The Electrical Insulation of the TF Coils of ITER

Abstract

The Toroidal Field (TF) system of ITER consists of 18 coils in which the winding pack (WP) is formed by 7 stacked double pancakes (DP). The conductors in the TF coil are operated in steady state mode with a current of 68 kA providing a flux of 5.4 T at the plasma axis. The conductors are wrapped with turn insulation and embedded in grooves manufactured in so called radial plates. The grooves are closed with covers, wrapped with glass and polyimide tapes and vacuum impregnated. This layout of the TF WP prevents the accumulation of stresses in the turn insulation, making unlikely the occurrence of a turn-to-turn short circuit. The insulation of the WP will undergo during ITER design lifetime fast neutron fluencies up to 3.2x1021n/m2, which is equivalent to 10 MGy. Standard epoxies degrade if submitted to such doses, developing mechanical properties that would not withstand the estimated operation in-plane shear stress in the range of 45 MPa. The use of a radiation-hard thermoset for glass-fiber composites (cyanate ester) is considered and the on-going extensive qualification work will be presented. The technical solution of how to isolate critical High Voltage (HV) areas like the joint connections or voltage taps is also discussed.