2024 Volume 19 Pages 1403003
Divertor heat loads are one of the most significant issues affecting fusion reactors. Atomic processes play a crucial role in reduction of the divertor heat load. Notably, elastic scattering between ions and neutral particles can be characterized as large-angle scattering. A large fraction of ion energy is transferred to neutral particles, and the ion direction can be significantly changed by a single large-angle scattering event. In abundant neutral particle regions such as divertor plasmas, the large-angle elastic scattering results in additional ion transport perpendicular to magnetic field lines. Effect of the additional ion transport is expected to be significant at low magnetic field strength and long Larmor radii, such as in a case of advanced divertors (e.g., Super-X and Snowflake divertors). In this study, we investigated the effect of the large-angle elastic scattering at low magnetic field strength and long divertor legs with reference to advanced divertor configurations using an orbital calculation. The large-angle elastic scattering transport is seen to cause a spread in density profiles and a reduction of heat flux. The results of this study show that for the short (long) leg divertor configuration like JT-60U (advanced divertor), the peak heat flux is reduced by around 15% (21%) when the magnetic field strength is 0.5 T in comparison to the model that assumes no guiding center movement due to the elastic scattering. It is also shown that the assumption of isotropic elastic scattering with neutral particles leads to excessive suppression of ion flows.
