Thermal energy mitigation and toroidal peaking effects in JET disruptions

Previous investigations on JET suggest half or less of plasma stored thermal energy W t h is radiated ( f rad , t h ≲ 0.5 ) using either massive gas injection (MGI) or shattered pellet injection (SPI) disruption mitigation. We investigate whether the apparent incomplete f rad , t h is explained by radiation peaking near the injection plume. High toroidal peaking throughout the pre-thermal quench is found in argon-deuterium MGI on JET, with typically >3× higher radiation near the injector than toroidally distant. Previously unexplained toroidal bolometry measurements in neon-deuterium SPI are reproduced with similar peaking using the Emis3D radiation analysis code. These observations align with results from Alcator C-Mod and KSTAR. This peaking is not captured by previous JET studies that found poor thermal mitigation. Two sets of neon-deuterium SPI and two sets of argon-deuterium MGI are analyzed using Emis3D. In SPI, f rad , t h rises from no-plume estimates of 0.31 and 0.66 to lower bounds of 0.84 and 0.92, respectively, and f rad , t h ∼ 1 is possible. In MGI, the toroidal spread of the peaking feature is poorly constrained. f rad , t h up to 0.85 and 0.65 are possible using the largest possible spread, increasing from 0.42 and 0.28, although f rad , t h ∼ 1 does not appear to be reached. Revised mitigation estimates on JET suggest a lower melt risk to the divertor in mitigated disruptions on ITER and SPARC than previously thought. However, peaking near injectors could increase flash melting risk on nearby plasma facing components.