Stability problems of high power ion cyclotron resonance heating systems

Ion cyclotron resonance heating (ICRH) is one of the most effective plasma heating methods. It has been very successfully applied in many tokamaks in the frequency range between 20 and 120 MHz with a total power of the order of 30 MW, 2 MW per unit. Because of plasma load changes, reasons for unstable reactions of the generator, conditions for their occurrence and possible improvements are discussed in some detail, as investigated on the ICRH systems for ASDEX Upgrade and Wendelstein W7-AS.