Feasibility of using Bernstein modes for current drive in toroidal devices

The feasibility of using Bernstein modes for producing electron cyclotron current drive in toroidal devices is examined. It is shown that the negative role of trapped particles may reduce upon increasing the longitudinal slowing-down factor of waves. Numerical geometrical-optics calculations of the propagation and absorption of waves were performed for the scheme in which radiation is launched from the low-field side as an ordinary wave, linearly converted into an extraordinary wave, and finally converted into Bernstein mode. An analysis is performed for medium-sized toroidal devices. Based on numerical simulation, the parameters determining the efficiency of current drive, namely, the characteristic values of the resonant energies and the longitudinal slowing-down factor of waves in the region where most of the microwave power dissipates, are found.