Reduced modeling of scrape-off losses of runaway electrons during tokamak disruptions

TL;DR

This paper introduces a simplified model for runaway electron losses during tokamak disruptions, emphasizing scrape-off effects and their importance in predicting runaway electron behavior in ITER-like scenarios.

Contribution

A new reduced model for runaway electron scrape-off losses compatible with 1D flux-surface averaged simulations is developed and implemented in the DREAM disruption tool.

Findings

Scrape-off losses significantly influence runaway electron mitigation strategies.

The model shows potential for complete runaway avoidance in ITER scenarios.

Results are sensitive to current profile dynamics and generation mechanisms.

Abstract

Accurate modeling of runaway electron generation and losses during tokamak disruptions is crucial for the development of reactor-scale tokamak devices. In this paper we present a reduced model for runaway electron losses due to flux surface scrape-off caused by the vertical motion of the plasma. The model is made compatible with computationally inexpensive one-dimensional models averaging over a fixed flux-surface geometry, by formulating it as a loss term outside an estimated time-varying minor radius of the last closed flux surface. We then implement this model in the disruption modeling tool DREAM, and demonstrate its impact on selected scenarios relevant for ITER. Our results indicate that scrape-off losses may be crucial for making complete runaway avoidance possible even in a $15\,\rm MA$ DT H-mode ITER scenario. The results are however sensitive to the details of the runaway electron generation and phenomena affecting the current density profile, such as the current profile relaxation at the beginning of the disruption.