bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase-matched second-harmonic generation from free-standing periodically stacked polymer films
Authors: Khanarian G. , Mortazavi M. A. , East A. J.
Published: July 2002

Visible green light has been observed by quasi-phase-matched second-harmonic generation from a periodic stack of free-standing poled polymer films, when pumped by a cw mode-locked near-infrared laser. The total thickness of the polymer film and phase-matching length was 300 μm with a conversion efficiency of 10−6–10−5 depending on absorption. A polymer thin film processing technique is described for this application that could make large area poled and stretched films with enhanced nonlinear optical susceptibilities.
GaAs/AlGaAs quantum dots by implantation induced intermixing
Authors: Prins F. E. , Lehr G. , Schweizer H. , Smith G. W.
Published: July 2002

By implantation induced intermixing we have realized GaAs/AlGaAs quantum dots with diameters down to 70 nm. In low-temperature photoluminescence an increasing shift to higher energies, up to 7 meV, with decreasing dot diameter is observed. From a simple model we conclude that a very steep lateral potential has been achieved and that the shift is partly due to the radial confinement. All dot structures show a high luminescence intensity and in the time integrated measurements no indication for a strong reduction of the energy relaxation is observed. This could be attributed to the measured carrier capture from the lateral barrier into the dots and by the shape of the radial potential which determines the energy levels in the dots.
Ultrafast photon-mode recording by novel photochromic polymer via photoinduced electron transfer
Authors: Nagamura Toshihiko , Sakaguchi Hiroshi , Muta Shigeki , Ito Toshiaki
Published: July 2002

The color change of a novel photochromic polymer film of 4,4′-bipyridinium-tetrakis [3,5-bis(trifluoromethyl)phenyl]borate was shown to occur in less than 20 ps by the ps-laser excitation of an ion-pair charge-transfer band due to photoinduced electron transfer, which may be applied to ultrafast photon-mode recording.
Fluid simulations of radio frequency glow discharges: Two-dimensional argon discharge including metastables
Authors: Lymberopoulos Dimitris P. , Economou Demetre J.
Published: July 2002

Two-dimensional self-consistent fluid simulations of a 13.56 MHz argon glow discharge including metastable species were performed as examples of a coupled glow-discharge/neutral-transport-and-reaction system. The electron density was found to peak in the radial direction. The metastable density profiles showed ‘‘hot spots’’ in both axial and radial directions.
Electron spin resonance study of the dangling bond in amorphous Si and porous Si
Authors: McMahon T. J. , Xiao Y.
Published: July 2002

We compare the electron spin resonance (ESR) signal of the dangling bond in porous silicon (PS) layers, produced by electrochemical etching, to the ESR signal from hydrogenated amorphous Si(a-Si:H) films. The anisotropy of the ESR signal from PS showed g values varying as for the Pb Si/SiO2 interface dangling bond. The g value varies from g∥=2.0020 to g⊥=2.0080 with an inhomogeneously broadened line width increasing from 1.8 to 3.8 G. An ESR powder line, with superhyperfine and strain broadening intrinsic to PS, has more anisotropy in g∥−g⊥ and less inhomogeneous broadening than does the dangling bond line in a-Si:H. No evidence was seen for light-induced metastability on a H-passivated PS film.
Eddy current microscopy using a 77-K superconducting sensor
Authors: Black R. C. , Wellstood F. C. , Dantsker E. , Miklich A. H. , Kingston J. J. , Nemeth D. T. , Clarke J.
Published: July 2002

We have used a scanning magnetic flux microscope based on a high transition temperature YBa2Cu3O7 superconducting quantum interference device (SQUID) to produce magnetic images of eddy currents in patterned Cu thin films and 11–30-μm-thick Cu on printed circuit boards. The fields produced by the eddy currents are imaged with a spatial resolution of about 80 μm over a 100-mm2 sample area. With the sample and SQUID at 77 K, the microscope uses typical probing fields of 80 nT and can obtain simultaneously eddy current and static magnetic field images. At probing frequencies of 26–100 kHz, the system achieves a field sensitivity of about 7 pT Hz−1/2.
Cryogenic field-effect transistor with single electronic charge sensitivity
Authors: Mar D. J. , Westervelt R. M. , Hopkins P. F.
Published: July 2002

We have fabricated matched pairs of cryogenic field-effect transistors with input charge sensitivity qn=0.01 e/√Hz at T=1.3 K, low input capacitance 0.4 pF, and extremely high input resistance in excess of 1015 Ω. Low leakage permits dc charge-coupled operation for times up to ∼103 s. The channel noise is characterized by a flat spectrum at high frequencies, and 1/f noise below a corner frequency fc<1 kHz. These devices can resolve charge differences as small as qn√fc=0.4e.
Photocurrent spectroscopy of Bragg mirrors in vertical cavity surface emitting lasers
Authors: Bae J. W. , Temkin H. , Parsons C. , Quinn W. E. , Brusenbach P. , Kim M. , Uchida T. , Swirhun S. E.
Published: July 2002

We describe a simple technique to precisely measure the reflectivity spectra of the Bragg mirrors in individual vertical cavity surface emitting lasers. Detailed reflectivity spectra are obtained by measuring the response of the active layer junction to light impinging upon the output mirror, corrected by the active layer response spectrum. Precise measurements of the emission spectrum of the laser with respect to the Fabry–Perot notch are then possible. In the temperature range of 20–100 °C we measure the rates of 0.56 and 0.62Å/°C for the mirror stack and the lasing wavelength, respectively.
Superconducting single crystals of TaC encapsulated in carbon nanotubes
Authors: Yosida Yositaka
Published: July 2002

