Vibration free 4.5K sorption cooler

At the University of Twente, a breadboard 4.5 K sorption cooler was developed under ESA contract. It has no moving parts and, therefore, is essentially vibration-free. Moreover, it has the potential of a very long life. This cooler is a favorite option for missions such as ESA's Darwin mission, which is a future space interferometer consisting of a few free flying telescopes and a central beam combiner. Because of the optics involved, hardly any vibration can be tolerated. The cooler consists of a hydrogen stage cooling from 80 K to 14.5 K and a helium stage establishing 10 mW at 4.5 K. Both stages use micro-porous activated carbon as the adsorption material. The two cooler stages need 8 W of input power and are heat sunk at two passive radiators at temperatures of about 50 and 80 K. We developed and built a demonstrator of the helium stage. In the paper, the design, realization and tests of this demonstrator cooler are reviewed.