MHD Modeling of SPI Injection in JET and KSTAR

Nonlinear 3D MHD simulations of shattered-pellet injection (SPI) in JET have been performed using the M3D-C1 and NIMROD extended-MHD codes with a single, monolithic pellet show a prototypical SPI-driven disruption. NIMROD simulations show a radiative thermal quench (TQ) which becomes more rapid as the pellet passes the safety factor q=3 surface. The results are similar for both a single, monolithic pellet and a pencil-beam model for the SPI plume. A scan in viscosity from 200-2000 m²/s for 2D MHD simulations using NIMROD shows no significant change to the predicted radiative collapse. An initially radiation-driven TQ is accelerated by MHD activity as the pellet crosses the q=2 and q=3/2 surfaces, leading to a radiation spike, global stochasticization of the magnetic field, and a complete TQ. Eventually a current quench (CQ), preceded by a current spike is seen as the ohmic heating balances the radiative cooling. Simulations of KSTAR SPI experiments have also been performed. These simulations lay the ground work for more-sophisticated validative and predictive modeling of SPI in JET and KSTAR and development of SPI disruption mitigation scenarios in ITER using both M3D-C1 and NIMROD.