Plasma Electric Field Research Articles

Theoretical-Computational Study of Atmospheric DBD Plasma and Its Utility for Nanoscale Biocompatible Plasmonic Coating.

In this study, time-dependent, one-dimensional modeling of a surface dielectric barrier discharge (SDBD) device, driven by a sinusoidal voltage of amplitude 1–3 kV at 20 kHz, in argon is described. An SDBD device with two Cu-stripe electrodes, covered by the quartz dielectric and with the discharge gap of 20 × 10−3 m, was assumed, and the time-dependent, one-dimensional discharge parameters were simulated versus time across the plasma gap. The plasma device simulated in the given arrangement was constructed and used for biocompatible antibacterial/antimicrobial coating of plasmonic particle aerosol and compared with the coating strategy of the DBD plasma jet. Simulation results showed discharge consists of an electrical breakdown, occurring in each half-cycle of the AC voltage with an electron density of 1.4 × 1010 cm−3 and electric field strength of 4.5 × 105 Vm−1. With SDBD, the surface coating comprises spatially distributed particles of mean size 29 (11) nm, while with argon plasma jet, the nanoparticles are aggregated in clusters that are three times larger in size. Both coatings are crystalline and exhibit plasmonic features in the visible spectral region. It is expected that the particle aerosols are collected under the ionic wind, induced by the plasma electric fields, and it is assumed that this follows the dominant charging mechanisms of ions diffusion. The cold plasma strategy is appealing in a sense; it opens new venues at the nanoscale to deal with biomedical and surgical devices in a flexible processing environment.

Enhanced transmembrane transport of reactive oxygen species by electroporation effect of plasma

AbstractRecently, plasma has been proposed as a new efficient tool for various biological and medical applications. The function of plasma is mainly realized through two aspects: Electric field and reactive species. However, because the interactions between plasma and cells are quite complicated, the synergistic effect of electric field and reactive species has not been studied in depth. In this paper, the synergetic effects of electric field and transportation of reactive species on cells are investigated by a two‐dimensional finite element model. The exposure of cells to plasma results in the sufficiently high transmembrane voltage (1 V) and electroporation. When the electric field of plasma is less than 104 V/cm, the radius of nanopores generated by plasma increases with the electric field. The further increase of electric field to 105 V/cm does not cause a significant increase of nanopore radius, whereas the pore density increases by five times. The increase of discharge frequency significantly decreases the time needed to generate stable nanopores. The nanopores enhance the diffusion of H2O2 generated by plasma through the cell membrane significantly. Compared with the reality that H2O2 does not freely diffuse across cell membranes, the “generation and enhanced transportation” effect will further expand the application range of plasma medicine.

Radial distribution of the plasma potential in a cylindrical plasma column with a longitudinal magnetic field

The possibility of controlling the electrostatic field distribution in plasma has yielded wide prospects for modern technologies. As a magnetic field primarily allows for creating electric fields in plasma, it serves as an additional obstacle for the current flow through a medium. In the present paper, an axially symmetric system is considered in which the magnetic field is directed along the axis and concentric electrodes are located at the ends. The electrodes are negatively biased. A model which solves the problem of the radial distribution of the plasma potential inside the cylindrical plasma column supported by the end electrodes is proposed. The most commonly encountered configurations of the electrical connection for the end electrodes are considered, and the particular solutions to the problem of the radial distribution are presented. The contribution of ions and electrons to the transverse conductivity is evaluated in detail. The influence of a thermionic element on the radial profile of the plasma potential is considered. To verify the proposed model, an experimental study of the reflex discharge is carried out with both cold electrodes and a thermionic element on the axis. A comparison of the computational model results with experimental data is given. The presented model makes it possible to solve the problem concerning the plasma potential distribution in the case of an arbitrary number of end electrodes, and also to take into account the inhomogeneity of the distribution of plasma density, neutral gas pressure and electron temperature along the radius.

