A Multi-Stage Hybrid 10 Kelvin Cooler

"We propose to develop a multi-stage hybrid cooler capable of providing 1 W of cooling at 10 K. To achieve the most efficient and reliable hybrid cooler possible, we propose to combine a multi-stage, linear-drive pulse tube with a low-temperaturereverse-Brayton stage. In this way we will take advantage of the strengths of each system, while minimizing their respective weaknesses. The system avoids the inherent losses associated with a regenerator at low temperature, as well as, the inefficienciesassociated with the Joule-Thompson process, by incorporating a novel turbo-expander in the low temperature reverse-Brayton stage. The use of a low-vibration, linear, compressor for the pulse-tube stage provides a large pressure ratio allowing the size andexpense of the recuperative heat exchanger to be minimized. These features result in a low-mass reverse-Brayton stage that can be fabricated reliably, at a reasonable cost, without sacrificing performance. The proposed hybrid cryocooler will achieveunprecedented efficiency below 10 K without resorting to high-unit-cost technologies such as super-critical shafts or extremely precise bearing clearances. The system will exhibit the high reliability and low vibration associated with pulse-tube andturbomachine-based reverse-Brayton systems. The result is a cryocooler that is ideally suited to cooling space-borne loads at or below 10 K. The proposed cooler can be employed in a wide variety of commer