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

The availability of compact cryogenic refrigerators is of importance for the development of both ground and space-borne instrumentation based on cryogenic detectors. In this article we report on the design and performance of a complete ground based cryogenic system consisting of a ${}^3\mathrm{He}$ cryosorption refrigerator, and designed to cool a 6×6 element detector array of tantalum based superconducting tunnel junctions (STJs). The refrigerator provides an operating temperature of 330 mK, with a hold time in excess of 7 h. The system 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 William Herschel Telescope, in La Palma.