Cryogenics最新文献

The SMC (Short Model Coil) R&D program was started at CERN around 2007 to develop the Nb₃Sn technology. The small magnet structure allowed relatively cheap and fast testing of various superconducting coils. One of the key questions to be answered, was related to the relation between the pre-stress and the magnet’s performance. To measure this dozens of strain gauges were installed on the coils, the axial tie-rods and the external shell. The experimental results of the strain measurements during all stages of the load: room temperature (RT) pre-stress, cool-down, powering, warm-up were analyzed in an extensive report [56]. A repeatable pattern of a decreasing strain after the warm-up, compared to the value before the cool-down, was observed on the external cylinder for all the tested coils. Values from 2 % to 50 % were reported.

In this work a viscoelastic model was used to explain this effect. The Nb₃Sn coil was treated as a composite material with decreasing stiffness due to mechanical damage. The Generalized Maxwell Solid model (Prony series model) was employed, including one spring and one damper, leading to a relatively simple model characterized by only two parameters. The two constants of the viscoelastic model were found: 1st – the relative relaxation moduli $\alpha$ based on a calibration curve derived from the experimental results of the SMC program and the 2nd one – relaxation time $\tau$ – based on minimizing the computational cost, by finding the asymptotic solution in one integration step. The model showed the capability of explaining the strain drop (loss of pre-stress) of more than 80 %. In addition to the viscoelastic effects, the role of friction coefficient was studied revealing the possibility of explaining up to 14 % of the strain drop. Yet, to fit with the experimentally measures strains on the SMC cylinder, especially during the RT pre-load, the most-probable value of the friction coefficient should be $\mu <0.4$. The strong impact of the stiffness of the G-10/G-11 laminate used to spread the load on the coil was found, indicating the need of knowing the elastic properties of this material very precisely. In addition, the experimentally measured strain values showed strong asymmetric, both in plane and along the magnet’s axis, revealing the potential sensitivity to the geometric imperfections and the need for 360° magnet models.

Residual-resistance-ratio (RRR) of Cu stabilizer in REBCO coated conductor is an important design parameter for REBCO magnets. Cu stabilizer with high RRR is especially beneficial for quench protections of REBCO magnets. In this work, we study RRR of electroplated Cu stabilizer in commercial REBCO tapes. We present RRR of over 180 samples measured for the quality assurance programs of REBCO magnet projects at the National High Magnetic Field Laboratory, USA (NHMFL). To investigate the factors that influence RRR, several samples were analyzed extensively by using scanning electron microscopy, secondary ion mass spectroscopy, and inductively coupled plasma mass spectroscopy. We found that RRR is strongly correlated with the grain size of Cu, which suggests that resistivity at low temperatures is dominated by grain boundary resistivity. In addition, low RRR corresponds to high concentration of chlorine impurity. This is explained by that higher chlorine impurity hindered the grain growth in the self-annealing process at room temperature which resulted in smaller grain size and low RRR. Annealing at 300C significantly enlarged the grain size and enhanced RRR. Due to the concern of critical current degradation, however, annealing is not recommended as a practical method to improve RRR of Cu in REBCO tapes.

High Temperature Superconductors (HTS) are very promising materials for possible application in future fusion magnets, with significant R&D progress on HTS conductors in recent years. However, since geometric and thermo-physical characteristics of HTS and LTS conductors differ significantly, some doubts have arisen if the approaches successfully used in numerical simulations of the thermal–hydraulic behavior of LTS conductors would be sufficient also for HTS, particularly in cases when fast transient processes (such as e.g. quench) are considered. In order to provide data for better understanding of the quench phenomenon in HTS conductors as well as for testing different numerical approaches and proper tuning of the numerical codes, a dedicated experimental campaign (Quench Experiment) was carried out at the SULTAN test facility within the international collaboration between the EUROfusion consortium and China. Our present study is a part of the work on analysis and interpretation of the data collected during this experiment. Simulations of the chosen experimental run were performed using two THEA models with different levels of complexity. Uncertain model parameters (thermal resistances and copper RRR) were explored across a wide range. Our goal was to identify the possibly simple model that accurately reproduces the experimental results.

