Gifford-McMahon Research Articles

Development of Compact 2K GM Cryocoolers

A compact 2K Gifford-McMahon (GM) cryocooler has been developed for cooling electronic devices, such as Superconducting Single Photo Detectors (SSPD). The heat exchangers, regenerators are optimized with the numerical simulation method developed for 4K GM cryocoolers. After optimizing, the cylinder length is reduced by 85mm compared with a commercial 0.1W 4K GM cryocooler. With no load on the second stage, a temperature of about 2.1K has been achieved. With 1W and 20 mW heat load, the temperature is 44.4K at the first stage and 2.23K at the second stage with an input power of about 1.1kW. And also, it is found that the temperature oscillation decreases as the average temperature decreases. A temperature oscillation of about ±20 mK has been achieved. The object of the project, target specification, and a summary of experiment results will also be introduced in this paper.

Development of Compact Dry 3He-4He Dilution Refrigerator for Transition Edge Sensor Microcalorimeter X-ray Detector Operation on Electron Microscopes

A compact dry 3He- 4He dilution refrigerator (DR) was developed for operation of a superconducting transition edge sensor (TES) microcalorimeter x-ray detector mounted on a transmission electron microscope. A Gifford-McMahon (GM)-type mechanical cryocooler was used as a DR pre-cooler to operate the TES microcalorimeter without consuming liquid helium. To reduce the noise and vibrations generated by the GM cryocooler, the DR was separated from the cryocooler in a split system that allows a remote helium cooling loop to pre-cool the DR. In the DR unit, the dilution components of the still, the heat exchangers, and the cascade pair of mixing chambers were assembled into a compact cylinder. A snout made from an oxygen-free copper rod was attached to the DR mixing chamber for placement of the TES microcalorimeter x-ray detector. The lowest temperature and the cooling power in the mixing chamber were measured to be 87 mK and 20 μW at 100 mK, respectively. The DR unit was shown to maintain the temperature on top of the snout such that it was below the temperature required for multi-pixel-array TES microcalorimeter x-ray detector operation.

Development of a large cooling capacity single stage GM cryocooler

Sumitomo Heavy Industries, Ltd. (SHI) has developed 4K Gifford–McMahon (GM) cryocoolers for various cryogenic fields including Magnetic resonance imaging (MRI) systems. However, for the purpose of cooling high temperature superconductor (HTS) devices, the needs for cryocoolers with a large cooling capacity in the range of 20–30K has been rapidly increasing.Recently, SHI developed a large cooling capacity single-stage GM cryocooler, for HTS applications. A typical cooling capacity is 46/52W at 20K or 85/96W at 30K with 6.9/7.9kW input power at 50/60Hz. The cooling capacity degradation caused by inclination is within 24%.And also, a low mechanical vibration and a low acoustic noise have been achieved because the displacer is driven by a motor instead of a pneumatic force. In addition, the cryocooler does not contain lead as a regenerator material, so it complies with restriction of hazardous substances (RoHS) directive.

The 5.8 T Cryogen-Free Gyrotron Superconducting Magnet System on HL-2A

A 5.8 T cryogen-free superconducting magnet (SCM) system with a warm bore hole of 160 mm in diameter, used for gyrotrons operating in the frequency range from 68 GHz to 140 GHz, is installed on the site of the HL-2A tokamak. The SCM consists of two separate solenoidal magnetic coils connected in series, a 4.2 K Gifford-McMahon (GM) refrigerator, a compressor, a coil power supply and two temperature monitors. The performance, test and preliminary experimental results of this SCM system are described in this paper. The magnetic field distribution was measured along the axis, and a dummy tube was used for adjusting the magnet system. Finally, the magnet was used for the operation of a 68 GHz/500 kW gyrotron, which is part of an electron cyclotron resonance heating (ECRH) system. With an additional auxiliary coil and after adjusting the magnet system, a maximum output power for the ECRH system of up to 400 kW was achieved.

