A current-driven resistive instability and its nonlinear effects in simulations of coaxial helicity injection in a tokamak

作者：Hooper E B^*; Sovinec C R

来源：Physics of Plasmas, 2016, 23(10): 102502.

DOI：10.1063/1.4964292

An instability observed in whole-device, resistive magnetohydrodynamic simulations of the driven phase of coaxial helicity injection in the National Spherical Torus eXperiment is identified as a current-driven resistive mode in an unusual geometry that transiently generates a current sheet. The mode consists of plasma flow velocity and magnetic field eddies in a tube aligned with the magnetic field at the surface of the injected magnetic flux. At low plasma temperatures (similar to 10-20 eV), the mode is benign, but at high temperatures (similar to 100 eV) its amplitude undergoes relaxation oscillations, broadening the layer of injected current and flow at the surface of the injected toroidal flux and background plasma. The poloidal-field structure is affected and the magnetic surface closure is generally prevented while the mode undergoes relaxation oscillations during injection. This study describes the mode and uses linearized numerical computations and an analytic slab model to identify the unstable mode.

• 出版日期2016-10