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  • Artikel: DFG Deutsche Nationallizenzen  (27)
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  • Artikel: DFG Deutsche Nationallizenzen  (27)
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  • 1
    Digitale Medien
    Digitale Medien
    Synergistic effects of the safety factor and shear flows on development of internal transport barriers in reversed shear plasmas (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 748-751 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A new suppression mechanism of turbulent transport, characteristic of the synergism between safety factor and shear flows, is proposed to explain the internal transport barriers (ITBs) observed in neutral-beam-heated tokamak discharges with reversed magnetic shear. It is shown that the evolution of turbulent transport with the strength of the suppression mechanism reproduces the basic features of the formation and development of ITBs observed in experiments. In addition, the present analyses predict the possibility of global ion and electron heat transport barriers. © 2002 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1445753
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  • 2
    Digitale Medien
    Digitale Medien
    Gyrokinetic study of ion temperature gradient instability in vicinity of flux surfaces with reversed magnetic shear (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 167-173 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Ion temperature gradient (ITG) driven instability is investigated in the vicinity of a flux surface where the magnetic shear reverses. The generic properties of the profile of the magnetic shear are taken into account with gyrokinetic stability theory in the local sheared slab geometry integral equation. The stability analysis shows that there are four distinct unstable ITG branches with significantly different eigenvalues and mode structures existing simultaneously in the vicinity of the minimum q layer. The variation of eigenmode structures with magnetic shear is investigated in detail. The mixing length estimation of the induced plasma transport is performed. Detailed numerical results are presented and general correlations with simulations and experiments are noted. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1326060
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  • 3
    Digitale Medien
    Digitale Medien
    Studies of instability and transport in sheared-slab plasmas with very weak magnetic shear (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3334-3340 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Ion temperature gradient (ITG or ηi) driven microinstabilities are studied, using kinetic theory, for tokamak plasmas with very weak (positive or negative) magnetic shear (VWS). The gradient of magnetic shear as well as the effects of parallel and perpendicular velocity shear (v(parallel)′ and vE′) are included in the defining equations. Two eigenmodes: the double (D) and the global (G) are found to coexist. Parametric dependence of these instabilities, and of the corresponding quasilinear transport is systematically analyzed. It is shown that, in VWS plasmas, a parallel velocity shear (PVS) may stabilize or destabilize the modes, depending on the individual as well as the relative signs of PVS and of the gradient of magnetic shear. The quasilinear transport induced by the instabilities may be significantly reduced with PVS in VWS plasmas. The vE′ values required to completely suppress the instabilities are much lower in VWS plasmas than they are in normal plasmas. Possible correlations with tokamak experiments are discussed. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.872474
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  • 4
    Digitale Medien
    Digitale Medien
    Studies of impurity mode and ion temperature gradient mode in toroidal plasmas (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3412-3419 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The impurity mode and ηi mode driven by impurity ions with outwardly peaked density profiles, near the boundary of tokamak plasmas, and the ion temperature gradient, respectively, are studied in high-temperature toroidal plasmas. The gyrokinetic theory is applied and finite Larmor radius effects of both hydrogenic and impurity ions are included. It is found that the impurity mode is enhanced by the ion temperature gradient. In addition, the impurity ions with outwardly peaked density profiles are demonstrated to have destabilizing effects on the ηi mode. These two modes are strongly coupled to each other so that it is impossible to distinguish between them when both the driving mechanisms are strong enough to drive the corresponding mode unstable independently. The correlation of the results with nonlinear simulations and the experimental observations are discussed. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871123
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  • 5
    Digitale Medien
    Digitale Medien
    Momentum-energy transport from turbulence driven by parallel flow shear (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3250-3261 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The low-frequency E×B turbulence driven by the shear in the mass flow velocity parallel to the magnetic field is studied using the fluid theory in a slab configuration with magnetic shear. Ion temperature gradient effects are taken into account. The eigenfunctions of the linear instability are asymmetric about the mode rational surfaces. Quasilinear Reynolds stress induced by such asymmetric fluctuations produces momentum and energy transport across the magnetic field. Analytic formulas for the parallel and perpendicular Reynolds stress, viscosity, and energy transport coefficients are given. Experimental observations of the parallel and poloidal plasma flows on the Texas Experimental Tokamak Upgrade (TEXT-U) are presented and compared with the theoretical models.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.870477