A dry 3He–4He dilution refrigerator for a transition edge sensor microcalorimeter spectrometer system mounted on a transmission electron microscope

A dry 3He–4He dilution refrigerator (DR) was developed for a superconducting transition edge sensor (TES) microcalorimeter installed on a transmission electron microscope. This system could be used for energy dispersive X-ray spectroscopy (EDS) with an excellent energy resolution. A Gifford–McMahon (GM)-type mechanical cryocooler was used as a pre-cooler for the DR to ensure liquid helium was not consumed during operation. To reduce sound and vibrations generated by the GM cryocooler, the DR was separated from the GM cryocooler in a split system. The TES microcalorimeter was glued onto the top of a copper rod referred to as the snout, which was attached to the mixing chamber of the DR. The cooling power in the mixing chamber was 30μW at 105mK. The lowest temperature in the mixing chamber was 74mK, and that at top of the snout was 86mK. An energy resolution of 7.6eV full width at half maximum for Si Kα X-rays of 1.74keV was obtained by TES microcalorimeter EDS performed with the transmission electron microscope.

Magnetic field harmonics measurements of conduction-cooled dipole magnet consisting of four race-track coils wound with coated conductors

To study the influence of coated-conductor magnetization, which is a critical problem when using it in accelerator magnets, we fabricated a few dipole magnets consisting of racetrack coils wound with coated conductors, cooled them using a Gifford-Mcmahon (GM) cryocooler, and measured their magnetic field harmonics (multipole components of magnetic field) using a rotating pickup coil system. We focused on the dipole and sextupole components of the magnetic field. The hysteresis loops of these components were measured at different temperatures. The temporal evolution of these components was measured, while the magnets were excited, and while the magnets were at their remnant states. The temperature dependence of the temporal evolution of the dipole and sextupole components was studied experimentally and numerically.

Design, microfabrication and measurement of cooling arm for fusion energy source application

The novel cooling arm plays an important role in thermal transfer in the production process of fusion energy. Its structure is designed and simulated by a finite element method. The result shows that the structure with two branches can obtain a temperature difference less than 1 mK among the grip surfaces of all the fingers. A (111) crystal orientation silicon is deployed to fabricate the cooling arm, because of its isotropic Young's modulus. The thermal conductivity of this material is measured by a Gifford-McMahon (GM) cooler. The result shows it has large thermal conductivity at cryogenic temperature, which excellently contributes to heat transfer. The cooling arm is obtained by a microfabrication process. With a uniform pattern width mask and optimised deep reactive ion etching process recipe, a nearly 90° vertical sidewall is obtained. The temperature distribution of the cooling arm is also measured by a GM cooler, and the result shows that the maximum temperature deviation is 0.48 mK among the 16 fingers. There is a good agreement between finite element analysis and the experimental result.

Recondensation performance of liquid helium cryostat for a 28 GHz electron cyclotron resonance ion source

Cryostat performance is essential for the stable operation of a superconducting magnet. A closed-cycle liquid helium cryostat was adopted for use for a superconducting electron cyclotron resonance (ECR) ion source by recondensing liquid helium vapor. The goal was to maintain the liquid helium filled reservoir at a constant level without transferring any liquid helium during the normal operation of the ECR ion source. To accomplish this, Gifford-McMahon (GM) refrigerators, which have two cold heads, were installed on the top of the cryostat. The cooling power of the GM cryocooler is 1.5 W at the second stage and 50 W at the first stage. Each stage was connected to the liquid helium reservoir, a radiation shield including high-Tc current lead, and related items. Before commissioning the ECR ion source, a preliminary evaluation of the recondensation performance was carried out with the magnet in partial operation. The design of the cryostat, its fabrication, and the experimental results are reported.

Long-Term Operation of the Superconducting Triplet Quadrupoles With Small Cryocoolers for BigRIPS In-Flight Separator and RI-Beam Delivery Line at RIKEN

We report long-term operation of the superconducting triplet quadrupoles (STQs) with small cryocoolers for the BigRIPS in-flight separator and RI-beam delivery line. Each STQ is cooled by liquid helium bath cooling method with a small stand-alone cryogenic system in which a Gifford-McMahon (GM)/Joule-Thomson cryocooler and a GM cryocooler are mounted on the cryostat. While the GM/Joule-Thomson cryocooler recondenses evaporating helium gas in the helium vessel, the GM cryocooler cools the 70 K shield and current leads by conduction. We operate 21 STQ systems forming beam lines for more than five years. We report on how we maintain cryocoolers without warming up the magnets. Operational experiences including troubles in the long-term operation are also reported.