A sorption J-T cooler for a cooling temperature of 5 K can be useful to cool the sensitive detectors and calorimeters, due to its vibration-free characteristic. It is a J-T cooler driven by the sorption compressor, that utilizes the adsorption phenomenon to create the pressure gradient. To maximize the mass flow rate, the switchless thin-plate type cell is adopted for the sorption compressor. The coiled tube-in-tube heat exchanger is fabricated to minimize the overall size of the cooler. After precooling the experimental apparatus with a two-stage G-M cooler, the open-loop test is performed to assess the mass flow rate characteristics of the J-T restrictor and the background heat ingress. In the closed-loop experiments, the cooling temperature below 5 K is achieved by the sorption compressor without heat load. The nominal mass flow rate from the sorption compressor is 1.3 mg/s with the pressure ratio between 5.9 and 6.6. Subsequently, the model of the heat exchanger is utilized to determine the maximum cooling capacity according to the inlet temperature of the high-pressure stream. Furthermore, the effectiveness and the overall COP of the sorption J-T cooler are analyzed. The maximum cooling capacity at 5 K in the experimental setup is predicted to be 3.4 mW and 4.9 mW with the original and improved heat exchangers, respectively.

The Small-angle Neutron Spectrometer at China Spallation Neutron Source (SANS_CSNS) is a functional apparatus utilized for the examination of structures and inhomogeneities within the size range of 1 to 100 nm. The development of sample environments for in situ experiments at low temperatures at SANS_CSNS is urgent in order to address the increasing demands of users. The CSNS Sample Environment Group has successfully designed and constructed an automated sample exchange cryostat for SANS experiments, capable of operating in a temperature range of 10 ∼ 500 K. This cryostat has been specifically engineered to accommodate up to four samples simultaneously and exchange samples automatically in order to optimize the utilization of neutron beams by minimizing the downtime associated with manual sample handling. The results of simulation and temperature measurement proved that sample temperature could be accurately controlled from 10 K to 500 K through the incorporation of a 4 K GM cryocooler and a heater. Furthermore, neutron scattering studies conducted on SANS_CSNS proved that this cryostat exhibits commendable temperature control capabilities and minimal background interference. This automated sample exchange cryostat will be available to researchers of SANS_CSNS in the following user programs.

The sub-Kelvin sorption cooler (SKSC) has emerged as a reliable and vibration-free solution for space cryogenics, establishing itself as a highly competitive choice. This paper focuses on the development of a ⁴He SKSC prototype designed for precooling an adiabatic demagnetization refrigerator (ADR). Based on the sorption refrigeration mechanism, the relationship between the amount of working medium and cooling performance is analyzed. Subsequently, each component of the SKSC is designed and constructed, resulting in the successful creation of a ⁴He SKSC prototype. Experimental testing demonstrates its capability to achieve a minimum temperature of 773 mK and provide a cooling capacity of 100 μW at 803 mK.

Many NASA’s highly sensitive instruments require advanced active cryocoolers to enable their detectors, optics, and low noise amplifiers to reach their full performance potential. These instruments include infrared, X-ray, millimeter-wave and quantum communication instrument systems for earth science, planetary science, and astrophysics. The operating temperatures of these instruments range from approximately 150 K to below 0.1 K. This paper first reviews the status of current active cryocooling technologies for these applications. It then describes the performance improvements needed for these cooling systems to support wider adaptation of advanced cryogenic instruments in future missions. In addition to enhancing cooler performance in terms of thermal efficiency, cooling capacity, size and mass, the paper also discusses the needs for developing high-power cryocooler control electronics, improving waste heat management subsystem, and reducing exported vibrations. Finally, the paper recommends strategies for NASA to support and coordinate cooler development efforts in NASA centers, cryocooler industries and academic institutes to advance technologies needed for future missions.

