Thermal load characterization during disruptions mitigated by shattered pellet injection on DIII-D

Conducted and radiated heat loads during disruptions are characterized under a variety of shattered pellet injection (SPI) scenarios on the DIII-D tokamak. Disruption heat loads are inferred from infrared (IR) thermography, and can detect both localized conduction as well as the more diffuse radiated heat loads on the first wall. Injecting the pellet from different toroidal locations allows the IR camera to compare near- and far- heat loads, relative to injection location. These comparisons support the existence of localized radiative heat loads in the vicinity of the injection location, of roughly 15% above the average value. This variation is relatively small compared to that resulting from changes in the radiating impurity injection quantity, which can change the radiative heat loads by up to 50%. The heat loads detected by IR thermography and by bolometry are compared with the available energy being dissipated in the plasma during the disruption, which is shown to be reduced by magnetic coupling to external conductors. The overall energy balance in these SPI shutdowns is compared with those during unmitigated disruptions.