Abstract Currently, most high-precision infrared detectors used in space operate in the liquid hydrogen temperature range and require a two-stage pulse tube cryocooler (PTC) to provide a cryogenic environment. However, the existing two-stage thermal-coupled PTC suffer from low cooling capacity and efficiency. Therefore, in this study, the 2nd-stage of the PTC is considered as a whole system and a Sage model is established. The model is coupled with different inertance tube combinations to comprehensively simulate the performance. The simulation results are compared with the experimental results from the published article. The accuracy of the model simulation is verified. 70% of the simulated values for the no-load optimal frequency deviate from the experimental values by 0-1Hz. 84% of the simulated values for the cooling capacity at 20K deviate from the experimental values within a range of ±20%. It is observed that all experimental values for the optimal frequency at 20K is consistently 2-4Hz higher than the simulated values. The reasons are revealed from the perspective of the phase angle between the mass flow and pressure wave inside the 2nd-stage regenerator. The research results provide a foundation for the application of Sage software in the study of overall performance of two-stage thermal-coupled PTC.

A single-stage adiabatic demagnetization refrigerator (ADR) precooled by a 3He sorption cooler has been designed, constructed, and experimentally validated as a lightweight and compact sub-Kelvin cooling solution for space applications. The hybrid cooling system utilizes a 3He sorption cooler to precool a chromium potassium alum (CPA) salt pill to 545 mK before demagnetization. The ADR comprises a CPA crystal grown directly on a gold-plated copper thermal bus, a tin superconducting heat switch (SCHS), a NbTi superconducting magnet, and a dual-layer magnetic shield. Experimental results demonstrate that, under a magnetic field of 3 T and a constant ramp-down rate of 2.67 mT/s, the ADR achieved a base temperature of 31.7 mK. In the absence of an external heat load, the hold time at 50 mK is approximately 6 h 48 min. The total system heat leak is about 2.82 mu W, mainly dominated by conduction through the Kevlar suspension. The influence of the applied magnetic field intensity on the base temperature was experimentally tested. Analysis further indicates that reducing parasitic heat loads and minimizing the thermal resistance between the CPA crystal and the copper thermal bus are crucial for achieving even lower base temperature.

This study presents the development and experimental characterization of a single-stage 3He sorption cooler. Operating on the principle of pressure reduction evaporation with activated carbon as the adsorbent, the system achieves stable sub-Kelvin cooling without moving parts. Key components include a sorption pump featuring optimized heat transfer fins, a three-stage pump tube designed to balance flow conductance with thermal isolation, and an evaporator incorporating internal fins to minimize Kapitza resistance. Theoretical analyses of condensation efficiency, self-cooling loss, and thermodynamic cycles were conducted, predicting high liquefaction rates at low condensation temperatures. The experimental apparatus integrates a two-stage GM cryocooler for precooling, a 1.2 K 4He bath for condensation, and a gas recycling system to manage the 3He inventory. Experimental results demonstrate a no-load minimum temperature of 287 mK and a cooling capacity of 2.5 & micro;W at 300 mK, exhibiting a quasi-linear relationship between temperature and cooling power in the low power regime.

The Stirling-type pulse tube cryocooler (SPTC), featuring no moving parts at the cold end, compact structure, and long operational life, has become the mainstream technology for space cooling in the liquid‑helium temperature range (≤4.2 K). After more than two decades of development, the no‑load minimum temperature of SPTC has been reduced from the 5 K range to 2.28 K; however, its relative Carnot efficiency generally remains below 0.4%, which is orders of magnitude lower than that of G‑M type pulse tube cryocoolers operating at the same temperature. Focusing on the three physical bottlenecks that limit the performance of SPTC in the liquid‑helium range—namely, the heat capacity mismatch of regenerator materials, the severe non‑ideal effects of helium as the working fluid, and the difficulty in controlling the multistage high‑frequency acoustic impedance network—this paper systematically reviews the research progress in cryogenic regenerator materials, interstage coupling structures, and low‑temperature phase‑shifting configurations. Emphasis is placed on recent advances in non‑traditional regenerative mechanisms such as spin frustration and optical phonons. The evolutionary logic and key control principles of three technical routes (gas‑coupled, thermally‑coupled, and hybrid pre‑cooling) are outlined, and the application prospects of active‑piston phase shifting are demonstrated. On this basis, the paper reveals the deep physical origins of the current efficiency bottleneck and envisions future breakthrough pathways for 4.2 K SPTC, including compressor efficiency and coupling, mixed‑working‑fluid acoustic dynamics, additively manufactured acoustic metamaterial regenerators, and digital twin combined with finite‑time thermodynamics.

