bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase modulation in InGaAsP barrier, reservoir, and quantum well electron transfer structures, grown by chemical beam epitaxy
Authors: Glick M. , Monnard R. , Dwir B. , Carlin J. F. , Rudra A. , Dupertuis M. A. , Reinhart F. K. , Weiser G.
Published: July 2002

We have measured phase modulation in the first chemical beam epitaxy grown InGaAsP/InP barrier, reservoir, and quantum well electron transfer structures. We obtain a negative refractive index change, Δn, similar to that found in the InGaAs/InAlAs system. Using new designs to reduce the leakage current in this material system, we obtain a leakage current <1 A/cm2. Our results show an unexpected negative Δn for both positive and negative bias, which we explain using calculations of the wave function.
Shapiro-like steps from a weakly coupled junction prepared with high-T
c superconducting materials
Authors: Kishino Seigô , Kuroda Hideaki , Shibutani Tuneo , Niu Hirohiko
Published: July 2002

A trilayer junction composed of YBa2Cu3Oy/La0.7Ca0.3MnOz/YBa2Cu3Oy is prepared and the current-voltage (I-V) characteristics are examined with and without microwave illumination. The flow of the superconducting current is observed through the trilayer junction. At the same time, the trilayer junction is illuminated with microwaves. Resultant I-V curves show Shapiro-like steps, the spacing of which is different from that of the real Shapiro steps as well as the increase of electrical resistance of the junction by the illumination. It is also observed that the Shapiro-like steps exhibit a kind of negative resistance on the current-voltage curve.
Photoconductivity investigation of the excitonic Auger recombination in GaAs/AlGaAs quantum wells
Authors: Ferreira A. C. , Holtz P. O. , Monemar B. , Sundaram M. , Merz J. L. , Gossard A. C.
Published: July 2002

The recently proposed Auger recombination mechanism in quantum wells (QWs) has been studied by means of excitation-dependent photoconductivity (EDPC) and photoluminescence (PL) in acceptor doped QWs. Free charge carriers are found to be formed although the optical excitation is resonant with the excitons well below the band gap at low temperatures. The carriers are monitored via EDPC measurements or via the enhancement of the free-to-bound transition observed in PL. The prerequisite for an excitonic Auger process in the model proposed is an ionized impurity, accomplished via the two-hole transition of the bound exciton.
Seeding of a titanium sapphire oscillator by a vertical-cavity surface-emitting laser in the nanosecond range
Authors: Boucher Y. , Georges P. , Brun A. , Pocholle J.-P. , Papuchon M.
Published: July 2002

A GaAs/AlGaAs vertical-cavity surface-emitting laser was used to seed a titanium-sapphire laser oscillator. Both lasers were pumped synchronously by the same frequency-doubled Nd:YAG laser in the nanosecond range. Even at low injection level, we obtained a strong narrowing of the emission spectrum of the oscillator (from 30 to 1 nm), as well as its tunability over a broad range of wavelengths (from 775 to 805 nm).
Molecular resolution imaging of physisorbed alcanol monolayers at the liquid/graphite interface with the scanning force microscope
Authors: Elbel N. , Günther E. , Seggern H. von
Published: July 2002

We report on a scanning force microscopy study of self-assembled octadecanol monolayers physisorbed at the liquid/graphite interface. The layers were found to be stable for reproducible imaging with applied forces up to about 1×10−9 N. We were able to observe both the long-range lamella structure of monolayers including domain boundaries, as well as the detailed arrangement of molecules within each lamella.
Phase-unifying mirrors as output couplers of XeCl laser resonators
Authors: Giuri C. , Perrone M. R. , Flori D. , Piegari A. , Scaglione S.
Published: July 2002

A phase-unifying (PU) mirror as output coupler of unstable resonators applied to high-gain, short-pulse XeCl lasers has been realized and tested. A high-mode volume, nearly diffraction limited beam has been extracted from the XeCl laser by using a PU-unstable resonator of magnification M=6.6. The evolution of the output beam intensity distribution along a propagation distance of about 30 m has been tested.
Molecular-beam epitaxial growth of InxAl1−xAs on GaAs
Authors: Chyi Jen-Inn , Shieh Jia-Lin , Lin Ray-Ming , Nee Tzer-En , Pan Jen-Wei
Published: July 2002

The surface reconstruction of InAlAs on GaAs between 490 and 700 °C has been investigated during molecular-beam epitaxial growth. It is found that the surface reconstruction of InAlAs is similar to that of AlGaAs alloy. The (2×1) and (1×1) surfaces occur at a substrate temperature between 490 and 650 °C, while at a temperature above 650 °C, the ordered As-stabilized (3×2 surface appeared during the steady-state growth. InAlAs/GaAs heteroepitaxial layers have been analyzed and reveal that the residual strain in the epilayers is strongly dependent on the composition as well as the thickness of the epilayer. These characteristics are consistent with the InGaAs/GaAs system.
Blue light generation using a high power tapered amplifier mode-locked laser
Authors: Goldberg Lew , Mehuys David
Published: July 2002

