6) Sub-mK refrigerators

Nuclear cooling is most often performed using adiabatic nuclear demagnetization of copper. I have employed this method altogether in four different refrigerators:

1) Rotating cryostat for investigating superfluid 3He down to 0.5
mK (constructed in the 80'ies and still operational). This operation was accomplished by floating the whole cryostat with measuring electronics on top of an air bearing. Extra care in balancing was exercized in order to avoid vibrations that could heat up the sample attached to the nuclear stage.

2) Microkelvin cooling of metals for quadrupolar ordering studies at Cornell University in the early 90'ies.

3) Double stage nuclear cooling for sub-nK investigations. In this work, the investigated sample is the second stage and its structure with well optimized thermal paths is of vital importance for the success of the cooling.

4) Recently, we have constructed a dry nuclear demagnetization cryostat that is able to reach temperatures down to 0.2 mK. The optimization work of the dry cooling system has benefitted from our collaboration with BlueFors Cryogenics Ltd. in Helsinki (Finland). In fact, the first dry dilution refrigerator of BlueFors was constructed in conjunction with my EU-project CARDEQ that was carried out between 2006 and 2009.
- Rotating cryostat for sub-mK temperatures [Cryogenics 23, 243 (1983)] 
- Nuclear demagnetization for muKelvin regime [Physica B 165, 793 (1990)] 
- Cascade nuclear cooling for pK temperatures  [JLTP 98, 449 (1995)]
- Dry nuclear demagnetization cryostat [RSI 85, 085106 (2014)] 

- Collaboration with BlueFors Ltd. [starting with the prototype in 2006]