Gifford-McMahon Research Articles

Continuous Wave Mode Test of Conduction-Cooled Nb3Sn Radio Frequency Superconducting Cavities at Peking University

A liquid helium-free cryostat for radio frequency (RF) test of the superconducting cavity is designed and constructed. Gifford-Mcmahon (G-M) cryocoolers are used to provide cooling capacity, and the heat leakage at 4 K is less than 0.02 W. Vertical and horizontal tests of two Nb3Sn cavities are carried out in the cryostat with different surface treatments outside the cavities. Both of the cavities achieve stable continuous wave (CW) operation. A novel treatment, which cold-sprayed a 3.5 mm thick Cu layer onto the outside of the cavity, enables the maintenance of an average temperature of 5.5 K in the cavity at a RF loss of 10 W, implying that the thermal stability and uniformity of the cavity has been significantly improved. Through the synergistic control of four metal film resistors, a cooling rate of 0.06 K/min near 18 K is realized, and the cavity temperature gradient is reduced to 0.17 K/m, which effectively improves the RF performance of the cavity. The maximum Eacc of the cavity reaches 3.42 MV/m, and the Q0 is 1.1 × 109. An electromagnetic–thermal coupling simulation model for the superconducting cavity is established and is in good agreement with the experimental results. The simulation results show that the cavity with a Cu-spraying treatment and the thermal links of 5N Al can satisfy the Eacc of 10 MV/m under conduction cooling.

Ultra-stable microwave cryogenic oscillator operated with a Gifford-McMahon cryocooler

We demonstrate for the first time an ultra-stable microwave cryogenic oscillator operated with a Gifford-McMahon (GM) cryocooler. Despite the high level of vibration generated by the GM, we show that an optimised design, with simple passive solutions, enables a sufficient mechanical decoupling to achieve a state-of-the-art frequency stability. The implemented 10 GHz cryogenic oscillator features a fractional frequency stability (ADEV, Allan deviation) σy(τ)<3×10−15 for 1s≤τ≤104s.

Pattern Excitation Tests of the Short Model Superconducting Magnet for a Compact Heavy-Ion Synchrotron

A project to develop a compact heavy-ion radiotherapy system is underway at the National Institutes for Quantum Science and Technology (QST). One of the aims of this project is to downsize the synchrotron by applying superconducting technology, and we have been developing a superconducting magnet for this system in collaboration with QST. This superconducting magnet was designed to generate a dipole field of 3.5 T at a rapid cycle of more than 0.64 T/s by applying the conduction cooling method and using 4K Gifford-McMahon (GM) cryocoolers. Such high-speed excitation generates large AC loss, and this heat generation is one of the major issues in this development. Therefore, we fabricated a short straight model magnet and carried out pattern excitation tests to verify the thermal design. This model magnet has the same cross section as the full scale magnet, but its length is shortened by 1/3. In the pattern excitation test repeated 50 times, the maximum coil temperature was calculated to be 4.03 K and measured to be 3.82 K. The quench occurred at 5.9 K, which is near the temperature of 5.76 K where the load factor is expected to be 100% in overload test. This pattern excitation test results shows that the coil performance was obtained as expected. Also, the consistency between the calculations and the test results confirmed that the conduction cooling method using 4K GM cryocoolers is applicable to the full scale superconducting magnet for the synchrotron. In this paper, the excitation test results are reported.

Acoustic Sensor Development for Quench Detection in HTS Conductors

A MEMS (Micro Electro-Mechanical System) acoustic sensor-array quench detection method has been proposed for quick, unobtrusive, and precisely localized detection of quench events in superconducting magnets. A cryogenic probe was designed and built to study the quench event in a gaseous coolant induced in a segment of an HTS tape and verify the effectiveness of acoustic MEMS sensors in detecting such events. Prior work characterized the performance of a commercially available Vesper MEMS microphone, and associated amplifiers, in cryogenic conditions which were utilized in this work. Critically, the application specific integrated circuit (ASIC) used to amplify the MEMS piezo-sensor output signal fails to operate at temperatures below 110 K. Thus, the ASIC was removed from the microphone package and replaced with a custom low temperature preamplifier which we have shown performs with no loss of function at temperatures as low as 10 K. The quench experiment is conducted using the probe within a two-stage Gifford-McMahon (GM) cryocooler in a gaseous helium environment, at cryogenic temperatures between 20 K to 60 K. Three temperature sensors within the sample region monitor temperature of the HTS sample tape and environment. The HTS sample, a 2 mm wide REBCO tape, is mounted within a square G10 tube. A linear array of the repackaged sensors is mounted to the tube to detect the quench event. The quench detection behavior using the sensors is compared with the readings from voltage taps on the sample. The response characteristics of the Vesper acoustic piezo-sensor with the newly identified, cryogenic-safe preamplifier in detecting quench events of REBCO tapes in gaseous helium are presented.

