Stabilization of the tearing mode in high-temperature plasma

Abstract

An analytical and numerical study of the stability of tearing modes is carried out using the Braginskii fluid equations. An electron temperature gradient coupled with finite (nonzero) parallel thermal conductivity causes large parallel currents to flow in the vicinity of the singular layer (where k⋅B=0). The pressure-driven currents are stabilizing and in the limit βL2s/L2n>1, where β is the ratio of the thermal to magnetic pressure and Ls and Ln are the magnetic shear and density scale lengths, the linear tearing mode no longer exists. In this high-β limit, the magnetic perturbation of the tearing mode is completely shielded from the singular layer so that no reconnection of the magnetic field can take place. The relationship between the tearing mode and previously investigated temperature-gradient-driven modes and the implications of the results for resistive modes in present and future tokamak discharges is discussed.