Gifford-McMahon Cryocooler 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.

Optimal Leveraging of a Gifford-McMahon Cryocooler’s Regenerative Cooling Power for SNSPD Applications

Superconducting nanowire single photon detectors (SNSPDs) offer unparalleled efficiency, minimal dark count rates, and picosecond jitter, making them ideal for single photon detector applications across the visible to mid-IR spectrum. A common cryogenic system used to reach these detectors’ optimal operating temperatures (>1 K) consists of Sumitomo’s compact RDK101 Gifford McMahon Cryocooler (GMC) running on an Zephyr air cooled compressor, coupled with a helium four (4He) adsorption stage. In this work, our aim is to provide measurements of the RDK101 GMC second stage regenerator tube cooling power at several locations along its length. We then characterise the performance of the adsorption cooler with heat loads applied to the regenerator tube. Our measurements demonstrate that heat loads of 1.2 W can be intercepted at the tube’s section near the GMC’s first cooling stage, with a negligible effect on the performance of the adsorption cooler. The thermal conductivity of yellow brass coaxial was characterised from 4 K to 40 K. Here we show that the heat load from 64 coaxial cable can be optimally intercepted with the defined regenerator cooling power. These results indicate that a 1024-pixel SNSPD array using a 32x32 row column multiplexing architecture could be successfully implemented in this cryogenic platform.

High Efficiency Operation of a 4K-Gifford-McMahon Cryocooler without Rotary Valve with a Metal Bellows Compressor

Traditional Gifford-McMahon cryocoolers are operated with an integrated rotary valve which regulates the compressed Helium supply and return into and from the cold head. Theory predicts that about 50% of the input energy is lost in this rotary valve [1]. In this work we removed the rotary valve from a Sumitomo RDK-101G cold head and drove the Gifford-McMahon cryocooler in Stirling-mode directly with a slow-moving metal bellows compressor at around 1.2Hz. We could demonstrate that the energy efficiency of the cryocooler system improves by almost 50%. As a result, we were able to operate this cold head with 650W of total electrical input power with a cooling power of 140mW at 4.2K on the second stage and no-load temperatures of below 40K on the first stage. This corresponds to a COP of 215mW/1000W which one of the highest COPs reached for small and medium size 4K GM and pulse tube cryocoolers.

Development of a 5 W/4.2 K two-stage pulse tube cryocooler

The 2.7 W/4.2 K two-stage pulse tube cryocooler (Model PT425) was developed and introduced by Cryomech, Inc. in 2021, which, at the time, was the largest, commercially available, 4 K pulse tube cryocooler. Our newest model, the PT450, has been successfully developed, providing a minimum of 5.0 W at 4.2 K on the 2nd stage with 65 W at 45 K on the 1st stage simultaneously, operating on either 60 or 50 Hz power. The PT450 answers the market’s need for the continuing development of large cryogen-free dilution refrigerators, superconducting magnets, helium liquefiers and other applications requiring large cooling capacities at 4 K.In addition, a new helium compressor (Cryomech CPA3027) has also been developed to provide sufficient helium flow for the PT450 and other large cooling power cryocoolers. This new model also allows multiple cryocoolers to operate on one compressor. The CPA3027 is the largest commercially available helium compressor for the Gifford-McMahon and pulse tube cryocooler market.The system configuration and main cooling performance of the PT450 cold head will be presented in this paper.

