bluuebunny/crossref_metadata_2025 huggingface dataset:
Persistent magnetic fields trapped in high T
c superconductor
Authors: Weinstein R. , Chen In-Gann , Liu J. , Parks D. , Selvamanickam V. , Salama K.
Published: July 2002

A study of field trapping by the incomplete Meissner effect was performed on YBa2Cu3O7−x at 77 K on both sintered and oriented grain samples. Fields of up to BT=1280 G have been trapped in small, oriented grain, planar samples. Circulating persistent current densities of up to 4800 A/cm2 are calculated. Based on these values hollow cylinders of 2 cm i.d. will trap fields of 6000 G. Initial creep is about 10%/week for both types of samples. Creep rate varies as (BT/BT,max)2. BT, due to an external field B0, is BT∝(1−e−cB0/BT,max). Lamination and mosaic assembly steps for producing practical magnets have been performed.
Experimental observation of two microwave radiation mechanisms with widely separated frequencies during the output pulse of a high-voltage virtual cathode oscillator
Authors: Haworth M. , Adler R. , Anderson B. , Connaughton M. , Dungan W. , Enns J. , Metz J. , Pelletier P. , Platt R. , Polaco J. , Rupp R. , Thode L. , Voss D.
Published: July 2002

Results from two 4 MV, 100 kA coaxial magnetically insulated transmission line virtual cathode oscillator experiments are presented. In both experiments, two distinct microwave pulses with vastly different frequencies were generated during the beam current pulse. The first, lower frequency pulse was found to be produced by an electron reflexing process, while the second, higher frequency pulse was due to the virtual cathode oscillation mechanism.
Ferroelectric bismuth titanate/superconductor (Y-Ba-Cu-O) thin-film heterostructures on silicon
Authors: Ramesh R. , Inam A. , Wilkens B. , Chan W. K. , Sands T. , Tarascon J. M. , Fork D. K. , Geballe T. H. , Evans J. , Bullington J.
Published: July 2002

The growth by pulsed-laser deposition of c-axis-oriented bismuth titanate (BTO)/YBa2Cu3O7(YBCO) superconductor heterostructures on [001]-oriented Si with epitaxial yttria-stabilized ZrO2 as a buffer layer is reported. X-ray-diffraction studies of the heterostructures show that all the layers grow in the c-axis orientation, with a rocking angle of 1.0°–1.2° for the bismuth titanate layer and 0.6°–0.8° for the YBCO layer. Rutherford backscattering ion channeling yields of 28% at the surface have been obtained. Transmission electron microscopy of cross-sectioned samples reveal that the BTO layer has a significant density of translational boundaries that propagate at 45° to the film surface. The BTO film exhibits ferroelectric hysteresis and a dielectric constant in the range of 180–200.
Electrical conductivity of a pure C60 single crystal
Authors: Wen C. , Li J. , Kitazawa K. , Aida T. , Honma I. , Komiyama H. , Yamada K.
Published: July 2002

The temperature dependence of the electrical conductivity of a C60 single crystal is presented in this letter. The single-crystal samples free from solvent contamination were grown up to a size of millimeters order by sublimation of C60 powder with oscillation of the crystal temperature. The electrical conductivity of the single crystal was measured at temperatures between 250 and 295 K. The sharp decrease of the electrical conductivity with temperature around 256 K was observed in association with the phase transition of C60.
X-ray and photoluminescence characterization of low temperature AlInAs grown by molecular beam epitaxy
Authors: Metzger R. A. , McCray L. G.
Published: July 2002

AlInAs lattice matched to InP was grown by molecular beam epitaxy over a temperature range of 150–400 °C and characterized by x-ray diffraction and photoluminescence. As-grown samples compared to those annealed at 500 °C showed no shift in the AlInAs x-ray diffraction peak for growth above 285 °C, indicating no detectable incorporation of excess As in this temperature range. Growth below this temperature saw a linear increase in the shift of the AlInAs diffraction peak due to incorporation of excess As, with samples grown at 150 °C showing a shift of 130 arcsec. Photoluminescence measurements of annealed AlInAs grown above 275 °C exhibited slight increase in PL intensity, while annealed samples grown below 260 °C exhibited large intensity degradation.
Photoemission study of porous silicon
Authors: Roy A. , Chainani A. , Sarma D. D. , Sood A. K.
Published: July 2002

We report x-ray photoelectron spectra from a porous silicon film (PSF) with a photoluminescence peak at 1.8 eV, as a function of argon ion etching time to probe the composition in the surface and the subsurface regions. The results clearly indicate that the surface layer is essentially a fluorine admixed SiO2 phase, while the Si:O:F composition of the subsurface region 2:1:0.2. With the possibility of the existence of hydrogen in this composition it appears that beyond the highly oxidized surface, PSF is a fluorine substituted siloxene derivative, which can be responsible for the visible photoluminescence.
Probing of surface acoustic wave fields by a novel scanning tunneling microscopy technique: Effects of topography
Authors: Chilla E. , Rohrbeck W. , Fröhlich H.-J. , Koch R. , Rieder K. H.
Published: July 2002

A new method for the investigation of SAW (surface acoustic wave) fields is presented using a modified version of a scanning tunneling microscope. By adding a high frequency sinusoidal signal to the dc tip voltage the tunneling current contains a component at the difference of the frequencies of this signal and the SAW. There is a remarkable variation of phase for areas much smaller than the SAW wavelength, due to different contributions of the normal and horizontal components of the SAW.
Nonequilibrium phase transformations of the Nb-Au alloy system by ball milling
Authors: Di L. M. , Bakker H.
Published: July 2002

