DIII-D neutral beam current drive experiments at high beta poloidal

Neutral beam current drive experiments in the DIII-D divertor tokamak are described. Plasma currents up to 0.34 MA have been sustained by neutral beams alone with H-mode quality energy confinement. Poloidal beta values reach βp = 3.5 without disruption or coherent magnetic activity, suggesting that these plasmas may be entering the second stability regime. At such high βp the trapped particle averaged toroidal drift is reversed over half of the plasma. In these experiments helicity, but not flux, conservation is observed. (author). 29 refs, 8 figs