Residual Gas Pressure Research Articles

Wafer-scale fabrication of evacuated alkali vapor cells.

We describe a process for fabricating a wafer-scale array of alkali metal vapor cells with low residual gas pressure. We show that by etching long, thin channels between the cells on the Si wafer surface, the residual gas pressure in the evacuated vapor cell can be reduced to below 0.5 kPa (4 Torr) with a yield above 50%. The low residual gas pressure in these mass-producible alkali vapor cells can enable a new generation of low-cost chip-scale atomic devices such as vapor cell optical clocks, wavelength references, and Rydberg sensors.

Effectiveness Spatiotemporal of Pressure Unloading and Gas Extraction in Remote Upper Protected Seam Mining.

Severe gas hazards are increasing in deep mining areas, and there exists an enormous traditional challenge for protected seam mining. In this work, we conducted a multifaceted investigation into the spatiotemporal effectiveness exerted by pressure unloading from a distant safeguarded stratum in concert with the application of gas extraction methodologies. The stress and displacement evolution in the protected coal seam (PCS) are analyzed by applying Flac3D, and then positives are verified by the measurement of coal seam deformation and investigation of the unloading boundary. The results show that diminution coefficient of 0.62, and record an expansive deformation rate of 5.83%. The opportune temporal window for effective gas drainage is discerned, with its time window spans from 58 to 67 days as the expanse between 350 and 400 m progresses at the working face. Continuous and effective gas extraction occurs when transverse cracks in the PCS reach an optimal state of pressure relief. The final cumulative gas extraction was 320,300 m3 with an extraction efficiency of 34.3%. A residual gas volume of 3.68 m3/t and a residual gas pressure of 0.5 MPa reflect the efficient gas extraction.

A novel interdisciplinary model for optimizing coalbed methane recovery and carbon dioxide sequestration: Fracture dynamics, gas mechanics, and its application

The Carbon Dioxide Enhanced Coalbed Methane (CO2-ECBM) technique significantly enhances clean energy extraction and mitigates climate change. Central to this process is the dynamic evolution of rough fracture networks within coal seams, influencing the migration of CO2 and natural gas. However, existing research lacks a comprehensive, quantitative approach to examining the micro-evolution of these fractures, including fracture roughness, fracture density, fracture touristy, and fracture size, particularly under thermo-hydro-mechanical effects. Addressing this gap, our study introduces an innovative, fractal model for quantitative analysis. This model intricately characterizes fracture networks in terms of number, tortuosity, length, and roughness, integrating them with fluid dynamics affected by external disturbances in CO2-ECBM projects. Upon rigorous validation, the finite element method analysis reveals significant impacts of micro-parameters on permeability and natural gas extraction. For instance, increasing CO2 injection pressure from 4 to 6 MPa changes fracture network density by up to 6.4%. A decrease in fracture density (Df) from 1.6 to 1.5 raises residual gas pressure by 2.7% and coal seam stress by 9.5%, indicating crucial considerations for project stability. Applying the proposed interdisciplinary model to assess CO2 emissions in Australia, it is can be obtained that when Df decreases from 1.6 to 1.5, the total amount of CO2 storage reduces by 17.71%–18.04%. Our results demonstrate the substantial influence of micro-fracture behaviors on CO2-ECBM projects, offering a ground-breaking solution for efficient greenhouse gas reduction and clean energy extraction, with practical implications for the energy sector's sustainability.

Determining the effect of laboratory testing conditions on working parameters of the ST-25 hall thruster

