Refrigeration for Photomultipliers

A closed-cycle mechanical refrigeration system has been adapted to cool photomultipliers automatically. Temperature is adjustable between +50 degrees and -55 degrees C and is stable to within +/-0.30 degrees C. An important feature of the design is the flexible connection to the cold box which allows extensive freedom of motion; this freedom is particularly important in astronomy where the cold box is mounted on the end of a telescope. Liquid Freon refrigerants have been used to cool photomultipliers for rocket flights. A brief description of two methods is given.