Conceptual design of the island divertor coils on the J-TEXT tokamak

Abstract

A set of new resonant magnetic perturbation (RMP) coils is designed for the J-TEXT tokamak to form the island divertor (ID) configuration [F. Karger, Phys Lett A, 61 (1977) 385]. This design is aiming at investigating the effect of ID on the peak heat load reduction in a tokamak. The RMP field generated by these new coils can produce magnetic island in the plasma boundary. The field line of this magnetic island is opened by divertor targets, so as to form the island divertor configuration. Therefore, the edge island should be a vacuum island, which can be described by an analytical mode with assuming linear superposition of the plasma equilibrium field and the magnetic perturbation in a vacuum approximation. Numerical calculations have been carried out to calculate several parameters for the island divertor configuration such as the perturbed magnetic field generated by the coils, its spectrum, the field line tracing and the Poincaré plot. Conceptual design is based on the m/n = 4/1 magnetic island, which can be generated by either 16 out-vessel saddle coils or 8 in-vessel S-type modular coils. Here, m and n are the poloidal and toroidal mode numbers respectively. The ID configuration can be then established by the boundary 4/1 island intersecting with proper divertor targets.