Plasma Generation Research Articles

Generation of high-density plasma via transparent electrode in capacitively coupled plasma

Generation of high-density plasma via transparent electrode in capacitively coupled plasma

Fiber laser tuning by means of nonthermal plasma as a temperature regulator

AbstractThis work presents a technique to obtain wavelength tuning for a fiber laser with a nonthermal plasma‐based temperature regulator system and a fiber Bragg grating (FBG). The plasma effect was generated in a dielectric barrier discharge (DBD) reactor filled with helium as the carrier gas for plasma generation. The temperature characterization of the DBD reactor had shown that the nonthermal heating mechanism of plasma could manipulate gas temperature from 25°C to around 145°C in ~10 min. By exploiting the rapid temperature change of plasma, the reflected wavelength of the FBG can be tuned accordingly. At a discharge voltage of 3 kV, the fiber laser was tuned within a range of 2 nm with 11.9 pm/°C tuning resolution. The fiber laser exhibits a thermally stable emission with very low shifting at a constant temperature value.

Effect of the magnetic field strength on the argon plasma characteristics of a helicon plasma source with a two-turn flat-loop antenna

New plasma applications in advanced fields, such as fundamental nuclear fusion research, require high-density, large-diameter plasma with a strong and non-uniform magnetic field. A helicon plasma (HP) source using a flat-type antenna is expected to be one of the promising methods for such applications. In this study, we developed an HP source with a two-turn flat-loop antenna connected to a 30 kW radio frequency power supply in the Compact Test Plasma device. In the argon plasma generation experiment with various magnetic fields, HP generation was observed for the first time in this device. The electron density was calculated from the dispersion relation with the magnetic field strength at 45 cm from the antenna surface, assuming a fundamental radial mode and an azimuthal mode of $m=0$ . The electron density expected from the experimental result was approximately in the same range as the calculation result by a factor of 2.3 to 3.5. In addition, the magnetic field strength and shape around the antenna are important factors in the plasma properties. This plasma source has been installed in the pilot GAMMA PDX-SC, which is under development for nuclear plasma research, and it contributes to the study of the HP generation process.

Effect of liquid surface depression size on discharge characteristics and chemical distribution in the plasma-liquid anode system

Atmospheric pressure plasma-liquid interactions exist in a variety of applications, including wastewater treatment, wound sterilization, and disinfection. In practice, the phenomenon of liquid surface depression will inevitably appear. The applied gas will cause a depression on the liquid surface, which will undoubtedly affect the plasma generation and further affect the application performance. However, the effect of liquid surface deformation on the plasma is still unclear. In this work, numerical models are developed to reveal the mechanism of liquid surface depressions affecting plasma discharge characteristics and the consequential distribution of plasma species, and further study the influence of liquid surface depressions of different sizes generated by different helium flow rates on the plasma. Results show that the liquid surface deformation changes the initial spatial electric field, resulting in the rearrangement of electrons on the liquid surface. The charges deposited on the liquid surface further increase the degree of distortion of the electric field. Moreover, the electric field and electron distribution affected by the liquid surface depression significantly influence the generation and distribution of active species, which determines the practical effectiveness of the relevant applications. This work explores the phenomenon of liquid surface depression, which has been neglected in previous related work, and contributes to further understanding of plasma-liquid interactions, providing better theoretical guidance for related applications and technologies.

Optimizing ammonia cracking in microwave argon plasma: Temperature control and ammonia delivery

