Stirling-type pulse-tube refrigerators for 4 K (ETF.6595)

Pulse-tube refrigeration is based on a new concept that offers great advantages for further simplification of cooling technologies. In this project we would like to develop pulse-tube refrigerators of the Stirling type for the important temperature region of 4 kelvin. We intend to use a type of compressor, the so-called flexure-bearing compressor, which is new for 4 kelvin pulse-tube refrigerators. These compressors are driven by a linear motor and have a high efficiency. Furthermore purification of the gas is not necessary, the lifetime is practically infinite, and the reliability is high. This is all in contrast to the usual type of compressors.
The system that we propose will operate at frequencies which are an order of magnitude higher and pressure amplitudes which are an order of magnitude lower than usual, so our system will differ from existing machines in many ways. The interplay between the various system parameters in pulse tube refrigerators driven by linear compressors and operating with a nonideal gas, is very complicated. This requires a strong effort in the modelling of the system. Therefore the Low-Temperature group and the Scientific Computing group have joined forces in a unique effort to tackle this problem.

Reliable, efficient, and easy-to-handle cryocoolers for the 4 kelvin temperature region are of great practical importance, e.g. for the cooling of superconducting-magnet systems such as in hospitals: SQUID's for magneto cardiograms and encephalograms and in MRI. In semiconductor industry cryocoolers are used for cryopumping. In this project we will also try to realize coolers which require input powers of only a few hundred watt. These coolers are candidates for active cooling of satellites. The new coolers can acquire an important share of the market. In addition the possibilities of low-temperature technologies in general will be extended.