheres has been used to test the performance of the device that may be employed in a broad range of applications.
Frequency-stabilized single-mode cw 118.8-μm CH3OH waveguide laser for large tokamak diagnostics
Authors: Fukuda Takeshi , Nagashima Akira
Published: July 2002

A frequency-stabilized single-mode cw 118.8-μm CH3OH waveguide laser was newly developed for polari-interferometry on the JT-60 tokamak. Interferometric plasma diagnostics on large fusion devices requires a mode purity of a source laser for the long-distance propagation and frequency stability to obtain an adequate fringe resolution. The accomplished performances are Δf/f<1×10−8, power stability <0.03%, and single EH11 mode to yield a Gaussian-shaped profile in the far field. Homogeneous pumping of laser media with a Ge étalon beam coupler and feedback stability control are the keys to the source far-infrared laser performances required for large tokamak diagnostics. The developed laser was totally adjustment free for more than 2 weeks and reliably in operation for 2 years, including the real-time electron density feed-back control on the JT-60 tokamak.
A high magnetic field EPR spectrometer
Authors: Muller F. , Hopkins M. A. , Coron N. , Grynberg M. , Brunel L. C. , Martinez G.
Published: July 2002

We describe a tunable electron paramagnetic resonance (EPR) spectrometer designed to operate at frequencies between 160 and 525 GHz and magnetic fields of up to 20 T. To operate in such a broad frequency range we use a very stable optically pumped far infrared laser. The performance of the spectrometer has been measured with solid and liquid samples. This allows us to outline the potential uses of the spectrometer.
Thermistor sensor and total emittance measurement
Authors: Varma S. P. , Singh Joginder
Published: July 2002

The developmental details of a thermistor bolometer-type infrared sensor made from chemically prepared oxides of nickel and manganese have been described. The response time/time constant of these sensors can be tailored to a low or high value depending upon the need. A procedure for determining the total emittance of the source by using these sensors in a scanner consisting of an infrared transmitting lens and preamplifier is also discussed.
A novel triggered spark gap for a high-power xenon flash
Authors: Parker Greg
Published: July 2002

The application of a standard automotive sparking plug as a series-triggered spark gap for a high-power xenon flash is described. The spark gap allows a standard xenon flashtube to be used at voltages considerably in excess of the tube self-breakdown voltage for the production of high-speed light pulses. A one-third peak height flash duration of 16 μs was achieved at 45 J total energy without the use of an afterglow quenching gas.
Low-speed crystal pulling mechanism
Authors: Gabršček S. , Holc J.
Published: July 2002

This note describes a hydropneumatic low-speed lowering mechanism which provides variable pulling rates down to 0.05 mm per hour.
Neutral atomic beam source by a spark-discharge method
Authors: Minowa Tatsuya , Katsuragawa Hidetsugu , Inamura Takashi
Published: July 2002

A spark-discharge method has been successfully applied to the generation of neutral metal atoms. The neutral atomic source developed by the method has advantages in simplicity, low cost, and high intensity. Resonance ionization spectroscopy of the Fe and Al atoms was carried out by using the spark-discharge method.
Simple Faraday cup with subnanosecond response
Authors: Chuaqui H. , Favre M. , Wyndham E. , Arroyo L. , Choi P.
Published: July 2002

A small Faraday cup of coaxial design for use in plasma physics experiments is presented. The construction permits an approximately 50-Ω geometry to be maintained, allowing direct coupling to coaxial cable. The detector rise time is less than 0.4 ns, and is designed for beam currents of between 0.1 and 100 A. The design is well screened to reject spurious electrical noise.
PEP as a synchrotron radiation source (invited)
Authors: Bienenstock A. , Brown G. , Wiedemann H. , Winick H.
Published: July 2002

The 16-GeV storage ring PEP has characteristics which enable it to operate in modes with very low emittance and to accommodate very long undulators, producing synchrotron radiation at x-ray wavelengths with extremely high brightness and coherent power. Two beamlines, each illuminated by a 2-m long, 77-mm period undulator magnet, are now operational and others are planned. In parasitic operation during colliding-beam runs at 14.5 GeV, these beamlines provide photons above 10 keV with a peak brightness of about 1016 photons/(s mm2 mrad2 ) within a 0.1% bandwidth. In low-emittance tests at 7.1 GeV, horizontal emittances of about 5 nm rad were measured, which is about the same as that planned for the new third-generation x-ray sources. With a current of 15 mA at 7.1 GeV, the present undulators deliver photon beams from 2.7 to 14 keV with a peak brightness of about 1017 . Higher performance levels are expected with the implementation of longer undulators and shorter period undulators. In the longer term, because of its large circumference and long straight sections, PEP could be further developed to achieve even higher performance levels with an emittance below 1 nm rad, very long undulators and picosecond bunches, resulting in one to two orders of magnitude higher brightness and coherent power.
Superparamagnetic Fe clusters in Ag matrix produced by sputter-gas aggregation
Authors: Hohl G.-F. , Hihara T. , Sakurai M. , Konno T. J. , Sumiyama K. , Hensel F. , Suzuki K.
Published: July 2002