Preliminary development of emissivity measurement system at low temperature based on radiometric method

Thermal radiation is a major part of heat transfer in cryogenic systems, especially in vacuum environment. The emissivity of materials is an essential factor of thermal radiation, which is difficult to be precisely predicted by theoretical calculation. Thus, the direct experimental measurement becomes an inevitable, reliable method. In this paper, a preliminary emissivity measurement system using the direct radiometric method was designed and built with a G-M (Gifford-McMahon) cryocooler as the cold source. The sample plate in the apparatus can be cooled to 9.2 K, while the sample thermal radiation shield and the optical path cover can respectively reach 46.7 K and 46.9 K. At present stage, MCT (HgCdTe) detector with an effective bandwidth 2–12 μm was used in this system, which achieved the measurements of emissivities of coating Nextel 811–21, 304 stainless steel and G10 composite from 240 K to 300 K. The reliability of the system was verified by comparing the measurement results with the data already published, and the dependence of the emissivities of these materials on temperature are analyzed.

Visual experimental study of slush hydrogen production by freezing-melting method

Slush hydrogen is a mixture of liquid hydrogen and solid hydrogen particles, and considered as an attractive propulsion fuel. The preparation process of slush hydrogen is complex. This paper describes a slush hydrogen preparation device which enables hydrogen liquefaction, liquid hydrogen storage, liquid hydrogen transfer, pumping decompression of liquid hydrogen, slush hydrogen observation, and hydrogen emission. In an open area, many tests using liquid hydrogen are conducted. The results show that 1) The scheme of hydrogen liquefaction using two-stage Gifford- Mcmahon (G-M) refrigerator is feasibility, and the liquefying rate of hydrogen is 0.45 L/h, which meets the consumption of slush hydrogen preparation. 2) In the triple-phase point state, average pressure and temperature of liquid hydrogen are measured as 7.1 kPa and 14.03 K respectively. Compared with NIST physical property data, the relative errors of pressure and temperature are 3.4% and 0.5%, respectively. 3) The formation process of solid hydrogen by the pumping decompression is observed. It is found that the solid hydrogen first nucleates on the Dewar wall. With the continuous run of the vacuum pump, the solid hydrogen gradually grows until dense solid hydrogen is formed, resulting that the light could not pass through it. It indicates that liquid hydrogen in the area near the gas–liquid interface could be completely frozen by the pumping decompression method. 4) The formation of slush hydrogen by a freezing-melting method is observed. It is found that the solid hydrogen forms porous structures due to the boiling fluctuation of liquid hydrogen during the freezing process, and the porous solid hydrogen in the liquid hydrogen forms a fragment or sheet shape again under the boiling action of liquid hydrogen during the melting process. When the vacuum pump is opened again, the violent boiling of the liquid hydrogen causes the fragmented solid hydrogen in the liquid hydrogen to be broken into irregular solid hydrogen particles again. Under the action of Gibbs free energy, irregular solid hydrogen particles form small spherical solid hydrogen particles suspended in liquid hydrogen. 5) Three states of liquid hydrogen, solid hydrogen in liquid hydrogen and slush hydrogen are visually compared. It is found that the observed slush hydrogen is a turbid and viscous state, which is a solid–liquid mixture of tiny solid hydrogen particles suspended in liquid hydrogen. At the same time, the weak motion behavior of viscous fluid is also observed. 6）The leakage heat of the slush hydrogen Dewar is calculated as 4.13 W by the liquid level drop rate, which is 1.66 times of the theoretical calculation, and it could provide a technical reference for the design of liquid hydrogen Dewar.