Light at 430 nm is generated by frequency doubling the high peak power output of a mode-locked compound cavity laser based on a tapered GaAlAs amplifier. The laser generated a peak 860 nm power of 12.7 W and pulse energy of 450 pJ. Using a 7.1 mm KNbO3 crystal, 45 mW of average blue light power was produced with a peak power of 1.6 W, minimum pulse length of 8.5 ps, and pulse energy of 30 pJ.
Inverse melting of a metastable Nb45Cr55 solid solution
Authors: Michaelsen C. , Oehring M. , Bormann R.
Published: July 2002

An Nb45Cr55 solid solution was prepared by mechanical alloying in a planetary ball mill and investigated by x-ray diffraction and calorimetry. It was found that the structure evolution upon heating exhibited three distinct stages, the first resulting in complete amorphization, whereas the second and third are related to the subsequent crystallization of the amorphous phase. These results are in agreement with the free-energy functions calculated from the thermochemical data of the system. They show that for a composition of Nb45Cr55 a second melting point (often termed ‘‘inverse melting point’’) exists at about 900 °C, below which the undercooled liquid has a lower free energy than the crystalline body-centered-cubic phase.
Intensity variation of photoluminescence in InxGa1−xAs/GaAs multi-quantum-well structures
Authors: Piao Z. S. , Jeon H. I. , Cha S. S. , Lim K. Y. , Suh E.-K. , Lee H. J.
Published: July 2002

We studied the influence of the sample structure on the photoluminescence intensity in terms of carrier diffusion and transfer phenomena in InxGa1−xAs/GaAs multi-quantum-well structures. Carrier injection from the barrier, cap, or buffer layers dominates the generation in the well when the well thicknesses are small and the excitation energy is larger than the band gap of the barrier layer. The carrier transport between wells also plays an important role in the photoluminescence particularly in the shallow wells and can be accounted for by phenomenologically introduced hopping time between wells. The hopping time varies from a few tens of picoseconds to a few hundreds of nanoseconds depending on the well composition and width. The strain relaxation of these strained layer quantum-well structures also leads to the intensity variation as well as the change in the peak position.
Planar-type Ba1−xKxBiO3 Josephson tunnel junctions prepared on SrTiO3 bicrystal substrates
Authors: Inoue Masumi , Imaeda Shigehiro , Tsukino Yoichiro , Fujimaki Akira , Takai Yoshiaki , Hayakawa Hisao
Published: July 2002

We have prepared planar-type Josephson junctions using Ba1−xKxBiO3 thin films deposited on SrTiO3 bicrystal substrates by the rf magnetron sputtering method, and investigated their properties. The current-voltage characteristics of the junctions were those of superconductor- insulator-superconductor junctions and both the Josephson current and the energy gap were observed clearly. The critical current density of the junction was 5.5×102 A/cm2 at 4.2 K and the IcRn product was 2.2 mV. A magnetic field applied perpendicular to the substrate modulated the critical current, which gave a clear Fraunhofer pattern.
Analog operation of a symmetric self-electro-optic effect device based on Wannier-Stark localization, and its gain characteristics: An all-optical analog transistor
Authors: Tominaga Kouji , Hosoda Makoto , Kawashima Kenji , Watanabe Toshihide , Fujiwara Kenzo
Published: July 2002

We propose a novel all-optical analog three-terminal device using a symmetric self-electro-optic effect device based on Wannier–Stark localization (WSL-S-SEED). The optical gain factor is derived theoretically from the ratio between derivatives of the two crossed photocurrent versus voltage curves, and a large gain is predicted near an operating point where the ratio is nearly equal to unity. The principle was verified experimentally using a WSL-S-SEED having the above characteristics, and a sufficient analog modulation of the optical output was observed.
Donor doping in metalorganic chemical vapor deposition of HgCdTe using ethyl iodide
Authors: Mitra P. , Tyan Y. L. , Schimert T. R. , Case F. C.
Published: July 2002

Highly effective donor doping during metalorganic chemical vapor deposition interdiffused multilayer growth of Hg1−xCdxTe is demonstrated using a novel precursor of iodine, ethyl iodide. It is shown that the doping level can be controlled in the range of 7×1014–2×1018 cm−3 with abrupt profiles and without any memory effect. Activation of the iodine as a singly ionized donor is shown to be near 100% at concentrations <1×1017 cm−3. Electron mobilities are ≥1×105 and ≥2×105 cm2/V s at 80 and 20 K, respectively, for concentrations of (1–3)×1015 cm−3 and x values ∼0.22. Auger limited lifetimes of ∼1 μs are observed for these layers at 80 K.
Rapid thermal annealing of MeV erbium implanted LiNbO3 single crystals for optical doping
Authors: Fleuster M. , Buchal Ch. , Snoeks E. , Polman A.
Published: July 2002

LiNbO3 single crystals (x cut) were implanted with 3.5-MeV Er ions with fluences up to 3×1016 cm−2. Upon annealing the implantation-amorphized surface layer regrows epitaxially, displaying either columnar or planar layer-by-layer growth, depending on the rate at which the samples are brought to the final temperature of 1060 °C. Low heating rates (≊10 °C/s) result in columnar regrowth, and 8-h anneals are necessary for complete dissolution of the grain boundaries. In contrast, using a rapid warm-up (100 °C/s), annealing for 1 min at 1060 °C is sufficient to restore a perfect crystal without grain boundaries. The advantage of the short anneal is that it leads to only minimal diffusion broadening of the Er profile. The maximum concentration of optically active Er ions is 0.18 at. %.
Theoretical analysis of a branch line quantum directional coupler
Authors: Vanbésien O. , Lippens D.
Published: July 2002

