Cold Atmospheric Pressure Plasma Jet Research Articles

Effects of different gas flow rates and non-perpendicular incidence angles of argon cold atmospheric-pressure plasma jet on silver thin film treatment

In this study, the influences of variations in the gas flow rate and incidence angles of argon cold atmospheric-pressure plasma jet on the morphology and absorption spectra of silver thin films (60 nm, 80 nm, and 100 nm film thickness) are investigated. To evaluate the surface morphology, atomic force microscopy (AFM) was employed on the silver thin film surface before and after plasma processing. To analyze the effect of plasma treatment on the grain size, the one-dimensional AFM surface profiles of Ag thin films are approximated using a Gaussian function. The absorbance of Ag thin films is measured in wavelength range of 190–1100 nm utilizing UV–Vis absorption spectrometer. Compared to the gas flow rates 0.5 standard litter per minute (SLM) and 2 SLM, surface treatment of Ag thin film with gas flow rate of 1 SLM increased the valley depth, the peak valley height, and the distance between two deepest valleys remarkably. A sequential argon plasma treatment (2-min plasma treatment perpendicular to surface was followed by 2-min plasma processing with non-perpendicular incidence angle of 60°) offers considerable improvement in the uniformity of grains and also changes shape of grains, especially the peak height (about 44 times higher than untreated sample) and area of grains (almost 136 times greater than untreated sample) which can be applicable for optical sensing technology.

Sensitive detection of HO radicals produced in an atmospheric pressure plasma using Faraday rotation cavity ring-down spectroscopy.

Cavity ring-down spectroscopy (CRDS) is a well-established, highly sensitive absorption technique whose sensitivity and selectivity for trace radical sensing can be further enhanced by measuring the polarization rotation of the intracavity light by the paramagnetic samples in the presence of a magnetic field. In this paper, we highlight the use of this Faraday rotation cavity ring-down spectroscopy (FR-CRDS) for the detection of HO2 radicals. In particular, we use a cold atmospheric pressure plasma jet as a highly efficient source of HO2 radicals and show that FR-CRDS in the near-infrared spectral region (1506 nm) has the potential to be a useful tool for studying radical chemistry. By simultaneously measuring ring-down times of orthogonal linearly polarized light, measurements of Faraday effect-induced rotation angles (θ) and absorption coefficients (α) are retrieved from the same data set. The Faraday rotation measurement exhibits better long-term stability and enhanced sensitivity due to its differential nature, whereby highly correlated noise between the two channels and slow drifts cancel out. The bandwidth-normalized sensitivities are αmin=2.2×10-11 cm-1 Hz-1/2 and θmin=0.62 nrad Hz-1/2. The latter corresponds to a minimum detectable (circular) birefringence of Δnmin=5×10-16 Hz-1/2. Using the overlapping qQ3(N = 4-9) transitions of HO2, we estimate limits of detection of 3.1 × 108 cm-3 based on traditional (absorption) CRDS methods and 6.7 × 107 cm-3 using FR-CRDS detection, where each point of the spectrum was acquired during 2 s. In addition, Verdet constants for pertinent carrier (He, Ar) and bulk (N2, O2) gases were recorded in this spectral region for the first time. These show good agreement with recent measurements of air and values extrapolated from reported Verdet constants at shorter wavelengths, demonstrating the potential of FR-CRDS for measurements of very weak Faraday effects and providing a quantitative validation to the computed rotation angles.

Cold Atmospheric Pressure Plasma Jet Reduces Trichophyton rubrum Adherence and Infection Capacity.

