X-RAY-ENERGY ANALYSIS FOR RADIO-FREQUENCY CURRENT DRIVE EXPERIMENTS IN THE DIII-D TOKAMAK

The X-ray energy spectra were measured during electron cyclotron curre nt drive (ECCD) and fast wave current drive (FWCD) experiments in the DIII-D tokamak. High energy electrons, over 100 keV, were observed dur ing ECCD near the plasma center and enhanced radially by the effect of downshifted frequency. Tail formation with the maximum energy of 50 k eV was observed clearly during 2 T, 0.8 MA FWCD experiments. For combi ned FWCD and ECCD, the bulk heating efficiency was increased over the case with FW only, with eta(e) approximately 2.3 x 10(19) m-3 keV/MW, and it was stronger for the counter (CTR) case than the co (Co) case. (Here Co corresponds to the direction of launched wave which will enha nce the plasma current. CTR refers to the opposite direction.) However , the coupling of FWs to high energy electrons produced by ECH was str onger for the Co case.