Beta and confinement experiments on the Doublet-3 with high power neutral beam heating

Results are dicussed of experiments on investigation into limiting beta values and energy lifetime in discharges with a limter and with a diverter at a power of neutral beam heating up to 7.5 MW. Both extremes for the ballooning modes have been studied at q's (large βsub(T), small βsub(p)) and at high q's (small βsub(T), large βsub(p)). The limits theoretically predicted for the ballooning modes were not exceeded in discharges discontinued by breakways; drop; the difference from the stability threshold for ideal ballooning modes made up not more than 20%. Studies on the energy lifetime show that the quantity tausub(E) grows linearly with the plasma current and decreases with a growth in the beam power, though it is noted that at high power levels tausub(E) probably approaches a certain asymptotic value. It is found that the diverter configuration permits to attain approximately twice as large confinement time as compared with the limiter. An analysis of the transport processes shows that the electron thermal conduction, which in diverter discharges is 2-3 times as low as that in limiter ones at comparable parameters, is the main mechanism of heat losses. A strong correlation is observed between the confinement improvement and the increase in the gap between the limiter and separatrix