This study aimed to evaluate the effects of cold atmospheric pressure plasma (CAPP)jet on Trichophyton rubrum growth, germination and adherence to nail. The effects of plasma jet on T. rubrum conidia germination and on mycelial growth were evaluated by in vitro assays. An ex vivo nail infection model was used to evaluate the effects on conidia adherence and infection. Biochemical analyses of nail fragments exposed or not to CAPP were performed by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Plasma jet exposure for 10 and 15min completely inhibited mycelial growth after only one exposure. Fifteen minutes of exposure could reduce conidia germination in suspension. Fungal suspensions exposed to plasma jet for 10 and 15min were not able to infect nail specimens. These results were corroborated by ATR-FTIR analyses of nail fragments. In conclusion, single exposure to CAPP for 15min was able to inhibit fungal growth, adherence and infection capacity. The results suggest that cold atmospheric plasma jet can be a promising alternative for the treatment of onychomycoses caused by T. rubrum.

The impact of cold atmospheric pressure plasma jet on seed germination and seedlings growth of fenugreek (Trigonella foenum-graecum)

The effects of cold atmospheric-pressure plasma jet (CAPPJ) were investigated on germination and early seedling growth of fenugreek (Trigonella foenum-graecum L) seeds. A two-electrode argon CAPPJ system with and without an additional grounded electrode [accelerating grounded (AG) electrode] was used at different exposure times. After 16 h of observation, the germination rates increased by 4 and 7 times, without and with using an AG electrode, respectively, for 1 min of plasma exposure. An increase in shoot fresh weight was observed, especially at 10 min exposure time. A high dry weight of root and shoot at 1 min-AG exposure time was observed. The root:shoot ratio was lower in plasma-treated seedlings, compared with the control plants. The study found that the O-radical emission line (777.4 nm) enhanced 5 times, due to the presence of an AG electrode, which increased the axial electric field and led to the formation of more streamers. The three stated effects (O-radicals, enhancement of the electric field and streamers) could be the cause for the stimulation of seed germination and seedling growth parameters when using the CAPPJ. The scanning electron microscope images showed the etching of the seed surface layers, which was more pronounced when an AG electrode was applied. The results of the current study indicate that the germination rates increased due to the increase of O-radical concentration and the etching of the seed surfaces.

1D time evolving electric field profile measurements with sub-ns resolution using the E-FISH method.

We present an approach for the measurement of time evolving electric field profiles in atmospheric pressure plasma discharges using electric field induced second harmonic generation (E-FISH). While the E-FISH effect has been known of for some time, recent advances in laser and detection technology have allowed the method to be utilized for spatial measurements of an arbitrarily applied electric field. A cylindrical lens is used to focus the femtosecond laser light to a line and an intensified charge coupled device is used for detection, allowing for one-dimensional (1D) spatial resolution on the order of ∼50 μm. Measurements have been carried out verifying the spatial resolution using a spatially periodic, localized electric field. Calibrated 1D electric field measurements have been completed with a time resolution of 500ps in a laminar cold atmospheric pressure plasma jet with argon core flow and N2 co-flow powered by a nanosecond (ns) pulse dielectric barrier discharge. The field was shown to propagate as an ionization wave, with a velocity of ∼0.3 mm/ns.

The synthesis of C, N-codoped TiO2 hollow spheres by a dual-frequency atmospheric pressure cold plasma jet

Titanium dioxide has been widely applied in many fields, but the photon utilization efficiency of it was low because of the wide band gap, amounting to 3.2 eV. Many studies have shown that doping TiO2 with nonmetals (N, S, C and so on) could narrow the TiO2 band gap. In the paper, the titanium tetraisopropoxide (TTIP) used as the precursor in the argon/oxygen which was driven by dual-frequency (100 kHz/100 MHz) atmospheric pressure plasma jet via tuning the nitrogen flow ratio was investigated. The structures of the synthetic C, N-codoped TiO2 hollow sphere were investigated by X-ray diffraction and Raman shift spectroscopy. The results indicated that the synthetic crystals consist of anatase and rutile. The scanning electron microscopy and transmission electron microscopy demonstrated that the synthetic crystals were hollow spheres. The elements of the C, N-codoped TiO2 were characterized by energy-disperse spectroscopy. The patterns reveal that carbon and nitrogen are incorporated in the deposited TiO2 crystal. The C element increased but N element decreased with the increase in nitrogen gas flow. The chemical bond and composition of TiO2 were characterized by X-ray photoelectron spectroscopy, which indicates that C is derived from the dissociation of tetraisopropoxide and N element is originated from the electron ionization of N2 molecules. The optical absorption of these samples was detected by UV–Vis absorbance spectra. The results indicated that the band gap of S1 and S2 is 2.91 and 3.10 eV, respectively. Excited species of the plasma discharge were diagnosed by optical emission spectroscopy.

