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The objective for hydrogen as a future energy carrier should be to produce it without emitting additional carbon dioxide into the atmosphere. A very effective process for hydrogen generation based on allotherm steam reforming using energy from biomass is developed and tested in a pilot facility. Excess chemical energy from the process is used to generate superheated steam (>1,200 °C). Steam is the gasification and oxidation agent, energy carrier for the process and supplier of hydrogen molecules, as it reacts with biochar at the bottom of the reactor. The produced synthesis gas has up to 61% of hydrogen. The handling of tars is much easier than in other systems due to the presence of excess steam. A demonstration facility has been designed with an overall efficiency of up to 70%, scaling up the pilot facility. Only waste biomass unsuitable for further usage is utilised, and the conversion rate of biomass to hydrogen is 10:1. [ABSTRACT FROM AUTHOR]

We developed a cryocooler system to reveal the temperature dependence of the quality (Q) factor of high-temperature superconducting (HTS) bulk coil and the power transfer efficiency (PTE) and power handling capability (PHC) of a wireless power transfer (WPT) system using the HTS bulk coil. The measured Q factors of the HTS bulk coil were 9051 at 77 K and 14 050 at 25 K. The measured PTEs and PHCs of the WPT system were 44.2% and 4.48 W at 77 K, and 50.8% and 25.2 W at 25 K. [ABSTRACT FROM AUTHOR]

• A two-stage gas-coupled Stirling/pulse tube refrigerator with a second-stage active phase shifter is developed. • The effect of the active phase shifter on the acoustic power and phase distribution is investigated. • The regulation of the inter-stage refrigeration capacity shift by the active phase shifter phase and amplitude is analyzed. • Experiment results are carried out to verify the theoretical and simulated analyses. The Stirling/pulse tube cryocooler (SPC) is one of the most promising cryocoolers for space applications due to its advantages like high efficiency and long lifetime. The second pulse tube stage is coaxial pneumatically coupled in series with the first Stirling stage. The SPC possesses a distinctive capability to dynamically adjust the inter-stage refrigeration capacity by actively controlling the Stirling displacer in the first stage. This enables the SPC to effectively cater to varying heat loads over time. Nevertheless, the investigation into the regulation mechanism of the second-stage phase shifter on inter-stage refrigeration capacity shift is hindered by the presence of the second-stage passive phase shifter. This manuscript proposes an SPC with a second-stage active phase shifter (APS), which can actively control the phase difference between the pressure wave and mass flow at the second-stage hot end of the pulse tube in real time. The effect of the APS phase and amplitude on the inter-stage refrigeration capacity shift is analyzed using the theoretical and numerical model proven by the experiment. The first experimentally reported SPC with a second-stage APS demonstrates a refrigeration capacity of 0.22 W at 20 K plus 3.11 W at 70 K, requiring a compressor electrical power of 220 W. The SPC achieves a no-load minimum temperature of 13.5 K. [ABSTRACT FROM AUTHOR]

Three distinct thermodynamic analysis models are developed and applied to a renowned cryogenic engine (PPG-102), namely the isothermal model, the ideal Schmidt model, and the ideal adiabatic model. Through a comparative analysis, the theoretical outcomes derived from these models are juxtaposed with the corresponding theoretical results from the existing literature. The comprehensive evaluation of these findings demonstrates significant convergence, with minor deviations primarily attributed to the inherent assumptions underlying each model. The design of the PPG-102 engine is meticulously executed within the Solidworks environment, allowing for the subsequent simulation under operating conditions identical to those of the computational models. Remarkably, the simulation results closely approximate the outcomes of the adiabatic analysis, thus corroborating the validity and effectiveness of this particular model. In this work, the presented models, initially developed for thermal Stirling engines, are augmented and applied to a cryogenics Stirling engine, offering a unique understanding of the workings of this apparatus. [ABSTRACT FROM AUTHOR]