We propose a new quantum directional coupler which consists of two parallel electron waveguides coupled by branch lines. The component is based on a high mobility modulation-doped heterostructure, where the channel is constricted by a double H gate pattern at nanometer scale. The theoretical analysis is conducted by the solving of the two-dimensional Schrödinger equation in the channel using mode matching techniques. Transmission and reflexion spectra calculated at the four ports of the structure show that 3 dB coupling coefficient along with a directivity of 17 dB can be achieved.
Radiation-induced defects in Czochralski-grown silicon doped with germanium
Authors: Schmalz K. , Emtsev V. V.
Published: July 2002

The formation of vacancy-oxygen complexes (A centers) in Czochralski (Cz)-grown silicon (Cz-Si) with Ge content of 1018–1020 cm−3 due to gamma irradiation was studied by deep level transient spectroscopy and Hall effect measurements. It was found that the A centers are not formed at the beginning of gamma irradiation and can be developed afterward only. In this case, the formation of A centers in irradiated Cz-Si:Ge is thought to be a result of annealing of specific radiation induced defects.
Estimation of electronic confinement in a quantum dot from envelope modulation of Coulomb blockade oscillations
Authors: Sakamoto T. , Hwang S. W. , Nakamura Y. , Nakamura K.
Published: July 2002

Envelope modulation of Coulomb blockade oscillations has been observed in the conductance of a semiconductor quantum dot weakly connected to two reservoirs through tunneling barriers and subjected to magnetic fields. Although the number of conductance peaks per modulation period has been reported to be constant, we find that in moderate magnetic fields the number of peaks per period decreases one by one as gate voltage is changed. This results from the electronic depopulation of a single Landau level per modulation period. Comparing this result with calculated energy levels, the strength of electronic confinement is estimated to be 2.2 meV.
Novel in situ method for locating virtual source in high-rate electron-beam evaporation
Authors: Bhatia M. S.
Published: July 2002

The concept of virtual source simplifies calculation of thickness distribution on extended substrates in high rate vacuum coating employing electron-beam heating. The height of the point (virtual source), from which vapor can be assumed to emanate in accordance with Knudsen’s cosine law, to yield the experimentally obtained thickness distribution, is calculated and this establishes the position of virtual source. Such as post facto determination is cumbersome as it is valid for the prescribed material evaporating at a certain rate in a specified geometry. A change in any of these entails a fresh measurement. Experimenters who use a large number of materials and deposit at different rates therefore have to carry out a number of trials before they can locate the virtual source at the desired deposition parameters. An in situ method for obtaining virtual source position can go a long way in reducing the labor of these experiments. A novel in situ method is described to locate the virtual source.
Atomic layer epitaxy of AlAs using ethyldimethylamine alane as a new aluminum source
Authors: Kano Nobuo , Hirose Shingo , Hara Kazuhiko , Yoshino Junji , Munekata Hiro , Kukimoto Hiroshi
Published: July 2002

Atomic layer epitaxy (ALE) of AlAs layers has been studied with the alternate supplies of ethyldimethylamine alane (EDMAAl) and arsine as aluminum and arsenic sources. Self-limiting growth at either one- or two-monolayer per source supply cycle is clearly observed under the specific growth conditions defined by the substrate temperatures (250–650 °C) and the flow rates of EDMAAl (0.8–1.1 and 1.5–1.7×10−2 sccm). Carbon concentration in the resultant AlAs layers is estimated to be about 1017–1018 cm−3.
Effects of radio frequency radiation on the dc SQUID
Authors: Koch R. H. , Foglietti V. , Rozen J. R. , Stawiasz K. G. , Ketchen M. B. , Lathrop D. K. , Sun J. Z. , Gallagher W. J.
Published: July 2002

The effects of radio frequency radiation on the dc SQUID are examined. Simulations show how the shape of the SQUID transfer characteristic is distorted by radio frequency interference (RFI). How this affects three commonly used SQUID modulation methods is discussed, and the results explain why we experimentally observe the bias current reversing readout method to be the least susceptible to RFI. The commonly seen increase in the low frequency flux noise power spectrum of dc SQUIDs in unshielded environments is also explained.
Time dependence of the electron-phonon coupling parameter of niobium
Authors: Mihailidi Margarita , Alfano R. R.
Published: July 2002

The time dependence of the electron-phonon coupling parameter for niobium for temperatures ranging from 292 to 7 K has been measured showing complex behavior and is in agreement with existing theory. The electrons are found to thermalize with phonons in 370 fs at 292 K and 250 fs at 7 K. The electron-phonon coupling parameter is found to decrease with decreasing temperature.
Experimental study on operation at room temperature of transverse flow carbon monoxide laser excited by radio frequency discharge
Authors: Uehara Minoru , Kanazawa Hirotaka
Published: July 2002

A high output and high conversion efficiency transverse flow carbon monoxide laser has been developed for operation at room temperature. The adoption of radio frequency discharge for excitation has permitted obtaining at room temperature (289 K), without xenon addition to the gas, a maximum output of 665 W at a conversion efficiency of the 10.7%. The output characteristics observed from the experiment are discussed, and the factors that effect laser output are considered.
Persistent photoconductivity in thin undoped GaInP/GaAs quantum wells
Authors: Elhamri Said , Ahoujja M. , Ravindran K. , Mast D. B. , Newrock R. S. , Mitchel W. C. , Brown G. J. , Lo Ikai , Razeghi Manijeh , He Xiaguang
Published: July 2002

