Investigating SPARC Runaway Electrons Under Various Disruption Scenarios with DREAM Simulations*

In SPARC tokamak, disruptions under 'primary reference discharge' (PRD) conditions of e>~7keV and P_fusion~140MW (Creely 2020 JPP) can generate significant seed runaway electrons (REs) through various mechanisms, including hot-tail and Dreicer generation, Compton scattering, and tritium beta decay. These seeds subsequently grow exponentially via the avalanche effect that is particularly pronounced in SPARC due to its high plasma current of 8.7MA. Thus, unmitigated SPARC disruptions can have several MA of RE current (Tinguely 2021 NF). 

We use the DREAM code (Hoppe 2021 CPC) to study the RE evolution during SPARC disruptions under various parameters, including scans of pre-disruption plasma current I_p, thermal quench time t_TQ, magnetic field strength B(8T or 12.2T), and different temperature/density/current profiles. Results from both fluid and fluid-kinetic simulations, presented herein, offer a comprehensive perspective on RE dynamics. 

The REMC design, a potential RE mitigation strategy, uses disruptions' intense electric field to induce magnetic fluctuations, thus increasing RE loss (Sweeney 2020 JPP). Comparative DREAM simulation results, reflecting transport with or without REMC, will also be presented.