Sorption Cooler Research Articles

Design and development of a 4He sub-Kelvin sorption cooler

The sub-Kelvin sorption cooler (SKSC) has emerged as a reliable and vibration-free solution for space cryogenics, establishing itself as a highly competitive choice. This paper focuses on the development of a 4He SKSC prototype designed for precooling an adiabatic demagnetization refrigerator (ADR). Based on the sorption refrigeration mechanism, the relationship between the amount of working medium and cooling performance is analyzed. Subsequently, each component of the SKSC is designed and constructed, resulting in the successful creation of a 4He SKSC prototype. Experimental testing demonstrates its capability to achieve a minimum temperature of 773 mK and provide a cooling capacity of 100 μW at 803 mK.

Investigation on the adsorption characteristics of activated carbons in the sub-Kelvin 4He sorption cooler

The adsorption characteristics of the selected activated carbon have an important effect on the performance of the sub-Kelvin helium sorption cooler. In this paper, a test system for the adsorption amount of the carbons based on a G-M cooler was built, which has the advantages of being detachable and high gas seal performance. The adsorption isotherm of the three carbons (5.3 K-40 K, 0–0.6 MPa) for 4He were experimentally tested, and the data were fitted according to the Dubinin theory. In addition, the calculation methods of sorption cooler were summarized and a model of cooling power prediction was established. Based on the above theoretical model and experimental data, a carbon with high specific surface area and excellent adsorption properties was selected as filler, and a prototype of 4He sorption cooler was developed. The lowest temperature and holding time of the prototype are 923 mK and 8.47 h, respectively, in good agreement with the theoretical model. The model and the experimental method can provide reference for the design of sorption coolers at sub-Kelvin temperatures.

Development of the sorption-integrated adiabatic demagnetization refrigerator (ADR) without active heat switches

This study reports on the test results of a proof of concept sorption-integrated adiabatic demagnetization refrigerator (ADR) for sub-Kelvin cooling. The configuration of the cooler is primarily simplified by eliminating heat switches which require active control. The whole refrigerator apparatus is composed of the high temperature superconducting (HTS) magnet to magnetize the single crystal Gadolinium Gallium Garnet (GGG), and the 4He sorption cooler. Both the sorption cooler and the magnet are cooled by a 4 K two-stage Gifford-McMahon (G–M) cooler. The sorption cooler consists of a sorption pump filled with activated carbon of 13.9 g and a gravitiy-assisted-4He thermosiphon with volume of 5.0 cm3. The pressure inside the thermosiphon is controlled by changing the adsorption capacity of the sorption pump. The performance of the developed cooler is preliminarily evaluated by a single-shot test. The sorption cooler precools the 3 T-magnetized GGG from 4.40 K to 1.94 K by evaporating the liquid helium contained in the thermosiphon. When helium inside the thermosiphon is evacuated by the sorption pump, the magnetized GGG is thermally disconnected from the 4 K heat sink. Subsequently, the GGG is adiabatically demagnetized by discharging the HTS magnet and reaches temperature of 0.55 K. However, after demagnetization, the gas helium inside the cooling system is condensed by the GGG, consequently reducing its cooling capacity. Detailed experimental results are presented and discussed in the remainder of the paper.

Analysis and test of 4He gas-gap heat switch for a sub-Kelvin sorption cooler

Gas-gap heat switches (GGHSs) are significant components in sub-Kelvin sorption coolers (SKSCs). To develop an effective GGHS for SKSCs, a complete GGHS theoretical model is proposed by integrating the adsorption characteristics of activated carbon and the principle of GGHSs. This model establishes a relationship between the temperature of activated carbon and the corresponding thermal conductance of GGHSs. Based on this model, a 4He GGHS was designed, which consists of two cylindrical copper blocks separated by a 0.2 mm gas gap and a surface area of 9.896 cm2. The device was charged with 100 kPa of 4He at 297 K. Near the base temperature of the GM cryocooler of 3 K, an ON thermal resistance of 20 K/W and an OFF thermal resistance of 21,650 K/W with 1 mW applied to the hot end were obtained, achieving a switching ratio of 1082.5. The experimental results were analyzed and compared with the theoretical data, and proved to be in good agreement. Finally, the GGHS was integrated with a SKSC, achieving an ultimate temperature of 773 mK.