DREAM: A fluid-kinetic framework for tokamak disruption runaway electron simulations

Avoidance of the harmful effects of runaway electrons (REs) in plasma-terminating disruptions is pivotal in the design of safety systems for magnetic fusion devices. Here, we describe a computationally efficient numerical tool, that allows for self-consistent simulations of plasma cooling and associated RE dynamics during disruptions. It solves flux-surface averaged transport equations for the plasma density, temperature and poloidal flux, using a bounce-averaged kinetic equation to self-consistently provide the electron current, heat, density and RE evolution, as well as the electron distribution function. As an example, we consider disruption scenarios with material injection and compare the electron dynamics resolved with different levels of complexity, from fully kinetic to fluid modes. Program summaryProgram Title:DreamCPC Library link to program files:https://doi.org/10.17632/vs3yvnrzg6.1Developer's repository link:https://github.com/chalmersplasmatheory/DREAMLicensing provisions: MITProgramming language: C++, PythonNature of problem: Self-consistently simulates the plasma evolution in a tokamak disruption, with specific emphasis on runaway electron dynamics. The runaway electrons can be simulated either as a fluid, fully kinetically, or as a mix of the two. Plasma temperature, current density, electric field, ion density and charge states are all evolved self-consistently, where kinetic non-thermal contributions are captured using an orbit-averaged relativistic electron Fokker-Planck equation, which couples to the plasma evolution. In the typical use case, the electrons are represented by two distinct populations: a cold fluid population and a kinetic superthermal population.Solution method: The system of equations is solved using a standard multidimensional Newton's method. Partial differential equations—most prominently the bounce-averaged Fokker–Planck and current diffusion equations—are discretized using a high-resolution finite volume scheme that preserves density and positivity.

Estimation of sheath electric field in inductively coupled hydrogen plasma on the basis of Doppler-broadened absorption spectrum of hydrogen Balmer-α line

We examined the applicability of the Doppler-broadened absorption spectrum of the hydrogen Balmer-α line to the estimation of the sheath electric field in plasma. The Stark splitting of the fine-structure components was calculated by solving the time-independent Schrödinger equation at various electric field strengths, and the theoretical absorption spectrum was obtained by the superposition of the fine-structure components with the same Doppler broadening widths. The spectrum of the Balmer-α line of atomic hydrogen, which was measured by standard diode laser absorption spectroscopy, was fitted with the theoretical spectrum. We succeeded in determining the translational temperature of atomic hydrogen, which was obtained from the Doppler broadening width, and the electric field strength by the spectral fitting. We have evaluated that the minimum electric field strength that can be detected by the present method is approximately 350 V cm−1 when the translational temperature of atomic hydrogen is 400–500 K.

Enhancing the shelf stability of fresh‐cut potatoes via chemical and nonthermal treatments

Fresh-cut foods have become highly popular as these commodities are convenient to manage with premium freshness and quality. However, the shelf life of fresh-cut potatoes is limited. The traditional practice consists of a set of operations including washing, peeling, slicing, chemical treatment, packing, and storage. Besides, various chemical or synthetic additives are being applied to tackle quality-related issues such as browning, textural degradation, microbial spoilage, and shelf-life stability. Nevertheless, the demand for natural additives and nonthermal preservation techniques has increased with growing concerns about the potential health risks of chemical additives. This review paper discusses the use of various synthetic and natural food additives alone or in combination with the emerging nonthermal technologies for enhancing the quality characteristics of fresh-cut potatoes. Overall, the nonthermal processing technologies including sonication, cold plasma, high-pressure processing, ultraviolet, and pulsed electric field would be promising treatments for the fresh-cut food industry compared with conventional approaches. Practical applications Fresh-cut potato is highly susceptible to microbial spoilage and undergoes rapid loss of quality due to high moisture content and rapid metabolic rate. Researchers are exploring alternative nonthermal processing technologies for producing shelf-stable food products using a clean label approach. This review covers some recent advances concerning the use of chemical compounds, including plant natural antimicrobials and antioxidants, as well as nonthermal technologies for the quality maintenance of fresh-cut potato. These technologies are known to be safe, cost-effective, and can be upscaled for use in existing processing lines of the food industry.

