Qualification of ITER Correction Coil Superconducting Joint

The correction coils (CCs) are a system of 18 superconducting coils composed of top CCs, side CCs, and bottom CCs, and are required to correct asymmetries and reduce magnetic error fields detrimental to the plasma performance of the ITER machine. The CC terminals will be connected with those of the superconducting busbars with twin-box joints. Qualification of the manufacturing procedure of the coil terminals is achieved by performing electrical tests of prototype joints in relevant conditions of current, temperature, and background field (4.5 K, 10 kA, and 2.5 T). In order to control the dc resistance and ac loss in series production, special tooling and manufacturing processes were developed. The main technological steps are conductor dejacketing, nickel removal, and silvering of the cable in the terminal, followed by cable compaction and tungsten inert gas welding of the termination box. To this end, two joint samples were manufactured in 2015 and 2016. The performance of the joint samples was verified before and after 1000 electromagnetic cycles. The qualification tests were carried out in the SULTAN facility and ASIPP facility. The test results show the dc resistance below 5-nΩ criterion and ac losses below 7 J/cycle.