Low-pressure Discharge Research Articles

Study on the impact of turbulent spatiotemporal propagation in the outlet passage on the performance of vertical axial flow pumps.

Abstract Pumping station engineering is crucial for our country’s national economy as a part of water conservancy infrastructure. The vertical axial flow pump commonly used in pumping station construction features a high flow rate and low discharge pressure. Understanding the impact of turbulence on the flow of water entering and leaving the pump unit is crucial for the efficient and reliable operation of a pumping station. This paper examines the internal flow and hydraulic characteristics of the device for vertical axial flow pump at a pumping station through numerical simulation technology and experimental validation. It is inferred that turbulent flow develops in the outlet flow passage while the pump device is currently functioning, impacting the impeller’s outlet bend and guide vane. This leads to the formation of vortices, backflow, and folding flow at the guide vane and outlet bend. As water flows out through the outlet passage, bias and backflow develop, causing erosion on both sides of the outlet pool and impacting the pump unit’s overall head and efficiency.

Photoionization ion mobility analyzer for on-site measurement of exhaled acetone by coupling miniature thermoelectric cooling dehydration

The breath concentration of acetone holds significant clinical importance, the development of on-site and accurate analyzer for exhaled acetone is highly demanded. A photoionization ion mobility analyzer based on a low-pressure krypton discharge lamp has been developed for direct and rapid determination of the acetone concentration. The difficulty for sensitive measurement of acetone by vacuum ultraviolet photoionization was the strong absorption of water molecules in the breath air. An online dehydration device with a miniature thermoelectric cooling quartz trap has been developed, which was capable for reducing the relative humidity from over 90 % to below 1 %. The dehydration could enhance the signal intensity of acetone about 85 times. The response time of current thermoelectric cooling dehydration was only 1/20 of the Nafion tube dehydration. A limit of detection 0.02 ppmV and linear response up to 2.0 ppmV were achieved. The interferences from ammonia in exhaled breath was eliminated using a calibration method based on ion number density, achieving recoveries ranging from 90 % to 110 %. In the final, the variation trends of exhaled acetone level in healthy individuals following the ingestion of glucose under fasting conditions were carried out to demonstrate the potential application of the analyzer.

Extreme ultraviolet emission spectra of a low-pressure microwave neon discharge

In this paper, in order to reveal the discharge mechanism and optimize the extreme ultraviolet (EUV) emission lines in intensity of a low-pressure microwave (MW) neon discharge, the EUV neon spectra is carefully characterized under varied MW powers and neon pressures. The corona balance is verified to be valid for the neon upper levels of the measured EUV lines, and the electron temperature T e is derived by the modified Boltzmann plot method and the line-ratio method. Both results of the methods present a decreasing trend of T e with growing neon pressure, but the values in a range of 1.87-5.77 eV deduced by the former method is in general lower than that calculated by the latter with a range of 2.23–5.58 eV in similar neon pressure range. It is also found that the increase of MW power from 90 to 135 W only leads to a slight increasing of T e . A global model is applied to estimate the electron density n e , which is found to lie in the order of magnitude of 1010 cm−3. The dependence of the plasma parameters on different discharge conditions is analysed in detail, which in turn provide a favourable basis for further optimization of the promising low-pressure MW discharge radiation source.

Optical actinometry for number density measurements in low-pressure plasmas: Advantages, error sources, and method validation

Number density of plasma-generated atoms or molecules is an important parameter for both fundamental research and applications. It can be measured in a straightforward manner, using vacuum-ultraviolet absorption spectroscopy, which is mainly possible in laboratory conditions as it may require bulky equipment, such as lasers. By contrast, optical actinometry is an alternative approach that only uses spontaneous emission from the plasma. This technique relies on the so-called corona excitation and uses emission line ratios between the gases with unknown and known concentrations (called actinometer in the last case). As a result of using line ratios, the additional density calibration is not required if the excitation cross sections are known. This study discusses Ar-based actinometry in low-pressure (roughly <1 kPa) plasma discharges with an emphasis on multiple line ratios. The work is particularly focused on the method’s applicability, the choice of Ar cross sections, and potential error sources. The influence of the additional excitation mechanisms is analyzed based on both experiments and modeling. The optical transitions for F, O, H, N, and P atoms along with expressions for their number density are presented, not requiring high optical resolution for measurements. For the sake of method validation, it is shown that in low-pressure radiofrequency discharges, a nearly excellent agreement between the actinometry data and the calibrated measurements can be achieved by careful selection of optical transitions.