Atmospheric pressure plasma jet assisted micro-milling of Inconel 718

Nickel-based superalloy Inconel 718 is one of the hardest materials owing to its high hardness and additional physical properties. It is the most commonly used superalloy in gas turbine, aerospace, and automobile sectors. Micro-milling is generally employed for precision manufacturing of tiny structures, but it is difficult to obtain good surface quality with micro-milling Inconel 718 because of its excellent mechanical properties like high strength and hardness. Atmospheric pressure cold plasma jet can effectively improve surface wettability without changing surface micromorphology, which is expected to have positive lubricating effects in micro-machining of difficult-to-cut materials. In addition, minimum quantity lubrication can induce coolants into the machining area more efficiently, and is especially appropriate for micro-machining. In this paper, we propose a composite micro-milling method combining plasma jet and minimum quantity lubrication to machine Inconel 718. The effect of plasma jet on machinability is investigated by performing micro-milling experiments under different atmospheres (dry, nitrogen jet, plasma jet, minimum quantity lubrication, and plasma + minimum quantity lubrication). Surface roughness, cutting forces, and residual stress are the measures using corresponding techniques. The results indicate that the atmospheric pressure cold plasma jet can efficiently improve surface quality and reduce cutting forces of Inconel 718.

Efficacy of cold atmospheric pressure plasma jet against Enterococcus faecalis in apical canal of human single-rooted teeth: a preliminary study

Many factors that may affect the success of root canal treatment are complexity of root canal system, especially in the apical part, and the virulence of bacteria such as biofilm formation. A cold atmospheric pressure plasma jet is a novel method for sterilization and applied for root canal disinfection. The purpose of this study was to investigate the effect of the cold atmospheric pressure plasma jet on Enterococcus faecalis (E. faecalis) biofilms infected in the apical root canals. Methods: Fifty-four single rooted-teeth were infected with E. faecalis for seven days and allocated into five groups. Group I performed as positive control. Group II-V were served as experimental groups: NaOCl, plasma, NaOCl + plasma and gas only, respectively. The disinfection was evaluated by colony count (per milligram) at the depths of 0.05 and 0.10 mm of root dentin. The remaining bacteria was also counted from the grounded root dentin. Data was analysed by one-way ANOVA and post hoc test, with a level of significance set at P<.05. Results: The NaOCl, plasma and NaOCl + plasma groups significantly reduced the E. faecalis, but no significant difference was found among these groups (P>0.5). The NaOCl + plasma group significantly reduced E. faecalis in the deeper dentin level compared to the other groups. Conclusion: The cold atmospheric pressure plasma jet had antimicrobial activity against E. faecalis biofilm as well as the use of NaOCl. The combined treatment yielded the most promising result and may be beneficial in root canal disinfection.

Non-Equilibrium Plasma Jet at Atmospheric Pressure Powered by Tesla Coil

The aim of this work presents the characterization of a plasma jet powered by Tesla coil. Tesla coil can be used for generation cold plasma from Dielectric Barrier Discharge (DBD). Tesla coil has been designed and constructed at Egyptian Atomic Energy Authority for multipurpose. The electrical characteristic of non-equilibrium plasma jet using rare gases (argon and helium) at atmospheric pressure has been studied. An atmospheric-pressure cold plasma jet generated by Tesla coil in a single-electrode configuration is characterized based on optical and electrical measurements.

