Bulletin of the American Physical Society
66th Annual Gaseous Electronics Conference
Volume 58, Number 8
Monday–Friday, September 30–October 4 2013; Princeton, New Jersey
Session DT2: High Pressure Discharges: Dielectric Barrier Discharges, Coronas, Breakdown, Sparks I |
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Chair: Brian Sands, UES Inc. Room: Ballroom II |
Tuesday, October 1, 2013 10:00AM - 10:15AM |
DT2.00001: Effect of electrodes photoemission on breakdown voltage of Townsend plasma discharges in helium and argon, gaseous and supercritical Deanna A. Lacoste, Hitoshi Muneoka, Thibault F. Guiberti, Keiichiro Urabe, Sven Stauss, Kazuo Terashima We report on the effect of light irradiation of tungsten electrode surface on the breakdown voltage in helium and argon for densities up to 23mol/L. The electric discharges were generated in a pin-to-plane electrode geometry, separated by a gap distance of 5$\mu $m, the pin electrode being the cathode. The applied voltage was generated by a DC power supply with a current limitation of a few tens of nano-amperes. Two light sources with wavelengths of 365 and 635 nm respectively, were used to irradiate the electrodes and the plasma zone and we studied the influence of the pressure, the temperature, and the light flux on the breakdown voltage. With a light flux of less than a few watts per square meter and by varying the pressure near the critical temperature, the breakdown behavior of both helium and argon follows a Paschen curve. In low temperature helium (down to 5.2 K), a strong effect of the light on the breakdown voltage has been found. In contrast, no significant effect has been observed for the breakdown behavior in argon as well as in helium at temperatures higher than 250 K. Based on the results, we propose a phenomenological interpretation of the influence of photoemission on the breakdown mechanism. [Preview Abstract] |
Tuesday, October 1, 2013 10:15AM - 10:30AM |
DT2.00002: Atmospheric Pressure Non-Thermal Air Plasma Jet Abdel-Aleam Mohamed, Ahmed Al-Mashraqi, Mohamed Benghanem, Samir Al Shariff Atmospheric pressure air cold plasma jet is introduced in this work. It is AC (60Hz to 20kHz) cold plasma jet in air. The system is consisted of a cylindrical alumina insulator tube with outer diameter of 1.59mm and 26mm length and 0.80mm inner diameter. AC sinusoidal high voltage was applied to the powered electrode which is a hollow needle inserted in the Alumina tube. The inner electrode is a hollow needle with 0.80mm and 0.46mm outer and inner diameters respectively. The outer electrode is grounded which is a copper ring surrounded the alumina tube locates at the nozzle end. Air is blowing through the inner electrode to form a plasma jet. The jet length increases with flow rate and applied voltage to reach 1.5cm. The gas temperature decreases with distance from the end of the nozzle and with increasing the flow rate. The spectroscopic measurement between 200nm and 900nm indicates that the jet contains reactive species such as OH, O in addition to the UV emission. The peak to peak current values increased from 6mA to 12mA. The current voltage waveform indicates that the generated jet is homogenous plasma. The jet gas temperature measurements indicate that the jet has a room temperature. [Preview Abstract] |
Tuesday, October 1, 2013 10:30AM - 10:45AM |
DT2.00003: A Statistical Photon Transport Model: Application to Streamer Discharges in Dry Air Zhongmin Xiong, Mark J. Kushner Photon transport and photo-ionization are necessary to advancing propagation of positive streamer discharges by providing seed electrons. Although plasma hydrodynamics may be well represented by local transport, photon transport is intrinsically non-local. On short time and spatial scales, photon transport may also be statistical which in turn may be partly responsible for streamer branching. In this paper we discuss results from a computational investigation of the consequences of statistical radiation transport and photoionization on streamer propagation. Radiation transport in \textit{nonPDPSIM,} the model for this study, uses a continuum approach in which photon flux from each emitting node is isotropic and every node within its absorption length receives flux. In reality, during any given time step photon emission may not be large enough for every node to receive a photon. To better reflect the statistical nature of photon transport, the emitted photon flux was discretized into particle-like packets which are isotropically but randomly emitted within a given solid angle. The time averaged flux is isotropic and all nodes within the absorption sphere receive flux, but in a statistical manner which allows for statistically long mean-free-paths. This model has been applied to simulations of positive streamer discharges in atmospheric-pressure, dry air with ns rise time voltage pulses. The results demonstrate that the statistical nature of photon transport producing stochastically distributed seeds of preionization, can be responsible for the branching of positive streamers. [Preview Abstract] |
Tuesday, October 1, 2013 10:45AM - 11:00AM |
