Non-equilibrium Plasma Research Articles

Laser and Astrophysical Plasmas and Analogy between Similar Instabilities

Multipulse laser–matter interactions initiate nonlinear and nonequilibrium plasma fluid flow dynamics and their instability creating microscale vortex filaments, loop-soliton chains, and helically paired structures, similar to those at the astrophysical mega scale. We show that the equation with the Hasimoto structure describes both, the creation of loop solitons by torsion of vortex filaments and the creation of solitons by helical winding of magnetic field lines in the Crab Nebula. Our experiments demonstrate that the breakup of the loop solitons creates vortex rings with (i) quasistatic toroidal Kelvin waves and (ii) parametric oscillatory modes—i.e., with the hierarchical instability order. For the first time, we show that the same hierarchical instability at the micro- and the megascale establishes the conceptual frame for their unique classification based on the hierarchical order of Bessel functions. Present findings reveal that conditions created in the laser-target regions of a high filament density lead to their collective behavior and formation of helically paired and filament-braided “complexes”. We also show, for the first time, that morphological and topological characteristics of the filament-bundle “complexes” with the loop solitons indicate the analogy between similar laser-induced plasma instabilities and those of the Crab and Double-Helix Nebulas—thus enabling conceptualization of fundamental characteristics. These results reveal that the same rotating metric accommodates the complexity of the instabilities of helical filaments, vortex rings, and filament jets in the plasmatic micro- and megascale astrophysical objects.

Quantitative analysis of optical emission spectroscopy for plasma process monitoring

Abstract Plasma parameters should be evaluated to control the plasma process adequately with non-invasive method, one of which is the optical emission spectroscopy (OES) measurement. Some OES studies are reviewed to measure electron density N e, electron temperature T e and electron energy distribution function (EEDF) of argon plasma with low-electron temperature (T e ∼ 1−10 eV) under not only low-pressure condition but also atmospheric-pressure discharge. The basics and applications of a method are described using the "collisional radiative model." The methods to deduce the plasma parameters are explained in terms of detailed description of kinetic balance of excited states with elementary processes in the non-equilibrium plasma. In addition, research results on the measurement method of electron temperature, density, and EEDF are introduced for the measurement of atmospheric-pressure non-equilibrium plasma using OES measurement of continuum emission.

Atmospheric pressure uniform dielectric barrier discharge (DBD) in a wide air gap initiated from a narrow starting point

Generating a uniform non-equilibrium plasma in atmospheric pressure air has always been a challenge. It is believed that the maximum spacing for generating a uniform non-equilibrium plasma in atmospheric pressure air, whether using AC or nanosecond pulse drive, is 4 mm. Discharges are always non-uniform when the spacing is greater than 4 mm. In this paper, we propose a new type of dielectric barrier discharge structure to address this challenge. The left end of the structure rapidly increases the discharge spacing from 0.5 mm to 6 mm, while the right side of the main discharge gap maintains a uniform spacing of 6 mm. Nanosecond pulse voltage is used to drive the plasma, an ICCD camera is used to capture the image of the plasma during a discharge pulse cycle, which indicates that a uniform plasma within the 6 mm spacing of the main discharge gap is generated. Upon further reducing the ICCD camera’s exposure time to 20 ns, it is revealed that the uniform plasma is formed due to the rapid propagation of the plasma from left to right at a speed of order of 105 m s−1. Due to the small transverse component of the external electric field, this rapid propagation behavior cannot be due to the external electric field. Therefore, this paper further proposes the hypothesis of electric dipole formation leading to this fast propagation. The hypothesis suggests that the charge separation on the surface of the anode forms an electric dipole, which generates a local discharge at its right end. This local discharge further triggers the discharge in the main gap, and the main gap discharge, in turn, forms a dipole due to charge separation again, by repeating this cycle, the plasma propagates rapidly to the right. Further analysis demonstrates that this dipole can indeed produce a strong electric field of up to 41 kV cm−1 at its right end, which is sufficient to induce a local discharge. Moreover, under such a strong electric field, the electron migration rate can indeed reach 105 m s−1. These findings support the plausibility of this hypothesis.

