Two-stage Pulse Tube Cryocooler Research Articles

A small two-stage pulse tube cryocooler operating at liquid Helium temperatures with an input power of 1 kW

The development of 4K two-stage pulse tube cryocoolers (PTCs) is commonly aimed at high cooling powers in order to compete with GM-cryocoolers. However, more sensitive applications still suffer from intrinsic disturbances of the cryocooler. To address this issue, the development of PTCs with small cooling powers is essential for sensitive measurements.Here we report the development of a new two-stage GM-type PTC, designed to work with a commercial Helium compressor with only 1kW electric input power. The pressure and mass flow oscillation is generated by means of a remote rotary valve. The PTC was modeled for the operation at temperatures near 5K with the simulation environments SAGE and REGEN. A first prototype was fabricated, operated and optimized in a test cryostat. Up to now, the PTC reaches a minimum temperature of 2.36K and provides a cooling power of 72mW at 4.2K and 120mW at 5K. This cooling power is sufficient for small cryoelectronic devices like single photon detectors, transition-edge bolometers or low-noise Nb-SQUIDs (superconducting quantum interference devices).

Design, construction and 13 K conduction-cooled operation of a 3 T 100 mm stainless steel cladding all-REBCO magnet

A conduction-cooled 3 T 100 mm winding bore multi-width and no-insulation (NI) all-REBCO magnet was designed, constructed and tested at 13 K. The magnet consists of a stack of double pancake (DP) coils wound with, for the first time, REBCO tapes having a 1 μm thick layer of stainless steel, named ‘metallic cladding’, that surrounds the tapes in a hermetic way to substantially reduce the NI charging delay. After construction, the magnet was cooled down to the target operating temperature of 13 K using a two-stage pulse-tube cryo-cooler. During charging–discharging tests up to 200 A, magnetic center field, voltage of each DP coil, power supply current, and magnet temperature were monitored. The charging time constant of the magnet was measured to be about 10.1 s, 13 times smaller than that of its NI counterpart. The magnet experienced, due to an unexpected power supply trip, a sudden discharge at a peak coil current density of 353 A mm2, yet it survived without any degradation. The results demonstrated strong potential of the metallic cladding NI-REBCO magnet for significant charging-delay reduction and self-protecting operation.

Numerical investigation of real gas effects on a two-stage pulse tube cryocooler performance

In this paper, a one-dimensional CFD code was developed to simulate a two-stage pulse tube cryocooler. The aim is to investigate the effects of real gas on cryocooler performance. Conservation equations were derived based on real gas equations of state in general form and then were discretized with control volume approach. Results based on four distinct equations of state including ideal gas, Van der Waals, Virial and Helium gas were compared. Results showed that at the first and second stage mean pressures of 25 and 12.5 bar, and the minimum no load attainable temperatures of almost 60 and 18 K, employing Helium equation of state, the deviation of almost 6.5 and 2.5% relative to ideal gas equation of state was observed respectively. Meanwhile the ideal gas equation of state was fairly accurate and could be proposed to reduce the calculation cost.

Numerical analysis of different valve effects on the cooling performance of a two-stage GM type pulse tube cryocooler

The cooling performance of GM type pulse tube cryocoolers (PTCs) is strongly affected by the valve setting for phase shifting. In this research, the effects of different valve openings on the no-load temperatures in a two-stage GM PTC have been investigated by numerical simulation. Results show that the no-load temperature at the 1st stage mainly depends on the openings of 1st stage orifice valve, and both 1st and 2nd stage double-inlet valves. While the no-load temperature at the 2nd stage below 10 K sensitively depends on the openings of both 1st and 2nd stage orifice valves, and 2nd stage double-inlet valves. There exist several local minimum no-load temperatures at the 2nd stage under different valve openings below 7 K. The best valve setting corresponds to minimizing the cold end phase angle, making the cold end acoustic power compensate the real gas enthalpy flow with maximum degree.

Experimental research on a 12.1 K gas-coupled two-stage high frequency pulse tube cryocooler

High frequency pulse tube cryocoolers (HFPTC) have been widely used in many fields like physics experimental research and aerospace, for no moving part in cold region, low vibration and long life. A gas-coupled two-stage high frequency pulse tube cryocooler with single compressor is introduced in this paper. In the first stage of the cryocooler, double-inlet and multi-bypass has been adopted as phase shifters. To get a better performance in phase shifting the reservoir and the inertance tube of the second stage has been located on the cold head of the first stage. With SS mesh screen as the regenerator of both stage, no-load temperature of 13.5K has been achieved. To improve the heat capacity of the regenerator of the second stage magnetic material Er3Ni has been employed in the second stage as regenerator matrix. With the charge pressure of 1.8MPa, input power of 260W and operating frequency of 23.5 Hz, the no-load temperature of 12.1K has been achieved.