Various compositions of Nb-Au alloys (intermetallic compounds and mixtures of intermetallic compounds) were subjected to heavy mechanical impact in a high-energy ball mill for 40 h. Nb-rich compounds transformed to the bcc solid solution of Au in Nb (down to about 60 at. % Nb), whereas compounds containing 50 at. % Nb or less transformed to the fcc solid solution of Nb in Au. Around 58 at. % of Nb a two-phase bcc/fcc region was found.
Raman scattering from diamond particles
Authors: Yoshikawa M. , Mori Y. , Maegawa M. , Katagiri G. , Ishida H. , Ishitani A.
Published: July 2002

Raman spectra of diamond powders with size less than 2 μm have been measured as a function of the particle size. The Raman line was found to become more asymmetric with some tailing towards lower Raman shifts, broader, and weaker with decreasing particle size. The observed result can be explained by a phonon confinement effect rather than by a strain effect. This work predicts that it is very difficult to detect Raman spectra of diamond particles with size less than ∼50 Å. A broad Raman band, whose intensity becomes stronger with decreasing particle size, was observed around 600 cm−1 in the spectra of diamond powders with particle size less than 2 μm. We hypothesize that the broad band arises from transverse acoustic phonons near the Brillouin zone boundary because of the relaxation in the wave vector selection rule.
Further evidence for quantum confinement in porous silicon
Authors: Behrensmeier R. , Namavar Fereydoon , Amisola G. B. , Otter F. A. , Galligan J. M.
Published: July 2002

The origin of the photoluminescence (PL) of porous silicon is being extensively investigated. In this letter, we offer detailed analyses of the PL spectra, of which about 3%–5% show small extrema that superimpose the larger main peak. Spacing between these smaller maxima is reproducible and independent of the main peak energy and sample history, while energy steps between them correlate with differences in the exciton energies due to changing the sizes of the quantum wires by complete monolayers of atoms.
Structural and electrical properties of La0.5Sr0.5CoO3 epitaxial films
Authors: Cheung Jeffrey T. , Morgan Peter E. D. , Lowndes Douglas H. , Zheng X-Y , Breen John
Published: July 2002

Epitaxial La0.5Sr0.5CoO3 films with very smooth surface morphology were grown on (100) SrTiO3 and (100) MgO substrates by pulsed laser deposition. Scanning tunneling microscopy reveals that the thin film is formed by the coalescence of many aligned square mesas. The growth proceeds from the edges of terraces which are stacked on the mesa. Spiral growth is never observed. Films display an crystallographically isotropic metallic-like electrical conductivity but become semiconductor-like after vacuum annealing. The energy for carrier activation is 0.3 eV. The change of the electrical resistivity of La0.5Sr0.5CoO3 with oxygen pressure at high temperature is much less sensitive than that of YBa2Cu3O7−x.
Epitaxial growth of Cu (001) on Si (001): Mechanisms of orientation development and defect morphology
Authors: Hashim I. , Park B. , Atwater H. A.
Published: July 2002

We describe the evolution of microstructure during ultrahigh vacuum ion beam sputter deposition of Cu (001) at room temperature on hydrogen-terminated Si (001). In situ reflection high energy electron diffraction indicates growth of an epitaxial Cu (001) film on Si (001) with the intensity of the Bragg rods sharpening during 5–20 nm of Cu film growth. Post-growth x-ray diffraction indicates the Cu film has a mosaic spread of (001) textures of about ±2° and that a small fraction (0.001–0.01) is of (111) textures. High-resolution transmission electron microscopy shows an abrupt Cu/Si interface with no interfacial silicide, and reveals an evolution in texture with Cu thickness so as to reduce the mosaic spread about (001). Moiré contrast suggests a nearly periodic elastic strain field extending into the Cu and Si at the interface. Other aspects of film growth which are critical to epitaxy are also discussed.
Electro-optical characterization of Pb(Zr,Ti)O3 thin films by waveguide refractometry
Authors: Potter B. G. , Sinclair M. B. , Dimos D.
Published: July 2002

Electric field-induced changes in the extraordinary and ordinary refractive indices of a Pb(Zr0.53Ti0.47)O3 thin film were independently determined using waveguide refractometry. Under an electric field, applied normal to the film plane and corresponding to saturation of the electric polarization, the ratio of the extraordinary to ordinary refractive index change (Δne/Δno) is found to be −4/1, contributing to a net birefringence change [Δ(ne-no)] of −0.021. Using this technique, both diagonal and off-diagonal elements of the electro-optic response tensor describing the macroscopic behavior of the polycrystalline film were accessed, illustrating the importance of this approach in evaluating orientation-specific electro-optic characteristics in these films.
Noise characteristics of YBa2Cu3O7−δ /CaRuO3/YBa2Cu3O7−δ Josephson junctions
Authors: Myers K. E. , Char K. , Colclough M. S. , Geballe T. H.
Published: July 2002

