Progress on a microgravity dilution refrigerator

We have developed a shallow, single-cycle, helium dilution refrigerator that contains rather coarse metal sponge to study the ability to control the location of the liquid helium for microgravity applications. We have tested the refrigerator on the ground while tilting to put the mixing chamber either somewhat above or somewhat below the still. We calculated that the system could be tilted between 5 degrees and 10 degrees in either direction without interrupting the cooling. The initial test of this refrigerator gave cooling to below 0.060 K and operation for tilts of +/-16 degrees. The insights gained from this refrigerator allow the design of a continuously operating version. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.