Experiments to generate a thin composite Fe-Ag film employing a sputter-gas-aggregation process are described. The magnetic properties are studied at low temperatures. In addition, the morphology is determined by high-resolution transmission electron microscopy and the structure by using x-ray diffraction and XAFS. Small clusters of about 11 Å in diameter are highly dispersed in an Ag matrix. They show the characteristics of interacting superparamagnets.
Compact convex crystal x-ray spectrometer
Authors: Ong C. X. , Wong C. S.
Published: July 2002

The construction of a compact and low cost convex crystal x-ray spectrometer is described. A mica sheet of about 100 μm thick is bent over a cylindrical surface to form the convex crystal. The spectrometer is expected to be able to cover the wavelength range between 1 and 19 Å. This spectrometer can serve as a convenient means for obtaining a preliminary scanning of the probable x-ray emission spectrum of plasma as a prelude to more careful and accurate spectral measurements.
An on-line Kerr spectrometer
Authors: Mallet G. , Vasilescu D.
Published: July 2002

A transient electric birefringence computerized spectrometer inducing Kerr effect in anisotropically polarizable solutions such as DNA is described. Rectangular unipolar or bipolar pulses up to 400 V (I<10 A) can be applied to solutions with relatively high conductivity. The software developed for recording the signal in a PC/AT computer, interpreting the shape of the signals and plotting the experimental and theoretical curves, is also described. The software is written in turbo Pascal 5.0, except for the Labcard driver, which is in 80286 assembly language. The performances of the apparatus have been checked on various DNA solutions.
Single-input double-tuned mutually coupled surface coil circuits: An analysis
Authors: Kan Siew , Gonord Patrick
Published: July 2002

The input reactance of a pair of coupled coils is a function of the latter’s primary, secondary, and mutual inductances as well as the secondary tuned frequency. It is thus possible to synthesize two appropriate equivalent inductances for use in a double-tuned probe by a judicious choice of these parameters. From a given coil configuration and hence the associated self and mutual inductances, the present note analyzes and derives the essential equations showing the possible values of the tuned secondary frequency to be used to design this type of probe circuit first proposed by Fitzsimmons, Brooker, and Beck [Magn. Resoh. Med. 10, 302 (1989)]. In cases where an intercoil coupling capacitor is needed, its value also can be calculated from a biquadratic equation. A numerical example is given to check the validity of the theoretical results.
Coils for generating uniform fields in a cylindrical ferromagnetic shield
Authors: Hosoya Mutsumi , Goto Eiichi
Published: July 2002

A Helmholtz coil is widely used for generating uniform magnetic fields. On the other hand, a ferromagnetic shield is the most common method to eliminate external magnetic fields. However, if a Helmholtz coil is used inside a ferromagnetic shield, the uniform magnetic field generated by the coil is disturbed because of the influence of the ferromagnetic shield. This article presents a new coil system that generates highly uniform magnetic fields in any direction even inside a ferromagnetic shield. This coil system does not waste valuable space inside the shield, because the coils are placed so that they touch the inner surface of the shield. The magnetic fields generated by the system were numerically calculated and confirmed by experiments. For a cylindrical shield of radius R0 with a ferromagnetic shielding disk at the bottom, the nonuniformity of the field is less than 1% within the space 0.7R0 from the central axis and below 3R0 from the top open edge of the shield.
A cw planar jet computer-controlled tunable IR diode laser spectrometer for the investigation of hydrogen-bonded complexes
Authors: Wang Zhongcheng , Eliades Michael , Carron Keith , Bevan John W.
Published: July 2002

