The relationship between r.f. current drive and the measured loop voltage in tokamak r.f. heating experiments

The properties of tokamak discharges are known to undergo noticeable variations during r.f. heating. In particular, a significant drop in the loop voltage has been observed in a number of experiments, which can be attributed to a decrease in the plasma resistance or inductance or to r.f. current generation. The problem is analysed from the circuit theory point of view. The ambiguities encountered in interpreting the loop voltage measurements in small tokamak experiments are discussed