Plasma-assisted surface modification of MXene/carbon nanofiber electrodes for electrochemical energy storage

Inferior ion diffusion and relatively low electrochemically active sites of MXene-based electrodes make them becoming a major challenge to develop advanced electrode. Surface modification of electrodes using non-thermal plasma is a great way to suppress these challenges through providing more space for energy storage and facilitating the diffusion of electrolyte ions. Herein, the effect of nitrogen and oxygen plasma treatments on MXene/carbon nanofiber electrode is reported to enhance the electrochemical performance. In this work, Ti3C2Tx MXene/CNF composites were fabricated using a hybrid needleless electrospinning/plasma method for the electrochemical energy storage. Surface modification of the composites was performed by a DBD plasma reactor under N2 and O2 gases at low-pressure glow discharge as a two-step plasma treatment process. The results revealed that total pore volume and the surface area of the plasma-treated Ti3C2Tx/CNF composite increased considerably due to the N2 and O2 plasma treatments. It was found that the electrochemical active surface area of the N2/O2-plasma-treated Ti3C2Tx/CNF electrode enhanced by approximately two times compared to the non-treated one, leading to the specific capacitance of 162 F/g at 1 A g−1 in a 2 M KOH electrolyte. The increase in electrochemical activity arises from separate doping of N2 and O2 plasma, which not only improves the pore structure and wettability, but also modifies the electrical conductivity and capacitance of the electrode. The N2/O2-plasma-treated Ti3C2Tx/CNF electrode achieved excellent cycling stability with 124 % capacitance retention after 10,000 cycles, while the capacitance retention of the pure N2 and O2-plasma-treated Ti3C2Tx/CNF electrodes as well as the non-treated one were 111 %, 105 % and 98 %, respectively. Additionally, an asymmetric supercapacitor N2/O2-plasma-treated Ti3C2Tx/CNF//AC based on the N2/O2-plasma-treated Ti3C2Tx/CNF as a positive electrode and activated carbon (AC) as a negative electrode was successfully constructed, which demonstrated an energy density of 26.3 Wh kg−1 with a power density of 750 W kg−1 at the current density of 1 A g−1 with excellent capacitance retention (102 %) after 5000 cycles. This work provides a highly efficient method for the surface modification of MXene-based electrodes through non-thermal plasma treatment.

Selection of reference genes for expression profiling in biostimulation research of soybean

BackgroundPlant biostimulants constitute a promising environmentally friendly alternative for increasing crop yield and tolerance to unfavorable conditions. Among various types of such formulations, botanical extracts are gaining more recognition as products supporting plant performance. Moreover, novel tools such as cold-plasma or low-pressure microwave plasma discharge are being proposed as techniques that might improve their efficacy. Elucidation of the biostimulant’s mode of action requires complex research at a molecular level. Transcriptional changes occurring after biostimulant spraying might be investigated using RT-qPCR. However, this technique requires data normalization against stable endogenous controls.ResultsHere, we tested the expression stability of ten candidate genes in soybean plants exposed to various biostimulants treatment. Selection of the best-performing reference genes was conducted using four algorithms (geNorm, NormFinder, BestKeeper, and ΔCt method). According to the obtained results, Bic-C2 (RNA-binding protein Bicaudal-C) and CYP (cyclophilin type peptidyl-prolyl cis–trans isomerase) showed highest expression stability, while expression of EF1B (elongation factor 1-beta) fluctuated the most among a tested set of candidate genes.ConclusionsOverall, we recommend using Bic-C2 together with CYP for the RT-qPCR data normalization in soybean biostimulation experiments. To our best knowledge, this is the first comprehensive study of reference genes stability in plants subjected to biostimulant treatment. The results of this study will aid in further biostimulant research in crop plants, facilitating analyses performed on the transcriptional level.Graphical

