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 CT1: Poster Session I (8:00-9:30AM) |
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Room: Ballroom Foyer |
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CT1.00001: PLASMA SCIENCE |
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CT1.00002: Experimental observation of dust ion acoustic wave propagation in a negative ion rich dusty plasma Nirab Chandra Adhikary, Heremba Bailung In the present work nonlinear propagation of dust ion-acoustic (DIA) solitary waves (SWs) in a negative ion rich dusty plasma is experimentally investigated. The effect of negative ions on the formation of rarefactive solitary wave in a dusty double plasma device is observed and its characteristics are analyzed. The important observation in this work is that; for the present dusty plasma condition, the applied electric perturbation cannot form a train of rarefactive solitons while propagating, until a sufficient amount of negative ions is introduced into the dusty plasma. It is also observed that the viscosity in the dusty plasma plays a crucial role in the formation and dissipation of solitary waves. The velocity and width of the solitary waves are measured and compared with numerical results obtained from the Korteweg--de Vries (K-dV) Burgers equation. [Preview Abstract] |
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CT1.00003: Afterglow Behavior of Laser-Breakdown Atmospheric Helium Plasmas E. Nedanovska, D. Riley, W.G. Graham, L. Huwel, T.J. Morgan, T. Murakami We present experimental and theoretical results on the temporal evolution of the electron density and temperature of a plasma formed by laser-induced breakdown in atmospheric helium. Plasma is created by a 9 ns, 140 mJ pulse from a Nd:YAG laser at 1064 nm and diagnosed with a separate laser using Thomson scattering with a 532 nm, 9 nm, 80 mJ probe beam during time delays ranging from 2 $\mu $s out to 22.5 $\mu $s. A zero-dimensional time-dependent global chemistry model is used to simulate the electron concentration, using pure helium and helium plus small amounts of humid air and molecular nitrogen. The effect of these small concentrations (1 ppm to 100 ppm) is significant and modifies the temporal decay behavior for both early and late times. Detailed analysis and comparisons with calculation will be presented at the conference. [Preview Abstract] |
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CT1.00004: NON-EQUILIBRIUM KINETICS OF LOW-TEMPERATURE PLASMAS |
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CT1.00005: Kinetics of Charged Particles in CF CF$_{4}$ at High Values of Reduced Electric Field Zoran Petrovic, Vladimir Stojanovic, Nikola Skoro, Dragana Maric, Zoran Raspopovic In this work we present results of our study of charged particle transport in dark Townsend discharges in CF$_{4}$ Monte Carlo technique, based on null collision method, already used for similar discharges in nitrogen, argon and hydrogen is used to obtain spatially resolved transport parameters for a range of reduced electric fields (E/N) from 700 Td to 20 kTd (1 Td$=$10$^{-21}$ Vm$^{2})$. In this work we focus on anisotropic scattering of electrons and we also obtain a consistent set of cross sections for ions and fast neutrals. Apart from the agreement of experimental and Monte Carlo results for electron and ion transport data, agreement with experimental results for spatially resolved optical emission and ionic energy distribution functions at high values of E/N is achieved. [Preview Abstract] |
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CT1.00006: PLASMA MODELING AND SIMULATION |
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CT1.00007: Mitigating chromatic effects for the transverse focusing of intense charged particle beams James Mitrani, Igor Kaganovich, Ronald Davidson A final focusing scheme designed to minimize chromatic effects is discussed. Solenoids are often used for transverse focusing in accelerator systems that require a charged particle beam with a small focal spot and/or large energy density A sufficiently large spread in axial momentum will reduce the effectiveness of transverse focusing, and result in chromatic effects on the final focal spot. Placing a weaker solenoid upstream of a stronger final focusing solenoid (FFS) mitigates chromatic effects on transverse beam focusing. J.M. Mitrani \textit{et al.}, Nucl. Inst. Meth. Phys. Res. A (2013) http://dx.doi.org/10.1016/j.nima.2013.05.09 [Preview Abstract] |
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CT1.00008: Semi-analytical modelling of positive corona discharge in air Francisco Pontiga, Khelifa Yanallah, Junhong Chen Semianalytical approximate solutions of the spatial distribution of electric field and electron and ion densities have been obtained by solving Poisson's equations and the continuity equations for the charged species along the Laplacian field lines. The need to iterate for the correct value of space charge on the corona electrode has been eliminated by using the corona current distribution over the grounded plane derived by Deutsch, which predicts a $cos^m\theta$ law similar to Warburg's law. Based on the results of the approximated model, a parametric study of the influence of gas pressure, the corona wire radius, and the inter-electrode wire-plate separation has been carried out. Also, the approximate solutions of the electron number density has been combined with a simplified plasma chemistry model in order to compute the ozone density generated by the corona discharge in the presence of a gas flow. [Preview Abstract] |
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CT1.00009: Collisional-radiative model for non-Maxwellian argon plasmas Allan Stauffer, Dipti Goyal, Reetesh Gangwar, Rajesh Srivastava We have applied our collisional radiative model [1] to inductively-coupled argon plasmas using a non-Maxwellian electron energy distribution function. We included detailed fine-structure cross sections calculated by our relativistic distorted-wave method as well as ionization processes to determine the population of the important excited levels of argon in the plasma for pressures in the range of 1-25 mTorr. We will present detailed results of our calculations and compare these with recent measurements of Boffard et al [2,3] including emission line ratios that can be used to determine plasma temperatures.\\[4pt] [1] R K Gangwar, L Sharma, R Srivastava and A D Stauffer, J. Appl. Phys. 111, 053307 (2012)]\\[0pt] [2] J. B. Boffard, R. O. Jung, C. C. Lin and A. E. Wendt, Plasma Sources Sci. Technol. 19, 065001 (2010)\\[0pt] [3] J. B. Boffard, R. O. Jung, C. C. Lin, L. E. Aneskavich and A. E. Wendt, J. Phy. D: Appl. Phys. 45, 045201 (2012) [Preview Abstract] |
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CT1.00010: PIC Simulations of Atmospheric Pressure Capacitive RF He/N$_2$ Discharges E. Kawamura, M.A. Lieberman, A.J. Lichtenberg, C. Lazzaroni, P. Chabert Atmospheric pressure rf micro-discharges have been extensively studied, due to emerging applications, particularly in medical and related areas. Because of their small size, diagnostics are difficult. A previous work studied discharges with a helium feed gas and small admixture of N$_2$ by using a 1D hybrid analytical-numerical model [1]. But this model did not consider sheath breakdown phenomena, thus limiting its applicability to the lower power range. To overcome this, we perform 1D particle-in-cell (PIC) simulations of atmospheric pressure capacitve RF He/N$_2$ discharges and use the results to guide the development of a model for the $\gamma$ mode of the discharge. We noted from [1] that the dominant species in He/N$_2$ discharges with 0.1\% N$_2$ were N${_2}^+$ ions, electrons, and metastable helium atoms He$^*$. This enabled us to develop a simplified cross-section set only involving those three species.\\[4pt] [1] C. Lazzaroni, P. Chabert, M.A. Lieberman, A.J. Lichtenberg and A. Leblanc, Plasma Sources Sci. Technol. {\bf 21}, 035012 (2012). [Preview Abstract] |
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CT1.00011: Modeling and simulation of high current flowing through a vacuum arc interacting with electrodes and shields Kai Hencken, Joschua Dilly Constricted vacuum arcs are typically found in specific vacuum interrupter types at high total currents. Such arcs are metal vapor arcs fed by the evaporation of material from the electrodes. In order to improve the performance of these breakers CFD simulations are an important tool. For a realistic simulation the conditions at the interface between the plasma and the electrodes are essential. This is the case especially at the arc roots, where high current densities occur. Here the microscopic processes of electron- and ion-flow into and out of the metal surface need to be taken into account; on the other hand the macroscopic current distribution is influenced by the current-voltage characteristic of this interface. In this contribution we present the physical model underlying the system of equations used for the plasma-electrode interface. In a second step these are implemented as boundary conditions for a simulation of the electric current distribution using a finite element approach. This is used as the basis to perform simulations of an vacuum arc interacting with a metal shield. A commutation of the current as a function of the surface temperature is found. [Preview Abstract] |
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CT1.00012: Higher Performance of Photon-enhanced Thermionic Emission Energy Converter by Contact Ionization Rate Enhancement Haruki Takao, Mark Cappelli, Tsuyohito Ito Traditionally, thermionic energy conversion is most efficient at high temperatures (\textgreater\ 1500 K). In a recent study [J.W. Schwede et al., Nature Materials 9, 762 (2010)], photon-enhanced thermionic emission (PETE) from semiconducting cathodes was shown to drastically increases the thermionically-driven cathode current density at relatively low cathode temperatures (500-1100K). However, at the high emitted current densities (3 - 30 A/cm$^2$) electron transport will be space charge limited. Last year (Bulletin of the American Physical Society, 57 (2012)), we demonstrated that using a particle-in-cell (PIC) method, continuous laser excitation of the cesium resonance level in a PETE thermionic discharge with cesium filling (resonance-enhanced PETE, or R-PETE) can suppress the space charge and boost the output current, to near ideal limits. In this presentation, we analyze the converter efficiency with an improved PIC simulation. The results suggest that increasing the probability of contact ionization on the semiconducting cathode surface may be a means of realizing the high efficiency and high current densities that an R-PETE converter can offer. [Preview Abstract] |
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CT1.00013: RF models for plasma-surface interactions Thomas Jenkins, David Smithe, Ming-Chieh Lin, Scott Kruger, Peter Stoltz Computational models for DC and oscillatory (RF-driven) sheath potentials, arising at metal or dielectric-coated surfaces in contact with plasma, are developed within the VSim code and applied in parameter regimes characteristic of fusion plasma experiments and plasma processing scenarios. Results from initial studies quantifying the effects of various dielectric wall coating materials and thicknesses on these sheath potentials, as well as on the ensuing flux of plasma particles to the wall, are presented. As well, the developed models are used to model plasma-facing ICRF antenna structures in the ITER device; we present initial assessments of the efficacy of dielectric-coated antenna surfaces in reducing sputtering-induced high-Z impurity contamination of the fusion reaction. [Preview Abstract] |
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CT1.00014: Evolution and dynamics of charged aerosols in plasmas Declan Diver, Euan Bennet, Hugh Potts, Charles Mahony, Paul Maguire, Davide Mariotti Understanding the evolutionary processes governing the dynamics and stability of charged macroscopic droplets in a discharge plasma is a central component of an innovative collaborative project on bacteria detection. Aerosolized bacteria samples will be injected into a discharge to acquire significant electrical charge. Two key aspects are then core to research: (i) the fluid stability of the charged aerosols under evaporative stress, and (ii) the stochastic component of their motion. (i) Initially stable charged aerosols subject to evaporation (continuously changing radius) may encounter the Rayleigh limit governing the maximum charge QR as a function of radius, arising from the electrostatic and surface tension forces. Additionally, the maximum surface field before charge emission QE can impose further constraints. (ii) A droplet is in any event subject to Brownian motion just like any other small particle, buffeted by a mixture of (dominant) neutrals and plasma, with the latter forming a sheath around the particle. The Brownian motion induced forces the sheath around the grain to move, incurring changes in impacting ion flux that can represent an additional drag term, changing the classical Brownian diffusion. We present analysis for a variety of discharge conditions. [Preview Abstract] |
