Development of high field Tokamak with force-balanced coil

Although high field is very favorable for magnetically confined fusion devices such as Tokamaks, electromagnetic forces derived from the field become serious. In particular, the large in-plane centering force hinders toroidal field coils from operating at higher fields. Instead of toroidal field coils, force-balanced coils (FBCs), by which this force is drastically reduced, are proposed for the coil system of a Tokamak. FBC can also provide enough poloidal flux for plasma breakdown and current induction during the ramp-up phase of the coil current. In this paper, how to design the FBC for Tokamaks is discussed. FBCs of ITER-EDA size were designed and compared with conventional toroidal field coil systems in terms of the electromagnetic force and the poloidal field in the vacuum vessel. The construction of a small Tokamak with FBCs, for the demonstration of Tokamak plasma confinement, was completed and plasmas have been generated in it.