20인치 극저온 고진공펌프 개발 및 GM 극저온냉동기 내구성 평가

This research paper handles fabrication and testing issues during localization of a 20-inch cryopump. The developed cryopump is equipped with a two-stage GM (Gifford- McMahon) cryocooler. The GM cryocooler can absorb heat of 80.21 W and 8.05 W at each stage under the temperature of 69.59 K and 17.98 K, respectively. At this time, The electric consumption is recorded to be 5.77 kW. Reliability test on the GM cryocooler is also being conducted to secure track-record in commercializing the developed cryopump (currently 6,500 hours passed). For the cryopump, using nitrogen gas, the ultimate pressure and pumping speed are measured to be 9.07×10SUP-9/SUP mbar and 11,473 L/s.

Development of a large capacity cryopump equipped with a two-stage GM cryocooler

• A 20-inch cryopump including a two-stage GM cryocooler has been developed. • Design methodologies behind the GM cryocooler and cryopump have been addressed. • The cooling capacities of the GM cryocooler exceed 80 W and 8 W at each stage. • The pump captures N 2 with 11,000 L s −1 and endures gas impulse of 2,500 mbar L. • The pump can evacuate down to ultimate pressure of 10 -9 mbar-class. Cryopump, which involves the removal of gas by cryo-sorption, condensation and solidification onto cryo-panels, is an ideal form of ultra-high vacuum (UHV) pump due to its contamination-free operation and black hole pumping speed. The high crossover of the cryopump can provide a clean vacuum environment. Since the cryopump utilizes the cryo-pumping effects mentioned above, a cryogenic environment is a prerequisite condition. In this research paper, a 20-inch cryopump, which is driven by a two-stage Gifford-McMahon (GM) cryocooler, is developed and tested. The GM cryocooler is designed by optimizing the opening timing of the rotary valve, and the corresponding thermal losses at its each stage have been analyzed. Under the thermal loads of 80 W and 8 W at each stage of the GM cryocooler, the temperatures are measured to be 66 K and 19.5 K, respectively. The cryopump is designed with the aspect of heat transfer assessment. The model described in this paper considers two major thermal loads; radiative heat ingress and enthalpy transfer by the existence of the gas. This simple model can readily predict the thermal loads on each stage of the GM cryocooler. Since all the cryo-panels are kept below 130 K during operation, the cryopump that has been developed is therefore compatible with a UHV pump. Using nitrogen gas, the ultimate pressure, pumping speed and crossover are measured to be 9.9 × 10 -9 mbar, 11,000 L s −1 and 2,500 mbar L, respectively. Through the experiments, it is also concluded that the numerical model above can explain the thermal characteristics of the cryopump reasonably well. The cryopump will be able to respond to the market needs of the large-size display and semiconductor manufacturing processes as well as increase its energy saving and process operability. Furthermore, the reliability of the GM cryocooler can also be improved through turndown operations.

Experimental study on a simplified precooled JT cryocooler for liquid hydrogen zero boil-off storage

For a hydrogen zero boil-off storage system in space, active cooling technique is one of the key technologies that requires effective cryocoolers. The precooled Joule-Thomson (JT) cryocooler working at liquid hydrogen temperature has no moving parts at low temperature with continuous refrigeration, making it reliable for space applications. In this study, a new simplified JT cryocooler with a large cooling capacity is proposed to approach liquid hydrogen refrigeration. In order to clarify cooling capacity characteristics of the simplified JT cryocooler, a laboratory prototype precooled by a Gifford-Mcmahon (GM) cryocooler is designed, fabricated and tested. The cool-down process of the simplified JT cryocooler is presented. A stable cooling capacity of 10.06 W at 20.7 K is provided by the cryocooler. The availability of the simplified JT cryocooler without a bypass assembly is verified.

Thermal characteristics of a helium-free superconducting magnet system for a fast-ramping heavy-ion synchrotron

A compact synchrotron has been proposed for the next generation heavy-ion therapy system at the National Institutes for Quantum Science and Technology (QST). In this synchrotron, four 90-degree superconducting bending magnets designed on the basis of the superconducting magnet for the rotating-gantry currently operated at QST are adopted to achieve a compact size. These NbTi superconducting bending magnets are conduction-cooled by several Gifford–McMahon (GM) cryocoolers and are designed to generate both the dipole field of 3.5 T and the quadrupole field of 1.5 T/m to operate at a ramp rate of 0.7 T/s. It is a challenge to remove the heat generated from AC losses at such a fast ramp rate, and keep the superconducting magnets from quenching during the continuous operation without using liquid helium. In this paper, we studied the feasibility for realizing a fast-ramping synchrotron by using a helium-free superconducting magnet system for heavy-ion therapy. Using the numerical models, we estimated the AC losses including eddy current loss in mechanical structures, iron loss and loss in superconductor to be about 212 J in a cycle duration of 20 s for each 90-degree superconducting bending magnet, and it was possible to eliminate that amount of AC losses by using GM cryocoolers. To validate the transient temperature rising during the continuous operation, a dynamic simulation was performed using the estimated AC losses as input, and the peak temperature at thermal equilibrium was evaluated to be lower than 5 K for a practical operation scenario of heavy-ion therapy irradiation.

