Effect of plasma elongation on current dynamics during tokamak disruptions

TL;DR

This paper studies how plasma elongation influences runaway electron generation and electric field diffusion during tokamak disruptions, revealing that elongated plasmas tend to produce smaller runaway currents.

Contribution

It provides new insights into the impact of plasma shaping on runaway electron dynamics, highlighting the reduction in runaway gain with increased elongation.

Findings

Elongated plasmas are less likely to generate large runaway currents.

Larger plasmas have lower induced electric fields, reducing runaway production.

Shaping effects decrease runaway avalanche gain.

Abstract

Plasma terminating disruptions in tokamaks may result in relativistic runaway electron beams with potentially serious consequences for future devices with large plasma currents. In this paper we investigate the effect of plasma elongation on the coupled dynamics of runaway generation and resistive diffusion of the electric field. We find that elongated plasmas are less likely to produce large runaway currents, partly due to the lower induced electric fields associated with larger plasmas, and partly due to direct shaping effects, which mainly lead to a reduction in the runaway avalanche gain.