Disruption Heat Loads on the JET MkIIGB Divertor

Disruption heat loads are one of the major concerns for the safe and reliable operation of plasma facing components. Understanding how the plasma energy is distributed during the disruption could help in developing design criteria.Although the stored energy of the JET plasmas is small compared to that foreseen for the next generation tokamaks, analysis of JET disruptions could still provide valuable information on the distribution of the energy loads. Combined analysis of divertor thermocouple and infrared camera measurements can provide some insight on the disruption heat load distribution. When the energy quench occurs at the same time as, or after, the loss of plasma vertical control, no significant divertor tile temperature increase can be observed for upwards (away from the divertor) events. When the plasma energy is lost with the plasma still in X-point configuration, the septum and the tiles wetted by the strike-points, often more than one tile per strike-point, experience a sharp increase in temperature, equivalent to up to 1MJ/m2, much larger than those experienced in faster quenches. Most of the disruptions purposely made to produce run-away electrons went towards the divertor and, although not systematically, lead to local (mostly at the septum) temperature increase equivalent to a load up to 2MJ/m2, often toroidally asymmetric.
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