Formation of snowflake diverted equilibria of CFETR

The Chinese Fusion Engineering Test Reactor (CFETR), a next-generation fully superconducting fusion reactor, is in the design stages. In this paper, we present three snowflake (SF) divertor configurations (SF+, exact SF, SF−), to demonstrate the possibility of attaining these SF configurations with two special additional poloidal-field (PF) coils set on the CFETR, where all PF coils are outside the TF coils. Starting from a single null divertor (SND), a sequence of desirable SF configurations can be realized whereby the PF-coil currents are below the maximal design limits. Compared to the SND, the potential properties of these SFDs, including low-poloidal-field area, flux expansion, connection length, are analyzed and presented in this paper. As the required currents in some PF coils are higher for a SFD than a SND, an operating space of coil currents for the SFD was calculated at a range of the internal inductance (li) and flux states. The result indicates that though the current in CS1 PF coil limits access to the lower li and flux state region, the PF coils system can provide ∼30 Wb for the flattop phase.