Gifford-McMahon Cycle Research Articles

Investigations on Thermodynamic Processes of a Novel Pneumatic Drive Asymmetric Gifford-McMahon Cycle Cryorefrigerator

Abstract In this paper, a numerical and experimental investigation is conducted on a novel pneumatic-drive asymmetric Gifford-McMahon cycle cryorefrigerator (GMCR). In the pneumatic-drive asymmetric Gifford-McMahon cycle cryorefrigerator, the duration of the assistance space exhaust process is kept higher than that of the assistance space intake process. Therefore, the displacer moves faster near the lower dead center (LDC) and slower near the upper dead center (UDC) inside the expander cylinder. The numerical model solves the governing equations of the refrigerant and dynamics of free-floating displacer iteratively to illustrate the refrigeration mechanism. Additionally, the model computes the performance parameters of the cryorefrigerator like refrigerating capacity and specific refrigerating capacity. By adopting the numerical model, the impact of the loitering time (LT) on the thermodynamic processes is elaborated. It is perceived that both refrigerating capacity and specific refrigerating capacity reduces with an increase in the loitering time. The experimental cooling characteristics are studied for different values of discharge to suction pressure ratios of helium compressor.

Thermo-hydrodynamic analysis and optimal design of a GM cycle cryorefrigerator using response surface methodology and particle swarm optimization

In this investigation, the response surface methodology is implemented to analyze the influences of high and low pressure of the compressor, frequency and waiting time of the rotary valve on the cooling capacity and COP of Gifford-McMahon (GM) cryorefrigerator. A one-dimensional numerical model based on finite volume discretization method (FVM) of the governing equations is employed to calculate the cooling capacity and COP of the Gifford-McMahon cryorefrigerator. Analysis of variance (ANOVA) is performed to visualize the impact of the aforementioned input parameters on both cooling capacity and COP. Finally, the particle swarm optimization (PSO) method is opted to optimize the regression equations so obtained from the response surface analysis, to maximize the cooling capacity and COP of the Gifford-McMahon cryorefrigerator. Results reveal that both COP and cooling capacity are not able to produce maximum performance at a particular combination of those input parameters. At a lower pressure ratio, the COP is maximum, while at a higher pressure ratio the cooling capacity is maximum. Furthermore, at a nominal value of waiting time, the cooling capacity is maximum and a higher value of waiting time the COP is maximum. It is observed that, after optimizing the parameters by PSO, the cooling power increases by 11.3% and COP increases by 6.43%.

Soft x-ray spectroscopic endstation at beamline 08U1A of Shanghai Synchrotron Radiation Facility.

A spectroscopic endstation with magnetic field, voltage, and low temperature control has been installed and commissioned at the soft X-ray beamline 08U1A of Shanghai Synchrotron Radiation Facility, which can obtain a magnetic field up to ±0.53 T, applied current and bias voltage, and cryogenic temperatures down to 14 K with a Gifford-McMahon cycle cryocooler. The endstation can perform soft X-ray absorption spectroscopy methods including total electron yield, fluorescence yield, and X-ray excited optical luminance. Combined with an elliptically polarized undulator and the in situ conditions, the endstation can effectively perform X-ray magnetic circular and linear dichroism experiments in the soft X-ray range between photon energies of 250 and 2000 eV.

SPINS-IND: Pellet injector for fuelling of magnetically confined fusion systems.

Using a Gifford-McMahon cycle cryocooler based refrigeration system, a single barrel hydrogen pellet injection (SPINS-IND) system is indigenously developed at Institute for Plasma Research, India. The injector is based on a pipe gun concept, where a pellet formed in situ in the gun barrel is accelerated to high speed using high pressure light propellant gas. The pellet size is decided by considering the Greenwald density limit and its speed is decided by considering a neutral gas shielding model based scaling law. The pellet shape is cylindrical of dimension (1.6 mm ℓ × 1.8 mm φ). For pellet ejection and acceleration, a fast opening valve of short opening duration is installed at the breech of the barrel. A three-stage differential pumping system is used to restrict the flow of the propellant gas into the plasma vacuum vessel. Diagnostic systems such as light gate and fast imaging camera (240 000 frames/s) are employed to measure the pellet speed and size, respectively. A trigger circuit and a programmable logic controller based integrated control system developed on LabVIEW enables to control the pellet injector remotely. Using helium as a propellant gas, the pellet speed is varied in the range 650 m/s-800 m/s. The reliability of pellet formation and ejection is found to be more than 95%. This paper describes the details of SPINS-IND and its test results.