Hydrogen has been conceived as an alternative to hydrocarbons to achieve a carbon–neutral society, with ammonia emerging as the most practical hydrogen carrier for long-distance transportation. Conventional thermo-catalytic cracking of ammonia is an energy-intensive process, leading to the consideration of low-temperature plasmas as potential alternatives. Recently, a surfatron-based Microwave Plasma Jet (MWPJ) was investigated, demonstrating the fundamental physical and chemical mechanisms of NH3 cracking. In this study, we present an optimization scheme for NH3 cracking using a surfatron-based argon MWPJ to improve H2 production rate and efficiency. Our approach included: (i) introducing downstream inlets of NH3 to decouple NH3 from plasma generation and (ii) adding additive (N2 or NH3) to the main Ar flow to elevate the gas temperature of the MWPJ. We found that both additives to the Ar flow raised the gas temperature from 2700 K up to 4200 K (N2) or 5400 K (NH3), showing a trade-off between gas temperature and the height of the MWPJ. The case with NH3 added to the main Ar flow showed better performance than the case with N2 due to the higher gas temperature and additional H2 production from the additive NH3. The main NH3 supply in the downstream showed no negative effect on the plasma generation and significantly increased the H2 production rate and efficiency, primarily due to the sufficient NH3 supply rate. Increased number of NH3 inlets also facilitated NH3 cracking, illustrating saturated performance with four inlets. To scale up this process, the obtained optimal geometry and operating conditions will be further explored using a high-power microwave system.

Polar cap region and plasma drift in pulsars

ABSTRACT Pulsars often display systematic variations in the position and/or intensity of the subpulses, the components that comprise each single pulse. Although the drift of these subpulses was observed in the early years of pulsar research, and their potential for understanding the elusive emission mechanism was quickly recognized, there is still no consensus on the cause of the drift. We explore the electrodynamics of two recently proposed or refined drift models: one where plasma lags behind corotation, connecting the drift with the rotational pole; and another where plasma drifts around the electric potential extremum of the polar cap. Generally, these are different locations, resulting in different drift behaviours, that can be tested with observations. In this study, however, we specifically examine these models in the axisymmetric case, where the physics is well understood. This approach seems counter-intuitive as both models then predict similar large-scale plasma drift. However, it allows us to show, by studying conditions within the sparks for both models, that the lagging behind corotation model is inconsistent with Faraday’s law. The modified carousel (MC) model, where plasma drifts around the electric potential extremum, not only aligns with Faraday’s law, but also provides a future direction for developing a comprehensive model of plasma generation in the polar cap region. Unlike previous models, which considered the drift only inside the discharging regions, the MC model reveals that the electric field between the discharges is not completely screened, and plasma drifts there – a paradigm shift for the drifting subpulse phenomenon.

Optimization and preparation for the start-up of the plasma ICR heating system at the KTM tokamak

The paper presents and discusses the results of the research on the preparation of the HF plasma heating system of the KTM tokamak for the start-up. The calculations have been performed to determine the parameters at which the most effective absorption of the HF radiation by the plasma of the KTM tokamak was expected, the results of measurements of the frequency response of the antenna-feeder device of the HF heating system generator of the KTM tokamak plasma have been presented. The result of the carried out work have shown that more efficient plasma heating on a KTM tokamak can be obtained at a frequency of 14 MHz.

Experimental Study on the Influence of Microwave Energy Pulse Width and Duty Cycle on Evaporation and Ignition Characteristics of ADN-Based Liquid Propellant Droplets

This study investigates the evaporation and ignition characteristics of a single droplet of ammonium dinitramide (ADN)-based liquid propellant utilizing a waveguide resonant cavity device, in conjunction with a high-speed photographic imaging system and testing system. Experimental methods are employed to analyze the impact of microwave pulse width and duty cycle on the puffing and meicro-explosion phenomena of the droplet, as well as the delay time and duration of ignition. The experimental findings reveal that increasing the duty cycle enhances the ignition success rate and diminishes flame development time. Specifically, elevating the microwave duty cycle from 60% to 80% reduces the ignition delay time of the droplet from 132.8 ms to 88.1 ms, and the ignition duration from 23.1 ms to 19.9 ms. Furthermore, an increase in microwave energy pulse width expedites the combustion process of the flame and influences plasma generation. Increasing the pulse width of microwave energy from 20 µs to 40 µs prolongs the ignition delay time from 140.3 ms to 200.5 ms and extends the ignition duration from 56.7 ms to 77.8 ms. Additionally, it is observed that a higher duty cycle leads to a more pronounced puffing phenomenon that initiates earlier. In contrast, a higher pulse width results in a more pronounced puffing phenomenon that commences later. This study provides a thorough investigation into the microwave ignition mechanism of ADN-based liquid propellants, offering theoretical insights into the ignition and combustion stability of such propellants in microwave-assisted ignition systems.

