Two-stage Gifford-McMahon Cryocooler Research Articles

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.

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.

Quench Analysis of 5.8 T Conduction-Cooled Superconducting Magnet

A 5.8 T conduction-cooled superconducting magnet has been developed in the Institute of Plasma Physics Chinese Academy of Sciences (ASIPP). The magnet has a warm bore diameter of 190 mm. It consists of four concentric closely compacted NbTi coils with an asymmetrical arrangement. A two-stage Gifford-McMahon cryocooler used to cool down the magnet from room temperature to 4.2 K. The magnet operated in the driving model with total energy 0.63 MJ and the temperature margin only 1 K at operating current 114.5 A, the maximum field up to 7.7 T. A quench protection circuit was designed to avoid damage during the quenching process. The protection circuit has adopted coil subdivision method. A 3D thermal, electromagnetic and electrical circuit coupled model was established to simulate the quenching process. The coupled model was solved by commercial finite element method (FEM) program. Using this model, the hot spot temperature of the coils, the variation of the current, and the voltage can be attained. The effect of a different number of coil subdivision on the quenching process has been studied.

Characterization of MEMS Acoustic Sensors and Amplifiers in Cryogenic Fluids for Quench Detection Applications in HTS CICC

An acoustic quench detection method utilizing MEMS (Micro Electro-Mechanical System) acoustic sensors is proposed. To investigate this method, a commercially available MEMS piezoelectric microphone, the Vesper VM1000, and two types of second stage amplifiers, using either an OPA344 or a LMH6629 based amplifier circuit, were characterized at cryogenic temperatures in helium gas. The MEMS microphones were in their original package with an integrated preamplifier. The tests were performed inside a two-stage Gifford-McMahon cryocooler from room temperature down to 60 K, at static pressures between 1.2 and 1.4 bar in gaseous helium, over the frequency band from 100 Hz to 10 kHz. Second stage amplifiers were needed to achieve signal to noise ratios approaching the manufacturer specified operating levels. The OPA344 based amplifier reduced in gain by >55 dB below 230 K, while the LMH6629 based amplifier performed well down to 60 K. The MEMS microphones appear to perform acoustic measurements down to 165 K but with some reduction in sensitivity down to 60 K. An acoustic model of the cryocooler plane wave tube calibration setup is developed and used to calibrate the microphone despite the presence of a significant thermal gradients down the plane wave tube.

Design and Evaluation of Prototype High-Tc Superconducting Linear Synchronous Motor for High-Speed Transportation

We developed a prototype of a high-Tc superconducting (HTS) linear synchronous motor (LSM) and evaluated its operational performances to obtain the preliminary design data for a test vehicle having a speed of 518.4 km/h. The HTS electromagnet was fabricated using a non-insulated (NI) GdBCO HTS coil, which was designed to produce a magnetomotive force of 300 kA-turns at a cooling temperature of 20 K. A two-stage Gifford-McMahon cryocooler was used to cool the electromagnet. The prototype was tested up to 2.7 kN sufficient to the required thrust of the test vehicle. The thrust characteristics shown by changing the operating conditions were also consistent with the simulation results. The HTS electromagnet was successfully operated during the test, and there was no fault in the NI HTS coils. Finally, we confirmed the design feasibility of HTS LSM for a test vehicle.

Quench Phenomena in a Conduction-Cooled Fast-Ramping High Temperature Superconducting Magnet

A conduction-cooled HTS magnet was tested to produce an AC magnetic field up to 4 T for an adiabatic demagnetization refrigerator (ADR). Quench detection was conducted by measuring the voltages in the conductor, and the protection system was constructed with an external dump resistor. The magnet, which is equipped with extensive copper thermal drains, was conduction-cooled by a two-stage Gifford-McMahon cryocooler to approximately 6 K. The magnet succeeded to stably generate an alternating magnetic field between 0 and 3.5 T at a ramp rate of 229 mT/s without any pre-quench signs; however, in the case of a maximum 4 T experiment, a quench occurred, and the magnet was permanently damaged. The quench location was identified as the place where the highest perpendicular field from the magnet was generated. It is speculated that the already-formed normal zone before quench grows very fast during the dump process, and part of the magnetic energy is dissipated in this normal zone, causing the excessive temperature rise of the conductor. The detailed experimental results are presented and discussed.

30 K to 2 K vibration free remote cooling systems

Absolut System has built a 30 K and a 10 K remote Helium cooling loops used as a vibration free cooling source, respectively for IR detectors electro-optical characterization test bench and two-stage optical cryostat. The circulation loops are based on a by-passed flowrate from either a two-stage Gifford–McMahon cryocooler or a two-stage Pulse Tube cryocooler. Dedicated compact and high efficiency tubes & shell heat exchangers have been designed and produced for the recuperators. The paper describes the design and the performances of the vibration free cooling system produced. The current work towards a 4 K low vibration cooling source will be introduced as well.

