Test results of a cable-in-conduit superconductor for the WENDELSTEIN 7-X stellarator

The superconducting magnet system of the modular stellarator WENDELSTEIN 7-X consists of 50 nonplanar and 20 planar coils. The nominal current is 16 kA at 6 T and at 4.2 K. The minimum bending radius of 0.2 m required the development of a suitable conductor. The concept is based on a NbTi forced-flow superconductive cable embedded in an aluminium alloy jacket. This is relatively soft during coil winding but gets its design strength by hardening during the impregnation process of the winding. As a step of the development programme, two 200 m long conductor lengths were fabricated by Europa Metalli, Italy, and Noell, Germany, together with SwissMetal, Switzerland. At Tesla, UK, each conductor length was wound to a planar coil of 0.2 m inner radius using the same winding and impregnation procedure as intended for the future series coils. The model coils were tested in the STAR facility at the Forschungszentrum Karlsruhe in order to investigate the behaviour of a long sample conductor. The model coils have been operated at various temperatures under self-field and background field conditions. Experimental results of the second model coil are presented, and a comparison to test results obtained for the LMI conductor is given.