A cryogen-free low temperature scanning tunneling microscope capable of inelastic electron tunneling spectroscopy.

The design and performance of a cryogen-free low temperature scanning tunneling microscope (STM) housed in ultrahigh vacuum (UHV) are reported. The cryogen-free design was done by directly integrating a Gifford-McMahon cycle cryocooler to a Besocke-type STM, and the vibration isolation was achieved by using a two-stage rubber bellow between the cryocooler and a UHV-STM interface with helium exchange gas cooling. A base temperature of 15 K at the STM was achieved, with a possibility to further decrease by using a cryocooler with higher cooling power and adding additional low temperature stage under the exchange gas interface. Atomically sharp STM images and high resolution dI/dV spectra on various samples were demonstrated. Furthermore, we reported the inelastic tunneling spectroscopy on a single carbon monoxide molecule adsorbed on Ag(110) surface with a cryogen-free STM for the first time. Being totally cryogen-free, the system not only saves the running cost significantly but also enables uninterrupted data acquisitions and variable temperature measurements with much ease. In addition, the system is capable of coupling light to the STM junction by a pair of lens inside the UHV chamber. We expect that these enhanced capabilities could further broaden our views to the atomic-scale world.

Engineering and science highlights of the KAT-7 radio telescope

The construction of the KAT-7 array in the Karoo region of the Northern Cape in South Africa was intended primarily as an engineering prototype for technologies and techniques applicable to the MeerKAT telescope. This paper looks at the main engineering and scien- tific highlights from this effort, and discusses their applicability to both MeerKAT and other next-generation radio telescopes. In particular we found that the composite dish surface works well, but it becomes complicated to fabricate for a dish lacking circular symmetry; the Stir- ling cycle cryogenic system with ion pump to achieve vacuum works but demands much higher maintenance than an equivalent Gifford-McMahon cycle system; the ROACH (Recon- figurable Open Architecture Computing Hardware)-based correlator with SPEAD (Stream- ing Protocol for Exchanging Astronomical Data) protocol data transfer works very well and KATCP (Karoo Array Telescope Control Protocol) control protocol has proven very flexible and convenient. KAT-7 has also been used for scientific observations where it has a niche in mapping low surface-brightness continuum sources, some extended HI halos and OH masers in star-forming regions. It can also be used to monitor continuum source variability, observe pulsars, and make VLBI observations

Numerical simulation and experimental investigation of a novel Scotch yoke for a Gifford-McMahon cryocooler

A novel Gifford-McMahon (GM) cycle, called an asymmetric GM cycle, is proposed. In an asymmetric GM cycle, the displacer moves slowly when it is adjacent to the upper dead point but moves rapidly when it is adjacent to the lower dead point. Therefore, the expansion process is longer, while the discharging process is shorter than in a conventional GM cycle. Meanwhile, the duration of the charging process can be kept the same as that in a conventional GM cycle. Accordingly, the phase shift between the pressure and the displacement can be improved, and the mass flow rate into the expansion space can also be increased. Therefore, the P-V work and the cooling capacity can be increased. To implement the GM cycle, a novel Scotch yoke was invented. In the Scotch yoke, there is a concave part at the upper center of the slide groove and a convex part at the lower center of the slide groove. The effect of the Scotch yoke has been confirmed by numerical simulation and experimental investigation. With a conventional Scotch yoke, the cooling capacity was 44 W at 37.4 K at the first stage and 1.0 W at 3.94 K at the second stage. With a novel Scotch yoke, the cooling capacity was 44 W at 35.9 K at the first stage and 1.0 W at 3.96 K at the second stage. The cooling capacity at the first stage at 40 K was improved by about 10%, from 51.5 W to 57.3 W.

