A self-contained 3He refrigerator suitable for long duration balloon experiments

We describe the design, development and test of a self-contained He-3 fridge, aimed to cool at less than or similar to 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. (C) 1998 Elsevier Science Ltd. All rights reserved.