Study on the Coupling Characteristics of Sub-Kelvin Sorption Cooler and 4 K Stirling-type Pulse Tube Cryocooler with Small Cooling Capacity

Study on the Coupling Characteristics of Sub-Kelvin Sorption Cooler and 4 K Stirling-type Pulse Tube Cryocooler with Small Cooling Capacity

Experimental study on a helium-4 sorption cryocooler

The sorption cooler is one of the commonly used Sub-Kelvin temperature refrigeration technologies, used in space exploration and ground experiments to provide a low temperature below 1 K. In this paper, a sorption cooler using helium-4 as the working gas has been developed. At a heat sink temperature of 3 K, the lowest no-load temperature of the developed sorption cooler is 843 mK and the hold time below 1 K is 4 hours. The effects of different sorption pump temperatures and sorption pump cooling rates on the refrigeration performance were studied through experiments. The test results show that during the condensation process, when the temperature of the sorption pump is higher than 45 K, the pump temperature has little effect on the liquefaction efficiency, and speeding up the cooling rate of the sorption pump is conducive to obtaining a lower refrigeration temperature.

Analysis of pump tube and orifice for a 4He sub-Kelvin sorption cooler

The sub-Kelvin sorption cooler (SKSC) has become one of the most significant refrigerators in the space sub-Kelvin temperature range due to its high reliability, long life, no interference, and portability. The refrigeration temperature of SKSC is determined by the saturated vapor pressure above the liquid working medium in the evaporator, which is not only related to the adsorption capacity of the adsorption compressor but may also be restricted by the flow resistance of the pump tube and the orifice (for 4He SKSC). In addition, the pump tube and the orifice will also affect the heat leakage of superfluid 4He and the heat insulation between the adsorption compressor and the evaporator. Therefore, when designing a 4He SKSC, the pump tube and the orifice are critical. In this paper, the above issues are comprehensively considered, and the allowable size range of the pump tube and the orifice under a given design condition is discussed.

Helium gas-gap heat switch for Sub-Kelvin refrigeration system

The heat switch is an indispensable thermal control device in the low-temperature system. The helium gas-gap heat switch plays a key role in Sub-Kelvin sorption coolers and adiabatic demagnetization refrigerators, and its effective switching between thermal conducting (ON state) and insulating (OFF state) is achieved by changing the pressure of the gas in the gap. In this paper, a4He gas-gap heat switch was designed. And the thermal characteristics at different cold block temperatures were experimentally tested, which provides a reference for the development of high-efficiency gas-gap heat switches.

Development of the integrated sorption cooler for an adiabatic demagnetization refrigerator (ADR)

The integrated refrigerator composed of sorption cooler and adiabatic demagnetization refrigerator (ADR) is proposed for sub-kelvin cooling without vibration. In this configuration, the demagnetization process of the ADR is supposed to start after the termination of the sorption cooling. The liquid helium-4 inside the thermosiphon of the sorption cooler should evaporate as quickly as possible. This paper presents the results of preliminary test of the sorption cooling process. The developed sorption cooler primarily consists of the sorption pump filled with activated charcoal of 5.2 g and the helium thermosiphon. The adsorption capacity of the sorption pump is experimentally confirmed. Furthermore, the empirical correlation of adsorbate concentration which predicts the experimental results within 15% error in the temperature range of 5–70 K is proposed. The sorption pump is thermally connected to the 4.5 K heat sink through a pure tin strap, and regulates its temperature by the heater installed on it. Sorption cooling experiment is conducted under two experimental conditions. The experiment shows that the cooler can refrigerate the thermal capacitor to 2.8 K from 4.5 K heat sink, and provides the cooling capacity of 2.29 J. Moreover, it is confirmed that the pumping speed of the sorption pump is dominantly affected by its transient cool-down process. The new configuration of the thermosiphon condenser is proposed to enhance the evaporation characteristic of liquid helium while the pumping speed of the sorption pump is not changed. Since the new thermosiphon has smaller gas volume, liquid helium evaporates more quickly due to the rapid reduction of the vapor pressure inside the thermosiphon.