φ20 cm 室温ボアRE 系5 T 高温超電導マグネットの開発

REBa2Cu3Ox (REBCO, RE = rare-earth) coated conductors are expected to show high performance in superconducting applications because of their high mechanical strength and high current density in magnetic fields. More characteristics data of REBCO coils with larger diameters are required for use of these conductors in practical superconducting applications. We fabricated a cryo-cooled high-temperature superconducting (HTS) magnet, which was composed of 24 pancake coils with an inner diameter of 260 mm, using REBCO coated conductors. The stored energy of the magnet was 426 kJ. The total length of the REBCO coated conductors was approximately 7.2 km. These conductors were laminated with a copper stabilizer and were fabricated by Fujikura Ltd. using ion-beam-assisted-deposition (IBAD) and pulsed-laser-deposition (PLD) methods. Before fabricating the magnet, all pancake coils were evaluated in terms of their V-I characteristics in liquid nitrogen in order to confirm the characteristics without degradation. After the fabrication, the magnet was cooled down to 24 K using a GiffordMcMahon (GM) cryocooler. We were successful in excitation of the magnet up to 5 T. Furthermore, we confirmed that a 1% current reversal of the coil current could stabilize the axial central magnetic field drift of the magnet.

Evaluation of a 5T 2nd Generation High Temperature Superconducting Magnet with a 200-mm-diameter Room Temperature Bore

Abstract REBCO coated conductors are expected to show high performance in superconducting applications, because of their high mechanical strength and high current density in the magnetic field. However, more characteristics data of REBCO magnet with larger diameter are required in order to apply these conductors in practical superconducting applications. In this work, we have succeeded in developing a 5 T cryo-cooled high-temperature superconducting (HTS) magnet, which was composed of 24 pancake coils with an inner diameter of 260 mm, using REBCO coated conductors. The stored energy of the magnet was 426 kJ. The total length of the REBCO coated conductors was approximately 7.2 km. These conductors were fabricated by Fujikura Ltd. using ion-beam-assisted deposition (IBAD) and pulsed laser deposition (PLD) methods. All pancake coils were confirmed the V-I characteristics without degradation in liquid nitrogen before fabricating the magnet. The magnet was cooled down to 24 K by a GM (Gifford-McMahon) cryocooler after the fabrication. The magnet could excite up to 5.0 T in 60 minutes, successfully. Furthermore, we confirmed that 1% current reversal of the coil current could stabilize the axial central magnetic field drift of this magnet.

Gifford-McMahon 冷凍機の2 段目蓄冷器内に挿入された ベークライト棒の効果

A novel regenerator structure for a two-stage Gifford-McMahon (GM) cryocooler is introduced in this paper. The structure has a bakelite rod inserted in the co-axial layout of the 2nd stage regenerator in which lead (Pb) spheres are filled as the regenerator material. Inserting the bakelite rod reduces the Pb weight, leading to a decrease in the heat capacity of the regenerator. To clarify the effect of the bakelite rod, two types of conventional GM cryocoolers with power consumption of 1.3 and 7.3 kW, respectively, are tested at the operating frequency of 1.2 Hz. From the experimental results, the lowest attainable temperature of the 2nd stage rises slightly as a result of reducing the Pb weight which is adjusted by the volume of bakelite rod. However, a reduction of Pb weight by approximately 40% does not affect the deterioration of the cooling power at above 9 K. These two GM cryocooler models show almost the same characteristics. Thus, this novel regenerator structure may be applied to most two-stage GM cryocoolers.

Operating characteristics of a three-stage Stirling pulse tube cryocooler operating around 5 K

A Stirling pulse tube cryocooler (SPTC) operating at the liquid-helium temperatures represents an excellent prospect for satisfying the requirements of space applications because of its compactness, high efficiency and reliability. However, the working mechanism of a 4K SPTC is more complicated than that of the Gifford McMahon (GM) PTC that operates at the relatively low frequency of 1–2Hz, and has not yet been well understood. In this study, the primary operating parameters, including frequency, charge pressure, input power and precooling temperature, are systematically investigated in a home-developed separate three-stage SPTC. The investigation demonstrates that the frequency and precooling temperature are closely coupled via phase shift. In order to improve the cooling capacity it is important to lower the frequency and the precooling temperature simultaneously. In contrast to the behavior predicted by previous studies, the pressure dependence of the gas properties results in an optimized pressure that decreases significantly as the temperature is lowered. The third stage reaches a lowest temperature of 4.97K at 29.9Hz and 0.91MPa. A cooling power of 25mW is measured at 6.0K. The precooling temperature is 23.7K and the input power is 100W.