The synthesis and electron microscopic studies of TaC single crystals encapsulated in carbon nanotubes are reported. The crystal structure is the NaCl type with the lattice parameter a0=4.455±0.003 Å. The typical crystalline size is ∼7 nm. The epitaxial growth of carbon nanotube on the {100} plane of the TaC single crystal is observed. The statistical growth model is adequate for explaining the crystalline-particle size distribution of the encapsulated crystals. Magnetic susceptibility measurements show a superconducting transition at 10.0 K, which is the expected critical temperature for the bulk TaC having the highest carbon composition.
Stable single mode hybrid laser with high power and narrow linewidth
Authors: Morton P. A. , Mizrahi V. , Tanbun-Ek T. , Logan R. A. , Lemaire P. J. , Presby H. M. , Erdogan T. , Woodward S. L. , Sipe J. E. , Phillips M. R. , Sergent A. M. , Wecht K. W.
Published: July 2002

We describe hybrid lasers combining a semiconductor gain section and fiber cavity with integrated chirped Bragg reflector. These devices have produced output powers of 27.5 mW in a narrow linewidth (400 KHz) stable single longitudinal mode. The use of a chirped reflector to stabilize the single mode output, and correct grating orientation are described. The laser output has a side-mode suppression ratio of over 55 dB at 27.5 mW output, and relative intensity noise (RIN) below 160 dB/Hz.
Interface roughness effects in resonant tunneling structures
Authors: Ting D. Z.-Y. , Kirby S. K. , McGill T. C.
Published: July 2002

We examine the effect of interface roughness on resonant tunneling in double barrier structures using an exactly solvable real-space three-dimensional supercell model. We find that scattering of off-resonance states into on-resonance states provides the dominant contribution to interface roughness assisted tunneling. Our analysis of the sensitivity of scattering strength to interface layer configurations reveals preferential scattering into k∥≊2π/λ states, where λ is the island size. We attribute the broadening and shifting of transmission resonances to lateral localization of wave functions, which we demonstrate directly. We also show that the degree of localization increases with island size.
Fast growth of Bi2Sr2Ca2Cu3O10+x and Bi2Sr2CaCu2O8+x thin crystals at the surface of KCl fluxes
Authors: Balestrino G. , Milani E. , Paoletti A. , Tebano A. , Wang Y. H. , Ruosi A. , Vaglio R. , Valentino M. , Paroli P.
Published: July 2002

We report a novel technique to grow crystals of the high-temperature superconductor Bi2Sr2Ca2Cu3O10+x and Bi2Sr2CaCu2O8+x (2223 and 2212 BSCCO phases), both pure and Pb substituted. The technique, based on chemical transport in a thermal gradient in molten KCl, is simple and inexpensive, and yields a continuous output of crystals, with growth times of a few minutes, i.e., orders of magnitude shorter than conventional flux methods. Depending on melt aging, crystals of either the pure 2223 or the pure 2212 BSCCO phases are obtained, having zero-resistance temperature of 105 and 90 K, respectively, and a transport critical current density of 104 A cm−2 at liquid nitrogen temperature.
Power saturation and the effect of argon on the electron spin resonance of diamond deposited from a microwave plasma
Authors: Lukins P. B. , Khachan J.
Published: July 2002

Electron spin resonance (ESR) of microwave plasma chemical vapor deposition diamond shows peaks associated with (i) a P1 substitutional nitrogen defect center, (ii) spin-spin interactions between the paramagnetic sites and neighboring protons, and (iii) a possible contribution from graphitic impurities or amorphous carbon. The P1 spectrum saturates at powers of the order of a few microwatts in contrast to other spectral components which do not display significant saturation. As a result, caution must be exercised when using ESR as a quantitative measure of diamond quality. Films grown from a gas mixture which includes argon do not show the P1 structure or its associated saturation effects. Instead, argon appears to etch or exclude nitrogen from the film leaving carbon-based radicals as the main paramagnetic species in the material.
Ultraviolet-laser-induced desorption of atoms, ions, and molecules from lithium niobate
Authors: Affatigato M. , Tang K. , Haglund R. F. , Chen C. H.
Published: July 2002

We report measurements of ultraviolet-laser-induced desorption of atoms, ions, and molecules from the surface of single-crystal, Y-cut lithium niobate at intensities below the plasma threshold. Particularly striking is the desorption of LiNbO3 molecules at intensities well below the threshold for the atomic and ion emission. Measurement of oxygen and niobium yields above and below the plasma threshold show changes in surface stoichiometry.
Carrier recombination studies of ZnCdSe/ZnSe single quantum wells grown by molecular beam epitaxy
Authors: Massa J. S. , Buller G. S. , Walker A. C. , Horsburgh G. , Mullins J. T. , Prior K. A. , Cavenett B. C.
Published: July 2002

Temperature dependent time-resolved photoluminescence has been used to study the excess carrier recombination in Zn0.75Cd0.25Se/ZnSe single quantum well structures grown by molecular beam epitaxy. For temperatures <100 K radiative excitonic recombination appears to dominate, and the photoluminescence (PL) decay time follows the linear dependence on temperature over the range 50–120 K. At higher temperatures the reduction in PL efficiency and decay time indicate that nonradiative processes associated with the ZnCdSe/ZnSe interfaces dominate the recombination. The results are consistent with theoretical predictions.
All-fiber femtosecond pulse amplification circuit using chirped Bragg gratings
Authors: Galvanauskas A. , Fermann M. E. , Harter D. , Sugden K. , Bennion I.
Published: July 2002

