Modeling runaway electron generation during massive gas injection induced disruptions*

Runaway electrons (REs) can damage plasma facing components in a tokamak. However, the generation of REs during disruption mitigation techniques is complex and not well understood. This work investigates RE generation during massive gas injection (MGI) induced disruptions in JET. RE distribution are evolved via the Kinetic Orbit Runaway electrons Code (KORC) incorporating field inputs from the extended-magnetohydrodynamic code NIMROD. Two dominant sources of RE generation are considered. The primary RE generation is considered by the hot-tail source in which rapid thermal quench rate enhances the primary RE seed. The secondary source of REs is avalanche source, where large-angle, knock-on collisions are considered by seed REs on the thermal population. A detailed analysis to understand the RE generation mechanism is carried out considering collisional and particle trapping effects. The validated simulations on the JET MGI experiments will be useful to extrapolate RE generation mechanisms in Fusion Pilot Plants.