Fast evaluation of the current drive efficiency by electron cyclotron waves for reactor studies

Abstract

The determination of the current driven by electron cyclotron waves is usually performed employing ray/beam tracing codes, which require as an input the magnetic equilibrium, the electron density and the electron temperature profiles on one side and the beam injection parameters on the other. In the frame of systems-code applications, however, a different approach is needed, as some of the required input quantities are not available. Here, a procedure to evaluate the achievable ECCD efficiency for given global reactor parameters is proposed. It relies on a single numerical evaluation of the current drive efficiency (based on the adjoint method and including momentum-conserving corrections) for suitably chosen input values. The results are shown to be in good agreement with the full numerical optimization of the ECCD efficiency for a number of reactor-relevant scenarios. As described in this paper, this approach does not include the effect of parasitic absorption from higher cyclotron harmonics, which becomes important starting from electron temperatures of the order of 30 keV.