Nonlinear Magnetohydrodynamic Simulation of Flux Amplification and Sustainment of Spherical Torus Plasmas by Multi-pulsed Coaxial Helicity Injection

摘要

Nonlinear dynamics of spherical torus plasmas during multi-pulsed coaxial helicity injection is investigated by three-dimensional magnetohydrodynamic (MHD) simulation. The second-order finite difference method for spatial derivatives and the fourth order Runge-Kutta-Gill method for time integration are applied in order to solve the MHD equations. Amplification of the magnetic flux and the plasma current against resistive decay which is related to the n = 1 kink instability in the central open flux column (COFC) is observed during driven phase. During decay phase, the magnetic configuration approaches the axisymmetric equilibrium state without flows due to the dissipation of magnetic fluctuations to increase the closed flux surfaces, and the injected current concentrated in the COFC diffuses towards the core region.