Microplasma Jet Research Articles

Micro-plasma jet improves triggering in pulsed power technology

Micro-plasma jet improves triggering in pulsed power technology

A novel micro-capillary discharge plasma jet triggered gas switch.

To reduce the working coefficient and jitter of the three-electrode gas switch used in linear transformer drivers, a novel trigger method that uses a nanosecond pulse in cooperation with the microplasma jet generated by capillary discharge was developed. A microplasma jet was generated by the nanosecond trigger pulse and injected into the follow-up breakdown gap of the gas switch to decrease the working coefficient. The influence of capillary parameters on the development of the microplasma jet was simulated. The results showed that the microplasma jet significantly reduced the breakdown delay time, jitter, and working coefficient. Increasing the capillary length and decreasing the diameter results in better triggered breakdown performance. Furthermore, the gas switch triggered by a positive pulse exhibits a lower breakdown delay and jitter. Combined with the intensified charge coupled device's shooting results, it can be concluded that the microplasma jet has a distinct influence on streamer formation, which is important for improving the working performance of the gas switch.

Design and characteristics of a fiber laser powered repetitive micro-plasma jet triggered gas switch.

To satisfy the need for low jitter in gas switches at repetition rate and enhance insulation reliability during high voltage operation of the trigger, we propose a micro-jet triggering system. This system requires less energy and can use a laser power supply as an energy source. It effectively improves the insulation stability of the trigger when working at high potentials and achieves a good triggering effect with low jitter at low working coefficients. The breakdown characteristics were tested by double-pulse experiments. Ensuring the same operating conditions for both pulses, the pulse interval was varied to obtain the breakdown voltage dispersion at different repetition rates. The results indicate that the dispersion of the breakdown voltages can reach 0.16% at a frequency of 50Hz with a pulse front of 30 μs, representing an order of magnitude reduction compared to the 1.45% at switching self-breakdown, and decreases further as the air pressure rises. In addition, the size of the microcapillary has an impact on the dispersion of breakdown voltage. It was found that for a range of lengths from 2 to 6mm and aperture sizes from 80 to 400μm, the trigger jitter was lower when the length was larger and the aperture was smaller. Furthermore, a trigger life test was performed on the ceramic capillary, and after one million triggers, the system remained stable with no degradation in trigger performance.

Helium metastable density determination in the COST reference source by absolutely calibrated optical emission spectroscopy

Helium metastable densities in the COST Reference Microplasma Jet are estimated for a variety of He/N2 admixtures and dissipated powers by applying a collisional-radiative model to absolutely calibrated optical emission spectroscopy measurements. This is accomplished by delineating the excitation mechanisms that result in the N2(C–B) and N2+(B–X) emission bands, the latter of which is strongly coupled to the presence of helium metastables. A number of other plasma parameters are established and discussed for each operating condition including the electron energy distribution function, reduced electric field, rate constants, and electron density. With these parameters, the reaction rates for the primary ionization pathways are also calculated, emphasizing the importance of helium metastables for discharge sustainment. Good agreement with the existing literature is found for most plasma parameters and for helium metastable densities, in particular. A clear [N2]−1 relationship between the nitrogen concentration and density of helium metastables is demonstrated, as has been identified in previous studies in analogous atmospheric pressure plasma jets. This validates the efficacy of this optical technique for determining helium metastable densities and establishes it as a viable, and in many cases, more accessible alternative to other means of quantifying helium metastables in low-temperature plasmas.

