Exploration of the influence factors on contact resistance obtained from sudden discharge test on the large-bore metal-as-insulation REBCO magnet

In this paper, the factors affecting the evaluation of the equivalent contact resistance of the magnet were investigated by sudden discharge tests in a large-bore conduction-cooled metal-as-insulation (MI) high-temperature superconducting (HTS) magnet with an inner diameter exceeding 450 mm and consisting of ninety double pancake coils. It was found that the evaluation results of the contact resistance of the magnet are influenced by the current, temperature, measurement position, and evaluation method. Subsequently, a power law relationship was used to describe the relationship of contact resistance with current and temperature, and the relationship of contact resistance with current showed an opposite trend to that expected, while the relationship with temperature was as expected. We compared the experimental results of other teams to try to provide a reasonable explanation for the above phenomenon. Additionally, we found a significant difference between the delay of the central and end magnetic fields and a difference in the evaluation results between the method of using the field to decay to 1/e of the initial value and the curve-fitting method. We analyze the reasons for these phenomena and give our explanations. Finally, based on our experimental results, a measurement method for the equivalent contact resistance of NI/MI HTS magnets was summarized to improve the evaluation accuracy. This paper is both the first systematic experimental study on the contact resistance of a large-scale object such as MI HTS magnets and a review of previous studies. The findings are hoped to provide guidance for evaluating equivalent contact resistance for NI/MI HTS magnets in future engineering applications.