Experimental test and evaluation of the Nb3Sn joint and header region for the westinghouse LCP coil

The Westinghouse LCP coil utilizes a supercritical helium forced-flow Nb3Sn cable enclosed in a stainless steel sheath. The helium flow to the conductor is supplied by a header system mounted on the top surface of the magnet. Each header also encloses the electrical joint between two lengths of cable. The superconducting stability of the joint area is essential under all current and field operating conditions. Experimental and analytical evaluation of the joint, header, and adjacent conductor has been performed to verify the helium flow distribution, pressure drop, and conductor and joint stability. This paper reviews the header and joint design and observed performance under forced-flow cooling and field conditions similar to those for the actual coil operation. The results showed a much higher than expected joint resistance which exceeded the design specification by an order of magnitude. Nevertheless, the joint and adjacent superconductor remained stable (at ∼ 13.5 kA) at a mass flow rate of ∼ 1.0 gm/sec which is one-half of the design inlet condition. These results and the required flow rates are discussed in terms of a forced cooled minimum propagating zone (MPZ). The observed hydraulic performance for the header region basically followed earlier flow measurements on forced cooled cables.