The object of this study is the ST-25 Hall thruster with limited discharge power, no more than 200 W, designed by Flight Control LLC (Ukraine). The problem that was solved in the current paper was to determine the effect of residual gas pressure in vacuum chambers on the operating parameters of the Hall thruster. To solve this task, the operating parameters of the ST-25 thruster were determined, which was tested in three vacuum chambers with different sizes of residual pressure. As a result of the laboratory study into the operating parameters of the ST-25 thruster, the volt-ampere characteristics of the engine discharge at fixed values of the working gas (xenon) flow rate were obtained. The dependences of the engine thrust on the mass flow rate of the working gas at fixed values of the discharge voltage were derived. Based on the experimental data, the dependences of the specific impulse of the engine anode unit on the discharge voltage, as well as the dependence of efficiency of the engine anode unit on the discharge voltage were calculated. The studies showed that when the residual pressure in the vacuum chamber is reduced by 2–3 times, the operating parameters of the engine increase by 15–20 %. Such a reduction in residual pressure increases thrust by 25–40 %. Special feature of the results is the determination of threshold values of residual gas pressure in vacuum chambers during experimental studies, in which the operating parameters of the Hall thruster are similar to its operating parameters under space conditions. This work’s findings could be used in practice when conducting experimental studies of electric rocket engines, when it is necessary to estimate the operating parameters of Hall thrusters that will be obtained under actual space conditions

Experimental investigation on the discharge and suction gas performance in the multilayer insulation microchannels

The use of cryogenic propellants is prioritized for powering Mars lander propulsion systems. To provide thermal protection for these cryogenic propellants, a combination of multilayer insulation (MLI) and foam is commonly employed. However, during the Mars lander ascent, space travel, and reentry, unique phenomena such as transient venting and suction of gas occur within the MLI, significantly compromising its insulation performance. In the current study, an experimental platform was developed to investigate the discharge and suction of rarefied gas in MLI microchannels. Based on the perforation MLI results, the residual gas pressure in the innermost layer reaches below 10 Pa after over 100 h of evacuation. Baked MLI exhibits favorable discharge gas performance, with an average pressure value (the sum of the interstitial pressure in MLI divided by the total number of layers) 30.85% lower than that of the original MLI. Evacuation rates are improved by 11.87% when the MLI is flushed with nitrogen (N2). The baking condition does not significantly affect suction gas properties. The thermal conductivity of residual helium (He) is much higher than that of air and N2. These findings offer valuable insights for the design of cryogenic propellant tanks, aiding in optimizing their insulation performance.

Centralized design and production of the ultra-high vacuum and laser-stabilization systems for the AION ultra-cold strontium laboratories

This paper outlines the centralized design and production of the ultra-high-vacuum sidearm and laser-stabilization systems for the AION Ultra-Cold Strontium Laboratories. Commissioning data on the residual gas and steady-state pressures in the sidearm chambers, on magnetic field quality, on laser stabilization, and on the loading rate for the 3D magneto-optical trap are presented. Streamlining the design and production of the sidearm and laser stabilization systems enabled the AION Collaboration to build and equip in parallel five state-of-the-art Ultra-Cold Strontium Laboratories within 24 months by leveraging key expertise in the collaboration. This approach could serve as a model for the development and construction of other cold atom experiments, such as atomic clock experiments and neutral atom quantum computing systems, by establishing dedicated design and production units at national laboratories.

Stability of electrons and X-rays generated in a pyroelectric accelerator

Conventional X-ray sources are far too bulky and require a high-power DC voltage. The pyroelectric X-ray generator technology has enabled us to develop portable, low-power X-ray sources for use in materials analysis, imaging, and other applications. Changing the temperature of single crystal lithium tantalate (LiTaO3) at moderate vacuum conditions gives an attractive possibility to generate and accelerate electron up to 100 keV. The electrons are ejected either from the crystal or from the target (depending on polarity). The electrons then generate X-rays via bremsstrahlung and characteristic X-ray emission processes. The aim of this experimental investigation is to explore the interesting feature of the pyroelectric accelerator that generates a monoenergetic electron flux with a stable value of peak energy for a long time. Here we present studies of features of electron flux in pyroelectric accelerator depending on the pressure of residual gas and the distance between the crystal and the target-collimator. We examine the correlation between monoenergetic electron production and avalanche discharge. We also studied outgassing from some accelerator components. The pyroelectric X-ray generator technology is currently being developed is a reliable, compact, stable, and reproducible X-ray source with controllable parameters, which does not require a high-power DC voltage or the use of hazardous (radioactive) materials.

