High power high temperature superconductor current leads at KIT

Abstract

Many large fusion devices presently under construction or in operation who comprise superconducting magnets like EAST, Wendelstein 7-X (W7-X), JT-60SA and ITER use High Temperature Superconductor (HTS) current leads to reduce the cryogenic load and operational cost. The Karlsruhe Institute of Technology (KIT) designed, constructed and successfully tested a 68kA HTS current lead demonstrator for ITER which led to the decision by ITER IO to use HTS current leads for the ITER magnet system. KIT has designed, constructed and tested the HTS current leads for W7-X, which are operational since 2015, and presently manufactures and tests also the HTS current leads for JT-60SA. All these current leads consist of a meander-flow type heat exchanger (HX) which is cooled by 50K helium and an HTS section. In all cases the first generation HTS material BSCCO is used embedded in a low conductivity matrix of AgAu. The technology developed in the past 20 years is now mature and would be able to be used for future fusion reactors like DEMO.In the meantime industry worldwide – with the exception of one company in Japan and another one in China – does not produce BSCCO tapes anymore; the second generation HTS REBCO is now used for application because of the better field performance in particular at high temperature. As the new material can only be produced in a multilayer structure rather than as a multifilamentary tape, the technology developed for BSCCO cannot be directly transferred to REBCO. Therefore several laboratories, in particular in Europe, are presently investigating how an HTS current lead made with REBCO could look like. This development will be the prerequisite for the construction of current leads for future fusion reactors as they have to handle high currents in the range of up to 100kA.The article discusses the status of the current lead development at KIT.