Enhancements of electric field and afterglow of non-equilibrium plasma by Pb(ZrxTi1−x)O3 ferroelectric electrode

Manipulating surface charge, electric field, and plasma afterglow in a non-equilibrium plasma is critical to control plasma-surface interaction for plasma catalysis and manufacturing. Here, we show enhancements of surface charge, electric field during breakdown, and afterglow by ferroelectric barrier discharge. The results show that the ferroelectrics manifest spontaneous electric polarization to increase the surface charge by two orders of magnitude compared to discharge with an alumina barrier. Time-resolved in-situ electric field measurements reveal that the fast polarization of ferroelectrics enhances the electric field during the breakdown in streamer discharge and doubles the electric field compared to the dielectric barrier discharge. Moreover, due to the existence of surface charge, the ferroelectric electrode extends the afterglow time and makes discharge sustained longer when alternating the external electric field polarity. The present results show that ferroelectric barrier discharge offers a promising technique to tune plasma properties for efficient plasma catalysis and electrified manufacturing.

Analysis of Hydrogen Combustion in a Spark Ignition Research Engine with a Barrier Discharge Igniter

Hydrogen fuel is gaining particular attention in internal combustion engines. In addition to zero-carbon emissions, major advantages relate to its combustion characteristics, which allow a significant increase in thermal efficiency under ultra-lean operation and with very low NOx levels. The ignition system is one of the main technology enablers, as it determines the capability to control ultra-lean operations, avoid backfire phenomena, and/or reduce the risks of abnormal combustions. The latter results from hydrogen’s low ignition energy and it is associated with factors like high-temperature residuals, hot spots, and irregular spark plug discharge. The ACIS gen 2-Barrier Discharge Igniter excels in accelerating the initial flame growth speed by the generation of non-equilibrium low-temperature plasma, a strong ignition promoter for the combined action of kinetic and thermal effects. Moreover, its volumetric discharge facilitates combustion initiation on a wide region, in contrast to the localized ignition of traditional spark systems. In this work we present for the first time, to the best of our knowledge, experimental results showing the performance of a hydrogen engine with a low-temperature plasma discharge. Tests were conducted on a single-cylinder research engine, achieving ultra-lean conditions with cycle-to-cycle variability results below 2.5%. The analysis indicates that the H2-BDI combined solution is capable of accelerating the evolution of the flame front compared to traditional spark plugs, leading to a significant reduction in the cycle-to-cycle variability. A meticulous adjustment of the BDI control parameters further enhances igniter performance and contributes to a deeper understanding of the innovative approach proposed in this study.

Photonic Properties of Thin Films Composed of Gallium Nitride Quantum Dots Synthesized by Nonequilibrium Plasma Aerotaxy.

Gallium nitride quantum dots (GaN QDs) are a promising material for optoelectronics, but the synthesis of freestanding GaN QDs remains a challenge. To date, the size-dependent photonic properties of freestanding GaN QDs have not been reported. Here, we examine the photonic properties exhibited by thin films composed of GaN QDs synthesized by nonequilibrium plasma aerotaxy. Each film exhibited two photoluminescence peaks after exposure to ambient air. The first peak was in the ultraviolet spectral region, and the second peak was in the visible region. Both peak positions depended on the QD size. Our findings, supported by transient absorption spectroscopy experiments, suggest that conduction band to valence band recombination was the cause of the ultraviolet photoluminescence and that recombination between the conduction band and an acceptor level was the cause of visible photoluminescence. Furthermore, we show that coating the surface of fresh QDs with Al2O3 suppressed the visible region photoluminescence, corroborating the conclusion that the photoactive defect was caused by oxidation in air.

Surface Modification of Polymers by Plasma Treatment for Appropriate Adhesion of Coatings.

