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  • 1
    Digitale Medien
    Digitale Medien
    Calculations of wave excitation and dissipation in Tokamak Chauffage Alfvén wave heating experiment in Brazil (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2437-2442 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The results of numerical calculations of Alfvén wave absorption are discussed for the experimental conditions foreseen for the Tokamak Chauffage Alfvén wave heating experiment in Brazil (TCABR) [Nucl. Fusion 30, 503 (1996)]. In particular, the effect of toroidal mode coupling on the power deposition of Global Alfvén Wave (GAW) eigenmodes is carefully investigated. Resonant absorption of the toroidally coupled sidebands causes a broad power deposition close to the plasma boundary which can surpass the power deposition of the main GAW at the plasma center. However, the wave absorption can be somewhat optimized by a proper choice of mode spectrum. The excitation of a pure mode spectrum centered at the toroidal mode numbers n=−4 and −6 leads to better plasma coupling than a spectrum centered at n=−2. Finally, it is shown that a small population of light impurities in a hydrogen plasma can strongly modify the dispersion of the GAW and the toroidal Alfvén continuum.© 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873515
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  • 2
    Digitale Medien
    Digitale Medien
    Anomalous electron precipitation near the Earth's auroral zone induced by the wave–particle interaction (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2269-2275 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The results of a numerical simulation of anomalous electron precipitation in the Earth's auroral zone induced by waves are discussed. In order to study the plasma electron–wave interaction, a two-dimensional quasilinear code has been used. A quasilinear operator models the electron Landau damping of any plasma eigenmodes: kinetic Alfvén waves, whistlers, lower hybrid waves, etc. The distribution function structure was analyzed. The electron current induced by waves, the density, and the plasma energy decay, which stimulates the electron precipitation, have also been investigated. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.872390
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  • 3
    Digitale Medien
    Digitale Medien
    Alfvén ion–ion hybrid wave heating in the Phaedrus-T tokamak (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1331-1339 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In the Phaedrus-T tokamak [R. A. Breun et al., Fusion Technol. 19, 1327 (1991)], Alfvén waves are indirectly driven by a fast wave antenna array. Small fractions of minority ions are shown to have a large effect on the Alfvén spectrum, as measured at the edge. An ion–ion hybrid Alfvén mode has been identified by measuring dispersion properties. Landau damping is predicted to be large and spatially localized. These Alfvénic waves are experimentally shown to generate correlated electron heating and changes in density near the core of the tokamak plasma. Fast wave antenna fields can mode convert at a hybrid Alfvén resonance and provide a promising route to spatially localized tokamak heating and current drive, even for low effective ionic charge Zeff≈1.3–2. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871786
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  • 4
    Digitale Medien
    Digitale Medien
    Influence of trapped electrons on the dielectric properties of the Earth's radiation belts (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3798-3808 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The dielectric tensor of an axisymmetric magnetosphere is derived by solving the Vlasov equations for trapped particles for a two-dimensional plasma model with circular magnetic field lines. Because of the nonuniformity of the geomagnetic field any Fourier harmonic of the perturbed current density (after its Fourier expansion over the geomagnetic latitude) is proportional to the sum over all harmonics of the oscillating electric field; that leads to additional wave dissipation effects. The resonant conditions for wave–particle interactions are discussed taking into account the cyclotron and bounce resonances; these conditions in magnetospheric plasmas are entirely different from the Landau damping resonant factor in the uniform magnetic field. The numerical calculations of the longitudinal permeability in the Earth's radiation belts (the equatorial distance of the magnetic field line is five Earth's radii) are carried out for short-period oscillations with the frequency ω∼2 s−1 and longitudinal wave numbers n=1,...,15. The different energy levels of the trapped electrons, T∼40–4000 eV, are considered. It is shown that, in the low-frequency region, the imaginary part of the longitudinal permeability decreases as ∼T−2.5 whereas the electron temperature increases. This decrease is stronger than ∼T−1.5 for plasmas in a straight magnetic field. For a given wave frequency, the basic contribution of trapped electrons to the imaginary part of longitudinal permeability is associated with the low numbers of bounce resonances and the low longitudinal wave numbers. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871512
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  • 5
    Digitale Medien
    Digitale Medien
