High temperature superconductor current leads proposal for ITER

In the ITER superconducting magnet system, operation currents up to 68 kA are required that have to be transferred from room temperature (RT) to 4.5 K by specially designed current leads (CL). The ohmic losses and the thermal conduction of conventional CL cause high heat loads to the refrigeration system. This load can be reduced drastically by the use of High Temperature Superconductor (HTS) current leads because the superconducting HTS part of this CL causes no ohmic losses and very poor thermal conduction. The Forschungszentrum Karlsruhe and the CRPP Villigen have designed and built a 70 kA current lead using Bi-2223 HTS superconductor in the frame of the European Fusion Technology Programme. This HTS CL was installed and tested in the TOSKA facility of the Forschungszentrum Karlsruhe showing that the current of 68 kA can be carried by the CL even when the highest temperature in the HTS part is 85 K. The CL shows a large safety margin in case of a loss of coolant and even cooling with LN2 has been demonstrated. The option that all ohmic losses in the temperature range between 4.5 K and approx. 80 K can be eliminated using HTS CL is very attractive for ITER because savings in investment and operation costs are possible by removing this load from the cryogenic system. The consequences with respect to investment and operation costs are discussed comparing the ITER design with and without HTS CL which demonstrates that HTS current leads are very attractive and should be used for ITER.