title: Dry demagnetization cryostat for sub-millikelvin helium experiments: refrigeration and thermometry.
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.
authors.affiliation: Low Temperature Laboratory, O.V. Lounasmaa Laboratory, Aalto University, FI-00076 AALTO, Finland.
authors.forename: I
authors.initials: I
authors.lastname: Todoshchenko
authors.affiliation: Low Temperature Laboratory, O.V. Lounasmaa Laboratory, Aalto University, FI-00076 AALTO, Finland.
authors.forename: J-P
authors.initials: JP
authors.lastname: Kaikkonen
authors.affiliation: BlueFors Cryogenics Ltd, Arinatie 10, 00370 Helsinki, Finland.
authors.forename: R
authors.initials: R
authors.lastname: Blaauwgeers
authors.affiliation: Low Temperature Laboratory, O.V. Lounasmaa Laboratory, Aalto University, FI-00076 AALTO, Finland.
authors.forename: P J
authors.initials: PJ
authors.lastname: Hakonen
authors.affiliation: Low Temperature Laboratory, O.V. Lounasmaa Laboratory, Aalto University, FI-00076 AALTO, Finland.
authors.forename: A
authors.initials: A
authors.lastname: Savin