A 3He pulse tube cooler operating down to 1.3 K

Regenerative cryocoolers that employ He-4 as working fluid can only reach a lowest temperature of about 2 K. This limitation can be overcome by the use of He-3 as working fluid. Here we report on the performance of a two-stage pulse tube cooler that consists of two parallel stages with independent gas circuits. The pressure oscillation in each stage is generated by means of a separate compressor in combination with a rotary valve. With He-4 in both stages, the minimum no-load temperature of the 2nd stage was 2.23 K, and cooling powers of 50 W at 53 K and 380 mW at 4.2 K were simultaneously available at electrical input powers of 4.54 and 1.45 kW to the 1st and 2nd stage, respectively. Using He-3 as working fluid in the 2nd stage, a minimum stationary temperature of 1.27 K has been achieved, which is, up to now, the lowest temperature obtained by regenerative cryocoolers. At an electrical input power of 1.3 kW, the 2nd stage provides a cooling power of 42 mW at 2.0 K and 518 mW at 4.2 K. With He-3, at the same operating condition, the cooling power at 4.2 K was found to be larger than with He-4. (C) 2004 Elsevier Ltd. All rights reserved.