Design and Preliminary Test at 77 K of a 5 T / 34 mm REBCO Dipole Magnet Insert for a 15 T Full-Service-Field Testing Facility

A new testing facility employing a 15 T transverse field to evaluate the full-service-field characteristics of superconducting materials is now under development in China. A primary objective involves producing a large bore 15 T dipole magnet to serve as the source of the transverse magnetic field load. In this study, we designed and constructed a compact high-temperature superconducting (HTS) dipole magnet insert, comprising six block-type double pancake (DP) coils wound with REBCO tapes. The insert features a user bore of 34 mm and an outer diameter of 110 mm, expected to generate a 5 T field at 4.2 K with an operating current of 278 A, within a 10 T low-temperature superconducting (LTS) background dipole magnet. According to numerical simulations, the sextupole coefficient <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$b_{\mathrm{3}}$</tex-math></inline-formula> is less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$5\times 10^{-3}$</tex-math></inline-formula> and the operating point <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$I_{\text{op}}/I_{\mathrm{c}}$</tex-math></inline-formula> is below 0.6 considering the screening current. Circumferential reinforcement structures were externally integrated to the REBCO coil assembly to mitigate electromagnetic stress under high background fields. The magnet was successfully charged to 43 A, achieving a central field of 0.71 T at 77 K, validating the winding process and joint techniques. The no-insulation characteristics were analyzed based on the test data. This work is important for advancing practical high-field HTS dipole magnets with high stability and field uniformity.