Arcs discharges during disruption and fast plasma shutdown by Explosive Gas Injection

Arc discharges are considered as a possible mechanism determining transition from relatively slow growth of the magnetohydrodynamic (MHD) perturbations to thermal quench (minor disruption) and subsequent transition to the major disruption with current collapse in the T-10 tokamak with tungsten limiters. The effect of the arc discharges is evaluated using analysis of the fast-scale (0.2–1.5 MHz) electromagnetic oscillations measured by movable magnetic and electric probes located near the plasma boundary at multiple positions inside the vacuum vessel and by postoperational inspection of the in-vessel components. Experiments using a special “arc” probe with castellated surface stimulating arc discharges indicated that transition to the major disruption is associated with enhanced electron emission from the plasma facing components. The role of the arcs is confirmed in experiments with initiation of the currents in the peripheral plasma using biasing (Ub 0–400 V) between the rail limiter and the movable tungsten electrode. Experiments indicated that critical surface current density is required for the arc initiation. The radial decay rate and frequencies of the electromagnetic oscillations measured in the T-10 experiments are found to be similar to the ones during arc discharges at the laboratory bench. Present experiments in the T-10 tokamak indicate that arc discharges could determine plasma-wall interaction during growth of the MHD modes and disruptions in tokamaks with all-metal first-wall.
Possibilities of the Explosive Gas Injection technique are considered for fast plasma shutdown in the T-10 tokamak.