Numerical Study of a 10 K Two Stage Pulse Tube Cryocooler with Precooling Inside the Pulse Tube

High efficiency cryocoolers working below 10 K have many applications such as cryo-pump, superconductor cooling and cryogenic electronics. This paper presents a thermally coupled two-stage pulse tube cryocooler system and its numeric analysis. The simulation results indicate that temperature distribution in the pulse tube has a significant impact on the system performance. So a precooling heat exchanger is put inside the second stage pulse tube for a deep investigation on its influence on the system performance. The influences of operating parameters such as precooling temperature, location of the precooling heat exchanger are discussed. Comparison of energy losses apparently show the advantages of the configuration which leads to an improvement on the efficiency. Finally, the cryocooler is predicted to be able to reach a relative Carnot efficiency of 10.7% at 10 K temperature.

Theoretical and experimental investigations on the cooling capacity distributions at the stages in the thermally-coupled two-stage Stirling-type pulse tube cryocooler without external precooling

The two-stage Stirling-type pulse tube cryocooler (SPTC) has advantages in simultaneously providing the cooling powers at two different temperatures, and the capacity in distributing these cooling capacities between the stages is significant to its practical applications. In this paper, a theoretical model of the thermally-coupled two-stage SPTC without external precooling is established based on the electric circuit analogy with considering real gas effects, and the simulations of both the cooling performances and PV power distribution between stages are conducted. The results indicate that the PV power is inversely proportional to the acoustic impedance of each stage, and the cooling capacity distribution is determined by the cold finger cooling efficiency and the PV power into each stage together. The design methods of the cold fingers to achieve both the desired PV power and the cooling capacity distribution between the stages are summarized. The two-stage SPTC is developed and tested based on the above theoretical investigations, and the experimental results show that it can simultaneously achieve 0.69W at 30K and 3.1W at 85K with an electric input power of 330W and a reject temperature of 300K. The consistency between the simulated and the experimental results is observed and the theoretical investigations are experimentally verified.

10 K high frequency pulse tube cryocooler with precooling

A high frequency pulse tube cryocooler with precooling (HPTCP) has been developed and tested to meet the requirement of weak magnetic signals measurement, and the performance characteristics are presented in this article. The HPTCP is a two-stage pulse tube cryocooler with the precooling-stage replaced by liquid nitrogen. Two regenerators completely filled with stainless steel (SS) meshes are used in the cooler. Together with cold inertance tubes and cold gas reservoir, a cold double-inlet configuration is used to control the phase relationship of the HPTCP. The experimental result shows that the cold double-inlet configuration has improved the performance of the cooler obviously. The effects of operation parameters on the performance of the cooler are also studied. With a precooling temperature of 78.5K, the maximum refrigeration capacity is 0.26W at 15K and 0.92W at 20K when the input electric power are 174W and 248W respectively, and the minimum no-load temperature obtained is 10.3K, which is a new record on refrigeration temperature for high frequency pulse tube cryocooler reported with SS completely used as regenerative matrix.

A closed-cycle 1 K refrigeration cryostat

A 1K closed-cycle cryostat has been developed to provide continuous cooling to a photon detector below 2K. A two-stage 4K pulse tube cryocooler is used to liquefy evacuated vapor from a 1K pumping port to form a closed-cycle refrigeration loop. A 1K instrumentation chamber, attached to the 1K cooling station, is designed to operate with helium inside and provide more uniform cooling. The design of the cryostat has no direct mechanical contact between the pulse tube cryocooler heat exchangers and the 1K cooling station resulting in almost no vibration transfer to instrumentation chamber. The cryostat can reach a no-load temperature of 1.62K and provide 250mW cooling power at 1.84K.

Theoretical and experimental investigations on Stirling-type pulse tube cryocoolers with U-type configuration to achieve temperature below 20 K

To achieve lower temperatures is a subject of recent research and development activities in the field of pulse tube cryocoolers. To reach a temperature of 20 K, multi-staging is necessary in Stirling-type pulse tube cryocoolers. In the present work, Sage software is used to design a three-stage gas-coupled as well as thermal-coupled pulse tube cryocooler. A single-stage and a two-stage pulse tube cryocoolers are developed, tested and are coupled by a thermal link to build up a three-stage thermal-coupled pulse tube cryocooler. The lowest temperature of 19.61 K is obtained with a cooling capacity of 220 mW at 30 K at the third stage operating at 17 bar charge pressure and 68 Hz frequency. The phase-shifting mechanism used is a double inlet valve at the third stage while the inertance tube is used for the other stages.