Ar(1s5) density in a co-axial argon plasma jet with N2–O2 shielding

Atmospheric-pressure microplasma jets (µAPPJs) are versatile sources of reactive species with diverse applications. However, understanding the plasma chemistry in these jets is challenging due to plasma-flow interactions in heterogeneous gas mixtures. Spatial metastable density profiles help to understand these physical and chemical mechanisms. This work focuses on controlling the shielding gas around a µAPPJ. We use a dielectric barrier discharge co-axial reactor where a co-flow shields the pure argon jet with different N2–O2 gas mixtures. A voltage pulse (4 kV, 1 µs, 20 kHz) generates a first discharge at the pulse’s rising edge and a second discharge at the falling edge. Tunable diode laser absorption spectroscopy measures the local Ar(1s5) density. A pure N2 (100%N2–0%O2) co-flow leads to less reproducible and lower peak Ar(1s5) density ( 5.8×1013cm−3 ). Increasing the O2 admixture in the co-flow yields narrower Ar(1s5) absorbance profiles and increases the Ar(1s5) density ( 6.9×1013 to 9.1×1013cm−3 ). The position of the peak density is closer to the reactor for higher O2 fractions. Absence of N2 results in comparable Ar(1s5) densities between the first and second discharges (maxima of 9.1×1013 and 9.3×1013cm−3 , respectively). Local Ar(1s5) density profiles from pure N2 to pure O2 shielding provide insights into physical and chemical processes. The spatially-resolved data may contribute to optimising argon µAPPJ reactors across the various applications and to validate numerical models.

Direct Writing of Fluorescent Patterns of Rare-Earth-Doped Nanophosphors by Microplasma Jet

Direct Writing of Fluorescent Patterns of Rare-Earth-Doped Nanophosphors by Microplasma Jet

Frequency-locked measurement of floating potential fluctuations in cold micro-plasma jets: Interactive surface feedback effects on reactive species generation

Frequency-locked measurements of floating potential fluctuations are carried out in a cold atmospheric pressure micro-plasma jet interacting with substrates of varying electrical permittivity (εr). The range of fluctuation frequencies (∼ 0.5–9 kHz) is compared with that determined from the time series of floating potential fluctuations and its fast Fourier transform. Results of these independent methods to determine the fluctuation frequencies are found to agree reasonably well, thereby affirming their existence in the micro-plasma jet. Substrate feedback effects dictated by εr are found to influence the amplitude of fluctuations and threshold breakdown voltage. The spectral emission line intensity corresponding to the reactive oxygen and nitrogen species, which is critical for biomedical applications, decrease drastically in the presence of stronger levels of fluctuations, indicating a bearing on their generation.

Flexible atmospheric brush-like microplasma jet source with needle-shaped protrusion electrode for internal surface treatment

In this paper, a flexible plasma jet source with newly designed needle-shaped protrusion (NSP) electrode capable of producing flexible atmospheric brush-like microplasma jet (FBµPJ) was developed and its application for internal surface treatment was investigated. The generator could maintain flexibility while possessing a certain degree of rigidity. Simulation and experimental results indicate that FBµPJ with NSP electrode was more efficient in generating the brush-like microplasma jets compared to conventional wire electrodes. The electrical characteristics showed that the discharge of this novel plasma source was a typical dielectric barrier discharge, and diverse oxygen-containing reactive species favorable for material surface treatment were observed. The internal surface of the silicone tube would get rougher and grafted with polar oxygen-containing functional groups after plasma treatment, and the inner surface can be transformed from hydrophobic to hydrophilic. Finally, the interfacial adhesion of the silicone tubes can be effectively enhanced by FBµPJ.

In vivo study on the repair of rat Achilles tendon injury treated with non-thermal atmospheric-pressure helium microplasma jet.

Non-thermal atmospheric-pressure plasma (NTAPP) has been widely studied for clinical applications, e.g., disinfection, wound healing, cancer therapy, hemostasis, and bone regeneration. It is being revealed that the physical and chemical actions of plasma have enabled these clinical applications. Based on our previous report regarding plasma-stimulated bone regeneration, this study focused on Achilles tendon repair by NTAPP. This is the first study to reveal that exposure to NTAPP can accelerate Achilles tendon repair using a well-established Achilles tendon injury rat model. Histological evaluation using the Stoll's and histological scores showed a significant improvement at 2 and 4 weeks, with type I collagen content being substantial at the early time point of 2 weeks post-surgery. Notably, the replacement of type III collagen with type I collagen occurred more frequently in the plasma-treated groups at the early stage of repair. Tensile strength test results showed that the maximum breaking strength in the plasma-treated group at two weeks was significantly higher than that in the untreated group. Overall, our results indicate that a single event of NTAPP treatment during the surgery can contribute to an early recovery of an injured tendon.