Strategies of Power Measurement and Energy Coupling Enhancement in Nanosecond Pulsed Coaxial Dielectric Barrier Discharges

Dielectric barrier discharges (DBDs) driven by nanosecond high-voltage pulses can be quite different from those driven by alternating current (ac) sources, on both electrical characteristics and plasma microparameters. In this article, the power measurement strategy in nanosecond pulsed coaxial DBDs is optimized. The effect of different experimental parameters on energy deposition and reduced electric field in plasma is investigated. First, the results measured using the instantaneous power (from the production of voltage and current) method and that using the v- q trace (Lissajous curve) method are compared and the source of divergence is analyzed. By comparing monitor capacitors with different materials and capacitances, it is demonstrated that the high-frequency response of the monitor capacitor is essential and the capacitance value can be adjusted according to the applied voltage, taking both the dynamic range of oscilloscope and the signal-to-noise ratio into consideration. Second, the influence of morphology of ground electrode, voltage rising time, and pulse width on energy deposition per-pulse and reduced electric field, obtained from the nitrogen spectral line-ratio, is studied. It is found that the copper foil promotes the discharge energy coupling per-pulse compared with the copper grid, while the reduced electric field obtained from the nitrogen line-ratio with the copper foil is weaker. A shorter rising time will also enhance the energy coupling per-pulse, as well as the reduced electric field.

Changes of the TiO2 thin film electro-optical properties in the Ar and N2 glow discharge plasma due to effects of the electric field in plasma's sheath

Titanium dioxide thin films were prepared on glass substrates by spin-coating sol-gel method. The samples were exposed to the N2 and Ar glow discharge plasmas. The properties of the crystal structure and electro-optical features were measured. The average crystallite size of the thin films was decreased at 30% and 41% by the plasma of N2 and Ar, respectively. We showed the changes in the charge distribution of the crystal unit cells and the chemical bonds’ characteristics that lead to alteration of the single-oscillator parameters. Due to the N2 and Ar plasmas, the third-order nonlinear susceptibility in long-wavelength was increased about 25% and 123%, respectively. An alteration occurred in the optical band gap through TiN formation on the surface of the TiO2 thin film in the N2 plasma. This empirical study illustrated more considerable changes in TiO2/Ar thin film, due to the stronger electric field in the sheath of Ar plasma.

Nonlinear Simulation of Ionospheric Irregularities at Mars

Abstract Motivated by the observations and linear theory analysis of ionospheric irregularities at Mars, we performed numerical simulations of the nonlinear evolution of the electromagnetic gradient drift instability in the Martian ionospheric dynamo region. The seeding source of ionospheric irregularities is perturbation zonal neutral wind. We found that the perturbation electric fields induced by the gradient drift instability can convect lower density plasma into higher density plasma at higher altitudes. Then, the associated perturbation magnetic field and electric field can cause the velocity shear of the plasma, which induced the Kelvin–Helmholtz instability at higher altitude. The Kelvin–Helmholtz instabilities furthermore lead to smaller-scale irregularities in plasma density, magnetic field, and electric field in the Martial ionosphere. Key points: (1) Nonlinear simulation of small-scale ionospheric irregularities at Mars was present. (2) Ionospheric irregularities at Mars can be seeded by the perturbation neutral winds. (3) Model results are comparable to linear theory analysis and satellite observations.

High precision two photon spectroscopy in hydrogen isotopes for the measurement of the electric field in plasmas generated in hollow cathode discharges

espanolEn esta tesis se midio la intensidad del campo electrico local en la zona de catodo en una descarga de catodo hueco en regimen de glow-discharge operada en hidrogeno, en un amplio rango de presiones y corrientes para estudiar la influencia del diametro (10 y 15 mm) y material del catodo empleado (acero inoxidable y tungsteno). El metodo se basa en el estudio del efecto Stark del nivel n=2, mediante la absorcion de dos fotones de 243 nm, circularmente polarizados en sentidos opuestos y en direcciones contrarias, para eliminar el efecto Doppler. Cuando el atomo se encuentra en el estado 2S, se fotoioniza modificando la impedancia del plasma, que puede ser detectada como la calda del voltaje en una resistencia (espectroscopia optogalvanica). El campo electrico local se determina comparando la separacion de las componentes Stark con los valores teoricos. EnglishIn this thesis, the intensity of the local electric field in the cathode region of a hollow cathode discharge operated in hydrogen was measured, in a wide range of pressures and currents to study the influence of the diameter (10 and 15 mm) and material of the cathode used (stainless steel and tungsten). The method is based on the Stark effect of the level n=2, via the absorption of two 243 nm photons, circularly polarized in opposite directions, to eliminate the Doppler effect. When the atom is in the 2S state, it photo-ionizes, modifying the impedance of the plasma, which can be detected as the voltage drop on a resistor (optogalvanic spectroscopy). The local electric field is determined by comparing the separation of the Stark components with the theoretical values.

