Critical Current Analysis of an YBCO Insert for Ultrahigh-Field All-Superconducting Magnet

With the development of superconducting magnet technology, high magnetic field experimental conditions can be more easily achieved than ever. Recently, a superconducting magnet with the center field of 25 T at 4.2 K and a worm bore size of 32 mm in diameter has been designed. The superconducting magnet consists of NbTi, Nb₃Sn coils, and YBCO insert. The YBCO insert has been designed, fabricated, and tested in the liquid helium at the Institute of Electrical Engineering, Chinese Academy of Sciences (IEE, CAS), to prove the technical feasibility to achieve the target of 25 T. The YBCO insert has the inner diameter, outer diameter, and height of 41, 124, and 115 mm, respectively. The critical current distribution of the YBCO insert at 77 and 4.2 K, self-field, and in a 15-T background field is given in detail, based on the electrical properties of an YBCO-coated conductor. An analysis on the critical current shows that the YBCO insert has a minimum critical current of 19.4 A at 77 K, 119 A at 4.2 K, at the self-field, respectively, and 177 A at 4.2 K in a 15-T background field. Preliminary tests in the liquid nitrogen and liquid helium show that the analysis on the critical current is reasonable and agrees well with the test. The analysis on critical current at 4.2 K shows that it is much reasonable for the YBCO insert to obtain a central magnetic field of up to 24 T in a 15-T background field. In this paper, the design, critical current analysis, and preliminary experiment are reported.