NIMROD Simulations of Multi-Injector Shattered Pellet Injection

Shattered Pellet Injection (SPI) is the primary candidate for disruption mitigation in ITER.  Single injector SPI

experiments show strong peaking of the radiation and significant n=1 activity.  NIMROD single injector SPI

simulations\footnote{C C Kim et al.Physics of Plasmas,26:042510,2019} reproduce these features.  It is believed that multi-injector SPI scenarios may mitigate

these undesirable features.  However, experimental demonstration of multi-injector SPI has proven to be challenging.

NIMROD simulations of multi-injector SPI in DIII-D have been performed.  We will describe the fragment plume

representation based on the statistical fragmentation model by Parks\footnote{P Parks.GA internal report,(GA-A28325),2016}.  Simulation results demonstrate

the key role of the fragment distribution in the efficacy of the dual injector scenario.  For the ideal case of

synchronized dual injectors, suppression of the usual n=1 activity is observed.  The more benign ideal dual injector also

results in higher radiation fractions.  We map the sensitivity of this optimal result to delays between the injectors

and differing fragment plume distributions.   Based on this sensitivity map, we present suggestions for the dual

injector experiments and extrapolate to ITER.