Measurement of halo current in the HT-2 tokamak and investigation of a scaling law

The halo current, which flows between the plasma and plasma facing components in a vacuum vessel during disruptions, was measured in the Hitachi tokamak HT-2 and the scaling law of the magnitude was examined based on the balance of the electromagnetic forces. Electrode plates were placed where they touched the plasma during the disruptions. A halo current flowed through the electrodes and the electrode currents were measured by Rogowski coils. The measurements showed the followings. (1) The halo current intensity IHL is large during vertical displacement event (VDE) with rapid IP decay and high toroidal field BT. (2) The product of IHL and duration time increases with IP but have no dependence on BT. (3) The halo current reduces the shell effect, destabilizing the plasma position. (4) A scaling law, based on a force balance on the plasma, gives an approximate estimation of the halo current magnitudes for various tokamaks. (author)