Fast wave helicity current drive in tokamaks

Several recent studies have suggested that plasma waves with intrinsic magnetic helicity, and therefore nonlinear polarization, may be effective in driving steady current in magnetized plasmas. Current appears as wave helicity is transferred to the background plasma in response to effects of wave dissipation and spatial inhomogeneities in the plasma. In this paper, we report on a study of helicity wave current drive (HWCD) over a broad frequency range that extends below and above the ion cyclotron frequency. The parameters of the Phaedrus-T tokamak at the university of Wisconsin-Madison are assumed in our calculations. Numerical calculations of the wave electric and magnetic fields, and the resulting steady current, have been carried out with the global 3-D code, FASTWAC, which is a version of FASTWA, modified to treat current drive resulting from wave helicity and momentum transfer. FASTWAC is based on the hot plasma dielectric tensor with small electron and ion gyro-radii. It includes particle trapping effects, and a variety of wave absorption processes, such as Landau damping, TTMP, ion cyclotron absorption, and collisions. (author) 10 refs., 2 figs