Disruption mitigation studies on the Mega Amp Spherical Tokamak (MAST)

Abstract

Disruptions pose a significant challenge in future devices where the increased stored energy can lead to unacceptably large transient heat loads on plasma facing components (PFCs). One means of mitigating disruptions is that of massive gas injection (MGI), which produces a radiative collapse of the plasma discharge through the injection of impurity gases. The MAST disruption mitigation system is capable of injecting up to 1.95bar litres into the MAST vacuum vessel over a timescale of 1–2ms, corresponding to a particle inventory of 5×1022, around 100 times the plasma particle inventory. High speed infrared thermography, offering full divertor coverage, has shown a 60–70% reduction in divertor power loads during mitigation. A combination of high temporal (0.2ms) and spatial resolution (1cm) Thomson scattering and soft X-ray camera array data show evidence for a cooling front associated with the inward propagation of the injected impurities.