Linear peeling-ballooning mode simulations in snowflake-like divertor configuration using BOUT plus plus code

We present linear characteristics of peeling-ballooning (P-B) modes in the pedestal region of DIII-D tokamak with snowflake (SF) plus divertor configuration using edge two-fluid code BOUT++. A set of reduced magnetohydrodynamics (MHD) equations is found to simulate the linear P-B mode in both snowflake plus and standard (STD) single-null divertor configurations. Further analysis shows that the implementation of snowflake geometry changes the local magnetic shear in the pedestal region, which leads to different linear behaviours of the P-B mode in STD and SF divertor configuration. Primary linear simulation results are the following. (1) The growth rate of the coupled P-B mode in SF-plus divertor geometry is larger than that in STD divertor geometry. (2) The global linear mode structures are more radially extended yet less poloidally extended in SF-plus divertor geometry, especially for moderate and high toroidal mode numbers. (3) The current-gradient drive (the kink term) dominates the P-B mode for low n, while the pressure gradient drive (ballooning) dominates for n > 25. In addition, constraints on poloidal field and central solenoid coils for snowflake geometry are briefly discussed based on conclusions in this paper.