A new 2D fluid-MC hybrid approach for simulating nonequilibrium atmospheric pressure plasmas: density distribution of atomic oxygen in radio-frequency plasma jets in He/O2 mixtures

A spatially two dimensional fluid-MC hybrid (fluid-kinetic) simulation method is developed and applied to the COST reference microplasma jet operated in helium with an oxygen admixture of 0.5%, excited by a single frequency voltage waveform with f = 13.56 MHz and ϕrms=275 V. The simulation approach is based on a fluid model augmented by a Monte Carlo module that generates electron impact rates for the continuity equations solved by the fluid module. This method is capable of providing the same level of accuracy as PIC/MCC simulations with an agreement within 5%–10% at atmospheric pressure, while being significantly faster (with a speedup factor of 30 for serial to 50 for parallel implementation). The simulation results are compared to previous measurements of atomic oxygen densities (Steuer et al 2021 J. Phys. D: Appl. Phys. 54 355204), and show a very good agreement. It is found that the buildup and saturation of the atomic oxygen density distribution along the jet are due to the interplay of chemical and electron impact reactions as well as of the gas flow. Comparing the simulation results to that of Liu et al 2021 J. Phys. D: Appl. Phys. 54 275204, it is inferred that fluid models where a 2-term BE solver is used, fail to describe the COST jet in an accurate manner due to the underestimation of the electron impact rates.

Synthesis of Green Zno/Fe3O4 Nanocomposite by Microplasma Jet and Anti-Bacterial Agent

There has been an increase in demand for nanocomposite, which has resulted in large-scale manufacturers employing high-energy processes and harmful solvents. Because of this, the need for environmentally benign "green" synthesis processes has grown. Other methods for making nanocomposite include using plants and plant products, bacteria, fungi, yeast, and algae. Green synthesis has minimal toxicity and is safe for human health and the environment compared to other processes, making it the ideal option for creating nanocomposite materials. This work reveals an environmentally friendly synthesis method for magnetic nanocomposites. In particular, they were using an aqueous extract of Artemisia to obtain ZnO/Fe3O4 using cold plasma technology. The magnetic nanocomposite was prepared with different concentrations (0.01, 0.02, and 0.03) of M and (2:8) of the aqueous extract. The structural properties were studied using X-ray diffraction, where the crystal size ranged from 30 to 40 nm, while the surface morphology was studied through the field emission scanning electron microscope, and it was found that the shape of the particles is semi-spherical and within a particle size range of 30 to 60 nm. "Green" magnetic nanocomposites showed low toxicity and high biocompatibility, allowing their application in biomedicine, where magnetic nanocomposites were employed as anti-agents for E. coli and S. aureus using the agar diffusion method. Its high effect on bacterial inhibition was noted when the concentration was increased, as the diameter of inhibition ranged (11-22) mm for E. coli and (15-24) mm for Staphylococcus aureus.

Experiment on inducing apoptosis of melanoma cells by micro-plasma jet

As a promising cancer treatment method, cold atmospheric plasma has received widespread attention in recent years. However, previous research has focused more on how to realize and expand the anti-cancer scope of plasma jet. There are also studies on the killing of small-scale cancer cells, but the effects of plasma jet on normal cells and normal cell clusters have been ignored. Therefore, we proposed a 50 µm sized micro-plasma jet device, and used the device to treat melanoma cells (A-375) and human glial cells (HA1800) to evaluate their anti-cancer effects and effects on normal cells. The experimental results show that this kind of micro-plasma jet device can effectively inactivate cancer cells in a short period of time, while having little effect on normal cells. This work provides a certain experimental basis for the application of fine plasma jet to clinically inactivate cancer cells.

