Utilization of electron cyclotron radiofrequency sources for current drive and thestabilization of neoclassical tearing modes (NTMs) in next step devices rests on the current density and current drive efficiency attainable. Optimization is reported of electron cyclotron driven current density and current drive efficiency with respect to source frequency as well as toroidal and poloidal launch angles for two launcher positions: an `upper port' position above the midplane and a `midplane' position at the heightof the magnetic axis. The plasma parameters were chosen to be representative of the next step towardsa fusion reactor (B = 5.3 T, ⟨ ne⟩ = 1.0 × 1020m-3, R = 6.2 m). Themodelling is performed with the TORAY code, launching a cone of electron cyclotron rays to account for a finite angular spectrum of injected waves. Current drive at each location is obtained with the Cohen linear model, which includes the effects of toroidal trapping, relativity and wave polarization. For the two launch locations, optimized central current drive efficiency is approximately equal. At plasma radius ρ = 0.835a for stabilization of the q = 2 NTM, the current density is 2.3 times greater and the integrated efficiency is 1.5 times greater for upper port launch relative to midplane launch. A broader range of frequencies for good current drive efficiency is obtained for upper port launch, and this will be reflected by a broader range of operating magnetic field at fixed electron cyclotron source frequency. Twenty megawatts of electron cyclotron power satisfy the criteria forcontrol of NTMs.
Fast physics-based launcher optimization for electron cyclotron current drive