Electron cyclotron current drive in a lower hybrid current drive plasma

Electron cyclotron (EC) current drive experiments were carried out in lower hybrid current drive (LHCD) plasmas on the WT-3 tokamak. Using oblique inj ection of EC waves, plasma current is ramped up in a frequency range omega/ Omega(e) similar or equal to 1.2-1.4, where Omega(e) is the EC frequency at the plasma centre. This ramp-up is ascribed to selective EC heating of fas t electrons in LHCD plasmas via the fundamental EC resonance at the upshift ed frequency due to the Doppler effect. Fast electron momentum distribution s are estimated from bremsstrahlung hard X ray spectra. These distributions indicate that the parallel momentum input to the fast electrons in the rel ativistic energy range from oblique EC waves is effective for efficient EC current drive. Current ramp-up is also observed in the second harmonic freq uency range omega/Omega(e) similar or equal to 1.9-2.2 In this case, bulk e lectrons are heated as well as fast electrons and no definite cause of curr ent ramp-up is clarified.