PROGRESS IN UNDERSTANDING HALO CURRENT AT JET

The poloidal distribution of the halo current density on the top dump plate in JET can now be measured thanks to a new set of Rogowskii coils. These are the first measurements in JET able to offer an insight in the width of the halo current interaction with the wall. Therefore they offer both validation of the assumption made for JET disruption design criteria and one additional point in the extrapolation of the expected halo current width, and hence halo current density (and related local electro-mechanical loads on in-vessel components) for ITER. During upward events, the measured current density is consistent with the measured total poloidal halo current. The halo footprint extends over most of the upper dump plate, converting to a halo current flux tube width of ∼100 mm. A set of four toridal field pick-up coils installed 90°apart now allows a more accurate measurement of the poloidal halo current, in particular its toroidal peaking factor, and direct comparison between halo and plasma asymmetries.