Simulation of DIII-D disruption with pellet injection and runaway electron beam*

The injection of a frozen impurity pellet as a disruption mitigation system (DMS) for the next generation of large tokamaks, including ITER, is a promising method for reducing the thermal and electromagnetic loads from a potential disruption without generating enough high-energy (runaway) electrons to damage the device. The effectiveness of this system has been tested on many experiments, with encouraging results. To further study its effects, we have modeled one such DMS experiment on DIII-D using the M3D-C1 nonlinear 3D extended MHD code (Jardin et al 2012 J. Comput. Sci. Discovery). Our model includes the injection and ablation of an argon pellet, impurity ionization and recombination, radiation, and the formation and evolution of runaway electrons, including both Dreicer and avalanche sources. We have found that our model provides reasonable agreement with the experimental results, in terms of the timescale of the thermal and current quench, and the magnitude of the runaway electron plateau formed during the mitigation. This provides a partial validation of the M3D-C1 DMS model, and further highlights the potential of using frozen impurity pellet injection for disruption mitigation in the next generation of large tokamaks. Disclaimer: This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.