In this study, recent advances in tailoring the surface properties of polymers for the optimization of the adhesion of various coatings by non-equilibrium gaseous plasma are reviewed, and important findings are stressed. Different authors have used various experimental setups and reported results that scatter significantly and are sometimes contradictory. The correlations between the processing parameters and the adhesion are drawn, and discrepancies are explained. Many authors have explained improved adhesion with the adjustment of the surface free energy or wettability of the polymer substrate and the surface tension of liquids used for the deposition of thin films. The adhesion force between the polymer substrate and the coating does not always follow the evolution of the surface wettability, which is explained by several effects, including the aging effects due to the hydrophobic recovery and the formation of an interlayer rich in loosely bonded low molecular weight fragments.

Study on the treatment of oily wastewater with non equilibrium plasma synergistic catalysts

Petroleum is currently a highly demanded power fuel, but oil fields produce oily wastewater during production. If not treated in a timely manner, it can cause serious ecological problems. To solve this issue, this article utilizes the non-equilibrium plasma generated by Dielectric Barrier Discharge (DBD) technology to treat diesel simulated oily wastewater under the synergistic effect of AC/Mn + TiO2 catalyst. The results indicate that: After 180 min of DBD treatment, the degradation rates of diesel and Tween-80 were 60.9% and 53.2%, respectively; after 180 min of synergistic DBD treatment with AC/Mn + TiO2 catalyst, the degradation rates of diesel and Tween-80 were 76.0% and 71.7%, respectively, with a significant increase in degradation rates. The SEM characterization of the catalyst before and after the reaction was compared, and it was found that the surface of the crystal after the reaction was smooth. XPS characterization showed that Mn electron migration leads to the generation of positively charged holes on the valence band of TiO2. These all demonstrate that the synergistic effect of DBD and catalyst promotes the degradation of oily wastewater.

Hydrogen generation by dielectric barrier discharge plasma assisted ammonia decomposition

Ammonia, which can serve as a hydrogen carrier for later dehydrogenation in zero-carbon hydrogen generation, is considered one of the key solutions. However, this solution is challenged by the high decomposition temperature and low reaction efficiency. In this paper, non-equilibrium plasma was used to effectively improve the reaction performance of ammonia decomposition to hydrogen and nitrogen using a dielectric barrier discharge reactor. Impacts of operating conditions including discharge parameters, diluted gases, and ammonia concentration on hydrogen generation were investigated. The ammonia decomposition breakdown voltage followed the order of 1 % ammonia/carbon dioxide (4000 V) > 1 % ammonia/nitrogen (3500 V) > 1 % ammonia/helium (1500 V) ≈ 1 % ammonia/argon (1500 V). The effect of pulse voltage and frequency is more significant on plasma-assisted ammonia decomposition compared to the pulse width. When the pulse frequency and width were 30 kHz and 100 ns at 298 K, the ammonia conversion reached 26.3 %, 34.1 % and 40.9 % at 5000, 7000, and 10000 V, respectively. With the addition of argon in 5 % ammonia/helium, the resulting penning effect makes the discharge easier and more uniform to promote ammonia decomposition. Furthermore, the kinetic analysis was investigated to better understand the conversion and utilization of ammonia in plasma-assisted reactions.

The Facile Construction of Anatase Titanium Dioxide Single Crystal Sheet-Connected Film with Observable Strong White Photoluminescence

Deposited by a reactive atmospheric pressure non-thermal TiCl4/O2/Ar plasma, anatase TiO2 single crystal sheet-connected film exhibits two large exposed {001} facets and a high concentration of oxygen defects. Strong white photoluminescence centered at 542 nm has been observed with naked eyes, whose internal quantum efficiency is 0.62, and whose intensity is comparable to that of commercial fluorescent lamp interior coatings. Based on the simulation results of a hybrid global–analytical model developed on this atmospheric pressure non-equilibrium plasma system, the mechanism of a self-confined growth of single crystal sheets was proposed. A high concentration of oxygen defects is in situ incorporated into the anatase crystal lattice without damaging its crystallographic orientation. This method opens a new way to construct 3D porous metal-oxide single crystal sheet-connected films with two exposing high energy surfaces and a large concentration of oxygen defects.