The Low-Temperature Adsorption Characteristics of Activated Carbon With 3He and 4He as Sorption Cooler Cryogens

Abstract As a commonly used sub-Kelvin refrigeration technology, helium sorption coolers play an important role in space and ground applications. The adsorption characteristics of the porous material inside the sorption cooler at low temperature have a crucial influence on its performance. At present, the analysis and calculation of sorption coolers are mainly based on helium 4 (4He) as the working gas, and there is a lack of systematic research on the low-temperature adsorption characteristics of helium-3 (3He) and its coupling effect characteristics of temperature, pressure, and mass distribution in different components. In this paper, a molecular model of activated carbon that is similar to the actual structure was constructed, and the adsorption isobars and isosteric heat of 3He and 4He at 0.8–5 K were comparatively studied based on the grand canonical Monte Carlo (GCMC) method. Besides, the influence of adsorption characteristics of 3He and 4He on the condensation efficiency, the mass distribution after condensation equilibrium, and the self-cooling loss of the sorption cooler were analyzed. The results show that for the 3He sorption cooler, the main factor affecting the condensation efficiency is the adsorbed helium in the sorption pump, while for the 4He sorption cooler, it is the adsorbed helium and the gas in the dead volume. For both 3He and 4He sorption coolers, the condensation efficiency increases as the sorption pump temperature increases or the heat sink temperature decreases, while the self-cooling loss decreases as the heat sink temperature decreases or the operating temperature increases.

Transition-Metal Nitroprussides Examined for Water Harvesting and Sorption Cooling.

Transition-metal pentacyanonitrosylferrates, commonly known as nitroprussides, have a long and documented history. Here, we synthesize cobalt and nickel nitroprussides (NPs) in order to probe their use as sorbents for water and fluorocarbon uptake for potential water harvesting and cooling applications. These NPs show stable and reversible equilibrium sorption isotherms at room temperature with peak uptake values of ∼40 wt % for H2O and ∼30 wt % for fluorocarbon R134a. At water harvesting conditions, working capacities of ∼19 wt % were obtained for NPs. At sorption cooling conditions, the working capacities favored nickel NP. Given the advantages of an easy, inexpensive, and scalable synthesis, this study demonstrates the potential for using nitroprussides for future water harvesting and adsorption cooling systems.

ATHENA X-IFU 300 K–50 mK cryochain test results

In the framework of the ESA X-ray mission ATHENA, scheduled for launch in 2030, an ESA Core Technology Program (CTP) was started in 2016 to build a flight like cryostat demonstrator in parallel with the phase A studies of the ATHENA/X-IFU instrument. As part of this CTP, called the Detector Cooling System (DCS), design, manufacturing and test of a cryostat including existing space coolers will be done. In addition to the validation of thermal performance, a Focal Plan Assembly (FPA) demonstrator using Transition Edge Sensors (TES) detector technology will be also integrated and its performance characterized versus the environment provided by the cryostat. This is a unique opportunity to validate many crucial issues of the cryogenic part of such a sensitive instrument.A dedicated activity within this CTP-DCS is the demonstration of the 300 K–50 mK cooling chain in a Ground System Equipment (GSE) cryostat. The studies are focused on the operation of the space coolers, which is made possible by the use of a ground cooler for cooling cryogenic shields and mechanical supports.This test program is also the opportunity to validate the operation of the cryochain with respect to various requirements, such as time constant and temperature stabilities. This would bring us valuable inputs to integrate the cryochain in DCS cryostat, X-IFU studies, SPICA and LiteBIRD missions.This paper is focused on the operation of the full 300 K–50 mK cryochain. In particular, the recycling options of the sub Kelvin cooler (sorption cooler + an ADR) versus the capability of 4 K and 2 K JT coolers are described. Results on the JT parameters validation campaign are summarized and eventually the results of the coupled test with sub Kelvin cooler will be presented and discussed.

