Temperature Argon Research Articles

Using magnesium hydride as the future dual-mode propellant for spacecraft: A simulation investigation

A dual-mode propulsion system stands as the important viable pathway for future multi-purpose deep space missions by the spacecraft, encompassing both nuclear thermal propulsion and nuclear electric propulsion. H2 and Mg emerge as potential mediums for nuclear thermal propulsion and nuclear electric propulsion, respectively, with the possibility of utilizing a single material, magnesium hydride (MgH2), to serve both purposes. However, how to release hydrogen completely and effectively in high hydrogen desorption pressure while retaining magnesium is the key problem. In this work, we proposed a novel MgH2 storage tank for zero gravity environments and investigated its hydrogen desorption process at high pressures of 4 ∼ 8 MPa using simulation, which is crucial for the hydrogen supply of nuclear thermal propulsion. We examined the effects of hydrogen desorption pressure, inlet temperature, and flow velocity of argon (Ar) on the desorption process. The simulation results indicated complete decomposition of MgH2 can be realized under 4 ∼ 8 MPa at 873 K. Moreover, the desorption pressure, inlet temperatures, and high flow velocities of Ar are suggested as 4 MPa, 773 ∼ 785 K, and 45 ∼ 100 m s−1 to achieve an average hydrogen desorption rate per unit thermal power of ≥ 20 mgH2 s−1. This work marks the first confirmation that MgH2 can decompose into H2 and Mg under high hydrogen desorption pressure at suitable thermal power, paving the way for its application as the hydrogen and Mg storage media in the dual-mode propulsion system of spacecraft.

Gain stability of Hamamatsu R5912-MOD photomultipliers at low temperature

The Photon Detection System (PDS) is a crucial component of the ICARUS detector in the Short Baseline Neutrino (SBN) Program at Fermi National Accelerator Laboratory (FNAL). It consists of 360 PhotoMultiplier Tubes (PMTs) 8” Hamamatsu R5912-MOD and, since June 2020, it has been operating at the liquid Argon cryogenic temperature. During these years, the PMTs have shown gain losses as an aging effect. Using a climatic chamber at the INFN Sezione di Catania, we confirmed a stable gain for a single PMT 8” Hamamatsu R5912-MOD when operated at room temperature, and a persistent gain loss at temperatures around -70 °C, although this temperature is rather higher than that of the liquid Argon.

A novel cryogenic VUV spectrofluorometer for the characterization of wavelength shifters

We present a novel cryogenic VUV spectrofluorometer designed to characterize wavelength shifters (WLS) crucial for experiments based on liquid argon (LAr) scintillation light detection. Wavelength shifters like 1,1,4,4-tetraphenyl-1,3-butadiene (TPB) or polyethylene naphthalate (PEN) are used in these experiments to shift the VUV scintillation light to the visible region. Precise knowledge of the optical properties of the WLS at liquid argon's temperature (87 K) and LAr scintillation wavelength (128 nm) is necessary to model and understand the detector response. The cryogenic VUV spectrofluorometer was commissioned to measure the emission spectra and relative wavelength shifting efficiency (WLSE) of samples between 300 K to 87 K for VUV (120 nm to 190 nm) and UV (310 nm) excitation. New mitigation techniques for surface effects on cold WLS were established. As part of this work, the TPB-based wavelength shifting reflector (WLSR) featured in the neutrinoless double-beta decay experiment LEGEND-200 was characterized. The WLSE was observed to increase by (54 ± 5) % from room temperature (RT) to 87 K. PEN installed in LEGEND-200 was also characterized, and a first measurement of the relative WLSE and emission spectrum at RT and 87 K is presented. The WLSE of amorphous PEN was found to be enhanced by at least (37 ± 4) % for excitation with 128 nm and by (52 ± 3) % for UV excitation at 87 K compared to RT.