Cryocooled Josephson standards for AC voltage metrology

The Josephson effect is worldwide used as a basis for constant reference voltages in national metrological institutes and in calibration laboratories of industry. Research on Josephson voltage standards is aiming at a fundamental change also in the metrology of the volt for AC and arbitrary waveforms: programmable Josephson voltage standards converting a digital code into a quantum-accurate stepwise waveform are already available in primary laboratories and even more advanced standards for converting sub-nanosecond binary coded pulses into any arbitrary signal with quantum accuracy are now actively developed and tested. A new experimental setup based on a two-stage Gifford-McMahon cryocooler has been developed at INRiM for the operation of AC-Josephson voltage standards. Among its distinct features, the possibility of employing both the aforementioned techniques (programmable and pulsed Josephson voltage standards) is particularly interesting. Quantum-based AC voltage sine waves have been synthesized with both programmable and pulse-driven arrays, although their accuracy is still limited by thermal oscillations due to the cryocooler piston motion.

СОВЕРШЕНСТВОВАНИЕ НИЗКОТЕМПЕРАТУРНОЙ СТУПЕНИ КРИОРЕФРИЖЕРАТОРА ГИФФОРДА-МАК-МАГОНА С РЕГЕНЕРАТОРОМ, ЗАПОЛНЕННЫМ ЦЕНОСФЕРАМИ

Creating Gifford-McMahon (GM) cryocoolers for cooling at temperatures below 4,2 K is a quantum leap in the development of techniques for obtaining helium temperatures. The paper provides a comparative analysis of different types of regenerator packing, which allow obtaining temperatures below 4,2 K. The advantages of cenosphere packing filled with helium are shown. Using a wave approach to modelling regenerator operation, we analyzed operation of a two-stage GM cryocooler, having a cooling capacity of 0,2 Watt at the temperature of 4,2 K. Calculated value of the length of the heat exchanger regenerator with the packing from cenosphere for such cryocooler was equal to 320 mm, i.e. substantially bigger than the length of the regenerator packed with intermetallic compounds of rare earth elements. The resulting length value does not exceed a technically possible size of regenerators for GM cryocoolers. Advantages of cenosphere packing can compensate for the increased size of a cryocooler.

Test Apparatus Utilizing a Gifford-McMahon Cryocooler to Measure the Thermal Performance of Multilayer Insulation

A vertical cylindrical calorimeter for measuring the thermal performance of multilayer insulation (MLI) has been developed. Two concentric oxygen-free high-conductivity copper drums are wrapped with sample MLI blankets, and are cooled using a two-stage Gifford-McMahon cryocooler. As the drums are vertically supported, the layer density of the MLI sample is unaffected by gravity. The inner drum is cooled by the 2nd stage of the cooler and is maintained at a temperature of about 6K. The outer drum is maintained at a temperature of about 65K by connecting it to the first stage of the cooler. The heat transfer through the blanket is determined by measuring the temperature difference across the stainless steel thermal resistance tube in a heat-flow meter placed between the drum and the cold finger of the cryocooler. The structure of the calorimeter, the calibration procedure, and results for heat flow through the MLI sample are reported.

Fabrication and Characterization of 4-T/203 mm RT Bore 2G HTS Magnet With No-Insulation Method

We fabricated superconducting magnet using second-generation (2G) high-temperature superconducting wire by SuNAM. Magnetic field strength at the center is 4 T, and room temperature bore diameter is 203 mm. The magnet consists of 30 double pancake coils (DPCs) with the inner diameter of 245 mm and outer diameter of 297 mm. All double pancakes were wound by no-insulation method and performance were tested separately before assemble. Tested DPCs were resistively connected by HTS tape(splice joint), and assembled coil was conduction cooled by a two-stage Gifford-McMahon cryo-cooler to the operating temperature of 8 K. The size of magnet is 452 mm in height. Current, voltage, and field strength were measured as a function of time with various ramping up and down conditions and results were compared with the simulated behavior. The coil generates 4 T when operating current ramped to 205 A by 0.03 A/s without quench. Initial cool down time was 72 h and the measure field homogeneity in 10 mm DSV was 0.015% and 0.012% in radial axis and vertical axis, respectively. The results showed that no-insulation winding method is a possible option for making compact magnet coil with sufficient structural integrity, thermal and electrical stability at the same time. The magnet showed quench at field strength of 4.49 T when ramped with 0.2 A/s to 235 A. The magnet showed same performance after recovery from quench.

