The relation between halo currents and plasma displacement/deformation in JET

In JET the magnitude of the total poloidal component of the halo current is up to 0.8 I/sub p0//q/sub 95/ where I/sub p0/ and q/sub 95/ are the plasma current and safety factor just prior to disruption. The halo current is often observed to be much smaller than this upper limit, depending on the achieved value of the plasma current vertical moment (I/sub p//spl times//spl Delta/z, where /spl Delta/z is the vertical displacement). The halo current density (I/sub h//(unit toroidal angle)) is observed to be largest during toroidally asymmetric disruptions. This observation is consistent with the idea of force balance: if the plasma/wall contact region is reduced because of a distortion of the plasma column the halo current density must increase to balance the destabilizing force.