Figure - available from: Journal of Physics D: Applied Physics
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(a) Schematic design of the atmospheric pressure plasma jet, and (b) typical image of plasma jet. (1) Helium gas inflow, (2) quartz dielectric, (3) grounded electrode, (4) high voltage electrode, (5) sample solution, (6) collimators, (7) OES.
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Potential in biomedical-related applications by atmospheric pressure plasma-treated water gradually increased recently. In order to enhance the generation of reactive species in atmospheric pressure plasma in regards to liquid treatment, this study aims to investigate the effect of external axial magnetic field on a helium atmospheric pressure plas...
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... A magnetic field perpendicular to the discharge symmetry can cause more excitation and ionization due to the electron's curved movement in the presence of a magnetic field [69]. It may not mean there is higher electron temperature which is the presumed situation in the axial fields [70]. It can be expected that there is higher excitation temperature in the presence of a magnetic field which is confirmed by the temperature enhancement from 5950 to 6500 K, as it is clearly shown in Fig. 6. ...
In the last decades, to improve the CAP treatment efficiency, its biological effects in combination with other physical modalities have widely investigated. However, the physical insight into most of supposed synergistic effects remained elusive. In this regard, the synergetic effect of cold plasma and magnetic field has been used for different applications, especially due to considerable synergistic in biological media reactivity. In the present paper, using a 420 mT N42 magnet, the effect of the perpendicular external static magnetic field (SMF) on the cold atmospheric pressure plasma (CAP) characteristics, such as electron temperature and density, is investigated based on the optical emission spectroscopy, utilizing the Boltzmann plot method, Saha-Boltzmann equation, and Specair software simulation. Results showed that the rotational and electronic excitational temperatures experienced 100 K and 550 K increases in the presence of SMF, respectively. In contrast, the vibrational and translational temperatures remained constant. Moreover, electron temperature was estimated as 1.04 eV in the absence of SMF and increased up to 1.24 eV in the presence of SMF. In addition, the Saha-Boltzmann equation illustrated that the electron density increased in the presence of the additional SMF. The results of the present study indicated that the magnetic field could be an assistant to the cold plasma effect, beneficial in medical applications due to modifications in plasma temperature and electron density.
... As charged particles move through the plasma, they experience the Lorentz force (Zhang et al. 2022;Lu et al. 2019;Fitzpatrick 2022). The behavior and path of a charged particle are determined by the Lorentz force, which causes it to move in a circular or spiral path (Tobias Tschang et al. 2020;Lucken et al. 2019). This circular motion frequency is known as the cyclotron frequency, ω c . ...
This research scrutinizes the impact of external magnetic field strength variations on plasma jet parameters to enhance its performance and flexibility. Plasma jets are widely used for their high thermal and kinetic energy in both medical and industrial fields. The study employs optical emission spectroscopy to measure electron temperature, electron density, and plasma frequency in a plasma jet subjected to varying magnetic field strengths (25, 50, 100, 150, and 250 mT). The results indicate that a stronger magnetic field results in higher electron temperature (1.485 to 1.991 eV), electron density (5.405 × 10¹⁷ to 7.095 × 10¹⁷), and plasma frequency 7.382 × 10¹² to 8.253 × 10¹² Hz. As well as the research investigates the influence of gas flow rate on gas temperature in the plasma jet. It is observed that gas temperature gradually drops with a growth in the flow rate of argon gas. The voltage and current waves have a sinusoidal waveform without elevation lines and with decaying waveforms. The existence of a strong magnetic field generates magnetohydrodynamic instability, leading to the plasma jet flame splitting. Understanding the effects of changing the strength of the external magnetic field on the plasma properties provides the ability to control the plasma Permart to make it suitable for many applications.
... The presence of a magnetic field in the plasma can help in increasing the ionization fraction of the medium due to frequent collisions among the particles [30,31]. Plasmas in the presence of a magnetic field show various interesting phenomena such as the pinch effect [32], mirror confinement [32], and atmospheric whistler waves [32] to name a few. ...
... Also, they observed that as the gas velocity is increased, the length of the plasma jet increases and it bends at the tip. Tschang et al [31] have studied the effect of an external axial magnetic field on a helium APPJ and reported that the electron temperature gradually increased with increasing magnetic field. Zhang et al [30] have established a 3D model to study the effect of permanent magnets and coaxial reflective antennae on the density and uniformity of the plasma. ...
