Neoclassical toroidal viscosity torque in tokamak edge pedestal induced by external resonant magnetic perturbation

Abstract

The characteristic profile and magnitude are predicted in theory for the neoclassical toroidal viscosity (NTV) torque induced by the plasma response to the resonant magnetic perturbation (RMP) in a tokamak with an edge pedestal. For a low-β equilibrium, the NTV torque is dominated by the toroidal component with the same dominant toroidal mode number of RMPs. The NTV torque profile is found to be localized, whose peak location is determined by profiles of both the equilibrium temperature (pressure) and the plasma response. In general, the peak of the NTV torque profile is found to track the pedestal position. The magnitude of NTV torque strongly depends on the β value at the top of pedestal, which suggests a more significant role of NTV torque in higher plasma β regimes. For a fixed plasma β, decreasing density hence increasing temperature can also enhance the amplitude of NTV torque due to the reduced collisionality in the 1/ν regime. Based on those findings, we identify the tokamak operation regimes where the significance of NTV torque in the edge pedestal induced by RMP can approach those from other momentum sources such as the neutral beam injections.