Self-consistent modeling of runaway electron generation in massive gas injection scenarios in ASDEX Upgrade

TL;DR

This paper presents a comprehensive simulation of runaway electron generation during massive gas injection disruptions in ASDEX Upgrade, successfully reproducing experimental observations and providing insights into impurity effects and RE suppression strategies.

Contribution

First successful simulation of a disruption in ASDEX Upgrade from MMI to RE beam, integrating plasma response and impurity transport with kinetic RE models.

Findings

Simulation accurately reproduces experimental plasma parameters.

Impurity transport and radiation induce thermal collapse and RE generation.

Results inform RE mitigation strategies for future fusion reactors.

Abstract

We present the first successful simulation of a induced disruption in ASDEX Upgrade from massive material injection (MMI) up to established runaway electron (RE) beam, thus covering pre-thermal quench, thermal quench and current quench (CQ) of the discharge. For future high-current fusion devices such as ITER, the successful suppression of REs through MMI is of critical importance to ensure the structural integrity of the vessel. To computationally study the interplay between MMI, background plasma response, and RE generation, a toolkit based on the 1.5D transport code coupling ASTRA-STRAHL is developed. Electron runaway is described by state-of-the-art reduced kinetic models in the presence of partially ionized impurities. Applied to argon MMI in ASDEX Upgrade discharge #33108, key plasma parameters measured experimentally, such as temporal evolution of the line averaged electron density, plasma current decay rate and post-CQ RE current, are well reproduced by the simulation presented. Impurity ions are transported into the central plasma by the combined effect of neoclassical processes and additional effects prescribed inside the $q = 2$ rational surface to explain experimental time scales. Thus, a thermal collapse is induced through strong impurity radiation, giving rise to a substantial RE population as observed experimentally.