Emes, Michael Robert; (2000) The development of a 10 mK refrigeration system for space. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Detectors already require cooling to millikelvin temperatures in space to maximize energy resolution so that more distant sources of radiation can be identified. The lowest temperature that has been achieved in orbit so far is 302 mK on the infrared telescope for space (IRTS) in 1995. The Japanese ASTRO-E satellite launched unsuccessfully in February 2000 was to achieve 65 mK. Future instruments such as ESA's x-ray evolving universe spectrometer (XEUS) will require cooling to 30 mK and below. This thesis presents the design of a cryogenic cooling system that will surpass the needs of XEUS and encourage the development of a new generation of very low temperature, high-resolution detectors for space. With a single mechanical cooler maintaining thermal shield temperatures of 150 K, 20 K and 4 K, the adiabatic demagnetization refrigerator (ADR) proposed cools from a bath temperature of 4 K to 10 mK. The maximum amount of time for which the ADR can maintain this temperature is around 145 hours with no cooling power on the detector stage. This value falls as the cooling power increases, with a heat lift from the detector stage of 100 nW possible for 30.6 hours' continuous operation. A recycle time of around two hours is required between successive cycles. In response to launch vibrations, the proposed system can theoretically withstand accelerations at least six times higher than typical launch qualification levels. The total mass of the system is around 100 kg, including ADR, thermal shields and mechanical cooler. This is very low considering that the design promises unlimited lifetime operation and cooling to an unprecedented level.

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