Nobeyama Radio Observatory Report: Number 585

Abstract

A cryogenic system was developed, which houses 3 cartridge-type superconductor-insulator-superconductor receivers for millimeter and submillimeter wavelengths. Since it was designed as a prototype receiver of the Atacama Large Millimeter/submillimeter Array (ALMA), high stability, accurate alignment, and easy handling were required. To meet these requirements, the cryogenic system included the following technologies: 1) a thermal link without screws for receiver cartridges; 2) a central support structure to reduce vacuum and gravitational deformation; 3) bellows structures to reduce mechanical vibration of the cryocooler; and 4) a 3-stage Gifford McMahon (GM) cryocooler with a He pot (temperature stabilizer) to reduce the thermal ripple. The cryostat and receiver cartridges are composed of three stages. The temperatures on the 4 K, 12 K, and 100 K stages of the cartridge are 3.5 K, 13.4 K, and 78.3 K, respectively. The thermal conductances of the thermal links showed high performances of 1.7 W K(sup -1) at the 4 K stage, 5.6 W K(sup -1) at the 12 K stage, and 3.3 W K(sup -1) at the 100 K stage. The mechanical vibration on the 4 K stage of the cartridge was reduced to one-tenth, as small as approximately 2 micrometer peak-to-peak, compared to that on the 4 K coldhead of the cryocooler, approximately 20 micrometer peak-to-peak. The temperature ripple on the cartridge was reduced to as small as 2 mK peak-to-peak, which corresponds to one-seventh of the ripple on the 4 K coldhead with a He pot.