The noise characteristics of YBa2Cu3O7−δ/CaRuO3/YBa2Cu3O7−δ edge junctions are reported. The junctions exhibit low 1/f noise in the range of operating temperatures from 65 to 77 K. At lower temperatures the level of 1/f noise increases, and in addition, telegraph noise dominates the noise power spectrum at discrete current biases that are junction dependent. The characteristic frequency of a particular switching process increases with temperature but may increase or decrease with increased bias current. These results are consistent with a description of the superconductor-metal interface in which oxygen deficiency and/or disorder gives rise to localized states which trap carriers and lead to noise in the junction transmission.
Four layer monolithic integrated high T
c dc SQUID magnetometer
Authors: Hilgenkamp J. W. M. , Brons G. C. S. , Soldevilla J. G. , IJsselsteijn R. P. J. , Flokstra J. , Rogalla H.
Published: July 2002

YBa2Cu3O7−x based monolithic integrated dc SQUID magnetometers, consisting of a dc SQUID integrated with a flux transformer on a single bicrystalline substrate, have been fabricated and characterized. The devices consist of four layers, including two superconducting layers, and first realizations operate up to 73 K. A maximum voltage modulation of 32 μV is observed at 40 K. A field sensitivity of 0.17 pT/√Hz is obtained above 200 Hz at 45 K and 0.49 pT/√Hz at 1 Hz and 65 K.
Plume-substrate interaction in pulsed-laser deposition of high-temperature superconducting thin films
Authors: Nakata Yoshiki , Kumuduni Wanniarachchi K. A. , Okada Tatsuo , Maeda Mitsuo
Published: July 2002

The interaction between a substrate and an expanding plume, which is produced in a pulsed-laser deposition process of high-temperature superconducting thin films, has been investigated by observing one-dimensional laser-induced fluorescence images of ablated yttrium oxide molecules. The results show the importance of fluid-like interactions of the ablated particles with the substrate. In relatively high oxygen pressure, it is found that the ablated particles are reflected and stagnate in front of the substrate, and are then transported by diffusion onto the substrate.
2.7–3.9 μm InAsSb(P)/InAsSbP low threshold diode lasers
Authors: Baranov A. N. , Imenkov A. N. , Sherstnev V. V. , Yakovlev Yu. P.
Published: July 2002

Lasing has been obtained in the wavelength range 2.7–3.9 μm in double heterostructure diode lasers with an active region made of InAs alloys. The devices were grown by liquid-phase epitaxy. Typical values of threshold current at 80 K were as low as 40 mA and the maximum operating temperature was 180 K. The blue shift of lasing modes was observed with current. This was explained by the increase of the carrier density in the active region above threshold due to intervalence band absorption.
Separately contacted electron-hole double layer in a GaAs/AlxGa1−xAs heterostructure
Authors: Kane B. E. , Eisenstein J. P. , Wegscheider W. , Pfeiffer L. N. , West K. W.
Published: July 2002

We describe a method for creating closely spaced parallel two-dimensional electron and hole gases confined in 200 Å GaAs wells separated by a 200 Å wide AlxGa1−xAs barrier. Low-temperature ohmic contacts are made to both the electrons and holes, whose densities are individually adjustable between 1010/cm2 to greater than 1011/cm2.
Rapid thermal oxidation of silicon in N2O between 800 and 1200 °C: Incorporated nitrogen and interfacial roughness
Authors: Green M. L. , Brasen D. , Evans-Lutterodt K. W. , Feldman L. C. , Krisch K. , Lennard W. , Tang H.-T. , Manchanda L. , Tang M.-T.
Published: July 2002

Oxynitrides can suppress the diffusion of boron from the polycrystalline silicon gate electrode to the channel region of an ultralarge scale integrated device, and are therefore important potential substrates for thin SiO2 gates. Direct oxynitridation of Si in N2O is a simple and manufacturable N incorporation scheme. We have used rapid thermal oxidation to grow O2- and N2O-oxides of technological importance (∼10 nm thick) in the temperature range 800–1200 °C. Accurate measurements of the N content of the N2O-oxides were made using nuclear reaction analysis. N content increases linearly with oxidation temperature, but is in general small. A 1000 °C N2O-oxide contains about 7×1014 N/cm2, or the equivalent of about one monolayer of N on Si (100). Nonetheless, this small amount of N can retard boron penetration through the dielectric by two orders of magnitude as compared to O2-oxides. The N is contained in a Si-O-N phase within about 1.5 nm of the Si/SiO2 interface, and can be pushed away from the interface by O2-reoxidation. We have measured Si/SiO2 interfacial roughness by x-ray reflectometry, and found that it decreases with increasing oxidation temperature for both O2- and N2O-oxides, although the N2O-oxides are smoother. The enhanced smoothness of N2O-oxides is greater the greater the N content. N2O-oxides are promising candidates for thin ultralarge scale integrated circuit gate dielectrics.
Epitaxial regrowth of ruby on sapphire for an integrated thin film stress sensor
Authors: Wen Q. , Clarke D. R. , Yu Ning , Nastasi M.
Published: July 2002

The formation of thin film ruby by the epitaxial growth of Cr-doped amorphous alumina on sapphire is described. The incorporation of Cr onto the Al cation sites has been found by ion channeling measurements. It is also confirmed by the observation of the R1 and R2 luminescence lines characteristic of ruby. The frequency of the R lines shift linearly with applied stress and the piezo-spectroscopic coefficient is the same as for bulk ruby.
Large-area, triple-layer, microchannel-plate arrays
Authors: Armentrout C. J.
Published: July 2002

