Cryogen-Free Dilution Refrigerator Precooled by a Pulse-Tube Refrigerator with Non-Magnetic Regenerator

摘要

We present a cryogen-free 3He/4He dilution refrigerator (DR) which was precooled by a 10 K pulse tube refrigerator (PTR), CRYOMECH, model PT805. The PT805 has no rare-earth materials in the second stage regenerator which are very expensive and normally generate oscillating magnetic fields with amplitudes of ~20 nT at low temperatures. The challenge for our application was that the base temperature of our PTR was 5.5 K which is ~3 K higher than that of a standard 4 K-PTR (~2.5 K). After being precooled by the PTR, the 3He of the DR was further precooled and liquefied in a Joule-Thomson stage before it entered the dilution unit. The 3He throughput which determines the cooling capacity of the dilution unit was up to 250 μmol/s, and its base temperature was 5.4 mK. "Dry" DRs are very reliable and user-friendly to operate, cool downs are automatic, and experimental conditions remain unchanged during sustained continuous operation of the cryostat. In our DR there are no magnetic field distortions because of the non-magnetic regenerators of the PTR.