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CT1.00015: Comparing fluid models for streamer discharges Aram H. Markosyan, Jannis Teunissen, Sasha Dujko, Ute Ebert Our recently developed high order fluid model, based on additional moments of the Boltzmann equation, for streamer discharges has shown excellent agreement with PIC/MC (Particle in cell/Monte Carlo) simulations in nitrogen. This motivates us to compare several commonly used fluid models for streamer discharges with the high order model. The fluid models considered in this work are: the first order model (also known as drift-diffusion-reaction, ``minimal'' or ``classical'' model), the first order model with an energy equation and the high order fluid model. As a reference we use PIC/MC simulations. We compare the models under STP conditions in argon, neon and nitrogen. [Preview Abstract] |
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CT1.00016: Coupled discretization of multicomponent diffusion problems in equilibrium and non-equilibrium plasmas Kim Peerenboom, Jan Ten Thije Boonkkamp, Jan Van Dijk, Gerrit Kroesen Solving balance equations is the essence of any fluid simulation of reactive, multicomponent plasmas. For plasmas in chemical non-equilibrium, balance equations are solved for all species of interest. When reactions are very fast with respect to transport time scales -- and the plasma approaches chemical equilibrium -- species abundances can be obtained from equilibrium relations. However, in many cases, balance equations still need to be solved for the elements, since the elemental composition can vary significantly in reactive multicomponent plasmas. Both in equilibrium and in non-equilibrium the species diffusive fluxes in these balance equations are governed by the Stefan-Maxwell equations. The use of Stefan-Maxwell diffusion leads to a coupled set of balance equations. Furthermore, this coupled set of equations is subject to charge and mass conservation constraints. Due to these complications the set of balance equations is often artificially decoupled to fit in the traditional finite volume discretization schemes and the constraints are explicitly applied. This approach can lead to very poor convergence behavior. We will present a new approach using a finite volume discretization scheme that takes into account the coupling and treats the constraints implicitly. [Preview Abstract] |
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CT1.00017: Three-dimensional Modelling of Two-phase Flow involving Droplets and Atmospheric Pressure Discharge M.M. Iqbal, C.P. Stallard, D.P. Dowling, M.M. Turner We employ a three-dimensional coupled fluid-droplet model (FD3d) to describe the complex mechanism of droplet-plasma interaction that occurs when a liquid precursor is injected through a nebulizer into an atmospheric pressure discharge (APD). The formation of conducting channels in the APD plasma illustrates that the electron concentration around the pulse of droplets emitted by the nebulizer is perturbed by the influence of different gas impurities due to the impact of Penning ionization. The development of the sheath potential around the pulse of HMDSO droplets is significantly stronger in the case of He-air than a He-N2 gas mixture, which illustrates the contribution of oxygen impurities. The volumetric density profiles of ionic species are discussed by describing the complex situation of two-phase flow at distinct driving frequencies (5 - 100 kHz). The uniform structure of APD plasma is formed by considering an appropriate size distribution of droplets because the non-uniformities grow due to the existence of larger radii of droplets. The comparison of numerical modelling results of droplet size distributions is performed with experimental measurements using laser diffraction particle size analysis technique. The desired properties of surface coating applications can be predicted by controlling various parameters mentioned in the fluid-droplet model. [Preview Abstract] |
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CT1.00018: Do dielectrics attract streamer discharges? Anna Dubinova, Jannis Teunissen, Ute Ebert Streamer discharges developing near dielectric materials can cause sparks and surface flashovers. This effect is to be avoided in high voltage technology. Dielectric materials tend to attract the discharge due to polarization effects resulting in the modification of the local electric field. Other mechanisms known for influencing streamer discharge propagation include photoionization, background ionization, accumulation of surface charge on the dielectrics and secondary electron emission. However, the actual physical mechanisms responsible for the surface flashovers are still under discussion. Developing advanced simulation tools, we aim at getting insight into the nature of streamer discharges in the presence of dielectrics in full 3D. We report the results of our simulations showing essential differences between a positive streamer propagating due to background ionization and due to photoionization. We compare our numerical results with experiments. We also describe a numerical method (a generalized Ghost Fluid Method) which allowed us to include dielectric interfaces into our streamer models, in an accurate and fast manner. [Preview Abstract] |
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CT1.00019: Phase Transformation of Droplets into Particles and Nucleation in Atmospheric Pressure Discharges M.M. Iqbal, C.P. Stallard, D.P. Dowling, M.M. Turner We investigate the mechanism of phase transformation of liquid precursor droplets into nano-particulates in an atmospheric pressure discharge (APD). This phase transformation is possible when the solid to a liquid mass ratio of slurry droplet reaches a threshold value. The behaviour of phase transformation of a single slurry droplet of HMDSO is described by developing a numerical model under the saturation condition of evaporation. It is observed from the temporal evolution of inner radius (R$_{\mathrm{i}})$ of a single slurry droplet that its value approaches zero before the entire shifting of a liquid phase and which explains with an expansion in the crust thickness (R$_{\mathrm{o}}$ - R$_{\mathrm{i}})$. The solid traces of nano-particles are observed experimentally on the surface coating depositions because the time for transferring the slurry droplet of HMDSO into solid state is amplified with an increment in the radii of droplets and the entire phase transition occurs within residence time for the nano-sized liquid droplets. The GDE coupled with discharge plasma is numerically solved to describe the mechanism of nucleation of nano-sized particles in APD plasma under similar conditions of the experiment. The growth of nucleation in APD plasma depends on the type of liquid precursor, such as HMDSO, TEOS and water, which is verified with a sharp peak in the nucleation rate and saturation ratio. [Preview Abstract] |
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CT1.00020: Kinetic Analysis of High Pressure DC Microplasmas via a One-dimensional PIC-MCC Simulation Hyonu Chang, Chang-Mo Ryu, Suk Jae Yoo Characteristics of dc high pressure argon microplasmas are studied by using a one-dimensional particle-in-cell and Monte Carlo collision simulation. The accelerated electrons inside the cathode fall region rapidly lose their kinetic energy near the cathode due to a high collision rate, and forming a highly non-uniform electron distribution in the positive column. This non-uniformity creates a difference between the electron diffusion current density and drift current density in the negative glow and positive column. An electric field is built to sustain continuity of the total current density. This retards the electron diffusion current in the region where the electron density gradient is large and induces an electron drift current in the region where electron density gradient is small. When the electrode gap is very small for electrons to diffuse in the entire volume of discharge, only one field reversal is shown in the negative glow. The discharge at atmospheric pressure has a shorter length of the cathode fall, a more biased electron distribution to the cathode, and a stronger negative electric field between the second and third field reversals due to an increased collision rate compared with that at 300 Torr. [Preview Abstract] |
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CT1.00021: Molecular dynamics simulation analysis of ion irradiation effects on plasma-liquid interface Yudai Minagawa, Naoki Shirai, Satoshi Uchida, Fumiyoshi Tochikubo Nonthermal atmospheric plasmas are used in a wide range of fields because the high-density plasma can be easily irradiated to various substances such as solid, liquid, biological object and so on. On the other hand, the mechanisms of physical and chemical phenomena at the plasma-liquid interface are not well understood yet. To investigate the effects of ion impact from plasma on water surface, we analyzed behavior of liquid water by classical molecular dynamics simulation. Simulation system consists of an irradiation particle in gas phase and 2000 water molecules in liquid phase. O$^{+}$ ion with 10 eV or 100 eV was impinged on the water surface. Ion impact induced increasing water temperature and ejection of water molecules. The averaged number of evaporated water molecules by ion impact is 0.6 molecules at 10 eV and 7.0 molecules at 100 eV. The maximum ion penetration depth was 1.14 nm at 10 eV and 2.75 nm at 100 eV. Ion entering into water disturbs the stable hydrogen bonding configurations between water molecules and gives energy to water molecules. Some water molecules rotated and moved by ion interaction impact on other water molecules one after another. When the water molecule near the surface received strongly repulsive force, it released into gas phase. [Preview Abstract] |
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CT1.00022: Transport Properties of Fluorine Ions in BF$_3$ Vladimir Stojanovic, Zoran Raspopovic, Jasmina Jovanovic, Zeljka Nikitovic, Zoran Petrovic Transport properties of F+ and F- ions in BF$_3$ in DC fields and at room temperature were calculated by using Monte Carlo simulation technique. Previously cross section sets were obtained by using Nanbu theory for resolving between elastic and reactive collision events and then resolving contribution of exothermic processes from available experimental data. We present transport coefficients for the conditions of low and moderate reduced electric fields E/N (E-electric field, N-gas density) accounting for non-conservative processes. [Preview Abstract] |
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CT1.00023: The rf breakdown voltage curves-similarity law Marija Savic, Marija Radmilovic-Radjenovic, Milovan Suvakov, Zoran Lj. Petrovic Capacitively coupled radio frequency (rf) discharges are attracting an increased attention due to their wide applications in many technological processes such as plasma etching for semiconductor materials, thin film deposition and plasma cleaning. One of the crucial problem in optimizing plasma technological process is determination of the plasma operating conditions which can be obtained from the breakdown voltage. It was shown that the RF breakdown voltage curves obey similarity law: Vrf $=$f(pd,f$\cdot$d$=$const), where p is the gas pressure, d is the interelectrode distance and f is t the operating frequency. We have performed calculations in argon by using Monte Carlo code considering only electrons motion. Simulation conditions were based on the experimental conditions. The obtain results confirm similarity law and satisfactorily agree with the available experimental data. [Preview Abstract] |
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CT1.00024: GLOWS: DC, PULSED, MICROWAVE, OTHERS |
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CT1.00025: Glow Discharge with Confinement of Electrons in an Electrostatic Trap Alexander Metel Theory based on the concept of the gas ionization cost $W$ is found to be in a good agreement with experimental study of the glow discharge with electrostatic trap in the gas pressure range 0.001-10 Pa. When the mean ionization length $\lambda $ of emitted by the cathode electrons exceeds the trap width $a=$4$V$/$S$, where $V $is the trap volume and $S$ is area of the trap boundary, and their energy relaxation length $\Lambda =$(\textit{eU}$_{c}$/$W)\lambda $, where $U_{c}$ is cathode fall of potential, is lower than the trap length $L=$4$V$/$S_{o}$, where $S_{o}$ is output aperture of the trap, $U_{c}$ is independent of the pressure $p$. In this middle pressure range due to multiplication of fast electrons in the cathode sheath $U_{c}$ diminishes about 2 times from its maximum W/e$\gamma $, where $\gamma $ is coefficient of ion-induced electron emission, with the discharge current reduction. At $\Lambda $\textgreater $L$ the cathode fall $U_{c}$ rises from hundreds to thousands of volts and $p$ tends to the discharge extinction pressure $p^{ex}$, at which the ionization length $\lambda $ of electrons with energy equal to the energy of electrons emitted by the cathode in the middle pressure range is equal to $L$. [Preview Abstract] |