Persistent photoconductivity has been observed at low temperatures in thin, unintentionally doped GaInP/GaAs/GaInP quantum wells. The two-dimensional electron gas was studied by low field Hall and Shubnikov–de Haas effects. After illumination with red light, the electron concentration increased from low 1011 cm−2 to more than 7×1011 cm−2 resulting in an enhancement of both the carrier mobility and the quantum lifetime. The persistent photocarriers cannot be produced by DX-like defects since the shallow dopant concentration in the GaInP layers is too low to produce the observed concentration. We suggest that the persistent carriers are produced by photoionization of deep intrinsic donors in the GaInP barrier layer. We also report observation of a parallel conduction path in GaInP induced by extended illumination.
Evidence of an energetic ion bombardment mechanism for bias-enhanced nucleation of diamond
Authors: McGinnis Sean P. , Kelly Michael A. , Hagström Stig B.
Published: July 2002

The effect of substrate bias voltage was investigated for bias-enhanced diamond nucleation pretreatments of diamond thin films in a microwave plasma chemical vapor deposition reactor. A critical bias voltage of approximately −200 V was observed for nucleation density enhancement from ∼104 cm−2 to ∼1010 cm−2. Furthermore, the nucleation density under bias conditions was five orders of magnitude lower for a small silicon region electrically isolated from the otherwise negatively biased silicon substrate. These results confirm that bombardment of the substrate by energetic cations plays a significant role in the diamond nucleation mechanism during bias pretreatments.
Low-temperature growth of SiC thin films on Si and 6H–SiC by solid-source molecular beam epitaxy
Authors: Fissel A. , Schröter B. , Richter W.
Published: July 2002

Epitaxial growth of stoichiometric SiC on Si(111) and 2°–5° off-oriented 6H–SiC(0001) substrates was carried out at low temperatures (800–1000 °C) by means of solid-source molecular beam epitaxy controlled by a quadrupole mass spectrometry based flux meter. The films were obtained on Si-stabilized surfaces showing (3×3) and (2×2) superstructures in the case of SiC(0001). The reflection high-energy diffraction (RHEED) patterns and damped RHEED-oscillations during the growth on 6H–SiC(0001) at T≳900 °C indicate that two-dimensional nucleation on terraces is the dominant growth process.
Continuous rotatable electrical feedthrough
Authors: Malic R. A. , Chaban E. E.
Published: July 2002

A rotatable electrical feedthrough, maintaining continuous contact (as opposed to a wiper arm), is described. The connector takes up rotations of at least 270° by means of a compact clock-spring arrangement.
Measurements of viscosity and density by a vibrational sphere
Authors: Guozhen Zhu , Laoli Xu
Published: July 2002

Our purpose is to explore a laboratory method for the relative measurements of viscosity and density for small samples of Newtonian fluids. A sphere was connected to one leg of a glass tuning fork and was electrically excited. The viscosity and the density of the measured fluid, in which the sphere was immersed, was calculated from the resonance frequency and resonance resistance of the system. The parameter of the vibrational system was selected according to an analysis of the theoretical condition of Stokes’ equation for a vibrational sphere. We calibrated the system in the range of 4–800 cP for viscosity and 0.82–0.88 g/cm3 for density. The maximum error of this sytem is less than ±1.5% for density measurements and ±5% for viscosity measurements.
Versatile infrared cell for i
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i
t
u transmission IR studies of heterogeneous catalysts
Authors: Friedman Robert Mark , Dannhardt Harry C.
Published: July 2002

An infrared cell is described that allows catalytic materials to be investigated by conventional transmission measurements at temperatures ranging from −196 to 600 °C over the spectral region from 10 to 6000 cm−1 using silicon windows and over any desirable spectral range using easily replaceable windows of choice. The sample environment can span vacuum to supra-atmospheric pressure. The thermal response of the cell is rapid, allowing it to be used for temperature programmed desorption studies along with the spectral examination of the catalyst. The sample can be in the form of a self-supporting wafer located at the center of the cell body and requiring the gas stream to pass through it. This configuration allows the cell to be used as a differential microreactor. The gas path length is short and the volume is small in order to minimize the spectral background from the ambient gas environment and to allow easy and rapid change of its composition.
Time-of-flight Thomson backscattering technique for large fusion devices
Authors: Salzmann H. , Hirsch K. , Gruber J. , Röhr H. , Brederlow G. , Witte K.
Published: July 2002

The application of 180° Thomson scattering to the JET tokamak for measuring electron temperature and density profiles is discussed. Spatial resolution along the laser beam is achieved by the use of subnanosecond laser pulses and high-speed detection allowing time-of-flight measurements. Gating tests of MCP photomultiplier and measurements of the stray light level in a full-scale optical setup show that the severe stray light problem in a backscatter geometry can be handled. Tests of a frequency-doubled iodine laser system are reported which demonstrate that a 1-pps operation of the system is feasible.
Composite video generation for an OMA vidicon detector
Authors: Cascio Horace E. , Balaban Robert S. , Smith Paul D.
Published: July 2002