Progress and Challenges of Sub-Kelvin Sorption Cooler and Its Prospects for Space Application

The helium sorption cooler plays an important role in both ground and space application because it does not require a magnetic field and is not dependent on gravity. At present, one research focus of sorption cooler is the development of multistage to overcome the disadvantages of the originally developed single-stage structure. The other focus is the development of continuous sorption cooler. Although the sorption cooler has been widely employed in astronomy and Earth atmospherics sciences, space mission and other fields, there are still lots of technologies that can be further improved, such as superfluid film suppression, the development of high on–off ratio gas-gap heat switch and rapidly responsive sorption pump. This paper reviews the principle, structure and performance parameters of the sorption cooler and its suitability to the space application. In addition, the technical challenges and the efforts that scholars are trying will also be introduced.

A Closed-Cycle Miniature Dilution Refrigerator for a Fast-Cooldown 100 mK Detector Wafer Test Cryostat

The forthcoming generation of cosmic microwave background polarization observatories is developing large format detector arrays which will operate at 100 mK. Given the volume of detector wafers that will be required, fast-cooldown 100 mK test cryostats are increasingly needed. A miniature dilution refrigerator (MDR) has been developed for this purpose and is reported. The MDR is precooled by a double-stage {^3}mathrm{He}–{^4}mathrm{He} Chase Research Cryogenics sorption refrigerator. The test cryostat based on this MDR will enable fast cooldown to 100 mK to support rapid feedback testing of detector wafers fabricated for the Simons Observatory. The MDR has been designed to provide a 100 mK stage to be retrocompatible with existing CRC10 sorption coolers, reducing the base temperature from 250 mK for the new generation of detectors. Other 250 mK cryostats can be retrofitted in the same way. This configuration will meet the cryogenic requirements for single-wafer testing, providing 5–10 upmu mathrm{W} of cooling power at 100 mk for over 8 h. The system operates in a closed cycle, thereby avoiding external gas connections and cold o-rings. No moving parts are required, with the system operated entirely by heaters.

Study of Uniformity and Reproducibility in the Performance of Helium-4 Sorption Coolers

The technology for low-power sub-Kelvin cooling is now established, and products are available that offer simple operation, with reliable and repeatable performance at relatively low cost. Self-contained, sealed sub-Kelvin modules can be added on or retro-fitted to low-power mechanical pre-coolers to extend their operating temperature downwards, from 4 K to the sub-Kelvin range. This technology offers fully automated operation requiring little or no cryogenics expertise and superior performance when compared to systems relying on pre-cooling with liquid cryogens. In this paper, we present data from testing 27 individual 4He modules of identical design and discuss some of the factors that determine reproducibility and reliability as well as overall performance.

Adsorption characteristics of helium on an activated carbon at 4–10 K and its prospective application in 4 K-class regenerative cryocoolers

Adsorption data of helium on activated carbon at low temperatures are essential for its use in sorption coolers, gas-gap heat switches and the regenerators of cryocoolers. Especially when an activated carbon is used as the regenerator material in a cryocooler, the high specific heat caused by the high amount of adsorbed helium is expected to solve the bottleneck problem that the conventional 4 K cryocooler regenerator material suffers. It also has the advantage of being non-magnetic. However, the amounts of helium adsorbed on on the activated carbon in the temperature range of 4–10 K are low. In this paper, the adsorption isotherms of helium on a coconut shell-based activated carbon in the pressure-temperature range (4–10 K, 0.5–3.5 MPa) were measured with a self-built adsorption apparatus, from which the isosteric heats of adsorption and the specific heats of the activated carbon with adsorbed helium were calculated. The helium flow resistance through the activated carbon was also measured to evaluate its feasibility in a cryocooler. Results indicate that the isotherms are type I and can be fitted by the Langmuir adsorption model. The isosteric heats of adsorption are around 279 J/mol and change little with the amount of adsorbed helium. The specific heats of the activated carbon with adsorbed helium depend on the adsorption temperature and pressure, and their average values at 4–10 K are the highest among the commonly used solid regenerator materials (lead, SS, Er3Ni and HoCu2) and gaseous helium under the pressures investigated, which are ascribed to the high amount of helium adsorbed and the high heat of adsorption of helium on the activated carbon. The helium flow resistance through a material is related to its size and surface roughness and the value through the activated carbon is moderate among the four commonly used solid regenerator materials. Activated carbon with adsorbed helium is suitable as a regenerator material of cryocoolers because of its high specific heat and moderate flow resistance.