Thermodynamic Characteristics of a Single Stage Pneumatically Driven Gifford–McMahon Refrigerator

Abstract At present, the demand for high cooling capacity Gifford–McMahon (GM) refrigerators is increasing to cool the high-temperature superconducting magnets in cryogenic temperature range. Therefore, it is necessary to enhance the cooling capacity of existing refrigerators, which needs a thorough understanding of related thermodynamic phenomena. In this paper, thermodynamic processes of a GM refrigerator are analyzed and its performance is compared with Carnot cycle, and Brayton cycle with and without work recovery. Subsequently, a mathematical model has been formulated for a pneumatically driven GM refrigerator by applying the fundamental principles of thermodynamics and mechanics. The model computes the influence of geometrical and operating parameters upon its refrigeration performance. Subsequently, the impact of valve opening intervals upon internal thermodynamic and dynamic processes is evaluated. The dynamic characteristics of the displacer motion, transient variation of mass flow, and pressure distribution are studied by the model for different values of idling angles. It is found that an increase in the idling angle of the rotary valve of GM refrigerator reduces its cooling capacity and enhances its specific cooling capacity. An experimental study has also been undertaken to corroborate the mathematical results.

Cryostat for HECRAL Superconducting Magnet

In order to support the normal operation of HECRAL (Hybrid superconducting Electron Cyclotron Resonance ion source with Advance in Lanzhou) superconducting magnet, a cryostat in the form of immersed in liquid helium was designed, which integrated two two-stage GM (Gifford-McMahon) cryocoolers, helium vessel, thermal shield, outer Dewar, suspension structures, service turret, binary current leads, corresponding monitoring and diagnosis system. The 1st cold head of the two-stage cryocoolers were used to cool the thermal shield and HTS (High Temperature Superconducting) current leads. Enough cooling capacity in the temperature region of 4.2K was supplied by the 2nd cold head to condense the saturated helium vapor evaporated by heat load (including static heat load and dynamic heat load), to realize the “0” liquid helium evaporation operation of the superconducting magnet. The corresponding heat load of the designed cryostat was analyzed, and the WST (Western Superconducting Technologies Co., Ltd.) was commissioned to install the cryostat and carried out cryogenic excitation test. The cryostat is now operated in IMP (Institute of Modern Physics, Chinese Academy of Sciences) and all parts of the magnet and cryostat are working normally, which ensures proper operation of the ion source.

극저온 냉각시스템용 스크롤 압축기 성능실험

This paper describes the performance test of a helium scroll compressor originally used for Gifford-McMahon (GM) cryocooler. This compressor can also be used for the reverse Brayton cryogenic refrigeration system. In this paper, the performance characteristics of a scroll compressor is experimentally investigated with helium and neon gas to obtain reference data for designing thermodynamic cycle of cryogenic refrigeration system. To maintain constant suction pressure during experiments, an experimental setup contains pressure regulation system which consists of three control valves and gas buffer. Pressures, mass flow rate and power consumption are measured for 400, 450, 500, 550 kPa of suction pressure condition. With experimental measurements, performance characteristics of a helium scroll compressor is investigated. The tested scroll compressor shows the higher isentropic efficiency with helium as a working gas than neon.

