Cryogenic Gas Research Articles

Slow molecular beams from a cryogenic buffer gas source

We study the properties of a cryogenic buffer gas source that uses a low-temperature two-stage buffer gas cell to produce very slow beams of ytterbium monofluoride molecules. The molecules are produced by laser ablation inside the cell and extracted into a beam by a flow of cold helium. We measure the flux and velocity distribution of the beam as a function of ablation energy, helium flow rate, cell temperature, and the size of the gap between the first and second stages of the cell. We also compare the velocity distributions from one-stage and two-stage cells. The one-stage cell emits a beam with a speed of about 82ms−1 and a translational temperature of 0.63 K. The slowest beams are obtained using the two-stage cell at the lowest achievable cell temperature of 1.8 K. This beam has a peak velocity of 56ms−1 and a flux of 9×109 ground-state molecules per steradian per pulse, with a substantial fraction at speeds below 40ms−1. These slow molecules can be decelerated further by radiation pressure slowing and then captured in a magneto-optical trap. Published by the American Physical Society 2024

A method to determine the phase-space distribution of a pulsed molecular beam

Abstract We demonstrate a method to determine the longitudinal phase-space distribution of a cryogenic buffer gas cooled beam of barium-fluoride molecules based on a two-step laser excitation scheme. Temporal resolution is achieved by a transversely aligned laser beam that drives molecules from the ground state $X^2\Sigma^+$ to the $A^2\Pi_{1/2}$ state around 860\;nm, while the velocity resolution is obtained by a laser beam that is aligned counter-propagating with respect to the molecular beam and that drives the Doppler shifted $A^2\Pi_{1/2}$ to $D^2\Sigma^+$ transition around 797\;nm. Molecules in the $D$-state are detected background-free by recording the fluorescence from the $D-X$ transition at 413 nm. A temporal resolution of 11\;$\upmu$s and a velocity resolution of 6\;m/s is obtained. In order to calibrate the absolute velocity, we have determined the Doppler free transition frequencies for the $X-A$ and $X-D$ transitions with an absolute accuracy below 0.3\;MHz. The high resolution of the phase-space distributions allows us to observe a variation of the average velocity and velocity spread over the duration of the molecular beam pulse. Our method hence gives valuable insight into the dynamics in the source.

Exploring the Potential of High Entropy Alloys: A Comprehensive Review on Microstructure, Properties and Applications: Part I

Over the past few years, there has been a notable surge in research interest surrounding high entropy alloys (HEAs) owing to their exceptional properties. Unlike conventional alloys, HEAs consist of five or more principal elements, which offer endless possibilities for developing new alloy systems. HEAs exhibit a high concentration of mixing elements, resulting in high disorderliness of the atomic structure within the material, known as high entropy. This unique nature provides HEAs with desirable properties, including excellent mechanical and physical properties at elevated temperatures, making them ideal for high-temperature applications like cryogenic engines and gas turbines. Moreover, HEAs have shown remarkable corrosion resistance, positioning them as viable options for applications in demanding environments such as marine settings, oil and gas pipelines and chemical processing plants. This comprehensive review paper analyses recent studies on various HEAs. Part I introduces HEAs and describes their synthesis, microstructure, hardness and strength properties.

DEVELOPMENT OF SCIENTIFIC FOUNDATIONS AND METHOD OF AUTONOMOUS POWER AND GAS SUPPLY OF REMOTE CONSUMERS FROM GAS DISTRIBUTION NETWORKS

The development and implementation of independent power supply systems with a high degree of autonomy is becoming an urgent task for the development of remote and inaccessible regions of the country, both due to the lack of energy capacities and accessible networks in newly developed areas, and the high cost of allocating separate power lines for remote and compact settlements. The increase in the scale of central networks is associated with high capital investments and long project implementation time, which creates inconvenience for consumers and the development of small and medium-sized enterprises. At the same time, unlike power supply, gasification issues, which are actively being resolved in all regions of the country, make it possible to connect new consumers of natural gas several times faster and cheaper, which is due to the high manufacturability and speed of construction of polyethylene gas pipelines of distribution networks, provided that gas pipelines pass in the region. In addition to lower capital and operating costs, the process of transporting energy resources through pipelines in the form of a primary source — gas — is characterized by significantly lower losses compared to water and electricity. At the same time, network gas in combination with trigeneration technologies and cryogenic hydrocarbon storage can be used not only as boiler fuel, but also as motor fuel, a source for generating electricity, heat and even cold with a replenished autonomous reserve. Thus, as an alternative solution to traditional power systems, it is proposed to use hybrid power systems — systems based on trigeneration plants with gas piston installations, turbine and screw machines, as well as cryogenic gas storage facilities that can provide the population with electricity, heat, cold and motor fuel. The article analyzed the state and development of the fuel and energy complex in Russia, conducted a study of the needs for heat, gas and electricity for an average compact settlement with small and medium-sized enterprises. Analysis and selection of equipment parameters for uninterrupted autonomous power supply of the economy was carried out.

