Recent studies have shown that helicon waves may be an attractive option for driving an efficient off-axis current drive in order to supplement bootstrap current for steady state operation in fusion reactors. Based on the China fusion engineering test reactor parameters, the helicon wave trajectories, profiles of driven current and current driven efficiency are calculated with the ray-tracing code GENRAY. Both the peak position and the peak value of driven current profiles are dependent on the wave frequency. In the frequency range of 1.6 GHz–2.0 GHz, the peak value increases with the increase of frequency, and the peak position has a slight change (concentrate around ρ= 0.75). High electron temperature and low electron density seem to be favorable for the helicon wave absorption. A driving current of I/P > 70 kA MW−1 at the off-axis position of ρ < 0.7 can be obtained with the electron temperature at the plasma center, Te(0) < 25.4 keV and the electron density at the plasma center, ne(0) ∼ 0.7 × 7.8 × 1019m−3–0.8 × 7.8 × 1019m−3. The current drive efficiency decreases with the increase of the electron density. Peak positon of the driven current profile is insensitive to the parallel refractive index n∥. It is found that the poloidal launch angle has some effect on the peak positon and its value.
Application of very high harmonic fast waves for off-axis current drive in the DIII-D and FNSF-AT tokamaks