The effects of the RF current drive on a hybrid RF-OH discharge, in which more than 70% of the plasma current is driven by the RF, have been extensively studied in the Petula-B tokamak. Observations of MHD activity indicate that the presence of RF-driven current cuppresses the growth of the MHD modes and allows stable low-q(a) (as low as 2) discharges with electron density and temperature profiles similar to those of the OH case.

In the PETULA tokamak, three series of discharges were run, with, successively, limiters made of tungsten, alumina and carbon. The characteristics of the plasma in these three situations are presented and compared. It is found that the lowest oxygen impurity level and lowest effective ion charge were obtained with the alumina limiter. With this limiter, the plasma energy confinement time is 50% higher than that found for the tungsten limiter. During a rather short period, the machine was operated with a carbon limiter which led to very resistive discharges and the appearance of disruptive instabilities related to a plasma-limiter interaction. From a technological point of view, the alumina limiter was appreciably damaged after about one thousand discharges whereas the carbon limiter appeared to withstand thermal stresses perfectly.

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The feasibility of two RF heating schemes, Transit Time Magnetic Pumping and Lower Hybrid heating, has been tested at the Grenoble Laboratory. TTMP results on PETULA were accurately consistent with theory; power absorption was only limited by the unfavourable scaling for small devices. -Launching of lower hybrid waves was made convenient by the grill concept. WEGA and PETULA B experiments showed that ions can be efficiently heated and interaction with electrons leads to non-inductive current drive. Tokamak discharges for which the current is entirely or mainly supported by waves have good confinement and stability properties.