Review Regarding the Influence of Cryogenic Milling on Materials Used in the Aerospace Industry

In the aerospace industry, an important number of machined parts are submitted for high-performance requirements regarding surface integrity. Key components are made of materials selected for their unique properties and they are obtained by milling processes. In most situations, the milling process uses cooling methods because, in their absence, the material surface could be affected by the generated heat (temperatures could reach up to 850 °C), the residual stress, the cutting forces, and other factors that can lead to bad integrity. Cryogenic cooling has emerged as a pivotal technology in the manufacturing of aeronautical materials, offering enhanced properties and efficiency in the production process. By utilizing extremely low temperatures, typically involving liquid nitrogen or carbon dioxide, cryogenic cooling can significantly enhance the material’s properties and machining processes. Cryogenic gases are tasteless, odorless, colorless, and nontoxic, and they evaporate without affecting the workers’ health or producing residues. Thus, cryogenic cooling is also considered an environmentally friendly method. This paper presents the advantages of cryogenic cooling compared with the classic cooling systems used industrially. Improvements in terms of surface finishing, tool life, and cutting force are highlighted.

Early detection of combustion instabilities in liquid rocket engines: Assessment of statistical, recurrence, and fractal analyses for sub- and supercritical pressure conditions

Safe shutdown of a liquid rocket engine in ground testing prior to the onset of damaging combustion instabilities through reliable detection of instability precursors would translate to time and cost savings in engine development programmes. Methods derived from statistical, recurrence, and fractal analysis have been successfully applied in the literature to detect precursors in unsteady pressure signals from canonical combustion experiments, gas-turbine combustion experiments, and sub-scale rocket combustion experiments operated at low pressures. In the present work, several such methods were applied to data from two cryogenic oxygen-natural gas rocket experiments operated at higher pressures than previously reported; both sub- and supercritical with respect to oxygen. The goal was to identify methods that can discern limit-cycle instabilities from intermittently unstable operation and are sufficiently responsive to be applied as emergency shut-down criteria in engine tests. Among the methods applied were the standard deviation, variance of the auto-correlation, the second spectral moment, the ratio between determinism and recurrence rate, the Hurst-exponent, and the multifractal range. The second spectral moment, the Hurst-exponent, and a measure derived from the multifractal spectrum all have short detection delays for instability onset and short-lived could be discerned from self-sustaining instabilities with an appropriate choice of threshold value. They also have moderate computation cost which makes them of interest for potential real-time implementation. The Hurst-exponent has the additional advantage of a common threshold value for all test cases addressed, demonstrating its potential for broader application independent of combustion device or operating conditions.

Coulomb Interaction-Driven Entanglement of Electrons on Helium

The generation and evolution of entanglement in many-body systems is an active area of research that spans multiple fields, from quantum information science to the simulation of quantum many-body systems encountered in condensed matter, subatomic physics, and quantum chemistry. Motivated by recent experiments exploring quantum information processing systems with electrons trapped above the surface of cryogenic noble gas substrates, we theoretically investigate the generation of entanglement between two electrons via their unscreened Coulomb interaction. The model system consists of two electrons confined in separate electrostatic traps that establish microwave-frequency quantized states of their motion. We compute the motional energy spectra of the electrons, as well as their entanglement, by diagonalizing the model Hamiltonian with respect to a single-particle Hartree product basis. We also compare our results with the predictions of an effective Hamiltonian. The computational procedure outlined here can be employed for device design and guidance of experimental implementations. In particular, the theoretical tools developed here can be used for fine-tuning and optimization of control parameters in future experiments with electrons trapped above the surface of superfluid helium or solid neon. Published by the American Physical Society 2024

Extraction Time Simulations of a Cryogenic Gas Stopping Cell Designed to Study the Properties of Superheavy Elements

Extraction Time Simulations of a Cryogenic Gas Stopping Cell Designed to Study the Properties of Superheavy Elements

Multicaloric Cryocooling Using Heavy Rare-Earth Free La(Fe,Si)13-Based Compounds.