    Alfvén wave current drive in the Phaedrus-T tokamak (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2263-2271 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The first experimental evidence of Alfvén Wave Current Drive (AWCD) in a tokamak is shown. In a low-density experiment, an estimated 20–35 kA out of 65 kA total current, or 30%–55% of the total current has been driven. The estimated efficiency for current driven per unit RF input power is approximately ICD/PRF≈0.2 A/W, which is near the predicted efficiency, and corresponds to the commonly used figure of merit, neR0ICD/PRF≈0.4×1018 A m−2 W−1, where ne is plasma density and R0 is the major radius. The significant 30%–40% drop in loop voltage observed cannot be explained by any plausible increase in electron temperature Te, or decrease in inductive plasma energy, or changes in plasma resistivity. Independently measured loop voltage, Te, effective ionic charge Zeff, and plasma inductance and resistance are all consistent with this conclusion. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871249
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  • 6
    Digitale Medien
    Digitale Medien
    Alfvén wave heating and current drive : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2050-2056 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Progress in the theory of Alfvén wave (AW) heating, current drive, and plasma flow, which may be relevant for improved confinement scenarios in tokamaks, is discussed. The effect of poloidal mode coupling on the power deposition of AW eigenmodes is investigated. Resonant absorption of the coupled side bands causes a broad power deposition close to the plasma boundary which can surpass the power deposition of the main global AW at the plasma center. A small population of impurities, such as carbon, in a hydrogen plasma can strongly modify the dispersion of the global AW, the AW continuum and the wave dissipation profile. The ponderomotive forces produced by rf fields are expressed as a sum of a gradient (radial derivative) part and of a wave momentum transfer force found to be proportional to wave dissipation. Finally, the rf force is balanced by the friction (or neo-classical viscosity) force to calculate relevant current drive and plasma specie flows. Estimates of AW power requirements to drive substantial heating, current, and poloidal flow are made for plasmas in the Tokamak Chauffage Alfvén wave experiment in Brazil (TCABR) [L. Ruchko et al., Nucl. Fusion 30, 503 (1996)]. The first results of Alfvén wave heating and current drive experiments with a low level of wave dissipation in the TCABR are discussed. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1350572
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  • 7
    Digitale Medien
    Digitale Medien
    Radial plasma transport and toroidal current driven by nonresonant ponderomotive forces (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 2882-2889 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A general form of the time-averaged ponderomotive force produced by radio frequency waves in magnetized plasma configurations is treated. Included in the ponderomotive force are components that result from plasma flow, the dynamo effect, and wave helicity. A detailed description of effects of individual components in the ponderomotive force on radio frequency (RF) driven transport and current is given.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.870528
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  • 8
    Digitale Medien
    Digitale Medien
    Calculations of Alfvén wave driving forces, plasma flow, and current drive in the Tokamak Chauffage Alfvén wave experiment in Brazil (TCABR) (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 210-215 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The current and plasma flows driven by ponderomotive forces are calculated for tokamak plasmas, using a kinetic code in the Alfvén range of frequencies. The rf (radio frequency) ponderomotive force is expressed as a sum of a gradient part and of a wave momentum transfer force, which is proportional to wave dissipation (electron Landau damping and transit time magnetic pumping). Finally, the rf force is balanced by the viscous force in the fluid momentum response to the rf fields in the plasma. The relative magnitudes of the different forces for kinetic and global Alfvén waves with low phase velocities are explicitly calculated. It is shown that, dissipating in electrons, Alfvén waves can drive ion flow via the gradient force, which is dominated in m=0-sideband harmonic resonance induced by toroidal mode coupling. Estimates of power requirements to drive substantial poloidal flow in the Tokamak Chauffage Alfvén wave heating experiment in Brazil (TCABR) [L. Ruchko, M. C. Andrade, R. M. O. Galva˜o, Nucl. Fusion 30, 503 (1996)] are made. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1332813
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  • 9
    Digitale Medien
    Digitale Medien
    Comment on "Alfvén wave current drive in tokamak rotating plasma with negative magnetic shear" [Phys. Plasmas 6, 4633 (1999)] (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3119-3119 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.874170
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  • 10
    Digitale Medien
    Digitale Medien
    Anomalous and neoclassical transport suppression by the radial electric field, induced by Alfvén waves in tokamaks (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 3548-3553 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The suppression of anomalous transport and/or reduction of neoclassical transport caused by the Alfvén-wave-induced shear of the radial electric field in tokamaks is investigated. The simple quantitative estimates reported in previous papers are checked by a consistent evaluation of the profile of the radial electric field created by the resonant absorption of Alfvén waves. The radial variations of the ion viscosity and heat conductivity across the mode conversion layer are evaluated both in the banana and potato regions. In agreement with previous analytical results, it is shown that the kinetic Alfvén waves may play the role of a convenient mechanism for reduction of anomalous and neoclassical transport and formation of transport barriers in tokamaks. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873615
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