In-fiber chirped Bragg gratings are used as stretchers and compressors for distortionless amplification of femtosecond pulses in chirped pulse amplification system. It is shown that using opposite directions of pulse propagation the effects of higher order dispersion and grating irregularities can be eliminated and the original pulse shape and duration can be recovered. Using these gratings a compact all-fiber system consisting of a mode-locked fiber oscillator and an erbium-doped fiber amplifier was built. 330 fs bandwidth-limited pulses from a fiber oscillator were stretched to 30 ps, amplified and recompressed back to 408 fs. The maximum energy of the pulses after the amplifier was 6 nJ and was at the threshold of nonlinear effects for a 30 ps stretched pulse.
Hydrogen passivation in nitrogen and chlorine-doped ZnSe films grown by gas source molecular beam epitaxy
Authors: Ho E. , Fisher P. A. , House J. L. , Petrich G. S. , Kolodziejski L. A. , Walker J. , Johnson N. M.
Published: July 2002

The incorporation of hydrogen in ZnSe:N and ZnSe:Cl films grown by gas source molecular beam epitaxy (GSMBE) using elemental Zn and H2Se as source material has been investigated. The hydrogenation behavior was found to be significantly enhanced when nitrogen was used as a dopant, and typically resulted in highly resistive films. On the other hand, Cl-doped ZnSe films showed a hydrogen concentration at or near the background levels independent of the Cl concentration. ZnSe was also grown by conventional molecular beam epitaxy with intentionally introduced H2 in order to clarify the source of the hydrogen. Significant hydrogen incorporation was observed in the MBE-grown ZnSe:N layers only when hydrogen gas was introduced. Injection of hydrogen in excess of the amount generated during typical GSMBE experiments was found to give rise to an unambiguous increase in the hydrogen concentration, but with a hydrogen:nitrogen ratio less than that measured in GSMBE films.
Thermally enhanced ultraviolet photosensitivity in GeO2 and P2O5 doped optical fibers
Authors: Lemaire P. J. , Vengsarkar A. M. , Reed W. A. , DiGiovanni D. J.
Published: July 2002

The 248 nm UV photosensitivity of H2 loaded optical fibers is shown to be significantly enhanced by increasing the temperature during the UV exposure. Heating to 250–400 °C resulted in dramatic UV reaction rate increases in GeO2 doped fibers. Increasing the core temperature during 248 nm irradiation caused P2O5 doped fibers to become photosensitive.
Measurement of the scrape-off layer density profile on ASDEX via an energetic neutral lithium beam
Authors: McCormick K. ,   ASDEX Team
Published: July 2002

By observation of the intensity of the collisionally excited Li resonance line along an energetic beam injected into a low-density plasma, it is possible to infer the density profile.1 On ASDEX this technique is employed to continuously measure the density profile at the plasma edge with sub-ms time resolution. The Li-beam diagnostic system is described and results presented, for a beam energy of 60 keV, which show the method to produce profiles with low statistical noise, enabling small changes in density to be followed. The inferred relative density profiles are found to be in agreement with those determined by Thomson scattering and a Langmuir probe.
Transient pulse response of In0.2Ga0.8As/GaAs microcavity lasers
Authors: Michler P. , Lohner A. , Rühle W. W. , Reiner G.
Published: July 2002

We investigate the transient emission of two In0.2Ga0.8As/GaAs microcavity laser samples with one and three quantum wells at 20 K following femtosecond optical excitation. The stimulated emission time is faster when the cavity resonance is tuned to shorter wavelengths within the gain spectrum of the quantum well. A larger number of quantum wells makes the dynamical response faster also. The narrowest pulse width observed is 6.8 ps, and the shortest rise time is 1 ps.
High-resolution data-acquisition system for high impedance measurements on semiconductors
Authors: Weissfloch P. , Benzaquen M. , Walsh D.
Published: July 2002

A microprocessor-based high-resolution data-acquisition unit for high impedance measurements is described. It allows the reading of up to 16 averaged voltages many times a second with five digit precision. This unit has many possible applications as flexibility has been emphasized in the design. Here it is used in conjunction with an external microcomputer to collect high-precision data needed for the analysis of transport phenomena in highly resistive semiconducting materials. To demonstrate the performance of the system, data obtained from such experiments are presented for very demanding samples.
Self-adjustable pre-event pulse generator for shock wave experiments
Authors: Kondo K. , Yasuo H.
Published: July 2002

A self-adjustable, pre-event pulse generator has been constructed for triggering diagnostic and driving instruments before impact in various shock experiments. The preset period before impact is based on the instant of impact and is independent of projectile velocity. A change in the target position is accounted for by a variable clock oscillator.
Sensitive high-T
c transition edge bolometer on a micromachined silicon membrane
Authors: Neff H. , Laukemper J. , Khrebtov I. A. , Tkachenko A. D. , Steinbeiss E. , Michalke W. , Burnus M. , Heidenblut T. , Hefle G. , Schwierzi B.
Published: July 2002