The present work is an investigation of the effect of an externally applied diverging magnetic field on a surface microwave-sustained plasma column. Microwaves are allowed to propagate through a tapered waveguide system containing a discharge tube made up of quartz. Argon gas flows down the tube from top to bottom maintaining a pressure of 1 Torr and a plasma is ignited within the tube owing to the surface microwave propagation. In the absence of a magnetic field, the plasma column exhibits discrete regions of overdense plasma near its center where the electric field of the incident microwaves is observed to be high. As the gas flows down the tube, the plasma density is also found to decrease and the resulting plasma profile is asymmetric about its length. However, in the presence of an axial, diverging magnetic field profile, an axial force acts on the plasma, and the discrete overdense plasma regions are found to get symmetrically arranged along the plasma axis. Interesting results are observed when the diverging magnetic field profile possesses an electron cyclotron resonance (ECR) corresponding to the microwave frequency. In the presence of an ECR, the electrons are expected to experience resonant heating by microwaves other than direct heating by these waves. Under such conditions, the discharge dynamics are governed by the resonance mechanism, and the bright spots of overdense plasma regions get shifted to the ECR positions. As the magnetic field strength increases, the overdense plasma moves axially away from the center. These results are a clear indication of a magnetically controlled particle flux over a target and can be exploited in various material processing applications, particularly for surface cleaning applications in the semiconductor industries.
... This decrease in the mean free path leads to an increase in breakdown voltage and a decrease in electron temperature, which can have detrimental effects on practical applications. 14,15,19 The influence of the parallel magnetic field, which is aligned with the direction of the applied electric field, on discharges has attracted less attention than that of the perpendicular magnetic field. However, it is important to note that a parallel magnetic field can induce cyclotron motion of free electrons through the introduction of the Lorentz force. ...
The combined influence of airflows and a parallel magnetic field on an AC-driven dielectric barrier discharge plasma is experimentally investigated through image analyses, electrical measurements, and optical diagnoses. After applying a parallel magnetic field, more discharge filaments are generated during one discharge cycle. Besides, the electrical and optical diagnoses show that the magnetic field can increase the plasma parameters, such as the electron temperature and electron density. When airflows and a parallel magnetic field are applied in combination, the discharge uniformity presented in the long-exposure images is significantly enhanced by the airflows and slightly improved by the magnetic field. With increasing airflow velocity, the distribution of discharge filaments goes through four phases, namely, spot-like distribution, line-like distribution, cotton-like distribution, and stripe-like distribution, among which the stripe-like distribution exhibits the highest discharge uniformity. High-speed video analyses reveal that the improved discharge uniformity can be attributed to the changed breakdown positions and the increased number of filaments. Although airflow can significantly improve the macroscopic uniformity of the discharge, it leads to a decrease in the maximum current pulse amplitude, electron temperature, electron density, and gas temperature. Applying a magnetic field in flowing air can not only improve the discharge uniformity but also ensure that the discharge has high maximum current pulse amplitude intensity, electron temperature, and electron density. Based on the analyses of the electron trajectory and the estimation of the force condition of the micro-discharge remnants, the modulated charged particles, reduced electric field, and pre-ionization degree are responsible for the changed discharge uniformity and plasma parameters in the parallel magnetic field and flowing air.
... The liquid activation efficiency of the plasma gasliquid two-phase flow, especially the concentrations of aqueous reactive species, is highly competitive with previous studies of plasma jet activation over the liquid surface. 26,27 As shown in Fig. 4(b), the production rates of all aqueous reactive species, determined by the product of concentration and water flow rate, increase logarithmically with airflow rate, with H 2 O 2 and NO 3 À being the most prominent. Production rates increase slowly at airflow rates above 8 L/min, implying that the trade-off between concentration and production rate should be the focus when the dilution effect of liquid volume dominates. ...
We report on our study of gas–liquid two-phase flow of air plasma and its associated dynamic behavior, droplet activity, and applications. The propagation of the air plasma jet within a Venturi configuration is significantly perturbed by the presence of water droplets due to the local modification of the electric field that results from polarization and charging of the droplets. This local modulation, in turn, decreases the discharge current pulses and the radiation intensity of optical emissions. With a change in inlet airflow dynamics from laminar to turbulent (5–10 L/min), the droplet diameter decreased exponentially under strong pressure from millimeter to several tens of micrometers, whereas the gas–droplet contact area increased substantially. The production of short-lived reactive aqueous species OH and O2− was enhanced at the gas–liquid interface of the biphasic plasma droplets, and the activities of different long-lived species (H2O2, NO3−, and O3) in the droplet were highly selective in droplet diameter and value of the Henry-law constants. This new plasma source architecture enables an in situ activation of water sprays by plasma jets at short time scales, providing a desirable and effective sterilization tool and wastewater treatment at a relatively low cost and ease of operation.
