Measured currents in JET limiters during disruptions

Structures mounted inside a tokamak must be able to withstand the electromagnetic forces which arise during disruptions of the plasma. This paper reports on halo current measurements in the JET tokamak during disruptions. A toroidally distributed array of current sensing tiles reveal that in many disruptions a high degree of toroidal uniformity exists. However in exceptional disruptions the halo current measured at different toroidal positions varies by more than a factor of 2. This latter class of disruption has been observed to result in an asymmetric displacement of the vacuum vessel. The total halo current is estimated to be up to 15% of the initial plasma current. The halo current width for a particular disruption is estimated to be 8 cm