Visual observations of the counterflow of the two liquid phases in the 4He- cycling 3He-4He dilution refrigerator

doi:10.1016/0378-4363(81)90184-4

Physica B+C

Volume 104, Issue 3, April 1981, Pages 371-377

https://doi.org/10.1016/0378-4363(81)90184-4 Get rights and content

Abstract

Droplets of diluted ³He are observed to fall from the upper inlet superleak of a glass, ⁴He-cycling dilution refrigerator. Their diameter and velocity are measured. Droplets of concentrated ³He are observed to ascend from the lower outlet superleak to the phase separation surface.

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Cited by (7)

Development of dilution refrigerators—A review
2022, Cryogenics
Citation Excerpt :
The work in Leiden was continued e.g. by Pennings et al. [39] who reached a minimum temperature of 8.3 mK. Brandt et al. [40] and Satoh et al. [35] made visual observations in glass versions showing that the diluted phase falls through the mixing chamber and tube in the form of droplets and not in a layer attached to the tube wall. Unlike 3He circulating DRs, the 4He-circulating DR can work at higher pressures.
Subkelvin refrigeration refers to the refrigeration below 1 K and is widely used in the fields of condensed-matter physics, quantum computing, and astronomical observation. Among the three conventional technologies, adsorption refrigeration, adiabatic demagnetization refrigeration, and dilution refrigeration, dilution refrigeration is the most popular with the advantages of lowest temperature down to several mK, continuous cooling, and relatively large cooling power. The method was first proposed in the 1950s and the first complete system was built in 1960s, followed by a successful commercialization. Since then, with the ever-increasing demands of low temperature physics research and due to its apparent advantages, it quickly becomes the most important technique to reach the millikelvin temperature range. The lowest temperature achievable nowadays by a conventional dilution refrigeration is 1.75 mK, and largest cooling power at 100 mK is 2 mW. In addition to the commercialization of dilution refrigeration, lots of other research, tailored to special applications, have also been done or going on, which include cold-cycle dilution refrigeration without room-temperature pumping system and zero-g dilution refrigeration for space applications, etc. The cold-cycle dilution refrigerator on the ground, driven by two adsorption pumps, can reach a minimum temperature of 8 mK and the corresponding cooling power was 60 μW at 110 mK. For zero-g space applications, an open-cycle dilution refrigerator was successfully operated in space for 2.5 years with a cooling power of 0.1 μW at 92.6 mK. Closed-cycle dilution refrigerators for zero-g environment are still under investigation. With a brief introduction on the thermodynamics of dilution refrigeration, this paper reviews the development of the conventional ³He-circulating dilution refrigerator, the ⁴He-circulating dilution refrigerator, the cold-cycle dilution refrigerator on the ground, and dilution refrigerators for space. Key issues related to non-conventional dilution refrigeration are pointed out with some discussions on their prospects.
Thermal activation in the quantum regime and macroscopic tunnelling in the thermal regime in a metabistable system consisting of a superconducting ring interrupted by a weak junction. Part III: Macroscopic quantum tunnelling in the thermal regime
1989, Physica B: Physics of Condensed Matter
When an external magnetic flux close to half a flux quantum is applied to a superconducting ring containing a weak superconducting junction, a SQUID, there can exist two metastable magnetic flux states by a potential energy barrier. If the junction has a sufficiently small capacitance, at very low temperatures intrinsic stochastic magnetic flux transitions due to macroscopic quantum tunnelling from one metastable flux state into another and vice versa are observed. Experiments are described showing macroscopic quantum tunnelling effects in an evaporated Nb device performed in a glass dilution refrigerator. A statistical analysis of the sampled data is made showing the measured distribution of the flux transitions in agreement with a pure stochastic transition process with a Poisson distribution. The measurements of the mean lifetimes are — in two ways — out of keeping with the theoretical predictions of the dissipative two-state Boson model. Firstly, although at fixed