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  • Digitale Medien  (24)
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  • Digitale Medien  (24)
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  • 1
    Digitale Medien
    Digitale Medien
    Combined kinetic and transport modeling of radiofrequency current drive (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4972-4982 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A numerical model for predictive simulations of radiofrequency current drive in magnetically confined plasmas is developed. It includes the minimum requirements for a self-consistent description of such regimes, i.e., a three-dimensional kinetic equation for the electron distribution function, one-dimensional heat and current transport equations, and resonant coupling between velocity space and configuration space dynamics, through suitable wave propagation equations. The model finds its full application in predictive studies of complex current profile control scenarios in tokamaks, aiming at the establishment of internal transport barriers by the simultaneous use of various radiofrequency current drive methods. The basic properties of this nonlinear numerical system are investigated and illustrated by simulations applied to reversed magnetic shear regimes obtained by Lower Hybrid and Electron Cyclotron current drive for parameters typical of the Tore Supra tokamak [Equipe Tore Supra, in Proceedings of the 12th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Nice, France, 1988 (International Atomic Energy Agency, Vienna, 1989), Vol. 1, p. 9]. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1318355
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  • 2
    Digitale Medien
    Digitale Medien
    Investigation of lower hybrid wave damping in the PBX-M tokamak (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 125-133 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Lower hybrid (LH) current drive experiments on the Princeton Beta Experiment-Modified (PBX-M) [Phys. Fluids B 2, 1271 (1990)] have shown that the current profile can be changed by varying the phase velocity of the waves. The radial profile of the current carrying electrons was deduced from two-dimensional hard x-ray tomography. For a certain range of phase velocities, there is a correlation between the peak of the fast electron profile and the launched wave spectrum, despite the presence of a wide spectral gap between the phase velocity and the thermal electron energy distribution. A new model is proposed to explain how first-pass wave damping is possible in such plasmas. The rf power can form a tail of energetic electrons, and subsequently waves with moderate phase velocity can damp on them. For waves with very fast phase velocity, there must be an upshift of the n(parallel) spectrum for any damping to occur. These hypotheses are supported by ray tracing results which are coupled to relativistic Fokker–Planck calculations of the electron distribution function. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.872122
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  • 3
    Digitale Medien
    Digitale Medien
    Plasma diagnostics using synchrotron radiation in tokamaks (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1612-1618 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Emission of synchrotron radiation for electron temperature diagnostics in dense and hot tokamak plasmas is discussed. This novel diagnostic scheme is motivated by the need to overcome several limitations of the familiar first and second harmonic method, caused by cutoff, refraction, and harmonic overlap. Emission at high harmonics is not restricted by density and temperature upper limits, and the method is then particularly appropriate for reactor relevant regimes. This method yields global information on the electron temperature profile, since the source of high harmonic emission is poorly localized in space. Synchrotron radiation is emitted by electrons over a wide spectrum of energies, ranging from thermal to superthermal values, and is therefore also useful to investigate deviations of the electron velocity distribution from the Maxwellian. In contrast, the source of the optically thick low harmonic radiation is highly localized in the ordinary space near the resonance points, which implies that the energy of the emitting electrons lies in the subthermal range. The basic theory of the method is presented and illustrated by numerical applications, for plasma parameters of relevance for International Thermonuclear Experimental Reactor (ITER) [ITER-JCT and Home Teams, Plasma Phys. Controlled Fusion 37, A19 (1995)]. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.872020
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  • 4
    Digitale Medien
    Digitale Medien
    Wave focusing near the electron cyclotron frequency in hot plasmas (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 876-882 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Microwave transmission spectra measured on the Tore Supra tokamak [Equipe Tore Supra, in Proceedings of the 12th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Nice, 1988 (International Atomic Energy Agency, Vienna, 1989), Vol. 1, p. 9] exhibit a systematic enhancement of the transmitted power at frequencies close to the electron gyrofrequency, often well beyond the corresponding level detected in vacuum. In order to explain such observations, the problem of electromagnetic wave propagation near the electron cyclotron frequency in a hot magnetized plasma is investigated in the framework of geometrical optics. The simple case of the ordinary mode injected vertically is studied by taking the finite plasma temperature and relativistic corrections to the dispersion relation into account, in contrast with the more familiar cold plasma ray-tracing approach. It is found that the ray trajectories are strongly affected by such effects in the anomalous dispersion region close to the cyclotron resonance. As a consequence of this analysis, it is shown that the local enhancement of the transmitted power observed experimentally can be explained as a focusing phenomenon related to hot-plasma corrections to the wave refractive index. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871438
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  • 5
    Digitale Medien
    Digitale Medien
