Effects of resistivity on linear plasma responses to resonant magnetic perturbations in tokamak plasmas

Abstract

Numerical studies are made of the effects of resistivity on linear plasma responses to resonant magnetic perturbations (RMPs) in tokamaks based on a reduced magnetohydrodynamic model. From a local two-field model, it is suggested that the ratio of the poloidal electron advection to the resistivity diffusion rate αm can be a figure of merit parameter in linear RMP penetration physics. The shielding efficiency is governed by αm, and when αm≳1, RMPs are effectively shielded. Global simulations using a four-field model [Hazeltine and Meiss, Phys. Rep. 121, 1 (1985)] show that there exists an effective threshold of the perpendicular electron flow (Ve,⊥c) beyond which RMPs cannot penetrate. Resistivity is found to determine Ve,⊥c which increases as resistivity becomes higher, making RMP penetration easier. At low resistivity, small Ve,⊥c renders the RMP penetration sensitive to ion collisionality and the change in q95. The kink response is observed to be closely related to the residual level of RMPs at rational surfaces and can be also strongly affected by resistivity.