Plasma parameters and electric field fluctuations in a cold micro-plasma jet interacting with a substrate

Interaction of a cold atmospheric pressure micro-plasma jet with different types of substrates having a range of electrical permittivity (εr), such as conductor (copper), semiconductor (p-type silicon), insulator (Teflon and quartz), and biological (goat skin), is carried out experimentally. The electric field fluctuations, cross-phase analysis, plasma parameters [electron excitation temperature (Texc) and electron density (ne)], average propagation velocity of the plasma bullet, gas temperature (Tg), power dissipated on the substrates, and substrate temperature are investigated during the interaction. Cross phase analysis and plasma bullet velocity support the return stroke phenomenon for high εr samples, such as copper and silicon, and a surface ionization wave is generated in the case of low εr samples, such as Teflon, quartz, and biological tissue. The highest substrate current (IS) is observed for copper due to its high conductivity. Tg and ne are affected by the interaction; however, Texc is observed to change only slightly. ne is comparatively higher for high εr samples, and for all samples, it increases initially and, thereafter, decreases as we get closer to the sample's surface. Tg is comparatively higher for low εr samples and increases axially downward from the orifice of the jet, it is lower and almost constant for copper and silicon. The electric field fluctuation (EZ and Eϕ components) frequencies lie up to ∼8 kHz with a peak amplitude at ∼1 kHz, which is found to be comparatively higher for low εr samples.

Construction of a Compact Array of Microplasma Jet Devices and Its Application for Random Mutagenesis of Rhodosporidium toruloides.

A small and efficient DNA mutation-inducing machine was constructed with an array of microplasma jet devices (7 × 1) that can be operated at atmospheric pressure for microbial mutagenesis. Using this machine, we report disruption of a plasmid DNA and generation of mutants of an oleaginous yeast Rhodosporidium toruloides. Specifically, a compact-sized microplasma channel (25 × 20 × 2 mm3) capable of generating an electron density of greater than 1013 cm-3 was constructed to produce reactive species (N2*, N2+, O, OH, and Hα) under helium atmospheric conditions to induce DNA mutagenesis. The length of microplasma channels in the device played a critical role in augmenting both the volume of plasma and the concentration of reactive species. First, we confirmed that microplasma treatment can linearize a plasmid by creating nicks in vitro. Second, we treated R. toruloides cells with a jet device containing 7 microchannels for 5 min; 94.8% of the treated cells were killed, and 0.44% of surviving cells showed different colony colors as compared to their parental colony. Microplasma-based DNA mutation is energy-efficient and can be a safe alternative for inducing mutations compared to conventional methods using toxic mutagens. This compact and scalable device is amenable for industrial strain improvement involving large-scale mutagenesis.

(Invited) Redox Chemistry Driven by Atmospheric Pressure Plasma Jet

Plasmas may be considered as mixed ionic and electronic conductors. From an electrochemical point of view, a conducting gas presents a wonderful opportunity to explore redox reactions without all the restrictions a solvent medium provides. Identifying a plasma medium suitable to allow electrochemical measurements can be technically challenging, often due to the electrical energy used to create the plasma. However, atmospheric pressure plasma jets (APPJ)1&2 have been shown to be accessible and convenient as laboratory plasma sources. They present a medium that may be considered as an electrode, due to the presence of electrons or as electrolytes, due to their electrical conduction.3 Although its definition is not too important, the presence of free electrons gives an opportunity to drive reduction processes.The interesting aspect of non-thermal plasmas, and the root of their interesting chemistry, is partly due to the imbalance of thermal kinetic energy distribution between the electron and all the other species, neutral or ionized. As a consequence plasma jets are found in routine industrial applications such as etching or cleaning of surfaces for adhesion promotion. Furthermore, there is a growing body of evidence to suggest that APPJ may be used for the treatment of solid tumors. These highly energized electrons can drive redox reactions, as well as other chemical reactions, at solid or liquid can be unexpected. In this presentation I will explore the use of APPJ for reduction of metal oxides under potentiostatic control and material synthesis.4-6 References Ratcliffe, L.V., et al., Surface analysis under ambient conditions using plasma-assisted desorption/ionization mass spectrometry. Analytical Chemistry, 2007. 79(16): p. 6094-6101.Golda, J., et al., Concepts and characteristics of the 'COST Reference Microplasma Jet'. Journal of Physics D-Applied Physics, 2016. 49(8).Rumbach, P.; Bartels, D. M.; Sankaran, R. M.; Go, D. B., The solvation of electrons by an atmospheric-pressure plasma. Nature Communications 2016, 6, 7248.Sener, M. E., Quesada Cabrera, R., Parkin, I.P., Caruana, D. J., Facile formation of black titania films using an atmospheric-pressure plasma jet, Green Chemistry 2022 , 24, 2499-2505.Sener, M. E., Palgrave, R., Quesada Cabrera, R., Caruana, D. J., Patterning of Metal Oxide thin Films using H2/He Atmospheric Pressure Plasma Jet. Green Chemistry 2020, 22, 1406-1413.Sener, M. E.; Caruana, D. J., Modulation of copper(I) oxide reduction/oxidation in atmospheric pressure plasma jet. Electrochemistry Communications 2018, 95, 38-42.

