Development of REBCO-based Symmetric Tape Round (STAR) wire forthe Next Generation High-field Compact 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 1.6 to 1.85 mm diameter using ultra-thin REBCO tapes where the superconductor film is positioned near the geometric center. Such Symmetric Tape Round (STAR) wires exhibit excellent tolerance to bend strain with a critical current retention of more than 97% when bent to a radius of 15 mm and an engineering current density (Je) of 406 A/mm2 at 4.2 K in a background field of 20 T. In the proposed program, AMPeers LLC will work to develop consistent and high performance STAR REBCO wires specifically for prototype CCT coils that require a minimum bending radius of 15 mm to be operated at 20 T. Various STAR REBCO wire geometries will be fabricated in lengths of few meters and optimized based on the electromagnetic and mechanical properties of these wires and the performance after being wound into the CCT structures. The optimal STAR REBCO wire geometry will be scaled up during the Phase II SBIR program to support the development of prototype CCT magnets. Commercial Applications and Other Benefits: 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.