Since 1997, Signaal Usfa has been working on the development of high reliability cryocoolers. These coolers have been developed with the aim to eliminate the lifetime determining factors of conventional cryogenic tactical coolers. The intention of this study was the development of a family of cryocoolers, which could be used to cover a large range of cooling powers. Today, these developments have resulted in the new range of flexure bearing cryocoolers currently available at Signaal Usfa, with cooling performances between 0.5 and 3 W @80K and estimated lifetimes of more than 20,000 hours MTTF. The basis for the extended lifetime of these coolers is our unique flexure-bearing compressor with moving magnet technology. Inside the linear dual opposed piston compressor both moving pistons are fully supported at the back and front of the piston by optimised flexure bearings. With this flexure bearing suspension, side loads on the piston-seals are avoided. A proper alignment procedure ensures no contact between piston and cylinder during operation, resulting in absence of wear of the piston coating, which normally determines the lifetime of a cooler. The moving magnet technology, as applied in our flexure bearing compressor, has several major advantages over moving coil linear motors as applied in most conventional linear compressors. First of all the coils, known to be a possible source for gas contamination, can be placed outside the hermetically sealed compressor housing containing the working gas. Avoiding any synthetic materials inside the cooler reduces the risk of gas contamination during the life of the cooler. The fact that the coils can be placed outside the hermetically sealed compressor also means that no glass feed-throughs are required. In this way, risks of glass feed-through leakage due to extreme temperature shocks or mechanical shocks are no longer present. Finally, the absence of moving coils in the compressor design also means that flying leads to supply power to the coils are no longer required. Several qualification tests have been performed on flexure bearing cryocoolers with different sizes of coldfingers resulting in technical specifications currently available at Signaal Usfa on all presented cooler types in the above mentioned range. A flexure-bearing cooler for applications requiring over 6 Watts cooling power at 80K is currently under development as well. Tests performed on a first prototype of this cooler have been successful. A cooling performance of more than 8W @80K for 23°C ambient temperature with 150 Wac input power has been measured.
Original publication: Proc. SPIE 4130
M. Meijers, A.A.J. Benschop and J.C. Mullié
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