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Dry Dilution Refrigerator for Experiments on Quantum Effects in the Microwave Regime

At the Walther-Meißner-Institut (WMI), a new cryogen-free 3He/4He dilution refrigerator (DR) has been completed; the cryostat will be employed to cool experiments on superconducting quantum circuits for quantum information technology and quantum simulations. All major components have been made at the WMI. The DR offers lots of space at the various stages of the apparatus for microwave components and cables. E. g., the usable space at the mixing chamber has a height of more than 60 cm and a diameter of 30 cm (mixing chamber mounting plate). To cool cables and cold amplifiers, the DR is equipped with a separate 4He-1K-loop which offers a cooling power of up to 100 mW near 1K. The refrigeration power of the still is 18 mW at 0.9 K; the diameter of its mounting plate is 35 cm. The cryostat rests in an aluminum trestle on air springs to attenuate building vibrations. It is precooled by a Cryomech PT410-RM pulse tube cryocooler (PTC) which is mechanically decoupled from the vacuum can of the cryostat by a bellows assembly. The two stages of the PTC are thermally connected to the DR via copper ropes. There are no nitrogen cooled traps with this DR to purify the gas streams of the 3He and 4He loops; instead, charcoal traps are mounted inside the DR at the first stage of the PTC. The dilution unit has three heat exchangers; its base temperature is 11 mK and its cooling power is 300 μW at 100 mK.