800MHz lower-hybrid current drive experiments on the Versator II tokamak

A 4-waveguide antenna structure (1.0 cm gap size and 0.19 cm wall thickness) has been used to inject LHRF power into plasmas through a side port and a top port at the same toroidal position. The purpose of these experiments is to find out the toroidal effect of lower-hybrid current drive efficiency. With identical plasma parameters (n-bar/sub e/≅4x10/sup 12/cm/sup -3/, I/sub p/≅35kA, B/sub t/≅8-10kG), the merit factor of current drive efficiency (S=n-bar/sub e/RI/sub rf//P/sub rf/) of side launching experiments is significantly higher by a factor of 2-3 compared to top launching results. This result seems to be consistent with ray tracing theory predicting an upshift of N/sub 11/ by the toroidal effect