LOW-ASPECT-RATIO TOKAMAK FORMATION AND SUSTAINMENT BY COAXIAL HELICITY INJECTION CURRENT DRIVE

Coaxial helicity injection is used to form and sustain low aspect rati o tokamaks at currents of up to 250 kA in the Helicity Injected Tokama k experiment. Plasma currents can be sustained at an average of 225 kA for 2 ms, with on axis electron thermal energies up to 80 eV, or for longer times, 140 kA average for 7 ms, many resistive diffusion times. Spectroscopic measurements of the higher current discharges suggest b urn-through of oxygen impurities. These plasmas have a rotating n = 1 distortion, appearing only on the outer, bad-curvature region. Equilib ria reconstruction, fitting to experimental data, shows tokamak q prof iles achieved with hollow plasma current profiles.