X-ray counterpart detection and gamma -ray analysis of the supernova remnant G279.0+01.1 with eROSITA and Fermi-LAT

A thorough inspection of known Galactic supernova remnants (SNRs) along the Galactic plane with SRG/eROSITA yielded the detection of the X-ray counterpart of the SNR G279.0+01.1. The SNR is located just $1.5 above the Galactic plane. Its X-ray emission emerges as an incomplete, partial shell of $ angular extension. It is strongly correlated to the fragmented shell-type morphology of its radio continuum emission. The X-ray spatial morphology of the SNR seems to be linked to the presence of dust clouds in the surroundings. The majority of its X-ray emission is soft (exhibiting strong O, Ne, and Mg lines), and it occurs in a narrow range of energies between 0.3 and 1.5 keV. Above 2.0 keV the remnant remains undetected. The remnant's X-ray spectrum is purely of a thermal nature. Constraining the X-ray absorption column to values which are consistent with optical extinction data from the remnant's location favors nonequilibrium over equilibrium models. A nonequilibrium two-temperature plasma model of $ kT keV and $ kT keV, as well as an absorption column density of $ N_ H cm^ $ describe the spectrum of the entire remnant well. Significant temperature variations across the remnant have been detected. Employing 14.5 years of Fermi-LAT data, we carried out a comprehensive study of the extended giga-electronvolt source 4FGL J1000.0-5312e. By refining and properly modeling the giga-electronvolt excess originating from the location of the remnant, we conclude that the emission is likely related to the remnant itself rather than being colocated by chance. The remnant's properties as determined by the X-ray spectra are consistent with the $ kpc distance estimates from the literature, which implies a source diameter of $ pc and an old age of $>7 10^5$ yrs. However, if the source is associated with any of the pulsars previously considered to be associated with the SNR, then the updated nearby pulsar distance estimates from the YMW16 electron density model rather place the SNR at a distance of $ kpc. This would correspond to a $ pc linear size and a younger age of $10^4-<7 10^5$ yrs, which would be more in line with the nonequilibrium state of the plasma.

Effect of gas components on the post-discharge temporal behavior of OH and O of a non-equilibrium atmospheric pressure plasma driven by nanosecond voltage pulses

Abstract OH radicals and O atoms are two of the most important reactive species of non-equilibrium atmospheric pressure plasma (NAPP), which plays important role in applications such as plasma medicine. However, the experimental studies on how the gas content affects the post-discharge temporal evolution of OH and O in the noble gas ns-NAPP are very limit. In this paper, the effect of the percentage of O2, N2, and H2O on the amount of OH and O production and their post-discharge temporal behavior in ns-NAPP is investigated by Laser-induced fluorescence (LIF) method. The results show that the production of OH and O increases and then decreases with the increase of O2 percentage. Both OH and O densities reach their maximum when about 0.8% O2 is added. Further increase the O2 concentration results in the decrease of the initial densities of both OH and O, and leads to their faster decay. With the increase of N2 percentage, it also results in the increase and then decrease of the OH and O densities, but the change is smaller. Furthermore, when the H2O concentration is increased from 100 ppm to 3000 ppm, the initial OH density increases slightly, but the OH density decays much faster. While the initial density of O decreases with the increase of the H2O concentration. After analysis, it is found that OH and O are mainly produced through electron collisional dissociation. O (1D) is critical for OH generation. O3 accelerates the consumption process of OH and O at high O2 percentage. The addition of H2O in the NAPP considerably enhances the electronegativity, while it decreases the overall plasma reactivity, accelerates the decay of OH and reduces the O atom density.

Nonlinear structures in a nonequilibrium plasma: impact of small fluctuations

Nonlinear structures in a nonequilibrium plasma: impact of small fluctuations

Production Characteristics of Volatiles from Anthracite Cracking via Microwave-Induced Discharge.