Improvement of 4 K cooling power by coaxial pipe regenerator for a Gifford-McMahon cryocooler

This paper presents the experimental results of 4.2 K cooling power of a Gifford-McMahon (G-M) cryocooler. To improve the cooling power, an original regenerator structure named coaxial pipe regenerator was applied to the second stage regenerator. This structure is that a stainless steel pipe is inserted in the coaxial direction of the second stage regenerator. An effect of the coaxial pipe is considered to rectify the helium flow in the regenerator that leads to an increase in the mass flow rate to the expansion space. Then, an improvement in the cooling power is expected. The second stage regenerator is comprised of three-layer of Pb (warm side), HoCu2 (middle) and Gd2O2S (cold side) spheres of which the volume filling rate is 50, 20 and 30%, respectively. The coaxial pipe is applied to each material layer independently to survey an improvement effect of the cooling power at 4.2 K. These coaxial pipe regenerators were tested with a G-M cryocooler of one-watt model (RDK-408D2, SHI) and a scroll-type compressor (SSC-3700, SUZUKISHOKAN). The three-layer regenerator (without coaxial pipe) obtained the cooling power of 1.70 W. When the coaxial pipe was applied to the Pb layer, the cooling power of 1.79 W was achieved with the electrical input of compressor of 7.06 kW. In contrast, the coaxial pipe of HoCu2 layer and Gd2O2S layer showed no conspicuous improvement. These results prove that the flow condition of helium in the Pb layer significantly affects the 4 K cooling power.

A 1-2 K Cryogenic System With Light Weight, Long Life, Low Vibration, Low EMI and Flexible Cooling Capacity for the Superconducting Nanowire Single-Photon Detector

This paper presents a 1-2 K cryogenic system for cooling the superconducting nanowire single-photon detector (SNSPD). The system is based on the Stirling-type pulse tube cryocooler (SPTC) and the Joule-Thompson (JT) cryocooler technologies and thus named as the hybrid cryogenic system. It eliminates any moving component at the cold end which endows it with evident advantages over the Gifford-McMahon (GM) cryocooler in terms of low vibration, low electromagnetic interference (EMI) and long life. It can operate at 1-2 K and has an expected mean-time-to-failure of 10 years. The overall weight is below 30 kg, which makes it an attractive cryocooler candidate for the space applications. Furthermore, the operating temperature can be adjusted conveniently for the SNSPD other than being at a fixed temperature as the superfluid helium does. The design approaches and system integration are described in detail, and the performance characteristics presented and discussed. The cooling system has an experimental cooling temperature of 1.52 K. It is also expected to reach 1 K and below provided that the further performance improvement is conducted.

Numerical simulation of a low temperature hybrid refrigerator combining GM gas expansion refrigeration with magnetic refrigeration

A hybrid refrigerator combining Gifford-McMahon (GM) gas expansion refrigeration with magnetic refrigeration, in which helium and magnetic materials regenerate each other, overcomes the low-temperature thermal saturation of regenerator materials and has been experimentally proved to reach a higher cooling power than pure GM refrigeration recently. Considering the complexity of the thermodynamics and fluid dynamics of the hybrid refrigeration, optimizations based on numerical simulation are necessary to provide useful guidance for practical design. In this paper, a transient 2D axis-symmetric model of a hybrid refrigerator is established. With this model, the effect of timing between GM refrigeration and magnetic refrigeration is studied and optimized by defining a phase angle. The corresponding cooling power and efficiency are obtained and compared with the results from pure GM refrigeration. Additionally, the operating frequency and the filling ratio of the regenerator are optimized. The results showed that the optimal phase angle is around 90°, which is close to previous experimental results, and within a certain range, the lower the temperature and frequency, the greater the advantage of hybrid refrigeration. At 4 K and 0.4 Hz, the cooling power and efficiency of hybrid refrigeration are 57% and 68% higher than GM refrigeration, respectively.

Attenuation of Gifford-McMahon cryocooler induced vibration using mechanical vibration isolators

Aiming to attenuate the vibration that is induced by a Gifford-McMahon (G-M) cryocooler, a method attenuating the vibration with mechanical vibration isolators (MVIs) is proposed. A scheme supporting the G-M cryocooler with one kind of supporting system that mainly comprises the MVIs is presented. The vibration response of the supporting system caused by the vibration of the G-M cryocooler are studied, and the effects of the structural parameters of the MVIs are investigated. The results show that reciprocating moving modes of the MVIs induce the modal characteristics of the supporting system, which further formed the vibration response of the supporting system under the excitation of the G-M cryocooler vibration. Structural parameters of stiffness and installation sites of the MVIs affect the reciprocating moving mode of the MVIs, through which the modal characteristics and the vibration response of the supporting system are affected. Through optimizing the installation sites of the MVIs, the vibration response of the supporting system is attenuated. It demonstrates that the method proposed in this paper is available for attenuating the cryocooler-induced vibration in the field of cryogenics and refrigeration.