Complex electron-ion-plasma surface modification of high-alloy stainless steel

The work is devoted to identification and analysis of patterns of change in the elemental and phase composition, defective substructure, mecha­nical (microhardness) and tribological (wear resistance and friction coefficient) properties of stainless high-chromium steel subjected to complex processing, combining vacuum irradiation of the samples surface layer with an intense pulsed electron beam of submillisecond exposure duration and subsequent nitriding under electron-ionic heating conditions. High-chromium steel AISI 310S, which in the initial state is a polycrystalline aggregate based on γ-iron, was used as the research material. Pulsed electron beam treatment of steel was carried out on a “SOLO” installation equipped with an electron source with a plasma cathode based on a low-pressure pulsed arc discharge with grid stabilization of the cathode plasma boundary and an open anode plasma boundary. Steel nitriding was carried out on a “TRIO” installation with a chamber size of 600×600×600 mm, equipped with a switching unit to implement the electron-ionic processing mode. Nitriding was carried out at 723, 793, and 873 K temperatures for 1, 3 and 5 h. It was found that electron-ionic nitriding of the samples pre-irradiated with an electron beam (10 J/cm2, 200 μs, 3 pulses at 723 and 793 K for 3 h) is accompanied by the formation of a ceramic layer containing only iron and chromium nitrides. The highest values of steel wear resistance after electron-ionic nitriding, exceeding the wear resistance of the initial steel by more than 700 times, are observed at nitriding parameters of 793 K, 3 h.

Low-pressure high-current magnetron discharge with electron injection: From self-sputtering with multiply charged metal ions to non-sputtering with “pure” gas ions

We report our experimental investigations of the effect on the ion composition, including the ion mass-to-charge composition, of electron injection into the plasma of a high-current pulsed magnetron discharge in the ultra-low operating pressure range. We show that changing the magnetron discharge voltage by injecting additional electrons with adjustable current allows implementation of two operating modes: one with a plasma in which metal ions dominate (including multiply charged ions for certain target materials with low sputtering yield), and the other a magnetron non-sputtering mode with plasma of only gaseous ions.

Characterization of low-pressure gaseous plasma radiation and its usage for inactivation of waterborne viruses

Water disinfection is a critical treatment step for removing harmful organisms from contaminated water sources. Vacuum ultra-violet (V-UV) radiation, generated by a low-pressure gaseous plasma discharge, consists of photons with high enough energy to break molecular bonds. In this work, we constructed and characterized a low-pressure capacitively coupled gaseous plasma and used it as a V-UV radiation source to inactivate MS2 bacteriophage, a surrogate for human enteric viruses. The treatment system allows for variation of gas composition inside the sample chamber and the modulation of V-UV radiation intensity. Both were used to separate the actual germicidal contribution of V-UV radiation from producing germicidal species by using virus inactivation to determine efficiency. OH* radical production was determined through the terephthalic acid chemical probe, which showed that when air was present in the sample chamber, it resulted in the highest OH* production and the best inactivation of MS2. Furthermore, we showcase that the OH* production rate was wavelength dependent and that ozone, generated by plasma treatment in the gas phase, leads to hydroxy terephthalic acid degradation, allowing us to determine better the actual OH* production rate with different treatment regimes. Lastly, by adding an OH* scavenger to the liquid, we were able to elucidate it as the primary inactivation agent in this setup while also providing evidence of its production in the bulk liquid by the transport and subsequent decomposition of the longer-lasting ozone molecule. This study demonstrates, for the first time, the applicability of low-pressure plasma radiation as a water treatment method.

On the possibility of accelerating charged particles in the low-pressure acoustoplasma and plasma bunches in the air

In this paper obtained results of two experimental investigations are presented: on the acceleration of electrons in low-pressure acoustoplasma discharge and acceleration of plasma bunch-plasmoids in the air. The first experimental results on the acceleration of electrons in the low-pressure discharge were obtained in 2008. In the current paper an attempt to explain the obtained results by means of wake accelerations of particles in electromagnetic fields without utilization of usual drivers is made. Formerly calculated theoretical data for accelerated particles even in the energy range of 10–100 eV are experimentally confirmed. Experimental investigations on origination and initiating acceleration of plasma bunches in crossed fields in the air were conducted in 2023. In the current paper the obtained first results on acceleration of the originated long-life plasmoids in the air are presented as an announcement of our planned subsequent corresponding investigations. To carry out corresponding experiments a unique experimental setup, as well as appropriate devices and equipment were developed. A new conceptual model of a plasmoid is offered. The realization of this concept opens the possibility of carrying out the experimental investigations of the phenomena of origination of long-life plasmoids in air. During the experimental investigations, any ionizing additives into the discharge were not injected.