Test of a Conduction-Cooled, Prototype, Superconducting Magnet for a Compact Cyclotron

A 208-mm inner diameter, 62-mm-tall, wind-and-react Nb3 Sn prototype magnet was tested to demonstrate its suitability for use in a compact superconducting cyclotron. The magnet and its 270 kg iron return yoke were cooled together by conduction using a 2-stage Gifford-McMahon cycle refrigerator. This paper presents thermal, electrical and electromagnetic data collected during the tests. Although the radiation shield for the assembly cooled to 47 K within one day, a total of nine days were needed to cool the magnet assembly to below 4 K, at an ultimate heat load of 0.2 W. The dominant heat load at each stage of the cold head was due to thermal conduction along the current leads. The coil was charged without quench to 211 A, generating a pole tip magnetic induction of 3 T. The test demonstrates the technical feasibility to design, manufacture and operate compact superconducting cyclotron magnets at currents in excess of 200 A. The results are being used to improve the design for future high-field, conduction-cooled superconducting cyclotrons.

A Review of Refrigeration Methods in the Temperature Range 4–300 K

In this paper, a comprehensive review of the principles of different refrigeration methods covering the temperature range from 4 K to 300 K is presented. The methods covered are based on steady state systems, such as the Carnot cycle, the vapor compression cycles: basic, cascade, and mixed gas refrigeration cycles, and the recuperative type cryocooler cycles: Joule–Thomson cycle, Brayton cycle, and Claude cycle, and periodic systems such as the regenerative type cryocooler cycles: Stirling cycle, pulse tube cycle, and Gifford–McMahon cycle. The current state of technology and challenges for further improvements are briefly summarized. Some comparisons and assessments are provided for these methods. It is seen that among other things, the selection of a proper refrigeration method is dependent on the following principal factors: (i) the refrigeration capacity required, (ii) the temperature level, and (iii) the application environment. Even though more than one refrigeration method may be suitable for a given application, the selection is further guided by considerations such as cost, reliability, size/compactness, and unit power. An attempt has been made in this paper to (1) present in-depth relevant details to understand the current state of engineering and technology, (2) provide a handy document for refrigeration designers in the industry, and (3) present the guiding principles in the selection of refrigeration methods.

Evaluation of Pulsed-Field Magnetization on a Superconducting Bulk Magnet System Using a 13 K Refrigerator

We developed a small-size superconducting bulk magnet system using a 13 K refrigerator. The industrial applications of bulk magnets demand the miniaturization of the magnet apparatus as well as the enhancement of the magnetic field. Downsizing of the apparatus can be achieved by restricting the magnetizing method to pulsed-field magnetization (PFM). PFM of a high-performance bulk, on the other hand, presents a difficult problem, i.e., large heat generation after the application of pulsed fields suppresses a trapped field. Therefore, a Gifford-McMahon cycle helium refrigerator with low ultimate temperature and large cooling capacity was adopted with the expectation to increase the Jc and quickly remove the heat. In a previous magnetizing test using a GdBa2Cu3O7-x bulk material, a trapped field of 2.76 T was achieved. In this paper, we evaluate a trapped field when applying a magnetic field of constant amplitude with varying temperature, and we used a multi-pulse technique with a stepwise cooling (MPSC) method in which several pulsed fields were applied as a function of the amplitude and temperature to improve the trapped field. We successfully trapped a magnetic field of 3.02 T.

Small-scale hydrogen liquefaction with a two-stage Gifford–McMahon cycle refrigerator

We manufactured a small-scale hydrogen liquefier with a two-stage 10 K Gifford–McMahon cycle (GM) refrigerator. It had a hydrogen tank with the volume of 30 L that was surrounded by a radiation shield. This liquefier continuously liquefied gaseous hydrogen with the volumetric flow rate of 12.1 NL/min. It corresponds to the liquefaction rate of 19.9 L/day for liquid hydrogen. We proposed a simple estimation method for the liquefaction rate and confirmed that the estimation method well explained the experimental result. To evaluate the estimation method, we applied the estimation method to other liquefiers. In case of a liquefier with the GM refrigerator, we confirmed the estimation method was available for predicting the liquefaction rate. However, in case of a liquefier with the pulse tube refrigerator, the results of the estimation indicated small values as compared with the experimental data. We discuss the details about the estimation method of the liquefaction rate for the small-scale liquefiers.