The characteristics of operating an extended-area, triple-layer microchannel-plate assembly are described in detail. The assembly has an anode array to produce 120 channels of information. When run in the pulse-counting mode, gains of up to 5×108 are obtained with very low levels of dark current. A number of special features and problems have been observed during operation. These include unexpectedly high count rates for each channel and severe gain variation along the length of the plate. A model distribution function for a pulse is derived and it is shown that this gain variation is due to space-charge effects that occur in the interstage gaps. This effect, although previously discounted, can consistently explain the data presented here and earlier by other authors. One assembly was rebuilt and now exhibits much greater uniformity in gain. Its pulse-height spectrum also has the unusually small, full-width at half-maximum: gain ratio of typically 50%.
Frequency modulated (FM) time delay photoacoustic and photothermal wave spectroscopies. Technique, instrumentation, and detection. Part III: Mirage effect spectrometer, dynamic range, and comparison to pseudo-random-binary-sequence (PRBS) method
Authors: Mandelis Andreas , Borm Linda L. M. , Tiessinga John
Published: July 2002

A detailed comparison is presented between the time delay and the pseudo-random-binary-sequence (PRBS) methods of excitation and mirage effect response. Both time delay domain dynamic system response and frequency domain spectral functions were calculated via FFT methods. The results show that the FM time delay spectrometer exhibits superior performance to the PRBS device and is optimally suitable for nondestructive and depth-profiling studies. The detailed examination of, and comparison between, the time delay and spectral dynamic functions of our FM time delay photothermal wave spectrometer and those of a PRBS-driven device has proven that the former apparatus is capable of producing superior quality time delay and spectral function information when tested on a fast, flat frequency response mirage effect system. The FM time delay photoacoustic/photothermal wave technique and instrumentation of this work holds excellent promise for nondestructive evaluation and depth-profiling applications in scientific research as well as industrial development laboratories.
Absolute detection efficiencies of microchannel plates for 0.1–2.3 keV electrons and 2.1–4.4 keV Mg+ ions
Authors: Müller A. , Djurić N. , Dunn G. H. , Belić D. S.
Published: July 2002

The absolute detection efficiencies of detectors consisting of two microchannel plates (MCP) in a chevron arrangement, were experimentally determined for 0.1–2.3-keV electrons and 2.1–4.4-keV Mg+ ions. Both detectors tested included a grid with 92.5% transmission in front of the first MCP. For the measurements, the observed detector count rates were compared to the corresponding particle currents collected in a Faraday cup and measured with a vibrating reed electrometer. The electron detection efficiency of the MCP detector, including the grid, decreases from 0.82 at 0.1 keV to 0.65 at 2.3 keV for electrons incident normal to the surface. The Mg+ ion detection efficiency for the same arrangement, but with 43° incidence angle, increases from 0.49 at 2.1 keV to 0.81 at 4.4 keV.
Perpendicular magnetic anisotropy and strong magneto-optic properties of SrRuO3 epitaxial films
Authors: Klein L. , Dodge J. S. , Geballe T. H. , Kapitulnik A. , Marshall A. F. , Antognazza L. , Char K.
Published: July 2002

Epitaxial films of the ferromagnetic perovskite SrRuO3 were measured with a bulk magnetometer and with a local magneto-optic Sagnac interferometer in transmission and in reflection. We find a magnetic easy axis perpendicular to the films, and for saturated remanent magnetization along this direction the Faraday rotation and the Kerr rotation at λ=840 nm are about 0.75×105 deg/cm and 0.85°, respectively. The temperature dependence of the remanent magnetization in the low temperature limit is dominated by spin-wave excitations, yielding a notable decrease with T3/2. Using Sagnac–Kerr scanning and transmission electron microscopy imaging we correlate the coercivity with the grain size.
Space plasma measurements with ion instruments
Authors: Kessel R. L. , Johnstone A. D. , Coates A. J. , Gowen R. A.
Published: July 2002

In this article we examine the factors which affect the determination of the plasma bulk parameters in space, with particular emphasis on the density determination. We make this assessment with reference to a particular instrument, the AMPTE-UKS ion instrument, in order to be specific, but the issues raised here are likely to be encountered in the use of any space plasma instrument containing electrostatic energy analyzers or microchannel plate detectors. We have established a mathematical formalism for determining these parameters by relating the measured counts to the distribution function in terms of the geometric factor. The geometric factor is determined in the calibration of the instrument which is described in some detail. Among the factors we have considered are our calibration techniques, MCP efficiency, detector energy, and angular resolution, as well as the approximations used in our mathematical formalism. To establish confidence in our determination, we used a computer simulation to look for systematic errors in the particular characteristics of the analyzer and to verify the method of extraction of plasma parameters. We can conclude that the detector resolution is adequate for determining density for both solar wind (<5% error) and magnetosheath conditions (<6% error). The detector resolution is also adequate for measuring velocity, <1% error for the solar wind and <3% error in the magnetosheath. The detector resolution is not adequate for determining temperature in the solar wind ∼50%; however, in the magnetosheath where the thermal spread is at least as large as the acceptance angles, the resolution is adequate (<6%). In addition, we tested the influence of the geometric factor on the output bulk parameters by varying the input velocity direction over the entire polar range. The systematic error in the output parameters was less than 5% in all cases.
Cross luminescence of several perovskite-type crystals
Authors: Kamenskikh I. A. , MacDonald M. A. , Mikhailin V. V. , Munro I. H. , Terekhin M. A.
Published: July 2002

