Production and heating of over-dense plasmas by 2.45 GHz electron Bernstein waves on the CHS

Summary form only given. Production of over-dense plasmas by launching 2.45 GHz microwaves under very low field conditions has been successfully demonstrated on CHS. In the experiment, microwaves systems were arranged to aim at taking place mode conversion of launched electron cyclotron wave effectively into electron Bernstein wave (EBW). One system (ECH#1) is launched nearly perpendicularly to the toroidal field, where FX-B conversion scenario is expected. Another (ECH#2) is launched obliquely for O-X-B conversion scenario. This experiment aims at clarifying the excitation, propagate and absorption of mode converted EBW. Power deposition profiles in produced over-dense plasmas were measured directly by using power modulation technique at various magnetic configurations where electron cyclotron resonance (ECR) and upper hybrid resonance (UHR) layers were scanned in space widely. Figure 1 is radial profile of electron temperature T_e, electron density n_e and electron pressure p_e. This figure also shows the response in p_e to ECH#1 or ECH#2 source p_e, and the coherence gamma_pe ² and phase difference between delta p_e and the modulated ECH power Phi_pe at B_t/B_res = 100%. Electron density exceeds 2-3 times O-mode cutoff density (n_co ~ 7.5x10¹⁶ m^-3). Power deposition profile corresponds to delta_pe-profile and the peak position is in over- dense region. Similarly, it was investigated in the cases of B_t/B_res = 70%, 50% and 20%.