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  • 1990-1994  (13)
  • 1985-1989  (12)
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  • 1
    Digitale Medien
    Digitale Medien
    Far field sheaths from waves in the ion cyclotron range of frequencies (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 2890-2900 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Experimental evidence suggests that unabsorbed wave energy in ion cyclotron range of frequency fast wave (FW) experiments can result in deleterious edge interactions. A model describing the formation of far field sheaths due to FW interaction with material surfaces is presented. Near conductors that do not conform to flux surfaces, an incoming FW causes the generation of a slow wave (SW) component. The E(parallel) of the SW drives an RF sheath, in a manner similar to what has been previously discussed for antenna (near field) sheaths. To assess the importance of the proposed mechanism, a heuristic scaling model of the resultant sheath voltage V is developed and compared with a numerical code. The model illustrates the important dependencies of V on the single pass absorption, edge density, FW frequency, FW cutoff location, and limiter/wall geometries and yields qualitative agreement with the experimental observations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.870529
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  • 2
    Digitale Medien
    Digitale Medien
    Runaway electrons as a diagnostic of magnetic fluctuations (abstract) : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4617-4617 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The transport of runaway electrons in a hot plasma can be comparatively easily measured by perturbation experiments. The runaway electron diffusion coefficient is determined by intrinsic magnetic fluctuations rather than electrostatic fluctuations because of the high energies involved. The results presented here demonstrate the efficacy of using runaway transport techniques for determining intrinsic magnetic fluctuations. This work was supported in part by U. S. Department of Energy under grant DE-FG05-88ER-53267 and the Texas Advanced Research Program.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1143686
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  • 3
    Digitale Medien
    Digitale Medien
    Analytic model for the runaway distribution function in the presence of spatial diffusion (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 684-690 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A steady-state kinetic model for runaway electrons in the presence of radial diffusion in a stochastic magnetic field is adopted and solved for a constant magnetic diffusivity. The model is constructed to recover the correct runaway production rate in the absence of spatial diffusion. The parallel energetic electron distribution function f is found by matching the solutions from three regions in parallel velocity space and is employed to form moments of f. Upper and lower bounds on the spatial diffusion are obtained by using these moments and the model exhibits the strong sensitivity to collisionality needed to explain the difference between similar plasmas with little or no hard x-ray signal and those with significant hard x-ray signals.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.870814
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  • 4
    Digitale Medien
    Digitale Medien
    A quasilinear, Fokker–Planck description of fast wave minority heating permitting off-axis tangency interactions (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 52-63 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The off-axis quasilinear fast wave minority heating description of Catto and Myra [Phys. Fluids B 4, 187 (1992)] has been improved and implemented in a code which solves the combined quasilinear and collision operator equation for the minority distribution function. Geometrical complications of a minority resonance nearly tangent to a flux surface in the presence of trapped as well as passing particles are retained. The tangency interactions alter the moments and the fusion reaction rate parameter in a model which explores heating on a single flux surface. The strong tangency interactions enhance the more familiar interactions due to trapped particles turning in the vicinity of the minority resonance. An asymmetry in off-axis heating effects occurs because heating on the low field side of the magnetic axis heats more trapped particles than high field side heating. This asymmetry is responsible for the better performance of the low field side case relative to the high and on-axis cases and provides some control over the power absorbed by and the energy stored in the trapped particles.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.870558
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  • 5
    Digitale Medien
    Digitale Medien
    Effect of drifts on the diffusion of runaway electrons in tokamak stochastic magnetic fields (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 176-186 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The quasilinear diffusion of runaway electrons in tokamak stochastic magnetic fields is examined. Previous models are generalized with respect to the spatial location and coherency of the perturbing magnetic fields, treatment of the radial as well as poloidal drift motion of the electrons, and the role of sidebands that arise from the beating of the electron drift motion with the applied perturbing fields. It is found that drift effects act to reduce the level of quasilinear diffusion by an amount that depends on the poloidal distribution of the magnetic turbulence. The results are employed to estimate the internal magnetic fluctuation levels at the edge during recent experiments on the TEXT tokamak [Phys. Fluids B 3, 2038 (1991)], where the drift modification effects are shown to be small. It is inferred that intrinsic magnetic turbulence controls runaway diffusion, but not the thermal diffusivity of the background electrons.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.860431
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  • 6
    Digitale Medien
    Digitale Medien
    Estimating the runaway diffusion coefficient in the TEXT tokamak from shift and externally applied resonant magnetic-field experiments (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2038-2049 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Two techniques are employed on the TEXT tokamak [Nucl. Fusion 29, 547 (1989); 30, 167 (1990)] to measure the runaway diffusion coefficient D: (i) displacing the plasma column, and (ii) externally applying resonant magnetic fields. Model diffusion equations for the experiments are solved to obtain analytic predictions which then can be used to interpret the measurements. The initial transient response of the x-ray flux to the perturbing shift or applied magnetic field is used to measure a D of order 1 m2 sec−1 near the edge that decreases inward.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.859670
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  • 7
    Digitale Medien
    Digitale Medien
    Magnetic field line ergodicity in the edge plasma due to an ion-Bernstein wave antenna (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 1293-1295 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Large ponderomotive forces can occur near a high-power ion cyclotron range of frequency antenna, particularly for the parallel electric field polarization used to excite ion-Bernstein waves (IBW). The magnetohydrodynamic (MHD) equilibrium of the edge plasma is modified by these forces when the antenna is highly localized poloidally and toroidally. Magnetic islands develop at the edge, near q=m/n, where ||m||≤πa/wa and ||n||≤πR/la, with wa and la the width and length of the antenna, respectively. Ergodicity of the magnetic field lines may be expected when the islands overlap. Numerical calculations of the island overlap criteria are presented for two examples relevant to present day (IBW) heating experiments.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.866760
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  • 8
    Digitale Medien
    Digitale Medien
    Induced azimuthal electric fields in a tandem mirror with throttle coils (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 2751-2752 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A tandem mirror with an axisymmetric center cell separated from quadrupole regions by a large mirror ratio throttle coil is considered. Passing particles induce an azimuthal electric field in the center cell that destroys the axisymmetry of the guiding center orbits. It is shown that the resulting neoclassical resonant-plateau transport is small if dielectric resonances can be avoided.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.865518
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  • 9
    Digitale Medien
    Digitale Medien
    Comments on "Bifurcation phenomena and the radial electric field in a nonaxisymmetric plasma'' [Phys. Fluids 29, 536 (1986)] (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 2760-2761 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The smallest total collisional entropy production rate technique of choosing among multiple ambipolar roots is contrasted with a linearized stability method in which only the ambipolar potential is perturbed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.865522
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  • 10
    Digitale Medien
    Digitale Medien
    Quasilinear theory of the ponderomotive force: Induced stability and transport in axisymmetric mirrors (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 1895-1905 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A kinetic theory of the ponderomotive force density produced by an electromagnetic cyclotron wave is developed within the quasilinear approximation. The theory is applied to identify the effects of the rf-plasma interaction in equilibrium, stability and transport in paraxial, axisymmetric mirror geometry. The force caused by nonresonant particles is shown to modify the usual magnetohydrodynamic interchange stability drive, and the corresponding arbitrary-m ballooning equation is derived. Resonant particle contributions to the force are shown to arise from the absorption of photon momentum and spin. This effect produces a radial particle flux, modifies the radial ambipolar potential profile, and couples transport and stability.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.864933
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