Performance of a precooled 4 K Stirling type high frequency pulse tube cryocooler with Gd2O2S

The efficiency of 4 K Stirling type pulse tube cryocoolers (SPTCs) is rather low due to significant regenerator losses associated with the unique properties of helium around 4 K and the high operating frequencies. In this paper, regenerator performance at liquid helium temperature regions under high frequencies is investigated based on a single-stage SPTC precooled by a two-stage Gifford-McMahon type pulse tube cryocooler (GMPTC). The 4 K SPTC used a 10 K cold inertance tube as phase shifters for better phase relationship between pressure and mass flow. The effect of the operating parameters, including frequency and average pressure on the performance of the 4 K SPTC, was investigated and the first and second precooling powers provided by the GMPTC were obtained. To reduce the regenerator heat transfer losses, a multi-layer regenerator matrix, including Gd2O2S (GOS) and HoCu2, was used instead of a single-layer HoCu2 around 4 K. A theoretical and experimental comparison between the two types of regenerator materials was made and the precooling requirements for a regenerator operating at high frequencies to reach liquid helium temperatures were given, which provided guidance for the design of a three-stage SPTC.

4 K high frequency pulse tube cryocooler used for terahertz space application

Terahertz (THz) frequency region, defined from 0.1 to 10 THz, is an important frequency band for radio astronomy and atmospheric science. As NbN Superconductor-Insulator-Superconductor (SIS) mixers used for terahertz detection, which are studied by the Purple Mountain Observatory (PMO), Chinese Academy of Sciences (CAS), work at 8-10 K, and require condition of micro vibrations, its astronomical observation in aerospace is limited by suitable refrigeration method. 4 K high frequency pulse tube cryocooler developed by Key Laboratory of Space Energy Conversion Technologies (SECT), Technical Institute of Physics and Chemistry (TIPC), CAS, offers an opportunity for the application of SIS mixers. This article introduces the progress of the two-stage high frequency pulse tube cryocooler researched by TIPC. The cryocooler has reached a no load temperature of 4.5 K which is the lowest temperature for this kind of cryocooler reported so far. The successful coupling between the THz component and the high frequency pulse tube cryocooler lays a solid foundation for space detection in the terahertz band.

Investigation of DC flow effects on a 4K two-stage pulse tube cryocooler

Sumitomo Heavy Industries, Ltd. (SHI) has been continuously developing 4K GM-type pulse tube cryocoolers for cooling superconducting magnets and pre-cooling ultra-low temperature refrigerators, such as dilution refrigerators, etc. In a double-inlet or a 4-valve GM-type pulse tube cryocooler, there is a gas circulation, called DC flow, generated by the pulse tube, the regenerator and the orifice. The performance of a pulse tube cryocooler is strongly dependent on the rate of such kind of flow. It is possible to improve the performance by optimizing the rate. In order to optimize the rate, a bypass line with a small valve is installed between the warm end of the pulse tube and the low pressure side of the compressor. The second stage cooling capacity at 4.2 K was improved by about 0.25 W after optimization of the rate by adjusting the opening of the valve. The details of the experiment results will be reported in this paper.

A modified two-stage pulse tube cryocooler utilizing double-inlet and multi-mesh regenerator

In this paper a thermally coupled Stirling-type two-stage pulse tube cryocoolers (TSPTC) is studied using a one-dimensional (1-D) CFD code. After validating the results of the simulations, effects of synchronous utilization of multi-mesh regenerator and double-inlet on the performance of the TSPTC are investigated. Results of simulations show that non-oscillating friction factors do not possess sufficient accuracy for calculation of oscillating friction losses in non-porous media. Whereas, using oscillating friction factor of non-porous media leads to sufficient accurate results. According to the results, using multi-mesh regenerator and double-inlet increases the COP and decreases the minimum attainable temperature of the system. It is observed that a minimum temperature of 18.2K is attainable using optimum multi-mesh regenerator and double-inlet; whereas, for a simple TSPTC with a uniform mesh regenerator, a minimum temperature of 26.4K is concluded.

Development of a compact superconducting magnet with a GdBCO magnetic lens

Concentration of a magnetic field has been achieved using a Gd–Ba–Cu–O (GdBCO) magnetic lens. A conduction-cooled compact high-field superconducting magnet with a GdBCO magnetic lens was developed. The magnet possessed a 10-mm room-temperature bore and consisted of two Nb–Ti solenoid coils and a GdBCO magnetic lens, which was installed at the center of the Nb–Ti coils in order to concentrate the background field generated by the Nb–Ti coils. The Nb–Ti coils and the GdBCO magnetic lens were cooled using a two-stage pulse-tube cryocooler. A concentrated magnetic field of 10.3 T was obtained at a background field of 5.6 T provided by the Nb–Ti coils. No degradation was found in the magnet during repeat excitation. The large field gradient generated by the GdBCO magnetic lens is expected to be used for the levitation of diamagnetic materials.

