Bulletin of the American Physical Society
62nd Annual Gaseous Electronics Conference
Volume 54, Number 12
Tuesday–Friday, October 20–23, 2009; Saratoga Springs, New York
Session KTP: Poster Session I (7:00-9:00PM) |
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Room: Saratoga Springs City Center Hall D |
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KTP.00001: GLOWS: DC, PULSED, RF, MICROWAVE, INDUCTIVE, OTHERS |
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KTP.00002: Radial Structure of Normal and Abnormal Modes of the DC glow discharge Valeriy Lisovskiy, Nadiia Kharchenko, Vladimir Yegorenkov As is known dc glow discharge can burn in normal and abnormal modes. The aim of our work was to study the radial distribution of plasma density in both modes. Experiments were performed in the nitrogen pressure range p = 0.1 -- 2 Torr and the dc voltage range U $<$ 600 V. It is shown that in the normal mode the discharge occupies only a part of the cathode area and the current density radial profile has a maximum at the center of the discharge spot and then it goes down rapidly to the border of the spot. With the dc current increasing the radial current density profile becomes broader and it's maximum value higher. The maximum value of the current density approaches a constant ``normal'' value before the transition of the discharge from the normal to the abnormal mode. In the abnormal mode the radial current density has almost a uniform profile across the electrode surface and the average current density increases with the dc current increasing. [Preview Abstract] |
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KTP.00003: Consequences of the local-mean-energy and the local-field approximation on the similarity parameters of abnormal glow discharges Gordon K. Grubert, Markus M. Becker, Detlef Loffhagen The local-mean-energy approximation and the local-field approximation are commonly applied to include the electron properties like transport and rate coefficients into a hydrodynamic description of gas discharge plasmas. Both the approaches base on the solution of the stationary, spatially homogeneous Boltzmann equation for the electron component, but the consequences of these approaches differ drastically. In particular, the similarity parameters of abnormal glow discharges can be used to illustrate the applicability of both the approximations. Additionally, the influence of rough and extended reaction kinetics has been studied. The analysis of discharges in argon and oxygen as representatives of rare and reactive gases, respectively, leads to the conclusion that the local-mean-energy approximation is to be strongly recommended for the application to hydrodynamic descriptions of discharge plasmas. [Preview Abstract] |
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KTP.00004: Line intensities in nitrogen low-pressure microwave discharges L.L. Alves, V. Guerra, C. Lopez, J. Cotrino This paper analyzes the intensity of radiative transitions in nitrogen low-pressure (0.3-0.5 Torr) microwave (2.45GHz) discharges, using both optical emission spectroscopy (OES) measurements and a 0D non-equilibriun kinetic model. The latter solves the homogeneous and stationary electron Boltzmann equation, coupled to the rate balance equations for the N$_{2}$(X, v=1-45) vibrationally excited states, the N$_{2}$(A$^{3}\Sigma _{u}^{+}$, B$^{3}\Pi _{g}$, C$^{3}\Pi _{u}$, a$^{1}\Sigma _{u}$, a$^{1}\Pi _{g}$, w$^{1}\Delta _{u}$, a$^{1}\Sigma _{g}^{+})$ electronic states, the N($^{4}$S, $^{2}$D, $^{2}$P) atomic states, and the N$_{2}^{+}$(X,B) and N$_{4}^{+}$ molecular ions. The plasma is produced by a surface-wave discharge, within an 8mm diameter quartz tube, at $\sim $55W power and $\sim $100mm axial length. The rotational (gas) temperature of the nitrogen plasma ($\sim $ 300-600 K) is experimentally determined from measurements of the band transition with the first positive system [FPS, N$_{2}$(B)--N$_{2}$(A)]. Comparison between simulations and measurements for the line intensity ratio $R$ of the first negative system [FNS-00, N$_{2}^{+}$(B,v=0)--N$_{2}^{+}$(X,v=0) at 391.4 nm] to the second positive system [SPS-25,N2(C,v=2)--N2(B,v=5) at 394.3 nm] are used to estimated the electron density ($\sim $ 10$^{11}$ cm$^{-3})$ and temperature ($\sim $ 3eV). We discuss the calculation of $R$ using different model approximations, analyzing its evolution with variations in the working parameters: electron density, gas pressure, and gas temperature. [Preview Abstract] |
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KTP.00005: Characterization of Electrical Discharges inside the Electron Sheath Yeong-Shin Park, Da-Hae Choi, Kyung-Jae Chung, Yong-Seok Hwang Electron sheath which occurs in front of a small positively biased electrode immersed in pre-existing plasma has been investigated by focusing on the onset voltages of the breakdown in the electron sheath. A model for electron sheath is established and thickness of the sheath is provided. The calculated electron sheath thickness is verified by Langmuir probe diagnostics and particle-in-cell simulation. Outbreak voltages of the breakdown in the electron sheath are gauged at various pressures and powers. Regarding the plasma as a cathode, biased electrode as an anode and electron sheath thickness as a discharge gap respectively, one-dimensional breakdown model is suggested. Applying Townsend's criteria of DC discharge to this breakdown model, a nonlinear equation for breakdown voltages is derived. Comparison of model-based numerical calculations to experimental results shows a good agreement between them. [Preview Abstract] |
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KTP.00006: Investigation of a medium-pressure Xe discharge in pulsed mode Mykhaylo Gnybida, Detlef Loffhagen, Dirk Uhrlandt The pulsed positive column in xenon plasmas at conditions of the contracted discharge has been studied by means of a time-and radial-dependent fluid model. The self-consistent model comprises the particle balance equations for the relevant species, the balance equation of the mean electron energy and the heavy particle temperature in the plasma, the Poisson equation for the radial space-charge potential, and a current balance determining the axial electric field. About 80 collision processes as well as 12 radiative processes are included in the collisional-radiative model. The electron transport and rate coefficients have been applied in dependence on the mean energy of the electrons, heavy particle temperature and ionization degree. Model calculations have been carried out for xenon plasmas in a discharge tube with an inner diameter of 6.5 mm at currents between 60 and 150~mA and pressures from 10 to 50~Torr. The main features of the pulsed xenon discharge at medium pressure are discussed. The results have been compared with experimental data of the axial electric field and of excited xenon atom densities. The agreement is well for the electric field. The model results reproduce the significant increase of low-lying (metastable and resonance) atomic levels densities in the afterglow phase of the pulse, which has also been observed in the experiments. [Preview Abstract] |
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KTP.00007: Long-path breakdown in micro-discharges Nikola \v{S}koro, Dragana Mari\'c, Gordana Malovi\'c, Zoran Lj. Petrovi\'c We report results of our studies of the influence of long-path breakdown to the shape of Paschen curves in micro-discharges. It has often been postulated that any departure from the rapidly rising left hand side of the Paschen curve is an indication of field emission effects with little attention being paid to a possibility of the long path breakdown. For that purpose, we designed complex electrodes that facilitate the long-path breakdown in the left branch of the Paschen curve. Along with the measurements of the breakdown voltages, we recorded emission profiles with ICCD camera, in order to follow the exact path of the discharge. Diameter of the electrodes in our experiment was 2 mm, while the electrode gap was between 500 microns and 1 millimetre. Our results show that the long-path breakdown leads to the shape of the left branch of the Paschen curve, which is either flat or broadened to the lower \textit{pd}-s. Quite often, this shape has been incorrectly attributed to the breakdown of the Paschen law even in standard dimension discharges. We have confirmed that when long path breakdown is possible the left hand side remains more or less constant as long as the effective \textit{d} is not the minimal gap and has enough room to increase. Simulations indicate that when field emission is important the voltage continues to drop rapidly towards smaller \textit{pd}. [Preview Abstract] |
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KTP.00008: Particle-in-cell simulations of electron transport in complex shape dc discharges Alex V. Khrabrov, Igor D. Kaganovich, Yevgeny Raitses, Vladimir I. Demidov, Dmytro Sydorenko A region of dc discharge near cathode, or negative glow, exists in very nonequlibrium state. Three distinct groups of electrons play different roles in discharge self-organization [1]: 1) fast electrons from cathode produce ionization; 2) very cold trapped electrons make up the plasma density; and 3) intermediate electrons conduct the current. These non-equilibrium conditions provide considerable freedom to choose optimal plasma parameters for many applications by controlling electron energy distribution function (EEDF). The EEDF modification is achieved by making use of additional biased electrodes or cathode voltage forms in afterglow [2]. We have performed particle-in-cell simulations in 1 and 2D geometry to demonstrate possible control of EEDF. \\[4pt] [1] V. I. Kolobov and L. D. Tsendin, Phys. Rev. A \textbf{46,} 7837 (1992). \\[0pt] [2] V.I. Demidov, C.A. DeJoseph, and V. Ya. Simonov, Appl. Phys. Lett. \textbf{91}, 201503 (2007). [Preview Abstract] |
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KTP.00009: Coupled plasma and gas dynamics in pulsed microplasmas Manish Jugroot There is a great interest in understanding plasmas in small spaces as the complexity of micro-technology systems increases. A self-consistent model of plasma and neutral gas dynamics is applied to pulsed atmospheric microplasmas in helium. Fluid equations of the self-consistent and time-dependant model are described with emphasis on the close coupling among plasma, neutral gas and the electric field. The microplasmas are studied from an initial cloud and both continuous and recurring voltage pulses are investigated. Gas heating and neutral depletion initiation are observed, highlighting the close interaction between neutral gas and charged species in governing the evolution of the microplasmas. [Preview Abstract] |