The ignition of anthracite with arc plasma has not been applied due to its low chemical effect and volatile content in anthracite. The nonequilibrium plasma generated by a microwave-induced discharge has the ability to break branch chains and aromatic ring structures by kinetic effects, which has the potential for anthracite cracking and ignition. This work investigated anthracite cracking by microwave-induced discharges under an Ar/N2 atmosphere. Results showed that the maximum levels of CO production, total gas production, and total gas generation rate occur in 20% argon content due to an increase in the number of electrons and a decrease in the total electronic states excitation rate constant with an increase in the argon content. The total gas production in plasma cracking is larger than that by pyrolysis, indicating the crack of polycyclic aromatic hydrocarbon by plasma. In addition, we attempted anthracite combustion under an 80% N2 and 20% O2 atmosphere.

Fabrication and structural and magnetic properties of spark plasma sintered group-IV diluted magnetic semiconductor Fe-doped SiGe alloys

Fe-doped SiGe bulk alloys are fabricated using non-equilibrium spark plasma sintering (SPS) and their structure and ferromagnetic and magneto-transport properties are investigated. X-ray diffraction and high-resolution transmission electron microscope measurements show that the obtained alloys are composed of SiGe polycrystals. Magnetization measurements reveal that the Fe-doped SiGe alloys exhibit ferromagnetism up to 259 K, and their Curie temperature increases with Fe doping concentration up to 8%. Moreover, transport measurements of the Fe-doped SiGe alloys show typical metal-insulator transition characteristics of doped semiconductors as well as anomalous Hall effect and intriguing positive-to-negative magnetoresistance, indicating that the obtained alloys are diluted magnetic semiconductors (DMSs). Our results provide insight into the SPS-prepared Fe-doped SiGe bulk alloys and may be useful for the design, fabrication, and application of group-IV DMSs.

Development of Cf/C-UHTC composite and study of its resistance to oxidation and ablation in high-speed high-enthalpy air plasma flow

This article contains the results of research on the development of a Cf/C-UHTC carbon fabric composite based on a viscose precursor and a combined matrix consisting of partially sintered ceramics in a system consisting of HfC–HfB2–NbC–NbB2–TiC–TiB2–B4C–SiC, amorphous carbon, and pyrocarbon. The SiC fraction does not exceed 8.5–9.0 wt%. In its initial state, the composite has open porosity, with apparent and true densities of 18–22%, 2.25–2.29 g/cm3 and 2.79–2.91 g/cm3, respectively. The bending strength and the elasticity modulus are 27.8 ± 0.7 MPa and 7.8 ± 0.2 GPa, respectively, and the fracture strain is 0.85 ± 0.05%. The tests for resistance to oxidation and ablation were carried out in a gas dynamic flow regime and non-equilibrium air plasma heating at flow rates of 4.5–4.8 km/s and breaking enthalpy of 45–50 MJ/kg. Heating was performed in the temperature range Tw = 1400–2700 °C at the critical point on the front surface of the samples. The average linear ablation rate and mass loss rate of the composite are 6.3 ± 0.3 μm/s and 6.22 ± 0.44 mg/s. The estimated value of the conductivity factor is 0.280–0.285 W/(m K). The performance ability of the composite arises from the formation and evolution of a passivating heterogeneous oxide film consisting mainly of titanium niobate Ti2Nb10O29, mixed solutions of Hf1−xTixO2, (Ti1−xHfx)1−yNbyOz and (Ti1−xHfx)NbO4 with broad homogeneity ranges, and also encapsulated carbide and boride particles. It is shown that the oxidation resistance of the composite increases as a result of the transition through a number of phases into a liquid state as the working temperature increases.

Nanoarchitectonics Solution Plasma Polymerization of Amino-Rich Carbon Nanosorbents for Use in Enhanced Fluoride Removal.

