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We describe a 4 He cryostat suitable for cooling a large (about 50 l in volume) multiband bolometric photometer for mm-waves. The cryostat features two large optical windows and a hold time longer than 2 weeks. The long hold time has been obtained using a 20 K vapour cooled shield for the liquid helium tank and superinsulation for the nitrogen tank. The tanks are supported by kevlar cords. The cryostat has been optimized for operation on long duration stratospheric balloon flights, and has been tested successfully at ground level and on two short balloon flights.

We describe the design, development and test of a self-contained 3 He fridge, aimed to cool at ≲0.3 K a bolometric detection system with a hold time of two weeks. The system is robust and suitable for operation on a long-duration stratospheric balloon payload. A physical model of the fridge has been developed, which describes the measured hold time, limiting temperature and load curve of the fridge. The system has been flight tested successfully during two balloon flights of the BOOMERanG payload in summer 1997.

A cryostat including a 3 He refrigerator has been designed, built, coupled to a multiband far infrared (FIR) photometer and successfully operated on a balloon flight. Here the cryostat, which is able to cool three bolometers to 0.3 K and one to 1.5 K, is described. The total holding time of the cryostat exceeds 5 days, being limited by exhaustion of the main 4 He and N 2 baths. The autonomy of the 3 He cryostat is more than 50 h, and the recycling time is ≈3 h. The performance of the system in the ARGO 1993 flight is also reported.

The connection of an aluminium container to thin walled stainless steel tubes for use in a cryostat is described. The resulting joint showed superleak tightness.