Superconducting transition edge bolometers on micromachined silicon membranes have been fabricated. The optical response is 580 V/W at a time constant of 0.4 ms. The detectivity D* is 3.8×109 (cm Hz1/2 W−1) at a temperature of 84.5 K and within the frequency regime 100<f<300 Hz. This is one of the fastest composite type bolometers ever reported. Upon thermal optimization, this type of detector should be competitive with state-of-the-art quantum detectors.
Simple line-sampling apparatus for line frequency stroboscopic observation of periodic phenomena using scanning electron microscopy
Authors: Ikuta T. , Mase H. , Shimizu R.
Published: July 2002

Detailed operations of the apparatus for the stroboscopic observation of periodic phenomena at the region of line frequencies, such as the magnetic domain response, under the scanning electron microscopy are described in this paper. To achieve the stroboscopic observation at such low frequencies, a new line-sampling technique has been introduced instead of the conventional point-sampling method. In addition to the line-sampling stroboscopy, a multiframe operation is also introduced to display the stroboscopic images of different phase values simultaneously. These operations are simply realized by applying the raster separation and the blanking on the display monitor scope under the multiple line-sampling during the one-drive period. To demonstrate the ability of this simple apparatus, some results of the stroboscopic observation of magnetic domains in an Fe–Si sample under a 60-Hz drive field are also presented in this paper.
Measurement of radial profile of the x-ray emission on the JFT-2M tokamak
Authors: Kawashima H. , Matoba T. ,   JFT-2M Group
Published: July 2002

Temporal and spatial profiles of the x-ray spectra in the range 3–400 keV have been measured for divertor plasmas on the JFT-2M tokamak with a recently developed pulse-height analyzer system. This detection system incorporates an array of six vertically placed sets of a high-purity germanium spectrometer. Each x-ray energy spectrum can be measured simultaneously with a sampling interval of 1–255 ms. Dynamic change of the electron temperature profile, such as time behavior with H-mode transition, can be measured with this system. It was observed that the electron temperature profile became broad just after the H-mode transition during neutral-beam heated discharge. In the lower-hybrid current drive experiments, the x-ray emission profile depended strongly on the density. The x-ray intensity from the peripheral region became strong with increase in electron density.
Multichordal spectroscopy on JT-60
Authors: Kubo H. , Sugie T. , Sakasai A. , Koide Y. , Nishino N. , Yokomizo H. , Takeuchi H. ,   JT-60 Team, Tanaka K. , Maezawa H. , Yamaguchi N.
Published: July 2002

In order to study impurity behavior on the JT-60 plasma, a spectroscopic diagnostic system, which is capable of measuring many spectra of impurity ions and their spatial distributions simultaneously, has been developed. This system consists of interchangeable unit-type spectrographs which have different lines of sight. Four types of grazing incidence spectrographs are prepared as unit-type spectrographs. These spectrographs cover the nominal wavelength regions 0.5–5, 0.5–50, 2.0–50, and 50–122 nm, respectively, and have holographic gratings with flat focal fields. Image-intensified 1024- or 512-channel photodiode arrays are used as detectors for all spectrographs. Four unit-type spectrographs are used for observing the main plasma, and two unit-type spectrographs are used for observing the plasma near the null point of the diverted discharge. One of these spectrographs has been calibrated absolutely in the wavelength region 27.5–120 nm using synchrotron radiation from the Photon Factory (National Laboratory for High Energy Physics).
NTT normal-conducting accelerating ring
Authors: Shibayama A. , Kitayama T. , Hayasaka T. , Ido S. , Uno Y. , Hosokawa T. , Nakata J. , Nishimura K. , Nakajima M.
Published: July 2002

A normal-conducting accelerating ring (NAR) has been constructed with a Chasman–Green-type lattice. The NAR has two basic aims. One aim is to prove the feasibility of the novel accelerating and storage scheme, in which the NAR accelerates the injected 15-MeV electrons to the final energy of 800 MeV, and directly stores them. The other aim is to make the NAR a multipurpose ring. That is, it acts as a booster for the superconducting storage ring, and it supplies the synchrotron radiation with the critical wavelength, 20.2 A. To achieve a high beam current, particular considerations have been taken with injection, rf system, magnetic field tracking, and vacuum formation. The NAR has experienced acceleration and storage at the final energy, 800 MeV. The initial beam current is about 20 mA in the 800 MeV storage mode.
Computer control system of the superconducting SR-light source ‘‘Aurora’’
Authors: Yamada Hironari ,   S. H. I. Accelerator Research Group
Published: July 2002

The Aurora is a compact SR-light system optimized for x-ray lithography. The system includes a superconducting electron storage ring, a 150-MeV race track microtron as an injector, and light beamlines. The SR-ring features a single magnet body, in which the 650-MeV electron beam orbits a true circular trajectory of 1 m diameter. The computer control system developed for Aurora has a three-level hierarchical architecture. The top level is the Central Intelligence System, and the second an Autonomic Control System (ACS). The bottom is an assembly of distributed local controllers linked to the ACS level through optical fibers. This system provides fully automatic and remote operation, and a powerful machine study capability through the associated man–machine console and the interpretive operation language.
Correlation of surface production of negative ions and the work function measured by laser-induced photoelectron current
Authors: Sasao Mamiko , Okabe Yushirou , Fujita Junji , Wada Motoi , Yamaoka Hitoshi , Ramos Henry J.
Published: July 2002