No-insulation (NI) coil has been recognized as the most practical solution at present to achieve ultra-high magnetic field with the REBCO high temperature superconductor thanks to its passive quench protection mechanism which is originated from the inter-turn current bypass. However, for the NI technique, one of the most important obstacles to a more general application is the field delay which is also a consequence of the lack of inter-turn insulation. The proportional and integral (PI) active feedback control of power supply has been developed to achieve a designed field ramping rate. The efficiency of this method could however be affected by the measurement accuracy of measuring equipment, sampling frequency, control accuracy of power supply and other factors. In this manuscript, we tried to use a more fundamental method to mitigate the field delay. The point is, though unlike in insulated coils the field generated is not proportional to coil current in NI coils, they do have a certain linear relation for a certain coil. Based on the lumped circuit model, the current charging curve corresponding to a desired field excitation could be calculated for a NI coil. We verified this method on several solder impregnated no-insulation coils (SINoInCs) to excite their field with different rates, for which the field delay with normal charging method could be very large because of the very low inter-turn resistance. The test results show that this kind of fast excitation method could successfully achieve the desired field with high accuracy and mitigate the field delay from 130 s to almost 0 s. Besides, the large overshoot current introduced by the fast charging does not quench the coils even with an overshoot current which is almost double of the coils’ operating current.

Given the rising global energy demands and the fluctuating nature of load demand, advancing various energy storage systems to enhance their efficiency is essential. Moreover, the increase in greenhouse gas emissions from various industries has prompted governments to implement carbon dioxide (CO₂) capture systems and invest in renewable energy sources. In this research, a cryogenic energy storage configuration is developed according to the air liquefaction process, liquefied natural gas (LNG) regasification operation, CO₂ capture cycle, and organic Rankine plant. During off-peak times, the air entering the energy storage system is compressed and liquefied using wind energy and the cold energy from LNG vaporization, producing 83.12 kg/s of liquid air. During on-peak times, the liquid air and LNG after recovering the cold energy enter the power generation cycle, generating 119 MW of electrical power. This power generation cycle includes a combustion chamber, gas turbine power plant, and organic Rankine cycles. Flue gases from the power generation cycles enter the amine-based CO₂ capture and then the output CO₂ is stored in liquid form. The storage and round-trip efficiencies of the present energy storage configuration are 67.97 % and 62.50 %, respectively. The results of exergy analysis show that the exergy efficiency of the whole system, off-peak, and on-peak sections are calculated as 64.88 %, 82.40 %, and 74.03 %, respectively. The pinch method for multi-stream exchangers (HX6, HX7, and HX8) is accomplished and the exchanger network related to each one is determined. Three-dimensional sensitivity analysis indicates that storage and round-trip efficiencies increase up to 80.45 % and 66.20 %, respectively when the power generation section pressure increases up to 110 bar and compressed air pressure decreases to 135 bar.

The paper addresses the implementation of a dual distribution function multiphase lattice Boltzmann method (DDF-MLBM) for studying the collapse of cavitation bubbles in cryogenic liquids. The present scheme incorporates the energy equation and imposes interparticle interactions and fluid–solid adhesive forces through the exact difference method (EDM). To accurately model phase changes and the molecular complexities of cryogenic fluids like liquid hydrogen ($L{H}_2$) and liquid nitrogen ($L{N}_2$), the Peng-Robinson (PR) equation of state is employed along with an acentric factor. The accuracy of the present numerical technique is evaluated using the Laplace law and the Maxwell equal area construction theorem for a two-phase liquid–vapor system in equilibrium. For transient solutions, the study compares results of heterogeneous cavitation with the analytical solution derived from the thermal Rayleigh-Plesset equation. The research investigates the impact of the distance between a cavitation bubble with an adjacent solid wall on velocity, pressure, temperature, and collapse time. Furthermore, it is assessed how surface wettability influences cavitation bubble collapse intensity. Additionally, the paper examines the collapse of a cavitation bubble cluster and evaluates the effects of different physical parameters on the collapse properties of the bubble cluster. The results underscore the significant influence of the distance between cavitation bubbles in the cluster, the distance between bubbles and the adjacent solid surface on the micro-jet velocity. Moreover, it is found that increasing the contact angle of the solid surface enhances the collapse intensity and micro-jet velocity of the collapsing bubble cluster.