Tungsten neoclassical transport in ITER pedestal for non-axisymmetric perturbations*

Tungsten transport in the pedestal region of ITER poses a serious threat to the device fusion performance due to radiation losses. The consequences of breaking the magnetic field symmetry in tungsten transport in the pedestal region of ITER are examined. The scenario considered is an inductive operation ITER H-mode plasma with Q ≈ 10, I_p = 15 MA and B_t = 5.3 T obtained from ITER integrated plasma simulations. Neoclassical transport calculations are performed with the SFINCS code for 3D MHD, free boundary equilibria, calculated with the VMEC code, considering: i) an axisymmetric case ignoring the discrete nature of the TF coils, ii) a set of equilibria with toroidal ripples ranging from 0.25% to 2% and iii) an equilibrium with the ELM control coil angle offsets maximizing the Resonant Magnetic field Perturbation (RMP) close to the LCFS.

The results indicate a negligible ripple effect on the radial electric field with respect to the theoretical axisymmetric case and a reduced E_r region for RMP fields. However, for the region with large electric fields, it is not possible to extract robust conclusions on tungsten flow direction due to, first, the possible radially non-local character of the dynamics and, second, the high poloidal Mach number for tungsten that puts into question the accuracy neoclassical theory ordering. Further advancements in modeling techniques are needed to address this issue to provide more accurate predictions, which, needless to say are of paramount importance for ITER.