A compact gantry delivering 70-220 MeV protons with fixed field in the superconducting magnets could reduce the cost and improve the adoption of proton therapy. While a number of magnet and cryogenics designs have been proposed, the combined capital and operating costs of state-of-the-art superconducting materials have not been analyzed. In response, we develop a thermoeconomic model of a multi-stage, conduction cooled gantry lattice and analyze the cryocooler operating cost, cryocooler capital cost and conductor capital cost for Nb-Ti, Nb3Sn, REBCO and Bi-2223 over a continuous range of magnet temperatures, and a differential evolution algorithm is used to identify the optimal combination of thermal intercept temperatures. Although Nb3Sn yields the lowest Net Present Value (NPV) of $111.7k at a magnet temperature of 9.4 K, the optimized Bi-2223 design at 12.8 K approaches the realm of commercial feasibility by offering improved thermal stability and forgoing the need for costly conductor heat treatment and magnet quench training. Furthermore, it was found that Nb3Sn was more cost effective than Nb-Ti and that REBCO was not economically viable for the parameters of this investigation. The thermoeconomic model developed herein can optimize conductor choices, magnet temperatures and thermal staging which has value for any conduction-cooled superconducting magnet.

Prior studies on cryogenic thermal contact resistance (TCR) measurement mainly focus on liquid nitrogen temperature region and above. There are limited solid TCR data in the lower temperature region. The present measurement is based on an RDK-408D2 two-stage G-M cryogenic refrigerator. By using the laminated method, the TCR data of brass samples in the temperature range of 10—30 K at different roughnesses and preloads are measured and the influence of different factors on TCR is discussed. The results show that the TCR of the brass contact surface in this temperature zone is between 6.89×10-4 and 1.86×10-2 m2·W/K. With a smaller roughness of the contact surface, higher temperature, and greater pre-tightening force, the TCR becomes smaller. This behavior is consistent with the conventional qualitative understanding. The above cryogenic experimental data can provide certain support for the calculation of TCR for related cryogenic application design.

We developed a cryocooler system to reveal the temperature dependence of the quality ( Q ) factor of high-temperature superconducting (HTS) bulk coil and the power transfer efficiency (PTE) and power handling capability (PHC) of a wireless power transfer (WPT) system using the HTS bulk coil. The measured Q factors of the HTS bulk coil were 9051 at 77 K and 14 050 at 25 K. The measured PTEs and PHCs of the WPT system were 44.2% and 4.48 W at 77 K, and 50.8% and 25.2 W at 25 K.

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Three distinct thermodynamic analysis models are developed and applied to a renowned cryogenic engine (PPG-102), namely the isothermal model, the ideal Schmidt model, and the ideal adiabatic model. Through a comparative analysis, the theoretical outcomes derived from these models are juxtaposed with the corresponding theoretical results from the existing literature. The comprehensive evaluation of these findings demonstrates significant convergence, with minor deviations primarily attributed to the inherent assumptions underlying each model. The design of the PPG-102 engine is meticulously executed within the Solidworks environment, allowing for the subsequent simulation under operating conditions identical to those of the computational models. Remarkably, the simulation results closely approximate the outcomes of the adiabatic analysis, thus corroborating the validity and effectiveness of this particular model. In this work, the presented models, initially developed for thermal Stirling engines, are augmented and applied to a cryogenics Stirling engine, offering a unique understanding of the workings of this apparatus.

As we look forward to the next generation of hyperspectral infrared (IR) atmospheric sounders, grating spectrometers hold promise for improved performance (e.g., horizontal and spectral resolutions) and more rapid revisit while reducing the size and complexity of the instrument. We briefly revisit the technology used in the Atmospheric Infrared Sounder (AIRS), recognizing that it was developed in the 1990’s and has matured key technologies in the areas of IR detectors, optical coatings, gratings, and cryocoolers. AIRS has been an unqualified success not only as a science and operational mission but also as a technology demonstration of the reliability and simplicity of grating spectrometer IR sounding instruments. Advancements in focal plane arrays (FPAs) have enabled a new class of grating spectrometer IR sounders that offer more spectral channels on a single FPA, mitigating some of the issues seen in AIRS that used linear arrays. These improvements have been manifested in the CubeSat Infrared Atmospheric Sounder (CIRAS) brassboard instrument, developed at the California Institute of Technology Jet Propulsion Laboratory with industry partner Ball Aerospace. Further enhancements beyond those used in CIRAS enable the development of a new class of instruments with a very long-wavelength infrared response and a very high spatial resolution (

