Beta and confinement experiments on Doublet III with high-power neutral beam heating

Beta and energy confinement experiments with up to 7.5 MW of neutral beam heating power injected into both limited and diverted equilibria are discussed. We have studied beta limits at both the low q (high β/sub T/, low β/sub p/) and high q (low β/sub T/, high β/sub p/) ends of the ideal MHD n = infinity ballooning limit curve. Discharges which disruptively terminate have not clearly exceeded predicted ballooning limits but have been within 20% of marginal stability for ideal ballooning modes. Energy confinement time studies show that tau/sub E/ scales linearly with plasma current and deteriorates with beam power, although there are indications that tau/sub E/ may be approaching a new asymptotic value at high power levels. We find that diverted equilibria afford up to a factor of 2 greater confinement times at high power levels. Transport analysis indicates that electron conduction is the major heat loss mechanism and that the electron conductivity is generally 2--3 times lower in divertor discharges compared to limiter discharges with comparable parameters. We observe a strong correlation between improved confinement and the separation between the limiter and separatrix flux surface