Splashing of tungsten-based anode during arc discharge

A unique mechanism of splashing from a tungsten-based anode was identified during arc discharge. Splashing occurred by breakoff of a liquid metal column, which elongates after a local concavity formed on the molten anode surface. Blue–violet luminescence, emitted by cerium ions originating from additives in the tungsten-based anode, was captured before the concavity formation. The surface temperature exceeded the boiling point of the additives at the time of splashing. The measured droplet speeds suggested that an electromagnetic force contributes the high-speed ejections. Energy dispersive spectrometry mapping also exhibited a remnant of the additives on the longitudinal cross-section of the anode after arc discharge. Based on these experimental facts, the mechanism of anode splashing in arc discharge was deduced as follows: bubble formation of additives at temperatures above their boiling point, bubble bursting at the surface, micro-plasma jet generation, liquid-column elongation and breakoff under an electromagnetic force, and consequent high-speed droplet ejection.

Improvement of electrical insulating properties for defective metal/epoxy resin interface in power modules by micro-plasma jet

High-voltage power modules inevitably face the critical problem of electric field distortion at triple-junction point (Cu/insulation substrate/potting material) and accidental introduction of unexpected micro-metal defects on insulation substrate, which damages electrical insulating properties and induces breakdown. In this study, a novel precise surface treatment method based on atmospheric pressure micro-plasma jet (μ-APPJ) is proposed for rejuvenating and improving electrical insulating properties of defective Cu/epoxy resin (EP) substrate in power modules. Results show that a typical μ-APPJ with a diameter of about 200 μm is developed to precisely treat the micro-level metal defect in Cu/EP interface, and a spherical-clustered Si-containing functional film (∼Si-O4) can be fabricated on EP substrate by optimized Ar/Hexamethyldisiloxane (HMDSO)/μ-APPJ, which significantly enhances the hydrophobicity of EP surface. Moreover, the plasma-assisted film deposition around μm-defect improves interface electrical properties of defective Cu/EP samples, evidenced by higher flashover voltages and suppressed partial discharge. Further analysis based on simulations reveals that the deposited typical film not only promotes charge mobility and creepage distance on EP, but also introduces additional trap levels that capture electrons and inhibit electric field around metal defects, thereby suppressing partial discharge failure and improving electrical insulating properties.

A chemiluminescence method induced by microplasma jet for nitrites detection and the miniature detection system using smartphone

A method of luminol-diazonium chemiluminescence (CL) induced by microplasma for hazardous substance detection is proposed. The luminol-diazonium CL is caused by microplasma jet, rather than hydrogen peroxide reagent or other oxidizing agents. The CL intensity is increased by the concentration of nitrites. Based on the process of microplasma generation and CL mechanism, the optimal work conditions of the method are obtained. The linear range for nitrites detection is 0.03–1 mmol L−1 with the limit of detection (LOD) of 0.01 mmol L−1. Furthermore, a miniature system using test paper and smartphone is designed for nitrites detection in emergency. The detection system is confined in the custom-tailored shell which is only 28 cm in length, 18 cm in width and 10 cm in height. After microplasma jet treatment, the color of the test paper changes with the NO2− concentration. The photographs of the test paper are taken by the built-in camera of smartphone and analyzed by visiting the website via smartphone. The LOD is 1 mmol L−1 obtained by the CL miniature detection system based on test paper and smartphone. The accuracy, reliability and practicability of the proposed method is verified in this paper.

