Effects of resonant magnetic perturbations on neutral beam heating in a tokamak

TL;DR

This study numerically investigates how resonant magnetic perturbations (RMPs) influence neutral beam heating efficiency in the EAST tokamak, revealing effects on fast ion distribution, loss mechanisms, and resonance behaviors.

Contribution

It introduces a numerical analysis of RMP effects on NBI heating, including a statistical method to identify non-integer resonances between RMPs and fast ions.

Findings

RMPs cause local fast ion accumulation and increased pressure.

The phase difference of RMPs affects fast ion radial profiles.

Some resonances between RMPs and lost particles are fractional, not integer.

Abstract

Effects of resonant magnetic perturbations (RMPs) on tangential neutral beam heating in the EAST tokamak are studied numerically. RMPs with linear resistive magnetohydrodynamics response are used in the modeling. A variety of representing configurations of RMP coil currents are examined and their effects on the NBI heating efficiency are compared, in order to find a parameter window where deleterious effects of RMPs on NBI heating efficiency are minimized. It is found that the internal redistribution of fast ions by RMPs induces local accumulation of fast ions, resulting in higher local fast ion pressure than the case without RMPs. It is also found that the toroidal phasing of the RMP with respect to the fast ion source has slight effects on the steady-state radial profile of fast ions. The dependence of fast ion loss fraction on the RMP up-down phase difference shows similar behavior as the dependence of the radial width of chaotic magnetic field on the phase difference. A statistical method of identifying resonances between RMPs and lost fast ions is proposed and the results indicate that some resonances between RMPs and lost passing particles may be of non-integer fractional order, rather than the usual integer order.