Increasing the operating frequency is a key strategy for the miniaturization of the pulse tube cryocoolers. In the pursuit of high frequency and compact system designs, maintaining the phase relationship between the pressure and mass flow within the regenerator is essential for sustaining the cooling performance of the cryocoolers. However, at super-high operating frequencies, precise control of the phase angle becomes increasingly challenging when using the inertance tube and reservoir as the phase shifter. In this paper, a three-dimensional model of the inertance tube and reservoir was developed to investigate the critical internal flow parameters at super-high frequencies. The mass flow amplitude and the phase angle along the tube were compared for single-diameter and dual-diameter inertance tube configurations at 150 Hz. Experimental validation was conducted to evaluate the impact of these configurations on the pulse tube cryocooler's performance. The results demonstrate that employing a dual-diameter inertance tube as the phase shifter significantly enhances the cooling performance in super-high frequency cryocoolers.

Abstract The suitable cryogenic environment is a necessary condition for ensuring the high precision and high sensitivity operation of space exploration equipment. The two-stage pulse tube cryocooler (PTC) is the basis for the normal operation of space exploration equipment working in the liquid hydrogen temperature range and cryogenic systems such as the Joule-Thomson cryocooler that requires pre-cooling in the liquid hydrogen temperature range. Currently, the 2nd-stage regenerator length-diameter ratio of most two-stage PTC are greater than 2.5. However, for occasions with high structural strength requirements and thermal coupling with large-area array detectors, small length-diameter ratio PTCs will be preferred. Therefore, a small length-diameter ratio thermal-coupled two-stage PTC was designed in this study, and experimental optimizations were conducted on the 2nd-stage inertance tube and double-inlet. After optimization, the lowest no-load cooling temperature of 11.75 K was obtained. With a total electric power of 290 W, a cooling capacity of 784 mW@20 K was obtained, resulting in a maximum relative Carnot efficiency (rCOP) of 4.36 %.

Abstract Sub-Kelvin technology plays a crucial role in both ground-based experiments and space exploration. 3 He sorption cooling is one of the few methods capable of achieving temperatures below 500 mK. The sorption cooler is based on the principle of liquid helium evaporation refrigeration, and the adsorption and desorption of helium gas are realized by periodically cooling and heating activated carbon. Due to its advantages, including compact size, light weight, absence of vibration and electromagnetic interference, and simple operation, it offers strong competitiveness in the field of space extreme low temperature refrigeration. In this paper, we present the design and performance evaluation of a closed-cycle single-shot 3 He sorption cooler, which incorporates a sorption pump filled with activated carbon granules. The 3 He sorption cooler, pre-cooled by a two-stage GM type pulse tube refrigerator and a superfluid helium bath, achieves a minimum temperature of 393.6 mK and provides a net cooling power of 200 µW at 486 mK. At a charge of 2 STP L 3 He, a single cycle can be maintained at temperatures below 400 mK for about 6 hours. The 3 He sorption cooler needs further optimization and is expected to be used for pre-cooling of the adiabatic demagnetization refrigerator in the future.

Infrared detectors play a pivotal role in human space exploration. The pulse tube cryocooler has become a crucial mechanical cooling device to ensure the reliable operation of infrared detectors. In order to address the growing demand for long-wave infrared detectors operating at approximately 60 K, this manuscript investigates the frequency characteristics of a 60 K coaxial pulse tube cryocooler, and explores methods to enhance the operating frequency while maintaining cooling efficiency. Theoretical analysis and simulation calculations were performed to investigate the effects of high operating frequencies on the weight and cooling performance of a pulse tube cryocooler system, aiming to optimize its structure and design. Analytical results were experimentally validated, confirming that increasing the operating frequency to 96 Hz maintained a relative Carnot efficiency of 16 % for the entire system. At an input power of 250 W, the pulse tube cryocooler achieved a cooling capacity of 10 W@60 K. The total system weight was 4.7 kg, a specific mass of 2.13 W/kg-a significant improvement over the conventional 60 K pulse tube cryocooler.

