Resonant Magnetic Perturbation for ELM Suppression with Helical Ferritic Steel Inserts in Tokamak DEMO Reactor

Edge localized mode (ELM) must be eliminated which enhances the erosion of divertor plates in the Hmode operation of tokamak reactors. Suppression of ELM has been experimentally achieved by the resonant magnetic perturbation (RMP) with multipartite coils. In a DEMO reactor with strong neutron flux, however, it is desired the coils near the first wall not to be put in. We propose an innovative concept of the RMP for tokamak DEMO reactors without installing coils but inserting ferritic steels of the helical configuration. Helically perturbed magnetic field is naturally formed in the axisymmetric toroidal magnetic field through the helical ferritic steel inserts (FSIs). The perturbation amplitude in the plasma pedestal region can easily be set above several 10^-4 of the toroidal field strength in the DEMO reactor condition, which is enough for the RMP to mitigate/suppress ELMs.