Analysis of Critical Current Measurement for No-Insulation HTS Coil

Investigating electromagnetic characteristics of no-insulation (NI) high-temperature superconducting (HTS) coils is critical for advancing the use of HTS in many areas, such as energy, medical, and transportation. In this article, the charging and overcurrent test and the sudden discharging test are carried out on a 367.6-mm diameter NI HTS coil to obtain the electromagnetic parameters. It is found that significant radial current generated in the NI HTS coil during testing will cause obvious deviations between the fitted coil voltage and power supply current curve and the E–J power law characteristics, resulting in significant errors in the measured critical current (I_c) and n-value. To address this issue, the influence of radial current is considered in measuring I_c and n-value, thus enabling the precise determination of these values. Meanwhile, a finite-element model based on the T–A formulation has been developed to model NI HTS coils and simulate transient electromagnetic behavior during coil operation. Furthermore, the current distribution in NI HTS coils with different aperture sizes as well as in HTS coils with different contact resistivities during the ramp process is investigated, and the effects of different factors on I_c and n-value measurement are analyzed. The results provide theoretical foundations for performance evaluation and design optimization of NI HTS magnet systems.