Effects of Plasma Ions/Radicals on Kinetic Interactions in Nanowall Deposition: A Review

Recent advances in the growth of carbon nanowalls (CNWs) and vertical graphene nanosheets using various plasma‐enhanced chemical vapor deposition (PECVD) methods are reviewed in this article. Growth methods are classified into hot‐ and cold‐wall reactors equipped with diverse plasma generation systems, and their respective characteristics are summarized, with particular attention to the behavior of reactive species, such as ions and radicals, generated within the plasma. Recent progress in this research domain is outlined for each method, and an organized account of the chemical kinetic phenomena occurring within the plasma is provided. Finally, future perspectives are discussed. Fundamental data are obtained through real‐time in situ measurements of ions and radicals, and the construction of a database from these data offers microscopic insights that significantly enhance processing outcomes for macroscopically controlling the mechanical shapes and chemical properties of CNWs.

Vivo application of a portable plasma generator in infected wound healing

AbstractIn this study, a portable plasma generator produced large‐area air plasma for treating infected wounds in BALB/c mice. Different plasma treatment times (30 s, 1 min, 3 min, and 4.5 min) were applied daily until the wounds healed completely. Results showed reduced inflammation and increased vascular endothelial growth factor (VEGF) expression in tissues treated for 1 and 3 min, promoting blood vessel proliferation and collagen fiber synthesis. However, treatment for 30 s and 4.5 min worsened inflammation and decreased VEGF expression. Overall, a 1‐min treatment was the most effective in promoting wound healing. Cold plasma shows promise for healing infected wounds, with treatment duration being a crucial factor.

Propagation effects in resonant high-order harmonic generation and high-order frequency mixing in a laser plasma

Propagation effects in resonant high-order harmonic generation and high-order frequency mixing in a laser plasma

Nitrogen oxides removal from hydrogen flue gas using corona discharge in marine boilers: Application perspective

This paper focuses on the combustion of hydrogen in boilers, as it appears to be a more effective method than using fuel cells for heating purposes due to higher boiler efficiency. One of the main disadvantages of hydrogen combustion in air is NOx formation. Therefore, the authors decided to introduce corona discharge as an innovative technique to clean hydrogen flue gas by effectively reducing NOx levels. The method involves generating positive plasma at atmospheric pressure by applying up to a 23 kV voltage difference between rod and ring-shaped electrodes. Experimental studies have shown that corona discharge can significantly lower the concentrations of NO and NOx in exhaust gases. The maximum DeNOx level was found to be 32.3%, while the plasma generator uses 17.5% of the power contained in burned hydrogen. The findings suggest that this technology holds potential for application in industrial hydrogen combustion systems, offering an environmentally friendly alternative to conventional NOx reduction methods.

Flexible thin-layer plasma sterilizer based on polyimide and efficacy evaluation under bending deformation

Cold atmospheric pressure plasma is receiving attention in biomedical treatment for its non-thermal, dry-type, and high-efficiency disinfection effects on bacteria, fungi, and viruses, compared to typical sterilization methods, such as pasteurization, chemical solutions, and ultraviolet radiation. There are great demands of plasma decontamination on the surface of complex 3D objects, with the request of large coverage, convenience, and uniformity, which still remains a challenge for the current plasma devices. In this work, a flexible thin-layer plasma source for sterilization is developed based on a polyimide substrate, and its plasma generation process is characterized by experiment and simulation. The influences of bending deformation are studied and evaluated by electrical waveforms, heat radiation, and ozone production, of which the mechanisms are further explained. Results illustrate that the variation in electron impact ionization induced by different curvatures is the main cause leading to the change in microparticle production, thus affecting the macroscopic properties of plasmas. Activations of the plasma sterilizer for 30 and 120 s reduce both S. aureus and P. aeruginosa on the flat surface by around 2.5 and 5 log colony forming units (CFU). However, the plasma sterilization effect decreases with an extent of about 1 log CFU when treating the curved surface, while being regained after conforming the plasma sterilizer to the curved surface. This kind of plasma generator offers significant flexibility and efficacy, being promising for the treatment of objects with irregular surfaces in future plasma biomedicine and material processing.