Residual gas noises in vacuum of optical interferometer for ground-based gravitational wave detection

Gravitational waves (GWs) are ripples in spacetime caused by most violent and energetic processes in the universe, such as the rapid motion of massive celestial bodies. The GWs carry energy when they propagate through the universe. The detection of GWs holds significance for advancing human understanding of the nature and driving scientific and technological progress. The continual upgrading and optimizing of GW detectors offer novel avenues for cosmic measurements. However, ground-based GW detectors based on a large interferometer necessitate addressing various noises which are harmful to the sensitivity of the GW detectors. Among these noises, the noise from residual gas in the light beam of the interferometer is a crucial factor to affect the sensitivity. Consequently, it is necessary to establish a vacuum system to shield the laser interferometer from the effects of gas flow. This paper focuses on China’s third-generation ground-based GWs detector, conducting theoretical analysis of the influence of residual gas noise on both a 20-meter arm-length prototype and a full-scale device with a 10-kilometer arm-length. In this paper, a theoretical model for the residual gas particles passing through the laser beam is established and the effect on the beam phase is analyzed. The theoretical simulations are performed to discover the relations between the residual gas noise and significant parameters such as gas pressure of the vacuum system, temperature, mass of residual gas particles, polarization rate of the residual gas, and the curvature radius of the test mass. The simulations indicate that when the residual gas pressure is below 2×10<sup>–6</sup> Pa, the GW detector can achieve the enough sensitivity, 10<sup>–24</sup> Hz<sup>–1/2</sup>, in a frequency range from 10 to 10<sup>3</sup> Hz. The findings of this research offer crucial theoretical insights for designing and constructing the vacuum systems in future third-generation GWs detector prototypes and full-scale devices.

Design of a temperature-limited emission current controller

In this study, we design and test a current controller for a source of thermionic electron emission operating in an ionization vacuum gauge. We use a precise and controlled source of current to transfer the emission current from the anode, which has a high potential in the circuit, to the cathode with a low potential. This eliminates the need for galvanic isolation or sources of floating voltage, which introduce noise to the system, for supplying the cathode and the anode. We show that this has a limited effect in terms of changes in the residual gas pressure on the emission current in the range from 10−4 to 10−2 Pa. The temporal stability of the emission current was determined for reference values ranging from 1 to 4 mA for both 10-min and 2-h periods, and it was found to be lower than 6 ppm. The proposed controller can be used in apparatus to measure electron impact-induced gas ionization.

An Invar-based dual Fabry–Perot cavity refractometer for assessment of pressure with a pressure independent uncertainty in the sub-mPa region

An updated version of an Invar-based dual Fabry–Perot cavity refractometer utilizing the gas modulation methodology has been characterized with regard to its ability to assess gas pressure in the low pressure regime, defined as the regime in which the instrumentation is mainly limited by the constant term a in the [(a)2+(b×P)2]1/2 expression for the uncertainty. It is first concluded that this ability is predominantly limited by three entities, viz., the empty cavity repeatability, the residual gas pressures in the evacuated (measurement) cavity, and the contamination of the gas residing in the measurement cavity that originates from leaks and outgassing. We then present and utilize methods to separately estimate the uncertainty of the updated refractometer from these entities. It was found that, when utilizing gas modulation cycles of 100 s and when addressing nitrogen, the system can assess pressure in the low pressure regime with an expanded uncertainty (k=2) of 0.75 mPa, mainly limited by the empty cavity repeatability and outgassing of hydrogen. This is more than 1 order of magnitude below the previously assessed low pressure performance of the instrumentation.