Electromagnetic–Computational Fluid Dynamics Couplings in Tungsten Inert Gas Welding Processes—Development of a New Linearization Procedure for the Joule Production Term

The finite volume method (FVM) was used to model a tungsten inert gas (TIG) arc welding process. A two-dimensional axisymmetric model of arc plasma integrating fluid–solid coupling was developed by solving electromagnetic and thermal equations in both the gas domain and the solid cathode. In addition, two additional coupling equations were considered in the gaseous domain where the arc is generated. This model also included the actual geometry of torch components such as the gas diffuser, the nozzle, and the electrode. The model was assessed using numerous numerical examples related to the prediction of the argon plasma mass fraction, temperature distribution, velocity fields, pressure, and electric potential in the plasma. A new linearization method was developed for the source term in the energy conservation equation, allowing for the prediction of Joule effects without artificial conductibility. This new method enhances the efficiency of the classical approach used in the literature.

Cryogenic RPWELL: a novel charge-readout element for dual-phase argon TPCs

The first operation of a cryogenic Resistive Plate WELL (RPWELL) detector in the saturated vapor of liquid argon is reported. The RPWELL detector was composed of a Thick Gas Electron Multiplier (THGEM) electrode coupled to a metallic anode via Fe2O3/YSZ ceramics (Fe2O3 in weight equal to 75%), with tunable bulk resistivity in the range 109–1012 Ω·cm. The detector was operated at liquid argon temperature in saturated argon vapor (90 K, 1.2 bar) and characterized in terms of its effective charge gain and stability against discharges. Maximum stable gain of G≈17 was obtained, without discharges. In addition, preliminary results from novel 3D-printed thermoplastic plates doped with carbon nanotubes are presented.

Spatial distribution diagnosis of electron temperature and density of argon inductively coupled plasma by tomographic optical emission spectroscopic measurement and collisional-radiative model

There are few reported cases in which the spatial distribution of spectral emission coefficients of plasmas from tomographic optical emission spectroscopy measurements is analyzed based on a collisional-radiative model to diagnose the spatial distribution electron temperature of Te and density Ne. This study aimed at in situ diagnosis of process plasma. The spectral radiance of 18 lines-of-sight was measured simultaneously in argon inductively coupled plasma. The spatial distribution of the excited level number density distribution was calculated from the spatial distribution of spectral emission coefficients obtained from spectral tomography calculations. The three-dimensional distribution of Te and Ne was analyzed using a collisional-radiative model from the obtained spatial distribution of the excited levels number density. The effects of power and pressure on the dependence of the spatial distribution of Te and Ne were discussed. Furthermore, data processing methods for spectral tomographic measurements with coarse wavelength resolution were also discussed.

Pool boiling simulation using molecular dynamics approach: Comparing the effectiveness of adding nanoparticles versus creating porous nanostructures

This paper presents the pool boiling process of argon atoms on the copper surface by employing molecular dynamics simulation. Through the application of molecular dynamics simulation, this study explores three cases: the plain surface, and adding platinum and aluminum nanoparticles to the argon fluid. The main objective is to offer a comprehensive comparative analysis to highlight the significance and innovation of this research. The investigation aims to assess the effectiveness of two methods for improving heat transfer: the addition of nanoparticles to the base fluid and the creation of porous nanostructure. By subjecting these approaches to identical simulation conditions, an enthralling evaluation unfolds. The simulation framework is first validated, and then the results are presented and compared with the case of creating porous geometry. The results reveal that while the evaporation rate has a similar impact in both cases, creating porous geometry results in a 3.68% higher argon temperature compared to adding nanoparticles. On the other hand, adding nanoparticles enhances the maximum heat flux by approximately 15% more than creating porous geometry. This research compares two approaches to offer valuable investigations and insights into enhancing heat transfer efficiency due to the growing demand for strategies that promote heat transfer.