Development of phosphor containing functional coatings via cold atmospheric pressure plasma jet - Study of various operating parameters

Abstract In this study, we deposited phosphorous containing functional coatings on the surface of polypropylene (PP) substrate by cold atmospheric plasma assisted polymerization using low temperature plasma jet. Triisopropyl phosphate (TIP) was used as precursor while the coating process was carried out as a function of deposition potential and monomer flow rate. The influence of various plasma polymerization operating parameters on the surface properties of functional coatings are examined by means of atomic force microscopy (AFM), Scanning electron microscopy (SEM) and X-ray photo electron spectroscopy (XPS). The reactive species involved during the in-situ polymerization were studied by optical emission spectroscopy (OES). The variation in hydrophilic properties of the surface coated film was investigated by measuring contact angle. Furthermore, the stability of post-plasma polymerized films was evaluated by measuring contact angle values 15 days after storing in various ambient conditions (air and distilled water). The characterization results clearly exhibited that phosphorus containing functional films could be successfully deposited on the surface of PP films and the retention of the functional groups could be tuned within the framework of the operating parameters.

The role of UV photolysis and molecular transport in the generation of reactive species in a tissue model with a cold atmospheric pressure plasma jet

Cold atmospheric pressure plasma jets (plasma) operated in ambient air provide a rich source of reactive oxygen and nitrogen species (RONS), which are known to influence biological processes important in disease. In the plasma treatment of diseased tissue such as subcutaneous cancer tumors, plasma RONS need to first traverse an interface between the plasma-skin surface and second be transported to millimeter depths in order to reach deep-seated diseased cells. However, the mechanisms in the plasma generation of RONS within soft tissues are not understood. In this study, we track the plasma jet delivery of RONS into a tissue model target and we delineate two processes: through target delivery of RONS generated (primarily) in the plasma jet and in situ RONS generation by UV photolysis within the target. We demonstrate that UV photolysis promotes the rapid generation of RONS in the tissue model target's surface after which the RONS are transported to millimeter depths via a slower molecular process. Our results imply that the flux of UV photons from plasma jets is important for delivering RONS through seemingly impenetrable barriers such as skin. The findings have implications not only in treatments of living tissues but also in the functionalization of soft hydrated biomaterials such as hydrogels and extracellular matrix derived tissue scaffolds.

Plasma‐mediated inactivation of E. coli: Influence of protein on wet surface and in liquid medium

Application of cold atmospheric‐pressure plasma (CAP) for wound treatment but also for decontamination of food or water often includes the presence of proteins. These proteins contain amino acids with functional groups such as thiol (SH) groups. Plasma‐mediated effects in biological systems involve reactive oxygen and nitrogen species (RONS). In this regard, the redox signaling is often mediated via thiol groups. The aim of this study was to investigate the influence of protein and SH group containing amino acid on the antimicrobial properties of plasma‐treated saline solution (0.85% NaCl, w/v) and on the direct CAP efficacy on solid wet agar plates. Plasma treatment of saline solution was realized using an AC‐driven pin‐to‐liquid discharge. After 10 min plasma treatment time, the amino acids L‐cysteine (contains SH group) or L‐alanine (no SH group) or bovine serum albumin (BSA; with approximately 6% cysteine content) was added together with the test microorganism Escherichia coli K‐12 (DSM 11250/NCTC 10538) for an exposure time of up to 60 min. The total viable cell count was determined in appropriate time intervals. A concentration‐dependent repeal of the antimicrobial efficacy was determined. Thus, 0.0025% of BSA did not have any influence whereas 0.25% of BSA (w/v) as well as the tested amino acids resulted in no inactivation of E. coli. The difference between L‐alanine and L‐cysteine was negligible, suggesting only a minor effect of the presence of SH groups. Dimerization of L‐cysteine was shown by LC/MS analyses whereas no derivatization of L‐alanine was detected. To test the influence of proteins in direct plasma treatment on wet surfaces, E. coli was plated together with BSA on soybean casein digest agar surface. Another setup based on agar plates which contained different concentrations of peptone (mixture of peptides and amino acids). The agar plates were punctually treated by the argon‐driven CAP jet kINPen® Med (neoplas tools GmbH, Greifswald, Germany). After overnight incubation, inhibition zones were analyzed. The bacterial growth was independent of protein or peptone content for this direct plasma treatment. Summarizing all, the antibacterial effect of plasma‐treated solution is strictly limited in the presence of proteins. This inhibiting effect is not dependent on chemical structures containing SH groups. In direct plasma application, none of the tested protein or peptide/amino acid content resulted in a diminished antimicrobial effect of the kINPen Med® when applied in a protein‐containing environment.

