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A 2-D fluid model is developed to study the pulsed discharges with pin--plane electrode in atmospheric pressure. A positive streamer forms at the pin electrode connecting to the applied voltage and then propagates toward to the ground plane electrode (cathode). Simulation results show if the streamer head is close enough to the cathode, in front of the original streamer a new streamer forms, and simultaneously a second positive current peak is observed, suggesting that the discharge mode transforms into glow mode. Otherwise, the discharge operates at corona mode. The characteristics of the two typical discharge modes are analyzed through the spatiotemporal evolution behaviors of conduction current, electron density, electric field, and electron flux. The transition between corona and glow modes depending on the discharge parameters such as applied voltage, curvature radii, and secondary electron emission coefficients are studied in this paper. It should be noted that no matter what discharge mode is, discharge with reversed direction appears at the falling edge of voltage pulse, which is caused by space charges [ABSTRACT FROM AUTHOR]

In this paper, an atmospheric pressure low-temperature plasma pencil generated in helium and helium/oxygen gas mixtures was characterized in detail for its discharge characteristics, plasma power, reactive plasma species produced, plasma density, and plasma temperatures using electrical and optical emission spectroscopy (OES) diagnostics, and its efficacy for biomedical application. A visible plasma plume length of approximately 27 mm was generated using a 60-kHz ac HV power supply. The OES results showed the most intensive plasma emission lines of OH transition A^2\Sigma^+(v=0,1)\toX^2\Pi(\Delta\nu=0) at 308 nm and OH transition A^2\Sigma^+(v=0,1)\toX^2\Pi(\Delta\nu=1) at 287 nm, O I transition 3p^5P\to 3s^5S^0 at 777.41 nm, O I transition 3p^3P\to 3s^3S^0 at 844.6 nm, and N2(C\-B) second positive system with electronic transition C^3\Piu{\to}B^3\Pig in the range 300–450 nm. The effects of controlled oxygen content on the plasma pencil and on various helium plasma emissions and electrical properties are studied. A spatial distribution of reactive plasma species produced by the plasma pencil is presented. The electron density of plasma jet was estimated to be in the order of 2.1\times 10^14~cm^-3 using Stark broadening line profile of the hydrogen alpha emission. The temperatures of afterglow plasma pencil were evaluated using OH rotational temperatures, and the results demonstrate temperatures of 316 and 362 K for pure He and He/ O2 gas mixtures (0.1% O2 ), respectively. Preliminary results on inactivation of Streptococcus pneumoniae on a solid surface and in liquid suspension were carried out using the plasma pencil for biomedical applications. [ABSTRACT FROM PUBLISHER]

In this paper, we demonstrate an atmospheric-pressure nonequilibrium Ar microplasma array confined inside photonic crystal fiber for the first time. The diameter and the length of each microplasma plume are 3.4~\mu \textm and 2 cm, respectively. The electron density evaluated from the Stark effect of Ar spectral line is up to 8 \times 10^16 cm ^-3 . The electron temperature calculated by the Ar collisional-radiative model is 0.85 eV, while the gas temperature obtained by fitting the N2 rotational spectrum is 500 K. [ABSTRACT FROM AUTHOR]

It is well accepted that increasing the frequency and reducing the electrode gap are effective ways to enhance the discharge stability in atmospheric radio-frequency (rf) discharges. In this paper, we explore a 1-D fluid model to investigate the discharge characteristics when the \alpha-\gamma mode transition occurs. The differential equation satisfied at the \alpha-\gamma mode transition point is given based on the governing equations. From the theoretical analysis and computational data, with an increase in the electrode gap, the power density coupled to the plasmas decreases, and the critical electron density modestly increases at the transition point; the electron temperature both in the sheath and bulk plasma decreases as the sheath shrinks. On the other side, as the frequency is raised, just at the mode transition point, the applied voltage reduces, and the plasma density increases almost exponentially with a higher electron temperature in the sheath. From the view point of application, the discharge driven by a high frequency at a narrow gap is desirable to produce a stable and high-density atmospheric plasma with a large power density coupled. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the self-absorption of Mg I–II emission lines on laser-induced breakdown spectroscopy (LIBS) experiments. We produced the plasmas in air at atmospheric pressure by focusing a Nd:YAG laser onto a pellet of finely powdered calcium hydroxide with a concentration of 625 ppm of Mg and recorded the intensity profiles of Mg lines at different delay times after the laser pulse from plasmas generated with different laser energies. We carried out the analysis of the line profiles within the framework of a homogeneous plasma in local thermodynamic equilibrium by a computer algorithm that calculates the emission spectra and matches them to the experimental measurements. It allowed evaluation and compensation of self-absorption by using the spectroscopic information saved on the optical thicknesses of the lines. After that, we performed the characterization of the plasma and correlated the self-absorption features with the different trends of the temperature, the electron density, and the Nl parameters obtained. At the early times of plasma evolution, we found that the fast expansion of the plume was dominant and the self-absorption effects are difficult to interpret within the current approach, supplying only qualitative information. On the other hand, at later times, the results obtained could be properly analyzed showing the practical usefulness of the method to provide valuable information for both basic and applied LIBS research. [ABSTRACT FROM PUBLISHER]