A highly effective superfluid film breaker for high heat-lift 1 K sorption coolers

Closed-cycle single-shot 4He sorption coolers are used to provide cooling below 1 K in a number of mm-wave astronomical receivers. Helium, condensed by a 4 K stage, fills a coldhead; the vapour above the liquid is then driven off by a charcoal sorption pump to reduce the pressure, and hence temperature, of the liquid until thermal equilibrium is reached with the heat load. The coldhead then maintains this equilibrium until the liquid has completely evaporated, at which point the cooler is recycled.Below the λ-transition temperature, the mass transport of superfluid 4He via the thermomechanical effect from the cold head into the pumping tube(s) has been shown to significantly reduce the hold time and cooling power of these systems. We present modelling and experimental demonstration of a mechanically simple and highly effective superfluid film breaker developed for the 1 K sorption cooler currently being used in the QUBIC experiment.

Development of a sorption-cooled continuous miniature dilution refrigerator for 100 mK detector testing

As the forthcoming generation of Cosmic Microwave Background observatories move towards the use of large format detector arrays operating at ~100 mK, the need for test cryostats capable of operating in this temperature regime is becoming more pronounced. This has strongly driven the development of several related systems, including the continuous miniature dilution refrigerator (MDR) reported here. The MDR is comprised of a thermally separated mixing chamber, step heat exchangers, twin stills and twin condensation pumps. The pumps are alternately cooled to ~300 mK by a pair of single-shot 1He sorption coolers (cycled in anti-phase) to circulate 3He in the system. The system is therefore closed-cycle, with the circulation of 3He, both in the MDR and sorption coolers, contained to the cold stage. As a result, the reliability of the system is improved through a mechanically simple design and the absence of external connections, gas handling systems, and cold o-rings.

MKID Large Format Array Testbed

The development of astrophysics kilo-pixel imaging systems requires a dedicated cryogenics and optics setup to measure the performance of the detector arrays in terms of sensitivity, crosstalk, dynamic range, and spatial response. We have developed such testbed for the characterization of large format arrays of microwave kinetic inductance detectors (MKIDs), capable of measuring detector chips of 6 cm × 6 cm, operating in the 350 and 850 GHz band. The testbed is a wide field camera that produces an aberration free image of the chip outside of the cryostat. The cryostat is based upon a commercial pulse-tube cooled 3 K system with an He3-He3-He4 sorption cooler that reaches a base temperature below 250 mK. We will describe the thermomechanical solutions implemented in our system to minimize the thermal loading on the cold stage, needed to reach the low base temperature. We will also give the optical design including straylight control.

A Continuous 100-mK Helium-Light Cooling System for MUSCAT on the LMT

The MUSCAT instrument is a large-format camera planned for installation on the Large Millimeter Telescope in 2018. MUSCAT requires continuous cooling of several large-volume stages to sub-Kelvin temperatures, with the focal plane cooled to 100 mK. Through the use of continuous sorption coolers and a miniature dilution refrigerator, the MUSCAT project can fulfil its cryogenic requirements at a fraction of the cost and space required for conventional dilution systems. Our design is a helium-light system, using a total of only 9 L of helium-3 across several continuous cooling systems, cooling from 4 K to 100 mK. Here we describe the operation of both the continuous sorption and the miniature dilution refrigerator systems used in this system, along with the overall thermal design and budgeting of MUSCAT. MUSCAT will represent the first deployment of these new technologies in a science-grade instrument and will prove the concept as a viable option for future large-scale experiments such as CMB-S4.