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CT1.00026: Research of the DC discharge of He-Ne gas mixture in hollow core fiber Xinbing Wang, Lian Duan Since the first waveguide 0.633 $\mu $m He-Ne laser from a 20 cm length of 430 $\mu $m glass capillary was reported in 1971, no smaller waveguide gas laser has ever been constructed. Recently as the development of low loss hollow core PBG fiber, it is possible to constract a He-Ne lasers based on hollow-core PBG fibers. For the small diameter of the air hole, it is necessary to do some research to obtain glow discharge in hollow core fibers. In this paper, the experimental research of DC discharge in 200 $\mu $m bore diameter hollow core fibers was reported. Stable glow discharge was obained at varioue He-Ne mixtures from 4 Torr to 18Torr. In order to obtain the plasma parameter of the discharge, the trace gasses of N$_{2}$ and H$_{2}$ were added to the He-Ne mixtures, the optical emission spectroscopy of the discharge was recorded by a PI 2750 spectroscopy with a CCD camera. The gas temperature (Tg) could be obtained by matching the simulated rovibronic band of the N$_{2}$ emission with the observed spectrum in the ultraviolet region. The spectral method was also used to obtained the electron density, which is based on the analysis of the wavelength profile of the 486.13nm H$_{\beta}$ line, and the electron temperature was obtain by Boltzmann plot methods. Experimental results show that it is very difficult to achieve DC discharge in bore diameter less than 50$\mu $m, and a RF discharge method was proposed. [Preview Abstract] |
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CT1.00027: The Child-Langmuir laws and cathode sheath in the N$_{2}$O Valeriy Lisovskiy, Ekaterina Artushenko, Vladimir Yegorenkov It is established which of the Child-Langmuir collisional laws are most appropriate for describing the cathode sheath in the N$_2$O. At low pressure $p < 0.3$ Torr the Child-Langmuir law version relating to the constant ion mobility. At $p > 0.75$ Torr one has to employ the law version for which it is assumed that ion mean free path within the cathode sheath is constant. In the intermediate pressure range $0.3 < p < 0.75$ Torr neither of the Child-Langmuir law versions gives a correct description of the cathode sheath in the N$_2$O. The ratio of the normal current density to the gas pressure squared $J/p^2$, the normal voltage drop and the cathode sheath thickness are determined. For the stainless steel cathode they equals to $U = 364$ V and $pd = 2.5$ Torr$\cdot$mm. At large N$_2$O pressure the above ratio remains constant and it amounts to $J/p^2$ = 0.44 mA/(cm$\cdot$Torr)$^2$ for any inter-electrode gap value we studied. On decreasing the N$_2$O pressure the ratio $J/p^2$ increases and for narrow gaps between electrodes it may approach several or even several tens mA/(cm$\cdot$Torr)$^2$. [Preview Abstract] |
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CT1.00028: VUV Emission of Microwave Driven Argon Plasma Source Julio Henriques, Susana Espinho, Edgar Felizardo, Elena Tatarova, Francisco Dias, Carlos Ferreira An experimental and kinetic modeling investigation of a low-pressure (0.1-1.2 mbar), surface wave (2.45 GHz) induced Ar plasma as a source vacuum ultraviolet (VUV) light is presented, using visible and VUV optical spectroscopy. The electron density and the relative VUV emission intensities of excited Ar atoms (at 104.8 nm and 106.6 nm) and ions (at 92.0 nm and 93.2 nm) were determined as a function of the microwave power and pressure. The experimental results were analyzed using a 2D self-consistent theoretical model based on a set of coupled equations including the electron Boltzmann equation, the rate balance equations for the most important electronic excited species and for charged particles, the gas thermal balance equation, and the wave electrodynamics. The principal collisional and radiative processes for neutral Ar(3p$^{5}$4s) and Ar(3p$^{5}$4p) and ionized Ar(3s3p$^{6}$ $^{2}$S$_{1/2})$ levels are accounted for. Model predictions are in good agreement with the experimental measurements. [Preview Abstract] |
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CT1.00029: On electric field magnitude on the cathode surface in the negative corona discharge A. Petrov, S. Savinov, N. Pestovskii, E. Korostylev, R. Amirov, I. Samoylov, S. Barengolts Negative corona discharge has been studied in air in the Trichel pulse mode in point-to-plane configuration on graphite cathodes. Electric field magnitude of the positive space charge in the active phase of a Trichel pulse has been estimated on the range of 10$^{7}$ V/cm. The discharge flame on the cathode surface is localized in the region with maximum electric field [1]. The wandering of the discharge is self-organized in such way that the electric field magnitude caused by the positive space charge in the region of the discharge flame localization exceeds the field magnitude on the microasperities in some distance from this region. So the proposed estimate of electric field magnitude is based on the results of the topography analysis of the cathode surface and on the results of registration of the discharge wandering over the cathode surface. Microasperities formed due to redeposition of erosion products with field magnification coefficient 10-10$^{2}$ were found. Finally the occurrence of electric field with magnitude 10$^{8}$ V/cm argues in favor of electroexplosive mechanism of cathode erosion in the negative corona discharge. [1] Loeb, L.B. Electrical Coronas. Their Basic Physical Mechanisms. Berkeley, CA: Univ. California Press, 1965, 694 p. [Preview Abstract] |
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CT1.00030: Axial structure of the dc hollow cathode discharge at different modes Valeriy Lisovskiy, Illia Bogodielnyi This paper reports the axial profiles of the electron temperature, plasma concentration and plasma potential in a dc hollow cathode discharge in nitrogen registered with probe technique. At low pressure (0.05 Torr) the discharge is shown to burn in a high-voltage (electron-beam) mode. Electron temperature does not exceed 1~eV in the total plasma region excluding an abrupt growth in the vicinity of the cathode sheath boundary. A potential barrier is found near the cathode sheath boundary, for the current value of 1 mA the height of this barrier amounts to about 8~V. At gas pressure $p \ge 0.15$ Torr two modes are well expressed: glow and hollow ones. At low discharge current a glow regime is observed in which the negative glow from the anode side possesses a wedge-like profile directed into the cathode cavity. At larger discharge current the discharge is burning in the hollow mode in which the cavity is filled with a high concentration plasma approaching 2$\cdot$10$^{10}$~cm$^{-3}$ and an electron temperature exceeding 2 eV. A potential well about 3 V deep is observed near the edge of the cathode cavity. On increasing the gas pressure the depth of the potential well in the cathode cavity decreases and it disappears at 0.5 Torr. [Preview Abstract] |
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CT1.00031: Physics and modeling of ITER glow discharge cleaning G.J.M. Hagelaar, D. Kogut, D. Douai, R.A. Pitts Glow discharge cleaning (GDC) is a common technique for the conditioning of tokamak vessel walls in order to improve the tokamak plasma performance and reproducibility. The GDC discharge is a dc low-temperature plasma discharge, operated when the tokamak magnetic fields are off, between several anodes inserted into the vessel, and the vessel walls serving as a cathode. The plasma is sustained by fast electrons emitted from the walls by ion impact, accelerated through a thin cathode sheath up to nearly the discharge voltage, and then penetrating very far into the plasma. On the other hand, the electric potential in the plasma bulk, which determines the wall ion flux distribution, seems to be controlled by low-energy bulk electrons. This paper presents a self-consistent 2D model of the GDC discharge with the aim to improve fundamental understanding and predict the wall current density distribution as input to the ITER GDC system design. The model is based on a hybrid approach, combining a fluid model of the plasma bulk with a Monte-Carlo simulation of the fast electrons. Comparisons are shown with experimental results obtained on a small scale test stand. [Preview Abstract] |
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CT1.00032: A novel self-excited oscillator as RF amplifier for capacitive discharge at atmospheric pressure Xiangyu Xu, Yingqi Ma, Yi Zhou, Yu Wang A novel self-excited oscillator was developed for exciting atmospheric pressure plasma via capacitive-discharge way. The oscillator was dominated by a RF transformer combined with a feedback inductor. The frequency range can be tuned from 1 to 15 MHz by changing the values of the resonant capacitor and the feedback inductor. The optimum output power was determined by the capacitive-discharge plasma's volume and the maximum value was about 80 W. By square-wave frequency modulation of the DC supply, the mode of filament discharge or glow discharge was successfully controlled by the oscillator excitation. The developed oscillator can be used for atmospheric pressure plasma for small volume and small power device applications, such as plasma jet, flat capacitor discharge, etc. [Preview Abstract] |
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CT1.00033: Plasma Photonic Crystals for Microwave Manipulation Benjamin Wang, Mark Cappelli A plasma photonic crystal was constructed for microwave manipulation and the performance of the device was characterized. A linear waveguide and square plasma photonic crystal was constructed from arrays of plasma glow discharge tubes. The transmission spectrums of the devices were measured and characterized. Finite difference time domain (FDTD) simulations of the designed 2D waveguide plasma devices in air were completed. The introduction of point and line defects in the plasma arrays allowed for waveguiding behavior and electromagnetic band gaps to be observed. [Preview Abstract] |
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CT1.00034: Simulations of energy and angular distributions in plasma processing reactors using CFD-ACE$+$ Ananth Bhoj, Kunal Jain, Mustafa Megahed Several plasma processing reactors employ energetic ion bombardment at the substrate to enable surface reactions such as plasma etching, deposition or sputtering. The knowledge and control of the energy and angular distributions is an important requirement and can be used to suppress or enhance reaction rates. The CFD-ACE$+$ platform is used for reactor scale modeling of generic inductively coupled and capacitively coupled rf plasma reactors. CFD-ACE$+$ has a coupled solver approach that includes modules to address in a sequential and iterative manner, fluid flow, heat transfer, the Poisson equation for electric fields, charged species transport equations for species fluxes, surface charge on dielectrics and chemical kinetics in the gas and on all plasma-bounding surfaces. The Monte Carlo transport module of CFD-ACE$+$ is based on the work of Kushner and co-workers\footnote{R. J. Hoekstra and M.J. Kushner, Journal of Applied Physics, 79, 2275 (1996)} and tracks pseudo-particles representing actual species based on source functions in the reactor. Model outputs for visualization include species densities and energy and angular distribution functions. Results discussed will include the effect of process variables such as pressure, power and frequency on the energy and angular distributions. [Preview Abstract] |
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CT1.00035: Simulations of DC planar magnetron discharges using CFD-ACE$+$ Ananth Bhoj, Kunal Jain, Mustafa Megahed Among the various kinds of plasma reactors, DC magnetron discharges are a class of reactors that utilize dc electric fields and strong magnetic fields to confine or otherwise manipulate the discharge properties and consequent details of sputtering to suit processing needs. In this work, the plasma modeling platform, CFD-ACE$+$, was used to simulate DC discharges in the presence of strong magnetic fields, not accounting for sputtering effects. CFD-ACE$+$ consists of several coupled physics modules and the partial list of those used here solve for volumetric and surface reactions, heat transfer, electromagnetics and species transport. Anisotropic electron transport in the presence of strong magnetic fields is included in the model. An axisymmetric DC discharge with a grounded anode and powered cathode and static magnetic field (also axisymmetric) was investigated. The effect of magnetization and secondary electron emission on plasma density and sheath thickness are discussed. The variation of species fluxes, energy and angular distributions at the cathode are examined. [Preview Abstract] |
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CT1.00036: MAGNETICALLY-ENHANCED PLASMAS: ECR, HELICON, MAGNETRON, OTHERS |
