Small scale helium-4 liquefaction using a two-stage 4 K pulse tube cooler.

On the basis of previous results obtained with a two-stage pulse tube cooler that was able to provide a net cooling power of up to 0.37 watt at 4.2 K, a somewhat modified version has been built to use it for small scale helium-4 liquefaction. This paper presents first results obtained with this liquefier, which was operated with a Gifford-McMahon-rotary valve and a Gifford-McMahon-type compressor of 6 kilowatts input power. After the initial cool down period of about two hours for the second stage, a steady liquefaction rate of 0.13 liter/hour at 4.2 K was obtained.