Investigation of high harmonic fast wave for current drive on CFETR

High harmonic fast wave (HHFW) current drive at frequency near the lower hybrid wave is calculated under CFETR conditions. Modelling results show that the HHFW has excellent off-axis current drive capacity with high efficiency in a wide range of n_// (1.5–2.9) and wave frequency (0.6–2.4 GHz), the peak driven current is about 35 kA/MW and the current drive efficiency η = n_eI_CDR/P ∼ 2.7×10¹⁹ AW^âˆ'¹ m^âˆ'². Under the same parameters, smaller n_// leads to more peaked driven current and higher wave frequency corresponding to more outside current peak position. The comparisons of driven current properties with LHCD indicate that the current drive efficiency of HHFW is comparable to LHCD and the driven current profile is also more flexible. Scanning results of density and temperature show that low density and/or high temperature help to obtain more driven current, and the current drive efficiency can be improved at high temperatures and/or high densities.