EQUILIBRIA OF RF TOKAMAK PLASMAS DURING CURRENT START-UP

Equilibria of r.f. Tokamak plasmas during lower hybrid (LH) wave-driven current start-up experiments in the WT-2 and WT-3 Tokamaks are studied by comparing spatial profiles of tail and bulk electrons with simple model equilibria for the electron tail. When the plasma current I(p) is smaller than the Alfven critical current I(A), the confinement areas of the tail and bulk electrons are not coincident. The cross-section of the outermost flux surface is always found to be larger than the tail cross-section. Particularly in the case of the small Tokamak WT-2 (a(L) = 9 cm) is the outermost flux surface coincident with the limiter circle and much larger than the tail cross-section, indicating that good confinement of bulk electrons which carry LH waves and provide electrons to the tail is crucial for r.f. current start-up.