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KTP.00010: Models of H$_{\alpha}$ Doppler emission profiles from low-pressure, hollow-cathode discharges in hydrogen A.V. Phelps Calculated Doppler profiles are compared with experiment for the H$_{\alpha}$ line excited in collisions of fast atoms, ions, molecules, and electrons with H$_2$ in low-pressure, high-voltage hollow-cathode hydrogen discharges. We test the proposal of Lavrov and Mel'nikov\footnote{B. P. Lavrov and A. S. Mel'nikov, Optics and Spectrosc. {\bf 79}, 842 (1995).} that their observation of fast H(n=3) moving away from the cathode is the result of acceleration of H$^-$ and its subsequent collisions with H$_2$. Our recent model\footnote{A. V. Phelps, Phys. Rev. E {\bf 79}, 066401 (2009).} is extended to include the kinetics of H$^-$. Because the cathode fall is mostly outside the cylindrical cathode, the cathode is approximated as a nearly transparent planar electrode with an unknown area for reflection of fast H atoms and for production of H$^-$. Calculated Doppler profiles are compared with emission measurements parallel to the tube axis for their wide range of pressures. Using experimental H$^-$ yields, the calculated H$^-$ contribution to the H$_{\alpha}$ wing is significantly smaller than that caused by H atoms reflected by the cathode and comparable with the noise in the measured data. [Preview Abstract] |
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KTP.00011: Factors of Local Plasma Heating near a Target during Pulse Rise Time Jae-Myung Choe, Gon-Ho Kim Factors to heat plasmas during a rise time of pulse on the electrode covered by plasmas are explained. When pulse applies to the target, electrons with energy of several tens eV are detected at an early time. Different from secondary electrons, they can be measured only while sheath expands by a pulse rise and ionized locally near the target. They cause increase of bulk plasma before secondary electrons do and the amount of generated plasmas is larger than the latter, which critically enhances ion flux to the target and blocks sheath expansion at the very beginning of pulse rise. From the measured energy and generation time, gained energy is proportional to a sheath speed expanding from the target and the mechanism can be explained by a Stochastic heating. Experiments are performed in Ar plasma with a pulse voltage of several kV and time-transient and spatial electron energy distributions processed by Wavelet transform algorithm are analyzed for the explanation. [Preview Abstract] |
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KTP.00012: Properties of a differentially pumped constricted hollow electrode plasma source Shantanu Karkari, Mubarak Mujawar The neutral beam injection heating system for ITER requires uniform, high density hydrogen plasma source for the negative hydrogen ion production at 0.3 Pa. In this paper we present a pulsed-dc discharge using a differentially pumped constricted hollow electrode acting as anode and distributed parallel plates acting as cathode. Preliminary investigation shows higher discharge current and lower sustenance voltage by reducing the effective area of the constricted anode. The plasma outside the parallel plates is found to be highly uniform. The electron temperature between the parallel plates is higher than in the bulk plasma which is suitable for the production of negative ions. [Preview Abstract] |
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KTP.00013: Low-pressure plasma discharge of Ar/N$_{2}$/CO$_{2}$ ternary mixture Gerardo Garcia-Cosio, Manuela Calixto-Rodriguez, Horacio Martinez A low-pressure DC plasma discharge sustained in a 1.6{\%}Ar-2.7{\%}N$_{2}$-95.3{\%}CO$_{2}$ ternary mixture is studied. This plasma was generated in the total pressure range of 0.5 to 8.7 Torr, power of 6.3 W and with 12 l/min flow rate of gases. The diagnostic has been made by optical emission spectroscopy (OES) using a spectrometer and the determination of electron temperature was obtained by the measurements with a Langmuir double Probe. The species observed in the plasma mixture were CO$_{2}$, CO$_{2}^{+}$, CN, CO, CO$^{+}$, O$_{2}$, O$_{2}^{+}$, N$_{2}$, N$_{2}^{+}$, NO, C$^{+}$, Ar, and Ar$^{+}$. The electron temperature was found to be of 10.63 eV, and the ion density in the order of 10$^{10}$cm$^{-3}$. [Preview Abstract] |
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KTP.00014: Influence of the Walls on the Formation of a DC Glow Discharge Vladimir Demidov, Yevgeny Bogdanov, Steve Adams, Anatoly Kudryavtsev 2D simulations of a DC glow discharge with a cold cathode in argon have been performed for various radii of the discharge tube. It is shown that the loss of the charged particles to the walls can significantly affect plasma parameters as well as properties of the cathode sheath. The longitude dimensions of the Negative Glow and Faraday Dark Space depend on the transverse loss of the charge particles and are not consistently predicted with a 1D model. The common assumption that the cathode sheath can be analyzed independently of the plasma also may not be valid. The transverse inhomogeneity of the plasma leads to a change in the current density distribution over the cathode surface. The thickness of the cathode sheath can vary with radial distance from the discharge axis, even for the case of negligible radial loss of the charge particles. The 2D model results provide an analysis of the conditions of applicability of the 1D model. [Preview Abstract] |
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KTP.00015: Positive point-to-plate corona discharge as influenced by different nitrogen pressure Aasim A. Azooz, Sabah I. Wais An empirical formula for IV characteristics in the nitrogen pressure ranged between (P$_{o}$-2.5P$_{o})$ is presented for a point-to-plate electrode corona discharge. Fast automatic data acquisition system is built to acquire the experimental data of the corona current and voltage and to determine the corona inception voltage. Three values of inception current (I$_{o}$= 0.1, 0.5, and 1.0 $\mu $A) are used to demonstrate that the minimum observed inception current gives more accurate inception voltage, for which the exponent n of a general formula I=A(V-V$_{o})^{n}$ has been optimized. The experimental investigation discloses that the inter-electrode separation S and the gas pressure have the strongest influence on both the dimensional parameter \textbf{A} and the corona inception voltage V$_{o}$. Of all potentially influential factors, a new empirical formula relating corona current, corona inception voltage, inter-electrode separation and gaps pressure is reached. [Preview Abstract] |
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KTP.00016: Super Hot Hydrogen Atoms in Microwave Plasmas Edgar Felizardo, Elena Tatarova, Francisco Dias, M Lino da Silva, Carlos Ferreira, Boris Gordiets ``Super hot'' (with kinetic energy in the range 4 - 8 eV) and ``hot'' (kinetic energy $\sim $ 0.3 eV) hydrogen atoms were detected throughout the volume of a surface wave (500 MHz) generated H$_{2}$ plasma column, at pressure p = 0.01 mbar, from the analysis of the H$_{\beta }$, H$_{\gamma }$, H$_{\delta }$and H$_{\varepsilon }$ emission line profiles. The profiles were found to evolve from single Gaussian to bi-Gaussian towards the column end. Population inversion between the levels 5$\to $4 and 6$\to $4 was detected from the measured relative intensities of transitions within the Balmer series. The Doppler temperatures corresponding to the H$_{\beta }$, H$_{\gamma }$, H$_{\delta }$, H$_{\varepsilon }$ line broadening are much higher than the rotational temperature, as measured from the hydrogen molecular Fulcher-$\alpha $ band (350 -- 500 K), and than the wall temperature (300 -- 450 K). At pressure p = 0.2 mbar, ``super hot'' atoms were not detected while ``hot'' atoms are present. It has also been found that the kinetic temperature of excited H ($n$ = 4 -7) atoms, as determined from the fitting of the spectral lines with a single Gaussian profile, increases with the upper level principal quantum number. These experimental results are analyzed in the framework of a kinetic model, which accounts for the generation of three groups of atoms. [Preview Abstract] |
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KTP.00017: Instability-driven ionization in a low-pressure helium discharge T.P. Hughes, M.M. Hopkins, P.S. Crozier, J.J. Boerner We have carried out modeling of a plane-parallel low-pressure helium discharge with a thermionic cathode. Initially, ionization is due to direct-impact of cathode-emitted electrons on the neutral atoms. When a sufficient density of trapped electrons is established, a strong electron-plasma two-stream instability develops which heats the trapped electrons. The ionization rate is then enhanced by the hot electrons and by the collective fields of the instability. We present results showing the effect of neutral density and applied voltage on the V-I characteristics of the discharge. [Preview Abstract] |
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KTP.00018: Development of a compact, versatile electron beam source S.G. Walton, C.D. Cothran, R.F. Fernsler, W.E. Amatucci, R.A. Meger The operating characteristics of a high-energy electron beam source are described. Electrons are extracted from a hollow cathode plasma and then accelerated by anode located downstream from the cathode. The anode to cathode surface area ratio is less than the root of the electron to ion mass ratio such that an electron sheath forms at the anode; a bias on this anode then accelerates the electron flux into a beam. A magnetic field assists the beam collimation. Paschen breakdown in the few Torr range at 500V initiates the hollow cathode plasma, and typical continuous operation requires less pressure and applied voltage. Varying the hollow cathode current allows direct control of the beam current, while the bias on the accelerating anode determines the beam energy. Beams at up to 5kV and 80mA have been produced with this device. Critical component designs for stable operation in both CW and pulsed operation are discussed. [Preview Abstract] |
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KTP.00019: CORONAS, BREAKDOWN, AND SPARKS |