Cross-luminescence excitation and decay of crystals RbCaF3, CsCaCl3, and CsSrCl3 have been studied in the vacuum ultraviolet region. It has been shown that decay curves are not single exponential. The effect of structural phase transition on the cross-luminescence decay time of RbCaF3 has been discovered.
A thermal conductivity microstructural pressure sensor fabricated in standard complementary metal-oxide semiconductor
Authors: Robinson A. M. , Haswell P. , Lawson R. P. W. , Parameswaran M.
Published: July 2002

We have investigated polysilicon-based microstructural thermal conductivity pressure sensors fabricated in complementary metal-oxide-semiconductor technology and operated as a Pirani gauge. The thermally isolated polysilicon resistor showed a 2% change over the pressure range 0.01–100 Torr when the device was operated with a constant current of 200 μA. Larger changes were observed at higher currents. The device was tested in SF6, N2, and He, and was most sensitive in He and least sensitive in SF6. Heat losses were calculated to be mainly due to heat conduction through the support arms, especially at low pressures, with heat conduction through the gas increasing to approximately 37% at 1 atm.
High-flux source of low-energy neutral beams using reflection of ions from metals
Authors: Cuthbertson John W. , Motley Robert W. , Langer William D.
Published: July 2002

Reflection of low-energy (<100 eV) ions from surfaces can be applied as a method of producing high-flux beams of low-energy neutral particles, and is an important effect in several areas of plasma technology, such as in the edge region of fusion devices. We have developed a beam source based on acceleration and reflection of ions from a magnetically confined coaxial rf plasma source. The beam provides a large enough flux (over 4 A ion current, or 5×1016 atoms/cm2 s at 10-cm range) to allow the energy distribution of the reflected neutrals to be measured despite the inefficiency of detection, by means of an electrostatic cylindrical mirror analyzer coupled with a quadrupole mass spectrometer. Energy distributions have been measured for oxygen, nitrogen, and inert gas ions incident with from 15 to 70 eV reflected from amorphous metal surfaces of several compositions. For ions of lighter atomic mass than the reflecting metal, reflected beams have peaked energy distributions; beams with the peak at 4–32 eV have been measured. The energy and mass dependences of the energy distributions as well as measurements of absolute flux, and angular distribution and divergence are reported. Applications of the neutral beams produced are described.
In situ observation of silicon hydrides on Si(100) surfaces during synchrotron-radiation-stimulated Si2H6 gas source molecular beam epitaxy
Authors: Yoshigoe A. , Mase K. , Tsusaka Y. , Urisu T. , Kobayashi Y. , Ogino T.
Published: July 2002

Silicon hydrides (SiHn) on the Si(100) surface during synchrotron-radiation (SR) stimulated Si2H6 gas source molecular beam epitaxy has been observed in situ at low temperatures (≤400 °C), by means of infrared reflection absorption spectroscopy using CoSi2 buried metal layer substrates. At high temperatures (400 °C, 370 °C), SiH is a dominant surface species, while with temperature decrease from 275 to 50 °C, the number of SiH decreases, and, on the other hand, SiH2 and SiH3 appear and increase. This result explains the change of reflection high-energy diffraction pattern from 2×1 to 1×1. The SiH in the bulk network has not been observed. SR irradiation on the film at 140 °C after deposition shows that SiH2 and SiH3 are easily decomposed to SiH and that SiH decomposes much more slowly than SiH2 and SiH3.
Magnetospheric plasma analyzer for spacecraft with constrained resources
Authors: Bame S. J. , McComas D. J. , Thomsen M. F. , Barraclough B. L. , Elphic R. C. , Glore J. P. , Gosling J. T. , Chavez J. C. , Evans E. P. , Wymer F. J.
Published: July 2002

A light-weight, low-power, plasma analyzer is described that can be used for measuring the plasma environments of spacecraft with constrained resources. A unique system using a single electrostatic analyzer coupled to a single array of channel electron multipliers allows measurement of the three-dimensional energy per charge distributions of both ions and electrons over E/q ranges from ∼1 eV/q to ≳40 keV/q. Particles selected by the analyzer are post-accelerated into the multipliers to maintain sensitivity for the lowest energy particles. An instrument using this concept called the magnetospheric plasma analyzer (MPA) is described. Presently, three MPAs are in geosynchronous orbits (GEO) aboard spacecraft with International Designators of 1989-046, 1990-095, and 1991-080. The MPA and its response characteristics are described, and examples of on-orbit data showing some of the MPA capabilities are presented.
Optical and electrical properties of materials
Authors: El-Kashef Hassan
Published: July 2002

An interferometric technique using a newly developed Mach–Zehnder interferometer is applied to measure the refractive indices of light transmitting fluids in general. It has been particularly used for determining the refractive indices and its variation with temperature for two solvents of laser dyes (toluene and carbon disulphide). Accuracy of 1×10−5 is achieved where no uncertainity of the measurements arising from the naked eye estimation. The obtained optical results have been used to calculate a number of different physical parameters such as the optical permittivity (or dielectric susceptibility), thermal coefficient of refractive index, temperature coefficient of permittivity, specific refraction, molar refraction, polarizability, radius of the molecule, relaxation time, temperature coefficient of volume expansion, characteristic impedance of matter, and the constant electric moment of a molecule. It is shown that the experimental results agree well with the calculated ones. The advantages of this technique and the sensitivity of the instrument are discussed.
Simulation of ion beam extraction from an ECR source
Authors: Spädtke P. , Tinschert K. , Ivens D.
Published: July 2002