    Modeling of the stabilization of neoclassical tearing modes by localized radio frequency current drive (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 312-322 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Numerical modeling of the stabilization of neoclassical tearing modes by localized radio frequency (rf) current drive is presented. The bootstrap current is self-consistently calculated from the pressure evolution equation, the rf current source is obtained from the ray-tracing code and the Fokker–Planck code, and the change of the driven current profile due to the change of the magnetic island width has also been taken into account by modeling the two-dimensional transport of the fast electrons induced by the rf wave. It is found that both parallel and the perpendicular transport of the fast electrons play important roles in the stabilization, and modulated and nonmodulated rf current drive have approximately the same stabilizing effect. The neoclassical tearing modes is shown to be stabilized by a continuous rf current drive. The simulation results essentially agree with experimental observations. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873799
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  • 6
    Digitale Medien
    Digitale Medien
    Fast electron transport and lower hybrid absorbed power profiles from hard x-ray imaging in the Princeton Beta Experiment-Modified (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 1548-1560 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Recent hardware improvements on the hard x-ray camera of the Princeton Beta Experiment-Modified (PBX-M) expand the capabilities for observing bremsstrahlung radiation from fast electrons during lower hybrid current drive (LHCD) experiments, thereby allowing accurate fast electron transport studies. Developed methods to directly invert two-dimensional x-ray images reveal radial profiles of the emitted intensity and isotropy. Such profiles extracted from lower hybrid (LH) modulation experiments permit computation of the lower hybrid power absorption profile. Results from application to the LH phase scans demonstrate the ability to control the peak location of the driven current. Incorporating these results into simulations using both a three-dimensional Fokker–Planck code and a simple modulation model provides lower and upper bound estimates for the hot electron diffusion coefficient D*. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871484
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  • 7
    Digitale Medien
    Digitale Medien
    Hot plasma effects on the polarization of electron cyclotron waves (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 660-665 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The evolution of the wave polarization during the propagation of electron cyclotron waves in hot plasmas is investigated. The coupled mode equations are solved in slab geometry, including the relativistic corrections to the dielectric tensor. This formalism is applied to purely ordinary or extraordinary modes, propagating obliquely with respect to the magnetic field in tokamak plasmas, in order to determine the rate of change of the mode purity due to finite temperature effects. It is found that such an alteration of the mode purity can be one to three orders of magnitude larger than in a cold plasma. However, the overall effect remains tolerable for most applications and typical parameters of magnetically confined plasmas. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873301
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  • 8
    Digitale Medien
    Digitale Medien
    Comments on "Analysis of electron cyclotron current drive using neoclassical Fokker–Planck code without bounce-average approximation'' [Phys. Plasmas 2, 4570 (1995)] (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2827-2828 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The conclusion reached in ref. 1 that the 3-D Fokker-Planck code verses the 2-D bounce-averaged code does not yield the correct current density is prove to be wrong. It is aruged that the results for the 3-D code are very close to those of the 2-D code that employs a bounce-average procedure.(AIP) © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871719
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  • 9
    Digitale Medien
    Digitale Medien
    Plasma diagnostics in the Tokamak Fusion Test Reactor using emission of electron cyclotron radiation at arbitrary frequencies (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2331-2336 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Emission of cyclotron radiation at arbitrary wave frequency for diagnostic purposes is discussed. It is shown that the radiation spectrum at arbitrary frequencies is more informative than the first few harmonics and it is suited for diagnosis of superthermal electrons without any "ad hoc'' value of the wall reflection coefficient. Thermal radiation from the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)] is investigated and it is shown that the bulk and the tail of the electron momentum distribution during strong neutral beam injection is a Maxwellian with a single temperature in all ranges of electron energies. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871915
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  • 10
    Digitale Medien
    Digitale Medien
    Hamiltonian analysis of fast wave current drive in tokamak plasmas (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 2908-2925 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The Hamiltonian formalism is used to address the problem of the direct resonant interaction between the fast magnetosonic wave and the electrons in a tokamak plasma. The intrinsic stochasticity of the electron trajectories in phase space is first derived. Together with extrinsic decorrelation processes, it assesses the validity of the quasilinear approximation for the kinetic studies of fast wave current drive (FWCD). A full-wave solution of the Maxwell–Vlasov set of equations provides the exact pattern of the wave fields in the tokamak geometry, consistent with a realistic antenna spectrum. The local quasilinear diffusion tensor is then derived from the wave fields and the driven current density profile, the power deposition profile and the current drive efficiency are computed, including possible nonlinear effects in the kinetic equation. Several applications of FWCD on existing and future machines are given, and the combination of FWCD with other noninductive current drive methods is investigated. Finally, an analytical expression for the current drive efficiency is derived in the moderate to high single-pass absorption regime.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.870531
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