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CT1.00037: Observation of counter flowing ExB drifts in annulus magnetized Shantanu Karkari, Sourabh Jain, Isheta Majumdar, Hasmukh Kabariya, Chiranjeev Soneji, Dhrumil Patel High density plasma sources based on magnetron devices are widely popular in thin film deposition systems. In this paper we present the characteristic properties of an intense magnetized plasma column produced using a d.c magnetron source. The plasma column extends up to a distance of 50 cm in the presence of uniform magnetic field ranging up to 150 mTesla. The device comprise of a hollow cathode of diameter 5 cm and a differentially pumped constricted hollow anode. Measurement of radial plasma parameters using planar Langmuir probe shows an off-centered density peak exceeding 10$^{17}$ m$^{-3}$ at a distance of 15 cm from the source. The detail analysis of the electron-saturation region of the probe characteristics in the central column shows a double hump structure at approximately 10 Volts above the plasma potential. This feature reveals the presence of an ion beam in the plasma column which is absent outboard from the axis. In addition energetic electrons having energies greater than 100 eV are also inferred from the probe characteristic. Preliminary assessment regarding the origin of these energetic particles is attributed to the possibility of a virtual anode inside the magnetron device. [Preview Abstract] |
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CT1.00038: Steady-state mode of DC magnetron sputtering of mosaic copper-graphite targets Alexander Pal, Yury Mankelevich, Valery Mitin, Tatyana Rakhimova, Alexey Ryabinkin, Alexander Serov Magnetron discharge provides broad possibilities for complex materials engineering, multicomponent coatings deposition in particular. Sputtering of the segmented or mosaic targets could easily create the necessary film composition. However the metal flux from the target can hardly be uniform. That is because removing a material is a ballistic process that considerably depends on many coupled processing parameters. The differences in the sputter yield of the different target segments should lead to non-uniform target erosion and distortion of the stoichiometry of a multi-element target material in the film. We investigated the magnetron sputtering of the mosaic targets containing materials with heavily different sputtering yield, namely copper and carbon. The mosaic targets consisted of copper disks with cylindrical graphite inserts. The relative area of the inserts was varied. It was found, that after transition regime an operational mode with equal erosion rate of metal and graphite elements were established. The ion flow redistribution due to graphitic insets protruding above the copper surface and the graphite sputtering yield increase due to Cu and Ar implantation can explain the effect of sputtering rate equalization for mosaic copper-graphite targets. The same processes should take place at sputtering of mosaic targets with small inserts of any composition. [Preview Abstract] |
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CT1.00039: High current density and low sputtering in cold cathode glow plasmas Sergey Zalubovsky, Svetlana Selezneva, David Smith, Darryl Michael, Timothy Sommerer We investigate the use of cold cathodes in long-life high-voltage gas switches In such an application the current density should be high (to maximize the device current rating), the gas pressure should be low (to maximize standoff voltage on the left side of Paschen's curve), and cathode sputtering should be minimized (for long device life). We focus here on the rate of cathode sputtering as a function of both cathode materials and plasma conditions. The plasma is magnetized to increase the current density, and operates at an intermediate gas pressure, so we estimate the ion energy distribution at the cathode surface as a function of plasma parameters using both semi-analytic expressions and a particle-in-cell simulation. [Preview Abstract] |
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CT1.00040: Electron transport in closed-drift EXB configurations - Collisional to turbulent transport Jean-Pierre Boeuf In closed-drift ion sources and Hall thrusters, the presence of a magnetic field perpendicular to the electron current between an emissive cathode and the anode leads to the formation of a large electric field in the plasma, which extracts ions from the source. In typical cylindrical configurations, the external magnetic field is radial and the electric field is axial, and a large electron current, the Hall current, flows in the azimuthal EXB direction (closed-drift). In Hall thruster conditions, it is known that collisions between electrons and neutral atoms cannot explain the observed electron current across the magnetic field. We use a 1D-3V Particle-In-Cell Monte Carlo Collision (PIC-MCC) model to study electron transport in these conditions. Electron and ion trajectories are described in 3D but Poisson's equation is solved in the azimuthal direction only (with periodic boundary conditions) to study the development of instabilities in this direction. Electrons gain energy form the given axial electric field and lose energy through collisions with neutral atoms. Simulations have been performed for different gas densities, plasma densities, and applied E and B fields. We find that instabilities of the azimuthal electric field take place quickly for values of the Hall parameter larger than one. We study the properties of these instabilities, compare them with those predicted by dispersion relations obtained in similar conditions, and analyze the deviation from classical mobility due to these instabilities. [Preview Abstract] |
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CT1.00041: Warm Magnetized Primary and Secondary Electron Vlasov Equilibria Robert Terry A Vlasov equilibrium is developed for steady state emission into a magnetized gap in coaxial geometry. The outer cathode boundary conditions are those of a perfect conductor that emits a Maxwellian electron flux radially, azimuthally, and axially. The interior anode boundary conditions are those of a perfect conductor with a fixed secondary emission coefficient ($0 < \gamma \leq 1$). The anode carries a fixed current and the radial gap is set to a fixed voltage. The angular momentum of emitted secondary electrons around the anode is found to materially change the orbit turning points. When energy conserving solutions are examined it is found that the secondaries axial velocities must remain bounded above by a well defined function of radius, magnetic field, and voltage. A fully nonlinear and self consistent Vlasov-Poisson problem is formulated and solved for the space charge distribution implied by the Vlasov equilibrium. The conditions for magnetic insulation of the secondary electron population are then established. [Preview Abstract] |
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CT1.00042: HIGH PRESSURE DISCHARGES: DIELECTRIC BARRIER DISCHARGES, CORONAS, BREAKDOWN, SPARKS |
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CT1.00043: Ignition mechanism of mercury-free HID lamps for automotive headlamps Tadao Uetsuki, Takao Shimada, Ryota Yamamoto, Kotaro Shimizu, Masaya Shido, Yukio Onoda It is important to decrease the ignition voltage of the mercury-free HID lamp for automotive headlamp in order to make their ballast smaller. We think it is necessary to understand how the discharge starts and grow in the HID lamp burner in order to decrease the ignition voltage. An ultra high speed camera was used for the observations of the discharge, the shutter speed of which is 5n seconds. As the result, we found the discharge grow through three stages. First, a very weak discharge occurs outside the burner. Second, the very weak plasma was formed near the cathode in the burner, and then it grew toward the anode. Finally, a strong discharge like streamer developed from the anode to the cathode. The weak plasma seems to be made by the strong electric field formed by the attached electric charge on the outside of the burner wall, which was formed by the first weak discharge that occurred outside of the burner. In this study we discuss these observations. [Preview Abstract] |
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CT1.00044: Thomson scattering in high-pressure microwave plasmas for plasma-assisted combustion in automobile engines K. Sasaki, S. Soma, Y. Ikeda Nonequilibrium plasmas are preferable in plasma-assisted combustion of automobile engines. We have developed a microwave plasma source, which can work at pressures higher than the pressure of atmosphere, with the intension of applying it to plasma-assisted combustion. In this work, we investigated the electron temperature in the microwave plasma source by laser Thomson scattering. The power supply for the discharge was a semiconductor-based microwave source at 2.45 GHz. We produced pulsed discharges with a duration of 2 ms. The discharge gas in this experiment was helium. We constructed a triple-grating spectrograph with a focal length of 200 mm and three diffractive gratings of 1800 grooves/mm. The light source was the second harmonic of a Nd:YAG laser (532 nm). The spectrum of the scattered laser light was recorded using an ICCD camera working at the photon-counting mode. The electron temperature observed experimentally ranged between 1 and 2.5 eV even when the plasmas were produced at pressures up to 0.3 MP. On the other hand, the gas temperature, which was evaluated from the optical emission spectrum of impurity OH, was lower than 1800 K. Therefore, we have confirmed that a nonequilibrium plasma can be produced in helium at pressures higher than the pressure of atmosphere. [Preview Abstract] |
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CT1.00045: Fluid modelling of the influence of the pulse width in N2-O2 barrier discharges M.M. Becker, R. Brandenburg, H. H\"{o}ft, M. Kettlitz, D. Loffhagen Recently, experimental investigations on pulsed driven dielectric barrier discharges in N2-O2 gas mixtures at atmospheric pressure have revealed that the time between subsequent microdischarges influences the discharge characteristics significantly (M. Kettlitz et al., J. Phys. D: Appl. Phys. 45:245201, 2012). Here, the influence of the pulse width in the range from 5 to 50$\, \mu$s on the particle densities and on the most important reaction kinetic processes in a gas mixture of 0.1 vol\% O2 in N2 is analysed. The studies are performed by means of a time-dependent, spatially one-dimensional fluid model taking into account balance equations for the densities of all relevant species and the mean electron energy, Poisson's equation as well as an equation for the surface charge density on the dielectrics. It is shown that in accordance with measurements the model predicts different current-voltage characteristics at the rising and the falling slope of the voltage pulse if the duty cycle is decreased from 50\% to 10\%. With decreasing pulse width the current maximum at the falling slope also decreases. It is confirmed by the theoretical investigations that for short pulse widths the charge carriers left in the gap play an important role in the reignition dynamics. [Preview Abstract] |
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CT1.00046: Investigating streamer to spark transition in supercritical N2 Aram H. Markosyan, Jin Zhang, Bert Van Heesch, Ute Ebert We simulate the thermal shock and the induced pressure waves caused by electrical breakdown of supercritical nitrogen. We investigate the temperature evolution after breakdown, thus predicting the recovery rate of a plasma switch based on supercritical liquids. The system of fluid equations is used to obtain the spatial and temporal evolution of liquid density, pressure, velocity and energy. We compare simulation and experimental results. [Preview Abstract] |
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CT1.00047: Electromagnetic Simulation of Long-Slotted Waveguide Antenna for Production of Meter-Scale Plasma under Atmospheric Pressure Haruka Suzuki, Suguru Nakano, Hitoshi Itoh, Makoto Sekine, Masaru Hori, Hirotaka Toyoda Atmospheric pressure plasmas have been given much attention because of its high cost performance and a variety of possibilities for industrial applications. In various kinds of plasma production techniques such as corona discharge, DBD, pulsed-microwave discharge plasma using slot antenna is attractive due to its ability of high-density plasma production. In this plasma source, however, size of the plasma has been limited up to a few cm in length due to its plasma production mechanism and increase in the plasma size was difficult. In this study, we have successfully increased the length of the slot-antenna plasma source up to 0.7 m by microwave power flow control inside the waveguide. In this plasma source, reflected power that induces standing wave is suppressed and long plasma is produced only by traveling waves inside a long slot. Three-dimensional electromagnetic field simulation is conducted and spatial slight fluctuation of the microwave power, i.e., standing wave, caused by slight reflection power at the end of the long slot antenna is investigated from the simulated result. Relation between spatial fluctuation of the microwave power and the emission intensity will be discussed. [Preview Abstract] |