Gas-coupled Stirling-type pulse tube cryocooler (SPTC) is currently the most compact and simplest configuration among all types of cryocoolers, but it is challenging to achieve a very low temperature. This paper investigates a gas-coupled SPTC which is capable of directly achieving a temperature of around 4 K. Theoretical analyses were performed based on SAGE to study the effects of employing one or more multi-bypass structures on apparent cooling performance, and internal working parameters. The simulation results indicate that the function of the multi-bypass is similar to that of a multi-stage gas-coupled structure, producing a pre-cooling effect on the lower-temperature section by increasing the acoustic power and the enthalpy flow in the pulse tube of the higher-temperature section. The cooperation of two multi-bypass structures can promote a higher enhancement of the cooling performance, but it is difficult to achieve the same cooling performance of a completely multi-stage gas-coupled SPTC due to weak phase-shifting capability and excessive reduction of the mass flow. Based on the model, the developed prototype has achieved a no-load temperature of 4.4 K, which shows the great potential of using a gas-coupled SPTC to obtain a cooling temperature below 4 K. [ABSTRACT FROM AUTHOR]

The use of helium recycling systems for magnetoencephalography (MEG) has rapidly expanded in recent years. Placing the cryocooler close to the MEG cryostat is expected to aid in achieving a high helium-recycling efficiency. However, the cryocooler typically introduces a large amount of magnetic interference in the MEG system owing to mechanical vibration, and electric and magnetic noise. In this study, we proposed a mobile reference sensor method using fluxgate magnetometers and vibration meters to reduce the noise originating from the cryocooler. We placed the MEG cryostat, which included superconducting quantum interference device (SQUID)-based MEG sensors and reference magnetometers, and a pulse-tube cryocooler inside a magnetically shielded room. We recorded the vibration and magnetic noise during the operation of the cryocooler using the vibration meters and fluxgate magnetometers placed on the cryocooler and reference SQUID magnetometers as the reference noise data. A noise reduction algorithm named time-shift principal component analysis (TSPCA) was applied to the recorded MEG sensor data by employing the reference noise data. A noise reduction ratio of –39 dB was achieved without temporal and spatial distortion of the MEG signal using an MEG phantom. Thus, we conclude that the mobile reference sensor method with the TSPCA algorithm is an effective technique for reducing the magnetic noise originating from the cryocooler. [ABSTRACT FROM AUTHOR]

The ideal Stirling cycle provides a clear control strategy for the piston paths of ideal representations of Stirling cycle machines. For non-equilibrium Stirling cycle machines however, piston paths aiming to emulate the ideal cycle's four strokes will not necessarily yield best performance. In this contribution, we ask the question: What are the COP-optimal piston paths for specific non-equilibrium Stirling cryocoolers? To this end, we consider a low-effort Stirling cryocooler model that consists of a set of coupled ordinary differential equations and takes several loss phenomena into account. For this model and an exemplary parameter set, piston path optimizations are done with an indirect iterative gradient method based on optimal control theory. The optimizations are repeated for two different kinds of volume constraints for the working spaces: one representing an alpha-Stirling configuration, the other a beta-Stirling configuration. Compared to harmonic piston paths, the optimal piston paths lead to significant improvements in COP of ca. 88 % for the alpha-Stirling and ca. 117 % for the beta-Stirling at the maximum-COP operational frequency. Additionally—and even though the optimizations were performed for maximum COP—cooling power was increased with even lager ratios. [ABSTRACT FROM AUTHOR]

The SCAPE (SuperConducting Arbitrarily Polarizing Emitter) undulator is under development at the Advanced Photon Source (APS). This new undulator requires a cryostat that will be designed based on expected heat loads. For instance, the expected heating of the beam chamber by electron beam is estimated to be at a level of 182 W – much higher than in planar SCUs. This and other challenges require careful thermal analysis of the LHe-based SCAPE cryostat. A detailed thermal model of the LHe-based SCAPE cryostat has been created in ANSYS. This paper presents calculated cooling capacity and temperatures of the SCAPE cryostat for the static and dynamic heat loads. [ABSTRACT FROM AUTHOR]