... A magnetic field perpendicular to the discharge symmetry can cause more excitation and ionization due to the electron's curved movement in the presence of a magnetic field [60]. It may not mean there is higher electron temperature which is the presumed situation in the axial fields [61]. It can be expected that there is higher excitation temperature in the presence of a magnetic field which is confirmed by the temperature enhancement from 5950 K to 6500 K, as it is clearly shown in Figure 6. ...
In the last decades, to improve the CAP treatment efficiency, its biological effects in combination with other physical modalities have widely investigated. However, the physical insight into most of supposed synergistic effects remained elusive. In this regard, the synergetic effect of cold plasma and magnetic field has been used for different applications, especially due to considerable synergistic in biological media reactivity. In the present paper, using a 420 mT N42 magnet, the effect of the perpendicular external static magnetic field (SMF) on the cold atmospheric pressure plasma (CAP) characteristics, such as electron temperature and density, are investigated based on the optical emission spectroscopy, utilizing the Boltzmann plot method, Saha-Boltzmann equation and Specair software simulation. Results showed that the rotational and electronic excitational temperature experienced 100 K and 550 K increases in the presence of SMF, respectively. While the vibrational and translational temperatures remained constant. Moreover, electron temperature estimated as 1.04 eV in the absence of SMF and increased up to 1.24 eV in the presence of SMF. In addition, the Saha-Boltzmann equation illustrated that the electron density increased in presence of the additional SMF. The results of the present study indicated that the magnetic field could be an assistant to the cold plasma effect, beneficial in medical applications due to modifications in plasma temperature and electron density.
... Vibrational temperature of N 2 , electron temperature, and density were calculated according to Fatima et al. 61 using the line ratio of nitrogen first negative (FNS) and second positive (SPS) system, which is a commonly used method. [61][62][63][64][65] Therefore, plasma emission spectrum along the line of sight of nitrogen mode with 8.5 kV pp and 5 kHz at 371.1, 375.4, 380.5, and 391.44 nm wavelength was measured using a spectrometer (USB2000+, Ocean Optics). ...
Plasma medicine demands for very specific plasma source configurations. Beside gasflow-driven jet arrays, dielectrical barrier discharges (DBDs) are commonly used to generate ambient air plasma at room temperature for decontamination. There, electrode and dielectric material limit its use in application. Especially, the decontamination of difficult, uneven, or edged surface geometries with DBDs can be rather challenging. Therefore, flexible polyethylene naphthalate-foil with a thickness of 250 μm, which was covered with electrode material by ion-beam sputtering, is characterized regarding its electrical and bactericidal performance for different power and electrode thickness configurations. Operating temperature, ozone production capability, and plasma parameters (electron temperature and density as well as vibrational temperature of N<sub>2</sub>) were used as characterization parameters. As electrode material, palladium sputtered with a thickness of 110 nm showed the best results of the tested materials. With operation parameters of 3 kHz and 5.5-6.0 kV<sub>pp</sub> for ozone and 5 kHz and 8.5 kV<sub>pp</sub> for nitrogen mode log reductions of up to 6.7 (nitrogen mode) and 5.3 (ozone mode), respectively, and D values of 1 min were accomplished for Escherichia coli.</i
... The ratio method is based on the relationship between the relative distribution of the excited-state vibrational energy levels [46,47]. The ratio of intensities of nitrogen emission at 391.4 and 394.3 nm is correlated with the reduced electric field, while the relative line-intensity ratio of 371.1 and 380.5 nm correlates to the electron density [22,48]. Calculation of E/n and N e was performed using the following empirical equations: ...
In this work, a surface dielectric barrier discharge (SDBD) device coupled with power electronics technology was designed for precise control of the ground-electrode temperature to investigate the dynamic behavior of the physicochemical processes and biological inactivation functions involved in SDBD plasma. It was found that an increase of the electrode temperature from 30 to 210°C reduced the initial breakdown voltage and increased the current pulse amplitude because the reduced electric field strength and average electron density of the SDBD plasma were consistently enhanced. The change in the plasma-chemistry mode (O3-dominant to NOx-dominant) was more sensitive to the ground-electrode temperature than that of the power density and gas temperature. O3 in the gas and liquid phases could not be detected at electrode temperatures above 90 °C, and the NOx mode almost immediately occurred after the plasma was turned on for ground-electrode temperatures of ≥180 °C. The increase in the electrode temperature increased the acidity of the plasma-activated water and, more importantly, short-lived reactive species OH and NO were detected at electrode temperatures ≥120 °C in the case of aqueous solutions treated directly with SDBD plasma. The biological inactivation function of the SDBD plasma, i.e. for bacterial suspensions and tumor cell cultures, was improved by about three orders of magnitude and 40% at the optimal electrode temperatures of 180 °C and 120 °C, respectively. This is an important breakthrough for development of SDBD-based biomedical devices for specific purposes on a commercial level by regulating the plasma chemistry through the ground-electrode temperature, overcoming the limitations of chamber heating and compressed air supply.