temperature the mean lifetime depends exponentially on the bias in the potential energy, a thermal quasi-Boltzmann distribution has not been found. Secondly, the mean lifetime of the two flux states in case of zero bias, symmetrical potential energy, does not clearly show the predicted T^1−2α dependence. It is conjectured that the system may not behave perfectly isothermal, because when a flux transition takes place between the metastable potential wells some energy will be dissipated possibly causing a temporary temperature rise due to self-heating. This effect is discussed in part II in relation with the data of the thermal activation experiments obtained with the same type of devices.
Visual observations and film recording of two-phase counterflow phenomena in a 4He-cycling dilution refrigerator
1986, Physica B+C
Measurements are presented of two-phase counterflow phenomena in a ⁴He-circulating dilution refrigerator. In order to make filmshots of these phenomena the measurements are performed in a refrigerator entirely made out of glass. Recording is done using an image intensifier assembly and a high speed camera. In a mixing chamber of the overflow type a lowest temperature of 120 mK is reached (at a very low flow rate). In this case most of the diluted phase is flowing along the wall of the counterflow capillary. After mounting a simple flow breaker on top of the counterflow capillary a flow of droplets appears and a lowest temperature of 30 mK is reached (at high flow rates). In this case the temperatures are consistent with estimations using a droplet flow theory and a measured heat leak of 4 μW. Also an experiment is described where a continuous flow of concentrated-phase droplets is created in the demixing chamber, ascending through the diluted phase in the counterflow capillary, until they disappear in a warmer region or reach the mixing chamber.
Dilution refrigerators
1982, Physica B+C
A survey is given of the various methods studied during the last decade to produce cooling by mixing the two liquid isotopes of helium in the so-called dilution refrigerator.
After a historical introduction, two main mixing processes are reviewed. Firstly, the ³He circulation through the mixing chamber where ³He is dissolved at the phase separation level into superfluid ⁴He, and secondly, a ⁴He circulation in which superfluid ⁴He is injected into the mixing chamber and falls as droplets containing dissolved ³He to a demixing chamber. Other investigated combinations are considered, such as: hybrid systems in which both circulations are put in series; double and triple mixing chambers in series; and especially the combination of the dilution refrigerator with the Pomeranchuk cooling making use of the negative slope of the melting curve of ³He during solidification under compression.
It seems that the exploration was very successful and almost completed.
STUDIES OF 4He-CIRCULATING DILUTION REFRIGERATOR.
1982, Proceedings of the International Cryogenic Engineering Conference
Investigations are reported on a dilution refrigerator through which superfluid ⁴He is circulated. This is known as the Leiden dilution refrigerator. It is found that the cooling behavior of the machine changes abruptly when the ⁴He-circulating rate exceeds a certain critical value. In the circulation rate region above this critical value a minimum temperature of 3.4 mK has been attained. This is the lowest temperature ever reached with the ⁴He -circulating dilution refrigerator. The temperature distribution along the counterflow tube also shows a drastic change at this critical circulation rate.
Distillation of nuclear polarization of 3He-4He mixtures in very high magnetic fields
1998, Journal of Low Temperature Physics

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References (17)

Cryogenics

Physica

Physica

Physica

Phys. Rev.

Phys. Rev.

Phys. Rev. Lett.

Cited by (7)

Development of dilution refrigerators—A review

Thermal activation in the quantum regime and macroscopic tunnelling in the thermal regime in a metabistable system consisting of a superconducting ring interrupted by a weak junction. Part III: Macroscopic quantum tunnelling in the thermal regime

Visual observations and film recording of two-phase counterflow phenomena in a <sup>4</sup>He-cycling dilution refrigerator

Dilution refrigerators

STUDIES OF <sup>4</sup>He-CIRCULATING DILUTION REFRIGERATOR.

Distillation of nuclear polarization of <sup>3</sup>He-<sup>4</sup>He mixtures in very high magnetic fields