Toroidal modeling of interaction between resistive wall mode and plasma flow

TL;DR

This paper investigates the nonlinear interaction between resistive wall modes and plasma flow in toroidal geometry, highlighting the role of neoclassical viscous torque in flow braking and mode evolution.

Contribution

It introduces a numerical model that simultaneously solves RWM dynamics and plasma flow, revealing the impact of initial conditions and viscous torque on mode stability.

Findings

Neoclassical viscous torque is the main momentum sink braking plasma flow.

Flow braking influences the growth or stabilization of RWMs.

Initial perturbation amplitude affects the evolution of initially stable RWMs.

Abstract

The non-linear interplay between the resistive wall mode (RWM) and the toroidal plasma flow is numerically investigated in a full toroidal geometry, by simultaneously solving the initial value problems for the n=1 RWM and the n=0 toroidal force balance equation. Here n is the toroidal mode number. The neoclassical toroidal viscous torque is identified as the major momentum sink that brakes the toroidal plasma flow during the non-linear evolution of the RWM. This holds for a mode that is initially either unstable or stable. For an initially stable RWM, the braking of the flow, and hence the eventual growth of the mode, depends critically on the initial perturbation amplitude.