Influence of a target on the electric field profile in a kHz atmospheric pressure plasma jet with the full calculation of the Stark shifts

The electric field in the head of the plasma bullet (ionization wave) in a cold atmospheric pressure plasma jet is measured using the Stark polarization spectroscopy technique, a noninvasive method. The jet is driven by 1μs long voltage pulses at 6 kV amplitude and 5 kHz frequency, and a helium gas flow of 1.5 slm. Two helium lines (447.1 nm and 492.2 nm) are studied, from which the peak-to-peak wavelength difference between the allowed and forbidden band of the spectral lines is determined. The full derivation to obtain the electric field from this peak-to-peak difference is included in this paper. The electric field is determined both inside and outside the capillary of the jet, up to about 2 cm in the effluent of the jet. Measurements are performed on the freely expanding jet, but especially the influence is studied when a target is placed in front of the plasma jet. Targets with different properties are used: insulating (polyvinyl chloride, PVC), conducting (copper), liquid (distilled water and saline), and organic (chicken breast). It is found that a target changes the electric field of the plasma jet and thus changes the plasma itself. This change depends on the dielectric constant or conductivity of the target: a higher dielectric constant or higher conductivity yields a higher electric field. For a low dielectric constant (ϵr≈3), the change in the electric field is negligible. Decreasing the distance between the target and the capillary to below 2 cm yields an increase in the electric field.

Formation of reactive oxygen species by irradiation of cold atmospheric pressure plasma jet to water depends on the irradiation distance.

Because application of cold atmospheric pressure plasma jet (CAPPJ) to biological samples have taken large attentions, it is important to examine the effects of various CAPPJ parameters on the generation of reactive species. Here, we investigated the generation of reactive species in water by CAPPJ irradiation by changing the following parameters: irradiation time, sample volume, and irradiation distance between the sample surface and plasma jet tip. We measured 1) change in the ESR signal intensity of 4-hydroxy-2,2,6,6-tetrametylpeperidine-1-oxyl (Tempol), 2) spin-trapping with 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 3) Fricke dosimeter reaction, and 4) hydrogen peroxide (H2O2) formation induced by CAPPJ irradiation. By the experiment of volume dependency, it is suggested that the reactive species detected in water are formed largely in the plasma gas phase. The reduction of ESR signal intensity of Tempol and the formation of DMPO-OH were strongly dependent on irradiation distance, but the relationship between H2O2 generation and distance was weak. The formation of species that oxidize Fe2+ to Fe3+ was shown by the Fricke dosimeter reaction, and reactions at irradiation distances longer than 3 cm were mainly attributable to H2O2. It may be possible to apply different reactive species to the samples by changing the CAPPJ irradiation distance.

Projekt PlasmaArt: primjena atmosferskog plazmenog mlaza u konzerviranju-restauriranju drvenih predmeta

The PlasmaArt project was realized as a collaboration between the Institute of Physics and the Croatian Conservation Institute. The project was funded mainly by the Funds of the Adris Group, and to a lesser extent by project IP-11-2013-2753 of the Croatian Science Foundation. The main idea of the project was to test the application of cold atmospheric plasma jets on wooden test plates that simulate wooden artwork for the purpose of disinfection and removal of stratigraphic layers of overpaint. For ethical reasons, experimental research was carried out not on real artwork, but on wooden test plates which had been prepared to simulate wooden artefacts. (The samples were silver- plated and gold-plated plates, painted and varnished to faithfully represent real artwork.) To test the efficiency of the disinfection effect, some of the test plates were contaminated with fungal mycelia, and to test the removal of stratigraphic layers, the rest of the silver-plated and gold-plated test plates were covered with several layers of paint and varnish. The prepared test plates were treated with cold atmospheric-pressure plasma jets. The results showed that the stratigraphic layers could not be removed, and it was not possible to remove each layer separately. As a result of the disinfection procedure, positive effects were obtained in comparison to standard procedures used in conservation, while the efficiency depended on the type of plasma and the length of the treatment. It was found that the cold atmospheric-pressure plasma jet was an effective source for disinfection of wooden artwork in the conditions described in this paper

