Adsorption pumping for obtaining ULT in 3He cryostats and 3He-4He dilution refrigerators

Novel designs of He-3 Cryostats and Dilution Refrigerators (DR), based on adsorption pumping of He-3 gas, are described for obtaining temperatures well below 0.3K. Using a new technique, extremely low temperature 3He refrigerators have been tested to T<235mK. The same technique enables the manufacture of a He-3 system, that can move up to a distance of about 0.5m. compact travelling The ability to travel from warm to cold zones; can be important for sample preparation in ultra high vacuum and to carry out STM measurements. Also described is a continuously operating sorption pumped DR, that can be installed inside a transport dewar with a neck diameter of only 51mm. The cooling time of the mixing chamber from 4.2K down to 50mK is similar to 2 hours. Removal of the insert from the cryostat requires approximately 30 minutes. The cooling power of the system is 40 microwatts at 100mK With two miniature silver heat exchangers the mixing chamber temperature cools to a continuous temperature of 15mK. A key distinguishing feature of this DR is the absence of a traditional gas handling system and sealed helium-3 rotary pump. This makes it easy for transportation and quick commissioning at a new site within a few hours.