Dilution refrigerator with no liquid helium supply

We have designed and constructed a 3He-4He dilution refrigerator which does not require the use of liquid nitrogen or liquid helium dewars. The 3He-4He mixture, compressed to 105Pa, is first precooled to near 12K in a closed-cycle regenerative refrigerator (AIR PRODUCTS DE202) then cooled to near 4.2K by a separate 4He compression stage. The mixture then undergoes a series of expansions and coolings in a heat exchanger which takes the temperature to below 0.1K. The limiting steady state temperature is 70mK and the total cool down time is 20 hours. This system is a test prototype which has enabled a number of problems to be analysed. It is equipped with a very basic dilution stage operating at 70mK. The chief aim was to verify the good working order of the ensemble. A new apparatus is being constructed which will reach near 20mK in less than 12 hours