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CT1.00048: The properties of isolated streamer discharges Jannis Teunissen, Ute Ebert We aim to understand how the basic properties of positive streamer discharges, such as their radius or velocity, depend on the discharge conditions. We systematically explore these properties by doing many simulations under different discharge conditions. The electric field, gas mixture, initial discharge seed and the source of free electrons are varied. The simulations are performed with a fluid model, assuming cylindrical symmetry. To eliminate effects from boundaries, we use a free-space field solver. We compare our results with previous studies and with experimental observations. [Preview Abstract] |
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CT1.00049: Development of a Nitrogen DBD-Plasmajet based on Capillary Discharge Design Bernhard Bohlender, Marcus Iberler, Joachim Jacoby This contribution is about a Nitrogen DBD-Plasmajet at atmospheric pressure. APGD (Atmospheric Pressure Gas Discharges) are used, e.g. for the treatment of surfaces. The experiment presented is such an APGD being developed for medical applications like the sterilization of instruments. The setup is an APGD based Plasmajet constructed as a capillary discharge. The capillary is made of Al2O3 with a thickness of 1.05mm. Within the capillary is the inner electrode with a borehole of 1.8mm. The outer diameter of the used capillary is 2.8mm. The outer electrode is attached on top of the capillary with a variable distance to the inner electrode's ending. The inner electrode is connected to a sinusoidal voltage of up to 10kV peak-to-peak amplitude at a frequency of 15kHz. The outer electrode is attached to ground potential. Nitrogen flows through the setup with atmospheric pressure, thus the plasma generated is being pressed out. The next step of the work is to find the resonance frequency of the set up. Simulations of the electrical circuit are performed. In Addition, optical and electrical measurements are planned in order to characterize the plasma parameters. The further development in the future includes a decrease of the size and a panel constructed of 3 to 4 identical capillary discharges to increase the area of the out coming plasma. Founded by BMBF, Willkomm Stiftung, HIC for FAIR [Preview Abstract] |
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CT1.00050: Simulations of pulsed gas breakdown between pin-to-pin electrodes Stepan Eliseev, Vladimir Kolobov, Anatoly Kudryavtsev Peculiarities of gas breakdown depend on many factors including gas type, geometry of electrodes, time-dependence of the applied voltage, etc. Effects of these factors on the breakdown dynamics and transitions from Townsend (diffuse) to streamer mechanisms remain not fully understood. This paper is devoted to simulations of Helium breakdown in a pin-to-pin electrode geometry using recently developed Adaptive Mesh Refinement (AMR) capabilities for plasma simulations [V.I. Kolobov {\&} R.R. Arslanbekov, J. Comput. Physics, 231 (2012) 839]. AMR enables high resolution of ionization fronts with sharp gradients of plasma properties developing on fast (electron) scale. We study dynamics of the breakdown phenomena depending on the voltage wave form (rise time), the product of gas pressure and the distance between the electrodes, and geometry of the electrode tip. Starting from a minimal plasma model (immobile ions, drift-diffusion transport of electrons, local ionization, and Poisson solver), we investigate effects of electron thermal diffusion, and background ionization on the development of ionization fronts. Results of simulations are analyzed using previously developed 1D theory of pulsed breakdown and compared with available experimental data for pulsed gas breakdown in similar geometries. [Preview Abstract] |
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CT1.00051: Time resolved mass spectrometry of positive ions originated from atmospheric-pressure plasma jet Nenad Selakovic, Nevena Puac, Dejan Maletic, Gordana Malovic, Zoran Lj. Petrovic We present time-resolved measurements of positive ions originated from the atmospheric pressure plasma jet (APPJ) by using HIDEN HPR60 mass energy analyzer. APPJ was made of Pyrex glass tube with two transparent electrodes (15~mm wide PET foil). The gap between the electrodes was 15~mm, excitation frequency 80~kHz and applied voltage 6-10~kV$_{peak-to-peak}$. Helium flow rate was kept constant at 4 slm. In all measurements the distance between the plasma source and mass spectrometer orifice was 15~mm. Spectrometer detector gating was synchronized with the applied current and voltage signals in order to track in time the signal of detected ions. The internal gate width of HPR60 analyzer was 0.1 $\mu$s. We performed time resolved mass spectrometry of most abundant ion species originated from plasma jet: N$_{2}^{+}$(36{\%}), N$^{+}$(20{\%}), O$_{2}^{+}$(18.5{\%}), O$^{+}$(16.8{\%}), H$_{2}$O$^{+}$(6.1{\%}), OH$^{+}$, NO$^{+}$, N$_{2}$H$^{+}$ and Ar$^{+}$ (a few percentage). Results have shown that maximum intensity of nitrogen ions is lagging the maximum of current and voltage signal and maximum intensity for oxygen species is in opposite phase with current-voltage signals. [Preview Abstract] |
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CT1.00052: Thermal ionization instability development in air plasma generated by repetitive ns dielectric barrier discharge Andrey Starikovskiy, Mikhael Shneider, Daniil Marinov, Svetlana Starikovskaia The aim of this paper is to study a transformation of a nanosecond discharge under conditions of high repetitive frequency in a barrier configuration of the electrodes. Nanosecond DBDs at atmospheric pressure are widely used for research in plasma medicine. At atmospheric pressure conditions the discharge develops as a set of microchannels bridging a gap between the electrodes covered with dielectric, the current in each microchannel is restricted by charging of a dielectric surface. With pressure decrease, a discharge becomes more uniform, still it is known that a slight change of a gas mixture composition, f.e. add of a fuel, may lead to significant problems with the uniformity. Estimations were made to analyze the possibility of discharge contruction due to thermal ionization instability development. We used the assumption that there is no convective cooling of the gas in the discharge cell. It was shown that NS discharge in DBD geometry is non-uniform. Initial electrical fields distribution and thermal ionization instability development form the non-uniform energy distribution in the discharge. This non-uniformity can play a key role in kinetic experiments in this type of the discharge. [Preview Abstract] |
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CT1.00053: Spreading of atmospheric pressure plasma jet on a dielectric surface Olivier Guaitella, Emeric Foucher, Ana Sobota, Antoine Rousseau Atmospheric pressure plasma jets are intensively studied for their potential application in surface treatment as well as biomedical applications. For both applications fields it is essential to understand the dynamics of a plasma jet impinging onto a surface. In this work a plasma jet source is used in a coaxial geometry with a single dielectric barrier discharge configuration powered at 30 kHz. The impact of the plasma jet on various dielectric plates is monitored directly with fast iCCD imaging. The spreading of the discharge over the surface is analyzed by examining the re-ignition of plasma on the other side of the dielectric plate. Properties of the impinging jet are deduced from the limit of re-ignition of the secondary plasma. Special care has been taken to relate the characteristic of the plasma jet source with the spreading of the jet on the surface. The results exhibit a very interesting dynamics of the spreading of the jet which depends on the energy dissipated in the source but also on the dielectric permittivity of the dielectric plate target as well as the whole configuration surrounding the capillary pipes in which the discharge is propagating. These properties are important for controlling any process involving the use of a plasma jet. [Preview Abstract] |
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CT1.00054: The effect of heating mode transition on the electron energy probability function through the variation of driving frequency Jung Yeol Lee, Hyowon Bae, Hae June Lee, John Verboncoeur During the last two decades, a number of applications such as a plasma display, surface treatment, and bio-medical devices~utilized sub-millimeter atmospheric pressure plasmas. Among them, the dielectric barrier discharge (DBD) is widely used as the simplest device which can sustain abnormal glow discharge with a micro-sized gap length. In this study, a particle-in-cell (PIC) simulation was selected to understand the discharge characteristics of a planar micro DBD with an input frequency from 13.56 MHz to 600 MHz. Along with two different heating modes, the alpha and the gamma mode, the sheath heating by secondary electron emission plays an important role for DBDs. The electron energy probability function (EEPF) shows a bi-Maxwellian profile in gamma mode. On the other hand, Ohmic heating is more dominant for electron temperature in alpha mode, and the increment of input frequency changes the ratio of secondary electron current to the total current through the relationship between the ion transit time and the driving period. Therefore, the transition mechanism of the EEPF in DBDs is very different from that of low pressure capacitively coupled plasmas. It means that it is possible to control the interactions between plasmas and neutral gas for the generation of preferable radicals by the variation of input frequency through the change of heating mode. [Preview Abstract] |
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CT1.00055: Dynamics of pulsed laser ablation plasmas in high-density CO$_{2}$ near the critical point investigated by time-resolved shadowgraph imaging Keiichiro Urabe, Toru Kato, Shohei Himeno, Satoshi Kato, Sven Stauss, Motoyoshi Baba, Tohru Suemoto, Kazuo Terashima Pulsed laser ablation (PLA) plasmas generated in high-density gases and liquids are promising for the synthesis of nanomaterials. However, the characteristics of such plasmas are still not well understood. In order to improve the understandings of PLA plasmas in high-density fluids including gases, liquids, and supercritical fluids (SCFs), we have investigated the dynamics of PLA plasmas in high-density carbon dioxide (CO$_{2})$. We report on experimental results of time-resolved shadowgraph imaging, from the generation of plasma plume to the extinction of cavitation bubbles. Shadowgraph images revealed that the PLA plasma dynamics showed two distinct behaviors. These are divided by gas-liquid coexistence curve and the so-called Widom line, which separates gas-like and liquid-like SCF domains. Furthermore, cavitation bubble observed in liquid CO$_{2}$ near the critical point showed peculiar characteristics, the formation of an inner bubble and an outer shell structure, which so far has never been reported. The experiments indicate that thermophysical properties of PLA plasmas can be tuned by controlling solvent temperature and pressure around the critical point, which may be useful for materials processing. [Preview Abstract] |
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CT1.00056: PLASMAS IN LIQUIDS |
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CT1.00057: Breakdown Voltage Scaling in Gas Bubbles Immersed in Liquid Water Sarah Gucker, Bradley Sommers, John Foster Radicals produced by the interaction of plasma with liquid water have the capacity to rapidly oxidize organic contaminants. This interaction is currently being investigated as a means to purify water. Direct plasma creation in water typically requires very high voltages to achieve breakdown. Igniting plasma in individual gas bubbles in liquid water on the other hand requires much less voltage. Furthermore, the use of an electrode-less plasma initiation in such bubbles is attractive in that it eliminates electrode erosion thereby circumventing the contamination issue. The breakdown physics of isolated bubbles in liquid water is still poorly understood. In this work, we investigate the relationship between applied voltage for breakdown and the associated pd. This is achieved by locating the breakdown voltage over a range of bubble sizes. This approach allows for the generation of a Paschen-type breakdown curve for isolated bubbles. Such a relationship yields insight into breakdown mechanics and even streamer propagation through water. [Preview Abstract] |