The extraction of ion beams from ECR ion sources is investigated. It is shown that for high magnetic fields within the extraction region, as in the CAPRICE-type ECR, all different charge states have to be simulated simultaneously to achieve the correct space charge distribution of the extracted ion beam. The change of the longitudinal velocity distribution for different charge states is taken into account. Beam emittance measurements made 280 mm behind the extraction system will be compared with the results of the simulation. Two possible extraction systems which should have influence on the beam characteristics are investigated.
Two-frequency plasma heating in a high charge state electron cyclotron resonance ion source
Authors: Xie Z. Q. , Lyneis C. M.
Published: July 2002

The performance of the Lawrence Berkeley Laboratory (LBL) advanced electron cyclotron resonance ion source, which is a single stage source designed to operate at 14 GHz alone (single-frequency heating), is enhanced by heating the plasma simultaneously with microwaves of 10 and 14 GHz (two-frequency heating). Production of high charge state ions was increased a factor of 2–5 or higher for the very heavy ions such as bismuth and uranium, as compared to single- frequency heating. Plasma stability was improved and the ion charge state distribution shifted to higher charge state. With two-frequency heating, the source can produce more than 1×109 pps of fully stripped argon. High charge state ion beams of bismuth and uranium produced by the source were injected into the 88-Inch Cyclotron at LBL. After acceleration to energies greater than 6 MeV/nucleon, the extracted beam intensities were 1×106 pps or higher for Bi50+,51+ and 238U52+,53+.
Vertical dispersion mode double-crystal spectrometer for advanced spectroscopy of laser-produced plasma
Authors: Renner O. , Kopecký M. , Wark J. S. , He H. , Förster E.
Published: July 2002

A vertical dispersion variant of the double-crystal spectrometer (DCV), which has been successfully used to study radiative transport in plasmas with large velocity gradients, is described. The full theory of the instrument is presented with particular reference to distortion of the spectral lines observed. The main characteristics of the DCV were computed by ray tracing procedures and compared with experiment. Due to its extremely high dispersion, the DCV minimizes geometric apparatus smearing, the distortion of the spectra is negligible a high spectral resolution (typically several thousand or better) can be achieved at relatively small source-to-detector distances. The instrument provides two sets of spectra with one-dimensional spatial resolution at the level of 10 μm, and its sensitivity to relative positions and shifts of the spectral lines may be estimated as one part in 105. The very high precision in wavelength determination, both absolute and relative, combined with an acceptable luminosity make this spectrometer especially useful for ultrahigh-resolution spectroscopy of laser-produced plasmas.
Diamond photoconducting detectors as high power z-pinch diagnostics (invited)
Authors: Spielman Rick B.
Published: July 2002

Diamond photoconducting detectors (PCDs) are one of the primary x-ray diagnostics for z-pinch experiments at Sandia National Laboratories’ Saturn facility. Diamond PCDs represent a significant advance in the state of the art for electrical x-ray detectors because of their stability of response, overall flatness of response, and ease of use. We have observed no aging effects in detectors used for years. Five PCDs on Saturn experiments where 1–3 TW of keV x-ray power is emitted in 5–20-ns pulses by z-pinch x-ray sources are routinely fielded. Typical PCDs used at Sandia have dimensions of 1 mm width ×3 mm long ×0.5 mm thick. The techniques used in the assembly, fielding, and calibration of diamond PCDs will be described.
Laser free measurements of absorption and fluorescence excitation spectra in a supersonic free jet
Authors: Graf Urs , Niikura Hiromichi , Hirayama Satoshi
Published: July 2002

Measurements of the absorption and fluorescence excitation spectra in a supersonic free jet are performed simultaneously with the use of a dc Xe lamp and lock-in detection. With this inexpensive equipment it is possible to measure spectral features from UV to VIS with absorbances as low as 5×10−6 and with a spectral resolution of 0.9 Å. Absorption and fluorescence excitation spectra of 9-cyanoanthracene, which is solid and nonvolatile under ambient conditions, are presented. Achievable signal-to-noise ratios are theoretically calculated and experimentally verified.
Polarization instability and relative intensity noise in vertical-cavity surface-emitting lasers
Authors: Kuksenkov D. V. , Temkin H. , Swirhun S.
Published: July 2002

We observe a polarization instability in circularly symmetric vertical-cavity surface-emitting lasers. A relatively long time, 3–5 ns, is required to establish a dominant polarization state. Under high-speed digital modulation this leads to strong enhancement, 20–30 dB, in polarization resolved low-frequency relative intensity noise. This polarization instability is accurately described by a simple rate-equation model. A similar increase in relative intensity noise, under dc bias, is caused by energy partition between orthogonally polarized modes.
The effect of mode scrambling on pulsed radar reflectometry applied to high shear devices
Authors: Donné A. J. H. , de Baar M. , Cavazzana R.
Published: July 2002

