Optimization of Multiple D2 SPI for Two-Staged Plasma Mitigation

This experiment focuses the physics behind the first stage in a staggered mitigation scheme, firing D2 shattered pellet injection (SPI) then D2/Ne SPI, on ITER. This injection scheme is favorable compared to injection of multiple D2/Ne SPI simultaneously due to the increased runaway electron avoidance (high density, dilution cooling lowers energy of initial RE seed). The goal of this experiment would be to find the best scheme for multiple D2 SPI to increase assimilation and get the fragments through the hot edge of the plasma. Previous single D2 SPI experiments on DIII-D showed an increase in overall electron density, ~70% reduction in stored thermal energy, and plasmas which survived SPI injection. Extrapolation of these results to injection of multiple D2 SPI, which is required for ITER, at different toroidal locations is unclear as well as implications of injection into a plasma with existing MHD is unclear. The data will also contribute to a larger database with complementary data from KSTAR and JET and can already on its own allow predictions for size and energy scaling.