ELECTRON-CYCLOTRON HEATING FOR ASSISTED BREAKDOWN IN NEXT STEP TOKAMAKS

Electron cyclotron assisted breakdown is discussed. The investigation is motivated by the interest in low voltage plasma formation in next generation tokamaks requiring an efficient and reliable non-inductive method of plasma ionization to assist ohmic breakdown. Two basic problems for solving the relevant transport equations, the electron cyclotron power deposition and the ionization rate in a large major radius tokamak, are investigated. It is shown that wave damping occurs at the electron gyrofrequency without mode conversion at the upper hybrid frequency, and that the ionization rate is nearly independent of the shape of the electron distribution but only depends on the average thermal energy.