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  • American Institute of Physics (AIP)  (30)
  • 2020-2024
  • 2010-2014  (6)
  • 2000-2004  (24)
  • 1
    Electronic Resource
    Electronic Resource
    Equilibrium and confinement of bunched annular beams (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 1422-1430 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The azimuthally invariant cold-fluid equilibrium is obtained for a periodic, strongly bunched charged annular beam with an arbitrary radial density profile inside of a perfectly conducting cylinder and an externally applied uniform magnetic field. The self-electric and self-magnetic fields, which are utilized in the equilibrium solution, are computed self-consistently using an electrostatic Green's function technique and a Lorentz transformation to the longitudinal rest frame of the beam. An upper bound on the maximum value of an effective self-field parameter for the existence of a bunched annular beam equilibrium is obtained. As an application of the bunched annular beam equilibrium theory, it is shown that the Los Alamos National Laboratory relativistic klystron amplifier experiment is operating slightly above the effective self-field parameter limit, and a discussion of why this may be the cause for their observed beam loss and microwave pulse shortening is presented. The existence of bunched annular beam equilibria is also demonstrated for two other high-power microwave (HPM) experiments, the relativistic klystron oscillator experiment at Air Force Research Laboratory and the backward wave oscillator experiment at the University of New Mexico. In general, the results of the equilibrium analysis will be useful in the determination of the stability properties of strongly bunched annular beams in HPM devices. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1459063
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  • 2
    Electronic Resource
    Electronic Resource
    Confinement criterion for a highly bunched beam (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 5206-5213 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonrelativistic motion is analyzed for a highly bunched beam propagating through a perfectly conducting cylindrical pipe confined radially by a constant magnetic field parallel to the conductor axis. In the present analysis, the beam is treated as either a thin rod distribution representing a continuous (unbunched) beam or periodic collinear point charges representing a highly bunched beam. Use is made of a Green's function to compute the electrostatic force on the beam due to the induced surface charge in the conductor wall. By analyzing the Hamiltonian dynamics, a criterion is derived for the confinement of unbunched and bunched beams. It is shown that for the confinement of beams with the same charge per unit length, the maximum value of the effective self-field parameter is 2ωp2/ωc2≅2a/L for a highly bunched beam with a(very-much-less-than)L. This value is significantly lower than the Brillouin density limit for an unbunched beam 2ωp2/ωc2=1. Here, a is the radius of the conducting cylinder, and L is the periodic spacing of the bunches. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1319639
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  • 3
    Electronic Resource
    Electronic Resource
    Kinetic study on replacement of hydrogen by deuterium at (100)Si/SiO2 interfaces (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 6536-6538 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The kinetics for the replacement process of hydrogen by deuterium at the (100)Si/SiO2 interface is studied. Metal–oxide–semiconductor devices were initially annealed in hydrogen and then reannealed in deuterium at various temperatures for various durations. The deuterium concentration CD, defined as the percentage of interface defects passivated by deuterium, was then determined by a technique that is solely based on electrical measurements. From fundamental kinetics, activation energy E for replacing hydrogen by deuterium at the (100)Si/SiO2 interface is determined to be 1.84 eV. This result suggests that the replacement of hydrogen by deuterium involves a process of the dissociation of molecular deuterium at the interface. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1412265
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  • 4
    Electronic Resource
    Electronic Resource
    Excitation of elastic surface pulses by fiber optics and near-field optical devices (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 5090-5096 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Elastic surface pulses or surface acoustic wave (SAW) pulses were launched at the surface by confining pulsed laser radiation with single-mode fibers and tapered fiber tips, produced by the focused ion beam technique, in near-field configuration. The propagation of the elastic surface pulses was studied in a point-source point-probe experiment. The transient surface displacements of the propagating SAW pulses were detected by an actively stabilized Michelson interferometer with sub-angstrom resolution. For tip aperture sizes in the micrometer range confinement effects could be observed, extending the frequency spectrum of the launched SAW pulses to approximately 800 MHz. The actual frequency spectrum was limited by the applied detection method. An inverse square root dependence of the SAW amplitude with propagation distance was confirmed experimentally, as expected for the excitation geometry employed. Results are presented for layered systems with dispersion of the ultrasonic surface pulses. The relevance of the frequency spectrum of the SAW pulse for the determination of elastic and mechanical film properties in dispersive media is discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1412583
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  • 5
    Electronic Resource
    Electronic Resource
    Investigation of phase transition thresholds by nonlinear transient laser gratings on silicon surfaces (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 3505-3510 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nonlinear transient laser gratings were excited by crossing two 180 ps Nd:YAG laser pulses (355 nm) at the silicon surface. The launched counterpropagating surface acoustic wave trains were detected outside the source with a cw laser probe-beam-deflection setup. Phase transitions occurring within the Gaussian fluence distribution of the grating induced characteristic changes in the amplitude of the corresponding grating oscillations involved and higher harmonics were found in the frequency spectrum. In the molten surface region, the amplitude decreased compared to the thermoelastic excitation, and second-harmonic generation was observed, whereas ablation generated an asymmetric profile with higher amplitudes and even the third harmonic could be detected. An accurate method is introduced to determine the ablation threshold (340 mJ/cm2 for silicon) from the transition of linear to nonlinear behavior in the distorted non-Gaussian amplitude distribution. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372373
