A closed-cycle dilution refrigerator for space applications

We discuss the development of a gravity-insensitive dilution refrigerator adapted from the open-cycle refrigerator used for the Planck mission. Since the He-3 and He-4 components are circulated (the He-4 by a fountain-effect pump operating at about 2 K, the He-3 by a compressor at room temperature) rather than ejected into space, the lifetime of a closed-cycle refrigerator is not limited by the quantity of He-3 and He-4 available. In this work, we concentrate on the design and performance of the cold end (counterflow heat exchanger and mixing chamber) of the refrigerator. We discuss the sizing of the heat exchanger and present cooling power measurements. We detail the working of the fountain pump. We also briefly touch upon some practical issues including the choice of a He-3 compressor and the pre-cooling requirements for the dilution refrigerator. (c) 2012 Elsevier Ltd. All rights reserved.