Cryogenics最新文献

Fusion magnets are mainly wound by Cable In Conduit Conductor (CICC), therefore the cables can resist electromagnetic force under the protection of stainless steel jacket with higher yield strength. The Institute of Plasma Physics Chinese Academy of Sciences (ASIPP) has been designing a compact fusion device. As a structural component of CICC, the conductor jacket in Central Solenoid (CS) magnet withstands great electromagnetic force. Consequently, a higher strength stainless steel named modified Nitronic 50 (N50H) with Yield Strength (YS) > 1500 MPa @ 4.2 K is adopted to fabricate CS jacket. In this paper, the compressing process of CS conductors with the circle in square structure is simulated by finite element method. The results reveal stress concentration on the jacket after compression, and with the increase of the jacket’ corner radius, the compressing stress decreases, while the electromagnetic stress increases. Through the analysis, the suitable corner radius of the jacket is selected. Subsequently, the corresponding jacket is manufactured, and the tensile test is carried out at 300 K, 77 K and 4.2 K. The results show the existence of stress concentration and prove that the jacket achieves YS > 1500 MPa @ 4.2 K performance and meets the design requirements.

At the European Spallation Source (ESS) ERIC, the liquid hydrogen moderator development is undertaken for its predominantly high parahydrogen fraction, which helps to attain a higher neutron intensity at a very high brightness. The Cryogenic Moderator System (CMS) is equipped with a catalyst to convert hydrogen from the ortho to the parastate to keep desirably high parahydrogen fractions of more than 99.5% in the cold moderators, which is required to deliver high brightness cold neutron beams to the neutron instruments. An in-situ measurement system for the ortho and para fractions of liquid hydrogen (OPMS) has been developed using a Raman spectroscopy to detect any undesirable shift towards a high orthohydrogen fraction caused by neutron scattering driven para-to-ortho back conversion. A Raman optics system was installed into a mock-up OPMS vacuum chamber and its performance evaluation tests have been conducted by flowing liquid hydrogen. It was verified that the developed Raman optics system succeeded in measuring the parahydrogen fraction with an accuracy of 0.1%, which met the requirement.

Preliminary demonstrations show Fiber Bragg Grating (FBG) sensors effectively measure low temperatures, such as in Helium cryostats. These sensors, resistant to electromagnetic interference, offer significant potential for monitoring strain and temperature within superconducting coils and cryogenic structures due to their compact size. Standard FBG sensors are constrained by the thermal expansion coefficient of the polyimide coating, restricting their use as embedded sensors during the heating process of Nb₃Sn superconducting coils. These sensors are currently unable to endure temperatures exceeding 400 °C, essential for fabricating Nb₃Sn coils through the wind and react technique. This study explores enhancing the endurance of FBG sensors through magnetron sputtering coating process with copper (thickness of 20 μm), which has a thermal expansion coefficient similar to Nb₃Sn coils. The results showed improved repeatability and survival for the copper-coated FBG in comparison to the standard polyimide-coated FBG from room temperature up to 939 K. Subsequently, the strain and temperature sensing capabilities of the FBG sensors with copper coating are evaluated using a separately developed controllable conduction cooling system, ranging from room temperature to 4.2 K. The findings in this paper demonstrate that the copper coating significantly enhances the durability of the FBG sensors under high temperatures. Additionally, the strain and temperature sensing characteristics of the sensors remain effective across a broad range from cryogenic to elevated temperatures. The homemade FBGs were independent of temperature below 30 K and responsible for the larger internal thermal strain of Nb₃Sn magnets during its pre-heat treatment and operation.

This paper presents a design study of a low-speed, high torque 20 kW class motor with a high-temperature superconductor (HTS) field coil for a liquid hydrogen centrifugal pump. The motor is designed based on three key concepts: 1) employing an axial-flux motor topology that can increase torque density by reducing the axial length together with a centrifugal pump; 2) using liquid hydrogen in a pump as a coolant for HTS coil; 3) adopting no-insulation (NI) YBCO solenoid coils as field coils of the motor to improve coil protection as well as mechanical stability. In the design process, first, an electromagnetic design of the axial type motor is obtained considering the required performance of previous commercial pumps. Considering the current and temperature margin to secure the HTS coils' stable operation, two types of HTS coils (solenoid type and triangle type) are designed and their performances are compared. Second, to evaluate validity of the electromagnetic designs, mechanical stresses in the HTS coils are estimated. By comparing the solenoid type and the triangle type, it is confirmed that the solenoid type has a distinct stress-reducing effect in terms of magnetic stress as well as rotational stress. Our design study results show the potential superior performance of the axial flux motor with HTS coils for several tens of kW applications with low speed and high torque loads such as liquid hydrogen pumps.

The X-ray imaging and spectroscopy mission (XRISM) is an X-ray astronomy satellite developed by the Japan Aerospace Exploration Agency (JAXA) and the National Aeronautics and Space Administration (NASA) to explore the evolution of the universe and its physical phenomena as the replacement for ASTRO-H. One of the primary scientific instruments of the XRISM is the Resolve, which utilizes an X-ray microcalorimeter array. This detector array is required to be cooled down to 50 mK using a complex cryogenic system with a multistage adiabatic demagnetization refrigerator (ADR) developed by NASA and a cryogenic system developed by Sumitomo Heavy Industries, Ltd. (SHI). The cryogenic system is required to cool the heat sink of the ADR to a temperature below 1.5 K in orbit for at least 3 years. To meet the specific requirements, we developed a hybrid cryogenic system consisting of a liquid helium tank, a 4K Joule–Thomson cooler, and two two-stage Stirling coolers. As a result, the specific requirements were verified by ground tests. This paper describes the design, including the major changes from ASTRO-H, fabrication, and results of the ground tests of the helium Dewar of the Resolve instrument.

