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
~ 7.5x10
¹⁶
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%.