Transcriptome analysis of Candida albicans planktonic cells in response to plasma medicine.

Introduction. Cold plasma is frequently utilized for the purpose of eliminating microbial contaminants. Under optimal conditions, it can function as plasma medicine for treating various diseases, including infections caused by Candida albicans, an opportunistic pathogen that can overgrow in individuals with weakened immune system.Gap Statement. To date, there has been less molecular study on cold plasma-treated C. albicans.Research Aim. The study aims to fill the gap in understanding the molecular response of C. albicans to cold plasma treatment.Methodology. This project involved testing a cold plasma generator to determine its antimicrobial effectiveness on C. albicans' planktonic cells. Additionally, the cells' transcriptomics responses were investigated using RNA sequencing at various treatment durations (1, 3 and 5 min).Results. The results show that our cold plasma effectively eliminates C. albicans. Cold plasma treatment resulted in substantial downregulation of important pathways, such as 'nucleotide metabolism', 'DNA replication and repair', 'cell growth', 'carbohydrate metabolism' and 'amino acid metabolism'. This was an indication of cell cycle arrest of C. albicans to preserve energy consumption under unfavourable conditions. Nevertheless, C. albicans adapted its GSH antioxidant system to cope with the oxidative stress induced by reactive oxygen species, reactive nitrogen species and other free radicals. The treatment likely led to a decrease in cell pathogenicity as many virulence factors were downregulated.Conclusion. The study demonstrated the major affected pathways in cold plasma-treated C. albicans, providing valuable insights into the molecular response of C. albicans to cold plasma treatment. The findings contribute to the understanding of the antimicrobial efficiency of cold plasma and its potential applications in the field of microbiology.

Kinetic simulations of capacitively coupled plasmas driven by tailored voltage waveforms with multi-frequency matching

Impedance matching is crucial for optimizing plasma generation and reducing power reflection in capacitively coupled plasmas (CCP). Designing these matchings is challenging due to the varying and typically unknown impedance of the plasma, especially in the presence of multiple driving frequencies. Here, a computational design method for impedance matching networks (IMNs) for CCPs is proposed and applied to discharges driven by tailored voltage waveforms (TVW). This method is based on a self-consistent combination of particle in cell/Monte Carlo collision simulations of the plasma with Kirchhoff’s equations to describe the external electrical circuit. Two Foster second-form networks with the same structure are used to constitute an L-type matching network, and the matching capability is optimized by iteratively updating the values of variable capacitors inside the IMN. The results show that the plasma density and the power absorbed by the plasma continuously increase in the frame of this iterative process of adjusting the matching parameters until an excellent impedance matching capability is finally achieved. Impedance matching is found to affect the DC self-bias voltage, whose absolute value is maximized when the best matching is achieved. Additionally, a change in the quality of the impedance matching is found to cause an electron heating mode transition. Poor impedance matching results in a heating mode where electron power absorption in the plasma bulk by drift electric fields plays an important role, while good matching results in the classical α-mode operation, where electron power absorption by ambipolar electric fields at the sheath edges dominates. The method proposed in this work is expected to be of great significance in promoting TVW plasma sources from theory to industrial application, since it allows designing the required complex multi-frequency IMNs.

Numerical investigation of discharge evolution and breakdown characteristics of ArF excimer lasers

The corona bar induced pre–ionization is a crucial preliminary process in the operation of ArF excimer lasers, directly impacting the uniformity and stability of output laser. The ultraviolet corona pre–ionization, as the mainstream method, is tightly coupled with the main discharge process, which complicates analysis. Here, we establish a numerical model of a single pulse discharge incorporating an external circuit to analyze the pre–ionization process and its influence on the breakdown characteristics. (1) By adopting detailed input parameters of photoionization model, we observe uniform and dispersed plasma propagation from the corona bar to the main gap. (2) An artificial boundary condition is proposed to investigate the phenomenological effect of high–energy electrons emission, emphasizing the influence of surface discharge along the cathode. (3) The propagation and breakdown characteristics of the two pre–ionization setup methods, photoionization and background electron density, are compared numerically. This study enhances the understanding of the pre–ionization process in ArF excimer lasers and provides theoretical insights for their optimization and design.

