Electrical Breakdown Characteristics in High-Vacuum Conditions for the Design of Superconducting Coils

In recent years, the utilization of high-temperature superconductors (HTS) in medical devices, such as magnetic resonance imaging (MRI) and particle accelerators for cancer treatment, has seen significant growth. This study focuses on the electrical insulation design of fast-ramping HTS saddle magnets, pivotal in reducing the volume and consequent operational costs of particle accelerators. Generally, these HTS magnets are operated under high-vacuum conditions to deter external heat intrusion and optimize thermal efficiency. However, their intricate geometries can inadvertently result in areas of localized vacuum degradation, undermining their electrical insulation capabilities, especially in environments with pressures less than 0.001 Pa. Further, this research delves into the influence of vacuum degree and insulator surface roughness on the electrical breakdown properties. The focus is primarily on the distinctions between sparkover and flashover. Due to their fast-ramping nature, HTS magnets undergo substantial current changes in short durations, leading to the induction of potentially dangerous voltages that might trigger electrical breakdown at sensitive junctures. In light of these challenges, we embarked on a series of experiments to understand electrical breakdown phenomena under diverse vacuum scenarios. These experiments, supplemented with finite element method (FEM) analysis, paved the way for the derivation of empirical formula. These formulas intend to guide the design of HTS magnets, ensuring their electrical insulation remains robust across a range of vacuum conditions.