Preliminary discharge-cleaning and arcing studies in mini-torus

Discharge cleaning was carried out in a small tokamak (Mini-Torus) with zero B⊥ and without limiter; the plasma contacted with the chamber wall closely. After 2000 shots the impurities consisting of water and other molecules were reduced by an order of magnitude. Probes of several materials placed close to the plasma acted as a kind of limiter. Unipolar arc tracks have been clearly observed with aluminum-coated glass probe. Arcing is closely related to initial electron bombardment.