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CT1.00058: Influence of gas and liquid condition on characteristics of self-organized pattern formation observed in atmospheric DC glow discharge Naoki Shirai, Hiroyuki Hirahara, Satoshi Uchida, Fumiyoshi Tochikubo Self-organized anode patterns were observed on the surface of a liquid anode when an atmospheric dc glow discharge with helium flow was generated. The pattern formation depends on current, gap length, and helium flow rate. With increasing discharge current or gap length, an anode luminous spot changed to self-organized patterns. Anode pattern formation also depends on liquid conductivity. Although the mechanisms of this pattern formation have not understood completely, we assume that the patterns depend on electronegative gas in the gap and temperature of liquid anode. In this study, we investigate anode pattern formation of the discharge by changing gas condition around the discharge and liquid temperature. When mole fraction rate of oxygen or carbon dioxide is increased, pattern formation is observed. On the other hand, when mole fraction rate of nitrogen is increased, pattern is not observed. If liquid temperature increases, pattern formation changes from dot pattern to stripe pattern. [Preview Abstract] |
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CT1.00059: Global modeling of micro plasma discharge in deionized water Soham S. Mujumdar, Davide Curreli, Shiv G. Kapoor, David Ruzic One of the major applications of plasmas in liquids is the micro electro-discharge machining process ($\mu$-EDM) where the material from one of the electrodes is removed by creating repeated pulsed plasma discharges in the inter-electrode gap filled with a dielectric liquid. One of the most commonly used dielectric for the process is deionized water. A model of a single plasma discharge event in deionized water during the $\mu$-EDM process is presented in this paper. The plasma is modeled using a global modeling approach where the plasma is assumed to be spatially uniform, and equations of mass and energy conservation are solved together in conjunction with the expanding plasma bubble dynamics. The model is simulated for different combinations of the applied electric field and the discharge gap distance to obtain complete temporal characterization of the H$_2$O plasma in terms of the composition of the plasma, temperature of the plasma and the radius of the plasma bubble. The model predicts time-averaged plasma temperature in the range of 12282-29572~K and electron density in the range of $5.12 - 30.22 \times 10^{24}$~m$^{-3}$ for applied electric fields in the range of 10 - 2000 MV/m and discharge gaps in the range of 0.5 - 20 $\mu$m. [Preview Abstract] |
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CT1.00060: PLASMA APPLICATIONS |
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CT1.00061: Characterization of Laser Produced Underwater Plasma L. Huwel, R. Haydar, T.J. Morgan, W.G. Graham Optical breakdown in water created by 10 ns pulsed Nd:YAG laser operating at $\lambda =$1064 nm was studied. Spatial and temporal information was obtained with two intensified CCD cameras while spectral data were recorded using a time-integrating spectrometer. We have studied three water samples with different impurity content (ultra-pure, distilled, and tap water) and followed the plasma evolution over a timespan of a few hundred nanoseconds. Images taken by the two synchronized cameras, systematically delayed relative to each other, show that the ``center of emission intensity'' in single plasma events moves toward the incoming laser beam. The emission is dominated by a broad, blackbody-like spectral feature with corresponding temperature of ca. 20000 K. Superimposed is a weak hydrogen Balmer-alpha line with a full width at half maximum exceeding 50 nm in some cases. Interpreted as purely Stark broadened, this width corresponds to electron densities well above 10$^{\mathrm{19}}$ cm$^{\mathrm{-3}}$. [Preview Abstract] |
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CT1.00062: Development of A Pulse Radio-Frequency Plasma Jet Shou-Guo Wang, Ling-Li Zhao, Jing-Hua Yang A small pulse plasma jet was driven by new developed radio-frequency (RF) power supply of 6.78 MHz. In contrast to the conventional RF 13.56 MHz atmospheric pressure plasma jet (APPJ), the power supply was highly simplified by eliminating the matching unit of the RF power supply and using a new circuit, moreover, a pulse controller was added to the circuit to produce the pulse discharge. The plasma jet was operated in a capacitively coupled manner and exhibited low power requirement of 5 W at atmospheric pressure using argon as a carrier gas. The pulse plasma plume temperature remained at less than 45 $^{\circ}$C for an extended period of operation without using water to cool the electrodes. Optical emission spectrum measured at a wide range of 200--1000 nm indicated various excited species which were helpful in applying the plasma jet for surface sterilization to human skin or other sensitive materials. [Preview Abstract] |
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CT1.00063: Pulsed Nanosecond Discharge Development in Liquids with Various Dielectric Permittivity Constants Andrey Starikovskiy The dynamics of pulsed nanosecond discharge development in liquid water, ethanol and hexane were investigated experimentally. High-voltage pulses with durations of 20 and 60 ns and amplitudes of 6-60 kV were used for discharge initiation. It is shown that the dynamics of discharge formation fundamentally differ between liquids with low and high dielectric permittivity coefficients. In water (high permittivity), two phases were observed in the process of the discharge development. The first phase is connected with electrostriction compression of the media near the needle tip and the formation of a rarefaction wave in the surrounding liquid. The second phase (the discharge phase) has a pronounced start delay, which depends on the voltage of the high-voltage electrode. Unlike in water, the first phase is essentially non-existent in liquids with low dielectric permittivity coefficients because of the small electrostriction forces and the low intensity of the rarefaction wave that is formed. The second phase in the process (discharge) begins at significantly higher voltages on the high-voltage electrode, immediately leading to the long branched structure of the streamer-leader flash. [Preview Abstract] |
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CT1.00064: Surface modification of fibers by conducting polymers and their use in composites Hande Yavuz, Gregory Girard, Jinbo Bai Due to the discovery of their incredible functional properties, carbon nanotubes (CNTs) have drawn a great deal of interest from both academic and industrial research teams in the past few years. Since novel materials are to be integrated in structural and functional applications in several fields, inclusion of CNTs as a reinforcement component in polymer matrix composites (PMC) could bring new solutions. However, in order to obtain more advanced CNTs composites, the amount of strong bonding between CNTs and matrix must be realized to ensure the effective stress transfer in a PMC. This research aims to establish an efficient dielectric barrier discharge technique for the surface modification of CNTs grafted carbon fibers (CNTs-CF) with plasma polypyrrole (PPPy) in order to be used in PMC. It is found that response surface methodology can be applicable in modeling to evaluate the effects of important process variables on electrical resistivity of CNTs-CF. From low to high plasma powers, X-ray Photoelectron Spectroscopy studies revealed the loss of $\alpha $- and $\beta $-carbons in pyrrole ring. The higher the plasma power the lower the electrical conductivity and the higher the mechanical properties. [Preview Abstract] |
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CT1.00065: Space -- time evolution of low-pressure H2 plasma induced by runaway photoelectrons produced by KrF laser pulse Alexey Zotovich, Andrey Volynets, Dmitry Lopaev, Sergey Zyryanov, Konstantin Koshelev, Vladimir Krivtsun, Dmitry Astakhov Extreme Ultraviolet Lithography (EUVL) at 13.5 nm is expected to provide the next generation of ULSI. One of hot EUVL problems is contamination of EUV multilayer optics that compels to search methods of in-situ cleaning. The most promising method is to apply H2 plasma generated over the mirror surface by itself EUV radiation. Therefore investigations of EUV-induced plasma are of great interest for developing such cleaning technology. To model evolution of EUV-induced plasma, the study of H2 plasma induced by photoelectrons extracted from a surface by KrF laser pulse has been done. The experiment was carried out by the space-time resolved probe technique while the analysis was made with using plasma model based on 2D PIC MC code as for electrons and for ions. Comparison of experimental and calculated evolution of probe characteristics provided correct applicability of the probe theory and allowed revealing key mechanisms and parameters which control the evolution of photoelectrons-induced plasma. [Preview Abstract] |
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CT1.00066: GREEN PLASMA TECHNOLOGIES: ENVIRONMENTAL AND ENERGY APPLICATIONS |
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CT1.00067: Flame generation and maintenance by non-stationary discharge in mixture of air and natural gas Henrique de Souza Medeiros, Julio Sagas, Pedro Lacava Plasma assisted combustion is a promising research field, where the high generation of reactive species by non-equilibrium plasmas is used to modify the combustion kinetics in order to improve the process either by increasing the production of specific species (like molecular hydrogen) or by decreasing pollutant emission. One typical issue observed in plasma assisted combustion is the increase of inflammability limits, i.e the observation of combustion and flame in situation where it is not observed in conventional combustion. To study the effect of a non-stationary discharge in flame generation and maintenance in a mixture for air and natural gas, the air mass flow rate was fixed in 0.80 g/s and the natural gas flow rate was varied between 0.02 and 0.14 g/s, resulting in a variation of equivalence ratio from 0.4 to 3.0. It is observed a dependence of inflammability limits with the applied power. The analysis by mass spectrometry indicates that the increase of inflammability limits with plasma is due not only applied power, but also to hydrogen production in the discharge. Visual analysis together with high speed camera measurements show a modification in spatial distribution of the flame, probably due to modifications both in flow velocity and flame velocity. [Preview Abstract] |
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CT1.00068: Decolorization of azodyes using the atmospheric pressure plasma jet Sasa Lazovic, Dejan Maletic, Natasa Tomic, Gordana Malovic, Uros Cvelbar, Zorana Dohcevic-Mitrovic, Zoran Lj. Petrovic Atmospheric pressure plasma jet operated in air/argon mixture is tested for decolorization of Bezactiv Orange V-3R dye used in the textile industry. The decolorization efficiency is determined by spectrophotometric measurements at 493.7 nm which corresponds to the breaking of dye N$=$N bond. The initial concentration of 50~mg/L of dye is reduced 50 times after 120 minutes of treatment by plasma. The results are compared to the efficiency of the suspended TiO$_{2}$ powder and activated by an UV lamp (300~W). The radicals responsible for removal of the dye are OH and super-anion radical. It is found that efficiency of the plasma and TiO$_{2}+$ UV is quite similar for the treatment times up to 60 min. After that, TiO$_{2}$ shows higher decolorization rates (100 times reduction after 90 min). However, when plasma and TiO$_{2}$ (but without the UV lamp) are applied together, it is found that there are synergetic effects and that the efficiency is increased. Plasma (less than 2 W) is not expected to produce high amounts of UV light in the atmospheric pressure. [Preview Abstract] |
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CT1.00069: Numerical modeling of CF4 decomposition in low pressure inductively coupled plasma: influence of the O2 concentration Mahsa Setareh, Morteza Farnia, Ali Maghari, Annemie Bogaerts Perfluorinated compounds (PFCs), which are stable and difficult to decompose, are widely utilized in microelectronic manufacturing. The global warming potential of PFCs is so high in comparison with CO$_{2}$ that finding a solution for abating PFC emission is crucial. For this purpose, we performed a numerical simulation of the CF$_{4}$ decomposition in an inductively coupled plasma reactor with radio frequency power supply, which is used in semiconductor chamber cleaning process. A zero dimensional modeling code Global\textunderscore kin developed by Kushner is applied to model the reaction set of CF$_{4}$/O$_{2}$ in typical plasma reactor conditions, such as 2kW power with frequency of 4 MHz, a pressure of 600 mTorr, and a typical residence time of 0.25 s. The model predicts that the reaction products of the CF$_{4}$ decomposition are mostly COF$_{2}$, CO$_{2}$ and CO. COF$_{2}$ is a toxic compound, but it can be hydrolyzed easily into HF and CO$_{2}$ using the scrubber in the reactor. By carefully altering the ratio between CF$_{4}$/O$_{2}$, the optimum ratio of the CF$_{4}$/O$_{2}$ gas mixture can be achieved, leading to more than 80{\%} of CF$_{4}$ decomposition. The numerical modeling results for CF$_{4}$ decomposition are validated based on experimental data from literature. [Preview Abstract] |