Optical-Pumping Double-Nuclear-Magnetic-Resonance System with a Gifford–McMahon Cryocooler

We have developed a system for performing optical-pumping and double-resonance NMR of semiconductors simultaneously or sequentially. The components include a cryosystem equipped with a Gifford–McMahon (GM) cryocooler, which cools the samples via thermal contact. The following benefits are derived from this feature. (1) A pickup coil and tank circuits for NMR can be built in a vacuum, which excludes rf discharges and/or arcing (breakdown) occurring in conventional systems employing a helium-gas atmosphere, allowing application of the stronger and more stable rf-pulses required for broad-line double-resonance NMR. (2) Heat around a sample generated by light irradiation can be drained through the thermal connection to a heat anchor, permitting the use of a light-power high enough to achieve large nuclear polarization by optical pumping. (3) A bottom-loading style can be adopted for the installation of a cryostat and a probe to an NMR magnet, allowing a more compact system.

Performance improvement of 2 stage GM-type pulse tube Cryocooler for cryopump

This paper describes experimental study and performance improvement of 2 stage Gifford-McMahon (G-M) type pulse tube cryocooler for cryopump. The objective of this study is to improve the efficiency of 2 stage pulse tube cryocooler for substituting 2 stage G-M cryocooler used in cryopump. The target cooling capacities are 5 W at 20 K and 35 W at 80 K for the <TEX>$1^{st}$</TEX> and the <TEX>$2^{nd}$</TEX> stage, respectively. These values are good cooling capacities for vacuum level in medium size ICP 200 cryopump. Design of the 2 stage pulse tube cryocooler is conducted by FZKPTR(Forschungs Zentrum Karlsruhe Pulse Tube Refrigerator) program. In order to improve the performance of 2 stage pulse tube cryocooler, U-type pulse tube cryocooler is fabricated and connecting tubes are minimized for reducing dead volumes and pressure losses. Also, to get larger capacities, orifice valves and double inlet valves are optimized and the compressor of 6 kW is used. On the latest unit, the lowest temperatures of 2 stage pulse tube cryocooler are 42 K (<TEX>$1^{st}$</TEX> stage) and 8.3 K (<TEX>$2^{nd}$</TEX> stage) and the cooling capacities are 40 W at 82.9 K (<TEX>$1^{st}$</TEX> stage) and 10 W at 20.5 K (<TEX>$2^{nd}$</TEX> stage) with 6.0 kW of compressor input power. This pulse tube cryocooler is suited for commercial medium size cryopump. In performance test of cryopump with 2 stage pulse tube cryocooler, pumping speed for gaseous nitrogen is 4,300 L/s and the ultimate vacuum pressure is <TEX>$7.5{\times}10^{-10}$</TEX> mbar.

SMES용 전도냉각형 고온초전도 자석의 설계, 제작 및 평가

본 논문은 초전도 에너지 저장장치(SMES)용 전도냉각형 고온초전도 자석의 설계, 제작 및 평가에 대해 기술한다. 고온초전도 자석은 황동 안정화재를 갖는 2개의 Bi-2223 다심 선재가 적층된 4-ply 도체로 제작된 22개의 double pancake coil(DPC)로 구성된다. 그리고, 각 DPC는 내경과 외경이 각각 500 mm, 691 mm이고 높이가 10 mm인 2개의 single solenoid coil로 구성된다. 코일 내부의 전기적 손실에 의해 발생된 열의 냉각을 위하여 DPC 사이에 두께 3 mm의 알루미늄 판이 내재된다. 고온초전도 자석은 2단 Gifford McMahon 냉동기에 의해 5.6 K까지 냉각된다. 충전전류가 증가할수록 방전시 고온초전도에서의 최대 온도가 증가 하였다. 충전전류가 360 A일 때 ��치 없이 고온초전도 자석에 1 MJ의 자기에너지가 성공적으로 저장되었다. 본 연구에서는 SMES용 전도 냉각형 고온초전도자석에 대한 열적, 전자기적 특성을 보이고, 본 연구를 통해 얻어진 결과는 전도냉각형 고온초전도자석의 최적설계 및 안정도 평가에 활용될 것이다. This paper describes design, fabrication, and evaluation of the conduction cooled high temperature superconducting (HTS) magnet for superconducting magnetic energy storage (SMES). The HTS magnet is composed of twenty-two of double pancake coils made of 4-ply conductors that stacked two Bi-2223 multi-filamentary tapes with the reinforced brass tape. Each double pancake coil consists of two solenoid coils with an inner diameter of 500 mm, an outer diameter of 691 mm, and a height of 10 mm. The aluminum plates of 3 mm thickness were arranged between double pancake coils for the cooling of the heat due to the power dissipation in the coil. The magnet was cooled down to 5.6 K with two stage Gifford McMahon (GM) cryocoolers. The maximum temperature at the HTS magnet in discharging mode rose as the charging current increased. 1 MJ of magnetic energy was successfully stored in the HTS magnet when the charging current reached 360A without quench. In this paper, thermal and electromagnetic behaviors on the conduction cooled HTS magnet for SMES are presented and these results will be utilized in the optimal design and the stability evaluation for conduction cooled HTS magnets.

