-
Author(s):
S. Bazdenkov, T. Sato, K. Watanabe and The Complexity Simulation Group
-
Title:
Multi-Scale Semi-Ideal Magnetohydrodynamics of a Tokamak Plasma
Date of publication:
Sep. 1995
-
Key words:
tokamak, fast current profile flattening, multi-scale semi-ideal MHD
-
Abstract:
An analytical model of fast spatial flattening of the toroidal current density and q-profile at the nonlinear stage of (m=1/n=1) kink instability of a tokamak plasma is presented. The flattening is shown to be an essentially multi-scale phenomenon which is characterized by, at least, two magnetic Reynolds numbers. The ordinary one, R_m, is related with a characteristic radial scale-length, while the other, R_m^ast, corresponds to a characteristic scale-length of plasma inhomogenety along the magnetic field line. In a highly conducting plasma inside the q = 1 magnetic surface, where q value does not much differ from unity, plasma evolution is governed by a multi- scale non-ideal dynamics characterized by two well-separated magnetic Reynolds numbers, R_m and R_m^astequiv(1 - q) R_m, where R_m^ast ~ 0(1) and R_m gg 1. This dynamics consistently explains two seemingly contradictory features recently observed in a numerical simulation [ Watanabe et al., 1995]: i) the current profile (q-profile) is flattened in the magnetohydrodynamic time scale within the q = 1 rational surface; ii) the magnetic surface keeps its initial circular shape during this evolution.
-
|