Ultrasound harmonic generation and atomic layer deposition of multilayer, deep-UV mirrors and filters with microcavity plasma arrays

In honor of Professor Kurt Becker’s pioneering contributions to microplasma physics and applications, we report the capabilities of arrays of microcavity plasmas in two emerging and disparate applications. The first of these is the generation of ultrasound radiation in the 20–240 kHz spectral range with microplasmas in either a static or jet configuration. When a 10times 10 array of microplasma jets is driven by a 20-kHz sinusoidal voltage, for example, harmonics as high as m = 12 are detected and fractional harmonics are produced by controlling the spatial symmetry of the emitter array. The preferential emission of ultrasound in an inverted cone having an angle of pm ,45^circ with respect to the surface normal of the jet array’s exit face is attributed to interference between spatially periodic, outward-propagating waves generated by the arrays. The spatial distribution of ultrasound generated by the arrays is analogous to the radiation patterns produced by Yagi-Uda phased array antennas at RF frequencies for which radiation is emitted broadside to arrays of parallel electric dipoles. Also, the nonperturbative envelope of the ultrasound harmonic spectrum resembles that for high-order harmonic generation at optical frequencies in rare gas plasmas and attests to the strong nonlinearity provided by the pulsed microplasmas in the sub-250-kHz region. Specifically, the relative intensities of the second and third harmonics exceed that for the fundamental, and a “plateau” region is observed extending from the 5th through the 8th harmonics. A strong plasma nonlinearity appears to be responsible for both the appearance of fractional harmonics and the nonperturbative nature of the acoustic harmonic spectrum. Multilayer metal-oxide optical filters designed to have peak transmission near 222 nm in the deep-UV region of the spectrum have been fabricated by microplasma-assisted atomic layer deposition. Alternating layers of ZrO_2 and Al_2O_3, each having a thickness in the 20–50 nm range, were grown on quartz and silicon substrates by successively exposing the substrate to the Zr or Al precursor (tetrakis(dimethylamino) zirconium or trimethylaluminum, respectively) and the products of an oxygen microplasma while maintaining the substrate temperature at 300 K. Bandpass filters comprising 9 cycles of 30-nm-thick ZrO_2/50-nm-thick Al_2O_3 film pairs transmit 80% at 235 nm but < 35% in the 250–280 nm interval. Such multilayer reflectors appear to be of significant value in several applications, including bandpass filters suppressing long wavelength (240–270 nm) radiation emitted by KrCl (222) lamps.Graphical abstract

Formation of wettability gradient surface on polyethylene terephthalate by maskless argon microplasma jet writing for droplet self-driven application

The preparation of wettability gradient surface (WGS) has drawn increasing attention in diverse applications. However, the existing methods for WGS fabrication involve complex, costly and time-consuming procedures. In this paper, a novel, simple and efficient method is proposed for the preparation of wettability gradient surface (WGS) on polyethylene terephthalate (PET) film by maskless atmospheric pressure microplasma jet writing. By controlling the plasma processing parameters, the characteristics of the WGS could be controlled by using different duration time differences, nozzle distance differences and gas flow rate differences. Scanning Electron Microscope (SEM), Atomic Force Microscope (AFM) and Fourier Transform Infrared Spectroscopy (FTIR) were used to observe the surface morphologies and the chemical compositions of the PET surface before and after plasma treatment. It showed that the surface roughness increased and hydrophilic functional groups (such as COC and CO) were introduced into the PET surfaces after plasma writing, which was the main reason for the improvement of plasma treated PET surface wettability. WGS can be fabricated by synchronously controlling the plasma processing parameters during the direct writing processing and droplet self-driving could be successfully realized. The maximum self-driving distance of 1 μL water droplet could reach 4.76 mm in this work.