Conduction-Cooled Superconducting Magnet With 250 mm Bore Size

A conduction-cooled superconducting magnet was designed, fabricated and tested. A two-stage Gifford-McMahon (GM) cryocooler with the second-stage cooling power of 1.5 W at 4.2 K is used to cool the superconducting magnet from room temperature to 4.2 K. The superconducting magnet has the operating current of 105.5 A, the effective warm bore size of 250 mm, the maximum center field of 4.5 Tesla. The superconducting magnet will be used for the material processing. In this paper, the detailed design, fabrication and test are presented.

Reduction of temperature fluctuation within low temperature region using a cryocooler

Modeling and experiments are performed to decrease temperature fluctuation generated by the periodic motion of the displacer in a Gifford-McMahon (GM) type cryocooler within the low-temperature region. The one-dimensional heat equation allows us to show that thermal diffusivity is an essential factor to achieve much smaller temperature fluctuation, and fiber-reinforced plastic (FRP) with low thermal diffusivity makes it possible to reduce the temperature fluctuation dramatically. Based on the model, experiments are performed to vary the thickness of two FRP dampers, on the cryohead of the cryocooler and on the sample stage. As a result, the FRP dampers enable us to achieve the temperature fluctuations of only 0.7 mK, corresponding to a standard deviation of 0.25 mK, when the sample stage is maintained at 4.2000 K, even if a GM cryocooler is utilized for cooling the temperature, which introduces an initial temperature fluctuation of 282 mK at the cryohead.

Thermal Performance of an Adhesive Bonded Superconducting Multichip Module (MCM) on a Gifford-McMahon Cryocooler

We report the experimental study of the thermal resistance of a flip chip bonded superconducting multichip module (MCM) in a liquid cryogen free environment. A 5×5 mm2 indium-tin bumped superconducting chip was flip chip bonded on a 1×1 cm2 superconducting carrier chip. A non-conductive adhesive was used as an underfill to enhance the robustness of the package. We designed a test bed where the LSCE module was mounted onto the cold head of a Gifford McMahon (GM) cryocooler. The module was conductively cooled down to 4 K and the thermal resistance between the chip and the carrier chip was analyzed. The experimental results showed that for the power dissipation (2 – 5 mW), which is typical for low temperature superconducting electronic LSCE devices, the thermal resistance was 20.1 +/− 1.9 K/W. Thermal model of the current LSCE package was investigated using COMSOL multi-physics. Theoretical estimates showed that for the current package setup the expected thermal resistance of the bump path to be 6.2 K/W. The discrepancy between the model and experimental analysis has been explained due to the presence of voids and inadequate bump contact area. To our knowledge, this is the first such experimental investigation of the thermal performance of adhesive bonded LSCE package on a cryocooler. This experimental analysis is of paramount importance for future trends in single chip and multichip module packaging of LSCE devices.

High-precision temperature control and stabilization using a cryocooler

We describe a method for precisely controlling temperature using a Gifford-McMahon (GM) cryocooler that involves inserting fiber-reinforced-plastic dampers into a conventional cryosystem. Temperature fluctuations in a GM cryocooler without a large heat bath or a stainless-steel damper at 4.2 K are typically of the order of 200 mK. It is particularly difficult to control the temperature of a GM cryocooler at low temperatures. The fiber-reinforced-plastic dampers enabled us to dramatically reduce temperature fluctuations at low temperatures. A standard deviation of the temperature fluctuations of 0.21 mK could be achieved when the temperature was controlled at 4.200 0 K using a feedback temperature control system with two heaters. Adding the dampers increased the minimum achievable temperature from 3.2 to 3.3 K. Precise temperature control between 4.200 0 and 300.000 K was attained using the GM cryocooler, and the standard deviation of the temperature fluctuations was less than 1.2 mK even at 300 K. This technique makes it possible to control and stabilize the temperature using a GM cryocooler.