Study Electron Cyclotron Double Mode Conversion in Overdense Plasma

Abstract

Double mode conversion from ordinary mode O to extraordinary mode X is used to achieve electron Bernstein wave (EBWs) for the electron cyclotron resonance heating (ECRH). The efficiency of the mode conversion depends on many parameters including the density gradient L n , magnetic field source B 0 and optimum launching angle N z. An analytical formalism together with a numerical computation have been employed, considering W7X stellarator main parameters, such as 140 GH z , k 0 = 29 cm −1 , 2.5 T and 2.4 ×10 20 m −3 , in order to investigate the efficiency of the mode conversion. The values of the density gradient Ln, obtained by numerical simulation, are from 1 to 10 cm. These values of L n correspond to the power transmission window T OSX from 88 to 29%. Moreover, the dispersion relation of the EBW mode propagation up to 10 harmonics, ω = 10ω ce , has been plotted to help a better visualization of the EBW mode heating. Finally, the power deposition profiles around the resonance layers were calculated and presented.