The SCAPE (Superconducting Arbitrarily Polarizing Emitter) undulator is under development at the Advanced Photon Source (APS) as a part of the APS upgrade at Argonne National Laboratory. This new undulator requires a cryostat to handle the heat load on the beam chamber at a level of 182 W – much higher than in APS planar superconducting undulators. These challenges require careful thermal analysis of the SCAPE cryostat. Despite relatively large heat loads, a cryostat that does not contain any cryogen is a desirable option. Based on the experience on demo scale tests on SCAPE, a cryocooler-based cryogen-free cryostat is proposed. A detailed thermal model of such a cryostat has been created in Thermal Desktop. This paper presents the calculated heat load and temperatures profile of this cryostat under the static and dynamic heat loads [ABSTRACT FROM AUTHOR]

The high-frequency pulse tube cryocooler (HPTC) has been attracting increasing and widespread attention in the field of cryogenic technology because of its compact structure, low vibration, and reliable operation. The gas-coupled HPTC, driven by a single compressor, is currently the simplest and most compact structure. For HPTCs operating below 20 K, in order to obtain the mW cooling capacity, hundreds or even thousands of watts of electrical power are consumed, where radiation heat leakage accounts for a large proportion of their cooling capacity. In this paper, based on SAGE10, a HPTC heat radiation calculation model was first established to study the effects of radiation heat leakage on apparent performance parameters (such as temperature and cooling capacity), and internal parameters (such as enthalpy flow and gas distribution) of the gas-coupled HPTC. An active thermal insulation method of cascade utilization of the cold energy of the system was proposed for the gas-coupled HPTC. Numerical simulations indicate that the reduction of external radiation heat leakage cannot only directly increase the net cooling power, but also decrease the internal gross losses and increase the mass and acoustic power in the lower-temperature section, which further enhances the refrigeration performance. The numerical calculation results were verified by experiments, and the test results showed that the no-load temperature of the developed cryocooler prototype decreased from 15.1 K to 6.4 K, and the relative Carnot efficiency at 15.5 K increased from 0.029% to 0.996% when substituting the proposed active method for the traditional passive method with multi-layer thermal insulation materials. [ABSTRACT FROM AUTHOR]

We designed a cryopanel system based on Molflow+ simulation and constructed for installation in a beam line of 70 MeV H- cyclotron to adsorb back streaming radioactive molecules from ISOL target. Since the target assembly is not hermetically sealed, a target leak can occur especially during high-power beam operation. The cryopanel surrounds the beam path to enhance adsorption efficiency and can be kept at temperature as low as 10 K. A beam test carried out at a current of ∼1 µA showed the panel temperature is not affected by beam pass. The vacuum in the panel region improves to better than 1 × 10-7 mbar so residual gas spectrum has a low background in detection of target leak. As part of the safety system against target damage, a fast closing valve is installed. These safety systems have been tested as essential components for radiation protection in ISOL operation. [ABSTRACT FROM AUTHOR]

The influence of the cooling method on thermal stability is a non-trivial aspect for superconducting material to be used in several applications, for example, in photon detection. Indeed, a wasteful cooling can induce quenches in the device that can lead to false counts. So far, the efficient cooling has been realized by immersion of the superconducting device in a liquid He bath. However, cheaper cryogen-free (CF) cooling techniques are now commercially available, as well as cryocoolers are becoming the only way to obtain a cooling environment in the liquid He shortage. Here we consider three different cooling methods: one is by liquid He in a standard cryostat and the other two are a dynamic or a static He gas cooling in a CF cryostat. Then, we are able to evaluate the performance of the cooling method by the impact on current-voltage curves at very high bias currents. In particular, we acquire current-voltage characteristics on ultra-thin microbridges made by two different superconducting materials commonly used in detectors fabrication, which are NbN and NbTiN. Here, the flux-flow instability (FFI) phenomenon is used as a tool to determine the influence of the three different cooling techniques on the voltage stability of the devices under current biasing. It results that the CF cooling method has performance comparable to liquid He bath. This finding supports the spread of the CF technique for applications, and it validates the FFI as a tool to test superconducting materials. [ABSTRACT FROM AUTHOR]

