Abstract
A cryogenic system has been designed and tested that reaches a temperature below 1.1K, with an rms temperature stability of 25μK. In this system a commercial pulse-tube cryocooler is used to liquify helium gas supplied from an external source. This liquid helium enters a 1K pot through a large-impedance capillary tube, similar to a conventional 1K 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 27mW. 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 3h and, with a flow rate giving a cooling power of 13mW, the helium cost is around $6 per day.
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