High frequency range lower-hybrid current drive on the WT-3 Tokamak.

The lower-hybrid current drive (LHCD) experiments with a high frequency range such as ω= (2-3) × (ΩeΩi) 1/2 on the WT-3 tokamak are reported. Experimental results on current sustainment and ramp-up in the low density region are basically consistent with the predictions based on the quasi-linear theory with the finite fast electron confinement time. But the density limit for LHCD is lower than that expected from ω2-scaling. It seems that the density limit is given by ωpe2/Ωe2=1 for the high frequency range. It is concluded that increase of ω is not effective to increase the density limit for LHCD in the high frequency range.