Dynamic change of a negative-ion production surface in an ion source due to cesium introduction and plasma ion bombardment has been studied by simultaneous measurements of photoelectron current by laser irradiation and negative-ion current. Strong dependences of production rates for negative ions by desorption (H−) and by sputtering (Au−) on the work function monitored by photoelectron current were observed. Peaks on mass spectra corresponding to He− were observed only when the monitoring signal indicated that the work function of a molybdenum-cesium surface was near the minimum.
X-mode broadband reflectometric density profile measurements on DIII-D
Authors: Doyle E. J. , Lehecka T. , Luhmann N. C. , Peebles W. A. ,   the DIII-D Groupa)
Published: July 2002

A 50–75 GHz, X-mode, broadband reflectometer system is installed and operational on DIII-D. Density profiles have been obtained under a wide range of operating conditions, including Ohmic, L-, and H-mode operation. Good agreement has been found with profiles obtained by Thomson scattering, but only with the use of fast sweeps. Profiles are calculated from the line-integrated phase data using a stable numerical inversion algorithm. Using these techniques, and allowing for the reset time of the tube, density profiles can be measured every 2.5 ms. The system is still under development: By adding an additional 50–75 GHz BWO and mixers, the system will be reconfigured to also act as a correlation reflectometer.
Neutron diagnostic for MTX
Authors: Ogawa T. , Oasa K. , Hoshino K. , Odajima K. , Maeda H. ,   The Microwave Tokamak Experimental Team
Published: July 2002

A neutron diagnostic system has been installed on the MTX tokamak. The diagnostic will be used to measure both the peak ion temperature and the ion response to intense free-electron laser microwave pulses (140–250 GHz, 1–8 GW, 20–50 ns). High-speed measurements are important for studying the intense microwave absorption process. A plastic scintillator with a polymer-clad silica bundle is used for fast time response detection. Five-channel proportional counters and fission counters are used to monitor the neutron yield for a source strength from 108 to 1013 n/s. This sytem has been calibrated with a 252Cf neutron source in the vacuum vessel and is being tested using the MTX ohmic plasma.
End effect in a coaxial cylindrical viscometer
Authors: Kobayashi Hiroshi , Nashima Takeshi , Okamoto Yoshizo , Kaminaga Fumito
Published: July 2002

The end effect in a coaxial cylindrical viscometer was determined as an effective length of an inner cylinder (bob) using the multiple bob method. In this viscometer, the data are for a rotating bob and not for a rotating cup. The end correction appears to increase over the Reynolds number 10, even in low viscosity and Newtonian liquids. It is shown that a conical end of the bob and a wide gap between the bob and cup give a larger end correction. The visualization of the liquid flow at the bottom of the bob makes it clear that the stream lines enter into the annular gap even in Couette flow, which is supposed to disturb the flow in the gap. With the increment of the Reynolds number, these entrances become larger, although the flow is not Couette but Taylor and turbulent flows.
Tunable x-ray polarimeters for synchrotron radiation sources
Authors: Hart M. , Siddons D. P. , Amemiya Y. , Stojanoff V.
Published: July 2002

We describe the design and optical characteristics of a tunable x-ray polarimeter set up at the National Synchrotron Light Source at Brookhaven. Initially, the energy range from 7.0 to 9.2 keV is covered with a polarization extinction ratio greater than 10 000 and a statistically limited sensitivity of 70 μrad in measurements of optical rotary power. First spectroscopic measurements on a wide range of cobalt compounds show optical activity, Faraday rotation, and circular dichroism in the energy region close to the cobalt K edge. More recently we have worked on a variety of samples containing iron near the iron K edge.
A low power 2.45 GHz ECR ion source for multiply charged ions
Authors: Liehr M. , Trassl R. , Schlapp M. , Salzborn E.
Published: July 2002

An electron-cyclotron-resonance ion source (ECRIS) designed for use on a high voltage terminal that has limited power availability and space has been built. To reduce the power consumption of the ion source, the necessary magnetic fields were produced entirely by permanent magnets. Eighteen FeNdB magnets divided into three hexapolar arrangements yielded a min-B structure with an axial magnetic mirror ratio of 4:1. The microwave power at a frequency of 2.45 GHz with up to 300 W cw was supplied to the plasma by means of a slotted line radiator. This antenna, known as a Lisitano-Coil, allowed the use of a plasma vessel much smaller in diameter than is usually required by the wavelength of the utilized microwaves. The ion source produced stable beams of multiply charged ions at various intensities up to a total ion current of 8 mA for oxygen.
Extraction characteristics of Na and Na2 negative ions from a small multicusp ion source
Authors: Yamaoka H. , Wada M. , Sasao M. , Tong X. M. , Fujita J.
Published: July 2002

Negative sodium ions and negative dimer ions of sodium are extracted from a sodium plasma. The extraction characteristics of Na− and Na2− from a low power discharge (about 1 W) through a single aperture (φ1.5 mm) are described. Both extracted currents of Na− and Na2− increase with the temperature of the heat shield inside the discharge chamber. The current ratio of Na− to Na2− is almost constant independent of discharge voltage. By increasing the discharge power, the value of the bias voltage of the plasma electrode that gives the optimum extraction currents of Na− and Na2− increases. The extracted current of Na2− is lower than that of Na− by two orders of magnitude.
Open-ended coaxial-line technique for the measurement of the microwave dielectric constant for low-loss solids and liquids
Authors: Jiang G. Q. , Wong W. H. , Raskovich E. Y. , Clark W. G. , Hines W. A. , Sanny J.
Published: July 2002

