All six high-temperature superconductor current leads (HTS CLs), which will connect JT-60SA's superconducting Toroidal Field (TF) coils with the power supplies, have been delivered to Naka, Japan – the location of where JT-60SA is being constructed.
The HTS CLs are one of the European in-kind contributions to the JT-60SA project (one of the three large projects covered by the Broader Approach agreement concluded between the European Atomic Energy Community (Euratom) and Japan), voluntarily contributed by Germany. KIT (Karlsruhe Institute of Technology), the designated German contributor, in consultation with F4E and JAEA selected the most advanced high temperature superconductor current lead design which KIT have already previously developed for the Wendelstein 7-X experiment.
The electrical connection between the warm power cables of the power supplies and the cold superconducting electrical network of the coils is realised by special helium-cooled connectors, the so-called current leads. In total, twenty-six such current leads are being produced. The additional 20 current leads will be used to connect the power supplies with the JT-60SA Poloidal Field (PF) coils and the central solenoid modules. The current leads use high-temperature superconductor (HTS) tapes to reduce the resistive losses while creating a thermal barrier to reduce the heat flow to the very cold electrical networks. Ten HTS CLs for the PF coils will be shipped around October 2016, while the delivery of the remaining ten HTS CLs is scheduled for 2017.
Mr Stefan Kaufmann, Member of the German Parliament, visited the JT-60SA Naka site recently and was able to see the high-temperature superconductor current leads delivered for the TF coils.
The delivered current leads will now be provided by JAEA to the manufacturer of the so-called coil terminal box (CTB) for the TF coils. The assembly of the cold end of the HTS CL with the superconducting network in the CTB requires some skills to achieve a very low contact resistance (in the order of one nano-Ohm) and an electrical insulated vacuum enclosure. For this reason representatives of the Japanese manufacturer and of JAEA visited KIT for several days of training.
"This achievement is marking a fundamental milestone of a complex multi-year programme, involving the fabrication of the components and the parallel development of the test facilities. This important EU contribution has been possible thanks to the extensive know-how, developed at KIT on high-temperature superconductors, coupled with the dedication of KIT researchers, engineers and professional personnel", said Prof. Dr. Joachim Knebel, Head of Division Mechanical and Electrical Engineering at KIT.