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KTP.00020: DC Breakdown of Low Pressure Gas in Long Tubes Valeriy Lisovskiy, Veronika Koval, Vladimir Yegorenkov We studied the dc breakdown of low pressure nitrogen in the pressure range p = 0.1 -- 2 Torr. The measurements were performed in the tube of radius R = 4 mm, whereas the inter-electrode gap values varied in the range L = 2 -- 250 mm. The conventional Paschen law was shown to hold in short discharge tubes for which L/R $\le $ 1. At L/R $>$ 1 the increase of the inter-electrode distance shifts the breakdown curves U(p) to higher breakdown voltage values U and lower gas pressure ones (larger products of gas pressure and inter-electrode distance pL). The breakdown curve minima lie on the same straight line. At L/R $>$ 10 increasing L makes the dc breakdown curves to shift to higher U values, their minima being observed almost at the same gas pressure value. Perhaps the electrons escaping to the tube walls due to diffusion perturb the electric field distribution and affect the development of the gas breakdown. [Preview Abstract] |
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KTP.00021: Modelling of a breakdown phenomena in dual-frequency discharges Marija Radmilovic-Radjenovic, Branislav Radjenovic Gas breakdown represents the first step in generation of plasma and therefore is one of the most fundamental processes. In large scale systems, the experimentally observed Paschen law has been successfully explained by the Townsend theory. This paper contains the results of the detailed simulation studies of low-pressure gas breakdown in dual-frequency rf discharges in argon. Calculations were performed by using a Particle-in-cell/Monte Carlo collisions (PIC/MCC) code with the secondary emission model adjusted to include the energy dependence of the secondary electron yield at large separations. The obtained simulation results represents breakdown voltage curves that disctate the breakdown voltage for a particular gas as a function of the pd product for dual- freqnecy discharges in argon. [Preview Abstract] |
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KTP.00022: Control of the energy deposited in a high voltage nanosecond discharge and combustion triggering in N$_{2}$/O$_{2}$/C$_{3}$H$_{8}$ mixtures at atmospheric pressure Nicolas Moreau, Sabrina Bentaleb, Pierre Tardiveau, Christian Postel, Fran\c{c}ois Jorand, Stephane Pasquiers The energy control in a point to plane corona discharge induced in dry air under nanosecond scale high overvoltage is investigated. The spatial behaviour of the discharge is described by CCD imaging coupled to energy measurements. The energy is modified by varying the voltage and the pulse duration. In previous works we obtained a diffuse regime and a streamer regime are obtained below 3 bar, and a leader-like regime above. In the diffuse regime, the discharge constricts in the point-plane axis when the energy increases while intensification of the emission can be observed on one or more filaments in the streamer one. The energy can be controlled till a pulse duration limit greater for the streamer regime than for the diffuse one. Below this duration limit, the current pulse ends with the voltage pulse. Difficulties appeared to control the energy in the leader-kind regime. The combustion triggering of N$_{2}$/O$_{2}$/C$_{3}$H$_{8}$ mixtures by one pulse and the flame propagation are studied at 1 bar. The diffuse regime disappears in mixtures with C$_{3}$H$_{8}$ and the discharge is a filamentary one. Combustion always triggers near the tip with a lower energy deposited limit of a few millijoules. [Preview Abstract] |
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KTP.00023: On the mechanism of the cathode erosion in negative corona discharge Alexey Petrov, Ravil Amirov, Igor Samoylov Negative corona discharge was investigated in atmospheric pressure air and SF$_{6}$ in Trichel pulse and glow mode in point-to-plane electrode configuration. As a cathode pointed carbon, copper and aluminum pins with tip size 0.02-1 mm were used. It is found that negative corona causes the erosion of cathode surface in form of nanometer-size craters and fissures. Observed etching may be explained in terms of microexplosive process. This process is initiated by interaction of the cathode surface with the cathode-directed ionization wave. This wave is registered as a Trichel pulse. Local electric field of the head of wave gives rise to the field emission from the cathode surface which initiates microexplosion due to Joule heating. It is assumed that a single Trichel pulse causes the ejection of an erosion fragment from the cathode surface and current on the cathode surface runs through the cross-section of elementary erosion fragment. The value of Trichel pulse action integral which depends on the cathode current density and pulse duration and serves as a criterion of micro-explosion is 10$^{9}$~A$^{2}$s/cm$^{4}$. Hence the conclusion has been made that erosion of the cathode in Trichel pulse mode of negative corona was caused by microexplosive processes. General erosion picture of the cathode surface depends on the discharge dynamics. Correlation between discharge dynamics, erosion picture and Trichel pulse parameters was found. [Preview Abstract] |
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KTP.00024: CAPACITIVELY COUPLED PLASMAS |
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KTP.00025: Sputter processes in capacitively coupled multi frequency discharges Stefan Bienholz, Egmont Semmler, Peter Awakowicz In material processing applications capacitively coupled plasmas have been of great importance over several years. For plasma deposition processes single frequency capacitively coupled discharges only play a minor role due to rather low deposition rates. In contrast a higher electron density, hence a higher ion flux can be achieved in magnetron coaters, which accordingly leads to significantly higher deposition rates. However, disadvantages such as limited target exploitation or restricted usage of non-conductive or magnetic targets are still present. In this contribution we propose a multi frequency driven capacitive discharge to combine the major advantages of both processes with respect to large scale applications. Whereas high electron densities and therefore a high ion flux can be achieved by using very high frequencies (VHF = 60-90\,MHz), an additional lower frequency (HF = 1-14\,MHz) gives a certain control over the ion bombarding energy. However complex frequency coupling limits the separated tunability. [Preview Abstract] |
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KTP.00026: PIC simulations of electrically asymmetric dual frequency capacitive RF discharges Zoltan Donko, Julian Schulze, Edmund Schuengel, Uwe Czarnetzki A geometrically symmetric dual frequency capacitively coupled RF discharge operated in argon at 13.56 MHz and 27.12 MHz with variable phase shift between the driving voltage waveforms is investigated by a 1d PIC simulation. Due to the Electrical Asymmetry Effect (EAE) a variable DC self bias is generated as a function of the phase shift, that allows efficient separate control of ion energy and flux at the electrodes. An analytical model demonstrates why the ion flux does not depend on the phase shift. The quality of this separate control is found to be better compared to conventional dual frequency discharges operated at substantially different frequencies, where limitations due to frequency coupling occur. The EAE is optimized by choosing optimum amplitudes of the low and high frequency voltage waveforms. For the first time non-linear self excited plasma series resonance (PSR) oscillations are observed in geometrically symmetric discharges. The PSR oscillations and non-linear electron resonance heating (NERH) are turned on and off depending on the electrical discharge asymmetry controlled by the phase shift between the driving frequencies. [Preview Abstract] |
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KTP.00027: 3D simulation of a radio-frequency driven microplasma jet Torben Hemke, Thomas Mussenbrock, Ralf Peter Brinkmann An increasing number of microplasma sources were developed in the last few years. These sources differ in geometries, single or array discharge configurations, DC or RF discharges, and the used chemistry - depending on the underlying application. In this paper we concentrate on a radio-frequency driven microplasma jet (refered to as the $\mu$-APPJ) invented by Schulz-von der Gathen and co-workers. The $\mu$-APPJ with an electrode gap of 1\ mm is driven at 13.56 MHz (approx. 10\ W), typical chemistry consists of He with addition of less than 1\% molecular oxygen. To study the $\mu$-APPJ in 3D we use a commercial computational fluid dynamics code (CFD-ACE+). We treat the electrons kinetically to build a look-up table for its transport coefficients and include a HeO$_2$ reaction chemistry scheme. We discuss basic insights into the fundamental mechanisms of the $\mu$-APPJ. Finally we present a brief discussion of the results of the 3D simulation compared with a simplified analytical model. [Preview Abstract] |
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KTP.00028: Charge dynamics in electrically asymmetric dual frequency capacitive RF discharges Julian Schulze, Edmund Schuengel, Uwe Czarnetzki, Zoltan Donko Charge dynamics in electrically asymmetric, geometrically symmetric dual frequency capacitively coupled RF discharges operated at 13.56 MHz and 27.12 MHz with variable phase shift between the driving voltage waveforms is investigated experimentally as well as by a PIC simulation and analytical models. Via the Electrical Asymmetry Effect a variable DC self bias is generated as a function of the phase shift. Differences between the DC self bias resulting from simulation/experiment and analytical/fluid models at small phase angles are explained by the charge dynamics within one low frequency RF period (not taken into account in the models). Depending on phase shift and pressure the excitation at the powered electrode is stronger or weaker compared to the grounded electrode (asymmetric excitation). The excitation dynamics is different at high (100 Pa) and low pressures (3 Pa): at low/high pressure the excitation is asymmetric at phase shifts of strong/weak DC self bias, respectively. This dynamics is understood in the frame of a simple analytical model. [Preview Abstract] |
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KTP.00029: Modeling of capacitively coupled radio-frequency discharges in nitrogen L. Marques, C.D. Pintassilgo, L.L. Alves, G. Alcouffe, G. Cernogora This paper reports the modeling of capacitively coupled radio-frequency discharges (13.56 MHz) in pure nitrogen, produced within a cylindrical parallel-plate reactor, similar to a GEC reference cell surrounded by a lateral grounded grid, at 0.2-3 mbar pressures and 5 -30 W coupled powers. This reactor is used to simulate, at laboratory scale, the N$_{2}$/CH$_{4}$ chemistry of Titan's atmosphere. We have used a 2D, time-dependent fluid-type code to describe the transport of electrons and positive ions N$_{2}^{+}$ and N$_{4}^{+}$ in the reactor, coupled to a 0D kinetic code for N$_{2}$. The fluid code solves the charged particle and the electron mean energy transport equations, coupled to Poisson's equation for the RF electric potential. The kinetic code solves the electron Boltzmann equation and the rate balance equations of 45 vibrationally excited states and 7 electronically excited states of the N$_{2}$ molecule, yielding a set of electron transport parameters and rate coefficients for the charged particle production and destruction. Model results are compared to measurements of the self-bias potential, the average electron density, and the line intensities of the FNS(0-0) [N$_{2}^{+}$(B,0)-N$_{2}^{+}$(X,0)] and of the SPS(0-2) [(N$_{2}$(C,0)-N$_{2}$(B,2)]. [Preview Abstract] |
