Influence of elongation and triangularity on plasma response to resonant magnetic perturbations

Systematic toroidal modeling of the plasma response to the n = 1-4 (n is the toroidal mode number) resonant magnetic perturbation (RMP) field is carried out in order to understand the plasma-shaping effect on controlling the type-I edge-localized modes (ELMs) in tokamak experiments. Considered are large variations of the plasma elongation and triangularity at a fixed edge safety factor q (a), for limiter plasmas with both single-null (SN) and double-null (DN) divertor-like boundary shapes. Numerical results assuming conformal 3D RMP coils show that (i) the optimum coil phasing between the upper and lower rows for ELM control becomes increasingly sensitive to the plasma elongation with higher-n toroidal spectra, (ii) the optimum coil phasing is however essentially independent of the plasma triangularity for all n = 1-4 RMP fields, (iii) with the same coil current and the optimum coil phasing, high elongation generally favors ELM control but it may be more challenging for plasmas with intermediate elongation and with lower-n (n = 1-2) RMPs, and (iv) higher triangularity is generally always better for ELM control with all n = 1-4 fields for both DN and SN divertor-like plasma boundary shapes.