High power impulse magnetron sputtering of a zirconium target

High power impulse magnetron sputtering (HiPIMS) discharges with a zirconium target are studied experimentally and by applying the ionization region model (IRM). The measured ionized flux fraction lies in the range between 25% and 59% and increases with increased peak discharge current density ranging from 0.5 to 2 A/cm2 at a working gas pressure of 1 Pa. At the same time, the sputter rate-normalized deposition rate determined by the IRM decreases in accordance with the HiPIMS compromise. For a given discharge current and voltage waveform, using the measured ionized flux fraction to lock the model, the IRM provides the temporal variation of the various species and the average electron energy within the ionization region, as well as internal discharge parameters such as the ionization probability and the back-attraction probability of the sputtered species. The ionization probability is found to be in the range 73%–91%, and the back-attraction probability is in the range 67%–77%. Significant working gas rarefaction is observed in these discharges. The degree of working gas rarefaction is in the range 45%–85%, higher for low pressure and higher peak discharge current density. We find electron impact ionization to be the main contributor to working gas rarefaction, with over 80% contribution, while kick-out by zirconium atoms and argon atoms from the target has a smaller contribution. The dominating contribution of electron impact ionization to working gas rarefaction is very similar to other low sputter yield materials.

Domain Decomposition Hybrid Implicit–Explicit Algorithm with Higher-Order Perfectly Matched Layer Formulation for Electrical Performance Evaluation under Low-Pressure Discharge Phenomenon

Low-pressure discharge events have a major impact on a satellite’s electrical performance. Most notably, a number of serious issues arise from the inability to directly modify satellite systems that operate in orbit. Accurate analysis of electrical performance is crucial for mitigating the issues arising from the low-pressure discharge phenomenon. Complex structures, such as intricate features and curved structures, are frequently used in satellite systems’ enormous microwave components. In this case, the finite-difference time-domain (FDTD) approach proposes the hybrid implicit–explicit (HIE) algorithm with a domain decomposition method to effectively simulate complex structures under the low-pressure discharge phenomenon. The bilinear transform method is adjusted in accordance with the implicit equations for the anisotropic magnetized plasma environment caused by the discharge. To end unbounded lattices, a higher-order perfectly matched layer is used at the boundary. An example of a microwave connector structure is used to show how well the algorithm performs electrically. According to the findings, the suggested algorithm behaves in a way that is consistent with both the traditional algorithm and the experiments. Furthermore, the phenomenon of low-pressure discharge has a notable impact on the electrical performance of microwave components.

Inception of positive wire-cylinder corona discharges in air in crossed electric and magnetic fields

A computational study of the inception of positive wire-cylinder corona discharges in low-pressure air in crossed electric and magnetic fields is performed. The inception voltages are calculated for a wide range of gas densities, wire radii, and applied magnetic fields. Conditions are considered when the reduced electric fields at wire electrodes reach extremely high values of about 10 kTd. An expression applicable at such strong fields for the ionization coefficient, which is a key parameter of the corona inception model, is presented against the values of electric and magnetic fields. Calculated inception voltages agree with a large quantity of available experimental data on low-pressure positive corona discharges, obtained both with and without the application of magnetic fields. The calculation results describe specific details of the non-monotonous dependence of the inception voltages on the magnetic field values, similar to those obtained in experiments.

