Low-cost, infinite-length 2G stand for cable-in-conduit fusion magnets

Second generation (2G) superconductors conductors are the enabling technology for ultra-high energy particle accelerators and compact fusion reactors, which would be impossible using the traditional superconductors. However, the superconducting layer in a 2G conductor is a thin brittle ceramic that can be easily damaged. This is why the 2G conductors are available in length is not enough to manufacture a practical magnet. We propose development of a new type of 2G superconducting cable that features two innovations: (i) small diameter and compatibility with the established automated wire layup methods, (ii) the cable length is unlimited. The key innovation is the distributed filament splicing made possible by the exfoliated superconductor technology. Multiple filaments can be continuously layered into a cable and joined with a thin layer of solder to form a distributed ultra- low resistance splice. During the Phase I effort, we will develop a method of rapid (< 3 s) fusion of narrow superconducting 2G filaments to achieve an inter-filament contact resistance on the level of the best 2G wire splices. Multilayer filaments, when bundled and stacked into multiconductor cable, would thus realize layer to layer current sharing. In this way, the defects and splices would statistically average, thus dramatically increasing the overall yield of a cable of practically unlimited length. The proposed Phase I activities will include the following tasks: (i) Develop a fast filament fusion process that enables inter-filament contact resistance below 200 nΩ*cm2. (ii) Manufacture a coil with purposefully cut filaments and evaluate the coil performance at 20 K in conduction-cooled mode. (iii) Evaluate performance of the coil at 4.2 K, 6 Tesla field at a federal accelerator facility. The technology promises to reduce the cost of the 2G conductors and make the compatible with the established magnet manufacturing techniques. The potential applications of the technology are cancer therapy machines, compact fusion reactors and industrial accelerators. The Phase II effort will be focused addressing the growing market of compact high-field fusion reactors.