A commercial vidicon detector, designed for scientific purposes with user-controlled target scanning, was modified to produce a computer-controlled optional composite video signal permitting rapid acquisition of two-dimensional data. A video preamplifier and a processing amplifier were incorporated in the camera head, and a special function card, providing the composite video signals, was inserted into a spare slot of the control unit; minor wiring changes were required to accommodate these modifications. A resolution in excess of 400 lines is obtained in the horizontal direction, and a 10-μ reticle is clearly resolved through a microscope.
Fast laser-induced aerosol formation for visualization of gas flows
Authors: Hassa C. , Hanson R. K.
Published: July 2002

Aerosol seeding of gas flows by laser-induced particle formation is demonstrated. A pulsed Nd:YAG laser (1.06 μ) is used to optically break down a mixture of SF6 and H2 in an inert carrier gas. Small sulfur particles form quickly and can be used to visualize gas flows by Mie scattering.
Apparatus for determining high-temperature, high-pressure coal plastic behavior under rapid heating conditions
Authors: Fong William S. , Peters William A. , Howard Jack B.
Published: July 2002

This paper describes a rapid-heating, fast response plastometer for measuring the plastic behavior of softening coals under a new range of conditions of industrial and scientific importance previously unattainable with conventional instruments. The results give insights on feedstock transformations in high-temperature processes such as gasification and combustion. The instrument determines the torque required for constant rotation of a thin disk embedded within a thin layer of coal heated between two parallel, metal plates. Heating rates, final temperatures, and sample residence times at final temperature can be separately selected and controlled over the ranges 40–800 K/s, 600–1250 K, and 0–40 s, respectively. The device is enclosed in a vessel designed for hydrogen or inert-gas pressures up to 10 MPa. Data from this apparatus are consistent with a physicochemical description of coal plasticity and with predictions from a simple model. Application of this instrument to other thermoplastic solids should be straightforward.
Laboratory-scale controlled-atmosphere chamber for use with premium coal samples
Authors: Filla B. James , Callanan Jane E.
Published: July 2002

The recent availability of premium coal samples makes it desirable to have the capability for working with these materials, in one’s own laboratory, in an atmosphere which can be controlled. A controlled-atmosphere chamber, large enough to allow for processing samples yet small enough to fit easily in an ordinary laboratory, has been designed and fabricated. The overall cost of this controlled-atmosphere chamber was competitive with commercially available systems. The major advantages of this specific system include: convenient size and reversible design for use in a limited work space; incorporation of a full vacuum antechamber that minimizes loss of the working chamber purified atmosphere; and a recirculating system with a bypass valve arrangement allowing separate or combined operation of oxygen and moisture removal systems. The design features were combined to create a unique apparatus capable of both the specific use for which it was intended and general controlled-atmosphere chamber applications. Compatible modular-design work chambers could have been purchased from commercial vendors; however, it still would have been necessary to custom fabricate both the antechamber and recirculation system to meet the requirements of the anticipated experimental work.
Advantages and limitations of eddy current displacement sensors in the measurement of standing wave ratios of transverse waves in stranded metal cables
Authors: Noiseux Denis U. , Beauchemin Réal
Published: July 2002

Eddy current displacement sensors have been used successfully to measure the standing wave ratios (SWR) of transverse waves in stranded metal cables. The difficult measurements are those of the minima. The effects of inclined transverse motions, longitudinal waves, and torsional waves on the measurement of the minima are discussed. Adequate centering of the sensor on the axis of the cable is critical; this centering is best done with conjugate sensors.
Gas phase cryogenic photoacoustic detector
Authors: Keffer Charles E. , Conner Charles P. , Smith William H.
Published: July 2002

A variable temperature cryogenic photoacoustic detector has been developed for making spectroscopic measurements on gas phase molecules. Temperatures in the range of 77–300 K are obtained with this device.
Microprocessor-based system for automatic x-ray diffraction and fluorescence
Authors: de Souza Astor M. , Scavarda do Carmo Luiz C. , Pereira Vandick J. E. , Soares Edmundo A.
Published: July 2002

A system based on a Z-80 microprocessor is used for x-ray analysis and goniometer control.
Large area lanthanum molybdenum electron emitters
Authors: Goebel D. M. , Hirooka Y. , Campbell G. A.
Published: July 2002

A large area, indirectly heated cathode capable of continuous, high- current electron emission is described. The cathode assembly utilizes an indirectly heated lanthanum molybdenum carbide (LaMo) disk as the thermionic electron emitter. Other cathode shapes are also discussed. The disk cathode emits up to 500 A of electrons at an average of 11 A/cm2 in continuous operation in a plasma discharge. LaMo material is machinable and is not fragile even after extended operation. Careful fabrication and conditioning of the LaMo carbide surface is required. The electron emission capability depends strongly on producing the proper fine grain structure of the molybdenum carbide surface layer to allow adequate diffusion of lanthanum to the surface. Failure to produce the correct surface structure results in intermittent electron emission. The electron emission was not affected by exposure to both air and water during operation, but the emission is poisoned by small amounts of tungsten on the surface. After proper preparation, this intermediate temperature electron emitter is very rugged and has a long lifetime.
Interfacing the Biomation 1010 to a 6502 based microcomputer
Authors: Sokol Paul
Published: July 2002

