Miniature milli-kelvin cryo-cooler

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).

Those that will benefit from this development are: UK Industry, those utilizing low temperature cryogenic temperatures in research, those wishing to use low temperatures but do not have the necessary infrastructure and knowledge and the development of applications and usage of low temperature cryogenics in non research applications (e.g. security, medical imaging). The technology proposed to be developed will be transferred to industry (as detailed in the Impact Plan) and discussion have already taken place (see letter of support). This new technology is set to have a profound impact on the use of low temperatures due to its extreme ease of use - it is a very small continuously operating milli-Kelvin cryo-cooler, a switch on and go system. This temperature region is still hampered by large and cumbersome systems requiring significant knowledge and expertise. This situation seriously affects the uptake and application of devices needing a low temperature (milli-Kelvin) to operate. There is significant interest in the use of low temperatures from potential applications of state-of-the-art cryogenic detectors (e.g. x-ray transition edge (TES) detectors) in biological imaging to quantum computing research. Where the ease of use and the relinquish of the need for the tradition low temperature cryogenics laboratory environment is important. For example the proposed cryo-cooler could be used to cool a TES array in an x-ray scanner at an airport where the fact that the detector is at milli-Kelvin temperature is irrelevant due to the continuous operation, and the fact that it will just need a standard mains connection. Appearing like an ordinary piece of equipment. The proposed development will be revolutionary and open up the application of this temperature region not only bringing commercial reward but widening research capability. This project will take 2 years to develop the cryo-cooler at which point it will be transferred to industry and offered to the physics community for the proposal and development of integrated systems (e.g. x-ray imaging system) where the complexity of the cryogenics has been the hindrance. As detailed in the impact plan, the low temperature community will be involved by our links with industry and their client base as well as publicity at conferences via talks and demonstrations at conference trade-stands. Cryogenics is an enabling technology and thus we will be promoting the cooler to the whole physics community, welcoming collaboration in order to foster further research and development utilising this technology development.