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  • 6
    Electronic Resource
    Electronic Resource
    Effective-mass enhancement and nonparabolicity in thin GaAs quantum wells (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 6945-6947 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study size quantization effects on the conduction band dispersion in GaAs/AlAs quantum wells using a semiempirical tight-binding method. For GaAs well thicknesses between 3 and 11 nm, we find a significant increase of the conduction band mass of up to 50% compared with bulk GaAs. Concomitantly, the confinement reduces the highest achievable group velocities for electrons in the Γ conduction valley of the well by up to 30%. We discuss some of the consequences for quantum-well-based devices. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1321773
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  • 7
    Electronic Resource
    Electronic Resource
    Impurity density profile measurements with a fast filter spectrometer and a modulated diagnostic beam on Tore Supra by charge exchange recombination spectroscopy (2002)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 1775-1778 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A simple interference filter spectrometer, together with a modulated neutral diagnostic beam is used on the Tore Supra tokamak for the measurement of carbon impurity profiles by charge exchange spectroscopy. A temporal resolution of 8 ms with a good signal to noise ratio is obtained with a neutral hydrogen beam of about 1 A equivalent neutral current at the plasma edge at 45 kV. Experimental results with ion cyclotron heating show that fast changes of the heating power are followed by transient modifications of the carbon impurity profile. The evolution of the C6+ profile from peaked to hollow and back to normal can be followed step by step and a typical diffusion time of about 30 ms is measured. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1459092
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  • 8
    Electronic Resource
    Electronic Resource
    Electrode-sheath voltages in high-pressure mercury arcs (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 1271-1275 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electrode-sheath voltages (ESVs) were determined as a function of time in high-pressure ac mercury arcs running at different frequencies in the range 50 Hz–5 kHz with sinusoidal wave forms. Besides the experimental investigations, a one-dimensional model was used to describe the arc-column properties. Measurements of the voltage across the arcs were compared with model calculations for the arc-column voltage only. The calculated voltages are mostly smaller than the measured ones, and it was concluded that the difference should correspond to the ESV. This voltage drop was compared with values obtained in a completely different way, namely, by measuring the voltage at different lengths of the arcs which were otherwise identic, and extrapolating it to zero length. As had been shown before, at 50 Hz this voltage drop has a very pronounced time behavior during a half cycle. The investigations were extended to higher frequencies, and the obtained differences are discussed. The field strengths were derived from the rise of the measured voltage versus the discharge lengths; a quantitative agreement with the calculated field strengths was obtained by choosing an appropriate pressure. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373814
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  • 9
    Electronic Resource
    Electronic Resource
    Improved algorithm for modeling collision broadening through a sequence of scattering events in semiclassical Monte Carlo (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 303-311 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An improved, more physically accurate algorithm is presented for modeling collision broadening in semiclassical Monte Carlo. More specifically, the method of connecting a sequence of collision broadened scattering events is addressed. Sequences of collision broadened scattering events are analyzed via basic theory and illustrated via first-principles simulations using the quantum transport simulator Schrödinger Equation Monte Carlo in which, in contrast to semiclassical Monte Carlo, real scattering and collision broadening are inseparable processes. It is demonstrated that the requirement for energy conservation in the coupled carrier-phonon system prohibits the accumulation of the uncertainty in the carrier energy associated with collision broadening through a sequence of scattering events, accumulation that is possible with the conventional treatment of collision broadening in semiclassical Monte Carlo. Based on this analysis, basic changes to the treatment of collision broadening in semiclassical Monte Carlo are suggested. The potential significance of these changes is then assessed via simplified semiclassical Monte Carlo simulations. In particular, the exaggeration of the high-energy tail of the carrier distribution possible with the conventional treatment of collision broadening in semiclassical Monte Carlo is demonstrated to be an artifact of the above described nonphysical accumulation of the collision broadening contributions, not of the form of the collision broadening used (Lorentzian, etc.) as often assumed; with this more physically accurate new algorithm, well-behaved high-energy tails of the carrier distribution are obtained even with full Lorentzian broadening. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371861
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  • 10
    Electronic Resource
    Electronic Resource
    Solid-state halogen atom source for chemical dynamics and etching (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 81 (2002), S. 1140-1142 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe a solid-state Br atom source for surface etching, kinetics, and reaction dynamics studies. Pulsed laser irradiation of crystalline KBr, near the bulk absorption threshold at 6 eV, produces hyperthermal Br atoms in dense plumes. The Br atom density and velocities may be controlled by choice of laser pulse power and photon energy. Single and multiple pulse excitation of KBr produces Br and Br* in controllable quantities and velocities, thus providing an attractive ultrahigh vacuum compatible solid-state radical atom source. The solid-state atom source is in principle extendable to other halogens using other alkali halides and perhaps other materials. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1488700
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