ECRH and Ohmic Plasmas in the Compact Toroidal Hybrid (CTH) Experiment

Plasma is generated in the low-aspect ratio CTH torsatron (R$_{O}$ = 0.75 m, R$_{O}$/a$_{p} \quad \le $ 4, B $\le $ 0.7 T) by electron cyclotron heating at a frequency of 18 GHz. Reliable breakdown at the fundamental frequency is obtained when RF power is launched into a broad, resonant saddle region present on the inboard side of the magnetic axis. Discharges up to 1 second duration have been produced with input RF power $\le $ 10 kW. Ohmic currents are induced in ECRH-formed plasmas by capacitor bank discharge into a dedicated OH transformer coil set. Present experiments have begun with low plasma currents of approximately 5 kA with an ohmic phase lasting 75 msec. These experiments are the first in the planned studies of equilibrium and stability of current-carrying stellarator discharges. Ongoing efforts aim at improving plasma operation and implementing SXR arrays and a full set of magnetic diagnostics.