Abstract The mechanical Joule-Thomson (JT) refrigerator operating in 2 K-class or 4 K-class temperature ranges serve as crucial equipment for space astronomical observation and deep space exploration. Current typical space-borne JT cryocoolers face multiple technical challenges due to their compressor operation at ambient temperatures, including excessive pressure ratio requirements, increased compressor stages, enlarged system volume/weight/power consumption, as well as complex configurations with multiple inefficient heat exchanger stages. This study analyzed the enthalpy of a typical helium throttling refrigeration cycle and found that there is an optimal pressure ratio for the throttling refrigeration. A quantitative comparison was made between operating at the optimal pressure ratio and operating at a typical 20 times pressure ratio, resulting in a 66 % increase in refrigeration capacity and a 28.1 % decrease in power consumption. This study innovatively proposes a novel solution by implementing cryogenic operation of the driver assembly and establishing a throttling refrigeration cycle with working fluid in sub-20 K temperature range. This approach fundamentally provides new possibilities for pressure ratio reduction in cryocooler systems.

Abstract A 4K hybrid JT cooler is developed to precool the adiabatic demagnetization refrigerator (ADR) for the Hot Universe Baryon Surveyor (HUBS) mission, which is proposed to study “missing” baryons in the universe. The 4K hybrid JT cooler is composed of a 4He JT cooler precooled by a two-stage thermally coupled pulse tube cooler. Recently, the two-stage pulse tube cooler is optimized to provide more precooling power for the JT loop. The performance of the hybrid JT cooler has been improved and special efforts have been made to optimize the compression system of the JT loop. Eventually, cooling power of 100mW is achieved at 4K which is able to meet the requirements of the ADR of HUBS.

The 4He Joule-Thomson cryocooler is a critical component of space cryogenic systems, as it is not only able to provide a stable precooling environment for sub-Kelvin refrigerators but also can directly provide cooling power for certain optical devices. To meet the cooling demand of multi-temperature in space detection missions, this paper presents the development and testing of a 4He Joule-Thomson cryocooler precooled by a two-stage pulse tube cryocooler. The hybrid cryocooler is capable of simultaneously providing cooling capacities at 80 K, 20 K, and 4 K. A no-load temperature of 3.77 K is achieved with a total input power of 462.4 W. Experimental results demonstrate that with a total input power of 632.1 W, the three-stage cooling capacities are 4.06 W at 69.83 K, 204.69 mW at 17.54 K, and 51.8 mW at 4.08 K, respectively.

The suitable cryogenic environment is a necessary condition for ensuring the high precision and high sensitivity operation of space exploration equipment. The two-stage pulse tube cryocooler (PTC) is the basis for the normal operation of space exploration equipment working in the liquid hydrogen temperature range and cryogenic systems such as the Joule-Thomson cryocooler (JTC) that requires pre-cooling in the liquid hydrogen temperature range. Based on the pre-cooling requirements of 4He JTC developed by our laboratory, a high efficiency thermally-coupled two-stage PTC utilizing double-inlet phase shifter and pure SS screen filling is designed, manufactured, and tested with an eye toward space applications. Under a total electric power of 185 W, a cooling capacity of 647 mW@20 K was obtained, resulting in a maximum relative Carnot efficiency (rCOP) of 4.90 %, which met the design target. In addition, the cooling characteristics and temperature stability of the PTC were tested.

The Diffuse X-ray Explorer (DIXE) is a high-resolution X-ray spectroscopic surveyor, planned to be mounted on the China Space Station. Its primary goal is to study the origin and evolution of hot baryons in the Milky Way. The Transition Edge Sensors (TES) detectors require an operating temperature below 100 mK to ensure excellent energy resolution. A two-stage Adiabatic Demagnetization Refrigerator (ADR) is incorporated into the system to achieve this ultra-low temperature. The two-stage thermally coupled pulse tube cryocooler (PTC) and the 4He Joule-Thomson cryocooler (JTC) provide the 4 K heat sink for the ADR. This paper describes the design of the DIXE cryogenic experimental system and the operational results of cooling from 300 K to 4 K. The total input electrical power for the PTC and JTC is 604.88 W. The evaporator temperature of the JTC operates stably at 4.33 K, ensuring the proper functioning of a two-stage ADR.