An interface to a Biomation 1010 transient recorder has been built with hardware and software sufficiently general for use with any computer which is based on the 6052 microprocessor.
High brightness electron beam produced by a ferroelectric cathode
Authors: Jiang B. , Kirkman G. , Reinhardt N.
Published: July 2002

We report experimental measurements of a high brightness electron beam produced by a ferroelectric cathode. Up to 36 A of current (10 A/cm2) were obtained at a voltage of 22.5 kV. Electron beam emission was obtained with a dc voltage held between the cathode and anode, and a gate pulse of 1–2 kV applied across the sample. The beam normalized emittance was measured at 10 kV to be 5 mm mrad with a normalized beam brightness of 1.2×1011 A/m2 rad2. This value of beam brightness exceeds that of thermionic cathodes. The ferroelectric cathode emission is found to exceed that of a thermionic cathode using the same geometry.
Diagnostic instrument for the measurement of poloidal magnetic fields in tokamaks
Authors: West W. P. , Thomas D. M. , Ensberg E. S. , deGrassie J. S. , Baur J. F.
Published: July 2002

A diagnostic system has been developed to measure the direction of the local magnetic field within the plasma of a tokamak by making use of Zeeman splitting in an injected neutral lithium beam. A linearly polarized dye laser is used to pump the π component of the 2S-2P resonant transition. The laser polarization is rotated at a fixed frequency, and phase analysis of the subsequent fluorescence identifies the local field direction. The instrument can monitor many radial points within the plasma simultaneously, allowing a current density profile to be determined on a single shot basis.
Resolution characteristics of Lawrence Livermore National Laboratory soft x-ray streak cameras
Authors: Glendinning S. G. , Medecki H.
Published: July 2002

Eight Lawrence Livermore National Laboratory (LLNL) x-ray streak cameras have been characterized for spatial resolution and for the line spread function contribution to the temporal resolution. The contrast transfer function of a gold resolution grid of varying spatial frequency was measured for each camera. In addition, the image intensifier tube normally used for LLNL streak cameras (ITT 4113) was characterized separately. Limiting visual resolution for the system was found at 10 line pairs/mm (lp/mm) at camera photocathode with a corresponding temporal line spread function of 440 μm FWHM. Limiting visual resolution for the intensifier was found at 14 lp/mm at intensifier photocathode. Comparisons to commerical streak camera models are underway.
Physics analysis database for the DIII-D tokamak
Authors: Schissel D. P. , Bramson G. , DeBoo J. C.
Published: July 2002

Centralized databases for handling reduced data for physics analysis have been implemented for the DIII-D tokamak. Each database record corresponds to a specific snapshot in time for a selected discharge. Features of the database environment include automatic updating, data integrity checks, and data traceability. Reduced data from each diagnostic comprises a dedicated dataset (a subset of the database) with quality assurance provided by a physicist. For the confinement database, these datasets will be used to create profile datasets which will be input to a transport code to create a transport dataset. The databases are implemented on a Digital Equipment Corporation VAX 8600 running VMS. The database management system is S1032 from Software House, Inc.
Hydrostatic pressure effect on the minimum temperature of a helium-3 cryostat
Authors: Takács L. , Takács J. , Reiff W. M. , Ramsden J. D.
Published: July 2002

A simple, efficient helium-3 cryostat for Mössbauer spectroscopy based on a closed-cycle carbon sorption pump is described. An unexpected variation of the minimum available temperature as a function of measurement time is described and explained as a hydrostatic pressure effect connected to the density maximum of liquid helium-3 at 0.515 K.
Soft x-ray imaging by a commercial solid-state television camera
Authors: Matsushima Isao , Koyama Kazuyoshi , Tanimoto Mitsumori , Yano Masaaki
Published: July 2002

A commerical, solid-state television camera has been used to record images of soft x radiation (0.8–12 keV). The performance of the camera is theoretically analyzed and experimentally evaluated compared with an x-ray photographic film (Kodak direct exposure film). In the application, the camera has been used to provide image patterns of x rays from laser-produced plasmas. It is demonstrated that the camera has several advantages over x-ray photographic film.
Null ellipsometer for the studies of thin films at gas–water interface
Authors: Ducharme Daniel , Tessier Alain , Leblanc Roger M.
Published: July 2002

Ellipsometry is a sensitive nondestructive optical technique which can be successfully used for determining the thickness of an optically transparent thin film deposited on a dielectric substrate. In this laboratory we have constructed a vertical null-type ellipsometer which has been used with a homemade aluminum Teflon-coated Langmuir trough, to study thin films at gas–water interface. Surface pressure, surface potential, and ellipsometric measurements have been performed simultaneously. Ellipsometric measurements have been done directly on the aqueous substrate contained in the trough, with and without the film, with reproducibility (±0.02°) and good signal stability (±0.1 mV) on the 10-mV scale. The performance of the homemade instrument had been checked against the known ellipsometric properties of spread arachidic acid on acidic water solution. In this paper, details of construction and performance of the ellipsometer as well as characteristics of the trough and ellipsometric study of β-palmitoyl-α-oleoyl-L-α-phosphatidylcholine is presented. Stability of the photometric signal as a function of the structure of the film-forming molecules is also discussed.
An automated light scattering system and a method for the i
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u measurement of the index of refraction of soot particles
Authors: Charalampopoulos T. T.
Published: July 2002

