Cryogenics最新文献

$\mathrm{Mg}{B}_2$ superconducting material has a wide range of application prospects for its high transition temperature, favorable structural characteristics and low cost. When using $\mathrm{Mg}{B}_2$ to produce superconducting energy storage magnets, it is necessary to twist superconducting wires into cables to increase their current carrying capacity. One typical cable is made of 6 $\mathrm{Mg}{B}_2$ superconducting wires wrapped around 1 central copper wire, forming a (6+1) structure. $\mathrm{Mg}{B}_2$ coils used for energy storage require solid impregnation and can be cooled by liquid hydrogen or solid nitrogen. Due to the need for fast charging and discharging of energy storage coils and low thermal conductivity of commonly used epoxy resin impregnation and solid nitrogen, it is necessary to consider the temperature variation characteristics caused by AC loss and eddy current loss during operation process. A coil with 8 turns in each layer and 4 layers is simulated using the (6+1)-structure cable. In order to obtain better temperature distribution results while reducing the time required for simulation operation, the simulation time is set to 1 s. The impact of epoxy resin properties and surrounding environments on the coil are then analyzed. The results indicate that increasing the thermal conductivity of epoxy resin can significantly reduce the maximum temperature of the coil, while only changing the cooling method is unhelpful in dealing with the problem of local overheating of the coil.

This paper focuses on the remote cryogenic helium circulating system for cooling the 10-Mvar class HTS DSC. The cryogenic system is an upgraded version to provide a cooling power about 200 W@20 K. Six cryogenic cryocoolers are employed as the cold source. Two cryogenic helium blowers are used to overcome the pressure drop. Circulating loop is divided into two branches, of each three coolers are installed in parallel and then as a whole connected to a helium blower in series. The detailed design, structure parameters, and optimization of the cooling system were described as well. In the experimental tests coupled with the rotor section of 10-Mvar HTS DSC, the magnet was firstly pre-cooled to about 110 K with liquid nitrogen, and then further cooled to around 34.5 K by the circulating helium gas. In the near future, the 10-Mvar class HTS DSC will be installed, tested and integrated into the power grid for practical application.

Superconducting cavity is the key equipment of the superconducting accelerator, which provides higher acceleration voltage and higher frequency power per unit length, and saves equipment space. Superconducting cavities need to be gradually cooled from ambient temperature (300 K) to the superconducting temperature (4.2 K or below) during the test and operation. The temperature difference on the cavity must be strictly limited during the cooldown process to prevent excessive thermal stress on the surface of the superconducting cavity. Since this cooldown process for the superconducting cavity is a typical large hysteresis, non-linear process that is difficult to control automatically using decoupled proportion integral derivative (PID) methods directly, a less efficient manual control scheme is normally adopted. In this paper, 3D numerical simulation, 1D pipe and 0D tank model with artificial neural network (ANN) were combined to generate a two-layer surrogate model that can balance computational accuracy and speed, to improve the automation and cooling efficiency of the superconducting cavity cooldown process. In order to achieve automatic control of the cooling procedure for the superconducting cavity, a model predictive control (MPC) approach was also built on the basis of this two-layer surrogate model. According to the results of the experiment test, the improved method could realize a quick and smooth cooldown process of the superconducting cavity, during which the temperature difference on the cavity could satisfy the requirements. Additionally, the improved automatic cooldown method was more adaptable and saved 29 % more time than the original manual control method. The foundation for a more intelligent automated control of future large cryogenic systems or other system with the large hysteresis, non-linear properties, was laid.

The gas gap heat switch (GGHS) used for controlling heat transfer between different stages can be an important component for the precooling process of some dilution refrigerators. In this paper, a novel circuit GGHS is a rotationally symmetric heat switch assembly with annular fin arrangements to strengthen the heat-transferring effect. A numerical model considering ⁴He actual gas properties is proposed to investigate the heat transfer characteristics in the circuit GGHS, in which the effects of charge pressure, cold end temperature, thickness and length of walls on the mean thermal conductance (MTC) are studied. Simulation results show that the MTC increases with the growing cold end temperature, wall thickness, and length, respectively. Given the pressure of 10 kPa, cold end temperature of 4.2 K, wall thickness of 0.97 mm, and wall height of 66 mm, the theoretical MTC is 0.828 W/K. Experimental results indicate that the proposed simulation model is reasonable. Furthermore, the increment of the MTC decreases with the growing temperature. The GGHS used in experiments had a cold end temperature of 4 K, wall thickness of 0.65 mm, and wall height of 33 mm; the measured MTC was 0.219 W/K. Only when the temperature is above 10 K does the charge pressure have a pronounced effect on the MTC. This study provides helpful theoretical guidance for the design and optimization of the circuit GGHS.

Global Change Observation Mission – Climate (GCOM-C) “Shikisai”, a satellite designed to observe global climate change, was launched from Tanegashima Space Center on December 23, 2017 by an H2A launch vehicle. The Second-generation GLobal Imager (SGLI) on GCOM-C is a multi-channel optical sensor for observing aerosols, vegetation, and temperatures. Through long-term monitoring, our understanding of climate change mechanisms will be improved. The infrared scanner (IRS) on SGLI has a Thermal InfraRed (TIR) detector requested to operate at 55 K. A Cooler Dewar Assembly (CDA) developed to keep the detector at 55 K is designed to minimize the heat load for the small cooler. The detector is supported on a thermal isolator made of Glass FRP and is thermally connected to the cooler by flexible thermal link. The Cooler Control Electronics (CCE) uses a heater to compensate heat load fluctuations, thereby maintaining temperature and stability. The heater power decreases gradually during five years, consequently decreasing the cooling power. Despite that cooler degradation, the detector temperature has been maintained at 55 ± 0.1 K for 5 years in orbit and has continued operating with 36 W power consumption. This paper describes the cooler Dewar Assembly and its five years of operation in orbit.

