Simulated and experimental investigation on synergy of LHW and IBW in HT-7

Abstract

By combining the lower hybrid current drive (LHCD) and ion Bernstein wave (IBW) heating codes, synergistic simulation of lower hybrid wave (LHW) and IBW is preliminarily done and used to investigate synergistic experiments of LHW and IBW in HT-7, offering an effective tool for analyzing LHW and IBW experiments, particularly separating the contribution of temperature and synergistic effect to driven current due to IBW heating. Results show that IBW can effectively heat plasma and play with LHW, hence modifying the LHW power deposition and plasma current profile. Compared with the LHW plasma, there is an increment in driven current in the case of the LHW + IBW plasma, due to a temperature increase and synergistic effect of LHW and IBW. Studies show that the driven current fraction of temperature contribution and synergistic effect depends significantly on the plasma parameters and the resonant layer. Compared with global IBW heating, localized IBW heating makes localized electron temperature higher, which is helpful in driving a larger off-axis current and benefits the hollow current profile, suggesting that off-axis IBW heating is preferred for a weak or negative magnetic shear plasma and for improving plasma confinement. Although the simulated results are not completely consistent with experimental measurements, they are nearly in agreement qualitatively. More work will be done later for further investigation.