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KTP.00030: Effect of the relative phase of the driving sources on heating of dual frequency capacitive discharges Dennis Ziegler, Jan Trieschmann, Thomas Mussenbrock, Ralf Peter Brinkmann The influence of the relative phase of the driving voltages on heating in asymmetric dual frequency capacitive discharges is investigated. Basis of the analysis is a recently published global model [1] extended by the possibility to freely adjust the phase angles between the driving voltages. In recent publications it was reported that nonlinear electron resonance heating (NERH) drastically enhances dissipation at moments of sheath collapse due to plasma series resonance (PSR) excitation [2]. This work shows that depending on the relative phase of the driving voltages, the total number and exact moments of sheath collapse can be influenced. In case of a collapse directly being followed by a second collapse ("double collapse") a substantial increase in dissipated power, well above the reported growth due to a single PSR excitation event per period, can be observed.\\[4pt] [1] D.\,Ziegler, T.\,Mussenbrock, and R.\,P. Brinkmann, Phys. Plasmas {\bf 16}, 023503 (2009)\\[0pt] [2] T.\,Mussenbrock, R.\,P. Brinkmann, M.\,A. Lieberman, A.\,J. Lichtenberg, and E. Kawamura, Phys. Rev. Lett. {\bf 101}, 085004 (2008) [Preview Abstract] |
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KTP.00031: Improving plasma density uniformities at VHF/UHF operating frequencies using a scalable, multi{\-}electrode, VHF/UHF plasma source David O'Farrell, Shane Linnane, Cezar Gaman, Bert Ellingboe At VHF/UHF operating frequencies significant electrode voltage non-uniformities develop over even modestly sized electrodes leading to plasma density non-uniformities. This has frustrated the use of higher operating frequencies in larger area PECVD processes despite the potential for increased deposition rates and improved film quality. A scalable, multi-electrode, VHF/UHF plasma source is described that enables high frequency large area operation without plasma non-uniformities. Plasma uniformity data is presented over a series of powers, pressures and operating frequencies. [Preview Abstract] |
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KTP.00032: Frequency Agile Tuning For Plasmas Excited Using RF Scott Heres, Michael Kabala, Carl Almgren, Cameron Moore, George Collins Frequency agile tuning, while commonly used at GHz range, presents a number of difficulties for realization at frequencies in the 10's of MHz. We describe methods to achieve frequency agile tuning to perform controllable impedance matching and discuss methods by which tuning ranges may be further broadened. [Preview Abstract] |
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KTP.00033: Computational Optimization of Magnetically Enhanced CCP Plasma Uniformity for Disk Etch Applications Vladimir Kudriavtsev, Wenli Collison, Huong Nguyen, Pat Ward, Michael Barnes, Mark Kushner Discrete track recording (DTR) is currently the most perspective way of nanomanufacturing of hard disk magnetic media. Using lithography and plasma etch steps it forms patterned narrow gaps. In this study we optimize magnetron plasma chamber uniformity to enable optimal plasma etch process. We have utilized HPEM plasma model to investigate CF4 capacitively coupled single frequency plasma enhanced with static magnetic field, and analyze radial plasma uniformity near disk surface. Results will be discussed for the spatial dependence of plasma density, ion and radical fluxes (CFx, F) as a function of chamber height, electrode to magnet distance and overall strength of magnetic field. Plasma density distribution and shape of visible plasma emissions are largely controlled by the shape of magnetic field lines. We were able to show in this study that full plasma model is required and use of only of the static magnetic field model is grossly insufficient and can lead to incorrect results. Through the use of computational model we have found optimal combination of governing parameters that control plasma uniformity across the disk, which was improved from 26{\%} down to 4{\%}. Using these parameters production plasma etch chamber was build and experimental studies further confirmed computational results. [Preview Abstract] |
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KTP.00034: Spatially resolved modeling of the plasma series resonance excitation in capacitively coupled plasmas Schabnam Naggary, Dennis Ziegler, Martin Lapke, Thomas Mussenbrock, Ralf Peter Brinkmann, Michael Klick It is widely acknowledged that the excitation of the plasma series resonance can be important for the heating of capacitively coupled plasmas. This holds particularly for the asymmetric case. Fundamental studies on this phenomenon has recently been performed by means of various nonlinear global models. However, it has been shown that only a spatially resolved model can describe the complete fine structure of the very complex nonlinear dynamics. [1] In this paper we discuss the excitation of the plasma series resonance using a spatially resolved model of an asymmetric capacitive discharge. It allows for a realistic geometry as well as for a simplified but self-constistent sheath model.\\[4pt] [1] T. Mussenbrock and R.P. Brinkmann, Plasma Sources Sci. Technol. {\bf 16}, 377 (2007). [Preview Abstract] |
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KTP.00035: INDUCTIVELY COUPLED PLASMAS |
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KTP.00036: Analytical modeling of the anomalous skin effect and negative power absorption in low pressure plasmas Thomas Mussenbrock, Martin Lapke, Thomas Eisenbarth, Ralf Peter Brinkmann The theory of the anomalous skin effect and related phenomena in a bounded low pressure plasma (below 1 Pa) is discussed. In this particular regime the relation between the high frequency current density and the electric field is nonlocal. To describe the situation, Maxwell's equations have to be coupled self consistently with Boltzmann's equation. In this paper we present an analytical, self-consistent solution to the one-dimensional problem of a plane wave propagating from the left half space into the right half space filled with a bounded homogeneous plasma. Particularly, we discuss phase mixing and negative power absorption, and finally the effect of the finite thermal velocity of electrons on the field distribution and the power deposition. [Preview Abstract] |
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KTP.00037: 2D Axisymmetric Simulation of an Inductively/Capacitively Coupled Plasma Reactor Emi Kawamura, Michael A. Lieberman, David B. Graves We use the commercial finite elements simulation package COMSOL to simulate a 2D axisymmetric TCP reactor. The simulation consists of four basic parts: an EM model, a Plasma Fluid Model, a Sheath Model, and a Gas Flow Model. For a pure argon plasma, the simulations were completed in less than an hour on a typical desktop machine with a 2GHz CPU and 4GB of memory. The EM model includes both inductive and capacitive coupling of the rf energy from the source coils to the target plasma via a dielectric window. The Plasma Fluid Model solves the time-dependent plasma fluid equations for the ion continuity and electron energy balance. The Sheath Model models an actual vacuum sheath of variable thickness with a fixed-width sheath of variable dielectric constant. The Gas Flow model solves for the steady state pressure, temperature and velocity of the neutrals. By varying the model parameters (e.g., pressure, input power, source coil configuration, chamber height), we observe the effect on the plasma (e.g., uniformity, density, capacitive coupling). [Preview Abstract] |
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KTP.00038: Additional planar antenna effect on the ferromagnetic core inductively coupled plasma Jin Young Bang, Chin Wook Chung The side type ferrite inductively coupled plasma (ICP) with 400 kHz driving frequency suitable for the next generation processing in large areas was recently developed in our previous work [1]. In this ICP, the plasma density at the edge of the chamber is higher than the center at high pressure because the plasma generation by heated electrons is localized at the edge and hardly diffuses to the center. In this paper, in order to improve the uniformity of the plasma density by increasing the ionization around center, a planar antenna whose driving frequency is 13.56 MHz was installed on the top of the chamber. The synergy effect was observed when the plasma was generated by two sources, and the uniformity could be controlled by applying only small power compared with that of the ferrite ICP to the additional planar antenna. \\[4pt] [1] Kyeonghyo Lee, Youngkwang Lee, Sungwon Jo, Chin Wook Chung and Valery Godyak, Plasma Sources Sci. Technol., 17, 015014 (2008) [Preview Abstract] |
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KTP.00039: Analysis of the environmental ramifications of an SF$_{6}$/O$_{2}$ etch using simulation James Munro, Jonathan Tennyson, Stephen Harrison, Daniel Brown Sulfur Hexafluoride (SF$_{6}$) is a processing gas that is used industry-wide in a range of processes for the dry etching of silicon. However, the performance and efficiency of different processes and machines can vary widely. Through simulation we can gain significant insight into the optimization problem and provide a low cost means for further development. SF$_{6}$ is very bad for the environment with a Greenhouse Warming Potential that is 22,000 times that of CO$_{2}$. Therefore it is vital that SF$_{6}$ is used sparingly and efficiently in every process. Simulation can help to find ways of remediating harmful waste gases and optimize the process for typical processing goals (e.g. etch rate, uniformity) as well as improving SF$_{6}$ consumption efficiency and other environmental measures. Here we present an full chamber 2D simulation of an SF$_{6}$/O$_{2}$ silicon etch process, building upon previous calculations of SF$_{6}$ plasma chemistries using Quantemol-P (J.J. Munro and J. Tennyson, J. Vacuum Sci. Tech. A, 26, 865). Etch rate, pressure and power trends along with chamber wide contour plots of gas-phase species concentrations and fundamental plasma properties are considered. [Preview Abstract] |