A system which enables fast and reliable measurements of the dielectric constant over continuous microwave frequency ranges for both solid and liquid low-loss materials is described. The main thrust of this work is the application of the open-ended coaxial-line probe technique, which has been used previously for soft biological materials, to low-loss solid samples. Using the instrumentation and procedure presented here, the dielectric constant for low-loss solids can be measured absolutely to ±2%–3% with routine care. The uncertainty can be reduced by about a factor of 2 by averaging several measurements. It is also smaller for liquid samples. This application features the use of relatively simple and readily available microwave components. Also, it is shown that a simple empirical relationship can be used to obtain the bulk dielectric constant from samples of a material in the form of thin slabs. The experimental results which are presented here for kapton, Teflon, Corning glass No. 0211, soda lime glass, magnesium oxide, sapphire, silicon, alumina, and lanthanum aluminate, as well as carbon tetrachloride, compare favorably with existing literature values.
High-performance InGaAs photodetectors on Si and GaAs substrates
Authors: Ejeckam F. E. , Chua C. L. , Zhu Z. H. , Lo Y. H. , Hong M. , Bhat R.
Published: July 2002

In this work, we demonstrate record low dark current operation of InGaAs (1.55 μm) p-i-n photodetectors on both silicon and gallium arsenide substrates using a wafer bonding technique. The photodetectors were made by first bonding the p-i-n epitaxial layers to the Si and GaAs substrate followed by chemical removal of the host (InP) substrate from the p-i-n structure. The photodetector was then fabricated atop the newly exposed p-i-n epilayers. Dark currents of as low as 57 pA on a GaAs substrate and 0.29 nA on a Si substrate were measured under 5 V reverse bias. The responsivity at 1.55 μm wavelength was measured to be 1 A/W, corresponding to an external quantum efficiency of 80%. The series resistance measured across the bonded interface gave 17 Ω on GaAs and 350 Ω on Si, respectively.
Negative metal-ion source for secondary-ion mass spectrometry
Authors: Yurimoto Hisayoshi , Mori Yoshiharu , Yamamoto Hironori
Published: July 2002

A small, compact negative-ion source based on plasma sputtering has been developed for secondary-ion mass spectrometry (SIMS). It can make precise measurements of the oxygen isotope ratios in minerals. From a copper sputter target, a high-density 63Cu− ion beam of 3 mA cm−2 has been obtained as the primary-ion beam with a size of 100 μm in diameter. The mass distribution of the ion beam is 99% Cu− and 1% Cu−2 ions; other ionic species comprise less than 0.1%. A typical beam stability for 10 min has been achieved at 0.4% (σ). These performances of the negative-ion source are useful to perform in situ analyses of insulator materials in SIMS. As an application, the high-mass resolution spectra for three isotopes of oxygen secondary ions from an insulator sample bombarded by the 63Cu− ion beam was studied.
Phonon-assisted transmission in resonant interband tunneling devices
Authors: Lyanda-Geller Yu. B. , Leburton J.-P.
Published: July 2002

We demonstrate that phonon-assisted transmission may play a considerably lower role in interband tunneling structures than in intraband tunneling based devices as a result of the symmetry difference between electron and hole states. An example of current–voltage characteristics is calculated for resonant interband tunneling structure with confined electron and hole states.
New approach of measuring the Q factor of a microwave cavity using the cavity perturbation technique
Authors: Subramanian V. , Sobhanadri J.
Published: July 2002

A new approach of measuring the quality factor of the reflection type microwave cavity resonator for calculating the complex dielectric permittivity of solid and liquid samples in the cavity perturbation technique is proposed. This approach, based on the measurement of reflected power from the cavity at resonance, effectively reduces the measurement procedure and increases the accuracy. As the quality factor can be measured very fast using this approach, this approach can be extended to monitor the conductivity decay of the semiconductor samples.
Hardware architecture for real-time laser range sensing by triangulation
Authors: Dalglish R. L. , McGarrity C. , Restrepo J.
Published: July 2002

A hardware-based system is described which generates a 3D mapping directly into a memory array of all surfaces visible in its field of view. The system uses a conventional scanning strip-light illumination technique and a CCD camera. However, instead of processing the 2D camera data in software, dedicated hardware detects and locates all visible surface elements and automatically loads the 3D coordinate and brightness data direct from the detection hardware into dual-ported memory. This allows the hardware to operate in real time at camera speeds and allows a very compact representation of the scene information in the natural coordinate frame of a triangulation-based system.
Isoelectronic line intensity ratios for plasma electron temperature measurement (invited)
Authors: Marjoribanks Robin S. , Budnik Fredric , Kulcsár Gábor , Zhao Liang
Published: July 2002

Strictly speaking, temperature is uniquely defined only in plasmas which are in complete thermodynamic equilibrium. In typical laser-produced plasmas, measurement of electron temperature amounts to a parametrization of some part of the distribution of electron energies, typically inferred from the recombination continuum, or from the ratio of spectral lines that are implicitly dependent on the electron distribution. Where the plasma is highly transient, suffers appreciable opacity, or is subject to a background radiation field, the interpretation of temperature from disparate spectral lines can become untrustworthy. For these complicated plasmas, a conceptually simpler spectral line diagnostic offers great advantages. A technique has been introduced that begins with plasmas that include two elements of similar atomic number, in a known ratio, and compares isoelectronic lines from ions that differ only in their nuclear charge Z, and thus in their ionization potentials χi. Since these two have different values of the same dimensionless parameter Te/χi, the ratio of intensities of isoelectronic lines can be interpreted to determine the temperature Te. The technique and its areas of advantage are described, the applications made to the special problems of laboratories elsewhere are summarized, and this particular progress in application to laser plasmas produced by high-intensity picosecond pulses are reported here.
Initial results of the 2.45 GHz excitation of the superconducting ECR ion source in its high-B modea)
Authors: Srivastava A. K. , Antaya T. A.
Published: July 2002

