Low-cost Manufacturing of Round REBCO Wires for Accelerator Magnets

There is substantial interest in the upgrading the existing High Energy Physics accelerators to higher energy levels so as to probe deeper into the subatomic scale and unlock the mysteries of the Universe. Such upgrades to higher energy levels would require use of High Temperature Superconductor (HTS) magnets which can generate magnetic fields levels of 20 T and beyond. Canted Cosine Theta (CCT) beam steering magnets using a smaller bend radius winding configuration is a leading design to generate multipole magnetic fields. A promising HTS candidate for use in accelerator magnets is RE-Ba-Cu-O (REBCO, RE=rare earth) coated conductors that are fabricated by a reel-to-reel thin film process. A challenge with REBCO coated conductors is their flat rather than a round geometry which makes it difficult to use them in accelerator magnets of complex shapes. Recently, we developed an innovative approach to fabricate round REBCO wires of 1.3 to 2 mm diameter using ultra-thin REBCO tapes where the superconductor film is positioned near the neutral plane. Such Symmetric Tape Round (STAR) wires exhibit excellent tolerance to bend strain with a critical current retention of more than 95% when bent to aradiusof15mmandanengineeringcurrentdensity(Je)ofnearly 600 A/mm2 at 4.2 K in a background field of 20 T. AMPeers has successfully scaled up fabrication of STAR wires to 60 meter lengths. The cost of STAR wires (or for that matter any round REBCO wire technology) is currently an impediment to large-scale commercialization. The main contributors to the cost of STAR wires are: the cost of individual REBCO tape strands used, fabrication cost and manufacturing yield. In the proposed program, AMPeers and University of Houston (UH) will tackle all three contributors to achieve a 5 fold reduction in the cost of STAR wires. In addition to meeting the needs of High Energy Accelerators that would operate at 20 T and beyond for High Energy Physics, the new technology would be highly impactful in the commercial market for accelerators which includes proton beam therapy in medicine, ion implantation for digital electronics, for safer use of nuclear energy, treatment of water and flue gases, pharmaceutical drug development and nuclear forensics and cargo screening for security. Additionally, the round REBCO wire technology developed in this program can enable commercialization of HTS in power applications such as generators, motors and transformers.