Two-stage super(3)He- super(4)He fridge for bolometric photometry

摘要

We describe the design, construction and performance of a double stage super(3)He- super(4)He refrigerator, built to cool down a multiband bolometric photometer at the MITO telescope. The fridge was optimized to work without external pumps, with the main cryostat providing a 4.2 K thermostat at sea level and a 4.0 K one at high mountain pressure conditions. The measured ultimate temperature of the fridge is 290 mK, with a hold time of 81 h. The external heat input on the cold flange is approximately 35 mu W, with the main bath at 4.0 K. The recycle time is 8 h with a heat input on the thermostat during recycling of approximately 6800 J. The cryostat can operate without any relevant changes to performance tilted down to 50 degree from the vertical position, as needed at the telescope focal plane.