Amino-functionalized carbon (NH2C) is an effective adsorbent in removing pollutants from contaminated water because of its high specific surface area and electrical charge. In the conventional preparation method, the introduction of amino groups onto the carbon surface is limited, resulting in low pollutant adsorption. Herein, we present simultaneous carbonization and amination to form NH2C via electrical discharge of nonequilibrium plasma, and the resultant material is applied as an effective adsorbent in fluoride removal. The simultaneous process introduces numerous amino groups into the carbon framework, enhancing the adsorption efficiency. The fluoride adsorption capacity is approximately 121.12 mg g-1, which is several times higher than those reported in previous studies. Furthermore, computational modeling is performed to yield deeper mechanistic insights into the molecular-level adsorption behavior. These data are useful in designing and synthesizing advanced materials for applications in water remediation.

Rapid Plasma Electrolytic Oxidation Synthesis of Intermetallic PtBi/MgO/Mg Monolithic Catalyst for Efficient Removal of Organic Pollutants.

The intermetallic PtBi/MgO/Mg monolithic catalyst was first prepared using non-equilibrium plasma electrolytic oxidation (PEO) technology. Spherical aberration-corrected transmission electron microscope (ACTEM) observation confirms the successful synthesis of the PtBi intermetallic structure. The efficiency of PtBi/Mg/MgO catalysts in catalyzing the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of NaBH4 was demonstrated. The activity factor for the catalyst is 31.8 s-1 g-1, which is much higher than reported values. In addition, the resultant catalyst also exhibits excellent catalytic activity in the organic pollutant reaction of p-nitrobenzoic acid (p-NBA) and methyl orange (MO). Moreover, benefiting from ordered atomic structures and the half-embedded PtBi nanoparticles (NPs), the catalyst demonstrates excellent stability and reproducibility in the degradation of 4-NP. This study provides an example of a simple method for the preparation of intermetallic structures as catalysts for organic pollutant degradation.

Process parameters optimization for red globe grapes to enhance shelf-life using non-equilibrium cold plasma jet

In this work, a non-equilibrium cold plasma jet (NECPJ) operated by a bi-polar pulse power source was designed and developed, and its impact on red globe grapes (Vitis vinifera) was analyzed for shelf-life enhancement. A total of 17 separate experiments were conducted using a Box-Behnken design to identify the optimum plasma process parameters, i.e., applied voltage, gas flow rate, and treatment time. Food quality parameters such as pH, total suspended solids (TSS), weight loss, total phenol and flavonoid content, vitamin C, contact angle, and firmness were studied. Field emission scanning electron microscopy (FESEM) images were also taken to see the effect of NECPJ treatment on grape surfaces and E. coli bacteria. The results showed that the linear, quadratic, and interaction effects of all three process parameters were statistically significant (p < 0.001, p < 0.01). Accordingly, the optimized plasma process parameters were identified as applied voltage 3.36 kV, gas flow rate 2.87 SLPM, and treatment time 1 min. A shelf-life study of twenty-eight days was done with and without plasma treatment. It was found that NECPJ-treated grapes had a higher shelf-life. The treated grapes contained higher levels of vitamin C, firmness, red grape color index, and total soluble solids than controls. It is inferred that NECPJ can help reduce red globe grape deterioration and maintain quality during post-harvest storage.

Gradient pulsed transient plasma for initiation of detonation

The formation of a gradient of atomic oxygen is demonstrated by means of a nanosecond non-equilibrium plasma for a varying gap size plane-to-plane electrode. Using a flat high-voltage electrode in front of a rounded triangle a 2.9 to 5 cm gap is formed over a 9.8 cm span. ICCD imaging determined an adequate ground electrode shape and slope to create a gradient. The plasma is formed by three consecutive high voltage pulses of -30, -40 and -50 kV in 100 mbar of air. O-TALIF measurements confirm that atomic oxygen production changed with gap size within the same plasma. This setup will be used to test detonation initiation by Zel’dovich gradient mechanisms in stoichiometric H2:O2 mixtures.Novelty and Significance: A novel configuration of a nanosecond non-equilibrium discharge was developed to create a controllable gradient of atomic oxygen. This was achieved by using varying gap plane-to-plane electrodes to generate an electric field of varying strength along the length of the gap. This setup will be tested in combustible mixtures to initiate a detonation wave using a gradient mechanism of Zel’dovich.