Development of high field tokamak with force-balanced coil

Although higher field is very favorable for magnetically confined fusion, electro-magnetic force derived from the field becomes serious. In the tokamak, the in-plane centripetal force and the out-of-plane overturning force make the design of toroidal field magnets difficult. In place of toroidal field coils (TFC) and poloidal field coils (PFC), force-balanced coils (FBC), by which these forces are reduced, are proposed for the coil system of tokamaks. The construction of a small tokamak with FBC, which is to demonstrate the tokamak plasma confinement, was finished and pre-tests for plasma generation are under way. The electromagnetic force on FBC of ITER size is calculated and compared with that on TFC and PFC system. (author)