Resistive switching properties of a nanostructured layer of mixed ZrO2 phases obtained in low-pressure arc discharge plasma

The controlled vacuum-arc synthesis of zirconium dioxide (ZrO2) nanoparticles is considered, which makes it possible to regulate the percentage ratio of the monoclinic and tetragonal phases. The samples were characterized using XRD analysis, SEM, HRTEM analysis, FT-IR analysis, TG/DTA analysis and EPR spectroscopy. It has been established that the formation of the tetragonal phase is associated with the formation of a large number of oxygen vacancies formed due to high-speed quenching of nanoparticles. Reducing the operating gas pressure in a vacuum chamber from 180 Pa to 30 Pa makes it possible to obtain nanoparticles up to 2 nm in size. The synthesized ZrO2 nanoparticles do not contain foreign impurities and when heated, the weight loss is up to 7 %. The process of local resistive switching in the contact of an atomic force microscope (AFM) probe to a nanostructured ZrO(2-x) layer on a conducting substrate has been studied. Cyclic current-voltage characteristics demonstrate the existence of stable states of high and low resistance, switched by changing the polarity of the applied voltage. The coexistence of the m- and t-ZrO2 phases (and the resulting oxygen nonstoichiometry in the interboundary regions) provides conditions for the formation/destruction of a filament from oxygen vacancies, which determine the conductivity of the dielectric in the LRS state.

Study on Ion Flux From Magnetically Confined Low-Pressure Arc Discharge With a Thermionic Cathode to Substrate for High-Throughput Film Deposition Processes

Study on Ion Flux From Magnetically Confined Low-Pressure Arc Discharge With a Thermionic Cathode to Substrate for High-Throughput Film Deposition Processes

Energy, exergy and economical analysis of N2O based cascade refrigeration system for ultralow temperature cooling applications using different eco-friendly refrigerants in high temperature cycle

Implementing the Montreal Protocol has limited the use of conventional refrigerants and has led industries to find optimal or economical eco-friendly refrigerants to reduce environmental hazards. The present study analyzes an N2O-based cascade refrigeration system for achieving ultralow cooling temperatures using different eco-friendly refrigerants with low GWP and ODP in a high-temperature cycle. 3E (Energy, Exergy, and Economy) analysis of a cascade refrigeration system using eco-friendly refrigerants such as R290, R1270, RE170, R600, R600a, HFE7100, and HFE7000 in the upper cycle and N2O in the lower cycle was conducted. The R744A/R600 pair performed best among the other refrigerant pairs due to its lower discharge pressure and compression ratio. The refrigerant pair R744A/R600 results in a higher cascade cycle COP of approximately 0.87, with 48 % exergetic efficiency, while the refrigerant pair R41/HFE7100 has the lowest COP (0.68) and lowest exergetic efficiency (42 %). The minimal operational cost varies from 73006 to 76907 USD per annum for refrigerant pair R744A/R600, while for the other pairs, the cost varies from 98625 USD to 114674 USD. The R744A/R600 refrigerant pair provides COP values that are 1.38–5.38 % greater than the others, with a 1.01–3.45 % variation in exergy efficiency.

Quantitative analysis of optical emission spectroscopy for plasma process monitoring

In the field of plasma materials processing, various plasma parameters should be evaluated quantitatively and precisely to control the plasma process adequately, particularly with non-invasive methods, one of which is optical emission spectroscopy (OES) measurement. It has sufficient scientific feasibility to derive the electron density N e, electron temperature T e, and the electron energy distribution function (EEDF) even for various processing plasmas in a state of non-equilibrium. In this review, previous studies are reviewed to measure the N e, T e, and EEDF values of argon plasma with low-electron temperature (T e ≃ 1–10 eV) under not only low-pressure conditions but also atmospheric-pressure discharge using the OES measurement. First, to diagnose low-pressure discharge argon plasmas, we explain the basics and applications of the “collisional radiative model”, which models the population kinetics of the excited states in plasma at the elementary process level in non-equilibrium plasma. Methods for analyzing the plasma parameters are shown from the actual measurement results of emission spectra, including machine learning analysis of the excited-state populations. Next, the research results of the method to measure N e, T e, and EEDF are introduced for the measurement of atmospheric-pressure non-equilibrium plasmas using OES measurement of continuum emission, which also includes methods based on machine learning and data-scientific methods for the analysis of the OES data observed as bremsstrahlung of free electrons scattered against neutral molecules.