Investigation of the temperature of electrons in a glow discharge plasma at direct current Ar and Ar/C2H2

This paper presents the results of the study of the electron temperature in argon and argon-acetylene plasma of DC glow discharge. The optical-emission method was used to determine the main parameter of the complex plasma. The dependence of the electron temperature on the operating pressure, voltage, and discharge time was determined from the intensity of spectral lines. The source voltage was varied from 1 kV to 1.5 kV, and the pressure was maintained between 0.1-1 torr. As a time-dependent function, the electron temperature was calculated every 20 seconds during a 200-second discharge. The results showed that in argon plasma, as the pressure increases, the electron temperature decreases up to a pressure value of 0.4 torr, subsequent increase leads to an increase in temperature. Also, with the increase in source voltage, a decrease in electron temperature within the error limits is observed. In addition, in dust plasma (PECVD in Ar-C2H2), the electron temperature as a function of pressure and source voltage showed a trend similar to that observed in argon plasma. However, the electron temperature in dust plasma increases as a function of time at the initial moment, after which it decreases sharply with time.

Molecular dynamics simulation of argon pool boiling: A comparative study of employing nanoparticles and creating tree-root type nanostructures

This paper is aimed to investigate the effectiveness of innovative nanostructured surfaces in terms of heat transfer and evaporation rate enhancement during the pool boiling process of argon atoms by employing molecular dynamics simulation. LAMMPS software and Lennard-Jones potential are used for the simulation and determination of the force field. The fundamental thought of creating these novel geometries (tree-root type nanostructures) is to use the branches as a barrier against liquid cluster separation, which leads to fluid temperature enhancement. First, the framework of simulation is validated, and then the results of creating two types of copper tree-root nanostructures are presented and compared with three cases which include: adding platinum, aluminum, and copper nanoparticles to the argon fluid on the plain copper substrate. The results revealed that creating tree-root type nanostructures postponed the separation of the liquid cluster in comparison with adding nanoparticles. In addition, the tree-root type nanostructures can enhance the evaporation rate and the argon temperature up to 60.05% and 17.13% more than adding nanoparticles, respectively. On the other hand, these nanostructures improve the maximum heat flux and corresponding convective heat transfer coefficient by 15.46% and 26.86% compared to the cases of adding nanoparticles, respectively.

Characterization of two SiPM arrays from Hamamatsu and Onsemi for liquid argon detector

Silicon photomultiplier is considered a substitute for traditional photomultiplier tube in the next generation of dark matter and neutrino detectors, especially in noble gas detectors like liquid argon. For seeking more choices operating in a cryogenic environment, two SiPM array candidates from Hamamatsu and Onsemi were selected to verify their feasibility and effectiveness in liquid argon temperature. In this work, by inheriting the circuit DarkSide Collaboration designed earlier, we developed a cryogenic electronics read-out system that connects and works with 1-inch 4 × 4 SiPM arrays at 87 K. The amplifier’s power dissipation is around 10 μW/mm2. Furthermore, multiple significant characteristics of both types of SiPM arrays were measured at liquid argon temperature, such as the breakdown voltage, the dark count rate, the single photoelectron performance, the signal-to-noise ratio, and the correlated signal probability.

Typical electrical, mechanical, electromechanical characteristics of copper-encapsulated REBCO tapes after processing in temperature under 250 °C

Heat treatments are inevitable not only in the production of rare earth barium copper oxide (REBCO) tapes, but also in their post-processing for applications, typically, in soldering and epoxy/wax impregnation during the fabrication of REBCO coils. In general, the heat treatment of REBCO tapes should be carried out at lower temperature for a shorter time, but the specific safe boundary of heat-treatment temperature and time for REBCO tapes is still unknown. Therefore, a comprehensive study on the typical electrical, mechanical, and electromechanical characteristics of REBCO tapes after heat treatments under temperature of 250 °C is necessary. This work focus on the copper-encapsulated REBCO tapes, which are more robust (while with much lower engineering current density) to be processed in application systems than the tapes without encapsulation. The critical current degradation, stress–strain characteristic, and electromechanical properties of REBCO tapes were measured after heat treatments at different temperatures in argon and oxygen atmosphere. A 2D finite element (FE) analysis model was established for detailed stress/train analyzes under tension and bending based on the analysis of residual stress/strain. The results indicate that the critical current of the copper-encapsulated REBCO tapes decreases with increasing heat-treatment temperature and dwell time, and is of no evident relation to atmosphere. In addition, increased temperature of heat treatment leads to an obvious decrease in the yield strength and critical tensile stress. This effect is mainly attributed to the degradation of mechanical properties of the encapsulated copper layer, which is demonstrated by the combination of our FE simulation and the experiments results. Interestingly, the change in the critical bending radius due to heat treatments was slight, because the bending axial strain of the REBCO layer remained almost unchanged after heating. It is also worthy to note that all the properties tested in this study were irrelevant to the external oxygen partial pressure during the heating process. As a practical conclusion for the application systems, an upper and atmosphere-irrelevant limit of processing temperature of 130 °C or 150 °C (2 h dwell time) was proposed for copper-encapsulated REBCO tapes, under which the critical current, yield strength, critical tensile stress/strain and critical bending radius of the copper-encapsulated REBCO tapes decay by <1% or 3%, respectively.