High-performance eight-channel system with fractal superconducting nanowire single-photon detectors

Superconducting nanowire single-photon detectors (SNSPDs) have become a mainstream photon-counting technology that has been used in various applications. So far, most multi-channel SNSPD systems, either reported in literature or been commercially available, are polarization sensitive, that is, the system detection efficiency (SDE) of each channel is dependent on the state of polarization of the to-be-detected photons. Here, we report on an eight-channel system with fractal superconducting nanowire single-photon detectors working in the wavelength range of 930-940 nm that all feature low polarization sensitivity. In a close-cycled Gifford-McMahon cryocooler system with the base temperature of 2.2 K, we install and compare the performance of two types of devices: (1) SNSPD, composed of a single, continuous nanowire, and (2) superconducting nanowire avalanche photodetector (SNAP), composed of 16 cascaded units of two nanowires electrically connected in parallel. The highest system detection efficiency (SDE) among the eight channels reaches 96−5+4%, with polarization sensitivity of 1.02 and dark-count rate of 13 counts per second. The average SDE for eight channels for all states of polarization is estimated to be 90 ± 5%. We conclude that both the SNSPDs and the SNAPs can reach saturated, high SDE at the wavelength of interest, and the SNSPDs show lower dark- (false-) count rates while the SNAPs show better properties in the time domain. Using this system, we showcase the measurements of the second-order photon-correlation functions of light emission from a single-photon source based on a semiconductor quantum dot and from a pulsed laser. We believe that our work provides new choices of systems with single-photon detectors combining the merits of high SDE, low polarization sensitivity, and low noise that can be tailored for different applications.

Multidimensional numerical simulation of thermodynamic and oscillating gas flow processes of a Gifford-McMahon cryocooler

Abstract The Gifford-McMahon cryocoolers are considered to be prominent candidates for the cooling of high-temperature superconducting magnets, liquefaction of permanent gases, helium recondensation in magnetic resonance imaging machines, cooling of superconducting quantum interference device, etc. In this paper, multi-dimensional numerical simulation is performed to visualize the oscillating heat and fluid flow processes that happen in a mechanically driven GM cryocooler. Influence of the ideal gas equation and real gas equation of states on the cooling behaviour is explained. The minimum achievable refrigeration temperature of a uniform mesh regenerator is compared with a multi-mesh regenerator. It is noticed that a multi-mesh regenerator produces a lower refrigeration temperature as compared to a uniform mesh regenerator. In addition to this, a one-dimensional simulation is conducted and results are compared with multi-dimensional numerical simulation. The no-load temperature value calculated by the one-dimensional model and multi-dimensional model with ideal gas is lower than that of real gas equations. Additionally, the refrigerating capacity calculated by the one-dimensional model and multi-dimensional model with the ideal gas equation is higher than those of the real gas equation of state.

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.

Development of a cryogen-free sub-3K low-temperature scanning probe microscope by remote liquefaction scheme.

We developed a new scheme for cryogen-free cooling down to sub-3K temperature range and ultra-low vibration level. An ultra-high-vacuum cryogen-free scanning probe microscope (SPM) system was built based on the new scheme. Instead of mounting a below-decoupled cryocooler directly onto the system, the new design was realized by integrating a Gifford-McMahon cryocooler into a separate liquefying chamber, providing two-stage heat exchangers in a remote way. About 10 L of helium gas inside the gas handling system was cooled, liquefied in the liquefying chamber, and then transferred to a continuous-flow cryostat on the SPM chamber through an ∼2m flexible helium transfer line. The exhausted helium gas from the continuous-flow cryostat was then returned to the liquefying chamber for reliquefaction. A base temperature of ∼2.84K at the scanner sample stage and a temperature fluctuation of almost within ±0.1 mK at 4K were achieved. The cooling curves, tunneling current noise, variable-temperature test, scanning tunneling microscopy and non-contact atomic force microscopy imaging, and first and second derivatives of I(V) spectra are characterized to verify that the performance of our cryogen-free SPM system is comparable to the bath cryostat-based low-temperature SPM system. This remote liquefaction close-cycle scheme shows conveniency to upgrade the existing bath cryostat-based SPM system, upgradeability of realizing even lower temperature down to sub-1K range, and great compatibility of other physical environments, such as high magnetic field and optical accesses. We believe that the new scheme could also pave a way for other cryogenic applications requiring low temperature but sensitive to vibration.

