SOLDER-FILLING OF A CICC CABLE FOR THE EFDA DIPOLE MAGNET

Several prototype Cable‐In‐Conduit‐Conductors (CICC) for the superconducting EDIPO (Efda DIPOle) revealed a degradation of their critical current (Ic) increasing with each loading cycle. The strong Lorentz‐forces during operation in combination with the limited support of the single strands against these forces are thought to be the cause of the permanent degradation of the brittle Nb3Sn superconductor from which the multi‐stranded CICC are made. In summer 2006 EFDA started to explore the possibility to remedy the Ic degradation by solder‐filling the conductor in order to mechanically stabilize the twisted‐strand cable inside the conduit. This solution was not considered as the main one, but as an emergency solution to be applied to the completed magnet, should every other option fail. The solder‐filling approach was previously applied with success in some cases. Some issues, however, needed to be clarified before this solution could be proposed for the EDIPO project. The most important among them are the choice of solder material, details of the solder filling process, and the thermo‐mechanical implications of a solder‐filled, high‐field, high‐current cable. This work, being reported here, made use not only of simulation but also of experiments, such as the mechanical testing of solder filled cables at cryogenic temperatures.