Comparative study of a conventional and snowflake divertor for the FAST (Fusion Advanced Studies Torus) tokamak

The SOL features of FAST in the snow flake (SF) configuration of the divertor are compared with those of the conventional single null case for three main scenarios: reference, advanced and extreme H-mode by means of the 2D edge code TECXY. The heat load onto the divertor targets is dramatically mitigated, much more than expected from the change of magnetic topology only, especially at the highest plasma densities. The accompanying large density increase and temperature drop indicate a much closer approach to plasma detachment. The load level with SF appears always manageable by the present technology without the help of injected impurities. Sputtering from the target also should become negligible. These changes are attributed to the much longer time spent by the SOL particles in the cold region of the X point where the length of the magnetic lines is highly increased and hence to the much stronger interaction of the plasma particle with the neutrals.