Low-cost structural high-current high-field REBCO cable development

Brookhaven Technology Group Inc. (BTG) and the Massachusetts Institute of Technology (MIT) propose a technology of a low AC-loss, high current cable for high-filed magnets with low ramping-field loss. This STTR effort is maturation of a joint MIT-BTG patent U.S. 11973968. It is recognized that REBCO superconductor is an enabling technology for ultra-high, > 20 T, magnets that are critical for the future compact fusion reactors, MNR spectrometers and particle accelerators. Current REBCO cabling technologies suffer from poor utilization of the filament, high AC loss and poor defect-tolerance. AC loss can be reduced by striating or slicing of the superconducting tape into narrower filaments. Both approaches proved to be technically challenging: it is difficult to handle narrow filaments and equally difficult deposit stabilizing copper layer on patterned REBCO layer without shorts. The proposed technology will incorporate the following innovations: (i) Rutheford-type cable with high current density and high transverse stress, (ii) partial filamentization of the exfoliated REBCO filaments. The partial filamentization process will leverage the recent advances in fiber laser and scan-head technologies. The BTGĺs exfoliated tape will be sliced in a pre-determined unique pattern into 1 mm wide filaments using a fiber laser with fast galvanic mirror scan head. The cuts would not completely separate into fine filaments so that the tape would not be mechanically compromised and could be safely handled during the cabling process. At the same time, the slices will prevent the formation of large current loops of the persistent current, thus effectively reducing the magnetic moment of the winding by at least a factor of 8. The partially filamentized tape will be wound around a flat central rod to form a compact cable using a REBCO Rutherford-type cabling method recently developed by MIT. It is wound around a flat former, thus forming a multi-layer cable. The partially filamentized conductor layer will be electrically connected to provide a current path around a current-blocking defect in a filament while maintaining a low magnetic moment of the cable. Phase I work will be carried out in collaboration with MIT. During Phase I effort BTG team will manufacture up to 10 meters of partially filamentized exfoliated tape and deliver to MIT team for cabling. The MIT team will manufacture 1.5 meters of the cable, bending and transverse strain tests. The results will be analytically evaluated, including AC losses. The Phase II work will focus on scaling up the process and building a test coil. 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.