A He-3 gas heat switch for the 0.5-2 K temperature range

We have constructed a prototype heat switch for use in a cyclic demagnetiza tion apparatus. The desired operating range of the switch is from 0.5 to 1. 8 K. The measured conductivity of the switch is 50 mu W/K at 1.5 K when 'of f' and 8 mW/K at 0.5 K when 'on'. The switching is carried out by He-3 gas which is admitted and extracted from the device by a miniature charcoal ads orption pump which is controlled by electrical heat and a weak thermal link to a pumped He-4 bath. In this paper we discuss details of construction an d the performance as a function of temperature, and consider the switching time between on and off states. (C) 2000 Elsevier Science B.V. All rights r eserved.