A study on the electrical insulation properties of solid nitrogen for cooling of the high temperature superconducting systems

Recently, for improvement of the magnetic field of high temperature superconductor (HTS) apparatus, many studies on operating in the temperature range of 20-65 K with liquid helium or the thermal conducting method using cryocooler are actively reviewed. Also, the cooling method of using solid nitrogen as cryogen is currently being suggested. Since nitrogen has a very large specific heat in solid state, it is expected that it can enable long-time operation without a continuous supply of cooling energy. However, there is still insufficient data on the characteristics of solid nitrogen such as thermodynamic properties and liquid-solid phase transition. Especially, there was almost no study done on the electrical insulation properties of solid nitrogen so far. In this study, solid nitrogen to find the electrical characteristics was made by using cryocooler and cryostat, and investigated the flashover discharge and breakdown. The results of this study will be useful as a basic data for electrical insulation design of the HTS system such as SMES using solid nitrogen as cryogen.