The performance of an actual free piston free displacer (FPFD) Stirling miniature cryocooler has been simulated based on the parameters affecting the performance of the cryocooler. The processes of compression and expansion in the cryocooler have been assumed to be polytropic with variable ratio of specific heats for the working fluid, i.e., helium. The effect of design parameters like piston spring stiffness, displacer spring stiffness, mass of the piston, displacer mass and frequency of operation on the cooling power of the cryocooler has been calculated. The parameters thus obtained with polytropic processes have been compared with the parameters obtained by assuming the compression and expansion processes to be isothermal. The amplitude of the piston and the displacer is not constant in the case of free piston free displacer cryocooler with linear motors. Linear motor drives have been used for eliminating the side forces on the cylinder walls and wear and tear of the reciprocating parts of the cryocoolers giving them a very long life. A computer program named CRYOJIN which was developed for the isothermal case has been modified for analyzing the real-time performance of the cryocooler for polytropic processes. The physical dimensions of Philips 1 W FPFD cryocooler have been taken for study and comparison. [ABSTRACT FROM AUTHOR]

Magnetic bearings offer the best solution to mitigate mechanical friction. A variety of geometries and new materials are being studied. The advantage of using a passive bearing system, like the Superconducting Magnetic Bearing (SMB), is that it offers low friction without the need of feedback control, increasing the reliability and decreasing the energy consumption. SMB devices work at very low temperatures that are often achieved with the use of Liquid Nitrogen inside of cryostats. This paper describes the design and experimental tests of a SMB passive magnetic bearing system. An innovative design of a cryostat that uses YBCO bulks refrigerated by a cryocooler is presented. With this setup, it is possible to perform vibration tests in several temperatures from 45K up to 77 K to find the resonance speeds at each temperature. Pieces of equipment that use SMB can benefit from reducing the working temperature. The mechanical response of the pinning force may vary with the choice of refrigeration used. To perform those tests, units of accelerometers are installed on the rotor body and displacement sensors monitor the behavior as function of the rotor speed. This improved magnetic bearing will be used in energy storage systems to reduce the instability of the rotor used in flywheel applications by changing the refrigeration temperature of the superconductor. This investigation can lead to an improvement of the levitation force, the levitation gap and damping. [ABSTRACT FROM AUTHOR]

The technology for low-power sub-Kelvin cooling is now established, and products are available that offer simple operation, with reliable and repeatable performance at relatively low cost. Self-contained, sealed sub-Kelvin modules can be added on or retro-fitted to low-power mechanical pre-coolers to extend their operating temperature downwards, from 4 K to the sub-Kelvin range. This technology offers fully automated operation requiring little or no cryogenics expertise and superior performance when compared to systems relying on pre-cooling with liquid cryogens. In this paper, we present data from testing 27 individual 4He modules of identical design and discuss some of the factors that determine reproducibility and reliability as well as overall performance. [ABSTRACT FROM AUTHOR]

The study of zero-boil-off (ZBO) storage is of great significance for the long-term storage of liquid hydrogen (LH 2). Preliminary experimental research on the utilization of cryocooler to achieve ZBO storage has been reported, but the optimization of the total power consumption has barely been considered. This paper will fully consider the working characteristics of the cryocooler, that is, refrigerator efficiency increases with the increase of its working temperature. A novel method to realize the cascade utilization of the cooling power of cryocooler is proposed, which can effectively reduce the total power consumption of ZBO system. A thermodynamic model has been developed to optimize the input power of cryocooler in LH 2 ZBO storage with cold shied and multilayer insulation (MLI). Thermal coupling characteristics of cryocooler, cold shield and MLI has been studied at the minimum input power. The mechanism and optimization strategy have been explained quantitatively. By optimizing position and temperature of cold shield, the input power of cryocooler can be reduced by 69.5%–74.4%. In addition, the effects of MLI thickness and boundary temperature on the optimization of the cold shield have been studied. The influence of LH 2 pressure in tank on cryocooler input power has also analyzed. • A novel method for cascade utilization of cryocooler is proposed for LH 2 ZBO system. • The coupled thermal interrelation in composite insulation system has been studied by a self-built thermodynamic model. • Input power reduction of cryocooler with one cold shield is 69.5%, and two for 74.4%. • Increasing LH 2 pressure to 1.2 MPa, input power decreases by 42.1% than 0.1 MPa。. [ABSTRACT FROM AUTHOR]