Fabrication and Characterization of 3-T/102-mm RT Bore Magnet Using 2nd Generation (2G) HTS Wire With Conducting Cooling Method

A conduction-cooled high-temperature superconducting magnet using 2nd generation HTS wire, which has a room-temperature bore 102 mm in diameter, has been developed and tested up to 3 T with the operating temperature of 20 K. The magnet consists of 22 double pancake coils (DPCs) with an inner diameter of 140 mm and outer diameter of 182 mm. Twenty-two double pancake coils were tested separately at 77 K for checking the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IV</i> -curve. Selected DPCs were resistively connected by HTS tape (Splice joint), and an assembled magnet coil with the size of 182.5 mm diameter and 242 mm in height was conduction cooled by a two-stage Gifford-McMahon cryo-cooler to 20 K. Current, voltage, and field strength were measured as a function of time with various ramping up and down conditions. The resulting performance data of the assembled magnet agreed well with the expectation from FEM simulation. The aimed field homogeneity of 0.1% in 10 mm diameter sphere volume was proved when operating current was 141.6 A at 20 K with central magnetic field intensity of 2.9975 T by hall sensor. The magnetic flux density at center showed nonlinear dependence with ramping current within the range of 0.05 A/sec ~0.15 A/sec because of charging delay. However, saturated magnetic flux density showed the same value of 2.9975 T regardless of ramping rate.

10 V programmable Josephson voltage standard circuits using NbN∕TiNx∕NbN∕TiNx∕NbN double-junction stacks

Using NbN∕TiNx∕NbN∕TiNx∕NbN double-junction stack technology we have demonstrated a programmable Josephson voltage standard chip that operates up to 10.16V output voltage cooled with a two-stage Gifford–McMahon cryocooler. The circuit uses double-junction stacks, where two junctions are fabricated in each stack, in order to integrate 327 680 junctions into a 15.3mm×15.3mm chip. A 1-to-32 microwave distribution circuit is also integrated on the chip. The chip is divided into 22 cells, which perform as an 11-bit digital-to-analog converter. The 21 working cells include 307 200 junctions biased with 16GHz microwaves at 10.2K that generated flat voltage steps with current margins greater than 1mA, which indicates good uniformity of the stacked junctions.

A 350 GHz SIS Receiver on the Nobeyama 10 m Submillimeter Telescope

Abstract We have developed a low-noise submillimeter-wave SIS receiver (320–360 GHz) for a 10 m submillimeter telescope, which was installed at Nobeyama in 2000 February. This receiver and a millimeter-wave SIS receiver are mounted on the ceiling of the Cassegrain receiver cabin of the 10 m telescope. Two curved mirrors couple a shaped Cassegrain beam from the subreflector to mixer horns. The minimum noise temperature measured in front of the receiver was 52 K in double sideband (DSB) at a local oscillator (LO) frequency of 354 GHz, which corresponds to three-times quantum limits ($3h\nu/k_{\mathrm{B}}$). This noise temperature contributions are resolved into the optics, mixer, and IF parts. The temperature ripple of a two-stage Gifford–McMahon cryocooler has been reduced to be 2 mK peak-to-peak at the mixer block with a helium pot temperature stabilizer. Mechanical vibration (30 ${\mu \mathrm {m}}$ peak-to-peak) of the cold head degrades the receiver stability.

磁性蓄冷材を使用した小型冷凍機 磁性蓄冷材を用いたＧＭ冷凍機における蓄冷器内の温度分布および流量分布

A two-stage GM cryocooler is commonly used in many cryogenic systems, such as a cryopump and an MRI. The lowest temperature for a conventional GM cryocooler, however, was limited to about 10K. Recently, magnetic regenerator materials, which have larger heat capacity below 10K than a conventional regenerator material of Pb, enable the GM refrigerator to achieve the liquid helium temperature level. In this temperature range, helium in the GM cryocooler cannot be regarded as an ideal gas. The purpose of this study is to investigate a regenerator, which is operated with non-ideal helium gas. The experimental results of the regenerator performance in a two-stage Gifford-McMahon (GM) cryocooler are described in this paper. Temperatures and pressure in the regenerator were measured and mass flow rate in the regenerator was calculated from these data. The temperature profile, temperature fluctuation and mass flow rate in the regenerator are compared between ideal gas operation and non-ideal gas operation. For ideal gas operation, the temperature profile was smooth and the temperature fluctuations at each positions are almost equal. For non-ideal gas operation, a steep temperature gradient and large temperature fluctuation, which almost covered the temperature difference of the regenerator were observed from the hot end to the middle of the regenerator. From the middle to the cold end, however, both the temperature gradient and the temperature fluctuation were very small. The mass flow rate in the regenerator for ideal gas operation decreased from the hot end to the cold end. For non-ideal operation, the mass flow rate increased. The difference between the regenerator for ideal gas operation and that for non-ideal gas operation was shown clearly.

Signal-to-noise ratio improvement of HTSC bolometers for cryocooler operation using a thermal compensation principle

This paper reports on the reduction of thermal fluctuations in a high T c superconductor (HTSC) bolometer using a compensation technique. The HTSC bolometer consisted of two meander-like YBCO structures separated by a distance of 5 mm on a silicon substrate. A two-stage Gifford-McMahon cryocooler with an additional thermostat was used to cool the samples to a temperature of ≈88 K, with a 5 mK fluctuation peak to peak. A factor of 100 improvement in signal-to-noise ratio was achieved during the compensation experiments.