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KTP.00040: Experimental observation of the transition from nonlocal to local kinetics in inductively coupled plasmas Hyo-Chang Lee, Min-Hyong Lee, Chin-Wook Chung The transition from nonlocal to local kinetics was observed through the spatially resolved measurements of electron energy distribution functions in inductively coupled plasmas. As gas pressures increase, the spatial profiles of the effective electron temperatures (Teff) from the electron energy distribution functions changed dramatically from hollow shapes to flat shapes. With further increases in gas pressure, the Teff had saddle-shaped profiles with the highest Teff in the vicinity of an antenna coil. These changes in the radial profiles of the Teff show a transition of the electron kinetics from nonlocal to local regimes. This transition occurred when the electron energy relaxation lengths became smaller than the antenna half size. [Preview Abstract] |
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KTP.00041: Measurement of the total energy lost per electron-ion lost in argon, helium and oxygen inductively coupled plasmas Ju-Hwan Ku, Young-Kwang Lee, Seung-Ju Oh, Chin-Wook Chung The total energy lost per electron-ion pair lost was measured at various gases (Ar, O$_{2}$, He, Ar/O$_{2, }$Ar/He) and in the pressure range of 5--50 mTorr in an inductively coupled plasma. A floating harmonics method [1] was used to measure the electron temperatures and ion fluxes at the chamber wall. The absorbed power was determined by measuring the antenna resistance and current. The total energy lost were determined from a power balance equation of a global model. The measured of the total energy lost per electron-ion pair ranged from 80 V to 250 V for Ar and from 70 V to 90 V for He, respectively. In molecular gas, it ranged from 250 V to 2300 V for O$_{2 }$plasma due to additional collisional energy losses. The measured total energy lost decrease with absorbed power and increase with pressure. In mixture discharges, the total energy lost rapidly increase with mixing ratio of oxygen in Ar/O$_{2}$ plasma while the total energy lost slightly decrease with mixing ratio of helium in Ar/He plasma. These experimental results were consistent with theoretical ones. \\[4pt] [1] M. H. Lee, S. H. Jang, C. W. Chung, J. Appl. Phys. 101, 033305 (2007). [Preview Abstract] |
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KTP.00042: Investigation of electron energy distribution function in a weak magnetic field in solenoidal inductive discharge Yeong-Kwang Lee, Ju-Hwan Ku, Chin-Wook Chung Plasma parameters such as electron temperatures, plasma densities, and dc plasma potential in the vicinity of electron cyclotron resonance (ECR) in the solenoidal inductive argon discharge have been investigated by observing electron energy distribution function (EEDF). Langmuir probe method system was built to study the EEDF dependencies on the radial position and rf driving frequency. The measurement was performed on the bulk plasma under range of weak dc magnetic field (0 - 20 G) at low pressure and power. In this study, the changes in the radial profile of the plasma parameters with respect to the varying the magnetic field was discussed. It was experimentally verified that no effective electron temperature maximum appear at ECR condition due to the characteristics of the local electron kinetics, while plasma density maximum appears at different magnetic field. Furthermore, the measured dc plasma potential largely increases with the rf driving frequency. These results are also compared with that of the typical planner inductive discharge [1].\\[4pt] [1] C.W. Chung, S. S. Kim, and H.Y. Chang, Phys. Rev. E 69, 016406 (2004) [Preview Abstract] |
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KTP.00043: The effects of magnetic field on the plasma parameters in a planar inductively coupled plasma etch system Jae-Chul Jung, Jae Hyun Song, Wan Soo Kim, Ki-Woong Whang In this paper, magnetic field effects on a planar inductively coupled plasma etch system were studied, in which the magnetic field was applied by the use of the permanent magnets in order to obtain a uniform, high density plasma with a large diameter ($\ge $150mm) at low gas pressure ($\le $10mTorr). Plasma parameters were measured by the double Langmuir probe and the power transfer efficiency by the impedance analyzer. Coupling mode conversion from the C- to L- mode was observed to result in big changes in the plasma density. When the magnetic field is applied, the density at the center linearly increased with the input power, and then a sharp increase in plasma density could be observed at a certain input power level which connects to a plasma density hysteresis loop. The plasma density increase with the decrease of RF power once the density jump occurred. Electron temperatures at the outer region became low after the mode transition, but the peak density increase by about 4 times. When the magnetic field configuration is optimized, the uniformity of density and temperature improved with the application of magnetic field. [Preview Abstract] |
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KTP.00044: OTHER PLASMA TOPICS |
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KTP.00045: Real time model based control of an inductively coupled plasma Bernard Keville, Miles Turner Process yield in many plasma assisted processes may be improved significantly by real time, closed loop control of certain plasma species. This presentation describes a control algorithm for the closed loop control of a low pressure, inductively coupled plasma simulation. The simulation consists of a global model of the plasma chemistry coupled to an equivalent circuit. The equivalent circuit incorporates an impedance matching box and a model of power coupling from the antenna into the plasma which has been derived from the wave equation and the two term solution to the Boltzmann equation. In addition, mass flow controller models and gas flow transport delays are included. This work indicates how a control algorithm may be determined from a control-oriented model of the process (model-based control) in order to guarantee a robustly stable closed loop response. In general, process parameters such as wall sticking coefficients are difficult to estimate and may change over time and process measurements may be noisy and indirect. This work will indicate how an optimal state estimator may be used to improve estimates obtained from noisy data and how such estimates may be used to adapt the control algorithm in real time in order to guarantee process stability despite changes in process parameters. [Preview Abstract] |
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KTP.00046: MAGNETICALLY-ENHANCED PLASMAS: ECR, HELICON, MAGNETRON, OTHERS |
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KTP.00047: 2D PIC simulations for an EN discharge with magnetized electrons and unmagnetized ions Michael A. Lieberman, Emi Kawamura, Allan J. Lichtenberg We conducted 2D particle-in-cell (PIC) simulations for an electronegative (EN) discharge with magnetized electrons and unmagnetized ions, and compared the results to a previously developed 1D (radial) analytical model of an EN plasma with strongly magnetized electrons and weakly magnetized ions [1]. In both cases, there is a static uniform applied magnetic field in the axial direction. The 1D radial model mimics the wall losses of the particles in the axial direction by introducing a bulk loss frequency term $\nu_L$. A special (desired) solution was found in which only positive and negative ions but no electrons escaped radially. The 2D PIC results show good agreement with the 1D model over a range of parameters and indicate that the analytical form of $\nu_L$ employed in [1] is reasonably accurate. However, for the PIC simulations, there is always a finite flux of electrons to the radial wall which is about 10 to 30\% of the negative ion flux.\\[4pt] [1] G. Leray, P. Chabert, A.J. Lichtenberg and M.A. Lieberman, J. Phys. D, accepted for publication 2009. [Preview Abstract] |
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KTP.00048: High speed images and electrical measurements of drift waves in magnetized microdischarges Tsuyohito Ito, Mark Cappelli High speed images and electrical measurements from E x B discharges in micro-scale magnetically confined plasmas are presented. The image sequences depict strong and highly-ordered drift waves and underlying smaller-scale turbulence near the plasma edge, with characteristic length scales larger than the electron cyclotron radius. The measured phase velocity of the large scale disturbances is in good agreement with that for classic density-gradient driven isothermal drift waves. Propagating azimuthal waves of mode numbers m = 3 -5 are clearly present in the image sequences, with mode excitation and mode frequency found to be dependent on discharge voltage. The experiments are compared to simple theory for drift-wave dispersion, and are found to be in good quantitative agreement. Dispersion characteristics extracted from the images are also compared to a limited set of measurements taken using Langmiur probes and segmented electrodes. These studies suggest that such magnetically confined microdischarges may provide a useful test-bed for simulations of plasma confinement and turbulence in plasmas of moderate ion temperature. [Preview Abstract] |
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KTP.00049: Time-resolved plasma parameters in HiPIMS discharges with titanium target Martin Cada, Petr Adamek, Stepan Kment, Petr Virostko, Zdenek Hubicka The paper deals with time-resolved measurement of electron effective temperature, electron density, plasma and ``floating'' potential in High Power Impulse Magnetron Sputtering (HiPIMS) system equipped with 2'' in diameter titanium target. The Langmuir probe was placed 70 mm from the target face and below the racetrack. The pressure of argon in a chamber was kept at 0.3 Pa, 2 Pa and 20 Pa. The temporal resolution of the Langmuir probe acquisition system reveals that T$_{e}$ decreases during pulse ON time approximately linearly for pressure 0.3 Pa and exponentially-like for pressures 2 and 20 Pa. The steady value of T$_{e}$ was approximately 0.4 eV for all the pressures. The maximal value was $\sim $2.2 eV and $\sim $0.6 eV for pressures 20 Pa, 2 Pa and 0.3 Pa respectively. Furthermore, the local maximum in T$_{e}$ at the end of the voltage pulse is observed only for working gas pressure 2 Pa. During the pulse OFF time we observed exponential-like decay of the electron temperature for all the pressures. The plasma density demonstrates steep increase during pulse ON time. For pressures 2 Pa and 20 Pa, the plasma density reaches the maximal value at time 25 $\mu $s and 70 $\mu $s after turn off of the plasma pulse. After that we observed recombination-like plasma decay followed by ambipolar diffusion. [Preview Abstract] |
