Optimization of helicon wave off-axis current drive in CFETR tokamak

Highlights: • A strong wave damping region is obtained in CFETR. • The launched poloidal angle $\theta$ 30 degree acts as a good choice of helicon wave in CFETR. • The driven current and its profile peak position are sensitive to $n_{//}$. • Helicon wave with wave frequency $f\sim 700$ MHz and $n_{//}\sim (2,3)$ is a promising scheme for effective off-axis current drive in CFETR. The China Fusion Engineering Testing Reactor (CFETR) is a tokamak reactor and aims to eventually reach DEMO relevant fusion power level of 1 GW. A lower single null configuration of the divertor design is proposed for the machine. To obtain the high performance operation of the plasma, both the hybrid and steady-state operating scenarios are suggested. In these scenarios, the plasma beta of $〈{\beta }_e〉\sim 1.6\%$ has been generally reached. In the paper, helicon wave propagation and current drive in CFETR are studied through GENRAY/CQL3D code. An analysis of the wave damping factor in CFETR plasma indicates that the electron Landau damping is dominant for the core plasma. According to the dimensionless parameter ${\xi }_e$ and ${\beta }_e$, a strong wave damping region is found. Based on the GENRAY simulation, the single pass power absorptions are generally obtained in both scenarios. Scanning of generated current on the launched poloidal angle indicates that high current drive efficiency is produced at $\theta \sim {30}^0$. For helicon wave with frequency $f=700$ MHz, calculations of the current drive show that off-axis current drive about 30 kA/MW and 50 kA/MW are obtained in the hybrid and steady-state scenarios respectively. Simultaneously, the lower plasma density and high temperature promote the high current generation. Moreover, the obtained current drive and its peak position are shown to be sensitive to the launched $n_{//}$. Finally, the helicon wave with frequency $f=700$ MHz and launched $n_{//}\sim 2.0$–3.0 is proposed to be a promising scheme for effective off-axis current drive in CFETR.