An automated laser light scattering system which uses a single detector to measure both classical and dynamic light scattering from soot particles in flames was designed, fabricated, and tested. Measurements of classical and dynamic light scattering along with extinction for a premixed methane/oxygen flame are presented, as a function of position in the flame. It is demonstrated that by introducing a theoretical relationship between the real and imaginary parts of the complex index of refraction, the optical properties of Rayleigh size soot particles can be directly inferred from such in situ measurements. The sensitivity of the inferred quantities to the measured parameters is assessed. Soot particles sizes, number densities and optical properties were simultaneously inferred. The potential for determining the in situ refractive indices of soot has been demonstrated.
Scaling to high average powers of a flash x-ray source producing nanosecond pulses
Authors: Davanloo F. , Bowen T. S. , Collins C. B.
Published: July 2002

Described here is the scaling of a repetitively pulsed, flash x-ray source to yield 140-mW average power in 15-ns pulses of radiation near 1 Å. Interchangeability of discharge anodes has provided for a significant fraction of the output to be extracted in the K lines of Cu, Mo, Nb, and Ag. In less than 1 min of experimental time, a peak spectral density is radiated that exceeds 1×1018 keV/keV. For some applications this device can offer a tabletop alternative to laser plasma x rays and to synchrotron radiation.
Low-pass filter in flux transformer circuits for SQUID magnetometers
Authors: Weyand K.
Published: July 2002

In order to eliminate extraneous alternating fields in magnetic field measuring setups using SQUID magnetometers, a compensating network has been developed which exhibits low-pass filter characteristics. Guidelines will be given for the optimal parameters of such circuits. On the basis of a network realized with a corner frequency of 1 Hz and with a stop-band attenuation of about 20 dB the reason why the theoretically total compensation is not achievable in practice is attributed to mismatched components and to eddy currents in the Dewar walls.
Micro Kelvin probe for local work-function measurements
Authors: Baumgärtner H. , Liess H. D.
Published: July 2002

This article describes a miniaturized Kelvin probe with a lateral resolution of 40 μm. Applied to a conducting or semiconducting surface, it allows a microscopic imaging of the difference of the work functions between the Kelvin probe and a sample. The signal resolution is better than 6 mV with an integration time of 300 to 400 ms, which is sufficient for most of the applications. The necessary steps to optimize the signal processing are described in detail.
Direct display of the valence-band dispersion in ultraviolet photoemission spectroscopy: Application to GaSe
Authors: Lévêque G.
Published: July 2002

We present the first experiment performed with a photoemission spectrometer displaying the image of the valence-band structure on a fluorescent screen in real time. The smooth image obtained after a 50-s integration time has been processed to improve the contrast and shows the valence band of GaSe as continuous lines. A three-dimensional character is apparent which is found to correspond to the contribution of the rhombohedral γ type of stacking in this layered compound.
Diamond synthesis using a new type of high-pressure apparatus
Authors: Kawashima Y.
Published: July 2002

A conversion of graphite into diamond was carried out by a new type of high-pressure apparatus using thermal stress. In this apparatus, high pressures and high temperatures were simultaneously generated by heating a metallic ball embedded in a ceramic cylinder. It was confirmed by an x-ray diffraction study that a part of the graphite sandwiched between the metallic ball and ceramic cylinder is transformed into diamond.
New compliant mounting for coupling microlensed fibers to semiconductor laser diodes
Authors: Benner A.
Published: July 2002

We demonstrate an optical fiber mounting device which allows microlensed fibers to be pressed repeatedly against the cleaved facets of semiconductor laser diodes without causing impact damage to the facet. The device constrains the fiber against lateral movement while using the resilience of a second fiber acting as a weak spring to allow compliance along the optical axis. Stability of the microlensed fiber is not affected.
Composite pulse magic echo sequence in three-level systems
Authors: Gengying Li , Dongsheng Wang , Xuewen Wu
Published: July 2002

Composite pulse quadrupole echo sequences significantly reduce distortions due to finite pulse-width effects, but they also produce phase dispersion leading to distortions of the quadrupolar powder line shape. In order to correct for phase errors arising from the composite pulse, we present the composite pulse magic echo sequence. It is demonstrated both experimentally and theoretically that the composite pulse magic echo sequence can eliminate phase distortions without considerably attenuating the signal-to-noise ratio. The performance of the new sequence is quite good.
Operation of large ‘‘field-free’’ ion sources in the presence of magnetic fields
Authors: Grisham L. R. , Kamperschroer J. K. , Wright K. E.
Published: July 2002

Large area 10×40-cm Lawrence Berkeley Laboratory ‘‘field-free’’ ion sources were used during the first 2.5 yr of the neutral beam injection heating experiment on the tokamak fusion test reactor. Although these ion sources were located inside magnetic shielding structures, interference from tokamak magnetic fields prevented beam operation under certain conditions when using hydrogen. The fields causing this interference have been studied, and modifications which allow operation of such sources in these fields have been made.
Cryogenic current comparator with increased resolution
Authors: van der Wel W. , Mooij J. E. , Harmans C. J. P. M.
Published: July 2002

High resolution in a cryogenic current comparator (CCC) can be attained with an unmodified commercial SQUID by involving geometrical aspects in the design considerations. A description of a CCC is given whose measured sensitivity (one flux quantum φ0 per 2.7-μA turn) agrees well with the calculated value, being high enough to meet the requirements for high-precision measurements of the quantized Hall resistance.
Noncontact methods used for characterization of high-T
c superconductors
Authors: Doss J. D. , Cooke D. W. , McCabe C. W. , Maez M. A.
Published: July 2002

