In 2006 I built and delivered a liquid-helium-cooled cryogenic sapphire oscillator to NICT in Tokyo. In August 2014 I upgraded that sapphire oscillator to use a cryocooler, hence saving them a lot of money as the cryocooler uses very little helium. The earlier version consumed 7 litres per day @ $50 a litre. It’s expensive to run.
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