1 K cryostat with sub-millikelvin stability based on a pulse-tube cryocooler

Abstract

A cryogenic system has been designed and tested that reaches a temperature below 1.1 K, with an rms temperature stability of 25 µK. In this system a commercial pulse-tube cryocooler is used to liquify helium gas supplied from an external source. This liquid helium enters a 1 K pot through a large-impedance capillary tube, similar to a conventional 1 K system operated from a liquid helium bath. Unlike a conventional system, however, the molar flow rate of the system can be varied by changing the pressure of the incoming helium. This allows for a trade-off between helium usage and cooling power, which has a maximum value of 27 mW. The measured cooling power and fraction of helium exiting the capillary as liquid agree well with predictions based on an isenthalpic model of helium flow through the capillary. The system is simple to use and inexpensive to operate: The system can be cooled to base temperature in about 3 hours and, with a flow rate giving a cooling power of 13 mW, the helium cost is around $6 per day.

Design and development of a cryogenic J-T valve for a 2 K cryostat with a single cryocooler

“…They measured the cooling capacity of the system at different 1 K station temperatures, achieving 1.62 K with no load. In another system designed by Demann et al [8], a capillary with large flow resistance was utilized to create sharp pressure drop for liquid helium. Li et al [9] proposed a superfluid helium production system using a G-M cryocooler and a J-T valve to reduce the pressure of liquid helium.…”

Experimental Observation of a Self-Heating Effect of Helium-4 Superflow

“…The experiment is carried out on a two-stage Gifford-McMahon refrigerator with a cooling power of 1 W at 4.2 K and a base temperature of 2.4 K. In order to reach the superfluid temperature regime, a liquid 4 He cryostat is constructed by following largely the design given in Ref. [18]. A stainless steel capillary, with an inner diameter (i.d.)…”