Final report of CCQM-K172 on measurement of Specific Adsorption A [mol/kg] of Ar on zeolite at liquid argon temperature (to enable a traceable determination of the Specific Surface Area by following ISO 9277)

Main textThe CCQM-K172 key comparison on measurement of Specific Adsorption A [mol/kg] of Ar on zeolite at liquid argon temperature (to enable a traceable determination of the Specific Surface Area by following ISO 9277) has been performed by the Surface Analysis Working Group (SAWG) of the Consultative Committee for Amount of Substance (CCQM). The objective of this key comparison is to compare the equivalency of the National Metrology Institutes (NMIs) and Designated Institutes (DIs) for the measurement of specific adsorption of Ar, BET specific surface area) of microporous substances (zeolites, sorbents, ceramics, catalytic agents, etc) used in advanced technology.In this key comparison, a commercial zeolite was supplied as a sample. Five NMIs/DIs participated in this key comparison. All participants used a gas adsorption method, here argon adsorption at 77.3 K, for analysis according to the international standard ISO 9277.In this key comparison, the degrees of equivalence uncertainties for specific adsorption argon, BET specific surface area were established.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Effect of Thermal Treatment of Symmetric TiO2 Nanotube Arrays in Argon on Photocatalytic CO2 Conversion

Symmetric titania nanotube arrays (TiO2 NTs) are a well-known photocatalyst with a large surface area and band edge potentials suitable for redox reactions. Thermal treatment of symmetrical arrays of TiO2 nanotubes in argon was used to change the carbon content of the samples. The influence of the carbon content in the structure of symmetrical TiO2 NTs on their photoelectrochemical properties and photocatalytic activity in the conversion of CO2 into organic fuel precursors has been studied. The structure, chemical, and phase composition of obtained samples were studied by X-ray analysis, Raman spectroscopy, and SEM with energy dispersive analysis. It is established that carbon-related defects in the samples accumulate electrons on the surface required for the CO2 conversion reaction. It has been shown for the first time that varying the carbon content in symmetric TiO2 NTs arrays by annealing at different temperatures in argon makes it possible to control the yield of methane and methanol in CO2 conversion. It is revealed that too high a concentration of carbon dangling bonds promotes the growth of CO2 conversion efficiency but causes instability in this process. The obtained results show a high promise of symmetric carbon-doped TiO2 NTs arrays for the photocatalytic conversion of CO2.

A revised Lennard-Jones potential for bubble nucleation study of argon based on the molecular dynamics simulation method