The ‘‘frequency squared scaling’’ law, relied upon to enhance the production of high charge state ions from electron cyclotron resonance (ECR) ion sources, indicates that low frequencies of operation may not be viable for production of high ion densities, and hence for the production of high charge state ions. The superconducting electron cyclotron resonance ion source (SCECR) at the National Superconducting Cyclotron Laboratory is a fully superconducting, hexapole stabilized tandem mirror ECR ion source with a multimode microwave cavity. When operated at its optimized high magnetic field (high-B) mode at 6.4 GHz, the high charge state current output of the SCECR approaches all existing ECR ion sources, including higher requency ECR ion sources (ECRIS). In this study, the SCECR is operated at 2.45 GHz in its high-B mode that is scaled down for that frequency of operation. Initial results with oxygen and argon ion production at 2.45 GHz are presented. It is demonstrated that the SCECR can produce a plasma from which multiply charged ions of up to O7+ and Ar13+ can be extracted with ion current intensities comparable to several higher frequency ECRIS. This study concludes that 2.45 GHz is indeed a viable frequency for production of moderate intensities of multiply charged ions. This may lead to a simpler, and more cost effective microwave apparatus, with a less demanding magnetic field configuration.
Preamplifier for electric-current noise measurements at low temperatures
Authors: Birk H. , Oostveen K. , Schönenberger C.
Published: July 2002

We have developed a current preamplifier that operates in a liquid-helium bath cryostat. It has been optimized for the measurement of dynamical electric-current fluctuations (noise) of high-impedance sources R≳100 MΩ. A bandwidth of up to 400 kHz has been achieved by effectively minimizing the capacitance of the input transistor with a dynamical feedback. The amplifier measures current noise in a scanning tunneling microscope (STM). It enables the measurement of shot noise for currents as low as 30 pA (sampling rate 5 s) for a high-impedance source with a resistance of R≳1 GΩ, a value typical for tunneling resistances in STM.
ITER physics program and implications for plasma measurements (abstract)
Authors: Mukhovatov V. , Costley A. E. , Bartiromo R. , Boucher D. , Fujisawa N. , Gribov Yu. , Janeschitz G. , Johnson L. , Kasai S. , de Kock L. , Marmar E. , Muraoka K. , Nagashima A. , Orlinski D. , Ortolani S. , Perkins F. , Petrov M. , Post D. , Putvinski S. , Rosenbluth M. , Sauter O. , Stott P. E. , Strelkov V. , Vayakis G. , Walker C. , Wesley J. C. , Yamamoto S. , Young K. M. ,   Joint Central Team and Home Teams
Published: July 2002

Key objectives of the first ten years of ITER operation are the investigation of the physics of burning plasmas and the demonstration of long-pulse ignited plasma technologies. These include studies of plasma confinement and stability, divertor operation, disruption mitigation and control, noninductive current drive, and steady state operation under conditions when the plasma is heated predominantly by alpha particles. The ITER operational plan envisages two and a half years for commissioning and initial operation with hydrogen plasmas at up to 100 MW of auxiliary heating power when initial tests of divertor operation and evaluation of disruption effects will be made. In order to meet the operational and programmatic goals, it will be necessary to make a wide range of plasma measurements. In this article the preliminary operational plan and physics program are presented and the implications for plasma measurements are outlined.
Application of a novel contactless conductivity sensor in chemical vapor deposition of aluminum films
Authors: Ermakov A. V. , Hinch B. J.
Published: July 2002

A novel contactless method for conductivity sensing is introduced that utilizes a driving coil and two tunable and near resonant coils. The design uses only inexpensive electronic components and a variable frequency rf generator. An algebraic expression for the response has been derived and simulations indicate a linear response to surface conductivity changes over at least four orders of magnitude. The sensitivity is shown to depend on the conductivity of the substrate, with a limit to conductivity changes as low as 10−4 Ω−1 for insulating substrates. An ultrahigh vacuum compatible version of this probe has been used to monitor in situ aluminum thin film growth by chemical vapor deposition on a native oxide covered, highly doped, Si(111) wafer. On this semiconducting substrate (3 Ω−1) a sensitivity to sheet conductivity changes as low as ∼2×10−2 Ω−1 has been demonstrated. The Al films show a discrete jump in differential sheet conductivity associated with Al cluster coalescence during growth.
Electron density profile reconstruction from multichannel microwave interferometer data at W7-AS
Authors: Koponen J. P. T. , Dumbrajs O.
Published: July 2002

A multichannel microwave interferometer has been built for the W7-AS fusion experiment in order to study temporal phenomena in plasma density. For this reason, electron density profile reconstruction methods based on regularization functionals were studied. Simulations showed, that the minimum Fisher-information approach (adapted from tomography) gives better results than the maximum entropy approach. This is due to the fact, that in the minimum Fisher-information method the reconstructed distribution is inherently assumed to be continuous, whereas the maximum entropy method the distribution is assumed to be noncontinuous. The profiles reconstructed from multichannel interferometer data are in good agreement with the profiles measured by other diagnostic systems.
High secondary electron emission for an enhanced electron density in election cyclotron resonance plasma
Authors: Schächter L. , Dobrescu S. , Badescu-Singureanu Al. I. , Baltateanu N.
Published: July 2002