The transition toward a carbon-neutral society based on renewable energies goes hand in hand with the availability of energy-efficient technologies. Magnetocaloric cooling is a very promising refrigeration technology to fulfill this role regarding cryogenic gas liquefaction. However, the current reliance on highly resource critical, heavy rare-earth-based compounds as magnetocaloric material makes global usage unsustainable. Here, we aim to mitigate this limitation through the utilization of a multicaloric cooling concept, which uses the external stimuli of isotropic pressure and magnetic field to tailor and induce magnetostructural phase transitions associated with large caloric effects. In this study, La0.7Ce0.3Fe11.6Si1.4 is used as a nontoxic, low-cost, low-criticality multiferroic material to explore the potential, challenges, and peculiarities of multicaloric cryocooling, achieving maximum isothermal entropy changes up to -28 J (kg K)-1 in the temperature range from 190 K down to 30 K. Thus, the multicaloric cooling approach offers an additional degree of freedom to tailor the phase transition properties and may lead to energy-efficient and environmentally friendly gas liquefaction based on designed-for-purpose, noncritical multiferroic materials.

Modulated turbulent convection: a benchmark model for large scale natural flows driven by diurnal heating

Our life is strongly affected by turbulent convective flows, driven by time-dependent thermal forcing, especially diurnal heating of the Earth’s surface by the Sun. In a laboratory experiment, we investigate their analogues: We study complex and extraordinary properties of turbulent buoyancy driven flows generated due to periodic modulation of the temperature of the plates of a Rayleigh–Bénard cell, with amplitudes both smaller and larger than either the positive or negative mean temperature difference between the top and bottom. We probe the turbulent flow of our working fluid – cryogenic helium gas – using temperature sensors placed in the cell interior and embedded in its plates. We discuss spatial and temporal structure of the heat flow, generalize validity of Nusselt versus Rayleigh number scaling Nu ∝\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\propto$$\\end{document} Raγ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\gamma$$\\end{document} with γ≈1/3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma \\approx {1/3}$$\\end{document} at very high Ra for modulated convection and argue that this system represents a benchmark model which helps us understand the energy budget of ocean currents or weather formation on Earth subject to diurnal Sun heating as well as similar natural flows on Earth-like planets.

Manipulating a beam of barium fluoride molecules using an electrostatic hexapole

An electrostatic hexapole lens is used to manipulate the transverse properties of a beam of barium fluoride molecules from a cryogenic buffer gas source. The spatial distribution of the beam is measured by recording state-selective laser-induced fluorescence on an emccd camera, providing insight into the intensity and transverse position spread of the molecular beam. Although the high mass and unfavorable Stark shift of barium fluoride pose a considerable challenge, the number of molecules in the low-field seeking component of the N = 1 state that pass a 4 mm diameter aperture 712 mm behind the source is increased by a factor of 12. Furthermore, it is demonstrated that the molecular beam can be displaced by up to ±5 mm by moving the hexapole lens. Our measurements agree well with numerical trajectory simulations. We discuss how electrostatic lenses may be used to increase the sensitivity of beam experiments such as the search for the electric dipole moment of the electron.

Investigations on Hydrogen Isotope Separation Factor Employing Palladium-Based Solid Metallic Membranes

At present, there are several methods for hydrogen isotope separation (in elemental form), the most important being cryogenic distillation, thermal diffusion, and gas chromatography. However, these methods have a series of drawbacks, namely, high complexity, high energy consumption, and associated costs. Taking into account these disadvantages, a promising separation method is the one based on solid metallic membranes because of its advantages like low energy consumption and reduced complexity. This method uses the difference between some of the isotopes’ properties, namely, solubility; diffusivity; and, implicitly, permeability. This work envisages the integration of an isotopic separation module, based on membrane permeation, on the exhaust gas line from the current experimental rigs employed at ICSI, to recover and store the hydrogen isotopes. We obtained a maximum separation factor of 5.66 for the lowest studied concentration of deuterium in the hydrogen isotopic mixture (0.05 atomic fraction). The results show that hydrogen isotope separation is possible using palladium/silver membranes. Still, the throughput of the permeated gas is very low, and a significant number of stages will be necessary to obtain the desired purity (above 99.5%).

