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  • 1
    Digitale Medien
    Digitale Medien
    Poloidal rotation effects on a simulated resistive kink mode (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 174-179 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Through the principal use of the reduced magnetohydrodynamic version of the finite aspect ratio code [L. A. Charlton et al., J. Comput. Phys. 86, 270 (1990)], an m/n=1/1 resistive kink mode was poloidally rotated with the accompanying rotational shear. It was observed that the growth rate of this unstable mode can either decrease or increase as the applied equilibrium rotation is increased to near poloidal sonic speeds. Shear in the poloidal rotation profile is stabilizing, but only if the destabilizing effects of bulk rotation can be overcome. Therefore, the mode's stability was sensitive to the location of the rotation's peak relative to the eigenmode's spatial extent. The destabilizing effects of bulk rotation are apparently a rotationally enhanced beta, and the stabilizing effects appear to be caused by exceeding a critical rotational shear spatially averaged over the eigenmode structure. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1326062
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  • 2
    Digitale Medien
    Digitale Medien
    Lower hybrid dissipative cavitons and ion heating in the auroral ionosphere (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 516-526 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In this paper numerical solutions of Zakharov-type equations for lower-hybrid (LH) waves, including pumping at the long wavelengths and dissipation at short wavelengths in the form of dissipative cavitons are described. The caviton is a quasistationary structure undergoing many sequences of collapse due to dissipation, created by ion–wave interactions, which is compensated for by constant pump action. The possibility of trapping of short-wavelength LH oscillations by much broader density cavitons is investigated both analytically and numerically. Analytic self-similar solutions corresponding to collapse of such cavitons are constructed and demonstrate cascading to shorter wavelengths, which develops faster than the three-dimensional (3-D) quasiclassical cavity contraction. Numerical solutions show the development of deep caviton modulation due to the instability of quasiclassical collapse. Results of the numerical and analytical investigation are used to explain the recent observations of cavity formation in the auroral ionosphere, and show that the measured structures could indeed arise from quasiclassical LH collapse. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.870976
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  • 3
    Digitale Medien
    Digitale Medien
    Nonlinear collisional absorption in laser-driven plasmas (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 4043-4049 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The collisional heating rate of a fully ionized plasma driven by a strong electromagnetic pump wave is re-examined both analytically and with two-dimensional particle-in-cell (PIC) simulations. The high frequency conductivity model of Dawson and Oberman [J. Dawson and C. Oberman, Phys. Fluids 5, 517(1962)] is extended for the case in which the quiver velocity vo=eE/mωo is much larger than the thermal velocity vth and its equivalence to the results of Silin [V. P. Silin, Sov. Phys. JETP 20, 1510 (1965)] is shown. The Dawson and Oberman model is reduced to two-dimensions for comparison with the PIC simulations. Excellent agreement between the theory and the simulations for vo/vth≤1 is obtained. However, when vo/vth(very-much-greater-than)1 and the excursion amplitude xo=eE/mω2o is larger than the Debye length λD, the simulations show enhancements in the collision frequency from the theory. A possible mechanism for this enhancement is provided. © 1994 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.870874
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  • 4
    Digitale Medien
    Digitale Medien
    Effect of externally imposed and self-generated flows on turbulence and magnetohydrodynamic activity in tokamak plasmas : The 41st annual meeting of the division of plasma physics of the american physical society (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1795-1801 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The effects of externally imposed and self-generated poloidal flows on turbulence and magnetohydrodynamic (MHD) activity are examined in the context of the possible Electric Tokamak (ET) [Phys. Plasmas 6, 4722 (1999)] plasmas and (circularized) DIII-D-like [Fusion Technol. 8, 441 (1985)] discharges. Global gyrokinetic particle simulations and reduced MHD calculations respectively show that ion temperature gradient driven turbulence (ITGDT) and resistive internal kink MHD activity can be reduced and/or suppressed with experimentally achievable externally imposed flows for possible ET start-up plasmas. Global gyrokinetic particle simulations of ITGDT also serve to demonstrate that self-generated flows are necessary to yield experimentally relevant radial correlation lengths in the case of DIII-D-like discharges. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.874000
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  • 5
    Digitale Medien
    Digitale Medien
