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  • 1
    Electronic Resource
    Electronic Resource
    The radial electric field dynamics in the neoclassical plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 4272-4282 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A numerical simulation and analytical theory of the radial electric field dynamics in low collisional tokamak plasmas are presented. An initial value code "ELECTRIC" has been developed to solve the ion drift kinetic equation with a full collisional operator in the Hirshman–Sigmar–Clarke form together with the Maxwell equations. Different scenarios of relaxation of the radial electric field toward the steady-state in response to sudden and adiabatic changes of the equilibrium temperature gradient are presented. It is shown, that while the relaxation is usually accompanied by the geodesic acoustic oscillations, during the adiabatic change these oscillations are suppressed and only the magnetic pumping remains. Both the collisional damping and the Landau resonance interaction are shown to be important relaxation mechanisms. Scalings of the relaxation rates versus basic plasma parameters are presented. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872590
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  • 2
    Electronic Resource
    Electronic Resource
    Neoclassical rotation of tokamak plasmas in the plateau regime (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3566-3568 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The poloidal rotation of tokamak plasmas is studied in the plateau regime. It is shown that the relaxation rate is given by vT/(qR)νˆ1/3O(1), while the inertia enhancement in this regime is 1+q2νˆ−1/3O(1), resulting from the time-dependent parallel viscosity, where q is the safety factor, νˆ=ε3/2ν* is the plateau collisionality parameter (ε3/2〈νˆ〈1), ε is the inverse aspect ratio, and ν* is the standard neoclassical collisionality parameter. An evolutionary equation for the radial electric field is derived. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871054
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  • 3
    Electronic Resource
    Electronic Resource
    Plateau regime dynamics of the relaxation of poloidal rotation in tokamak plasmas (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3023-3031 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theory of the relaxation dynamics of the radial electric field toward its neoclassical value in the regime of subsonic poloidal rotation is presented. It is shown that the relaxation occurs via damped oscillations on time scales proportional to the ion transit time. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871638
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  • 4
    Electronic Resource
    Electronic Resource
    Physical mechanism of enhanced stability from negative shear in tokamaks: Implications for edge transport and the L-H transition (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2221-2223 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The enhancement of stability to ballooning modes from negative shear in tokamaks is shown to be a simple consequence of the orientation of the convective cell with respect to the toroidally outward effective gravity, g↘. For modest positive shear, convective cells remain oriented along g↘ as they map along field lines. In contrast, for negative shear or very positive shear convective cells twist strongly away from g↘ and are less strongly driven. The twist of convection cells is controlled by the profile of the vertical magnetic field along the outer midplane, Bz. Twist is a minimum in regions where Bz is independent of the major radius. Transport should be highest in such locations. Resistive ballooning modes in the tokamak edge are strongly stabilized by modest values of negative shear. Tokamak discharges with finite values of βp develop regions of local negative shear on the outside midplane of the plasma torus. This local negative shear should self-stabilize resistive ballooning modes at finite values of the poloidal beta. This effect may impact the transition to high confinement operation (H-mode). © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871928
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  • 5
    Electronic Resource
    Electronic Resource
    Resistive ballooning modes in scrape-off layer of tokamak plasmas (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3764-3768 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Analytical and numerical study of the stability of the resistive ballooning modes (RBM) in the scrape-off layer (SOL) of a tokamak plasma is performed. It is shown that the stability of the RBM is controlled by the two parameters λ=(me/mi)1/2νeiqR/vTe—the "effective strength'' of the Debye sheath current, and mˆ=mL0/a the dimensionless poloidal number, where the characteristic scale L0 is given in the main text as a function of the basic plasma edge parameters. For λ(approximately-greater-than)1 the coupling to the sheath is unimportant and the unstable spectrum is virtually unchanged from that in the closed flux region. For λ〈1 the sheath current has a strong destabilizing influence on long wavelength modes. The general case of arbitrary λ and mˆ is studied numerically and the spectrum of the unstable RBM is found. The influence of the diamagnetic effects is also investigated. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871075
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  • 6
    Electronic Resource
    Electronic Resource
    New unstable branch of drift resistive ballooning modes in tokamaks (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 781-791 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Drift resistive ballooning modes (DRBM) are studied for present-day tokamak edge plasmas. A ballooning equation has been derived for DRBM, corresponding to an "optimal ordering,'' i.e., such a choice of the length and time normalizing units that make the three terms in the vorticity equation to be of the same order. A simple criterion to distinguish strong and weak ballooning regimes for DRBM has been obtained. The DRBM in the strong ballooning regime have been studied and it has been found that they are robustly unstable with an ideal growth rate γ∝cs/(RLn)1/2. The weak ballooning regime also has been studied. It has been found that there exist two different unstable branches in this case. The first one has been identified as a conventional DRBM studied earlier. It has been shown, however, that this solution is stabilized when magnetic shear sˆ=aq'/q is order of 1. The other branch has a stronger ballooning structure compared to the conventional DRBM branch and is localized on the outside of the torus. It is less unstable for a weak shear, but is the only one that is robustly unstable for sˆ∼1. A numerical simulation has shown that this branch matches the strong ballooning solution. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871431
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