Bubble nucleation in boiling heat transfer is a microscale phenomenon, which is usually investigated by the molecular dynamics simulation method with the study object of argon. The simple potential model of argon favors revealing the bubble nucleation mechanism. However, the published works indicate that the required heating temperature for achieving bubble nucleation inside liquid argon is unreasonable and usually over the critical temperature. Therefore, in this study, a revised Lennard-Jones (L-J) potential for bubble nucleation study of argon is proposed based on the “PK” norm that bubble nucleation happens when the average kinetic energy of a group of liquid atoms exceeds their potential barrier (absolute value of atomic potential energy). The parameters α and β are added to the original L-J potential to weaken the phase transition barrier and reduce atomic balance distance, corresponding to the functions of lowering onset nucleation temperature and avoiding the unreasonable change of liquid argon properties, respectively. Besides, a moving top wall based on the force balance is conducted to maintain the simulation system pressure at the expected value. Simulation results indicate that based on the revised L-J potential and pressure controlled at one atmosphere, only the evaporation phenomenon happens when the heat source temperature is fixed at 85 K within the simulation time of 10 ns, while it converts into the bubble nucleation phenomenon as the thermostat temperature is raised to 90 K, which is very close to the onset boiling temperature of liquid argon (87.2 K). In addition, the relative differences between the original and revised potentials in the density, thermal conductivity, and thermal diffusion coefficient are 1.31%, 33.50%, and 233.33%, respectively. The difference in the third property is significant, but compared with the benchmark value obtained by the popular property database RefProp, the computational accuracy of the revised potential is higher than the original potential. Hence, the revised L-J potential is more suitable for the bubble nucleation study of argon by using the molecular dynamics simulation method.

Development of Low Temperature Analog Readout (LTARS 2018) for LAr-TPCs

We have developed an analog front-end electronics, called LTARS2018[1], for TPC-applications, targeted at dual-phase liquid argon TPCs for neutrino experiments and negative-ion μ - TPCs for directional dark matter searches. This electronics have a wide dynamic range for input charge up to 1600 fC and a function to output a signal with an appropriate time constant for signals having various peaking times, these unique properties may make the LTARS2018 multi-purpose. In this paper we will report results of the LTARS2018 performance check at room temperature and liquid argon temperature. In addition, we discuss the design concept and characteristics of a new electronics (LTARS2020) that been modified to improve performance in liquid argon.

Mathematical model of the QUENCH-06 experiment with sensitivity and uncertainty analysis in hydrogen generation

During the cooling of the reactor core, as a result of a severe accident, a strongly exothermic oxidation reaction of the zirconium cladding occurs and leads to hydrogen production, this has been observed in Fukushima, Chernobyl and Three Mile Island accidents. Several experiments have been carried out for the understanding of the phenomena that are involved in a severe accident and of the adequate mathematical modeling of the behavior of these scenarios. The objective of this work is to develop a reduced model of low computational cost that simulates the cooling phenomenon considering the heat transfer for the fuel rods, the thermohydraulic phenomena in the coolant, and the hydrogen generation focus on the QUENCH-06 experiment, where the purpose of this experiment is to investigate the cooling process of fuel rods in a severe accident scenario in a light-water nuclear reactor. The reduced model is solved numerically. It is implemented in a C++ compiler and it is validated with the data of the experiment, obtaining a deviation in the integral hydrogen generation of -4.7%. Subsequently, a sensitivity and uncertainty analysis is carried out to determine the parameters involved with greater relevance in the integral hydrogen generation. The results show that the variables with the greatest impact on hydrogen generation are: the variation of the steam flow, the convective heat transfer coefficient, and the inlet temperature of steam and argon, the latter with the largest value of the Pearson's correlation coefficient.

Studying the Synergistic Roles of Nanostructures on the Rapid Boiling Process Using Molecular Dynamics Simulation

In this work, the rapid boiling heat transfer over an integrated surface with cavities and pillars at nanoscale is investigated using molecular dynamics simulations. To elucidate the roles of cavities and pillar when they are combinedly integrated with a surface, the comparisons of the results have been made with those obtained on surface with only cavities, surface with only pillars and smooth surface. The results show that surface with only cavities reduce the bubble nucleation time as compared to smooth surface. On the other hand, the surface with only pillars offers higher argon temperature and evaporation rate near liquid cluster detachment from solid surface than surface with cavities and smooth surface. The bubble nucleation is explained by the contest of average kinetic and potential energies of liquid atoms. For surfaces with cavities and pillars, the total energy of atoms in the vicinity of nanostructures becomes greater than zero faster than smooth surface leading to early bubble nucleation, and bubble nucleation tends to start from the vicinity of nanostructures. Furthermore, the integrated surface takes the advantage of both cavity and pillar, and as a result it has lowest bubble nucleation time and higher evaporation rate and heat flux than other surfaces.

