小型2K GM 冷凍機の開発

Abstract

Conventional 4K GM (Gifford-McMahon) cryocoolers, while providing highly reliable cooling solutions for largescale superconducting applications such as magnetic resonance imaging (MRI) and superconducting magnets, encounter several difficulties including physical size and temperature reached when being fitted into a superconducting electronic device system. To create a suitable cooling solution for such devices, we developed a new, compact 2K GM cryocooler. The heat exchanger and regenerator were optimized using a numerical simulation method developed for 4K GM cryocoolers. Although development is still in progress, we successfully reduced the total length of the expander cylinder to about 240 mm. A series of performance tests of the prototype unit have shown that, under no-load conditions, the lowest temperature at the second stage reached about 2.1 K and temperature oscillation was less than ±21 mK. With a 1 W / 20 mW heat load, the temperature was 44.4 K at the first stage and 2.23 K at the second stage, which we believe shows sufficient cooling capacity for small-scale superconducting electronic device cooling. As future work, we will focus on a compact design for not only the expander cylinder, but also the compressor and drive system, and finally provide a complete compact cooling system solution.