Parametric Study of Helicon Wave Current Drive in NCST

Helicon waves (HW) are fast magnetosonic waves that can efficiently drive off-axis plasma current in tokamak plasmas through electron Landau damping (ELD) and transit-time magnetic pumping (TTMP) effect. Simulation of helicon wave current drive (HCD) were conducted for the purpose of increasing the discharge current of the NCST, combined with theoretical analysis of wave absorption based on the dispersion relation. Key findings are as follows: (1) When the wave frequency f > 40 MHz, ELD becomes the dominant absorption mechanism for HW in NCST, which is confirmed by the significant increase in the Landau damping term with frequency (Fig. 1). (2) At a frequency of approximately 65 MHz, HCD effectively supplements the bootstrap current for the NCST scenario. (3) Under the optimal parameter combination ( $${n_\parallel }= - 3.8$$ , $$\beta ={10^ \circ }$$ ), the maximum current drive efficiency reaches 136 kA/MW. These results clarify the parameter range for efficient HCD, validate HCD as a feasible non-inductive current drive solution for compact spherical tokamaks, and thereby provide critical theoretical guidance for the design and construction of NCST’s helicon system.