System and Experiments for Research of Lower Hybrid Current Drive on HT-7

A megawatt grade of lower hybrid wave system was developed on the superconductive tokamak HT-7, and it has been used for lower hybrid current drive (LHCD) experiments for 5 yr. The experiments reveal the dependence of the current drive efficiency on plasma density and the toroidal magnetic field. Long-pulse tokamak discharges have been successfully sustained by LHCD. Plasma current rampup driven by the lower hybrid wave has been studied in detail. Some evidence suggests that the rampup may be used as a method to modify plasma current profile.