... The dominant method for temperature determination is optical emission spectroscopy of OH and N 2 emissions [83,100,115,122,123,173,[180][181][182][183][184][185][232][233][234][235][236]. Besides, rotational Raman spectroscopy [137,189,191,192], broadband UV absorption spectroscopy [231] and pressure broadening [100] were employed for the estimation of gas temperature in discharges in contact with liquids. ...
... Under the studied experimental conditions, transient glow discharge develops on the metallic target after the streamer phase with a temperature of about 460 K. The influence of the magnetic field on the improvement of the plasma jet properties was studied by Tschang et al and it is found that magnetic field does not influence the plasma jet in the sense of an increase in gas temperature [232]. The liquid film discharge, developed by the Bruce Locke group, represents the peculiar arrangement of constricted discharge at elevated pressure with unique properties [115,185,236]. ...
The study of plasma–liquid interactions has evolved as a new interdisciplinary research field driven by the development of plasma applications for water purification, biomedicine and agriculture. Electrical discharges in contact with liquids are a rich source of reactive species in gas and in liquid phase which can be used to break polluting compounds in water or to induce healing processes in medical applications. An understanding of the fundamental processes in plasma, and of the interaction of plasma with liquid, enables the optimization of plasma chemistry in large-scale plasma devices with liquid electrodes. This article reviews recent progress and insight in the research of low-temperature plasmas in contact with liquids at atmospheric pressure. The work mainly focuses on the physical processes and phenomena in these plasmas with an attempt to provide a review of the latest and the most important research outcomes in the literature. The article provides an overview of the breakdown mechanisms in discharges in contact with liquid, emphasizing the recently studied specifities of plasma jets impinging on the liquid surface, and discharge generation with a high overvoltage. It also covers innovative approaches in the generation of plasma in contact with liquids. Novel phenomena detected by the imaging techniques and measurement of discharge parameters in the reviewed discharges are also presented. The results, the techniques that are applied, and those that may be applied in further studies, are listed and discussed. A brief overview of the applications focuses on the original approaches and new application fields. Future challenges and gaps in knowledge regarding further advancement in applications are summarized.
... Lastly, high electron densities have been observed inside the capillary tube in two He AC powered jets: 9 × 10 13 cm −3 in Tschang et al (2020) [116] and 1-8 × 10 14 cm −3 in Jõgi et al (2014) [110] inside the capillary tube. The first case is unique since it is the only jet examined (through N 2 line ratios) in the presence of a strong external magnetic field (2 Tesla) impacting on a small liquid target [116]. ...
... Lastly, high electron densities have been observed inside the capillary tube in two He AC powered jets: 9 × 10 13 cm −3 in Tschang et al (2020) [116] and 1-8 × 10 14 cm −3 in Jõgi et al (2014) [110] inside the capillary tube. The first case is unique since it is the only jet examined (through N 2 line ratios) in the presence of a strong external magnetic field (2 Tesla) impacting on a small liquid target [116]. Jõgi et al (2014) [110] have reported the highest values but comparison with the other papers is difficult since the densities are examined inside the capillary tube of a micro-plasma jet with a small inner diameter of 80 μm. ...
Plasma jets are sources of repetitive and stable ionization waves, meant for applications where they interact with surfaces of different characteristics. As such, plasma jets provide an ideal testbed for the study of transient reproducible streamer discharge dynamics, particularly in inhomogeneous gaseous mixtures, and of plasma-surface interactions. This topical review addresses the physics of plasma jets and their interactions with surfaces through a pedagogical approach. The state-of-the-art of numerical models and diagnostic techniques to describe helium jets is presented, along with the benchmarking of different experimental measurements in literature and recent efforts for direct comparisons between simulations and measurements. This exposure is focused on the most fundamental physical quantities determining discharge dynamics, such as the electric field, the mean electron energy and the electron number density, as well as the charging of targets. The physics of plasma jets is described for jet systems of increasing complexity, showing the effect of the different components (tube, electrodes, gas mixing in the plume, target) of the jet system on discharge dynamics. Focusing on coaxial helium kHz plasma jets powered by rectangular pulses of applied voltage, physical phenomena imposed by different targets on the discharge, such as discharge acceleration, surface spreading, the return stroke and the charge relaxation event, are explained and reviewed. Finally, open questions and perspectives for the physics of plasma jets and interactions with surfaces are outlined.