Development of a Small-Size Superconducting Bulk Magnet System Using a 13 K Refrigerator

We developed a small-superconducting bulk magnet system using a 13 K refrigerator. The industrial applications of bulk magnets demand the miniaturization of the magnet apparatus as well as the enhancement of the magnetic field. A Gifford-McMahon cycle helium refrigerator with the ultimate temperature of 13 K at the 2nd stage was adopted, and a bulk material of 60 mm diameter and 20 mm thickness reinforced by a stainless steel ring was located on a cold stage. When a magnetic field of 7.74 T was applied, the trapped field reached 2.76 T, which is the highest ever reported for a pulsed-field magnetization of 60 mm class bulk material.

Development of a small-size superconducting bulk magnet system especially designed for a pulsed-field magnetization

We developed a small superconducting bulk magnet system that was especially designed for a pulsed-field magnetization. The industrial applications of bulk magnets demand the miniaturization of the magnet apparatus as well as the enhancement of the magnetic field. A Gifford-McMahon cycle helium refrigerator with the ultimate temperature of 13 K at the 2nd stage was adopted, and a GdBa 2Cu 3O 7− x bulk material of 60 mm diameter and 20 mm thickness reinforced by a stainless steel ring was located on a cold stage. The total length of the magnetic pole was 570 mm including the refrigerator, therefore, the system could easily be managed. A cooling test and a magnetizing test were carried out using a Hall sensor and thermocouples adhered on the top surface of the material. In the cooling test, the value of 22.5 K at the cold stage was achieved in 3 h. In the magnetizing test, five successive pulsed-fields of the same strength were applied while changing the applied field, and the time responses of the trapped flux density and temperature were measured at each stage. When a magnetic field of 6.97 T was applied, the trapped field reached 2.04 T, which is the highest ever reported for a pulsed-field magnetization of ϕ60 mm class bulk material.

Development of GM cryocooler separate type liquid-helium-free 3He-4He dilution refrigerator system

We developed the new liquid-helium-free dilution refrigerator system, in which the Gifford-McMahon (GM) cycle cryocooler and dilution refrigerator (DR) unit are separated. We obtained the base temperature below 50 mK in this DR system. In usual liquid-helium-free DR systems, the DR unit directly couples with GM-cryocooler in the same vacuum chamber. Therefore the mechanical vibration of GM-cryocooler is hardly removed from DR unit. In order to eliminate the vibration problem, the separated vacuum chamber contacting the GM-cryocooler is connected with the DR unit chamber by the flexible hose with length of about 1 meter. Thin flexible tubes used for circulation of the refrigerant gas and radiation shield are installed in the connection hose. The 4He gas, cooled in the GM-cryocooler unit, transfers to the DR unit throw the thin flexible tubes. After cooling the DR unit, the gas returns to GM-cryocooler unit with cooling of the radiation shield. We expect that our separate-type dilution refrigerator becomes a useful piece of apparatus for the low temperature experiments.

Liquid hydrogen and helium targets for radioisotope beams at RIKEN

Compact liquid hydrogen, deuterium, and helium targets were constructed for radioisotope beam experiments at RIKEN. Hydrogen, deuterium, or helium gas is liquefied by a Gifford–McMahon cycle refrigerator instead of being supplied as a cryogenic liquid. The liquefied gas is accumulated in a target cell placed at the center of a γ -ray detector array. The targets were operated stably in several experiments.

The design and performance of a Bi-2223/Ag magnet cooled by a single-stagecryocooler

The design and fabrication of a split coil Bi-2223/Ag tape superconducting magnet cooledby a single-stage cryocooler is presented. The magnet consists of six double-woundpancakes impregnated by epoxy resin with inner diameter 50 mm and outer diameter98 mm. Critical currents of individual pancakes, double pancakes and the whole magnet aremeasured, calculated and discussed. The magnet’s performance was tested at liquid heliumand nitrogen temperatures as well as at solid nitrogen temperatures and cooled by anAL230 single-stage Gifford-McMahon cycle cryorefrigerator. The measured magnetcurrents are compared with those estimated by calculations using short sample data.

