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arXiv · 1407.8335

Dry demagnetization cryostat for sub-millikelvin helium experiments: refrigeration and thermometry

I. Todoshchenko·J. -P. Kaikkonen·R. Blaauwgeers·P. J. Hakonen·A. Savin
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Abstract

We demonstrate successful "dry" refrigeration of quantum fluids down to $T=0.16$\,mK by using copper nuclear demagnetization stage that is pre-cooled by a pulse-tube-based dilution refrigerator. This type of refrigeration delivers a flexible and simple sub-mK solution to a variety of needs including experiments with superfluid $^3$He. Our central design principle was to eliminate relative vibrations between the high-field magnet and the nuclear refrigeration stage, which resulted in the minimum heat leak of $Q=4.4$\,nW obtained in field of 35\,mT. For thermometry, we employed a quartz tuning fork immersed into liquid $^3$He. We show that the fork oscillator can be considered as self-calibrating in superfluid $^3$He at the crossover point from hydrodynamic into ballistic quasiparticle regime.

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I. Todoshchenko, J. -P. Kaikkonen, R. Blaauwgeers, P. J. Hakonen, A. Savin. 2014-07-31. Dry demagnetization cryostat for sub-millikelvin helium experiments: refrigeration and thermometry. https://doi.org/10.1063/1.4891619

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