Noncontact eddy-current techniques for characterizing superconductors between 5 MHz and 1 GHz are described. Both a transmission and a frequency-modulation technique rely on modification of the mutual inductance between a pair of coupled inductors. The sample is placed between the inductive sensors; the magnitude of eddy currents induced in the sample, a function of conductivity, modifies the mutual inductance. The frequency-modulation method (where the sensors are the inductive section of a series-resonant LC circuit in an oscillator) is particularly useful for determining the critical temperature (Tc) and transition width for superconducting samples.
Computer automated laser absorption calorimeter
Authors: Gallant D. J.
Published: July 2002

An automated apparatus for the measurement of laser optical absorption is described. This device was designed for state of the art sensitivity along with computer controlled data collection and analysis. A sample carousel was incorporated in the calorimeter to improve sample throughput by reducing the number of vacuum breaks. The calorimeter has been used with various laser sources ranging in wavelength from 1.319–0.351 μm. Parts with total absorptions as low as 20 parts per million have been measured with a reproducibility of 10%. The system was calibrated using a photometric technique with an absorption accuracy of 5%.
Ion beam reflection in a 180° bending magnet system
Authors: Sakurai K. , Oka Y. , Kaneko O. , Kuroda T.
Published: July 2002

Several kinds of bending magnet systems are used in present neutral beam injectors. In these systems the fringe magnetic field due to finite dimensions of the bending magnet plays an important role in the ion beam deflection. The power deposition profile on the ion dump surface is strongly influenced by the exit angles of the reflected ions with respect to the magnet boundary. However, it is not easy to predict the exit angles of the ions because both focusing and defocusing forces act on these ions during their reflections, and hence it is difficult to predict whether the power density on the ion dump surface increases or decreases. In order to investigate the effect of the fringe magnetic field on beam reflection in a 180° bending magnet system, we calculate power deposition profiles on the ion dump surface by applying a Monte Carlo technique. The computational results show that the power deposition profile is very sensitive to change of the magnetic field strength. When the magnetic field strength increases by 5%, for example, the maximum power density shows an increase of 80%. We also compare the calculated power deposition profile with the experimentally measured profile. The measured profiles are in good agreement with the calculated ones without considering the beam expansion due to a space-charge effect of the reflecting ions.
XRD array, grazing incidence spectrometer, and x-ray imaging camera on PBFA II
Authors: Derzon M. S. , Sweeney M. A. , Grandon P. , Ives H. C. , Kensek R. P. , Mix L. P. , Stygar W. A.
Published: July 2002

Target diagnostics on PBFA II will include a time-resolved x-ray diode array, an energy-resolved, time-integrated x-ray camera, and a grazing incidence spectrometer. A clean vacuum, independent of that on PBFA II, will be supplied to the detectors to maintain more reproducible calibrations. We also describe the diagnostics and outline the calculations which determined the shielding required. Based on the calculations the background due to bremsstrahlung in the least sensitive diagnostic is 12 eV/pixel. The appropriate shielding is being built to field these diagnostics.
Novel tunable reentrant microwave cavity
Authors: Migliuolo M. , Castner T. G.
Published: July 2002

A cylindrical reentrant cavity is discussed that features a tunable resonant frequency. The tuning range can, in principle, be as large as a factor of 3, but the present design achieved only a 28% tuning range. Such a system could be utilized where it is necessary to tune the resonant frequency over a limited range, as in magnetic resonance experiments.
Computerized microreactor and video microscopy system for coal pyrolysis studies
Authors: Glass Micheal W. , Zygourakis Kyriacos
Published: July 2002

The development of a captive sample microreactor, its integration into a video microscopy system, and its use for studies on coal pyrolysis are presented. The reactor can operate as a high-temperature microscope hot stage allowing for direct viewing of the pyrolysis process under an optical microscope equipped with a video camera. By using a microcomputer and specialized video equipment, process information such as elapsed time and reactor temperature are superimposed in alphanumeric form on the video signal. Complete histories of fast experiments can thus be stored on videotape for postprocessing and analysis of transient phenomena. The reactor is controlled via a microcomputer with custom-built analog interfaces. A digital algorithm combining internal model control and feedback control is implemented for accurate programming of the reactor temperature. Heating rates as high as 1000 °C/s can be achieved with good reproducibility. Some experimental results are presented to outline the capabilities of the apparatus and to suggest other potential applications.
Diagnostics with charged fusion products in ASDEX
Authors: Bosch Hans-Stephan
Published: July 2002

A diagnostic for measuring the spectra of 3-MeV protons and 1-MeV tritons from DD fusion reactions in a tokamak has been developed. The emphasis in this work was on obtaining an energy resolution high enough to get information on the ion energy distribution from the energy spectra of the charged fusion reaction products. This low-noise system allowed the first direct measurement of the spectra of 1-MeV tritons from a tokamak. The diagnostic system is described, and measurements of the ion temperature and spectra resulting from non-Maxwellian ion distributions are presented. Rotating the detector from shot to shot to get different lines of sight, it is even possible to obtain an emission profile of the fusion reaction products.