DT2.00004: Measurement of activated species generated by AC power excited non-equilibrium atmospheric pressure Ar plasma jet with air engulfment Keigo Takeda, Kenji Ishikawa, Hiromasa Tanaka, Hiroyuki Kano, Makoto Sekine, Masaru Hori Non-equilibrium atmospheric pressure plasma jet (NEAPPJ) is very attractive tool for bio and medical applications. In the plasma treatments, samples are typically located at a far region from main discharge, and treated in open air without purge gases. Influence of air engulfment on generation of activated species in the NEAPPJ in open air is a large issue for the application. In this study, the AC excited argon NEAPPJ with the gas flow rate of 2 slm was generated under the open air condition. The densities of the grand state nitrogen monoxide (NO) and the ground state O atom generated by the NEAPPJ were measured by laser induced fluorescence spectroscopy and vacuum ultraviolet absorption spectroscopy. The length of the plasma jet was around 10 mm. Up to 10 mm, the NO density increased with increasing the distance from plasma head, and then saturated in remote region of plasma. On the other hand, the O atom density decreased from 10$^{\mathrm{14}}$ to 10$^{\mathrm{13}}$ cm$^{\mathrm{-3}}$ with increasing the distance. Especially, the amount of decrease in O atom density became the largest at the plasma edge. We will discuss the generation and loss processes of activated species generated in the NEAPPJ with the measurement results using spectroscopic methods. [Preview Abstract] |
Tuesday, October 1, 2013 11:00AM - 11:15AM |
DT2.00005: Diagnostics of the Cold Atmospheric Plasma Jet David Scott, Yash Jain, Alexey Shashurin, Michael Keidar Cold atmospheric plasmas (CAP) may have the ability to improve cancer treatment, though the mechanisms of which are yet to be fully understood To this end a better understanding of the CAP physics is required. Recent works have shown that Raleigh microwave scattering (RMS) can successfully be used to obtain the absolute value of the electron density in CAP. The fabrication and calibration of an atmospheric condition RMS apparatus to estimate electron density has recently been completed. The plasma electron density will be analyzed with varying gas mixtures, flow rates, and input power frequencies. Helium and oxygen will comprise the preponderance of input gases. The plasma gun is made of a Pyrex syringe and yields plasma with a diameter of 3 mm and length of 2 -- 4 cm. In addition, a novel CAP extension has been fabricated that will yield a plasma with 1.25 mm diameter via flexible conduit. This design is intended for in-vitro CAP treatment of cancer cells. The electron density of this in-vitro apparatus will also be analyzed under varying input conditions. Photographing via an intensified charged-coupled device will be performed concurrently with density measurements in order to analyze the life-cycle of the CAP, including the streamer head and afterglow regions. [Preview Abstract] |
Tuesday, October 1, 2013 11:15AM - 11:30AM |
DT2.00006: Pressure dependence of electrical breakdown in water vapour Colin Kelsey, Bill Graham, Ken Stalder, Tom Field, David Patton, Tom Gilmore The relationship of breakdown voltage to the electric field strength and number density of a gas is a fundamental part of plasma physics. It is well studied and understood for parallel plate geometries where the relationship is described by Paschen's Law and thousands of experiments have been performed to measure such curves under a wide variety of conditions. Here we produce a plasma by applying a voltage in a point to plane geometry in a conducting liquid. Shadowgraph images show a vapour layer forming on the point and subsequent light emission indicates plasma creation within the vapour. However the processes are not spatially or temporally reproducible. In order to gain further understanding of the underlying physics of the plasma formation we are determining the electric field strength with at the aid of simulations,\footnote{L. Schaper PSST. 20 (2011) 034003} experimentally determining the breakdown voltage and varying the gas density by performing the experiments and simulations at different pressures. Preliminary results indicate electric field strengths of about 10$^{7}$V/m and that the plasma persists throughout voltage pulses of up to 2 ms. [Preview Abstract] |
Tuesday, October 1, 2013 11:30AM - 11:45AM |
DT2.00007: Electron properties of the plume of an atmospheric pressure helium plasma jet Wameedh Adress, Elena Nedanovska, Gagik Nersisyan, David Riley, William Graham Atmospheric pressure plasma, APP, jets, are now attracting great interest because of their potential uses in many applications; for example surface modification and plasma medicine. These applications require an insight into their plasma chemistry, which is strongly influenced by the electron energy distribution function. Here we report the use of Thomson scattering to measure the electron properties in the plume created by a 20 kHz, 2mm diameter helium APP jet operating into the open air. A 532nm Nd:YAG laser beam is focussed into the plasma plume. The temporally and spatially resolved spectra of light at 90$^{\circ}$ to the laser direction is detected. The spectra contain light from Thomson Scattering from electrons, along with Rayleigh and Raman scattering from atoms and molecules. These components are resolved in a manner similar to that described in ref 1. Our measurements reveal a ``ring-like'' radial distribution of both the electron density and temperature, with outer values of $\sim$ 7 x 10$^{13}$ cm$^{-3}$ and 0.4 eV and inner values of $\sim$ 2 x 10$^{13}$ cm$^{-3}$ and 0.1 eV respectively at 4 mm from the end of the quartz tube.\\[4pt] [1] A. F. H. van Gessel et al. Plasma Sources Sci. Technol. 21 (2012) 015003\\[0pt] [2] D.Breden et al Appl. Phys. Lett. 99 (2011) 111501 [Preview Abstract] |
Tuesday, October 1, 2013 11:45AM - 12:00PM |
DT2.00008: ABSTRACT WITHDRAWN |
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