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  • Oxford University Press  (51)
  • American Institute of Physics (AIP)  (32)
  • American Association for the Advancement of Science (AAAS)
  • 1995-1999  (93)
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  • 1
    Electronic Resource
    Electronic Resource
    The stability of advanced operational regimes on the Tokamak Fusion Test Reactor : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1589-1595 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The performance of the Tokamak Fusion Test Reactor [D. Meade and the TFTR Group, in Plasma Physics and Controlled Nuclear Fusion Research, Washington, D.C., 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. I, pp. 9–24], as defined by the maximum fusion power production, has been limited, not by confinement, but by stability to pressure-driven modes. Two classes of current profile modification have been investigated to overcome this limit. A new technique has been developed to increase the internal inductance of low-q (q(approximate)4), high-current (Ip〉2MA) plasmas. As was the case at higher edge q, the disruptive β limit has been found to increase roughly linearly with the internal inductance, li. Plasmas with hollow current profiles, i.e., reversed shear, are also predicted and experimentally observed to have increased stability in the negative shear region to ballooning and kink modes. However, performance of these plasmas is still limited by pressure-driven modes in the normal shear region. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872290
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  • 2
    Electronic Resource
    Electronic Resource
    A magnetohydrodynamic stability study of reverse shear equilibria in the Tokamak Fusion Test Reactor (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1673-1681 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A study is presented of the low-n (n=1,2,3) magnetohydrodynamic stability of equilibria with reverse shear safety factor profiles. The low-n stability boundaries are found to be characterized by resonance structures due to internal so-called "infernal'' mode types of instabilities. The parametric dependence of shear reversal width and depth, current, and pressure gradient on the beta limit are determined by using profile models that allow each parameter to be varied independently. Reverse magnetic shear is found to have a stabilizing influence for modes with toroidal mode numbers n≥2 leading to the possibility of improved β limits in the Tokamak Fusion Test Reactor (TFTR) [Plasma Phys. Controlled Nucl. Fusion Res. 26, 11 (1984)]. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871687
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  • 3
    Electronic Resource
    Electronic Resource
    Perturbed-angular-correlation studies of In-vacancy pairs in Hg1−xCdxTe (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 3576-3583 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interaction of vacancies with 111In atoms is studied in Hg1−xCdxTe compounds via perturbed-angular correlation (PAC) experiments, for x=0.065, 0.21, 0.44, and 0.95. In the low-x (Hg-rich) compounds, Hg vacancies are created by heating in vacuum. For the x=0.21 alloy, we have previously shown that InC-vacC pairs (A centers consisting of an In atom on a cation site and a vacancy at a neighboring cation site) are abundant after quenching from elevated temperatures. These defects are characterized by two PAC signals with quadrupole interaction frequencies νQ1=83 MHz and νQ2=92 MHz, and asymmetry parameters η1=η2=0.08. For the x=0.065–0.44 alloys, the data presented in this article show that the fractions f1 and f2 of In atoms associated with these two frequencies vary with x according to whether one or two Hg atoms are nearest neighbors to the Te atom that is bound to the In atom and the vacancy. The data are explained by the polarizable point-ion model. For the x=0.95 compound, PAC signals are observed only when stable In is added to the compound, indicating that the presence of In creates vacancies, and that self-compensation via A centers is dominant. In this case, the well-known frequencies νQ4=100 MHz and νQ5=112 MHz are seen for samples quenched from several different temperatures between 325 and 525 °C, or slow cooled from 475 °C or below. In contrast, for a sample slowly cooled from 525 °C, the frequency νQ6=60 MHz was dominant. This signal could be due to InC−vacC pairs in which the vacancy is singly charged, or to In-group I pairs. We attribute the frequencies νQ4=100 MHz and νQ5=112 MHz, like νQ1 and νQ2, to InC-vacC pairs having doubly charged vacancies. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371261
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  • 4
    Electronic Resource
    Electronic Resource
    Writing on perpendicular patterned media at high density and data rate (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5318-5320 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The feasibility of reversing single bit per particle media at a 1 GHz data rate with a density of 100 Gb/in.2 is examined. The media particles are cubic with 40 nm side length, 80 nm center to center spacing and perpendicular uniaxial anisotropy. Micromagnetic simulations are employed, and writing of data is done via an elongated probe to provide localized fields at the particle being reversed. The reversal of individual elongated particles is also examined with fields from a moving probe. A 1 GHz data rate appears to be more attainable with cubic particles than with elongated particles. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370238
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  • 5
    Electronic Resource
    Electronic Resource
    Calibration of the Joint European Torus energetic ion and alpha particle collective Thomson scattering diagnostic receiver : Proceedings of the 12th topical conference on high temperature plasma diagnostics (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 1167-1170 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The receiver of the Joint European Torus (JET) energetic ion and alpha particle collective Thomson scattering diagnostic is calibrated assuming blackbody emission from the torus vacuum vessel (VV) and using electron cyclotron emission (ECE). The 32 receiver channels are absolutely calibrated with a mechanical chopper in the quasioptical arm of the receiver, alternating the receiver view between the torus vacuum at 320 °C and room temperature. This calibration is noisy due to the small difference between torus and room temperatures. A more accurate relative calibration is achieved with the ECE during plasma shots. The intensity of the ECE is found to be a smooth function of frequency, which enables the combination of the ECE calibration with the VV calibration. The accuracy of the absolute VV calibration is hereby improved to nearly the same standard as the relative ECE calibration. ECE signals measured by the calibrated receiver agree well with standard JET ECE diagnostics. Based on mathematical considerations presented here, noise is injected into the receiver final intermediate frequency stage during VV calibrations to provide more bit transitions for accurate analog-to-digital (AD) conversion of the low level calibration signals. This yields a resolution which is better than 1% of an (AD) step. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149475
