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 3He and 4He components are circulated (the 4He by a fountain-effect pump operating at about 2 K, the 3He 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 3He and 4He 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 3He compressor and the pre-cooling requirements for the dilution refrigerator.

► We present a progress report on a dilution refrigerator for space applications.
► We present a new heat exchanger design in combination with a superleak.
► We present experiments on the performance of two type of heat exchangers.
► We present experiments on the performance of the fountain pump.
► We specify the interface requirements of the refrigerator.