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KTP.00050: Transport in low-temperature magnetized plasma with significant ionization rate Laurent Liard, Ane Aanesland, Jean-Luc Raimbault, Pascal Chabert, Stephane Mazouffre In low-temperature plasma used for microelectronics, the ionization fraction remains sufficiently small (around 10$^{-4})$ for the neutral density to stay uniform in the reactor. However, with high electronic density reactor, such as helicons or ICP's, the ionization fraction can be significant, reaching 10$^{-2}$. This fraction may even reach 10 {\%} in plasma thrusters. Theoretical works have shown that when the electronic pressure, $nekBTe$, reaches the same range than the neutral pressure, nnkBTn, a neutral depletion at the center of the discharge occurs. In this poster, experimental study of this phenomenon is presented: Aanesland \textit{et al.} and O'connell \textit{et al.} have measured the ground state density of xenon atoms using TALIF. Their results confirm that the neutral density obtains a minimum at the center of the discharge. Moreover, time resolved measurements of TALIF shows that this phenomenon gathers two different phenomena with their own time scale. Space resolved measurements of the argon metastable temperature have also been performed to estimate the influence of gas heating in neutral depletion, and compared with previous theoretical work. [Preview Abstract] |
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KTP.00051: Fluid modeling of a high power positive column: Competitive effects of magnetic field and neutral depletion Laurent Liard, Jean-Luc Raimbault, Pascal Chabert Transport phenomena in low temperature plasmas only need charged particles dynamics to be considered when the ionization fraction is small. However, recent reactor discharges such as ICP's and helicon allow high ionization rate, which changes drastically the transport dynamics. Recently, several authors included neutral dynamics in classical low-temperature discharge models and showed that, when electronic (ne kB Te ) and neutral (nn kB Tn ) pressure are on the same range, neutrals are pushed away from the discharge centre, resulting in neutral depletion effects. In this paper, we add to the neutral depletion model an axial magnetic field. Exact numerical solutions of the fluid model are found, but we also derive an approximate analytical solution. Densities spatial profiles, electronic temperature and edge-to-center ratio are presented as a function the magnetic field amplitude. On one hand, the presence of the magnetic field confines the plasma and so limits the diffusion of charged species to the wall. This goes against the neutral depletion effect. But on the other hand, the electronic density in a helicon discharge is strongly dependant of the magnitude of the magnetic field, which in turns tends to increase the depletion effect at fixed power. [Preview Abstract] |
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KTP.00052: Magnetic Electron Filtering by Fluid Models for the PEGASES Thruster Gary Leray, Pascal Chabert, Allan Lichtenberg, Michael Lieberman The PEGASES thruster produces thrust by creating positive and negative ions, which are then accelerated. To accelerate both type of ions, electrons need to be filtered, which is achieved by applying a static magnetic field strong enough to magnetize the electrons but not the ions. A 1D fluid model with three species (electrons, positive and negative ions) and an analytical model are proposed to understand this process for an oxygen plasma with p = 10~mTorr and B$_{0}$ = 300~G [1]. The resulting ion-ion plasma formation in the transverse direction (perpendicular to the magnetic field) is demonstrated. It is shown that an additional electron/positive ion loss term is required. The solutions are evaluated for two main parameters: the ionizing fraction at the plasma center (x = 0), n$_{e0}$/n$_{g,}$ and the electronegativity ratio at the center, $\alpha _{0}$=n$_{n0}$/n$_{e0}$. The effect of geometry and magnetic field amplitude are also discussed. \\[4pt] [1] Leray G, Chabert P, Lichtenberg A J and Lieberman M A, \textit{J. Phys. D: Appl. Phys., Plasma Modelling Cluster issue}, to appear (2009) [Preview Abstract] |
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KTP.00053: HELICON, MAGNETRON AND OTHER PLASMA SOURCES |
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KTP.00054: ABSTRACT WITHDRAWN |
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KTP.00055: DIELECTRIC BARRIER DISCHARGES, DISPLAYS |
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KTP.00056: Voltage slew rate dependence of plasma excitation in 10-200 Torr argon-nitrogen gas mixture DBD Feng Liu, George Huang, Biswa Ganguly Argon-nitrogen gas mixture dielectric barrier discharge (DBD) excited by short (rising time$\sim $20 ns) and long (rising time$\sim $100 ns) 3 to 6 kV high-voltage pulses was investigated in the pressure range of 10-200 Torr. Time resolved spectra of Ar (2P$_{1}$-1S$_{2})$, Ar$^{+}$ (4P-4D$^{o})$, N$_{2}$ (C$^{3}\Pi _{u}$ -B$^{3}\Pi _{g})$, and N$_{2}^{+}$(B$^{2}\Sigma _{u}^{+}$-X$^{2}\Sigma _{g}^{+})$ were recorded while the applied voltage kept constant during measurements; the influence of different applied voltages and nitrogen concentration on the observed spectra were also obtained. Mean electron energies, T$_{e}$, were derived from the ratio of the measured emission intensities by comparing excitation rates calculated using BOLSIG+ code, assuming a Maxwellian EEDF. The T$_{e}$ of short-pulse excited DBD was in the range of 6-8 eV and it decreased by about 0.5 eV for lower voltage slew rate excitation under the same experimental conditions. The pulsed DBD plasma processes with different slew rate were analyzed based on the dependence of observed emission spectra and T$_{e}$ on the discharge operating parameters. The discharge voltage, current and power deposition were also estimated from applied voltage and current measurements. [Preview Abstract] |
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KTP.00057: ABSTRACT WITHDRAWN |
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KTP.00058: HIGH PRESSURE GLOW DISCHARGES |
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KTP.00059: Numerical study of discharge progress and characteristics in Microhollow Cathode Discharge Guangqing Xia, Genwang Mao, Maolin Chen The two-dimensional numerical model for Microhollow cathode discharge(MHCD) consists of the continuity equations for electron and ion and Poisson's equation. The model considers the drift-diffusion approximation for the flux of electron and ion and accounts for the mean electron energy dependence of the ionization rate. In the numerical study, two molybdenum foils with 100 $\mu $m thickness are stacked on an alumina foil with 250 $\mu $m thickness. The ports with the hole diameter 100 $\mu $m are drilled. The discharge occurs in argon with the pressure 100 Torr. The computation results show the potential profile, electron density, ion density and electron temperature distribution. The potential contour shows that the axial electric field is dominant at the discharge initialization and then the radial electric field becomes very important as the forming of the cathode sheath. The results indicate the temporal dynamic behavior of MHCD with the electron density of order 10$^{19 }$m$^{-3}$, electron temperature of several to tens of eV. The peak electron/ion density occurs near the region of the cathode and the dielectric as well as near the anode at the discharge initialization, then localizes along the centerline of the hollow near the cathode. Most of the model predictions are in agreement with experimental data for MHCD under the similar conditions. [Preview Abstract] |
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KTP.00060: Spectroscopic investigations of an atmospheric pressure singlet oxygen plasma source Joao Santos Sousa, Gerard Bauville, Bernard Lacour, Pascal Jeanney, Lionel Magne, Vincent Puech Microcathode sustained discharges (MCSD) offer the possibility to produce DC non-thermal plasmas at high gas pressure. The remarkable stability of MCSD has allowed us to operate glow discharges, free from the glow-to-arc transition, in He/O2/NO mixtures, at atmospheric pressure, with low values of E/N [1]. As a result, these MCSD can efficiently generate large amounts of O2(1D) and O3, which makes them very useful for many biological applications [2]. From optical measurements we deduced the gas temperature, the O density profiles, the O3 spatial distribution, and the yield of O2(1D). The gas temperature in the MCSD was determined from the high resolution spectra of O2 atmospheric band at 760 nm. The O density profiles were measured by Two-photon Absorption Laser Induced Fluorescence spectroscopy, while the O3 density distributions have been obtained by UV absorption spectroscopy. The density of the O2(1D) was evaluated from IR emission at 25cm downstream from the MCSD. The effect of different parameters such as gas flows and mixtures, and discharge current are discussed in the study. [1] J.S. Sousa et al., Appl. Phys. Lett. 93, 011502 (2008) [2] J.S. Sousa et al., these proceedings [Preview Abstract] |
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KTP.00061: Modeling of the spatiotemporal behavior of an argon glow discharge at atmospheric pressure Markus M. Becker, Detlef Loffhagen The spatiotemporal behavior of gas discharges is described by means of a fluid model which comprises the coupled set of balance equations for the densities of electrons, ions and neutral particles, the electron energy balance equation as well as Poisson's equation for the electric potential. This system of equations is numerically solved using a stabilized finite element method. The discharge voltage required for the solution of Poisson's equation is determined from the solution of the external electric circuit equations taking into account the time-dependent capacity and resistance of the plasma. In the present contribution first results related to an argon plasma at atmospheric pressure in a discharge configuration designed to generate small homogeneous high-pressure glow discharges\footnote{W. B\"otticher et al., \textit{Appl. Phys. B} \textbf{54} (1992) 295} are presented. Main features of the temporal evolution of the discharge, which can be divided into Townsend, ignition, quasi-steady-state and recombination phase, are discussed. It is found that the cathode-fall thickness and current density in the quasi-steady state are of the order of the values given by the similarity laws for normal glow discharges. [Preview Abstract] |