Development of cryogenic tensile testing apparatus for lattice strain measurement using synchrotron radiation for REBCO composite conductors

REBa2Cu3O7−δ (REBCO) composite tapes are candidate conductors for future accelerator magnets. Given that REBCO is a brittle oxide film, stress/strain management is important in the mechanical design of a magnet. Therefore, the strain state of a superconducting film should be predicted under various operating conditions. A quantum beam is a useful tool in evaluating the strain state of a superconducting material in a composite conductor. Although various cryogenic tensile testing machines, in combination with neutron beam and synchrotron radiation, have been developed, they are not necessarily optimized for measuring highly textured materials such as REBCO films. This study reports a novel cryogenic tensile testing apparatus that can be used at the beamline of a synchrotron radiation facility. In this system, a superconducting tape is cooled using a Gifford–McMahon (GM) cryocooler through 2.5 m long thermal links made of 5 N high-purity aluminum. This enables a compact cryogenic loading system that can be mounted on the goniometer of a beamline. Lattice strain measurements using synchrotron radiation were conducted at 40 K, 77 K, and 300 K for a commercially available (Y,Gd)BCO coated conductor at BL28B2 in SPring-8. The onset strain of film fracture determined from the lattice strain measurement at 77 K agreed well with the irreversible strain of critical current at the same temperature. The residual and fracture strain of the (Y,Gd)BCO film at 77 K was evaluated as well.

Long term operation of the superconducting triplet quadrupoles with cryocoolers

Superconducting triplet quadrupoles (STQs) with cryocoolers characterize the BigRIPS in-flight separator and radioactive isotope (RI) beam delivery lines in the RIKEN RIBF (Radioactive Isotope Beam Factory) project. The STQ magnet is a large-aperture superferric quadrupole triplet cooled by liquid helium bath cooling method in a single cryostat. The STQ cryostat is designed to be operated continuously with a Gifford-McMahon (GM)/Joule-Thomson (JT) cryocooler and a GM cryocooler. We operate 22 STQ systems for more than twelve years without warm-up the magnets. We report operational experiences, such as degradation of cooling capacity and failures of compressors, in the long-term operation of the STQ systems. Replacement of ageing cryocooler unit is discussed to improve the cooling capacity.

Development of switchless thin-plate type sorption compressor cell for 5 K sorption J-T refrigerator

A sorption J-T (Joule-Thomson) refrigerator is a J-T refrigerator using a sorption compressor that compresses refrigerant by adsorption and desorption in sorption cells. When the sorption cell of the compressor is cooled, the refrigerant is adsorbed on the adsorbent, reducing the pressure of the cell. In contrast, when the cell is heated, its pressure increases due to desorption of the refrigerant from the adsorbent. The sorption cells should operate in pairs to produce a continuous pressure gradient for J-T expansion since the cell can create pressure periodically. Therefore, to increase cooling capacity of the refrigerator, it is indispensable to reduce the cycle time by accelerating thermal response of the sorption cell. This paper suggests a thin-plate type sorption cell to maximize the heat diffusion to the adsorbent. Furthermore, because its temperature can be altered rapidly, the sorption compressor can operate without a heat switch to regulate heating and cooling of the sorption cell. The sorption cell is made of stainless steel 304 with width and length of 100 mm and height of 4.6 mm, respectively. The activated charcoal with two different nominal sizes is charged into the cell as an adsorbent of helium for cooling at 5 K. On the top and the bottom side of the cell, the cold head of G-M (Gifford-McMahon) refrigerator and the polyimide film heater are attached to adsorb and desorb helium in the cell, respectively. Its ability to build the pressure is verified by heating the cell which contains constant mass of helium. Furthermore, the mass of helium adsorbed on activated charcoal at various temperature are measured by expanding helium from a reservoir to the sorption cell to construct the precise prediction model. Subsequently, the operation parameters for sorption compressor are determined employing a prediction model which is validated by the cooling-down and the heating-up experiment. The predicted mass flow rate and the cycle time of the compressor are 2.37 mg/s and 55.4 s, respectively. Consequently, the cooling capacity of the sorption J-T refrigerator with recuperative heat exchanger is predicted as 2.2 mW at 5 K.