Machine learning-based system for vacuum leakage detection in EAST fusion device

In order to achieve real-time monitoring of partial pressures of residual gases and timely detection of vacuum leakage in fusion devices, a machine learning-based system was successfully developed on the LabVIEW software platform for its first-time application in the EAST fusion device. This system acquires partial pressure data from the quadrupole mass spectrometer (QMS) in both histogram and P&T scanning modes to identify the nature of vacuum leakage. The backpropagation (BP) neural network algorithm is employed for leakage detection. To train the BP neural network model, historical data from normal and leakage scenarios on the EAST device are utilized as inputs. Subsequently, the trained model is integrated into the system. The BP neural network model exhibited an identification accuracy of 95.27 % on the test set, effectively detecting water and gas leakage on EAST. Consequently, this system enables rapid detection of vacuum leakage in fusion devices, facilitating prompt mitigation of their impact on plasma experiments and ensuring the device's safety and stability.

Development of an accelerator-based neutron source to prototype Mo-99 production, Part II: A liquid LBE loop under a high vacuum

To provide US domestic supply of Mo-99 without using high-enriched uranium (HEU), a subcritical uranium target assembly (UTA) is irradiated by an accelerator-based neutron source to create Mo-99 through fission. Part I of this work discusses the design of a liquid lead–bismuth eutectic (LBE) windowless target for an accelerator-based neutron source development. Part II discusses how to couple this windowless target to an accelerator operating at an ultra-high vacuum and the subcritical UTA cooled by water at room temperature.Due to the windowless design of the target, the liquid LBE flow shares an ultra-high vacuum (<1.3 × 10−7 Pa or 10−9 Torr) space with the accelerator. As a result of this shared vacuum space, the LBE system must operate at a high vacuum (10−3 ∼ 10−6 Pa or 10−5 ∼ 10−8 Torr). A magnetic rotary motion feedthrough unit utilizes magnetic fluid to allow rotation of the pump while maintaining a high vacuum environment. Prior to testing the LBE system under vacuum, a pump curve measurement is performed to estimate flowrate in the system. This measurement also generates data on orifice loss coefficients, which are compared to correlations in literature. The second experiment investigates vacuum level in the LBE system during operation. High vacuum is maintained (10−3 ∼ 10−5 Pa or 10−5 ∼ 10−7 Torr) during system operation, and a residual gas analyzer (RGA) scan shows that partial pressures of residual gases in the LBE system lower over the duration of LBE system operations. The third experiment investigates the gravity driven liquid LBE flowing out of the target chamber in the return line, which is partially full. If the liquid LBE is not drained quickly enough, flooding in the target chamber could occur. The coefficient n in the Manning equation is found to be around 0.008 s/m1/3. The last experiment performed is a demonstration that a vacuum jacket could provide sufficient thermal insulation to allow coupling between 300 °C LBE loop and a water tank at room temperature. The results from these experiments have influenced the development of the neutron source for the future commercial scale Mo-99 production system.

Non-isothermal consolidation: A systematic evaluation of two implementations based on multiphase and Richards equations

In this paper, the governing equations of non-isothermal two-phase flow in unsaturated, deformable porous media are presented based on different representations of the gaseous phase along with their implementations in the open-source FEM code OpenGeoSys 6. As one implementation utilises the Richards equation to represent the unsaturated system whereas the second implementation relies on a two-component two-phase flow formulation, the impact of a free gaseous phase on model predictions is illustrated by a series of tests of increasing complexity, motivated by similar investigations in Task C of the DECOVALEX 2023 project. We demonstrate that the governing equations of both implementations collapse and become identical in fully saturated regions and that the numerical implementations remain stable in the special cases. Furthermore, the implicit assumptions made in the Richards equation are explicitly applied to the physically more complex and comprehensive TH2M model. Thus, the impact of a constant residual gas pressure on the model predictions is investigated. Finally, the examples chosen for this work feature thermal consolidation and pore fluid pressurisation effects in the Opalinus Clay due to heat release from a nuclear waste canister as well as dry-out with subsequent resaturation of a bentonite buffer around the heat source. All test cases are evaluated on the level of the governing equations of each model as well as on the level of results obtained by each model for a discussion of conceptual model uncertainty.

