Simulation Center for Runaway Electron Avoidance and Mitigation

Runaway electrons are extremely high energy electrons driven by electric fields in plasmas due to the decrease of electron collision frequency with increasing velocity. These electrons can be generated during a major disruption in burning fusion plasma experiments and can reach relativistic velocity and severely damage the plasma facing components of the device, thus posing a major risk for tokamak fusion in general. It is now widely recognized that an adequate disruption mitigation system (DMS) is essential for the safe operation of the upcoming burning plasma experiments such as ITER. Though the basic physics mechanisms are known, the detailed quantitative dynamics of how the electrons interact with various physical effects in the plasma can only be predicted through advanced simulation. The United States is responsible for the design and implementation of the DMS on ITER, and in July 2016 the Simulation Center for Runaway Electron Avoidance and Mitigation (SCREAM) was launched, as a joint Fusion Energy Sciences (FES) and Advanced Scientific Computing Research (ASCR) partnership. SCREAM is a comprehensive theory and simulation SciDAC center that provides physics guidance in the avoidance and mitigation of runaway electrons, and in tandem with domestic and international experiments, helps establish the qualitative and quantitative bases for safe operational scenarios and viable mitigation techniques. The SCREAM center assembles a national team of experts in runaway electron physics, tokamak disruptions, magnetohydrodynamic (MHD) simulation, and advanced algorithms and computing. The team combines advanced simulation and analysis capability facilitated by direct participation of ASCR SciDAC institutes with theoretical models and code development by FES scientists to focus on the runaway risk for ITER and tokamaks in general. The analysis of and validation against experimental results is leading this center to a predictive capability for ITER, investigating new ideas for understanding and mitigating the disruption driven runaway electron phenomenon.