Combination of helical ferritic-steel inserts and flux-tube-expansion divertor for the heat control in tokamak DEMO reactor

Takizuka, Tomonori*; Tokunaga, Shinsuke; Hoshino, Kazuo; Shimizu, Katsuhiro; Asakura, Nobuyuki

Edge localized modes (ELMs) in the H-mode operation of tokamak reactors can be suppressed/mitigated by the resonant magnetic perturbation (RMP), but RMP coils are difficult to be applied to DEMO reactors with strong neutron flux. We propose an innovative concept of the RMP without installing coils but inserting ferritic steels of the helical configuration. Helically perturbed field is naturally formed in the axisymmetric toroidal field through the helical ferritic steel inserts (FSIs). When ELMs are avoided, large stationary heat load on divertor plates can be reduced by adopting a flux-tube-expansion (FTE) divertor like an X divertor. Separatrix shape and divertor-plate inclination are similar to those of a simple long-leg divertor configuration. Combination of the helical FSIs and the FTE divertor is a suitable method for the heat control to avoid transient ELM heat pulse and to reduce stationary divertor heat load in a tokamak DEMO reactor.