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

## TL;DR

This paper predicts the profile and magnitude of neoclassical toroidal viscosity (NTV) torque induced by plasma response to resonant magnetic perturbations in tokamak edge pedestals, highlighting its dependence on plasma parameters and potential significance in tokamak operation.

## Contribution

It provides a theoretical prediction of NTV torque profiles and magnitudes in tokamak edge pedestals, emphasizing the influence of plasma parameters and identifying regimes where NTV torque is significant.

## Key findings

- NTV torque is dominated by the toroidal component matching RMP mode number.
- The NTV torque profile peaks near the pedestal, influenced by temperature and pressure profiles.
- Higher plasma beta enhances the NTV torque magnitude.

## Abstract

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