Cooling performance of hybrid refrigerant of solid nitrogen and small amount of neon for the purpose of HTS power applications

We have investigated cooling performance of a hybrid refrigerant of solid nitrogen and small amount of neon by using a short sample of Bi-2223/Ag tape as a cooling target. Solid nitrogen is expected as a heat capacitor for HTS applications operated below triple point temperature of nitrogen, and we have proposed in our previous study a method for overcoming the problem of its thermal contact with a cooling target with the aid of small amount of liquid neon. This paper discusses the phase state as well as the quantity of neon required for such an improvement. Nitrogen gas was introduced into a sample chamber through a mass flow controller, and then was liquefied and solidified by a Gifford-McMahon cryocooler. After that, in order to improve thermal contact of the solid nitrogen with the sample, neon gas was also introduced into the chamber at 25 K where neon can be liquefied. Cooling performance of such a hybrid refrigerant with different inputs of neon was evaluated by measuring temperature rise of the sample with the transportation of overcurrent. As a result, neon could suppress the temperature rise even in gas state, and the existence of liquid neon could additionally suppress the temperature rise. Furthermore, the required proportion of the liquid neon to the solid nitrogen was very small. From these results, we concluded that introducing neon until neon can be liquefied was the best way to make the most of the potential of the hybrid refrigerant.