Absence of synergistic effects in quasi-simultaneous sputtering of tungsten by Ar and D ions

A quartz crystal microbalance was used to experimentally study the erosion of tungsten during rapidly alternating bombardment with 2 keV argon and deuterium projectiles. A key goal was to investigate whether the mean sputtering yield of the alternating irradiation can be predicted from data for sputtering yields of single ion species. In addition, influences by residual gas pressure in the UHV experiment and variable ion fluxes have been studied. Our results show that the mean sputtering yield of irradiations with alternating ion species can be well predicted for a range of different fluence ratios as a simple superposition of individual sputtering yields, weighted by the respective relative fluences. This finding supports that no synergistic sputtering effects were relevant in the investigated low-flux regime.

A modified pump-down model for high vacuum packaging of vacuum insulation sandwiches under readsorption effect

Thermal insulation performance and service life of vacuum insulation sandwiches depend significantly on the internal residual gas pressure. Degradation of the vacuum can lead to a dramatic increase in thermal conductivity, so the initial internal pressure should be kept as low as possible during fabrication. In this paper, the evacuation and outgassing of vacuum insulation sandwiches are studied by modeling and experimental methods. A modified pump-down model for vacuum insulation sandwiches, called the recombination-dissociation-limited model, is proposed based on diffusion, recombination, and dissociation. The results show that the recombination and the dissociation of hydrogen on the inner surface have a hysteresis effect on the evacuation process, which explains well that the pressure inside the device remains above the ultimate pressure of the vacuum system after packaging. The experimentally measured evolution of the pressure and outgassing rate in the vacuum insulation sandwiches agree well with the calculated results. The simulation analyses the effects of temperature, pump-out port size, and ultimate pressure on evacuation efficiency. It provides a theoretical basis for predicting the dynamic pressure evolution during high vacuum packaging and selecting effective parameters in the packaging process.

Ultra high vacuum beam pipe of the Einstein Telescope project: Challenges and perspectives

The Einstein Telescope (ET) is a project aiming to realize a facility to host a gravitational wave (GW) detector of the third generation. The new instrument will change our vision of the Universe by observing millions of GW signals emitted during the coalescence of stellar and intermediate-mass black hole binary systems. It will permit to shed light on the first phase of the Universe formation and it will contribute to solving the dark matter enigma. The new GW detector is conceived as a series of six nested Michelson interferometers forming a triangle of 10 km side. The laser light biasing the interferometers must propagate in large ultra-high vacuum (UHV) tubes in order to reduce the noise induced by the residual gas pressure fluctuations, setting a requirement on the residual pressure in the 10−10 mbar range. The vacuum system will be made of a pipe with a 1 m diameter and an overall length of 120 km, making ET one of the largest UHV systems ever made. The giant UHV project asks for attentive optimization of material choice, manufacturing processes, post-processing treatments of the tubes, and pumping systems in order to find a cost-effective solution. In this article, we shortly review the vacuum solution adopted in the case of the second generation of GW detectors. After a general description of the main elements that constitute the ET vacuum system, the detailed design being the subject of the next 3 years of work, we will present a refined calculation of the noise due to residual-gas pressure fluctuations in the ET beam pipe.

Investigation, simulation and first measurements of a 2 m long electron column trapped in a Gabor-Lens device

Various Gabor-Lenses (GL) were investigated at Goethe University. Confinements of sufficient electron densities (ne ∼ 1 · 1015 m3) were reached without any external source of electrons. Focusing of ion beams by low energy was demonstrated, long term stability and reproducibility were approved. Main differences compared to experiments and investigations of the pure non-neutral in Penning-Malmberg traps [1] are higher residual gas pressure and therefore higher collision rates, higher bulk temperatures, self-sustaining electron production process, much higher evaporation cooling rate. GL2000 is a new 2 m long device and was mainly designed for focusing of ion beams in energy ranges up to GeV but also for investigation of non-neutral plasma parameters. The confined electron column is much longer compared to previous constructed Lenses. This makes ion and hadron beam focussing much more efficient, in addition new physical phenomena can be expected and investigated. Simulation results of steady-and thermal equilibrium states with various external parameters and first measurements will be presented. The first operational tests show that it is possible to confine a two-meter long electron column.

