Toroidally resolved radiation dynamics during a gas jet mitigated disruption on Alcator C-Mod

Abstract

Measurements of the radiation dynamics during an Alcator C-Mod disruption induced by a high pressure He/Ar gas jet are presented. Data are analysed from four 22-channel Absolute eXtreme UltraViolet diode arrays viewing on horizontal planes from different toroidal and vertical locations, both towards and away from the gas jet. Prior to the loss of the core plasma stored energy, strong emission is seen from a shell at the plasma edge that expands toroidally and poloidally away from the the gas jet at 650 m s−1, consistent with neutral expansion rates. Both the energy loss from this region and from the bulk plasma are shown to be of comparable magnitudes and important in dissipating the electron thermal energy outside the q = 2 surface. During the thermal quench, line-integrated brightnesses exceed 100 MW m−2. But while the brightness ratio of equivalent toroidally/vertically spaced views varies from 0.4 to 4.0, energy loss integrated over the disruption is shown to be symmetric to within 25%. Radiative energy loss local to the gas jet is shown to preheat nearby surfaces making them more susceptible to melting when the bulk of the thermal energy is lost.