Energy Confinement in Alcator

Stable discharges with peak density fe =1.5xlQ15am-3 have been obtained in deuterium at BT =8.7T in the Alcator tokamak. Complete thermal equilibration between electrons and ions is observed, with peak temperatures of 900eV. The maximum value of fiTE is 3x1013cm-3.s. . Nearly classical behaviour, from the viewpoint of energy confinement, is observed. At the highest densities, a regime is attained where the anomalous electron thermal conductivity observed at lower densities is suppressed, and the dominant role in energy confinement can be attributed to neoclassical ion thermal conduction. The anomalous electron thermal conduction varies inversely with density. The observed ion thermal conductivity is neoclassical at high density, but seems to be somewhat greater at density less than 2x10 cm 3 Dependence of energy confinement on B is also investigated. With constant fi and IP, no significant effect of increasing BT on tE is observed. However, the highest achievable density and TE increase with B T. Stable operation of high current, low qL discharges has been achieved. Energy confinement for such discharges is described. Some improvement in TE is observed at high current.