Intensive field measurements for characterizing the permeability and methane release with the treatment process of pressure-relief mining

Characterizing the permeability evolution and methane release is of great significance for the safe mining of the high gas outburst seams, as well as coal and gas simultaneous extraction. It contributes to reduce methane emissions from coal mining for greenhouse effect control. Theoretical analysis, laboratory testing, and numerical simulation are widely used methods to characterize the permeability and methane release with the treatment process of pressure-relief mining. However, these methods cannot fully reflect the complexity of filed practice. In this study, we report the effectiveness of protective coal seam (PCS) mining and the pressure-relief area in the protected coal seam (PDCS) based on detailed and integrated field measurements in a Chinese coal mine. To the best of our knowledge, it is the first time to measure the permeability coefficient and gas pressure evolution in the PDCS during the process of PCS longwall mining. The evolution of the permeability coefficient in the pressure-relief area during PCS mining can be divided into four stages: slowly decreasing, sharply increasing, gradually decreasing, and basically stable. The maximum permeability coefficient is 322 times of the initial value and stabilized at 100 times after the goaf compacted. The gas pressure evolution in the PDCS indicates that the strike pressure relief angle is 52.2° at the active longwall face zone, and 59.3° at the installation roadway side. The inclined pressure relief angles at the lower and upper sides of the longwall face are 75° and 78.9°, respectively. The residual gas content and gas pressure of the PDCS in the pressure-relief area are reduced to less than 6 m3/t and within 0.4 MPa, respectively. The field measurements further prove that pressure-relief mining can prevent coal and gas outbursts in PDCSs. The field observations in this paper can serve as benchmark evidence for theoretical analysis and numerical simulations, and also provide insights into realizing safety mining in similar conditions.

Spontaneous and photo-induced decay processes of WF5 - and HfF5 - molecular anions in a cryogenic storage ring.

Spontaneous and photo-induced decay processes of HfF5 - and WF5 - molecular anions were investigated in the Double ElectroStatic Ion Ring ExpEriment (DESIREE). The observation of these reactions over long time scales (several tens of ms) was possible due to the cryogenic temperatures (13K) and the extremely low residual gas pressure (∼10-14mbar) of DESIREE. For photo-induced reactions, laser wavelengths in the range 240 to 450nm were employed. Both anion species were found to undergo spontaneous decay via electron detachment or fragmentation. After some ms, radiative cooling processes were observed to lower the probability for further decay through these processes. Photo-induced reactions indicate the existence of an energy threshold for WF5 - anions at about 3.5eV, above which the neutralization yield increases strongly. By contrast, HfF5 - ions exhibit essentially no enhanced production of neutrals upon photon interaction, even for the highest photon energy used in this experiment (∼5.2eV). This suppression will be highly beneficial for the efficient detection, in accelerator mass spectrometry, of the extremely rare isotope 182Hf using the 182HfF5 - anion while effectively reducing the interfering stable isobar 182W in the analyte ion 182WF5 -. The radionuclide 182Hf is of great relevance in astrophysical environments as it constitutes a potential candidate to study the events of nucleosynthesis that may have taken place in the vicinity of the solar system several million years ago.

EXPERIMENTS ON THE INTERACTION OF HYDROGEN ISOTOPES WITH LITHIUM CERAMICS OF DIFFERENT GRADES

This paper describes the results of experiments on the interaction of hydrogen isotopes with lithium ceramics of different grades. The studies were carried out in two stages: a cycle of work on saturation of samples in a deuterium medium was conducted at a facility for studying the interaction of gases with materials (CorrSiC’a)) based on an industrial highvacuum tube furnace GSL-1600, at temperatures of 300 °C, 500 °C, 700 °C; hermal desorption (TDS) experiments at a facility, where the sample is heated by a non-contact method (induction heating) at a rate of 2 K/s and 10 K/s, at a pressure of residual gases in the installation chamber ~10−4 Pa. The values of the activation energy of deuterium gas release from lithium ceramics of different grades are obtained.