The advantages of no-insulation (NI) coils – such as higher current density, better mechanical integrity, thermal stability, and self-protecting properties over insulated coils make them a more attractive technological choice for high-field magnets, in rotating machines and in linear actuator applications [1]. However, in such applications, the coils are subjected to time-varying magnetic fields which cause magnetisation loss. The loss might vary based on the field angle and frequency that the coil is exposed to. This loss causes a parasitic heat load which can have a significant impact on cryogenic system design. As such, to successfully design systems, the behaviour of this loss under different conditions must be investigated. In this work, magnetisation loss in a double-pancake, solder-impregnated NI coil wound with Shanghai Superconductor REBCO coated conductors is investigated experimentally and numerically. Experiments were carried out at 77 K under AC external magnetic fields up to 100 mT for various field angles and frequencies. Numerical results from a 2D axisymmetric model [2] of the NI coil implemented in COMSOL Multiphysics are then compared with the measured loss values. Furthermore, the current density distributions and magnetic field penetration profiles are analysed to understand the magnetisation loss behaviours.
[1]S. Hahn, K. Radcliff, K. Kim, S. Kim, X. Hu, K. Kim, D. V. Abraimov and J. Jaroszynski, “Defect-irrelevant’ behavior of a no-insulation pancake coil wound with REBCO tapes containing multiple defects,” Supercond. Sci. Technol., vol. 29, Art. no. 105017, September 2016.
[2] R. C. Mataira, M. D. Ainslie, R. A. Badcock, and C. W. Bumby, “Finite-element modelling of no-insulation HTS coils using rotated anisotropic resistivity,” Supercond. Sci. Technol., vol. 33, Art. no. 08LT01, June 2020.
This work was in part supported by the New Zealand Ministry of Business, Innovation and Employment under the Advanced Energy Technology Platform program “High power electric motors for large scale transport” contract number RTVU2004 and in part supported by the Air Force Office of Scientific Research under award number FA2386-22-1-4054.