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  • 6
    Digitale Medien
    Digitale Medien
    Existence of ion temperature gradient driven shear Alfvén instabilities in tokamaks : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 1917-1924 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The existence of unstable ion temperature gradient driven Alfvén eigenmodes (AITG) is demonstrated in tokamak plasmas, which are ideally stable with respect to magnetohydrodynamics (MHD). Conditions for the destabilization of such modes are quantitatively discussed on the basis of numerical solutions of a set of one-dimensional integral equations along the ballooning coordinate (quasi-neutrality and parallel Ampère's law). Furthermore, theoretical analyses of the eigenmode dispersion relation, which is given in a compact analytical form in the small ion orbit width limit (compared to the radial wavelength), provide a basis for explaining the general properties of the modes. It is emphasized that instability requires both sufficiently strong thermal ion temperature gradients and that the plasma be not too far away from ideal MHD marginal stability. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873449
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  • 7
    Digitale Medien
    Digitale Medien
    Plasma rotation and electrostatic potential formation at the edge due to suprathermal particle lossesf| (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1583-1591 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Generation of the edge radial electric field and corresponding plasma rotation is studied for toroidal confinement systems with a separatrix configuration of magnetic surfaces. It is shown that classical acceleration of plasma by ion orbital losses can explain the electric field and the plasma rotation observed near walls when plasma flow to the neutralizing wall is included.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.870710
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  • 8
    Digitale Medien
    Digitale Medien
    Magnetic and velocity shear effects on ηi-modes in plasmas with ion temperature anisotropy (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4120-4127 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Ion temperature gradient (ITG or ηi) driven microinstabilities are studied, using fluid and kinetic theories, for plasmas with ion temperature and temperature gradient anisotropy. The sheared slab geometry model (nonlocal scheme) is employed. The effects of a parallel velocity shear and a perpendicular velocity shear on the modes are investigated. It is shown that the anisotropy in ion temperature gradient enhances (reduces) the stabilization from a magnetic shear for η⊥〉η(parallel) (η⊥〈η(parallel)). An anisotropy of T⊥〉T(parallel) in ion temperature is found to give an overall stabilizition (destabilization) for low (high) magnetic shear, s(circumflex)∼0.1 (s(circumflex)∼0.4). Parametric dependence of the instabilities is systematically analyzed. Previous results from the shearless toroidal model are confirmed with a sheared torus. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1394776
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  • 9
    Digitale Medien
    Digitale Medien
    Study of microinstabilities in toroidal plasmas with negative magnetic shear (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3065-3072 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The microinstabilities driven by a parallel velocity shear, and a temperature gradient of ions are studied in toroidal plasmas with negative magnetic shear. Both the fluid and the gyrokinetic formulations are investigated. It is found that for a broad range of parameters, the linear growth rates of the modes are lower and the threshold temperature gradient ηicr is higher for plasmas with negative magnetic shear compared to plasmas with positive magnetic shear of equal magnitude. The reduction in the growth rate (with negative shear), although not insignificant, does not seem to be enough to account for the dramatic improvement in the confinement observed experimentally. Other possible physical mechanisms for the improved confinement are discussed. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871654
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  • 10
    Digitale Medien
    Digitale Medien
    Convective amplification of drift-acoustic waves in sheared flows (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3742-3750 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The evolution of wave packets is investigated in a cold-ion plasma model with sheared magnetic and velocity fields. Wave packets may be amplified by the drift Kelvin–Helmholtz mechanism even when the velocity shear is such that normal modes are stable. It is shown that the logarithm of the convective amplification can be an order of magnitude greater than the logarithm of the steady-state amplification often taken as the measure of convective instability. For a given wave number, the maximum of either of these amplifications decreases only as the inverse of the perpendicular component of the velocity shear. © 1994 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.870848
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