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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 3701-3707 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Analytic calculations of electron transport across a Schottky barrier in 6H–silicon carbide are presented. The treatment includes the effect of barrier height fluctuations and image charge lowering on both the thermionic emission and electron tunneling processes. The results show that barrier height inhomogeneities are very important, and can lead to reverse current densities that are orders of magnitude higher than obtained from a simple theory. Formation of detrimental filamentary currents are predicted. The results are in very good agreement with published experimental data at 300 K. Finally, under forward biasing conditions, the analytical theory yields ideality factors of 1.037 in close agreement with measurements. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1029-1037 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The kinetic singular layer equation is derived from the ballooning representation formalism. The mode frequency and the ion-ion collision frequency are assumed to be lower than the ion transit frequency. It is proven that the balance between the instability drives and the small-parallel-ion-velocity (SPIV) effect, instead of inertia effect, has to be imposed on determining the eigenfrequency. Consequently, it is found that the resistive effect is ignorable, while the dominant collisional effect appears to be the collisional contribution to the SPIV effect, leading to the conclusion that the customary resistive magnetohydrodynamic modes, such as the resistive interchange, resistive ballooning, and tearing modes, are nonexistent in this description. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3614-3622 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A new non-perturbative and non-variational solution method is proposed for the gyrokinetic equation, based on a suitable approximation for the linearized Fokker-Planck collision operator. The approach, which allows, in principle, the accurate evaluation of arbitrary moments of the distribution function for a weakly collisional magnetoplasma with toroidal equilibria of arbitrary aspect-ratio, is susceptible of numerous significant applications, both for transport calculations, i.e., in particular, leading to the evaluation of neoclassical fluxes, as well for the investigation of linear stability analyses of dissipative perturbations. © 1995 American Institute of Physics.
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2469-2476 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Extensive magnetohydrodynamic–gyrokinetic hybrid simulations have been carried out to study the excitations of Alfvén instabilities by trapped energetic ions in tokamak plasmas. Depending on the parameters, the most unstable mode can be either the toroidal Alfvén eigenmode (TAE) or the energetic-particle mode (EPM). In both cases, the dominant instability driving mechanism is the resonance with the trapped-particle magnetic precessional drifts. The mode frequencies of the most unstable modes, meanwhile, tend to be near the toroidal frequency gap in order to minimize the continuum damping. It is also demonstrated that the instabilities can be quenched by reversing the magnetic precessional drifts via either negative magnetic shear or locating the magnetic turning points in the inner (strong B) side of the torus. © 2000 American Institute of Physics.
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1403-1409 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Gyrokinetic theory for ballooning modes with frequency lower than the thermal ion bounce frequency is presented. Due to a vast difference of the centrifugal and the Coriolis forces experienced by ions and electrons, the parallel electric field effect is found to be excited even in this low frequency case. Nevertheless, it is proved that, under suitable ordering assumptions, the magnetohydrodynamic (MHD)-structure-like ballooning mode equation can still be obtained. The kinetic effects are found to appear in three aspects: enlarging the magnitude of the apparent inertia, resulting in a real shift of the marginal frequency, and contributing a stabilizing term. © 1998 American Institute of Physics.
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1792-1801 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Braginskii's two-fluid equations, with collisional effects neglected and electron fluid assumed to be isothermal along the magnetic field lines, are employed to obtain the singular mode equations. While the ordering analysis in the paper indicates that, in the intermediate frequency regime (i.e., that with the frequency of the modes higher than the ion acoustic frequency along the magnetic field lines, but lower than the electron one), the stabilizing finite Larmor radius (FLR) effect on the modes dominates over other collisionless, two-fluid effects, the paper is devoted to the investigation of the comparable frequency regime (i.e., that with the frequency of the modes comparable to the ion acoustic frequency along the field lines). It is found that, in such a regime, the parallel electric field is excited and the plasma behaves nonadiabatically. The singular mode equations consist of two coupled second-order partial differential equations, in which the FLR, the plasma compression, and the parallel electric field effects are present. The results are discussed, and a comparison with the ideal magnetohydrodynamic formalism is given.
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 444-449 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: For circular tokamaks, it is demonstrated, both analytically and numerically, that there exists a new frequency gap within the shear Alfvén continuous spectrum around the Alfvén frequency, ωA=vA/qR, due to the ion compressibility effect. Here, vA denotes the Alfvén speed, q is the safety factor, and R the major radius. The frequency gap width, meanwhile, is proportional to the core ion beta, βi (ratio between core ion and magnetic pressures), and, correspondingly, the new discrete toroidal Alfvén eigenmode (TAE) inside the gap is referred to as βTAE. Collective excitations of the βTAE by energetic ions are also analyzed. © 1998 American Institute of Physics.
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  • 8
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2653-2663 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: By investigating the conservation laws of guiding-center mechanics, an extension of quasi-helical static magnetohydrodynamic equilibria to incorporate strong flow is obtained, subject to suitable ordering assumptions. Such equilibria correspond to self-consistent Fokker-Planck kinetic equilibria in the presence of a quasi-helical magnetic field. The effect of small symmetry-breaking contributions in the magnetic field is investigated. © 1996 American Institute of Physics.
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  • 9
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 4610-4619 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: With the two time scale feature revealed, an analytical method is developed to solve the combined eigenvalue and initial value problem describing the ion temperature gradient (ITG) modes in the toroidally rotating plasmas. With full gyrokinetics and toroidal geometry effects being taken into account in an ordering consistent manner, dispersion relations are obtained for ITG modes both of toroidal and slab-like branches. The results show that the sonic rotation can be harmful for the stability, while subsonic rotation with flow shear can be expected to be stabilizing. The existence of the flow shear leads the time evolution of the fluctuation signals to display two different time scales—a fast oscillating (either fast or slow growing) signal with its amplitude modulated by a slowly varying envelope, resembling fishbone-like fluctuations. © 1996 American Institute of Physics.
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  • 10
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 636-642 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Analytical equilibria for axisymmetric plasmas with an anisotropic energetic-particle component are obtained by expansions in the inverse aspect ratio and core- and hot-plasma betas. Upon the analytical equilibria, the energetic-particle-modified Mercier criterion [L.-J. Zheng and S.-T. Tsai, Phys. Fluids B 4, 1416 (1992)] is evaluated. A drift-nonreversed energetic-particle component is shown to make stabilizing terms to the criterion, which originate from the additional Shafranov shift of magnetic surfaces and the stabilizing kinetic energy contributed by the energetic particles. The results confirm that interchange modes in tokamaks can be stabilized by properly introducing drift-nonreversed energetic particles.
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