The increasing demand for lightweight, high efficiency cooling systems in space cryogenic detection necessitates advancements in pulse tube cryocooler (PTC) design. Traditional two-stage PTCs precool the second-stage hot end to 80 K using the first stage, but the second-stage compressor operates at ambient temperature, inducing significant thermal losses in the transition regenerator due to temperature gradients. This inefficiency, coupled with low operating frequencies and high mass/volume limitations, impedes performance. This study proposes a new single-stage high frequency PTC system to replace traditional second-stage units, addressing compactness and efficiency challenges. The system employs liquid nitrogen precooling (total mass: 2.6 kg) and integrates an inertance tube-gas reservoir phase shifter with a stainless steel screen regenerator. A multi-physics coupling model optimizes phase modulation, enabling direct cooling in the 80 K range. At 1 MPa and 56 Hz with 10 W input power, the system achieves a no-load temperature of 15.8 K after precooling. Operational testing demonstrates 0.5 W effective cooling capacity at 25.5 K and a specific mass cooling power of 192 mW/kg. Frequency optimization reveals enhanced performance near 60 Hz, achieving a record low no-load temperature of 13.5 K at 62 Hz and effective cooling within the 20 K range. Further integration with a micro compressor (300 g, 30 W) is proposed, leveraging first-stage PTC precooling to minimize system volume and mass. This design advances high frequency PTC technology for space applications, offering superior cooling density and operational flexibility compared to traditional architectures.

A micro coaxial pulse tube cryocooler has been developed to meet the requirements of high operating temperature infrared detection in space applications. To increase the efficiency of the cryocooler, the optimization experiments were designed. Driven by a double-piston opposed linear compressor with the mass less than 200 g, this cryocooler uses the inertance tubes and a reservoir as phase shifter and has the regenerator with a diameter of 10 mm. The effect of the operating frequencies and charging pressure on cooling performance were investigated through a series of experiments. This cryocooler can provide a cooling power of 0.61 W at 150 K with an input electric power of 10 W. This paper describes the optimizing processes and presents test data in detail.

In response to the inadequate cooling capacity of traditional single-stage pulse tube cryocoolers (PTCs) in the 20 K temperature zone, and the challenges posed by multi-stage systems, including excessive volume/weight and significant thermodynamic irreversibility between high/low temperature zones, this study proposes an innovative single-stage PTC architecture based on an 80 K precooling environment. The design aims to achieve dual objectives of system compactness and thermodynamic performance enhancement by replacing the second stage in traditional two-stage coupled systems with an optimised single-stage configuration. The following technical innovations have been identified: Firstly, the integration of components across the full temperature range at 80 K operation eliminates the substantial temperature gradient caused by traditional transitional regenerators, thereby achieving a more uniform axial temperature distribution and reducing regenerator thermodynamic losses. Secondly, pioneering frequency elevation to 59 Hz (approximately double that of traditional two-stage systems) enables miniaturization through high frequency operation. Thirdly, a cold inertance tube-cold gas reservoir hybrid phase-shifting system (currently under experimental verification) combined with liquid nitrogen (LN2) precooling is being developed. Operating at pressure of 1 MPa, this configuration has been shown to achieve breakthrough cryogenic performance. It has been demonstrated that this configuration attains a no-load temperature of 14.8 K with 5 W input power, while achieving 0.3 W cooling capacity at 25.7 K. This architecture provides an optimised power-to-mass ratio solution for spaceborne cryogenic systems, establishing a new technical method for the miniaturisation development of space refrigeration technologies.

The 4 He Joule-Thomson cryocooler (JTC) utilizes the Joule-Thomson (JT) effect of 4 He to typically achieve the temperature of about 4.5 K. When the 4 He JTC obtains the temperature of about 4.5 K, the working fluid behind the JT impedance is a two-phase fluid and has a high velocity. In addition, the pressure of the working fluid behind the JT impedance must be below 130.23 kPa to obtain <4.5 K. Thus, it is crucial for the low-pressure, high-speed two-phase flow to have a low flow resistance in the evaporator. The evaporators used in the 4 He JTC before are filled with copper wire screens, which have a large flow resistance. Thus, considering no gravity in space, a new evaporator using centrifugal force with spiral flow channels is designed, manufactured, and applied in the hybrid 4 He JTC.

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 mu W at 803 mK.

The 4He Joule-Thomson cryocooler (JTC) ensures the operation of space detectors working within the 4 K temperature range, such as the Block Impurity Band Infrared Detector (BIBID). In addition, the 4He JTC is one of the essential components of the 300 K to 50 mK space cryochain. It can precool sub-Kelvin refrigerators, such as the adiabatic demagnetization refrigerator (ADR) and the dilution refrigerator (DR). With the development of space science, the need for cooling power at the 4 K temperature range is growing. Thus, a thermal performance model of the 4He JTC precooled by a two-stage thermally coupled pulse tube cryocooler (PTC) is designed, manufactured, and tested with an eye toward space applications. A four-stage compression system with a high operating frequency and large pistons is designed and used to drive the JT cycle. This 4He JTC has a total mass of 55 kg and can provide a cooling capacity of 105 mW at 4.41 K with a total input electric power of 548 W.