Effects on the Magnetic Field Stability of Coupling Currents Existing in a Two-Tape Bundle of a HTS Insert Prototype

Abstract

The High Field Laboratory for Superconducting Materials (HFLSM) is developing a 33 T Cryogen-free Superconducting Magnet (CSM). The major part of the magnetic field will be achieved thanks to a High Temperature Superconductor (HTS) insulated insert based on the Robust Coil concept. This design features, for each turn, two tapes wound together, in direct contact to enhance the coil's protection. However, a drawback of this architecture is the development of coupling currents caused by variations in the axial component of the magnetic field. These currents lead to additional losses and affect the quality of the magnetic field. This work focuses specifically on the impact of these coupling currents on the magnetic field quality at the location of the future samples in the context of developing a user magnet. The case study of this work is a large-scale prototype of the future HTS insert. To achieve this objective, numerical simulations were conducted to differentiate what are the qualitative effects of coupling currents and screening currents. The results showed that these currents have opposite effects on the magnetic field at the sample position. Additionally, the large-scale prototype experienced long current plateaus, during which the magnetic field was measured. The variations of the latter were driven by the relaxation of these opposing effects, each exhibiting different rates and relaxation times.