An ultrasensitive computer-controlled tunable infrared diode laser cw planar supersonic jet spectrometer for second derivative detection of hydrogen-bonded complexes is described. Spectroscopic analyses of transitions in carbon monoxide monomer permit detection limits to be set at 2.9×106 molecules/cm3/quantum state. Simultaneously recorded spectra of the ν2C≡O stretching vibrations in OC—HCl and OC—HBr are presented to illustrate the performance of this supersonic jet spectrometer for investigating weakly bound hydrogen-bonded dimers.
A multipoint correlation method for bulk trap and interface state measurements in MOS structures from capacitance, voltage, and current transients
Authors: Dmowski K. , Bethge K. , Maurer Ch.
Published: July 2002

A multipoint correlation method is described to improve the analysis of the energy resolution of bulk traps and interface states in metal-oxide-semiconductor structures measured by constant voltage, constant capacitance, and current deep-level transient spectroscopy. The results obtained for the proposed method are given with those obtained for both Lang’s method and the method utilizing an exponential weighting function.
A sensitive interferometric accelerometer
Authors: Stephens M.
Published: July 2002

An interferometric accelerometer developed for use in characterizing isolation systems for gravitational wave detectors is described. A Nd:YAG laser is frequency locked to a Fabry–Pérot cavity in which one mirror is flexibly mounted. At 100 Hz the displacement sensitivity is 1.0×10−14 m/√Hz, 100 times more sensitive than the piezoelectric accelerometers normally used for such measurements. The sensitivity of the accelerometer is limited by the frequency noise of the laser.
The fabrication of thin-film thermocouples for determining the temperature and thermal conductivity within a flexible material
Authors: Rimai D. S. , Anne R. , Bowen R. C.
Published: July 2002

Thin-film thermocouples were produced on flexible polymeric and paper substrates using evaporation techniques. These devices were found to be simple to produce, durable, and to have good temperature sensitivity. These devices allow the temperature and thermal conductivity of thin coatings to be determined in a variety of processes with minimal impact to the process or loss of heat through the leads.
Pressure sensitive capacitance study in laser-induced chemical vapor deposition processed nanosized Si3N4
Authors: Wang Wei-Xiang , Li Dao-Huo , Liu Zong-Cai , Liu Song-Hao
Published: July 2002

Pressure sensitive capacitance of laser-induced chemical vapor deposition processed nanosized silicon nitride has been studied. It is found that the capacitance varies linearly with the pressure and its sensitivity is as high as 2.64 pf/Torr. The capacitance pressure sensitivity results from the huge interfaces and microvoids existing in the nanomaterials.
A new concave electrostatic lens with periodic electrode configuration
Authors: Nakata Shuhei
Published: July 2002

To obtain a large aperture lens with outstanding focal length homogeneity, a concave electrostatic quadrupole lens with a periodic configuration of the electrodes was developed and its performance was numerically studied. By adjusting the azimuthal angle (θc) of the electrode to an adequate periodic function along the lens axis, the integration of the field gradient along the axis, for a period (∫φdz/∫dz), becomes equal to an ideal quadrupole field distribution. To verify the usefulness of the lens, the beam spot distortion of the paraxial beam, which had an initial beam diameter of 90% of the lens radius, was calculated. The results revealed that the error of the focal length inside 90% of the lens radius was only 0.012% when the lens has nine period per unit length. Also, by considering the characteristics of the modified Bessel function, a simple formula for the uniformity of the focal length was obtained, and this expression agreed well with the simulation results.
Space-charge neutralization lens and its application
Authors: Sun B. H. , Cheng Q.
Published: July 2002

The space-charge neutralization lens (S-C neutralization lens) is investigated from the theoretical point of view. The working parameters and the focal length formulas of the lens are given. According to this article, a S-C neutralization lens has been designed and used as a focusing and transmission unit in the intense beam facility at the Institute of Nuclear Research of Lanzhou University. The experiments show that it has an excellent operating characteristic for focusing intense beams and adjusting optical-path matching.
Time-resolved energy spectrum of a pseudospark-produced electron beam
Authors: Ding B. N. , Myers T. J. , Rhee M. J.
Published: July 2002

For the first time a time-resolved energy spectrum of a pseudospark-produced electron beam is constructed. A small portion of electron beam sampled at its axis is injected into a vacuum and the electrons passed through a negatively biased electrode are measured by a Faraday cup. The time-resolved energy spectrum is determined by analyzing the Faraday cup current waveforms measured at various bias voltages. The resultant spectrum reveals that the instantaneous beam energy is nearly monoenergetic. The energy is monotonically decreasing in time and resembles the anode-cathode voltage waveform. This suggests that electrons are accelerated by the full instantaneous anode-cathode voltage.