A Measuring System for HTS Wires and Coils Properties at Low Temperatures

The use of high temperature superconducting materials (HTS) in various applications, requires knowledge of their critical parameters like critical current, critical magnetic field and critical temperature, in DC applications like high magnetic field generators, superconducting magnetic energy storage system (SMES), magnetic resonance imaging (MRI), magnets for particle accelerators, SC Maglev trains and other applications. Also, these parameters are important for specific properties in alternating current applications like fault current limiters, transformers, generators, motors, and power transmission lines. An important characteristic that needs to be tucked into consideration for AC applications is the power losses that occur in the HTS superconducting materials, which limits the maximum performance that the superconducting materials can attain for these applications. In order to measure these characteristics, which depend on the type of material used, but also on the temperature and other parameters, it is necessary to use an appropriate setup device that allows both obtaining the working temperature range (4.2 K to 300 K and other necessary parameters like high vacuum 10-6 mbar, high current supply (500 A), high magnetic field measurement system (1-10 T), etc. For the cryogenic cooling of the entire system, a closed cycle Gifford-McMahon type cryocooler is used, with two cooling stages, stage I at 50 K and second stage at 4.2 K (liquid Helium temperature). The set-up system used for measurement of the parameters of HTS superconducting materials (YBCO, BSCCO or MgB2) and the various coils made with them, is described in this article together with its functional parameters and some experimental results obtained by testing an YBCO coils system. The maximum generated magnetic flux density was 5 T in the centre of the coils system.

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.

Influence of a Magnetic Field on the Gifford-McMahon Cryocooler of the Liquid Hydrogen Target at the BM@N Facility

Influence of a Magnetic Field on the Gifford-McMahon Cryocooler of the Liquid Hydrogen Target at the BM@N Facility

Thermostructural Analysis of Large Cryopumping Test Facility

To create high and ultra-high vacuum environments in large-size chambers for applications in space research, nuclear fusion, accelerators, etc., vacuum pumps with fast pumping speeds are essentially required. To cater to this need, one promising solution is the cryopump, which offers efficiency, a low cost, and applicability. The Institute for Plasma Research is working to develop large-size cryopumps and to develop performance testing and design validation for such cryopumps. In this paper, the Large Cryopumping Test Facility (LCTF) is conceptualized. It houses a large cryopump designed to achieve the pumping speed of ~50 000 L/s for nitrogen gas. The LCTF includes a dome chamber to make the pumping speed measurements per the American Vacuum Society standard and a hybrid cryopump with a 1250-mm opening diameter. The present work illustrates the configuration of the cryopump and its subsystems. The pump will be cooled by liquid nitrogen (LN2) to an 80-K temperature and a Gifford-McMahon cryocooler for up to a 10-K temperature. Here, a new geometrical concept for the pump is considered where the annulus LN2 bath cools the array panels and baffles and also acts as a radiation shield to protect the 10-K cryopanels from radiation heat load. A detailed investigation of the thermal and structural analysis for the LCTF is discussed to validate the performance of the pump and the robustness of the system.

Development of a prototype superconducting radio-frequency cavity for conduction-cooled accelerators

The higher efficiency of superconducting radio-frequency (SRF) cavities compared to normal-conducting ones enables the development of high-energy continuous-wave linear accelerators (linacs). Recent progress in the development of high-quality Nb$_3$Sn film coatings along with the availability of cryocoolers with high cooling capacity at 4 K makes it feasible to operate SRF cavities cooled by thermal conduction at relevant accelerating gradients for use in accelerators. A possible use of conduction-cooled SRF linacs is for environmental applications, requiring electron beams with energy of $1 - 10$ MeV and 1 MW of power. We have designed a 915 MHz SRF linac for such an application and developed a prototype single-cell cavity to prove the proposed design by operating it with cryocoolers at the accelerating gradient required for 1 MeV energy gain. The cavity has a $\sim 3$ $\mu$m thick Nb$_3$Sn film on the inner surface, deposited on a $\sim4$ mm thick bulk Nb substrate and a bulk $\sim7$ mm thick Cu outer shell with three Cu attachment tabs. The cavity was tested up to a peak surface magnetic field of 53 mT in liquid He at 4.3 K. A horizontal test cryostat was designed and built to test the cavity cooled with three Gifford-McMahon cryocoolers. The rf tests of the conduction-cooled cavity, performed at General Atomics, achieved a peak surface magnetic field of 50 mT and stable operation was possible with up to 18.5 W of rf heat load. The peak frequency shift due to microphonics was 23 Hz. These results represent the highest peak surface magnetic field achieved in a conduction-cooled SRF cavity to date and meet the requirements for a 1 MeV energy gain.

