Asymmetric Wall Force Reduction in ITER and JET Disruptions

Full text: It has been thought that asymmetric vertical displacement event (AVDE) disruptions in ITER might produce large electro-mechanical forces on the walls and other conducting structures surrounding the plasma. It is shown that ITER AVDE disruptions should produce a small asymmetric wall force, comparable to JET. This is demonstrated in simulations with the M3D 3D MHD code and confirmed in JET experiments in which the current was quenched with massive gas injection (MGI). In ITER the current quench (CQ) time, τ_CQ, is less than or equal to the resistive wall penetration time, τ_wall. JET is in a different parameter regime, with τ_CQ > τ_wall. JET simulations were validated by comparison to JET shot 71985 data and were in good agreement. The wall time was then artificially increased, keeping τ_CQ fixed, and it was found that the wall force decreased. The reduction of the asymmetric wall force was also found in experimental data of JET MGI mitigated disruption shots. Further simulations were carried out of ITER AVDEs. The asymmetric wall force was calculated for a wide range of CQ times. For τ_CQ < τ_wall, the force was not much larger than in JET. A fast CQ may cause production of runaway electrons (REs). The effect of replacing part of of the current with REs on MHD behaviour will be discussed. Simulations using a modified version of M3D with a fluid RE model will be presented. Work supported by the U.S. Department of Energy and Euratom research and training programme 2014-2018 under grant agreement No. 633053, within the EUROfusion Consortium. Views and opinions herein do not necessarily reflect those of the European Commission. (author)