Helicon and lower hybrid current drive comparisons in tokamak geometry

The parallel current driven by applied helicon waves is evaluated in tokamak geometry along with the radio frequency (rf) power absorbed by the passing electrons. The results are compared to the corresponding expressions for lower hybrid current drive. The efficiency of both current drive schemes is found to be the same in the single wave frequency, single mode number limit. The evaluation of the parallel currents is performed using an adjoint technique and tokamak geometry is retained by using an eigenfunction expansion appropriate for a transit averaged long mean free path treatment of electrons making correlated poloidal passes through the applied rf fields.