Design and Performance of Cryogenic Enclosures for Long Duration Testing of Large Samples

We have designed a large helium dewar as part of an experiment to investigate gravitational radiation. Two such dewars have been constructed. Our use requires a nonmagnetic dewar to cool an aluminium antenna of approximately 5000 kg to below helium temperatures and to keep the antenna in a stable low temperature environment for extended time. This requires a low temperature volume of 1.5 m inner diameter and 3.1 m length and a cooling system capable of efficiently removing the room temperature enthalpy of 8.5 × 108 J. Our solution to this problem is of wider application than simply gravity wave detection so we have discussed the design philosophy in some detail. As constructed, the apparatus uses less than 1 l of helium per hour when cold.