Non-Resonant Microwave Discharge Start-Up in Heliotron J

Abstract

The non-resonant microwave discharge in strong magnetic fields was investigated in Heliotron J under the condition, ωce/ωMW > 1 (ωce and ωMW are the angular electron cyclotron frequency and the angular microwave frequency, respectively). Following the production of a non-resonant microwave discharge plasma, it undergoes several phases in sequence: breakdown and formation of pre-ionized plasma, increase in linear and nonlinear phases of plasma density, and quasi-stationary stage. Several modes of non-resonant microwave discharge were investigated. In the power-scanning mode in non-resonant microwave discharge, a higher plasma density than that in the constant-power mode is achieved. The maximum average density achieved in the experiments is substantially greater than the critical density for O-wave (ordinary waves) 7.45 ⸱1016 m -3 and can reach the value of 2.5⸱10 18 m -3. .