Neutron imaging of an operational dilution refrigerator

C R Lawson,S J Horney,W Kockelmann,A T Jones,O Kirichek

doi:10.1038/s41598-022-05025-0

C R Lawson, S J Horney + Show 3 more

Open Access

https://doi.org/10.1038/s41598-022-05025-0

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Journal: Scientific Reports	Publication Date: Jan 21, 2022
Citations: 6	License type: open-access

Affiliation: Rutherford Appleton Laboratory

Abstract

The invention of the 3He/4He dilution refrigerator opened a new chapter in experimental ultra-low temperature physics. Dilution refrigerators became essential for providing ultra-low temperature environments for nuclear demagnetisation experiments, superconducting-qubit quantum processors and highly sensitive bolometers used in fundamental physics experiments. Development of dilution refrigeration technology requires thorough understanding of the quantum mechanical processes that take place in liquid helium at ultra-low temperatures. For decades the quantum fluids research community provided valuable information to engineers and designers involved in the development of advanced dilution refrigerators. However, the lack of methods that allow the measurement of physical parameters of liquid helium during the operation of a dilution refrigerator was hindering development of the technology. Here we show direct imaging of an operational dilution refrigerator using neutron radiography. This allows direct observation of the dilution process in 3He/4He mixtures and opens an opportunity for direct measurement of the 3He concentration. We observe the refrigerator behaviour in different regimes, such as continuous circulation and single shot, and show that our method allows investigation of various failure modes. Our results demonstrate that neutron imaging applied to the study of dilution refrigeration processes can provide essential information for developers of ultra-low temperature systems. We expect that neutron imaging will become instrumental in the research and development of advanced dilution refrigerators.

Highlights

The invention of the 3He/4He dilution refrigerator opened a new chapter in experimental ultra-low temperature physics
High power dilution refrigerator (DR) can be found in applications such as: sub-millikelvin nuclear demagnetisation experiments[9], cooling of superconducting-qubit quantum processors[12,13,14] and fundamental physics experiments that require ultra-low temperatures for highly sensitive bolometers like the cryogenic underground observatory for rare events (CUORE)[15], or extremely low noise displacement sensors used in the MiniGRAIL resonant mass antenna for detection of gravitational waves[16,17]
We study the DR’s behaviour when operated in different modes, including initial helium condensation, phase separation of the 3He/4He mixture, continuous circulation, and the single shot regime

Summary

Introduction

The invention of the 3He/4He dilution refrigerator opened a new chapter in experimental ultra-low temperature physics. The dilution refrigerator (DR) is quite simple in construction, easy to operate, and can work in high magnetic fields (as is often required in ultra-low temperature experiments)[2] It is used in sub-millikelvin systems as a base from which lower temperatures can be reached. High power DRs can be found in applications such as: sub-millikelvin nuclear demagnetisation experiments[9], cooling of superconducting-qubit quantum processors[12,13,14] and fundamental physics experiments that require ultra-low temperatures for highly sensitive bolometers like the cryogenic underground observatory for rare events (CUORE)[15], or extremely low noise displacement sensors used in the MiniGRAIL resonant mass antenna for detection of gravitational waves[16,17]

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