Effects of Bleaching Gel with a Neutral pH and Nonthermal Plasma (Electric Currents and Magnetic Fields) on Dental Hard Tissues

Tooth bleaching gel, that comes in direct contact with the tooth surface for a long time, affects hard dental tissue. Nonthermal plasma consists electrons, ions, charged particles, electric filed and magnetic field. The motion of an electrically charged particle such as electron and ion can generate both electric and magnetic field. This study was conducted to investigate how tooth bleaching with 15 % hydrogen peroxide (HP) and plasma (from electric currents and magnetic fields) affects hard dental tissue. Extracted human teeth were treated with 15 % HP, with and without plasma. We fabricated a 15 % HP gel with neutral pH, and applied the gel and plasma to tooth surfaces for 30 minutes. The overall color change following 15 % HP gel and plasma was higher than in the other groups, and there were no significant changes in microhardness or mineral contents. Application of 15 % HP and plasma showed a bleaching high effect, with no damage to hard dental tissue. Even though 15 % HP has adverse effects, results can be effective without danger if treatment times are kept short.

2D atomic crystal molecular superlattices by soft plasma intercalation

Two-dimensional (2D) atomic crystal superlattices integrate diverse 2D layered materials enabling adjustable electronic and optical properties. However, tunability of the interlayer gap and interactions remain challenging. Here we report a solution based on soft oxygen plasma intercalation. 2D atomic crystal molecular superlattices (ACMSs) are produced by intercalating O2+ ions into the interlayer space using the plasma electric field. Stable molecular oxygen layer is formed by van der Waals interactions with adjacent transition metal dichalcogenide (TMD) monolayers. The resulting interlayer gap expansion can effectively isolate TMD monolayers and impart exotic properties to homo-(MoS2[O2]x) and hetero-(MoS2[O2]x/WS2[O2]x) stacked ACMSs beyond typical capacities of monolayer TMDs, such as 100 times stronger photoluminescence and 100 times higher photocurrent. Our potentially universal approach to tune interlayer stacking and interactions in 2D ACMSs may lead to exotic superlattice properties intrinsic to monolayer materials such as direct bandgap pursued for future optoelectronics.

Foodborne Viruses and Innovative Non-Thermal Food-Processing Technologies.

In recent years, several foodborne viruses’ outbreaks have been recorded worldwide. Μost of the foodborne viruses have a low infection dose, are stable and can persist and survive in foods for a long time without loss of infectivity. The most important foodborne viruses are: human norovirus (HuNoV), human rotavirus (HRV), hepatitis A virus (HAV), hepatitis E virus (HEV), human astrovirus (HAstV), Aichi virus (AiV), sapovirus (SaV), human adenovirus (HAdV) and enterovirus (EV). In recent years, innovative non-thermal food-processing technologies including high-pressure processing (HPP), cold plasma (CP), ultraviolet light (UV), irradiation and pulsed electric field (PEF) for improving the quality and safety of foods, including foods of animal origin, have been under research. This review presents the recent data on foodborne viruses and reviews the innovative non-thermal technologies for the control of the foodborne viruses in foods.

