Miniature milli-kelvin cryo-cooler

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We propose the development and construction of the world's first milli-Kelvin cryo-cooler, transforming the use of the milli-Kelvin temperature domain in the same way 4 K cryo-coolers have for the liquid helium region. It will enable those inexperienced with such low temperatures to easily access very low temperatures in a bench top system. We propose to construct a small cooler module, a continuous adiabatic demagnetisation refrigeration (cADR) which will extend any 4 K cryo cooler to a milli-Kelvin (<100 mK) cryo cooler. Current 4 K pulse tube coolers can reach 4 K from room temperature within 2 hours, we anticipate a further 2 hours for the cADR to achieved <100 mK, giving a complete cool down from room temperature to <100 mK in 4 hours. By controlling the ADR's various magnetic fields, the proposed cryo-cooler module can provide a highly stable temperature anywhere from the base temperature of the attached 4 K cryo-cooler to <100 mK. This therefore represents a complete cryo-cooler solution and thus extreme ease of use for a technology which is still large and cumbersome. The technology to enable this proposal for a ground based system has come about by the large investment in developing ADR technology for future space missions at the Mullard Space Science Laboratory (MSSL).