Low-cost, compact dilution refrigerator: operation from 200 to 20 mK

We have developed a self-contained (portable) 3He-4He dilution refrigerator which has been operated below 0.020 K without the use of external pumps or gas handling system. Using charcoal pumps for all pumping, the system requires, besides the usual liquid helium and nitrogen baths, only modest electronics for heaters and thermometers. This device has the advantages of low cost and simple operation and does not require extensive maintenance or operator expertise. The refrigerator can operate below 0.020 K for more than 10 hours before the charcoal pumps need to be recycled