Post disruption reconnection event driven by a runaway current

TL;DR

This study uses numerical simulations to explore how runaway electrons influence magnetic reconnection after plasma disruptions, revealing their role in island rotation and nonlinear behavior.

Contribution

It provides new insights into the nonlinear dynamics of runaway electrons and their impact on magnetic island behavior during post-disruption reconnection.

Findings

Runaway electrons cause poloidal island rotation.

Microlayer width triggers runaway nonlinearity.

Island rotation slows as it saturates.

Abstract

The role of a runaway current in a post disruption plasma is investigated through numerical simulations in an asymmetric magnetic reconnection event. While the runaways do not alter the linear growth of the island, they lead to a rotation of the island in the poloidal direction as found in [C. Liu et al. Physics of Plasmas 27, 092507 (2020)]. The role of a microlayer smaller than the resistive one is thoroughly investigated. While the resistive layer controls the transition of the island from the linear to the nonlinear stage, the microlayer width causes the runaways to become nonlinear as soon as the size of the island exceeds it. Moreover, this transition of the runways electrons to the nonlinear phase is accompanied by a drastic redistribution of runaways within the island with respect to the symmetric case. The influence of the electron skin depth on the linear evolution is also taken into account. Finally, nonlinear simulations show that the rotation frequency tends toward zero when the island saturates.