Influence of a liquid surface on the NOx production of a cold atmospheric pressure plasma jet

In this work a cold atmospheric pressure plasma jet was mounted above a distilled water reservoir to study the influence of a water surface on reactive oxygen and nitrogen species (RONS) generation. The RONS, namely O3 and NO2, were measured by multi-pass cell Fourier transform infrared absorption spectroscopy in the far-field of the jet. A shielding gas device was used to control the ambient environment of the effluent. The liquid surface has nearly no influence on the RONS dynamics as a function of shielding gas composition. It was found, however, that the interaction with the liquid surface increases the density of NOx by a factor of 2–3 due to local increase in H2O concentration through evaporation of water from the liquid surface. In contrast to the case of ambient humidity increase, this locally higher H2O density distinctly influences the ratio of water to oxygen and nitrogen which results in a higher generation of OH molecules.

Study of a Cold Atmospheric Pressure Plasma jet device for indirect treatment of Squamous Cell Carcinoma

PurposeThe possibility of obtaining plasmas at low temperatures and atmospheric conditions, the Cold Atmospheric Plasmas (CAPs), has triggered several studies on its possible medical applications. The use of CAPs devices applied to oncological treatments is still in a pre-clinical stage, but early investigations have shown promising results, both in vitro and in vivo. In this work, is reported the study of a custom made Cold Atmospheric Pressure Plasma jet device for indirect treatment of Squamous Cell Carcinoma. MethodsThe plasma plume produced by the jet device was characterized by optical emission spectroscopy and the vulnerability of two different cell lines, SCC-15 (Squamous Cell Carcinoma) and HGF-1 (non-cancer cell line) to different working parameters factors such as the volume of medium used on indirect plasma treatments, the number of cells used in the biological assays and the volume of treated medium in contact with the cultured cells were systematically tested and studied. ResultsThe effectiveness of CAPs’ treatments is time, volume and cell dependent. Cancer cells, specifically SCC-15 cells have shown to be more sensitive to indirect plasma treatments than the non-cancer cell line used in the present work. ConclusionsAccording to the obtained results, this study showed that thein vitro anti-cancer capacity of the developed jet plasma device will be higher when small volumes of medium are used together with moderate plasma treatment times, keeping the non-cancerous cells almost unaffected.

Effect of plasma on gas flow and air concentration in the effluent of a pulsed cold atmospheric pressure helium plasma jet

In this work, we report on the flow effects induced by a nanosecond pulsed helium cold atmospheric pressure plasma jet impinging on a glass substrate. Gas temperature measurements have been performed using optical emission spectroscopy including rotational spectra of OH(A-X) (0,0) and N2(C-B) (0,0) and resonance broadening of a helium emission line at 667.8 nm. The measured increase in gas temperature was less than 15 K. We have measured the air concentration distribution in the jet effluent by means of Rayleigh scattering exploiting the large difference in Rayleigh cross-section of air and helium. The obtained results show that the plasma causes a broadening of the helium channel suggesting an enhanced gas velocity and mixing with the ambient air. The impact of the plasma on the jet effluent is polarity dependent and is larger in the case of positive applied voltage pulses. Using an estimation of the increased gas velocity required to obtain the observed air concentrations, we have shown that both gas heating and electrohydrodynamic (EHD) forces related to the propagation of an ionization front are not causing the observed phenomena. The surface charge which can exist for a much longer time than the duration of the applied voltage pulse is the primary cause of the EHD forces on the bulk charges which lead to significant different air concentration profiles in the jet effluent for plasma on and off.

