THE COMPLEX FOR PHYSICAL STUDIES AT ULTRALOW TEMPERATURES

The complex developed at Department N 12 (Quantum Liquids and Crystals) includes four refrigerators producing ultralow temperatures:

- the nuclear demagnetization refrigerator;
- the dilution refrigerator with a hybrid circulation system;
- the dilution refrigerator with a condensation-adsorption pumping system;
- the dilution refrigerator with an outer circulation system.

All the refrigerators and the related thermometry systems were developed and produced at ILTPE NAS of Ukraine.
In 2001, the Complex for physical studies at ultralow temperatures was given the status “National Property of Ukraine” (Resolution of the Cabinet of Ministers of Ukraine N 1709 of 19.12.2001).
The Complex is available for performing joint experiments at temperatures below 0.3 K. ILTPE NAS of Ukraine welcomes offers from the scientists of Ukraine and other countries and is ready to consider the corresponding physical problems.

Nuclear demagnetization refrigerator

(A.A.Golub, V.A.Goncharov, V.R.Litvinov, V.A.Mikheev, E.Ya.Rudavskii, Yu.A.Tokar’, A.M.Usenko, V.A.Shvarts, “The nuclear demagnetization refrigerator with an automated system of data control, acquisition and processing”, FNT, 21, 974, 1995)

Placed in operation in 1985. Incorporates the following basic elements: - a dilution cryostat with a degree chamber; - an Al thermal valve; - a Cu nuclear demagnetization stage; - a magnetic system; - a thermometry system; - an experimental device for physical studies; - an automated system of data control, acquisition,, and processing. The nuclear stage is made as a bundle of 4000 close-packed glass-fibre isolated Cu wires 0,5 mm in dia. The mean-square magnetic field of 7 T accommodates 23 moles of Cu. Minimum temperature in the coolant plate – 0,7 mK. Residual heat gain – 0,25 nW/coolant mole. The refrigerator is used to investigate low-temperature nuclear magnetism and phase separation in solid 3He-4He solutions.

Outer circulation dilution refrigerator

(B.N.Esel’son, V.A.Goncharov, E.Ya.Rudavskii, V.K.Chagovets, S.I.Tarapov, “The simple continuous-refrigeration dilution cryostat for production of ultralow temperatures”, Collection: “Design and Engineering of Cryogenic Systems”, Kiev, Naukova Dumka, p. 18, 1981).

Placed in operation in 1980. Incorporates the following basic elements: - a dilution cryostat with a degree chamber; - a superfluid 4He thermal valve; - a two-chamber system for changing “in situ” superfluid helium solution concentration; - a thermometry system; - a system for operation at high pressure; - an automated data acquisition and processing system; - an ultrasound spectrometer for studying acoustic properties. Refrigerating capacity - 100 µw at 100 mK. Minimum temperature - 12 mK. The refrigerator is used to study superfluid helium isotope solutions.

Condensation pumping dilution refrigerator

(V.I.Sobolev, L.A.Pogorelov, V.N.Repin, V.E.Sivokon’, Author’s Certificate N 1290817, 1985; V.E.Sivokon’, V.V.Dotsenko, L.A.Pogorelov, V.I.Sobolev, FNT, 19, 444-449, 1993)

Vapor pumping from the vaporizer and 3He condensation and recycling to the dilution chamber are provided by a cooling plate (condensation pump). The condensation pump is cooled by two independent adsorption refrigerators with 3He vapor pumping. Specifications: Low-temperature 3He circulation cycle. Maximum 3He circulation rate - 200 µmole/s. Minimum resultant temperature - 10 mK. Operating time - unlimited. Liquid helium demand ~ 10 l/day. Thermometers: crystallization (primary), carbon (secondary). Merits: compactness; no mechanical 3He pumping systems; no throttles; no mechanical switching elements in the low-temperature section. The refrigerator is now used in experimental studies of two-dimensional electron systems localized over the superfluid helium surface.

Dilution refrigerator with a hybrid circulation system

(A.S.Rybalko, V.A.Mikheev, V.I.Kolesnik, B.I.Beloborod’ko, FNT, 19, 720, 1993; A.N.Gan’shin, V.N.Grigor’ev, V.A.Maidanov, G.A.Mikhailov, V.A.Mikheev, N.F.Omelaenko, A.A.Penzev, V.N.Repin, E.Ya.Rudavskii, A.S.Rybalko, Yu.A.Tokar’, V.A.Shilin, FNT, 27, N 7, 799-810, 2001).

The complex incorporates a dilution refrigerator with a hybrid 3He circulation system, a vibration protection system and an automated system of control, acquisition, and processing the experimental data. It permits the realization of different experimental conditions that can be used in a wide range of physical investigations at ultralow temperatures. The circulation of 3He in a dilution refrigerator can be realized both a mechanical pump, and two alternately operating adsorption pumps, located at the liquid helium temperature. Refrigerator has eight discrete silver heat exchangers which were made at the Department of Physics of the Lancaster University (UK). With their use the minimum temperature is about 5 mK at the cryogenic pumping regime. The refrigerator is rather economical in the temperature range over 20 mK with using a mechanical pump. At circulating 10-4 mol / sec. consumption of liquid helium is about 7 liters per day. The refrigerator is now used to study kinetic processes in quantum crystals.