Heating in Toroidal Plasmas

Abstract

One effect of launching lower hybrid waves in low density plasmas ( < 2.1013 cm-3) in Petula is to make loop voltage drop. Plasma current is kept constant in those experiments by a chopper with quasi fixed voltage and variable frequency. This voltage decrease can be interpreted as a change in plasma inductance, or plasma resistance or as current generation. Detailed analysis of loop voltage and current derivative shows that the inductance change hypothesis can be rejected in this experiment. The observed chopper operation is best simulated when assuming an RF generated current proportional to the applied power which is a function of time. Due to the long time constant involved in the primary winting and plasma currents, it is not easy to discriminate between current generation and increased conductivity unless the generated current is larger than be initial plasma current.