In this article the effect of mode scrambling on the operation of pulsed radar reflectometers working in the ordinary polarization mode on devices with a high magnetic shear is studied. Mode scrambling occurs when the magnetic field changes considerably on length and/or time scales which are similar to or smaller than those of the probing wave. In this case the polarization of the mode is not conserved during passage through the plasma, and power is transferred from ordinary to extraordinary mode and vice versa. Calculations with a full-wave code are performed for two different high-shear devices: the RFX reversed field pinch and the LHD torsatron. The conclusion of the work is that the density profiles in these devices can excellently be measured by a pulsed radar reflectometer operating in the ordinary mode.
Subnanosecond polarized microfluorimetry in the time domain: An instrument for studying receptor trafficking in live cells
Authors: Martin-Fernandez M. L. , Tobin M. J. , Clarke D. T. , Gregory C. M. , Jones G. R.
Published: July 2002

We describe an instrument designed to monitor molecular motions in multiphasic, weakly fluorescent microscopic systems. It combines synchrotron radiation, a low irradiance polarized microfluorimeter, and an automated, multiframing, single-photon-counting data acquisition system, and is capable of continually accumulating subnanosecond resolved anisotropy decays with a real-time resolution of about 60 s. The instrument has initially been built to monitor ligand–receptor interactions in living cells, but can equally be applied to the continual measurement of any dynamic process involving fluorescent molecules, that occurs over a time scale from a few minutes to several hours. As a particularly demanding demonstration of its capabilities, we have used it to monitor the environmental constraints imposed on the peptide hormone epidermal growth factor during its endocytosis and recycling to the cell surface in live cells.
Simulation and design of a superconducting eddy current probe for nondestructive testing
Authors: Claycomb James R. , Tralshawala Nilesh , Cho Hsiao-Mei , Boyd Mike , Zou Zhongji , Xu Xin Wen , Miller John H.
Published: July 2002

Numerical modeling studies were carried out for the design and performance evaluation of an eddy current probe for superconducting quantum interference device (SQUID) based noncontacting electromagnetic nondestructive testing. The probe utilizes high-Tc SQUID from electromagnetic interference and to focus magnetic flux due to the eddy current excitation coil into the object under test (OUT). This is very important in order to achieve “self-nulling,” where the probe responds only to the defects in the OUT. Simulations are carried out with the eddy current probe located a finite distance above a defect free conducting half-space of infinite thickness. Eddy current densities in the OUT are then calculated for various probe designs. These eddy current densities give an indication of the flux focusing, and hence increased spatial resolution for combinations of HTS and μ-metal shielding. Shielding factors are also calculated for the screening of the primary excitation field and the “defect-free” eddy current field. Agreement with the analytical solution of a simple solenoid above a conducting half-space verifies the numerical method.
A reflection-mode apertureless scanning near-field optical microscope developed from a commercial scanning probe microscope
Authors: Wurtz G. , Bachelot R. , Royer P.
Published: July 2002

We have developed a polyvalent reflection-mode apertureless scanning near-field optical microscope (SNOM) from a commercial scanning probe microscope (SPM). After having explained our motivations, we describe the instrument precisely, by specifying how we have integrated optical elements to the initial SPM, by taking advantage of its characteristics, and without modifying its initial functions. The instrument allows five different reflection-mode SNOM configurations and enables polarization studies. Three types of SNOM probes can be used: dielectric, semiconducting, and metallic probes. The latter are homemade probes whose successful use, as probes for atomic force microscopy, by the commercial SPM has been experimentally demonstrated. Using silicon–nitride (dielectric) probes, one of the five configurations has been experimentally tested with two samples. The first sample is made of nanometric aluminum dots on a glass substrate and the second sample is the output front facet of a laser diode. The preliminary SNOM images of the latter reveal pure optical contrasts.
Fast pulsed radar reflectometry for the Textor Tokamak
Authors: Hugenholtz C. A. J. , Donné A. J. H. , Elzendoorn B. S. Q. , van Gorkom J. C. , Kooijman W. , van der Laan H. A. , van de Pol M. J. , Putter A. J. , van Ramele H. J. F. , Smit D. , de Vries P. C. , Wijnoltz F. , Pysik W. , Waidmann G. , Ermak G. P.
Published: July 2002

Progress in fusion research shows an increasing demand for diagnostics with high temporal and spatial resolution in order to study small and fast phenomena in fusion plasmas. Therefore, a new ten-channel pulsed radar reflectometer is under development for the TEXTOR Tokamak, to measure electron density profiles in the range of 0.4–4×1019 m−3 at a high repetition rate of 2 MHz. An additional feature of this diagnostic is the possibility to perform correlation measurements at 10 MHz repetition rate to investigate density fluctuations. The reflectometer will scan the plasma with 1-ns-long radar pulses in the 18–57 GHz range. In spite of the long flight time of the pulses of about 100 ns, the above mentioned high repetition rates could be achieved by time multiplexing the generation and reception of the radar pulses. Temporal selection of the received pulses is performed by fast switching of the local oscillators inputs of the heterodyne receiver, to generate time windows in which the reception of the reflected pulses is expected. An embedded VME controller will manage the system and store the data with a speed of 20 Msamples/s, up to a maximum of 64 Mbyte data per plasma shot. In order to facilitate the handling of such a huge amount of data, an advanced data reduction scheme is being developed. Remote operation with a fast data link from FZ Jülich (Germany) to FOM Nieuwegein (The Netherlands) will be possible.
Superconducting magnetic shields for SQUID applications
Authors: Claycomb J. R. , Miller J. H.
Published: July 2002