The possibility of increasing the electron cyclotron resonance (ECR) plasma electron density by secondary electron emission has already been pointed out and tested by different authors. In this work the effective secondary electron emission coefficient σeff under electron impact was measured and its evolution studied as a function of the primary electron beam energy and intensity of the target bias. The usual parameters of the ECR plasma such as the electron temperature, the plasma electric potential, and the ambipolar diffusion effects in the ECR plasma chamber have been considered during these measurements. With that end in view a research facility delivering electron beams with energies in the 0–15 keV range and intensities in the 1×10−11–2×10−5 A range was developed. The study of the effective secondary electron emission coefficient σeff was carried out on different targets made of graphite, of metals such as pure and technical Al, Ta, Ni, stainless steel, and of metal-dielectric structures Al–Al2O3. For some Al–Al2O3 structures high values of σeff strongly dependent upon the primary electron beam energy and intensity and upon the target negative bias have been obtained. Such a dependence was not observed for metals. The use of highly emissive metal-dielectric structures in the plasma chamber of an ECRIS should lead to a significant enhancement of the ECR plasma electron density and consequently of the production of highly charged ions.
A high-temperature torsion apparatus for the high-resolution characterization of internal friction and creep in refractory metals and ceramics: Application to the seismic-frequency, dynamic response of Earth’s upper mantle
Authors: Gribb Tye T. , Cooper Reid F.
Published: July 2002

The design and performance of a compact apparatus for the characterization of internal friction in simple shear at elevated temperature (⩽1400 °C) and low frequencies (⩽1 Hz) are described. High-temperature components are fabricated from a refractory molybdenum alloy that is straightforwardly machined. The apparatus has demonstrated, at high temperature, a torque resolution of 2×10−5 N m and an angular displacement resolution of 4×10−6 rad; for the specimen size we employ, these limits provide a shear stress and strain resolution of 2 kPa and 5×10−7, respectively. The apparatus, while applicable to dynamic and static mechanical analyses of any engineering material, was developed for the characterization of internal friction (attenuation) in synthetic silicate aggregates representative of Earth’s upper mantle; we discuss the constraints inherent in the required tests, as they affect apparatus design (including materials selection) and experimental protocol. Static and dynamic data at 1250 °C for a polycrystalline aggregate of ferromagnesian olivine of controlled, uniform (∼3 μm) grain size are presented and discussed.
Torsion cantilever as magnetic torque sensor
Authors: Rossel C. , Willemin M. , Gasser A. , Bothuizen H. , Meijer G. I. , Keller H.
Published: July 2002

A macroscopic cantilever for capacitive torque magnetometry has been developed and tested. It is based on torsion arms in order to obtain better damping against external vibrations than with ordinary cantilevers of similar size but anchored on one side. Microfabricated out of silicon-on-insulator wafers by deep reactive ion etching, the sensor consists of a long (14 mm) and thin (40 μm) cantilever with two capacitive plates, anchored at its center to a rigid frame by two torsion bars having a rectangular cross section (80×40 μm2). By comparing the theoretical and experimental resonance frequencies in three different oscillation modes, we show that the elastic properties of the torque sensor can be evaluated with good accuracy. Calibrations performed with a piece of Fe2O3 audiotape and a cylindrical NdFeB magnet yield a torque sensitivity better than 5×10−13 N m under optimized conditions. This device can also be used as a sensitive Gauss meter to detect magnetic fields down to 10 nT.
Preparation of silver tips for scanning tunneling microscopy imaging
Authors: Iwami M. , Uehara Y. , Ushioda S.
Published: July 2002

A simple reliable preparation method of silver tips for scanning tunneling microscopy imaging with atomic resolution is presented. The procedure is based on two-step electrochemical processing; ac electropolishing and subsequent dc electroetching. The quality of the tip is improved by applying high bias voltage pulses while the tip is within tunneling range. This indicates that the end of the tips are sharpened by field evaporation of silver ions.
Electron cyclotron emission imaging diagnostic system for Rijnhuizen Tokamak Project
Authors: Deng B. H. , Hsia R. P. , Domier C. W. , Burns S. R. , Hillyer T. R. , Luhmann N. C. , Oyevaar T. , Donné A. J. H. ,   RTP team
Published: July 2002

A 16-channel electron cyclotron emission (ECE) imaging diagnostic system has been developed and installed on the Rijnhuizen Tokamak Project for measuring plasma electron cyclotron emission with a temporal resolution of 2 μs. The high spatial resolution of the system is achieved by utilizing a low cost linear mixer/receiver array. Unlike conventional ECE diagnostics, the sample volumes of the ECE imaging system are aligned vertically, and can be shifted across the plasma cross-section by varying the local oscillator frequency, making possible 2D measurements of electron temperature profiles and fluctuations. The poloidal/radial wavenumber spectra and correlation lengths of Te fluctuations in the plasma core can also be obtained by properly positioning the focal plane of the imaging system. Due to these unique features, ECE imaging is an ideal tool for plasma transport study. Technical details of the system are described, together with preliminary experimental results.