Numerical simulation of a two-stage pulse tube cryocooler considering influence of abrupt expansion/contraction joints

The accuracy of local energy loss correlations in simulation of abrupt expansion/contraction joints under oscillating flow conditions of pulse tube cryocoolers (PTCs) is investigated in this paper. Different friction losses of non-porous media are investigated as well. In this respect, detailed analyses of the flow and heat transfer in various components of a two-stage PTC under oscillating flow conditions are carried out by a developed 1-D code and also FLUENT software. Comparison of 2-D and 1-D simulations results shows that steady friction factors do not possess sufficiently accurate predictions of losses under oscillating flow conditions. Whereas, oscillating friction factors and steady local energy loss coefficients are successful in calculating of losses under oscillating flow conditions of the PTCs. Furthermore, considering flow streamlines in all components of the PTC, 2-D flow effects occurring in the abrupt expansion/contraction joints of the pulse tube sections with small aspect ratios (length to diameter ratio) reduces the accuracy of the supplied coefficients results in 1-D CFD code.

Study of mass flow distribution between stages in a two-stage pulse tube cryocooler capable of 1.1 W at 4.2 K

The mass flow distribution among stages is important for design and optimization of multi-stage cryocoolers, which has been seldom investigated due to the complicated mutual interference among stages. The cooling performance’s dependence on operating parameters was investigated in a home-made separate two-stage pulse tube cryocooler (PTC), in which mass flow to each stage can be conveniently adjusted. The numerical study revealed the dependence of cooling performance of the second stage on mass flow rate and precooling temperatures. The experiments with different mass flow rates were performed and results agreed well with simulation. Cooling power of 0.7 W at 4.2 K was obtained with single-compressor and mass flow rate of 3 g s−1 on the second stage; in the two-compressor driving mode, 1.1 W at 4.2 K was achieved with input power of 11.7 kW, which is the largest cooling power ever obtained at liquid helium temperatures in a separate PTC.

Investigations of a two-stage pulse tube cryocooler operating down to 2.5 K

A two-stage pulse tube cryocooler (PTC) which produces a no-load temperature of ∼2.5 K in its second stage at an operating frequency of 1.6 Hz has been designed and fabricated. The second stage of the system provides a refrigeration power of ∼250 mW at 5.0 K. The system uses stainless steel meshes (mesh size 200) along with lead (Pb) granules and combinations of Pb, Er3Ni, and HoCu2 as the first and second stage regenerator materials, respectively. Experimental studies have been carried out on different pulse tube configurations by varying the dimensions of the pulse tubes and regenerators to arrive at the best one, which leads to the lowest no-load second stage cold head temperature. Using this configuration, detailed experimental studies have been conducted by varying the volume percentage ratios of the second stage regenerator materials such as HoCu2, Er3Ni, and Pb (with an average grain size of ∼250 μm). This article presents the results of our experimental studies on cryocoolers with the regenerator material arranged in layered structures. Comparative studies have also been presented for specific cases where the regenerator materials are arranged as a homogeneous mixture in the second stage. The experimental results clearly indicate that the design of PTCs should use only layered structures of regenerator materials and not homogenous mixtures.

8 T cryogen free magnet with variable temperature space

A conduction cooled 8 T superconducting magnetic system with variable temperature insert is developed and tested. The cryomagnetic system is based on a commercial two-stage pulse tube cryocooler with cooling power of 1W at 4.2 K. The compact superconducting magnet is manufactured from NbTi wire and impregnated with epoxy resin by "wet" technology. The clear diameter of variable temperature space is 20 mm. The system provides temperature range of 5.5-300 K. The variable temperature space is filled by low pressure helium gas. To eliminate the overheating of the magnet at high temperatures the heat switch is used in thermal coupling between variable temperature space and the 4K stage. The system design, manufacturing and test results are presented.

A two-stage Stirling-type pulse tube cryocooler with a cold inertance tube

A thermally coupled two-stage Stirling-type pulse tube cryocooler (PTC) with inertance tubes as phase shifters has been designed, manufactured and tested. In order to obtain a larger phase shift at the low acoustic power of about 2.0 W, a cold inertance tube as well as a cold reservoir for the second stage, precooled by the cold end of the first stage, was introduced into the system. The transmission line model was used to calculate the phase shift produced by the cold inertance tube. Effect of regenerator material, geometry and charging pressure on the performance of the second stage of the two-stage PTC was investigated based on the well known regenerator model REGEN. Experimental results of the two-stage PTC were carried out with an emphasis on the performance of the second stage. A lowest cooling temperature of 23.7 K and 0.50 W at 33.9 K were obtained with an input electric power of 150.0 W and an operating frequency of 40 Hz.