Direct cooling of cryogenic hydrogen can be achieved by flow through a stack or regenerator of a thermoacoustic refrigerator. In addition, using a catalytic stack, the ortho-parahydrogen transformation can be conveniently realized in the same device. Analysis of this system element is carried out by integrating one-dimensional thermoacoustic equations with addition of empirical ortho-parahydrogen conversion reaction. Calculations in a standing-wave catalyzed setup demonstrate a selection process for optimal acoustic impedance and stack pore dimensions, showing significant advantage over non-catalyzed hydrogen- and helium-based stacks of similar kind. Results are presented for hydrogen flow characteristics and distributed heat load due to ortho-parahydrogen conversion inside a stack. The stack performance is also quantified at variable flow rate of hydrogen, stack length, mean pressure, and supplied acoustic power.

With the rapid progress of the superconducting quantum computing technology, the cryogenic technology capable of providing appropriate cooling in the millikelvin temperature region is desirable. The cryogen-free dilution refrigerator featuring high reliability, long lifetime, and continuous cooling has become one of the most promising cryocooler candidates for this purpose. As one of the key components of the dilution refrigerator, the impedance component is used to control the flow and to liquefy ³He, which is crucial to achieving the millikelvin temperature. In this paper, a throttling model is proposed to analyze the dilution cycle and to eventually improve the refrigeration performance, which focuses on the influences of the complex physical properties of ³He and the dilution cycle from the subcooled state to saturation state. The effects of the inlet pressure and inlet temperature on the flow rate are studied, and the energy conversion on the throttling process is discussed. It indicates that the throttling model can reasonably predict the flow rate under different inlet pressure and inlet temperature and is helpful to the design and optimization of the millikelvin cryogen-free dilution refrigerator.

Nonlinear error compensation is a significant factor that affects the measurement accuracy of temperature sensors. Cryogenic temperature sensors require a precise calibration technique to achieve accurate temperature measurements. BP (Back Propagation) neural networks are not suitable for sensor temperature prediction due to slow convergence and poor learning ability. In this study, a Chebyshev polynomial-based BiLSTM (Bi-directional Long Short-Term Memory) algorithm (C-BiLSTM) is proposed to improve the accuracy of measurement. Firstly, we demonstrate vacuum packaged temperature sensors based on zirconium oxynitride (ZrO_xN_y) thin films with ultra-high sensitivity at cryogenic temperatures. Secondly, a dataset consisting of sensor resistance and temperature values was obtained from five above-mentioned sensors, which contains 29 calibration points in the temperature range of 16 K-300 K measured by the Calibration System. Then, the dataset was divided into two temperature ranges (16 K-54.358 K and 40 K-300 K). In the range 16–54.358 K, 14 set-points are selected as training set and 3 set-points as testing set. In the range 40–300 K, 12 set-points are selected as training set and 2 set-points as testing set. Thirdly, a neural network model was built and trained using the TensorFlow framework. By comparing C-BiLSTM we proposed with the BP neural network and BiLSTM, the results show that the C-BiLSTM model converges faster and greatly improves the prediction accuracy after adding Chebyshev polynomial features. The fitting error and prediction error are less than 1 mK in the temperature range of 16 K-40 K. They can also keep less than 10 mK even at the wide temperature range of 40 K-300 K, which is a significant improvement respect to improving the accuracy of temperature measurement.

China Fusion Engineering Test Reactor (CFETR) has more advanced design parameters compared to the International Thermonuclear Experimental Reactor (ITER), particularly demanding a high yield strength (over 1500 MPa at 4.2 K) for jacket material in the cable-in-conduit conductor (CICC). Modified N50 austenitic steel, due to its excellent mechanical properties at liquid helium temperature, has been identified as a promising candidate material for the jacket material. However, while some research focuses on the mechanical properties of modified N50 steel at cryogenic temperatures, little is known about the cryogenic physical properties that are critical for conduit jacket applications. In this study, a modified N50 steel was prepared and characterized in terms of tensile properties and physical properties at cryogenic temperatures. We tested the tensile properties of the modified N50 at 4.2 K, 77 K, and room temperature (RT). Additionally, we measured the thermal conductivity, thermal expansion, specific heat capacity, and magnetization of the modified N50 from 4 K to 300 K. These results could provide a more comprehensive reference for applying the modified N50 steel in jacket materials for the CFETR.

Hydrogen-driven heavy-duty trucks are a promising technology for reducing $C{O}_2$ emissions in the transportation sector. Thus, storing hydrogen efficiently onboard is vital. The three available or currently developed physical hydrogen storage technologies (compressed gaseous, subcooled liquid, and cryo-compressed hydrogen) are promising solutions. For a profound thermodynamic comparison of these storage systems, a universally applicable model is required. Thus, this article introduces a generalized thermodynamic model and conducts thermodynamic comparisons in terms of typical drive cycle scenarios. Therefore, a model introduced by Hamacher et al. [1] for cryo-compressed hydrogen tanks is generalized by means of an explicit model formulation using the property $c_{v2P}$ from REFPROP [2], which is understood as a generic specific isochoric two-phase heat capacity. Due to an implemented decision logic, minor changes to the equation system are automatically made whenever the operation mode or phase of the tank changes. The resulting model can simulate all three storage tank systems in all operating scenarios and conditions in the single- and two-phase region. Additionally, the explicit model formulation provides deeper insights into the thermodynamic processes in the tank. The model is applied to the three physical hydrogen storage technologies to compare drive cycles, heat requirement, dormancy behavior, and optimal usable density. The highest driving ranges were achieved with cryo-compressed hydrogen, however, it also comes with higher heating requirements compared to subcooled liquid hydrogen.