A new multijunction grill-type launcher has been tested on the Petula-B tokamak. In this new launcher, the RF power is divided by means of an E-plane junction, and the phase between each resultant wave is obtained by a suitable reduction in the height of the waveguides. Data obtained on Petula-B indicate that both the heating efficiency (4.5 eV × 1013 cm−3·kW−1) and the parametric dependences of the reflection coefficient are very similar to those of a conventional grill. Therefore, such a multijunction grill may greatly simplify the construction of grills considered for use in future large-scale tokamaks.

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.

The experimental data obtained by three different measurements related to the hot electron population involved in ion stripping in an electron cyclotron resonance ion source (ECRIS), i.e., electron cyclotron emission, bremsstrahlung x-ray radiation, and diamagnetism are presented and shortly discussed. The volume-averaged electron energy essentially depends upon the working pressure, and does not vary much with the rf power, at least above 200 W. The main effect of increasing the rf power is to raise the electron density.