High frequency surface helicity injection in toroids with moving boundaries

Recently it has been argued that the negative results of F-θ pumping experiments on helicity injection may be due to the effects of a moving plasma boundary. The paper re-examines the possibility of helicity injection at the plasma edge using oscillating fields around the ion cyclotron frequency. It is found that a combination of ion inertial effects and ion dissipation can lead to a significant helicity injection at the plasma surface. Estimates of the surface helicity injection indicate that steady state currents in a tokamak may be driven efficiently using this method. (author). 13 refs