Parametric study of thermal effects in a capillary dielectric-barrier discharge related to plasma jet production: Experiments and numerical modelling

In the present work, a capillary dielectric-barrier discharge of the coaxial electrode configuration, commonly employed to atmospheric-pressure cold plasma jet production, is studied in terms of thermal effects. The discharge is driven by sinusoidal high voltage in the kHz range and operates with helium gas channeled into a capillary dielectric tube having one end opened to the atmospheric air. The voltage amplitude and frequency, gas flow rate, and discharge volume are varied independently, and thermal effects are investigated by experimentally acquired results coupled with numerically determined data. The experiments refer to electrical power measurements, time-resolved temperature measurements, infrared imaging, and high resolution optical emission spectroscopy. The numerical modelling incorporates an electro-hydrodynamic force in the governing equations to take into account the helium-air interplay and uses conjugate heat transfer analysis. The comparison between experimental and numerical data shows that power is principally consumed in the dielectric barrier-helium interface resulting in the dielectric heating. A linear relation between steady state temperatures and supplied power, independent of the designing and operating conditions, is experimentally established. However, the gas flow rate affects the thermal effects differently compared to the other parameters, supporting the idea of a twofold nature of these systems, i.e., electrical and hydrodynamic. The main claim states the possibility of correlating (both experimentally and numerically) designing and operating parameters for evaluating heat distribution and gas temperature in capillary dielectric-barrier discharges used for plasma jet production. This is of high importance for processing temperature-sensitive materials, including bio-specimens.

An Investigation of the Control of Electron Energy in the Atmospheric-Pressure Helium Plasma Jet

In this paper, an investigation of the control of electron energy in the atmospheric-pressure helium plasma jet produced by a needle–plane discharge system has been performed by means of the numerical simulation based on a 2-D self-consistent fluid model. Due to the consideration of practical application of the cold atmospheric-pressure plasma jet (CAPPJ) in the fields of biomedicine, in this paper, the mean electron energy (MEE) nearby the cathode plane is accounted for. The parameter dependences of the MEE have been systematically calculated. The considered parameters include the voltage amplitude and rising time $t_{r}$ of the applied voltage pulse as well as needle electrode radius. The voltage amplitude is changed in the range from 3 to 19 kV, and $t_{r}$ is from 1 to 200 ns. The spatial electric field has also been analyzed in detail because of its dominant role in controlling electron energy. In addition, the effect of electron energy on the production of the reactive species OH, O3, and H2O2 has also been investigated when considering the addition of humid air to the working gas helium. This paper gives the following significant results. For a given $t_{r}$ , the MEE increases almost linearly with increasing voltage amplitude. The effect of voltage amplitude on the MEE becomes much more evident for smaller $t_{r}$ and is obviously weak for the $t_{r}$ with a few hundreds of nanoseconds. Fixing the voltage amplitude, the MEE decreases with the increase in $t_{r}$ . The dependence of the MEE on $t_{r}$ is evident for a high voltage amplitude and the reverse is true for the lower voltage amplitudes. As a whole, the higher voltage amplitude and smaller rising time $t_{r}$ or their synergism should be considered for obtaining high electron energy. Especially, an MEE of about 10 eV can be obtained, which covers the energy thresholds inducing all the processes of dissociative electron attachment to water molecule and thus is of essential importance for the production of the reactive species such as OH, H2O2, and O3 in the interactions of plasmas with the aqueous solution embedded in biofilms or tissues. The needle electrodes with different radii result in a minor variation of the MEE under the fixed voltage amplitude and $t_{r}$ . Therefore, changing the radius of the needle electrode is not an effective solution to the control of electron energy in the CAPPJ. Furthermore, the parameter dependence of the spatial electric field is similar to that of the MEE, which reveals the dominant role played by the spatial electric field in controlling electron energy in CAPPJs. Considering the addition of humid air to the working gas helium, with the increase in electron energy, the averaged densities of OH and O3 increase, but that of H2O2 decreases.