    Radial electric field required to suppress ion temperature gradient modes in the Electric Tokamak (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 4722-4727 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The Electric Tokamak (ET), currently under construction at the University of California–Los Angeles, is designed to rotate poloidally via a radial current induced by fast wave rf heating fast enough to bifurcate the plasma into a global "H mode" ("high confinement mode"). A global gyrokinetic code is used to explore and illustrate some of the effects on ion temperature gradient turbulence. The realistic radial electric field required to completely suppress these modes for ET parameters is demonstrated to be 〈−30 V/cm at its maximum near the half radius. The effects of both a poloidally supersonic bulk rotation threshold and the shear in this rotation near that supersonic threshold were shown to be important in reducing these modes. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873759
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  • 6
    Digitale Medien
    Digitale Medien
    Plasma heating through a supercritical oblique collisionless shock (1987)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 1110-1114 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Electron and ion dynamics are investigated through particle simulation of a supercritical oblique collisionless shock. As θ deviates from 90°, ions are accelerated and trapped in the electrostatic wells and later become detrapped; this results in strong ion heating perpendicular to B0. Below a critical angle θte electrons are strongly energized along B0, and heated. A large parallel electron current builds up and induces new transverse electromagnetic components in the ramp of the shock. For weaker angles, ion heating vanishes below a second critical angle θti.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.866309
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  • 7
    Digitale Medien
    Digitale Medien
    Erratum: "Electrostatic instabilities of velocity-space-shell distributions in magnetized plasmas'' [Phys. Fluids 29, 2569 (1986)] (1987)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 1575-1575 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.866530
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  • 8
    Digitale Medien
    Digitale Medien
    Erratum: "Unified theory and comparative study of cyclotron masers, ion-channel lasers, and free electron lasers'' [Phys. Fluids B 3, 1270 (1991)] (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 3203-3203 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.860004
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  • 9
    Digitale Medien
    Digitale Medien
    Plasma physics at the final focus of high-energy colliders (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 1384-1389 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The plasma physics associated with intense electron and positron beams in high-energy colliders is discussed. The focusing and plasma oscillation of these beams are studied in the presence of an externally supplied plasma (a plasma lens) and in the self-consistent fields of the interpenetrating beams. A plasma lens can provide strong focusing of a beam by shielding the beam's radial space-charge electric field and allowing it to self-pinch in its self-generated azimuthal magnetic field. The focusing force of a plasma lens can be equivalent to quadrupole magnet strengths of the order of hundreds of MG/cm. Theoretical and computational work characterizing the aberrations and final spot sizes possible with plasma lenses is presented. Furthermore, when the e+ and e− beams overlap at the interaction point (i.e., collide), they behave (temporarily) as a two-component plasma. The self-pinching or disruption of one beam by another in the e+e− plasma is modeled analytically and with two-dimensional particle-in-cell simulations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.859560
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  • 10
    Digitale Medien
    Digitale Medien
    Relativistic particle dynamics in a steepening magnetosonic wave (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 1001-1010 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Acceleration of both electrons and ions to relativistic energy by large amplitude magnetosonic waves is investigated by use of numerical simulation. Nonlinear effects are shown to form the saturation mechanism and limit the amplitude below the level where a particle specie can undergo unlimited acceleration, which is expected theoretically. Spiky structures appear both in density and field waveforms that are characteristics of the relativistic regime. Both electrons and ions are strongly accelerated by Elx×Bz drift and Ety field, but their resonance features versus fields are strongly different. Around the trapping time, relativistic electron solitonlike wavelets are triggered from the main wave ramp; a few mechanisms are proposed for their interpretation. Both electrons and ions are strongly heated at the expense of the wave energy. This damping in association with the large space charge effects resulting from the spiky structures is the origin of some observed saturation level in the field energy.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.859021
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