We investigate the shielding of superconducting and μ-metal forms in axial and transverse directed background magnetic noise fields. Analytical expressions are obtained for the improvement in signal-to-noise ratio obtained by placing a superconducting disk in the presence of a dipole source and a uniform noise field. Axial and transverse shielding factors are then compared for identical superconducting and μ-metal cylinders. The signal-to-noise ratio is found to be infinite at certain points inside a superconducting cylinder as well as a superconducting cylinder with a central partition. Shielding factors obtained here are relevant to SQUID measurements of small dipole source fields in the presence of large background noise fields such as those encountered in biomagnetism and nondestructive evaluation.
Instrumentation for millimeter-wave magnetoelectrodynamic investigations of low-dimensional conductors and superconductors
Authors: Mola Monty , Hill Stephen , Goy Philippe , Gross Michel
Published: July 2002

We describe instrumentation for conducting high sensitivity millimeter-wave cavity perturbation measurements over a broad frequency range (40–200 GHz) and in the presence of strong magnetic fields (up to 33 T). A millimeter-wave vector network analyzer (MVNA) acts as a continuously tunable microwave source and phase sensitive detector (8–350 GHz), enabling simultaneous measurements of the complex cavity parameters (resonance frequency and Q value) at a rapid repetition rate (∼10 kHz). We discuss the principle of operation of the MVNA and the construction of a probe for coupling the MVNA to various cylindrical resonator configurations which can easily be inserted into a high field magnet cryostat. We also present several experimental results which demonstrate the potential of the instrument for studies of low-dimensional conducting systems.
Comparison between the discharge development in the two- and three-electrode spark gap switches
Authors: Golnabi Hossein
Published: July 2002

Results of numerical simulation of two- and three-electrode spark gaps operating with pure nitrogen gas are compared. Our result show that in both cases the discharge process evolves via two stages very similar to that was reported in nitrogen glow discharge studies. First, the primary electrons produce positive nitrogen ions; second, the produced ions can disturb the applied field, and can create the space charge region. The undulations observed are because of the secondary effects, in particular, the cathode-directed streamers. The delay time for the three-electrode spark gap is more than that of the two-electrode discharge. Current growth is faster for the two-electrode spark gap in comparison with the three-electrode one. The oscillations are more enhanced for the case of the three-electrode spark gap. Our simulation method provides both temporal and spatial information concerning the operation of such switches. The reported results are helpful in design and optimization of both the two- and three-electrode spark gaps.
Role of low charge state ions in electron cyclotron resonance ion source plasmas
Authors: Drentje A. G. , Girard A. , Hitz D. , Melin G.
Published: July 2002

We have tried to shed more light on the possible mechanisms of the beneficial effect of gas mixing for highly charged ion production, in particular on the presence of an ion cooling effect. For the first time a method was applied to deduct the ion temperature from all measured ionic currents. The ion temperature values derived showed a clear decreasing trend in conjunction with mass changes of the gas mixture, consisting of “pure” argon (no mixing gas), argon plus natural oxygen, argon plus isotopic O18, or argon plus Ne22. Each of the applied mixing gases gives a higher charged ion (HCI) output (highest for O18) as well as a lower ion current for the singly charged beam-particle output. The relative high particle fraction (about 40%) of singly charged nonbeam particles is an indication that effective plasma ion cooling is possible. Although the differences in ion temperature calculated are small, the effect is likely substantial, since the ion confinement has a dependency with (Ti)−5/2. Hydrogen currents (residual) are observed to be smallest for the best HCI-confined plasmas; so far no explanation for this can be given.
Progress report on the mVINIS ion source
Authors: Dobrosavljević A. , Efremov A. , Draganić I. , Dekić S. , Stalevski T.
Published: July 2002

The mVINIS ion source is one of the major machines of the TESLA Accelerator Installation, at the Vinča Institute of Nuclear Sciences. It is an electron cyclotron resonance ion source with multiple applications. It can serve as an injector for an isochronous cyclotron providing heavy ions for several high energy experimental channels (radiation physics, radiation biology, physics of thin crystals, nuclear physics) or as a stand alone machine directly delivering multiply charged ions to the low energy experimental channels (physics of multiply charged ions, surface physics, surface modification of materials). This article describes the completion of mVINIS that included the finalization of its safety and control systems, the fine adjusting and calibration of its gas inlet system, and the installation of the solid substance inlet system. The recent results obtained with ion beams produced from gases and solid substances are presented, showing the wide capabilities of this machine. The ion beams obtained from mVINIS have been used in the channel for modification of materials since May 1998.
Effect of cesium and xenon seeding in negative hydrogen ion sources
Authors: Bacal M. , Bruneteau A. M. , Deniset C. , Elizarov L. I. , Sube F. , Tontegode A. Y. , Whealton J. H.
Published: July 2002

It is well known that cesium seeding in volume hydrogen negative ion sources leads to a large reduction of the extracted electron current and in some cases to the enhancement of the negative ion current. The cooling of the electrons due to the addition of this heavy impurity was proposed as a possible cause of the mentioned observations. In order to verify this assumption, we seeded the hydrogen plasma with xenon, which has an atomic weight almost equal to that of cesium. The plasma properties were studied in the extraction region of the negative ion source Camembert III using a cylindrical electrostatic probe while the negative ion relative density was studied using laser photodetachment. It is shown that the xenon mixing does not enhance the negative ion density and leads to the increase of the electron density, while the cesium seeding reduces the electron density.