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KTP.00062: Fluid modeling of a microwave micro-plasma at atmospheric pressure J. Gregorio, C. Boisse-Laporte, L.L. Alves This paper presents the modeling of an argon micro-plasma produced by microwaves (2.45 GHz) at atmospheric pressure. The study uses a 1D stationary fluid-type code that solves the transport equations for electrons, positive ions, and the electron mean energy, together with Poisson's equation for the space-charge electrostatic field, Maxwell's equations for the electromagnetic excitation field and the gas thermal energy equation (ions are assumed to be in thermal equilibrium with the neutral gas). The model uses a simple kinetic scheme for Ar that includes the ground state, a lumped Ar(4s) excited state, and the Ar$^{+}$ and Ar$_{2}^{+}$ ionization states. The main features are: (i) the existence of combined kinetic-transport features, affecting the populations of both ions species (with similar densities); (ii) a strong decrease in the near-wall values of the electron mean energy, leading to a reduction in the production / destruction rates of Ar(4s) by electron impact, and causing its main production channel, near the wall, to become the electron dissociative recombination of Ar$_{2}^{+}$; (iii) a self-consistent profile of the gas temperature with a small axis-to-wall variation ($\sim $70K). [Preview Abstract] |
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KTP.00063: Microwave micro-plasma sources at atmospheric pressure J. Gregorio, O. Leroy, P. Leprince, C. Boisse-Laporte, L.L. Alves This paper studies two linear resonator sources, which use a continuous 2.45 GHz microwave excitation to produce stable micro-plasmas, in air and in argon, at atmospheric pressure. In both sources, ``large'' volume micro-plasmas ($\sim $10$^{-4}$-10$^{-2}$ cm$^{3})$ are produced and sustained within the 50-200 $\mu $m gap delimited by two metal electrodes (with either 6 mm or 14 mm in length), placed at the open-end of a microstrip-like planar transmission line. The excitation can use ``high'' powers ($\sim $50 W), for long periods, without visible damages of the electrodes, even in air discharges. Particular attention is given to the design and optimization of the sources (in terms of frequency tuning and power coupling), using both simulations and experiments. OES diagnostics allow deducing the rotational, vibrational and excitation gas temperatures, and the electron density (using Stark broadening measurements of the H$_{\beta }$ line-emission profile). Both sources have similar quality factors ($\sim $15), yielding high-density ($\sim $10$^{14}$ cm$^{-3})$, non-equilibrium micro-plasmas, with rotational temperatures ($\sim $600-1500 K) much lower than vibrational and excitation temperatures ($\sim $4500-6000 K). [Preview Abstract] |
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KTP.00064: Comparison of different fluid models for the atmospheric pressure DC glow microdischarge in helium Anatoly Kudryavtsev, Eugene Bogdanov, Kirill Kapustin, Alexander Chirtsov One- and two-dimensional self-consistent fluid simulations of a DC microdischarge in helium at atmospheric pressure were performed. The plasmachemical model used includes five atomic and two molecular excited levels of helium and more than 80 reactions between them. Comparison of simulation results obtained by using this reaction set both with approach of Maxwellian and non-Maxwellian EDF with results from previous papers is presented. Simulations predict main observed properties of DC glow discharge, including formation of the normal current density when discharge occupies only part of cathode (the normal glow discharge). Gas heating was found to play an important role in shaping discharge profiles both in the cathode sheath and plasmas. Basic plasma properties such as density of charged and excited particles, electron and gas temperatures, electric field profiles etc. appeared to depend on choice of reaction set and EDF shape. [Preview Abstract] |
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KTP.00065: Modeling of a microwave plasma torch L.L. Alves, R. Alvarez, L. Marques, S.J. Rubio, A. Rodero, M.C. Quintero This paper presents simulation results for a microwave plasma torch (MPT, at 2.45 GHz). The particular device under study couples the MPT (connected to a coaxial waveguide) to a cylindrical reactor chamber, where it produces helium plasma at atmospheric pressure. The study gives a 2D description of the MPT-reactor system, based on an electromagnetic model (that solves Maxwell's equations adopting a time-harmonic description, to calculate the distribution of the EM fields and the average power absorbed by the plasma) and a hydrodynamic model (that solves the Navier-Stokes' equations for the flowing neutral gas, to calculate the distribution of velocities, mass density, pressure, and temperature within the reactor). Model results, such as the power transmission coefficient and the gas temperature, are particularly dependent on the reactor dimensions, the electron density and temperature, and the gas input flow. Comparison between simulations and measurements reveals common variation trends, with changes in the reactor height, for the power reflected by the system, and yield a qualitative agreement for the axial profile of the gas rotational temperature. [Preview Abstract] |
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KTP.00066: Characterization of a Martian Simulated Discharge Dereth Drake, Svetozar Popovic, Leposava Vuskovic We performed a detailed characterization of a Martian simulated discharge at Mach 2.15. Supersonic flow was generated using a convergent-divergent nozzle upstream of the discharge region. Gases were premixed in the stagnation chamber at room temperature by adding 2.75{\%} N$_{2}$ and 1.55{\%} Ar to pure CO$_{2}$. A cylindrical microwave cavity was used to sustain a discharge in the mixture in the pressure range of 100-600 Pa. Optical emission and absorption spectroscopy were used to determine excited state populations and electron temperature from the Ar spectra. The gas temperature and electron density were determined from the CO {\AA}ngstrom bands and N$_{2}$ C$^{3}\Pi _{u}$-B$^{3}\Pi _{g}$ system, respectively. Results were compared with a kinetic model that included adequate concentrations of CO$_{2}$, N$_{2}$, and Ar, along with CO, O$_{2}$, and NO, in the discharge mixture. [Preview Abstract] |
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KTP.00067: Numerical Simulations of Atmospheric Pressure Discharge using Three-dimensional Fluid Model Muhammad M. Iqbal, Miles M. Turner We elaborate the three-dimensional numerical simulations of uniform and filamentary atmospheric pressure discharge in the parallel-plate dielectric barrier geometry with symmetric boundary conditions. The analysis of spatio-temporal species distribution demonstrates that the different discharge regimes are distinguished with their distinctive properties in the uniform glow and filamentary discharges. The spatial profile of electron density along with surface charge density enhances the understanding of a breakdown pulse for the quarter of a cycle. The temporal evolution of current density exhibits that it increases from 20 to 50 KHz, start decreasing and follows an approximate stable path at higher frequencies. The emergence of filaments is analyzed in the lower frequency regime, which explains the precise internal details of their temporary shapes and patterns during the growth and decay phases of filamentary atmospheric pressure discharge. The noticeable structures of filaments are marked at lower frequencies prominently than higher frequencies because the filaments coalesce and form a uniform distribution of discharge plasma at higher frequencies. The movement of filaments is examined with the slice distributions of electrons, which illuminate the path and constricted part of electron density inside the filaments. [Preview Abstract] |
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KTP.00068: Characterisation of Sub-Millimetre Plasmas J. Greenan, C.M.O. Mahony, P.D. Maguire, D. Maric High pressure molecular gas hollow cathode (HC) plasmas have potential biomedical applications[1,2]. Issues however remain with geometries presented by realistic applications. Here we investigate the electrical {\&} optical characteristics of such a geometry, a 2~mm diameter HC with a variable precisely positioned anode cathode gap. We present HC electrical measurements including static IV, Paschen curves {\&} other derived scaling characteristics eg j/p$^{2}$[3] for various gases (inert and molecular), pressures ($>$100mTorr) {\&} gaps ($<$1 mm). Analysis of these discharge characteristics sheds light on the HC effect in our sub-mm geometries, including instabilities, oscillations {\&} self-pulsing. Investigations of electron distribution {\&} gas temperature via optical emission spectroscopy are under way; plasma density may also be attainable. Other studies include molecular gas dissociation and detection of NxOy {\&} other molecular gases via FTIR spectroscopy using optics developed for point source plasma measurement.\\[4pt] [1] McLaughlin et al 2008 \textit{Diamond {\&} Related Mat} \textbf{17} 873\\[0pt] [2] Mariotti et al 2004 \textit{PSST} \textbf{13} 207\\[0pt] [3] Petrovic et al 2008 \textit{J Phys D }\textbf{41} 194002 [Preview Abstract] |
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KTP.00069: Interactions between atmospheric pressure plasma jets Qais Th. Algwari, Colm O'Neill, Deborah O'Connell Cold atmospheric pressure plasmas offer a unique environment for treatments of soft materials. Here we investigate the possibility of exploiting the interaction of two or more atmospheric pressure plasma jets for increased control and manipulation. The interaction zone itself offers the possibility of a more controllable gentle environment for delicate treatments. The interaction between two counter-streaming atmospheric pressure plasma jets is investigated. The individual plasmas are formed inside a glass tube between two ring electrodes surrounding the tube and driven using a kHz excitation frequency. Gas is supplied between the two electrodes and this design produces significant plasma jets (few centimeters) at both the powered and grounded electrode side. The emission from these jets, while continuous to the naked eye, of a time scale of micro-seconds emits discrete plasma pockets (from both the grounded and powered electrode side). The dynamics of the interaction between these plasma pockets is presented. [Preview Abstract] |
