Absorption of fast waves by electrons on the DIII-D tokamak

Efficient direct heating of electrons by fast waves has been observed on the DIII-D tokamak. The measured fast-wave heating efficiency was independent of magnetic field, in contrast to the strong inverse magnetic field scaling predicted by the theory of single-pass damping, indicating multiple-pass absorption. The central heating of electrons by the fast waves had a strong dependence on the target eelctron temperature. {ital H}-mode plasmas were obtained with fast-wave heating alone for the first time in the direct electron heating regime.