Disruption design criteria for JET in-vessel components

Abstract

In view of the substantial modification in the JET plasma facing components foreseen for the 2004 shutdown, the design criteria for in-vessel components have been updated building up on the operational experience with divertor plasmas gained since the early '90s. Typically the most demanding design loads occur during disruptions and vertical displacement events (VDEs). In fast disruptions (e.g. density limit driven) the largest contribution to the loads comes from currents induced by fast change of the poloidal field, which tends to be proportional to the plasma current decay rate, the maximum of which has been observed to be linear with the pre-disruption plasma current. This implies that in the fastest events the current quench has a fixed duration at JET, about 10 ms. Usually VDEs take place on a longer time scale, and therefore halo currents determine the worst loading condition in these cases. Analysis of recent VDE data confirmed the previously observed magnitude of asymmetries: the toroidal peaking factor (TPF) up to 1.8 in upward VDEs and up to 1.4 in downward VDEs; the ratio average poloidal halo to initial plasma current (f) up to 23% in upward VDEs and up to 30% in downward VDEs. Experimental evidence to justify the new criteria and recipes on how to apply them to JET are included. The data used for the revision of the design criteria are discussed and compared with the assumptions used in the design of the components already present in the JET vacuum vessel.