Development and characterization of a slow wavelength shifting coating for background rejection in liquid argon detectors

We describe a technique, applicable to liquid-argon-based dark matter detectors, allowing for discrimination of alpha-decays in detector regions with incomplete light collection from nuclear-recoil-like events.Nuclear recoils and alpha events preferentially excite the liquid argon (LAr) singlet state, which has a decay time of ∼6ns. The wavelength-shifter TPB, which is typically applied to the inside of the active detector volume to make the LAr scintillation photons visible, has a short re-emission time that preserves the LAr scintillation timing. We describe the production method and characterization of a wavelength-shifting polymeric film – pyrene-doped polystyrene – which we developed for the DEAP-3600 detector. At liquid argon temperature, the film’s re-emission timing is dominated by a modified exponential decay with a time constant of 279(14)ns, and has a wavelength-shifting efficiency of 46.4(2.9)% relative to TPB, measured at room temperature. By coating the detector neck (a region outside the active volume where the scintillation light collection efficiency is low) with this film, the visible energy and the scintillation pulse shape of alpha events in the neck region are modified, and we predict that through pulse shape discrimination, the coating will afford a suppression factor of O (105) against these events.

Argon diffusion in graphene oxide and reduced graphene oxide foils

Measurements of argon diffusion coefficient vs. temperature in graphene oxide (GO) and reduced graphene oxide (rGO) have been performed. GO and rGO foils have been employed with a thickness of 15 μm. GO has been reduced in vacuum at a temperature of 130 °C for 30 min. Measurements have been obtained by controlling the gas pressure gradient applied to two faces of the thin foils versus the time and the temperature. The measured Ar diffusion coefficients have been compared to those obtained for N2 in the same foils. In particular, the calculated room temperature Ar and N2 diffusion coefficients in GO are 2.95 × 10−3 cm2/s and 0.168 × 10−3 cm2/s respectively. At 100 °C in rGO the Ar and N2 diffusion coefficients are 2.15 × 10−3 cm2/s and 0.4 × 10−3 cm2/s respectively. Consequently, the Ar diffusion coefficients in GO and rGO appear greater than the nitrogen ones. The high diffusion coefficient of Ar increases with the temperature and decreases going from GO to rGO, due to the highest compactness and density of the reduced GO foil. The smaller diffusion coefficient of N2 increases both with the temperature and going from GO to rGO, due to the partial water molecules and oxygen functional groups removal. The obtained results, their correlation with the inner structure of the graphene sheets and the comparison with the literature data are presented.

Plasma assisted combustion of methane-air mixtures: Validation and reduction

For several years now plasma assisted combustion has been the subject of intense research due to stabilization effects a plasma can have on flames. Particularly, experiments have shown the promising impact of Nanosecond Repetitively Pulsed discharges on combustion while not exceeding an energy consumption of a few percent of the flame power. In this work, an incremental methodology with a step-by-step approach has been used to build a single plasma mechanism upon which combustion is added using the GRI 3.0 and Konnov v0.6. The methodology focuses on three key aspects of plasma assisted combustion: fast gas heating, slow gas heating and radical production. Selected experiments focusing on one or more of these aspects allow to validate the mechanism in large ranges of temperature (300-1500 K) and pressure (0.1-1 bar) in air, methane-air and argon diluted mixtures using glow and spark discharges. These experiments include a plasma assisted ignition case on which the ignition delay time is well captured by the mechanism. Slow gas heating has been modeled using a vibrational relaxation model validated against a detailed vibrational description. Discussions on ambiguous rates for critical reactions of excited nitrogen quenching are made in the light of their impact on the results on the chosen experiments. Finally, the resulting 100-species GRI 3.0-based and 264-species Konnov v0.6-based plasma mechanisms are reduced to make them suitable for multi-dimensional simulations. The DRGEP reduction method, based on plasma experiments and canonical combustion cases, is applied allowing to reduce the number of species by a factor larger than two. For the GRI-3.0 plasma mechanism, the reduced mechanism contains 47 species and 429 reactions. Hence significant performance is gained, opening the way to multi-dimensional simulations of plasma assisted combustion.