Catalyst‐free pretreatment of raw wheat straw by atmospheric‐pressure pulsed air discharge for enhancement of sugar production

AbstractThis study presents atmospheric‐pressure plasma as a novel catalyst‐free pretreatment method for raw wheat straw (RWS) biomass. The work explores the effects of processing parameters, such as milled particle size, moisture content of RWS, and plasma generations, on pretreatment efficiency. To understand the mechanisms behind the enhanced pretreatment efficiency, various analysis techniques were used to analyze the physical and chemical properties of RWS before and after pretreatment. The analysis reveals that plasma pretreatment significantly damages the surface smoothness of RWS and enhances the decomposition of lignocellulosic structures. These effects are primarily attributed to the reactive species generated by the pulsed discharge, rather than the accompanying UV radiation, acidification, or heating actions during plasma pretreatment.

Heavy Naphtha Desulfurization by Ozone Generated via the DBD Plasma Reactor

This work presents an investigation into the ultra-desulfurization of heavy naphtha fuel (model using BT and DBT) using oxidation and solvent extraction techniques. Ozone produced by the DBD (Dielectric barrier discharge) plasma generator was employed in the oxidation process as an oxidant, and acetonitrile was used as a solvent extraction. Box-Behnken experimental design was adopted in the current study to examine oxidation desulfurization by non-thermal plasma for the various operation conditions including time, flow rate, and temperature on sulfur removal efficiency. Acetonitrile with an oxidized oil/solvent ratio of 1:1(v/v ratio) was utilized as the extraction solvent. The results showed that the maximum sulfur removal of about 91% was obtained with a temperature of 50°C, flow rate of 75 ml/min, and time of 4 hours.

Study on the influence of side-blown airflow velocities on plasma and combustion wave generated from fused silica induced by combined pulse laser

This study examines the impact of variations in side-blowing airflow velocity on plasma generation, combustion wave propagation mechanisms, and surface damage in fused silica induced by a combined millisecond-nanosecond pulsed laser. The airflow rate and pulse delay are the main experimental variables. The evolution of plasma motion was recorded using ultrafast time-resolved optical shadowing. The experimental results demonstrate that the expansion velocities of the plasma and combustion wave are influenced differently by the side-blowing airflow at different airflow rates (0.2 Ma, 0.4 Ma, and 0.6 Ma). As the flow rate of the side-blow air stream increases, the initial expansion velocities of the plasma and combustion wave gradually decrease, and the side-blow air stream increasingly suppresses the plasma. It is important to note that the target vapor is always formed and ionized into plasma during the combined pulse laser action. Therefore, the side-blown airflow alone cannot completely clear the plasma. Depending on the delay conditions, the pressure of the side-blowing airflow, the influence of inverse Bremsstrahlung radiation absorption and target surface absorption mechanisms can lead to a phenomenon known as the double combustion waves when using a nanosecond pulse laser. Both simulation and experimental results are consistent, indicating the potential for further exploration of fused silica targets in the laser field.

The Innovation in Air Plasma Spray for Hardfacing

Thermal spray coating plays a significant role in industry. The wear-resistant deposition helps to provide a longer life cycle for the components. There is an ongoing effort to develop coatings that improve the coefficient of friction. Compared with other deposition techniques, plasma spray coating can be recommended for a wide range of substrate materials to produce a stable, wear-resistant material. The plasma-sprayed deposition not only improves tribological performance but also embeds the desired mechanical and physical properties. In plasma spray technology, the inert gas used is mostly plasma jet. To create the wear-resistant coatings, the engineers apply self-flux or cermet powder, both of which are expensive materials. Some positive results of deposition using the amorphous powder encouraged the engineers and researchers. But in a few of the investigations on the air plasma spray Fe-based powder, the plasma generation gas is ordinary air. This innovation served to save on production costs. The aim of this work is the study of Fe-based spraying, applying the modification of a plasma torch. Both of the innovations help to enhance the hardfacing effect for wear resistance.