Recent breakthroughs in space science have motivated space exploration programs in many countries including China. Cryocoolers, which provide the mandatory low-temperature environment for many sensitive yet delicate space detectors, are crucial for the proper functioning of various systems. One benchmark for the cryocooler performance is attaining the liquid helium temperature. However, even with complex configurations and multiple driving sources, only a few cryocoolers to date can achieve this goal. Here we report a high-frequency pulse tube cryocooler (HPTC) driven by a single non-oil-lubrication compressor which is capable of reaching the liquid helium temperature while offering other advantages such as high compactness, excellent reliability and high efficiency. The HPTC obtains a no-load temperature of 4.4 K, which is the first realization of cooling below the 4He critical point with a gas-coupled two-stage arrangement. The prototype can provide a cooling power of 87 mW at 8 K, and 5.2 mW at 5 K with a 425 W input electric power, showing leading-level efficiency. Moreover, we demonstrate the ability of the cryocooler to simultaneously provide cooling power at different temperature levels to meet different requirements. Therefore, the prototype developed here could be a promising cryocooler for space applications and beyond. [ABSTRACT FROM AUTHOR]

• Silver oxide has large specific heat at low temperatures by optical phonon mode. • Evolution algorithm can calculate phonon density of states from specific heat. • Mold sintering provides high-density spherical particles from powder sample. • Silver oxide as a regenerator material is useful developing low-noise refrigerators. In regenerative cryocoolers, magnetic specific heat is often utilized for heat regeneration at cryogenic temperature, such as below 20 K. Magnetic regenerator materials of rare earth compound which have sufficient specific heat enabled cryocooler to reach below 4 K. However, the magnetic noise emitted from the magnetic materials during the refrigeration cycle affects the performance of noise-sensitive devices. In this study, we propose a non-magnetic regenerator material having "optical phonon degree of freedom" even at cryogenic temperatures, in which silver oxide (Ag 2 O) is selected. Ag 2 O decomposes at temperature above 410 K in ambient atmosphere, whereas we succeeded in fabricating a sintered Ag 2 O bulk and small particles of the size of 0.5 mm with high-density more than 90%. Specific heat measurement down to 100 mK was performed for the sintered bulk sample of Ag 2 O. Below 10 K, a non-Debye behavior was observed, suggesting the contribution from optical phonon modes. Calculation of the phonon density of state (phDOS) performed by the Evolution Strategy algorithm in addition to the first-principles calculation reveals that phDOS has several distinct peaks at low energies, and the low-energy optical phonons contribute to the non-Debye behavior. The low temperature specific heat of Ag 2 O enhanced by the optical phonons is larger than conventional non-magnetic regenerator materials when compared in terms of specific heat per volume. Moreover, the calculation of cooling performance of cryocooler using Ag 2 O particles is found to be reached below 4.2 K. This study shows that non-magnetic material with low temperature specific heat enhanced by optical phonon mode can be used as a regenerator material for regenerative cryocoolers. [ABSTRACT FROM AUTHOR]

A parametric study has been carried out using the software REGEN 3.3 to optimize the regenerator of a miniature Stirling cryocooler operating with a warm end temperature of 300 K and cold end temperature of 80 K. Regenerator designs which produce the maximum coefficient of performance (COP) of the system is considered as an optimized regenerator. The length and diameter of the regenerator were fixed from the cooler system requirements. Single mesh regenerators made of 200, 250, 300, 400 and 450 Stainless Steel wire meshes were considered and the optimum phase angle and mesh size were obtained. A maximum COP of 0.1475 was obtained for 300 mesh regenerator at 70° phase angle. Then multi mesh regenerators were considered with finer mesh on the cold end and coarser mesh on the hot end. The optimum size and length of each mesh in the multi mesh regenerator and the optimum phase angle were calculated. The maximum COP of 0.156 was obtained for 200 300-400 multi mesh regenerator at 70° phase angle. The COP and net refrigeration obtained for an optimized multi mesh regenerator was found to be significantly higher than that of a single mesh regenerator. Thus a multi mesh regenerator design with a proper combination of regenerator mesh size and length can enhance the regenerator effectiveness.