Evaluating the effectiveness of combined use of non-thermal atmospheric pressure plasma and frequently-modulated electric field signal in skin wound healing

Background Scientists around the world are interested in applying physical phenomena to various fields of science. The development of entire areas united by one concept (‘plasma medicine’, etc.) stands as a bright example. Present work focuses on only two concepts of interest, which are plasma jet and electric field, as far as results of their combined use in clinical practice and in surgery remain understudied. Objective Experimental evaluation of the effectiveness of physical methods of treatment in skin wound healing. Material and methods The study was carried out on 45 small laboratory animals (rats). They were divided into 5 groups of 9 individuals in each according to method chosen for experimental wound healing. To generate the plasma jet, a portable generator was used, which is the original development of specialists of the Peter the Great St. Petersburg Polytechnic University. Planimetric and histological measurements were analysed. The antibacterial effectiveness of methods under research was investigated using Staphylococcus aureus 209P, cultivated in vitro on 6- and 12-millimeter discs. Discussion The combined use of non-thermal atmospheric pressure plasma and frequency-modulated electric field signal exhibited the ability to accelerate eschar separation by 52.1% (p < 0.05) and stimulate restorative regeneration by 56% (p < 0.05). Combination of physical methods of treatment demonstrated pronounced antibacterial effect. A histological examination on biopsy sample on the 21st day of observation revealed formed (mature) granulations and large number of newly formed vessels. The cellular composition of epidermal basement membrane showed high level of differentiation. Conclusion The data obtained suggest that the use of the proposed methods in clinical practice will improve the treatment process of the patients with wounds of different etiology.

Investigation on High Velocity Plasmas and Field Aligned Currents at High Latitudes

The interaction of high velocity plasma with Earth’s magnetic field is fundamental and offer many questions on high latitude electrodynamics. The problems associated with influence of electric field and Field Aligned Current (FAC) generation is investigated with the aid of spherical cap harmonic analysis at 830 Mag. Lat. in southern hemispheres. The investigation is done on the cases with different Interplanetary Magnetic Field (IMF) conditions after the earth directed solar events. The helio-plasma parameters viz., density, velocity, energy, electron temperature are also noted during the field aligned current studies. It seems that, due to external magnetic field influence polarization of plasma electric field take place (reorientation of the convective cells). It happens with different orientation as per the magnitude and direction of By and Bz component and the horizontal currents. It is noted that the FAC value also depends on kinetic energy of the plasma streams and conductivity of external loading. As the plasma decelerates by force Jsw X Esw, the resultant current may extend along the field lines. Increases in the FAC density are seemed to be proportional to the transmission function.

Application of Thomson scattering to helicon plasma sources

The possibility of performing electron density and temperature measurements in a high power helicon plasma is a crucial issue in the framework of the AWAKE (Advanced WAKefield Experiment) project, which demonstrates acceleration of particles using $\text{GeV}~\text{m}^{-1}$ electric fields in plasmas. For AWAKE, a helicon is currently envisaged as a candidate plasma source due to its capability for low electron and ion temperature, high electron density and production of an elongated plasma column. A plasma diagnostic to accurately determine the electron density in AWAKE regimes would be a valuable supporting tool. A demonstration Thomson scattering (TS) diagnostic was installed and successfully tested on the resonant antenna ion device (RAID) at the Swiss Plasma Center of Ecole Polytechnique Fédérale de Lausanne. RAID produces a helicon plasma column with characteristics similar to those of the AWAKE helicon source, and is therefore an optimal testbed for application to the AWAKE device. The spectrometer employed in RAID is based on polychromators which collect the light scattered by plasma electrons in spectrally filtered wavelength regions. Results from TS on RAID demonstrate conditions of electron density and temperature respectively of $n_{e}=1.10\,(\pm 0.19)\times 10^{19}~\text{m}^{-3}$ and $T_{e}=2.3\,(\pm 0.6)~\text{eV}$ in a steady-state discharge in an Ar plasma with 5 kW of RF power. If the same polychromator system is used for AWAKE, where the electron density attained is $2\times 10^{20}~\text{m}^{-3}$ , the contribution to measurement error due to coherent scattering is ${\sim}2.5\,\%$ . Presented here are details of the TS diagnostic and the first tests in RAID, and the expectations for the system when employed on the AWAKE device.

