
Author(s):
H. Sugama, T.H. Watanabe and W. Horton

Title:
Collisionless Kineticfluid Model of Zonal Flows in Toroidal Plasmas
Date of publication:
Dec. 2006

Key words:
closure model, zonal flows, geodesic acoustic modes, ion temperature gradient modes, electron temperature gradient modes

Abstract:
A novel kineticfluid model is presented, which describes collisionless time evolution of zonal flows in tokamaks. In the new zonalflow closure relations, the parallel heat fluxes are written by the sum of short and longtimeevolution parts. The former part is given in the dissipative form of the parallel heat diffusion and relates to collisionless damping processes. The latter is derived from the longtimeaveraged gyrocenter distribution and plays a major role in describing lowfrequency or stationary zonal flows, for which the parallel heat fluxes are expressed in terms of the parallel flow as well as the nonlinearsource and initialcondition terms. It is shown analytically and numerically that, when applied to the zonal flow driven by either ion or electron temperature gradient turbulence, the kineticfluid equations including the new closure relations can reproduce the same longtime zonalflow responses to the initial condition and to the turbulence source as those obtained from the gyrokinetic model.

