Reliability Considerations for the ITER Poloidal Field Coils

Since it is practically impossible to remove the Poloidal Field (PF) coils from the assembled ITER (International Thermonuclear Experimental Reactor) tokamak without major interruption in operation, the design of these coils shall provide their high reliability under high voltage operation. The design of the coil insulation relies on a separation of functions: mechanical function of the load transmission, performed by glass-fiber impregnated with epoxy resin on one side, and the independent electrical barrier made of polyimide tapes on the other side. Numerical simulation has shown that the maximum electrical field in the coil is lower than 4 kV/mm, which is taken as the design criterion for the PF insulator system. In case of a single insulation failure in a coil, its functionality can be recovered by installing a so-called jumper to by-pass the faulty double pancake. The design of the jumpers and their installation procedure are described.