Cooling Capacity Characteristics of Low Power Consumption （2 kW Class） 4 K-GM Cryocoolers

From the COP （Coefficient of Performance） equation, there are two ways to improve the cooling efficiency of cryocoolers: （1） increasing the cooling capacity, and （2） decreasing the electrical input power. In recent years, we have focused on the possibility of method （2） for a 4 K-GM （Gifford-McMahon） cryocooler. In this paper, a 7 kW class compressor, which is commonly connected to a 4 K-GM cold head, was replaced with a low power consumption （2 kW class） compressor. The experiments achieved a measured cooling capacity of 0.95 W at 4.2 K with a cold head reciprocation speed of 36 rpm and a compressor electrical input of 1.9 kW. The calculated COP and the relative Carnot efficiency were 5.0×10-4 and 3.5 %, respectively. A low reciprocating speed was selected to secure sufficient expansion work in the second expansion space. This is an effective method to improve the cooling capacity at 4.2 K by a low power consumption compressor.

Design, construction and performance testing of a 1.5 T cryogen-free low-temperature superconductor whole-body MRI magnet

This work describes the design, construction and testing of a 1.5 T cryogen-free low-temperature superconductor niobium–titanium whole-body magnet with a bore diameter of 850 mm that is suitable for clinical magnetic resonance imaging (MRI) applications. The magnet is actively shielded and passively shimmed to achieve confinement within a 0.5 mT stray magnetic field at 2.5/4 m radial/axial positions and 12.1 ppm field inhomogeneity over a 45 mm diameter of spherical volume. The magnet is conductively refrigerated using a two-stage Gifford–McMahon cryocooler and can be maintained at a steady temperature below 5.7 K during MRI scanning. The MRI scanner assembled with the designed cryogen-free magnet demonstrated stable performance and provided MRI images with good quality and high contrast.

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.

Influence of drive chamber discharging process on non-linear displacer dynamics and thermodynamic processes of a fluidic-driven Gifford-McMahon cryocooler

Abstract Continuous effort is made on Gifford-McMahon cryocoolers (GMC) to amplify its refrigeration power, so they can be used to cool the cryopumps, high Tc magnets and development of efficient small-scale hydrogen liquefiers, etc. The fluidic-driven GMC is considered to be more reliable and prominent candidate than the mechanically-driven GMC due to its structural simplicity and reliability. Nonetheless, cooling mechanism of the fluidic-driven GMC is complicated, as the displacer motion inside the displacer cylinder is simultaneously controlled by the pressure difference between drive chamber and compression/expansion chamber. Different paths of displacer can be traced inside the displacer cylinder for different drive-chamber discharging process, hence, pressure–volume power of compression and expansion chambers, and refrigeration power changes. A theoretical study is conducted in present paper to visualize the influence of drive-chamber discharging process on the thermodynamic characteristics of fluidic-driven GMC for the first time. Thermodynamic cycles are drawn at the expansion chamber of the fluidic-driven GMC for different values of drive-chamber discharging process for two types of valve timing arrangements. Energy and work loss behaviors in different components of the GMC are also analysed. Adequate experimental investigations have also been carried out on a fluidic-driven displacer type GMC to verify the simulation results.

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.