Dynamics of kinetic geodesic-acoustic modes and the radial electric field in tokamak neoclassical plasmas

We present edge gyrokinetic simulations of tokamak plasmas using the fully non-linear (full- f ) continuum code TEMPEST. A non-linear Boltzmann model is used for the electrons. The electric field is obtained by solving the 2D gyrokinetic Poisson equation. We demonstrate the following. (1) High harmo...

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Bibliographic Details
Published in:Nuclear fusion 2009-06, Vol.49 (6), p.065023-065023 (8)
Main Authors: Xu, X.Q, Belli, E, Bodi, K, Candy, J, Chang, C.S, Cohen, R.H, Colella, P, Dimits, A.M, Dorr, M.R, Gao, Z, Hittinger, J.A, Ko, S, Krasheninnikov, S, McKee, G.R, Nevins, W.M, Rognlien, T.D, Snyder, P.B, Suh, J, Umansky, M.V
Format: Article
Language:English
Subjects:
Exact sciences and technology
Gyrokinetics
Magnetic confinement and equilibrium
Physics
Physics of gases, plasmas and electric discharges
Physics of plasmas and electric discharges
Plasma dynamics and flow
Power exhaust
divertors
Tokamaks
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Summary:We present edge gyrokinetic simulations of tokamak plasmas using the fully non-linear (full- f ) continuum code TEMPEST. A non-linear Boltzmann model is used for the electrons. The electric field is obtained by solving the 2D gyrokinetic Poisson equation. We demonstrate the following. (1) High harmonic resonances ( n > 2) significantly enhance geodesic-acoustic mode (GAM) damping at high q (tokamak safety factor), and are necessary to explain the damping observed in our TEMPEST q -scans and consistent with the experimental measurements of the scaling of the GAM amplitude with edge q 95 in the absence of obvious evidence that there is a strong q -dependence of the turbulent drive and damping of the GAM. (2) The kinetic GAM exists in the edge for steep density and temperature gradients in the form of outgoing waves, its radial scale is set by the ion temperature profile, and ion temperature inhomogeneity is necessary for GAM radial propagation. (3) The development of the neoclassical electric field evolves through different phases of relaxation, including GAMs, their radial propagation and their long-time collisional decay. (4) Natural consequences of orbits in the pedestal and scrape-off layer region in divertor geometry are substantial non-Maxwellian ion distributions and parallel flow characteristics qualitatively like those observed in experiments.
ISSN:0029-5515
1741-4326
DOI:10.1088/0029-5515/49/6/065023