Design and performance of a portable He-3 cryogenic system for ground based instrumentation

The availability of compact cryogenic refrigerators is of importance for th e development of both ground and space-borne instrumentation based on cryog enic detectors. In this article we report on the design and performance of a complete ground based cryogenic system consisting of a He-3 cryosorption refrigerator, and designed to cool a 6x6 element detector array of tantalum based superconducting tunnel junctions (STJs). The refrigerator provides a n operating temperature of 330 mK, with a hold time in excess of 7 h. The s ystem is designed to be portable, to provide a very stable focal plane, and to minimize the use of magnetic materials. Such a system has been used to host the focal plane assembly of S-Cam, the first optical camera for ground based astronomy utilizing an array of STJs, recently installed at the Will iam Herschel Telescope, in La Palma. (C) 1999 American Institute of Physics . [S0034-6748(99)03710-7].