CCT quadrupole magnet R&D using REBCO tapes

Background Canted Cosine-Theta (CCT) quadrupole magnets have gained significant attention in particle accelerators due to their intrinsic advantages in field quality, compact structure, and stress management. High-temperature superconducting (HTS) REBCO tapes offer exceptionally high critical current density and excellent in-field performance, making them ideal candidates for high-gradient magnet applications. However, directly winding flat REBCO tapes into complex three-dimensional CCT grooves presents severe mechanical challenges, including critical current degradation risks caused by bending and twisting strains.

Purpose This study aims to design, construct, and test a prototype REBCO CCT quadrupole magnet using a direct multi-layer tape winding strategy with superconducting joints, validating its technical feasibility and evaluating the impact of the winding process on conductor performance.

Methods Based on the optimized geometric structure of the CCT quadrupole magnet, a simplified winding technique was implemented where multiple layers of REBCO tapes—rather than complex cables—were wound directly into the former channels. To achieve a continuous current path and streamline fabrication, these multi-layer tapes were connected via low-resistance superconducting joints into a single conductor loop. Mechanical winding verification and critical current (I_c) transport measurements were carried out on the prototype immersed in liquid nitrogen at 77 K. The I_c values of the REBCO tapes were systematically characterized and compared before and after winding.

Results The prototype magnet was successfully fabricated without mechanical defect. Liquid nitrogen test results showed that the critical current of the wound REBCO tape closely matched its pre-winding baseline, confirming that the adopted winding procedure introduced only minimal performance degradation. The superconducting joints also maintained stable current transport during cryogenic operation.

Conclusions The experimental results demonstrate that the proposed direct multi-layer REBCO tape winding method combined with superconducting joints is technically feasible and effective. This approach significantly simplifies the fabrication process while preserving conductor performance, providing essential technical support for the future development of high-gradient CCT HTS quadrupole magnets.