Massive Gas Injection Experiments at JET – Performance and Characterisation of the Disruption Mitigation Valve

Disruptions, the fast accidental losses of the plasma current and stored energy in tokamaks, are a critical issue for reactor-scale fusion facilities like ITER. They present a serious risk of damage to the plasma facing components. The avoidance of such damage is also essential for the upcoming ITER-Like Wall (ILW) experiments (Be and W used as plasma-facing material in the main chamber and divertor, respectively) at JET, the tokamak experiment closest to ITER in terms of operating parameters and size. Massive Gas Injection (MGI) is considered one of the most viable methods for disruption mitigation. The injection of noble gases is preferred because of their high recycling and low sticking probabilities to the wall, which should enable a reliable plasma breakdown and normal plasma operation after injection. To allow scaling of the mitigation efficiency towards ITER and to study the possibility of a JET protection by MGI, a Disruption Mitigation Valve (DMV) has recently been brought into operation at JET. The JET set-up and the function principle is explained in this article. Furthermore, first results of its performance by means of Time Of Flight (TOF) measurements during various gas injections are presented. Finally, the implications on the machine condition and the subsequent machine operation are discussed.
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