Application of New Figures of Merit for Multi-Stage Cryocoolers
Kadin, A. M.
Webber, R. J.
Track, E. K.
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Evaluation of the overall performance of a multi-stage cryocooler, including the cooling power available on the intermediate stages, is not trivial, but is necessary to choose or design efficiently a cooler for a defined application. We have recently proposed two simple definitions of electrical “figures of merit” (FoM) for multi-stage cryocoolers that represent the distributed refrigeration power for applications where heat-sinking of power and signal leads at intermediate stages is available. These FoMs are designed to have universal applicability and to convey the relative performance of such cryocoolers in a much more effective manner than simple weighted averages based on the coefficient of performance (CoP) of the various stages. We demonstrate the utility of these FoMs by applying them to a four-stage cryocooler over a broad range of temperatures, enabling us to determine the optimal operating temperature and heat lift of each stage of the cooler. We also show, using properties of a real superconducting electronic system operating at 4 K, how these FoMs can be used to help in the specification and design of an improved multi-stage cryocooler to fit efficiently the needs of such a system.