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CT1.00070: Plasmas in conducting solutions for treatment of contaminated water Colin Kelsey, Bill Graham, Ahmad Mashal, David Rooney, Robert G\'amez Sans A plasma produced in a conducting liquid is compared with more conventional advanced oxidation processes currently used in wastewater treatment such as the Fenton Process. The plasma was produced using a four electrode setup with driving circuitry producing 100 kHz bipolar square waves of approximately 300V. We compare the effectiveness of the two processes by comparing the reduction in chemical oxygen demand achieved by each. Results indicate that for treatment times of 40 seconds our bench system can achieve a 50\% COD reduction across a wide range of input COD concentrations, which is better than the reduction achieved by the single dose Fenton treatment process. Using electrical measurements the efficiency of the plasma process is determined to enable initial estimates of the feasibility of the process for industrial use. Chemical measurements on the plasma system are used to gain insight into the mechanisms underlying the process. These measurements include hydrogen peroxide production rate, which was determined to be 0.5 mg per minute, pH change, which increases with time, but tended to values of 1-3 pH units for characteristic treatment times, and temperature. [Preview Abstract] |
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CT1.00071: Optimization of Industrial Ozone Generation with Pulsed Power Jose Lopez, Daniel Guerrero, Alfred Freilich, Luca Ramoino Ozone (O3) is widely used for applications ranging from various industrial chemical synthesis processes to large-scale water treatment. The consequent surge in world-wide demand has brought about the requirement for ozone generation at the rate of several hundreds grams per kilowatt hour (g/kWh). For many years, ozone has been generated by means of dielectric barrier discharges (DBD), where a high-energy electric field between two electrodes separated by a dielectric and gap containing pure oxygen or air produce various microplasmas. The resultant microplasmas provide sufficient energy to dissociate the oxygen molecules while allowing the proper energetics channels for the formation of ozone. This presentation will review the current power schemes used for large-scale ozone generation and explore the use of high-voltage nanosecond pulses with reduced electric fields. The created microplasmas in a high reduced electric field are expected to be more efficient for ozone generation. This is confirmed with the current results of this work which observed that the efficiency of ozone generation increases by over eight time when the rise time and pulse duration are shortened. [Preview Abstract] |
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CT1.00072: Plasma Acid Formation from the Interaction of a Gliding Arc Plasmatron and Water Ryan Robinson, Alexander Gutsol, Alexander Rabinovich, Alexander Fridman Recently there has been an increased interest in hydrogen production and the bio-medical applications from plasma treated water. Research shows that the interaction of non-thermal plasma discharges and water produces an acidic solution. Hydrogen peroxides and nitrates are commonly produced from the interaction depending on the gaseous environment of the plasma. This study investigates the production of a ``plasma acid'' from a water spray through a thermal discharge, provided by a DC gliding arc plasmatron (GAP). This method allows for a continuous processing of water rather than the batch processing of other methods that rely on surface interaction with plasma on a volume of water. Air, oxygen, and nitrogen were used as the carrier gas of the water spray and the tangentially fed gas in the discharge region. The production of nitric acid and peroxide was specifically monitored using methods from pH metering, spectrophotometry, and specialized test strips. From air and nitrogen environments there was a small production of peroxide, and larger concentrations of nitric acid. Oxygen environments produced much larger concentration of peroxide, while marginal amounts of nitric acid. In all of the environments, the absorption spectrums showed the presence of other compounds. [Preview Abstract] |
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CT1.00073: Sputtering deposition of ZnGaInON with tunable bandgap for photovoltaics Ryota Shimizu, Koichi Matsushima, Daisuke Yamashita, Giichiro Uchida, Hyunwoong Seo, Kazunori Koga, Masaharu Shiratani, Naho Itagaki A material having tunable bandgap is required for significant advance in third generation photovoltaics. Here we propose a novel oxynitride semiconductor ZnGaInON(ZGION), that is a mixed crystal of ZnO, GaN, and InN, and has wurtzite crystal structure. [1] It is fabricated by RF magnetron sputtering. The fascinating feature of ZGION is that the bandgap and the carrier density are controlled by changing the chemical composition ratio. The bandgap has been tuned in a wide range from 1.8 eV to 2.7 eV by controlling [In]/([Zn]$+$[Ga]$+$[In]), being ascribed to the narrow bandgap of InN. While the electron carrier density has been reduced from 1.34x1021 cm$^{-3}$ to 7.61x1020 cm$^{-3}$ by increasing [Ga]/([Zn]$+$[Ga]$+$[In]), suggesting that Ga ions play important roles in suppression of carrier generation via anion vacancy formation. These results indicate that ZGION is a potential material for photovoltaics.\\[4pt] [1] N. Itagaki, et al., ``Oxynitride semiconductor,'' U.S. Patent No. 8274078 (2012). [Preview Abstract] |
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CT1.00074: PLASMA PROPULSION AND AERODYNAMICS |
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CT1.00075: The PEGASES gridded ion-ion thruster physics, performance and predictions Ane Aanesland, Dmytro Rafalskyi, Jerome Bredin, Pascaline Grondein, Noureddine Oudini, Pascal Chabert The PEGASES (Plasma propulsion with Electronegative gases) thruster is a gridded ion thruster that accelerates alternately positively and negatively charged ions to provide thrust. Over the last years various prototypes have been tested, adequate diagnostics have been developed and analytical models and simulations are made to better understand and control the physics involved. The plasma density in the region of the ion-ion plasma predicts that the performance of the PEGASES thruster can be comparable to existing thrusters on the market. We have recently provided the first experimental proof-of-concept, accelerating alternately positive and negative ions from an ion-ion plasma within a 10 kHz cycle. Here we present the state of the art in the PEGASES development and discuss the various physics involved and its possible future in space. [Preview Abstract] |
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CT1.00076: Pulsed plasma thruster by applied a high current hollow cathode discharge Masayuki Watanabe The pulsed plasma thruster applied by a high current hollow cathode discharge has been investigated. In this research, the pseudo-spark discharge (PSD), which is a one of a pulsed high current hollow cathode discharge, is applied to the plasma thruster. In PSD, the opposite surfaces of the anode and cathode have a small circular hole and the cathode has a cylindrical cavity behind the circular hole. To generate the high speed plasma flow, the diameter of the anode hole is enlarged as compared with that of the cathode hole. As a result, the plasma is accelerated by a combination of an electro-magnetic force and a thermo-dynamic force inside a cathode cavity. For the improvement of the plasma jet characteristic, the magnetic field is also applied to the plasma jet. To magnetize the plasma jet, the external magnetic field is directly induced nearby the electrode holes. Consequently, the plasma jet is accelerated with the self-azimuthal magnetic field. With the magnetic field, the temperature and the density of the plasma jet were around 5 eV and in the order of 10 19 m$^{-3}$. The density increased several times as compared with that without the magnetic field. [Preview Abstract] |
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CT1.00077: Analysis of the potential oscillation in Hall thrusters with a two-dimensional particle-in-cell simulation parallelized with graphic processing units Min Young Hur, Ho-Jun Lee, Hae June Lee, Won Ho Choe, Jong Ho Seon Oscillations of the plasma potential have been observed in many Hall thruster experiments. It was estimated that the oscillations are triggered by the interaction between the plasma and the dielectric materials such as secondary electron emission, but detailed mechanism has not been proven. In this paper, the effects of the interaction between the plasma and dielectric material are simulated with a two-dimensional particle-in-cell (PIC) code for the acceleration channel of the hall thruster. Especially, the simulation code is parallelized using graphic processing units (GPUs). To analyze the effect, the simulation is confirmed to change following two parameters, magnetic flux density and secondary electron emission coefficient (SEEC). The particle trajectory is presented with the variation of the SEEC and magnetic flux density as well as its curvature. [Preview Abstract] |
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CT1.00078: Simulation of electrospray cone-jet mode for electric propulsion applications Manish Jugroot, Martin Forget Understanding the space and time-dependant dynamics of the initiation of electrosprays is highly interesting especially for highly conductive fluids. A multi-component model, coupling fluid dynamics, charged species dynamics and electric field is applied to flows in capillaries and externally-wetted needles. The simulations describe the charged fluid interface with emphasis on cone-jet transition under the effect of an electric field. The time evolution capture of the interface highlights the close interaction among space charge, coulombic forces and the surface tension in the small scale flows. Droplet, cone-jet and ion modes will be discussed with potential applications to colloid electric spacecraft propulsion. [Preview Abstract] |
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CT1.00079: Efficiency of plasma density control with dc discharge and magnetic field for different surface types in low pressure hypersonic flow Irina Schweigert Recently the problem of communication blackout during reentrant flight still remains unsolved. The spacecrafts enter the upper atmospheric layers with a hypersonic speed and the shock heated air around them becomes weakly ionized. The gas ionization behind the shock front is associative in nature and occurs through chemical reactions between fragments of molecules [1]. The formation of a plasma layer near the surfaces of spacecraft causes serious problems related to the blocking of communication channels with the Earth and other spacecrafts. A promising way of restoring the radio communications is the application of electrical and magnetic fields for controlling the plasma layer parameters [2]. Nevertheless the flux of electrons and ions on the surface charges it that essentially decrease the effect of electro-magnetic control of local plasma density. In Ref.[3] it is shown that there is the way to remove the surface charge using the lateral diode string structures. Based on two dimensional kinetic Particle in cell Monte Carlo collision simulations, we study the possibility of local control the plasma layer parameters near a flat surface of two different types. The gas velocity distribution is set with a model profile. We apply DC voltage up to 4 kV and magnetic field B up to 200 G. 1. I.D. Boyd (2007). \textit{Phys. Fluids} 19, 096102\textunderscore 1. 2. M. Keidar, M. Kim, I. D. Boyd (2008). \textit{J. Spacecr. Rockets} 45, 445. 3. \textbf{A. Starikovskiy, R. Miles, }AIAA Meeting (Dallas, USA, January 2013) paper N2013-0754 [Preview Abstract] |
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CT1.00080: Dielectric barrier discharge control and thrust enhancement by diode surface Andrey Starikovskiy, Martiqua Post, Nickolas Tkach, Richard Miles The problem of the charge removal is very simple: we need a surface which will conduct the current in one direction and will have high resistance in another to avoid the leakage during the forward discharge development. Lateral diode string structures were designed and successfully manufactured on a 3-inch 4H-SiC semi-insulating wafer. The experiments with direct thrust measurements at low pressure conditions were performed as well as experiments of jet formation at pressure P $=$ 1 atm. It was shown that the plasma conductivity is limiting the charge transfer through the surface. The minimal pulse width value could be estimated as a plasma recombination time. The surface becomes effective suppressor for the reverse breakdown when the conductivity of plasma layer is small enough with compare to the surface conductivity. It means that the reverse breakdown with nanosecond-range delay removes efficiently all surface charges. Effective flow acceleration using diode surface is possible with long pulses with allow full plasma recombination between leading and trailing pulse fronts. [Preview Abstract] |