• A review of current magnet technology points to the future landscape for NMR. • The 1986 HTS technology paradigm shift has been delayed by a decade for NMR. • We provide reasons for this delay and assess future ultrahigh-field NMR magnets. • A persistent mode 1.8 GHz HTS NMR is possible, but faces major obstacles. • A helium-free persistent mode 10-20K, 700-800 MHz HTS NMR magnet is pending. Superconducting magnet technology changed dramatically with the discovery of high temperature superconductors (HTS) in 1986, an event which drove the development of much higher field magnets. However, this technology paradigm shift has been delayed by as much as a decade in the case of NMR magnets. In this paper, we will provide a historical perspective to the reasons for this delay and assess the future prospects for high- and ultrahigh-field NMR magnets resulting from current trends in the development of HTS magnet technology. [ABSTRACT FROM AUTHOR]

A looped-cascade thermoacoustic driven cryocooler is proposed and theoretically studied in this paper. This system is capable of achieving ideal acoustic fields by employing different-diameter resonance tubes. It overcomes the limitations of current configurations and possesses the advantages of high efficiency, large capacity and compact size. First, power matching between the engine-stage number and the working temperatures is investigated. Theoretical results show that either too few or too many engine stages induce negative effects: the former results in low efficiency and the latter results in over-high heating temperatures. Then, thermodynamic characteristics of the three-stage system are presented. Simulation results show that a cooling power of 1.17 kW and an overall relative Carnot efficiency of 15% can be achieved at 110 K, which is superior to the performance of the existing looped configurations. The distributions of key parameters are also presented for a better understanding of the energy conversion process. Finally, the effects of the crucial parameters—resonance-tube area-ratio and engine-regenerator area-ratio—are presented. Simulation results show that having an either too low or too high area-ratio has a significant negative effect on system performance due to improper phase relations and low acoustic impedance. • A cascade looped thermoacoustic driven cryocooler is introduced and numerically investigated. • Different-diameter resonance tubes are employed to achieve better performance. • Area ratio between adjacent resonance tubes has a significant impact on the performance. • Total exergy efficiency: 15% and cooling power: 1.17 kW are achieved at 110 K [ABSTRACT FROM AUTHOR]

Complex cryogenics still represents a strong limitation to the spread of Josephson voltage standards, and cryogen-free cooling is particularly suitable to simplify their operation. The main downsides of liquid-helium-free systems are related to the chip thermalization: Indeed, at low temperature, the heat transfer between the chip and the coldplate of a cryocooler in vacuum is strongly affected by the quality of the interfaces. In order to increase the thermal performances of cryocooled programmable Josephson standards, we devised and tested a special cryopackage: The chip is embedded into a sandwich structure with high-thermal-conductivity materials subject to a controlled mechanical pressure to reduce the thermal contact resistances. A thin sapphire lamina placed upon the chip allows the heat to be dissipated from the top, thus creating an additional path for the thermal flow. A special bridgelike system with a screw is used as a reproducible torque-to-force converter to exert known pressures to the sandwich. Furthermore, we analyzed the effect of thermal contraction to the actual pressure exerted on the chip, showing a nonnegligible increase when cooled down to cryogenic temperature that can be calculated and corrected for. [ABSTRACT FROM AUTHOR]

Abstract Propellant conditioning is a challenge for the development of cryogenic upper stages with re-ignitable main-engines. The VINCI engine needs for its operation propellant under specific conditions w.r.t. pressure and temperature to avoid cavitation inside the propellant pumps. After long ballistic phases the temperature of the propellant can increase to the respective saturation temperature of the tank pressure due to radiative solar heating. By means of the proposed feed line evaporation cooler 1stly the usual release of the tank pressure for thermally conditioning the propellant and 2ndly the follow-on re-pressurization of the tank with Helium can be avoided. Furthermore, this feedline evaporation cooler allows cooling only the propellant amount that is actually consumed by the engine. In this paper the design of the EC test unit, the LH 2 test bench and respective results of the tests performed with LH 2 will be presented in order to demonstrate the technology's capability and readiness. Additionally, a possible design and assembly on the A6 upper stage propulsion module is suggested. Highlights • Chosen Al cooler design is capable to fulfill the Ariane 6 strength requirements. • Nozzles, capillary tubes, related dimensions of sub-scale cooler already real scale. • Applied 2-phase model is well applicable for involved Hydrogen flow boiling process. • Evaporation cooler fulfills 5 K cool down requirement with estimated efficiency. • mass saving for A6 GTO single-re-ignition is 87 kg, for LEO dual re-ignition 224 kg. [ABSTRACT FROM AUTHOR]