On the magnitude and distribution of halo currents during disruptions on MAST

Recent results from MAST in which all halo current paths are monitored suggest that, during disruptions, the plasma responsible for the generation of halo current acts more as a voltage source than a current source. As a result the resistance of the current path along which the halo current must flow has a profound impact on the magnitude of the current. This may provide opportunities for directing the current away from sensitive components in future devices such as ITER. Analysis of data from over 3800 disruptions shows that the halo currents on MAST are relatively benign, having a peak value less than 25% of the pre-disruption plasma current with a rather symmetric distribution near the centre column ( average toroidal peaking factor similar to 1.1). The low peaking factor favourably reduces the tilting/bending forces in the region of the centre column, which has limited space for bulky supports.