Effects of reversed magnetic shear on the plasma rotation stabilization of resistive wall modes in tokamaks

Abstract: Effects of reversed magnetic shear on the plasma rotation stabilization of resistive wall modes in tokamaks are investigated using the AEGIS code. MHD equilibria in toroidal configuration from circular cross-sections to realistic CFETR-like scenarios with various magnetic shear profiles are considered. Two critical aspects of the $n=1$ RWM are examined: the influence of toroidal rotation on the unstable regime and the toroidal rotation frequency thresholds required for complete stabilization. It is found that strongly reversed magnetic shear consistently broadens the unstable $\beta_{\rm N}$ window in both circular and CFETR equilibria when toroidal rotation is included. Furthermore, reversed magnetic shear significantly reduces the rotational stabilization, resulting in narrower stability windows and notably higher toroidal rotation frequency thresholds required for complete RWM suppression compared to the cases with positive shear only. These results clearly demonstrate that the reversed magnetic shear in the advanced tokamak configuration imposes more stringent requirement for the effective toroidal rotation stabilization of the $n=1$ RWM.