Design of a 800 kJ HTS SMES

In the context of a DGA (Delegation Generale pour l'Armement) project, we have designed and are going to build a 800 kJ SMES. It is based on Bi-2212 PIT tapes from Nexans operating at 20 K. Their engineering current densities exceed 300 MA/m/sup 2/ at 20 K and 5 T making them excellent candidates. The coil consists in 26 stacked pancakes (O = 814 mm; h = 182 mm). The conductor is made of 4 soldered tapes or 3 soldered tapes + one stainless steel tape depending on its location inside the coil. The stainless steel significantly reinforces the conductor. The conductor is insulated by Kapton. To make the cryogenics very transparent and easy for the SMES user, the coil is conduction cooled using a large capacity Gifford-McMahon cycle cryocooler. The SMES design is presented as well as some qualification tests (critical stresses, connections, etc.) for the key issues of the project.

Development of pellet injector system for large helical device

A multi-pellet injector system has been developed as a fundamental fueling tool for the Large Helical Device (LHD). Since a primary goal of the LHD project is demonstration of steady-state high-temperature plasmas, highly reliable and reproducible performance is prerequisite for the LHD pellet injector. The helium Gifford-McMahon (GM) cycle cryogenic refrigerator and conventional pipe-gun mechanism have been employed along with these requirements. Since the triple point temperature of hydrogen is lower than those of isotopes; deuterium and tritium, a careful and steady temperature control is necessary in pellet formation. The amount of propellant gas has been minimized by small reservoir to reduce heat load and inflow into the plasma vacuum chamber. Both robustness and flexibility have been realized by using the programmable logic controller combined with GUI on WindowsNT. The pellet injector has demonstrated continuous hundreds of injection without any fail and has been applied for the LHD experiment successfully.

Evaluation of the Refrigeration in the Gifford-McMahon-Cycle Refrigerator Based on the Thermoacoustic Theory

We have measured the refrigeration of the Gifford-McMahon-Cycle (G-M) refrigerator by using Pb, Er3Ni and NdAg as regenerator materials. The magnetic intermetallic compounds Er3Ni and NdAg exhibit a specific heat anomaly corresponding to the magnetic ordering at 7 and 22 K, respectively and possess a larger volumetric specific heat at low temperatures than that of the conventional regenerator materials Pb. We analyzed how the performance of the refrigerator is influenced by the differences in the specific heat of the regenerator materials based on the Tominaga thermoacoustic theory. We found that the refrigeration performance, as well as the lowest temperature reached in a given G-M refrigerator, is determined by the ratio of the specific heat of the regenerator material over that of the helium gas, and the volume expansion coefficient and mean temperature of the helium gas. We can predict the lowest temperature attainable by a given regenerator material in the ordinary G-M refrigerator only from the temperature dependence of the product of these parameters.

磁性Ｓｂ化合物の蓄冷材応用

In order to obtain high regenerative effectiveness, the heat capacity of the regenerator materials must be larger than that of helium, which is used as the working gas. For a magnetic regenerator material to be effective in the low temperature range, its transition temperature must be within the range in which the helium regenerative operation is performed.Materials with different heat capacities are arranged in multi-layers in a regenerator to obtain higher regenerative efficiency. The relative effectiveness of multi-layer regenerators for liquefied helium was analyzed by computer simulation and experimental results. New materials, including heavy rare-earth and antimony (Sb) compounds, were used as the magnetic regenerator materials. Antimony compounds have especially sharp single-phase transitions in the low temperature range. In this study, the central results were the measured heat capacities of HoSb and DySb, which are anti-ferromagnetic materials with large spin values in the low temperature range.The relation between refrigeration capacity and regenerative effectiveness was investigated when these multi-layer regenerative materials were packed into the second stage of a Gifford-McMahon cycle cryorefrigerator.