Disruption mitigation efficiency and scaling with thermal energy fraction on ASDEX Upgrade

Disruption mitigation remains a critical and unresolved issue for ITER. Measurement uncertainties preventing quantification of a system's efficacy remains a significant hurdle in producing and validating a viable disruption mitigation system. This study addresses this issue through the creation of a dataset on the ASDEX Upgrade tokamak targeted at developing analysis techniques to quantify mitigation that are applicable irrespective of the disruption mitigation system being studied. These experiments used a range of thermal energy fractions to address concerns for ITER from JET massive gas injection (MGI) experiments showing a decrease in efficacy with increasing thermal energy fraction. The dataset produced in this study used MGI valves in two toroidal locations. The high resolution foil bolometers and AXUV diode arrays were used to infer radiation emission profiles at varying toroidal distances from the injection location. The fueling efficiency of the two systems was found to be comparable and toroidal asymmetries over the entire disruption were found to be negligible. The AXUV diodes were cross-calibrated with the foil bolometers and used to estimate the thermal energy radiated and magnetic energy coupled to the vessel structure and coils. It was estimated that 75-95% of the thermal energy was radiated and an almost constant 60% of the total magnetic energy was coupled. Radiated energy fractions of 0.8-1.0 were calculated and no decrease as a function of thermal energy fraction was found. A +/- 20% variation in the coupled magnetic energy was explored and it did not alter this trend.