In this work, new equations of state for the binary mixtures H₂ + Ar, H₂ + He, and H₂ + Ne are presented. The equations are formulated in terms of the reduced Helmholtz energy and allow for the calculation of all thermodynamic properties over the entire fluid surface including the gas phase, liquid phase, supercritical region, and equilibrium states. The models are validated by comparisons with experimental data and their physical behavior is analyzed. Furthermore, the new equations of state are compared to other state-of-the-art models from the literature.

In large-scale, high-field superconducting magnets used for magnetic confinement fusion, high energy accelerators, and magnetic resonance imaging, the insulating system made from glass fiber reinforced resin-based composites is the key component, which mainly plays the role of mechanical support, fixing and protecting superconducting conductors, as well as electrical insulation. Vacuum Pressure Impregnation (VPI) approach is widely used in the manufacturing of the insulation system. The second curing cycle is generally required after the first VPI and curing process. For example, after the superconducting coil is cured in the mold, the de-molding process requires the superconducting coil to be reheated according the curing temperature. Moreover, for large-scale superconducting magnets, the superconducting coil needs to undergo a second VPI process after the first VPI process to fix the coil in the coil case. In this work, the tensile and shear properties of pure epoxy resin and the glass fiber reinforced resin-based composite, were investigated at both room and cryogenic temperatures and the effect of the second curing cycle on the mechanical properties was analyzed. Additionally, the strain evolution of the Nb-Ti superconducting coil during the second curing cycle was measured using the Fiber Bragg Grating (FBG) sensors embedded in the composite. The results indicate that the second curing cycle will not introduce additional strain to the previously cured resin matrix, but the defective or weak parts of the resin matrix may be affected by the new added epoxy resin and a little extra strain has been observed.

Tunnel magnetoresistance (TMR), recognized for its high sensitivity and low power consumption, holds significant promise in the domain of weak magnetic field detection. Using superconducting materials as magnetic concentrators can achieve several hundred to even a thousandfold amplification of magnetic fields, making it one of the most effective approaches to enhance the magnetic field resolution of TMR sensors. This paper utilized the flip-chip bonding process to integrate TMR with the high-temperature superconductor YBCO (YBa2Cu3O7-δ), and successfully developed TMR-YBCO composite magnetic sensor. Building upon this foundation, through optimization of the fabrication process and the pioneering use of a structural design incorporating the filling of annular holes with superconducting concentrators, the sensitivity of the sensor was further enhanced. Finally, the magnetic field resolution was increased by 1030 times compared to TMR sensors, reached to 2.9pT/Hz1/2 at 1 Hz. Simultaneously, results from frequency band testing indicated excellent frequency band characteristics, with a frequency response range exceeding kHz.

High-temperature superconducting (HTS) pinning magnetic levitation (maglev) has garnered significant attention in high-speed maglev transportation due to its inherent self-stability, low energy consumption, and absence of mechanical friction. Ensuring the safe and stable operation of HTS pinning maglev systems necessitates a dedicated focus on the performance and stability of HTS bulks levitated above the permanent magnetic guideway (PMG). Previous research has indicated that variations in the temperature within the HTS bulk can impact the levitation performance of the system. This temperature-related phenomenon occurs when the external magnetic field applied to the HTS bulk changes. However, it is noteworthy that previous levitation force tests for HTS magnetic levitation systems have been limited to quasi-static or low-speed studies. The exploration of dynamic levitation forces, particularly at high speeds, has remained constrained due to the associated high costs. Therefore, the objective of this study is to investigate dynamic levitation forces while the HTS pinning maglev system is in motion at high speeds, utilizing a self-developed ultra-high-speed maglev test rig. Initially, the relationship between the levitation force and the vertical displacement of the HTS pinning maglev system is examined based on quasi-static experiments. Subsequently, comparative studies are conducted to measure levitation forces at varying speeds. Finally, the correlation between running speed and dynamic levitation force is discussed. The investigation reveals that the levitation force experiences only a marginal decrease as the running speed increases. At a running speed of 240 km/h, the attenuation rate of the levitation force is approximately 2.478 %, demonstrating the commendable stability of HTS pinning maglev systems. The article concludes by presenting the dynamic levitation characteristics and their attenuation trends to speed. These findings can serve as valuable references for future design and practical implementation of HTS pinning maglev systems.

Future space telescopes, such as those proposed for the Far-infrared Surveyor Mission, are expected to employ actively cooled optical arrays with a similar overall surface area compared to the James Webb Space Telescope. Therefore, there is a need for a cryogenic cooling system with a thermal bus architecture that can distribute cooling to these large optical arrays. Recent experimental research of helium Pulsating Heat Pipes (PHPs) has shown that helium PHPs can transfer heat over long distances (on the order of 2 m) with high efficiency, and also have the ability to act as a passive thermal switch upon the removal of the cooling source. PHPs’ high thermal performance, passive switching capability, low mass, and ease of manufacturing make them an appealing option compared to high-purity metal straps for a thermal bus architecture on large cryogenic space telescopes. A novel architecture for the thermal control of optical arrays is proposed utilizing unique configurations of helium pulsating heat pipes that minimize mass, maximize thermal performance, and reduce the risk of mission failure.