The plasma parameters in the 2.45 GHz electron cyclotron resonance (ECR) proton ion source have been measured and optimized at low pressures. These parameters are important as they are related to the beam parameters of the ion source. A detailed plasma characterization study has been conducted using hydrogen as a working gas in the operating pressure and power range 10^-4 – 10^-3 mbar, 400–1000 W of the ion source, respectively. The plasma parameters have been measured in the ECR zone of the plasma chamber. An automatic Langmuir probe and data acquisition system has been used to measure these parameters. In the above-mentioned power and pressure range, the plasma density, plasma electron temperature, and plasma potential measured are in the range 4 \times 10^11 – 6.5 \times 10^11 cm ^-3 , 4–11 eV, and 30–40 V, respectively. The variation of plasma parameters with neutral gas pressure is studied for different microwave powers. A 0-D (global) model has been developed to compare the measured plasma parameter data with the calculated ones. The ion species content in the plasma was measured after extraction using a magnetic mass analyzer and a Faraday cup. A plasma-based model has been developed to compare the measured ion species fraction data with the calculated ones by taking the measured ECR plasma parameters as input. [ABSTRACT FROM PUBLISHER]

The plume of a cathodic arc operated in atmospheric pressure gas is examined using an intensified camera and a spectrograph. A 0.2-J pulse arc is shown to generate a glowing jet $\approx 10$ mm in extent. Images recorded in the first microseconds after ignition show that the jet has a smaller core \approx 2$ mm in length. A spatially resolved Stark broadening measurement is performed along the jet core. The measured electron density is 1– 2 \times 10^{20} \text{m}^{\vphantom {R^{R}}-3} . A model for the cathodic arc plasma–gas interaction is presented. The obtained equilibrium between the forward and reverse charge exchange processes is suggested as enabling the extended jet core. [ABSTRACT FROM PUBLISHER]

A 1-D self-consistent fluid model was employed to investigate the effect of driving frequency on the discharge characters of a dielectric barrier discharge at atmospheric pressure in argon excited by a periodic Gaussian voltage. The simulation results indicate that there are two discharge modes: 1) Townsend and 2) glow modes in the multipulse discharge and different transitions between them during the discharge take place with the increase in driving frequency. When the driving frequency is 1 kHz, there is a tendency of transition from the Townsend mode through glow and finally back to the Townsend one during the positive half-circle of applied Gaussian voltage. However, the discharge in the half-circle can all along operate in the glow mode with the higher driving frequency. Moreover, when the driving frequency is sufficiently high, there are also distinct fluctuations of spatial performance of the charge densities in the positive column during the glow discharge. This is caused by the fact that a lot of charged particles created in the gas gap have not enough time to drift and diffuse to the dielectric barriers, and then these particles are preserved in the local discharge gap at such a high frequency. A comparison of the spatial and temporal evolutions of the electron density at different driving frequencies indicates that the increase in the driving frequency can enhance the plasma chemistry and also expand its volume. [ABSTRACT FROM AUTHOR]

An atmospheric pressure needle plasma is generated with a hollowneedle-plate dielectric barrier discharge, and the plasma parameters are measured by optical emission spectroscopy. The length of the needle plasma reaches 3 cm with an argon flow rate in the range from 3.5 to 6.1 ml/min when the applied voltage is 7.2 kV. The spatial distribution of oxygen-atom spectral-line intensity indicates that there is a large concentration of excited oxygen atoms in the middle of the plasma. Gas temperature is estimated by simulating the spectrum of OH radical around 309 nm. The spatial distribution of gas temperature along the plasma is uniform. Gas temperature decreases with the increase in argon flow rate. Electron density determined by the Stark broadening of H\alpha is in the range from 5.8 \times 10^14 to 6.0 \times 10^14\ \cm^-3 when the electron temperature is 1–4 eV. The application of plasma in the modification of material surface is demonstrated. [ABSTRACT FROM PUBLISHER]