The design and development of the cryogenic compressed gas refueling system

As a new economical, efficient and feasible high density hydrogen storage method, cryogenic compressed hydrogen has been widely explored by scholars in recent years. In this paper, a new cryogenic compressed hydrogen refueling system based on liquid nitrogen cooling is proposed on the basis of the existing high pressure hydrogenation station at normal temperature. The main operating modes of the system include precooling, refueling and standby mode. During the refueling process, it can generate cryogenic compressed hydrogen at 80K temperature and 35MPa pressure, with a mass flow rate of 1kg/min. Additionally, when the cryogenic compressed hydrogen tank requires refueling at high temperatures, the system can provide precooling to reduce hydrogen loss and increase the refueling speed. To validate the feasibility of key equipment and the proposed system, helium gas is used as the working medium for testing. The construction of the cold box, compressor, and cryogenic tank have been completed, and the system is expected to undergo commissioning in the near future.

Influence of source parameters on the longitudinal phase-space distribution of a pulsed cryogenic beam of barium fluoride molecules

Recently, we have demonstrated a method to record the longitudinal phase-space distribution of a pulsed cryogenic buffer gas cooled beam of barium fluoride molecules with high resolution. In this paper, we use this method to determine the influence of various source parameters. Besides the expected dependence on temperature and pressure, the forward velocity of the molecules is strongly correlated with the time they exit the cell, revealing the dynamics of the gas inside the cell. Three observations are particularly noteworthy: (1) The velocity of the barium fluoride molecules increases rapidly as a function of time, reaches a maximum 50–200 µs after the ablation pulse and then decreases exponentially. We attribute this to the buffer gas being heated up by the plume of hot atoms released from the target by the ablation pulse and subsequently being cooled down via conduction to the cell walls. (2) The time constant associated with the exponentially decreasing temperature increases when the source is used for a longer period of time, which we attribute to the formation of a layer of isolating dust on the walls of the cell. By thoroughly cleaning the cell, the time constant is reset to its initial value. (3) The velocity of the molecules at the trailing end of the molecular pulse depends on the length of the cell. For short cells, the velocity is significantly higher than expected from the sudden freeze model. We attribute this to the target remaining warm over the duration of the molecular pulse giving rise to a temperature gradient within the cell. Our observations will help to optimize the source parameters for producing the most intense molecular beam at the target velocity.

Study of long-term in-orbit pressure control of liquid krypton cryogenic storage tank

Due to its high specific impulse, low toxicity, contamination, safety, and cost, krypton has gradually replaced other propellants as the primary choice for electric thrusters on deep-space exploration and large-orbit transfer missions with long-range, long-duration, and large-thrust requirements. However, due to the cryogenic propellant itself having a low boiling point, controlling the pressure change of krypton cryogenic propellant during the process of long-term cryogenic storage has emerged as one of the most important issues that must be resolved and proven to achieve non-destructive storage of cryogenic propellant. This paper examines the necessity and viability of a cryogenic gas propellant liquefaction storage scheme and quantifies the effectiveness of tank pressure control of the supercooled liquid krypton injection mixing scheme to solve the problem at present. Its purpose is to offer scheme examples for the design of a krypton thruster propellant storage unit and the in-tank pressure control during the long-term application process.

Failure Analysis of Cryogenically Treated and Gas Nitrided Die Steel in Rotating Bending Fatigue

<div>AISI H13 hot work tool steel is commonly used for applications such as hot forging and hot extrusion in mechanical working operations that face thermal and mechanical stress fluctuations, leading to premature failures. Cryogenic treatment was applied for AISI H13 steel to improve the surface hardness and thereby fatigue resistance. This work involves failure analysis of H13 steel specimens subjected to cryogenic treatment and gas nitriding. The specimens were heated to 1020°C, oil quenched followed by double tempering at 550°C for 2 h, and subsequently, deep cryogenically treated at −185°C in the cryochamber. Gas nitriding was carried out for 24 h at 500°C for 200 μm case depth in NH<sub>3</sub> surroundings. The specimens were subjected to rotating bending fatigue at constant amplitude loading at room temperature. Measurement of surface roughness, hardness, and microstructural analysis indicated improved fatigue life for cryogenically treated specimens as compared to gas nitride, which could be attributed to fine carbide precipitation accountable for the delayed crack initiation and propagation.</div>