Mathematical analysis of the 09 March 2012 intense storm

The in-depth investigation of the parameters of the solar wind, the zonal geomagnetic indices and the interplanetary magnetic field (IMF) is the key to furthering space weather researches. The investigations got meaning through modeling various interplanetary parameters and geomagnetic indices. These models, built on the basis of the correlations between solar wind parameters and zonal geomagnetic indices, and that must strictly obey physical principles, will not only reveal the properties of geomagnetic activity but also allow estimates of their formations. This study focuses on the 2012 March 09 phenomenon, the first intense geomagnetic storm of the 24th solar cycle. The deeper understanding of the storm depends on a correct interpretation and visualization of the relationship between solar wind plasma parameters (solar wind dynamic pressure (P), flow speed (v), electric field (E), magnetic field (Bz), proton density (N), temperature (T)) and zonal geomagnetic indices (AE, ap, Kp, Dst). The study investigates, visualizes and interprets the solar wind plasma parameters and zonal geomagnetic indices themselves. The storm variables set included of observations of ten variables from NASA are described. By this investigation a covariance matrix indicates the strength of bivariate relationships, a dendrogram indicates hierarchical clustering into groups, and factor analysis indicates three distinct eigenvectors. In addition, linear and nonlinear models about the problem are introduced to readers. The author discuses mathematically what happened in the storm on 2012 March 09 at the beginning of the 24th solar cycle. The aim of this work is to help the reader understand the storm by providing the models that the representatives of parameters and indices coexist.

Dependence of discharge ignition on initial condition in atmospheric cascade glow discharges

A two-dimensional numerical fluid model was developed to study the effects of initial discharge conditions on the discharge dynamics and characteristics of atmospheric cascade glow discharge including dielectric barrier pulsed discharge and radio frequency (RF) discharge burst. In the dielectric barrier pulsed discharge, the second discharge in the pulse voltage falling phase develops faster than the first discharge in the pulse voltage rising phase, which is demonstrated by the spatiotemporal evolution of discharge and can be attributed to the initial discharge conditions in terms of electron and ion density and their spatial distribution. On the other hand, in the pulse modulated RF discharge coupled with pulsed discharge, the initial conditions of RF discharge can be influenced by the pulsed discharge. The ignition dynamics of RF discharge is compared with and without the pulsed discharge in terms of plasma densities and electric field to show the role of residual plasma species in the initial discharge conditions. It proposes that the discharge ignition both in the pulsed discharge and the RF discharge is dependent on the density and spatial profile of plasma species in the initial discharge conditions, which helps ignite and achieve stable operation of atmospheric glow discharge.

Negative electric potential in a cylindrical plasma column with magnetized electrons

The possibility of creating adjustable electric fields in plasma opens up a wide range of applications for plasma technologies. However, the question with regards to the conditions, under which the plasma potential along the magnetic field line, resting on the electrode, repeats the potential of this electrode, turns out to be quite complex. In the present paper, an axially symmetric system with a magnetic field directed along an axis is considered. At the ends of the system, there are electrodes with a given negative potential. A simplified model of the system is proposed, taking into account the near-electrode voltage drop and continuity of the current in the circuit of the end electrodes. Within the framework of this model, an analytical formula is derived for the plasma potential on the axis of such a system, depending on its parameters. This formula can serve as a guide for experimenters when choosing experiment parameters, the purpose of which are to create a negative radial electric field in plasma. The data, obtained using the proposed model, are compared with existing experiments, and their agreement is demonstrated.

Designing Resonance Microwave Cavities to Optimize Plasma Generation

Methodology for designing the 2.45-GHz microwave (MW) coupling system to optimize the hydrogen plasma density in an electron cyclotron resonance (ECR) plasma reactor is presented. Two different plasma generator systems have been studied by experiments and 3-D simulations to find the criteria to reach an optimized design. The experimental work includes the detailed measurements and calculations of the electron energy distribution functions (EEDF) and ultrafast photography diagnostics to estimate the spatial distributions of plasma unbalanced charge density, potential, and electric field for both cases. It demonstrates that to simulate in 3-D, the distribution of the resonant stationary electric field along the entire MW driver system can be used to improve the design in order to reach higher plasma densities and temperatures.