Current driven by the fast Alfvén wave is measured at the fourth and eighth harmonics of the deuterium ion cyclotron frequency in identical plasmas on the DIII-D tokamak. In non-sawtoothingdischarges with neutral beam injection heating, the radial profile ofthe fast wave current drive (FWCD) is determined by the response of theloop voltage profile to co- and counter-antenna phasings. The dimensionless current drive efficiency is a factor of two greater for the eighth harmonic case compared to the fourth harmonic case. Modelling of the fast wave absorption using a ray tracing code shows that the decrease in FWCD efficiency for the latter situation can be explained by high harmonic damping of the fast waves on energetic ions.
Effects of ion cyclotron harmonic damping on current drive in the lower hybrid frequency range
Application of the intermediate frequency range fast wave to the JIPP TII-U plasma