Design, construction and test of a 13 T no-insulation REBCO magnet: validation of an improved circuit model considering the screening current

Abstract No-insulation (NI) (RE)Ba 2 Cu 3 O y (REBCO (RE = Rare Earth)) magnets show great potential in producing ultra-high magnetic field due to their excellent self-protection behaviors, high current density, and compact structure. However, the complexity of their fabrication process, along with the intrinsic screening current induced in the coated REBCO layer, poses challenges for large-scale applications. The screening current not only generates an unwanted irregular magnetic field and overstress, but also leads to a non-uniform current distribution within winding, affecting the inductance and dynamic voltages of NI REBCO magnets. To accurately simulate the electromagnetic behaviors of each pancake coil in an NI REBCO magnet, we propose an improved network circuit integrated with the homogenous T-A formulation model. This model accounts for the screening current and simulates the detailed electromagnetic characteristics of each pancake coil without the need for pre-calculating the current-dependent inductance matrix. A 13 T NI REBCO superconducting magnet was developed for high-frequency gyrotrons in our lab. The design, construction and energizing test of this magnet are presented. The accuracy and validity of the improved circuit model are verified by comparing experimental voltage measurement with simulated results with or without considering the screening current. The voltage data reveals significant dynamic drift during the low-current ramping stage, attributed to the temporal changes in the screening current before it reaches saturation.