Lower-Hybrid Current Drive in the PLT Tokamak

Order-of-magnitude improvements in the level and duration of current driven by lower-hybrid waves have been achieved in the PLT tokamak. Steady currents up to 165 kA have been maintained for 3.5 sec and 420 kA for 0.3 sec by 800-MHz rf power alone. The principal current carrier appears to be a high-energy (\ensuremath{\sim} 100-keV) electron tail, concentrated in the central 20- to 40-cm core of the 80-cm-diam discharge column.