Effects of ion-plasma treatment temperature of the aluminium coating on the structure and phase composition of the VT6 titanium alloy

In this study, we studied the effects of aluminum coating treatment temperature on the microstructure and phase composition when applied to a VT6 titanium alloy substrate within a low-pressure arc discharge plasma environment. The ion-plasma treatment was conducted at 450 and 500 °C, employing argon shielding, while the aluminum coating was deposited using the vacuum-arc process, resulting in a coating thickness of ~3 μm. Microstructural analysis was performed using a scanning electron microscope, and the structural and phase composition were examined using X-ray diffraction (XRD) imaging in symmetric imaging mode with CuKα radiation. Our findings demonstrate that the application of the aluminum coating initiates the formation of a near-surface α-stabilized layer, extending up to 2.5 μm in thickness due to the heat generated during the ion cleaning process. Subsequent ion-plasma treatment further results in the development of a TiAl3 intermetallide site, reaching thicknesses of up to 1.5 μm, while the α-stabilized region expands to 5.5 μm. Higher temperatures during the treatment process contribute to an increase in the thickness of these aforementioned layers and also lead to the emergence of an intermediate TiAl intermetallic layer.

Spatially resolved TALIF investigation of atomic oxygen in the effluent of a CO2 microwave discharge

A diagnostic setup for one-dimensionally spatially resolved two-photon absorption laser-induced fluorescence (TALIF) detection of ground state oxygen atoms ( 2p43P2,1,0 ) is developed. The goal of this study is to investigate the evolution of temperatures and absolute number densities of oxygen atoms along the effluent of a low-pressure CO2 microwave discharge in order to gain insights into some of the mechanisms governing the post-discharge regime. The plasma source is operated at conditions of 600 W– 1200 W of absorbed power with flow rates of 74 sccm and 370 sccm pure CO2 at pressures between 1.2 mbar and 5 mbar with specific energy inputs up to 111.9 eV/molecule. These operating conditions exhibit high CO2 conversions (up to 90%) at low energy efficiencies (2%–7.4%), due to direct electron impact dissociation driving the conversion process resulting in splitting of CO2 into CO and metastable oxygen atoms. The TALIF measurements yield spatially resolved translational temperatures between 1000 K– 1600 K for most operating conditions and axial positions along the effluent. Reference measurements with xenon 6p′[3/2]2 are used for absolute number density calibration. The resulting axially resolved number density profiles of ground state atomic oxygen increase along the effluent, even at considerable distances of several centimeters from the active discharge, before they reach a maximum between 5×1020 m−3 and 2.2×1021 m−3 depending on the condition, and decrease after that. This behavior indicates the potential significance of quenching of metastable oxygen atoms within the post-discharge regime of the investigated CO2 discharges. The measured spatially resolved number density evolutions are qualitatively consistent with quenching via wall collisions being the dominant deactivation mechanism, underlining the importance of particle-wall interactions.

Dyeing jute-cotton blended fabric with natural dyes: A chemical-free approach of LPGD plasma technology using O2 and N2 gases

In response to growing environmental concerns in the textile industry, this study investigates the effects of a low-pressure glow discharge (LPGD) plasma with oxygen (O2) and nitrogen (N2) gases on the dyeing process of jute-cotton (JC) blended fabrics, using coffee extract as a natural dye source. The hydrophilic properties of all the JC blended fabric samples were enhanced due to plasma treatments. The contact angles of the samples were significantly decreased from 131° to 52° (O2) and 55° (N2) after 20 minutes of plasma treatment. Compositional analysis revealed new functional groups e.g., CO and N−H, on the fabric's surface after plasma treatment. Surface morphology analysis indicated that the surface roughness of the treated fabric was increased with plasma treatment time. The improvement of the wicking properties of the fabric with contact time was also observed. All the plasma-treated fabric samples exhibited good colour strength (k/s), wash fastness, and rubbing fastness. After plasma treatment with O2 gas for 20 minutes, the k/s value had increased from 3.6 to 4.9. Washing and rubbing (dry) color fasting ratings were enhanced from 1 to 3 and 2–4, respectively, following a 20-minute plasma treatment with O2 gas. Although both O2 and N2 plasma treatment showed a significant impact on the dyeing properties of JC blended fabric, O2 gas provided better results compared to N2 gas plasma treatment.