Experimental setup for the measurement of optical properties in the vacuum ultraviolet region

Abstract This work presents an experimental setup designed for measuring optical properties in the vacuum ultraviolet (VUV) region. Originally developed for the characterization of ICARUS photomultiplier tubes, the setup has been recently employed to measure the conversion efficiency of para-Terphenyl coatings, acting as wavelength shifters, as a function of thickness. The VUV region is of particular interest in particle physics experiments utilizing cryogenic noble gases as scintillating media. The setup includes a deuterium light source, a mirror system, an intensity monitor, and a sample chamber to host sample and photodetector. An example measurement of para-Terphenyl conversion efficiency — as wavelength shifter — with varying thickness is presented, demonstrating the versatility and effectiveness of the presented system.

Novel device to study double-alpha decay at the FRS Ion Catcher

A novel system has been developed to detect simultaneous double-alpha emission from purified and weightless sources. The system includes the collection of 224Ra low-energy recoils in purified helium buffer gas from the decay of 228Th. The recoil products are thermalized and collected in a cryogenic buffer gas cell and extracted into an RF-ion guide for mass selection. The mass-separated ions are implanted at low kinetic energy into a thin carbon foil placed between two large-area double-sided silicon strip detectors to observe correlated alpha-particle emission. The apparatus is described in detail, including insights into its experimental performance.

Exploring the Potential of Metal-Organic Frameworks for Cryogenic Helium-Based Gas Gap Heat Switches via High-Throughput Computational Screening.

With the advantages of a long lifetime and high reliability, gas gap heat switches (GGHSs) are attractive in many thermal management applications, especially in space-borne cryogenic systems. The performance of a GGHS is significantly affected by the adsorption characteristics of the adsorbent in the sorption pump. Compared with the commonly used adsorbent in the GGHSs (activated carbon), metal-organic frameworks (MOFs) have larger surface areas, higher pore volumes, and exceptional tunability, which motivates this study to explore their potential for application in cryogenic GGHSs. To this end, two performance metrics, the required volume of adsorbent (vsor) and total input heat (qtot), were computed for about 6000 MOFs via molecular simulations and compared with those of activated carbon. It is found that over 2300 MOFs possess a smaller vsor than activated carbon, and the smallest vsor of MOFs is about 12.7% of that of activated carbon. vsor and qtot generally change in the same direction, which implies it is possible to reduce both parameters simultaneously by choosing a suitable MOF. Structure-performance analysis reveals that 1/vsor consistently increases first and then decreases with pore limiting diameter, largest cavity diameter, available pore volume, accessible surface area, helium void fraction, and bulk density. Descriptor ranges corresponding to high-performing MOFs were identified based on Precision-Recall analysis. Notably, Zr-containing MOFs are particularly likely to have smaller vsor values than activated carbon. It is anticipated that the promising MOFs identified by this study will motivate further experimental investigations, and the insights into structure-performance relationships can serve to guide the rational design of novel MOF candidates for GGHSs.

Study on transferring the refrigeration power in the temperature-distributed regenerative refrigeration cycle

The temperature-distributed regenerative refrigeration cycle utilizes the real-gas properties to generate the temperature-distributed refrigeration power and improves the cooling performance and liquefaction rate of cryogenic gases. The temperature-distributed refrigeration power is distributed in the volume of the regenerator. It is challenging to transfer this distributed refrigeration power, and the regenerative heat loss is usually inevitable. The transfer process of the temperature-distributed refrigeration power is studied in this paper. A comprehensive investigation into associated influencing factors is presented in this paper. Furthermore, a parameter of the temperature-distributed transfer coefficient (TTC) is proposed to evaluate the transfer process. This study extends into a broader range of the discrete transfer method from liquid-helium temperatures to ambient temperatures and further analyzes the rules from scattered points to multiple points. The internal DC flow method is adopted to eliminate the radial thermal resistance and improve the TTC, recognizing the constraints of the traditional distributed transfer method (coiling heat exchange tubes outside the regenerator). The TTC of the distributed method with the DC flow is improved around 1–2 times by optimizing the mass flux of multi-strand DC flow and temperature range. It is also improved 1.5–2 times by combining the DC flow and discrete method. Additionally, the TTC is improved about 1–1.5 times with the DC flow when using the refrigeration power for gas liquefaction.