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CT1.00081: Time-Resolved Laser-Induced Fluorescence Measurements of the Ion Velocity Distribution in the H6 Hall Thruster Plume Christopher Durot, Alec Gallimore We developed a technique to measure time-resolved laser-induced fluorescence signals in plasma sources that have a relatively constant spectrum of oscillations in steady-state operation but are not periodically pulsed, such as Hall thrusters. We present the first results using the new technique to capture oscillations in a Hall Thruster. The ion velocity distribution function in the plume of the H6 Hall thruster is interrogated during breathing mode oscillations. The breathing mode is characterized by an oscillating depletion and replenishment of neutrals at a frequency of about 10-25 kHz. We use laser modulation on the order of megahertz, well above the time scale of interest (about 0.1 ms). Band-pass filtering and phase-sensitive detection (with a time constant on the order of microseconds) raise the signal-to-noise ratio and demodulate the signal while preserving time-resolved information. Following phase-sensitive detection, we average over transfer functions to finish recovering the signal. This technique has advantages such as a shorter dwell time than other techniques and the lack of a need for triggering for averaging in the time domain. [Preview Abstract] |
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CT1.00082: Successful experiments on an external MHD Accelerator: wall confinement of the plasma, annihilation of the electrothermal instability by magnetic gradient inversion, creation of a stable spiral current pattern Jean-Pierre Petit, Jean-Christophe Dore MHD propulsion has been extensively studied since the fifties. To shift from propulsion to an MHD Aerodyne, one only needs to accelerate the air externally, along its outer skin, using Lorentz forces. We present a set of successful experiments, obtained around a model, placed in low density air. We successfully dealt with various problems: wall confinement of two-temperature plasma obtained by inversion of the magnetic pressure gradient, annihilation of the Velikhov electrothermal instability by magnetic confinement of the streamers, establishment of a stable spiral distribution of the current, obtained by an original method. Another direction of research is devoted to the study of an MHD-controlled inlet which, coupled with a turbofan engine and implying an MHD-bypass system, would extend the flight domain to hypersonic conditions. [Preview Abstract] |
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CT1.00083: Airflows Induced by Asymmetric Bipolar Voltage Pulses in Dielectric Barrier Discharge Plasma Actuator Junya Suzuki, Masanori Deguchi, Yoshinori Takao, Koji Eriguchi, Kouichi Ono Dielectric barrier discharge (DBD) plasma actuators have recently been intensively studied for the flow control over airfoils and turbine blades in the fields of aerospace and aeromechanics. The unidirectional gas flow (main flow) is assumed to be induced by the electrohydrodynamic (EHD) body force, where the ambient gas flows are also induced, depending on operating parameters of the discharge such as voltage waveform and amplitude, electrode size and configuration, and dielectric thickness and permittivity. This paper presents experimental studies of airflows in DBD plasma actuators, induced by employing asymmetric bipolar voltage pulses. Schlieren and ICCD imaging exhibited that a variety of flows such as a reverse directional flow, a vortex flow, and a combination of them occur at the opposite side of the main flow, which correlates with the dynamic behavior of DBD plasmas being established. [Preview Abstract] |
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CT1.00084: Initial Experiments of a New Permanent Magnet Helicon Thruster J.P. Sheehan, Benjamin Longmier A new design for a permanent magnet helicon thruster is presented. Its small plasma volume ($\sim$10 cm$^{-3}$) and low power requirements ($<$100 W) make it ideal for propelling nanosatellites ($<$10 kg). The magnetic field reached a maximum of 500 G in the throat of a converging-diverging nozzle and decreased to 0.5 G, the strength of earth's magnetic field, within 50 cm allowing the entire exhaust plume to develop in the vacuum chamber without being affected by the chamber walls. Low gas flow rates ($\sim$4 sccm) and high pumping speeds ($\sim$10,000 l/s) were used to more closely approximate the conditions of space. A parametric study of the thruster operational parameters was performed to determine its capabilities as both a thruster and as a plasma source for magnetic nozzle experiments. The plasma density, electron temperature, and plasma potential were measured in the plume to characterize the ion acceleration mechanism. [Preview Abstract] |
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CT1.00085: Fluid simulation of a xenon microwave plasma cathode: focus on electron current avalaible and its extraction Laurent Liard, Yu Zhu, Gerjan Hagelaar, Jean-Pierre Boeuf Electron sources are a major part of electric propulsion systems, for neutralization of ion beams. Recently, different plasma sources have been investigated as possible alternative cathodes. We presented here a 2D fluid simulation of resonant cavity microwave plasma which has shown promising results [1]. The resonant part of the cylindrical cavity eases the plasma breakdown, and the plasma is then sustained by the microwave through a dielectric. The fluid code has been extensively described in [2]. Results show typical working conditions, and stress the maximum electron current that could be extracted from this kind of discharge, given an absorbed power. Results on the extraction aperture dimensions, and its effect on the actual current obtained are also commented. \\[4pt] [1] K. D. Diamant, IEEE Trans. On Plasma Sci. 37.8, p. 1558 (2009)\\[0pt] [2] Hagelaar, G. J. M., Makasheva, K., Garrigues, L. and Boeuf, J.-P. \textit{J. Phys. D: Appl. Phys.} \textbf{42 }(2009) 194019 [Preview Abstract] |
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CT1.00086: GAS PHASE PLASMA CHEMISTRY |
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CT1.00087: Positive {\&} negative streamers in uniform dielectric barrier discharge in atmospheric air Chong Liu, Alexander Fridman, Danil Dobrynin One of the most promising and exciting applications of atmospheric air plasmas is medicine. Nanosecond-pulsed Dielectric Barrier Discharge is uniquely suited because, on the one hand, it can be applied directly to the biological target delivering all active species that non-equilibrium plasma can produce, and it produces highly uniform plasma independently of the features of the biological target which permits effective characterization and control of the plasma. Currently, there is no adequate model of the uniform dielectric barrier discharge development in atmospheric air. Here we show that DBD uniformity strongly depends on applied electric field in the discharge gap. We show that the discharge uniformity may be achieved in the case when : 1) strong over voltage (provided by fast rise times), when positive streamers are formed, and 2) short pulse duration that prevents discharge overheating due to rising conductivity which leads to formation of filaments. In the case of strong over voltage on the discharge gap, there is transition from filamentary to uniform DBD mode which may be fundamentally explained by transition from positive to negative streamers. [Preview Abstract] |
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CT1.00088: Ion and atomic species produced in large scale oxygen plasma used for treatments sensitive materials Kosta Spasic, Nikola Skoro, Nevena Puac, Gordana Malovic, Zoran Lj. Petrovic Asymmetric CCP plasma system operating at 13.56~MHz was successfully used for treatments of textile, seeds and polymers. Central electrode (aluminium rod) was powered electrode while the cylindrical wall of the chamber was grounded electrode. We have used mass spectrometry for detections of ions and neutrals in order to get better insight in plasma chemistry involved in surface reactions on treated samples. Besides of ions, one of the important species for surface modifications is atomic oxygen. Actinometry was used as an additional diagnostic tool to determine the extent of atomic oxygen produced in plasma. Measurements were made in several different mixtures of oxygen with addition of several percent of argon. The range of pressures investigated was 150 to 450~mTorr for powers from 100 to 500~W. Measured atomic oxygen density has a steady rise with power (10$^{\mathrm{19}}$-10$^{\mathrm{20}}$~m$^{\mathrm{-3}})$. Apart from atomic oxygen species we have detected mass spectra of positive and negative ions. Most abundant ion was O$_{\mathrm{2}}^{\mathrm{+}}$ while the amounts of O$^{\mathrm{+}}$ and O$^{\mathrm{-}}$ were smaller by the order of magnitude compared to O$_{\mathrm{2}}^{\mathrm{+}}$. [Preview Abstract] |
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CT1.00089: Ignition in Ethanol-Containing Mixtures after Nanosecond Discharge Ilya Kosarev, Aleksandr Pakhomov, Svetlana Kindysheva, Nikolay Aleksandrov, Andrey Starikovskiy We study experimentally and numerically kinetics of ethanol ignition after a high-voltage nanosecond discharge. Active particles are produced in a high--voltage nanosecond discharge to favor the ignition of C$_{2}$H$_{5}$OH-containing mixtures at elevated gas temperatures. We consider stoichiometric ($\varphi =$ 1) and lean ($\varphi =$ 0.5) C$_{2}$H$_{5}$OH:O$_{2}$ mixtures (10{\%}) diluted with Ar (90{\%}). The gas temperature behind a reflected shock wave ranges from 1100 to 2000 K and the corresponding pressure ranges from 0.2 to 1 atm; these parameters are obtained from measured shock wave velocity. The ignition delay time is measured behind a reflected shock wave with and without the discharge using detection of CH radiation. Generation of the discharge plasma is shown to lead to an order of magnitude decrease in ignition delay time. It is shown that the observed effect of nonequilibrium discharge plasma on ethanol ignition is induced by chain reaction acceleration due to active species generation in the discharge rather than due to fast gas heating. The calculated ignition delay times are compared with the experimental data. [Preview Abstract] |
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CT1.00090: Vapor trapping of evaporated liquids during injection into low pressure plasma John Poulose, Caroline Liu, Daisuke Ogawa, Matthew Goeckner, Lawrence Overzet Liquid injection into low pressure plasma creates a transient change in the gas pressure and plasma properties. Controlling the pressure transient created by evaporation of injected liquids can help reduce unwanted changes in the plasma parameters. We are using an orifice downstream of the liquid injection point to separate the liquid droplets and the evaporated gas from those droplets. Modifying the orifice area to allow droplets to pass through but substantially reduce the conductance of vapor is being tested. The upper chamber, between the injector and main chamber, is utilized to remove the vapor which initially evaporates off the injected droplets through a rough pump. Additionally, controlling the direction of the droplet injection will assist in targeting the liquid directly into the plasma. To this end, a bellows and injector holder/positioner has been attached to a flange providing approximately fifteen degrees of polar rotation. This is will allow the liquid to reach the plasma, with a reduced pressure transient so that the plasma parameters are maintained. In this poster, we will describe the background of the problem, experimental setup, and results. [Preview Abstract] |
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CT1.00091: Syngas production from tar reforming by microwave plasma jet at atmospheric pressure: power supplied influence Henrique de Souza Medeiros, Lucas S. Justiniano, Marcelo P. Gomes, Argemiro Soares da Silva Sobrinho, Gilberto Petraconi Filho Now a day, scientific community is searching for new fuels able to replace fossil fuels with economic and environment gains and biofuel play a relevant rule, mainly for the transport sector. A major process to obtaining such type of renewable resource is biomass gasification. This process has as product a gas mixture containing CO, CH4, and H2 which is named synthesis gas (syngas). However, an undesirable high molecular organic species denominated tar are also produced in this process which must be removed. In this work, results of syngas production via tar reforming in the atmospheric pressure microwave discharge having as parameter the power supply. Argon, (argon + ethanol), and (argon +tar solution) plasma jet were produced by different values of power supplied (from 0.5 KW to 1.5 KW). The plasma compounds were investigated by optical spectroscopy to each power and gas composition. The main species observed in the spectrum are Ar, CN, OII, OIV, OH, H2, H(beta), CO2, CO, and SIII. This last one came from tar. The best value of the power applied to syngas production from tar reforming was verified between 1.0 KW and 1.2 KW. [Preview Abstract] |
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