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  • 6
    Electronic Resource
    Electronic Resource
    First results of collective scattering on JET (invited) : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 275-280 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The fast ion and α-particle diagnostic at JET is based on collective Thomson scattering of high power millimeter-wave radiation. The principal aim of the diagnostic will be the measurement of the spatially resolved velocity distribution of fast α particles when tritium is introduced in JET plasmas, although several other applications are foreseen. The diagnostic uses a 140 GHz, 500 kW, gyrotron as the source of probing radiation and a heterodyne detection system. The diagnostic came into operation during the last JET operational campaign. First measurements were made of the thermal and mildly suprathermal (induced by ion cyclotron resonance heating) ion feature. The results confirmed expectations, indicating that the diagnostic should give the predicted performance for observation of α-particle populations in the DT phase. The signal-to-noise ratio is limited by the noise on the background radiation (electron cyclotron emission), which has a minimum around 140 GHz only when JET is operated at B∼3.4 T. To further improve the S/N and to make the diagnostic suitable for operation at higher field, which is now being considered for some of the DT plasmas, a viewing dump will be installed before the DT phase. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147822
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  • 7
    Electronic Resource
    Electronic Resource
    Determination of the relative densities of high-voltage stressed-generated traps near the anode and cathode in 10-nm-thick silicon oxides (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3089-3093 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The relative densities of high-voltage stress-generated traps near the anode and cathode in 10-nm-thick silicon oxides have been measured after both positive and negative gate voltage stressing. The density of traps near the stress anode and cathode were approximately equal after negative gate voltage stressing. The density of traps near the stress cathode was higher than near the stress anode after positive gate voltage stressing. These results implied that impact ionization near the anode was not a significant generator of traps in 10-nm-thick oxides. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361251
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  • 8
    Electronic Resource
    Electronic Resource
    Analysis of phase shifts due to etching in photoreflectance spectra of a GaAs/AlGaAs single-quantum well structure (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 2672-2678 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Room-temperature photoreflectance measurements of a GaAs/Al0.2Ga0.8As single-quantum well structure showed well defined Franz–Keldysh oscillations in the neighborhood of the GaAs and Al0.2Ga0.8As band-edge energies. That experiment investigated the origin of the Franz–Keldysh oscillations by sequential etching and photoreflectance analysis of the grown layers and showed that the phase of the Franz–Keldysh oscillations shifted as the upper Al0.2Ga0.8As barrier was etched, with eventual phase reversal when roughly half of the upper barrier was removed. Here, these phase shifts are determined accurately using a novel Kramers–Kronig approach and they are interpreted in terms of optical interference effects using both a simple two-ray model and a multiple-reflection treatment incorporating a calculation of the Seraphin coefficients. The results also enable the thickness of the layers removed to be determined. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358734
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  • 9
    Electronic Resource
    Electronic Resource
    Reassessment of the assignment of the InM2+3+VM2+ defect in CdTe and ternary II-VI compounds (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 1776-1781 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Previous perturbed angular correlation (PAC) spectroscopy measurements on the donor indium in CdTe and its alloys have revealed several defect complexes. One defect characterized by two sets of quadrupole interaction parameters, νQ=83 MHz, η=0.08 and νQ=92 MHz, η=0.08, was observed in Hg0.8Cd0.2Te (x=0.2 MCT) and attributed to the substitutional indium–metal vacancy complex InM2+3+VM2+. A defect characterized by νQ=61±1 MHz and asymmetry parameter η between 0 and 0.19 was seen in CdTe and widely attributed to the same complex. Both of these assignments were based mainly on an observed relationship between complex formation and the loss of metal ions. In this article we present PAC measurements on 111In-doped x=0.45 MCT (Hg0.55Cd0.45Te). These measurements reveal defects having quadrupole interactions very similar to those seen previously in CdTe and in x=0.2 MCT. Two unique defect fractions f1 and f2, characterized by νQ1=60±3 MHz, η1≈0–0.2, and νQ2=87±4 MHz, η2≈0–0.15, were seen in x=0.45 MCT, in some cases simultaneously. The observation of both of these interactions in the same material—if they correspond to the defects seen in CdTe and x=0.21 MCT—precludes the possibility that they both correspond to precisely the same defect. We also observed a change in the relative fractions of these two defects with time at room temperature; the fraction f2 vanished over a period of a day, while f1 and f0 (the fraction of indium atoms in sites having cubic or higher symmetry) increased. While we cannot rule out the possibility of a slow electronic transition, at present we favor a model in which one of the interactions (probably the one near 60 MHz) corresponds to a complex in which indium is paired to a fast-diffusing monovalent metal ion like Ag+, Cu+, or Li+. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360207
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  • 10
    Electronic Resource
    Electronic Resource
    Third-order nonlinearities and coherent transient grating effects of narrow-gap semiconductors in the midinfrared (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3371-3375 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Picosecond excitation-probe measurements using a far-infrared free-electron laser (CLIO) have revealed large nonlinearities for indium antimonide at 4.7 μm. A theoretical model is described to determine the cw third-order nonlinear susceptibility and the interband relaxation time of the semiconductor which were found to be −8.6×10−11 m2 V−2 and 0.3 ns, respectively. Furthermore, the observation of the associated coherent transient grating effects allows us to obtain a coherence time of the laser system (2.5 ps) and the χ(3) of the transient grating which was found to be −7.2×10−13 m2 V−2. The measurements were performed at room temperature on undoped bulk InSb. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359964
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