Modelling of runaway electron dynamics during argon-induced disruptions in ASDEX Upgrade and JET

TL;DR

This study models runaway electron dynamics during argon-induced disruptions in ASDEX Upgrade and JET tokamaks, successfully reproducing plasma current evolution and highlighting the models' applicability across different machine sizes.

Contribution

The paper introduces a fluid modelling framework that simulates runaway electron generation and loss during disruptions, applicable to different tokamak sizes.

Findings

Model accurately reproduces plasma current evolution during disruptions.

Assumptions about hot-tail electron loss are necessary for high initial temperatures.

Models are applicable to both small and large tokamaks.

Abstract

Disruptions in tokamak plasmas may lead to the generation of runaway electrons that have the potential to damage plasma-facing components. Improved understanding of the runaway generation process requires interpretative modelling of experiments. In this work we simulate eight discharges in the ASDEX Upgrade and JET tokamaks, where argon gas was injected to trigger the disruption. We use a fluid modelling framework with the capability to model the generation of runaway electrons through the hot-tail, Dreicer and avalanche mechanisms, as well as runaway electron losses. Using experimentally based initial values of plasma current and electron temperature and density, we can reproduce the plasma current evolution using realistic assumptions about temperature evolution and assimilation of the injected argon in the plasma. The assumptions and results are similar for the modelled discharges in ASDEX Upgrade and JET, indicating that the implemented models are applicable to machines of varying size, which is important for the modelling of future, larger machines. For the modelled discharges in ASDEX Upgrade, where the initial temperature was comparatively high, we had to assume that a large fraction of the hot-tail runaway electrons were lost in order to reproduce the measured current evolution.