Study of the influence of magnetic shear on the linear MHD instabilities in the pedestal of elongated divertor configurations using CLT code

Edge localized modes resulted from magnetohydrodynamic (MHD) instabilities in the pedestal region are a significant concern for future tokamaks. In this work, Ci-Liu-Ti (CLT), an MHD code in the three-dimensional toroidal geometry, is applied for the linear simulation of the ideal pedestal MHD instabilities. The simulations are performed for the experimental advanced superconducting tokamak-like elongated divertor configuration with large triangularity, which is generated by the high-accuracy free-boundary equilibrium solver (CLT-EQuilibrium, i.e., CLT-EQ) developed recently. The present work focuses on the influence of the magnetic shear, which is scanned by adjusting the pedestal current with a fixed pedestal pressure profile. As the pedestal current increases, both the local (S_local) and global (S_global) magnetic shear decrease. The ballooning mode is destabilized along with the decrease of S_local, and stabilized when S_local is negative for the whole region of bad curvature, which implies the access of the second stable region. Further increase of the pedestal current leads to the destabilization of the kink mode, which is stabilized again until S_global is negative at the location of significant gradient of current density. The simulated results are consistent with the findings in Radovanovic et al. Nucl. Fusion 62 (2022) 086004 and C. K. Sun et al. Phys. Plasmas 25 (2018) 082106, which indicates the availability of CLT in the linear simulation of the ideal pedestal instabilities.