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KTP.00070: Unconfined cylindrical RF discharge at atmospheric pressure Yvonne Sutton, George Naidis, Peter Johnson, Jon Moore, David Sharp, Nicholas Braithwaite Electrical and optical data for a vertical arc discharge sustained at 325 kHz in atmospheric pressure, ambient air have been compared with a fluid model based on the dominant collision processes in nitrogen --oxygen mixtures. This particular non-equilibrium discharge, has been used as an acoustic source; the present analysis is of the unmodulated RF arc. For a 15 mm long, 20 mA discharge, observations and the model reveal that the gas temperature is about 3000 K, the axial field is $\sim $100 kV m$^{-1}$ and the electron density is $\sim $ 2 $\times $ 10$^{17}$~m$^{-3}$; the column radius is $\sim $1 mm in terms of optical emission, but the gas temperature width is about three times broader. [Preview Abstract] |
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KTP.00071: Characterization of microplasmas and nanoplasmas in ambient and above atmospheric pressure liquids and gases David Staack, Aditya Chitre DC glow discharges, DC corona discharges, and nanosecond pulsed corona discharges are investigated in various high density liquids and gases. The discharges are characterized by microscopic visualization, voltage-current measurements, and optical emission spectroscopy. The plasma are investigated with regards to their small feature size, high energy density properties, discharge scaling laws, and instabilities. For operation in gases above atmospheric pressure the DC glow microplasma discharges behave as pressure scaled version normal glow discharges though there are significant temperature effects and the ionization overheating instability becomes more prevalent at higher pressures. Energy densities in the plasmas may range to as high as 10$^{26}$ J/m$^{3}$ in pulsed and transient high density discharges. Temperatures range from near ambient to thermal plasma conditions depending on increasing with operating density and pulse duration. In pulsed high energy density operation in liquids and high pressure gases a short ($\sim $50 ns) transition from non-thermal to thermal regime is observable. For operation in liquids and very high pressure gases discharge features $\sim $ 200 nm in size are apparent leading to the possibility of direct write nanofabrication by PECVD and plasma etching techniques using such nanoplasmas. [Preview Abstract] |
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KTP.00072: Structure of a micro hollow cathode discharge in the normal regime at medium pressure range in pure argon Claudia Lazzaroni, Pascal Chabert, Antoine Rousseau, Nader Sadeghi A microplasma is generated in the 400 $\mu $m diameter micro hole of a molybdenum-alumina-molybdenum sandwich (MHCD type) at medium pressure (30-300Torr) in pure argon. Experiments are performed during the normal regime, when the plasma is not only confined in the hole but also expands on the cathode backside. Imaging and emission spectroscopy allows the discharge structure to be studied and is used to infer the electronic density in the micro-hole via the Stark broadening of the H$_{\beta }$ line. We find strong maxima of the plasma emission in the vicinity of the sheath edge. To explain some of the experimental observations, we use a one dimensional transport model to obtain the radial evolution of the charged-particles densities and fluxes. The result of this model is used as an input parameter of a sheath-model which allows the sheath thickness to be calculated as a function of pressure. The sheath size variation with pressure is well correlated with the maxima of plasma emission. [Preview Abstract] |
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KTP.00073: THERMAL PLASMAS: ARCS, JETS, SWITCHES, OTHERS |
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KTP.00074: Experimental study of vacuum arc with different electrode materials Dingge Yang, Shenli Jia, Lijun Wang, Liuhuo Wang, Zongqian Shi The material of electrodes is essential to affect the characteristics of vacuum arcs and the interruption performance of vacuum circuit breakers. In order to clarify the effect of electrode material on arc appearance and breaking capacity, experiments of cup-shaped axial magnetic field electrodes made of Cu and Cu70Cr30 were conducted respectively in a detachable vacuum chamber, with arc current varying from 5kA to 25kA (rms). The diameter of the electrodes is 58mm and the gap distance was fixed at 10mm in the experiments. The appearances of arc column, cathode surface and anode activities were recorded by a digital high-speed camera and the arc voltage was measured by a high-voltage probe of oscilloscope. The photos of contact surface erosion after experiments were also given. The experimental results of Cu electrodes were compared with those of Cu70Cr30 electrodes, the differences of the two kinds of vacuum arcs were given and those influencing the breaking capacity were also illustrated. [Preview Abstract] |
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KTP.00075: Structure and expansion characteristics of laser ablation tin plasma into a vacuum Qiushi Zhu, Junzaburo Yamada, Nozomu Kishi, Tomonao Hosokai, Masato Watanabe, Akitoshi Okino, Kazuhiko Horioka, Eiki Hotta The structure and expansion characteristics of the plasma plume produced by laser ablation of a bulk tin target in vacuum have been investigated. A Q-switched Nd: YAG laser with 1064 nm wavelength, 5 ns pulse width, and the order of 10$^{11}$ W/cm$^{2}$ power density was employed to create ablation plasma. Time-of-flight (TOF) measurements using a movable Faraday cup were conducted to study the velocity distributions of the tin ions in the ablation plume. The results exhibited triple-peak structure of the TOF spectra: two groups of fast ions with the mean velocity of $\sim $100 km/s and $\sim $60 km/s respectively, and a dominating slow ion group with the velocity less than 50 km/s. By fitting the velocity spectrum of the slow ion group with shifted-Maxwell-Boltzmann distribution, a multimodal structure with three distinct velocity distributions attributed to the ions with different charge states was obtained. The evolution dynamics of the Sn I and Sn II in the erosion tin plasma plume were compared using the optical emission lines. The results displayed different plume shapes of Sn I and Sn II due to different contributing factors towards the expansion dynamics; the drift velocity of Sn II in the plasma plume was in good agreement with the TOF results of the Faraday cup experiment. [Preview Abstract] |
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KTP.00076: Two-temperature modeling of a magnetically rotating arc Margarita Baeva, Detlef Loffhagen, Dirk Uhrlandt A three-dimensional, two-temperature MHD model of a DC plasma torch has been developed to study the behavior of a magnetically rotating arc in argon at atmospheric pressure. The torch consists of a 10~mm long rod-type cathode with a diameter of 3~mm surrounded by a 25~mm long hollow anode with a diameter of 10~mm. The arc is supplied by a current of 200~A. Without external axial magnetic field a heavy particle temperature $T_{h}$ of about 14000~K and 8000~K is obtained near the cathode tip and downstream in the plume, respectively. Significant temperature differences between the electron temperature $T_{e}$ and $T_{h}$ up to a factor of 1.4 are found in the arc fringes. When applying an external axial magnetic field of 0.04~T, the high temperature plasma inside the torch is retracted axially and expanded radially. It is involved in rotation due to the Lorentz force and a backflow appears in front of the cathode close to the axis. The inflow and backflow gases impinge onto the anode. $T_{e}$ and $T_{h}$ are about 18000 and 13500~K, respectively, at maximum. The $T_{e}$ profile gets broader than that of $T_{h}$. Both profiles are prolonged towards the anode. A similar behavior is observed for the arc power density and the electron density distribution. [Preview Abstract] |
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KTP.00077: Microwave Argon Plasma Torch Edgar Felizardo, Mariana Pencheva, Evgenia Benova, Fransisco Dias, Elena Tatarova A theoretical and experimental investigation of a microwave (2.45 GHz) Argon plasma torch driven by a surface wave is presented. The theoretical model couples in a self-consistent way the wave electrodynamics and the electron and heavy particle kinetics. The set of coupled equations includes: Maxwell's equations, the electron Boltzmann equation, including electron-electron collisions, and the particle balance equations for electrons, excited atoms (4s, 4p, 3d, 5s, 5p, 4d, 6s), and atomic (Ar$^{+})$ and molecular ions (Ar$_{2}^{+})$. The input parameters of the model are: gas pressure (760 Torr), plasma radius ($R$ = 0.75 cm), dielectric permittivity ($\varepsilon _{d}$ = 4.0) and tube thickness (d = 0.15 cm) as well as the measured axial profile of the gas temperature (3500 K - 1500 K). The latter was determined from measurements of the rotational temperature of the OH molecular band in the range 306 - 315 nm. Phase and amplitude sensitive recording provides the data for the axial wavenumber and wave attenuation coefficient. The wavenumber decreases along the generated plasma torch. The electron density (N$_{e})$ axial profile as determined from measurements of H$_{\beta }$ Stark broadening is in agreement with the theoretical one. [Preview Abstract] |
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KTP.00078: Wave Driven Ar--N$_{2}$--H$_{2}$ Plasma J. Henriques, F.M. Dias, E. Tatarova, C.M. Ferreira An experimental investigation of the spatial structure of an Ar--N$_{2}$--H$_{2}$ plasma torch is presented. A surface wave induced microwave (2.45 GHz) plasma torch is created using a conventional, surfaguide based set-up. A cylindrical, fused quartz discharge tube (with internal and external radii R$_{1}$=7.5 mm and R$_{2}$=9.0 mm, respectively) is filled by an Ar(78{\%})--N$_{2}$(20{\%})--H$_{2}$(2{\%}) gas mixture at atmospheric pressure. A spectroscopic imaging system able to couple the plasma-emitted radiation into a SPEX 1250M spectrometer, equipped with a nitrogen cooled CCD camera, was used to measure 2D(r,z) profiles of emission intensities and line profiles. Abel inversion has been applied to derive the radial profiles from the side-on measurements. The H$_{\beta }$ line profiles have been measured to determine the corresponding Doppler temperature and the electron density. The measurements are well fitted by Voigt profiles, whose Gaussian and Lorenzian components have been deconvoluted. In this way, hyperthermal hydrogen atoms have been detected. The measured Doppler temperatures (5,000--8,000 K) are higher than the rotational temperature by a factor of about 2. The 2D map of the electron density (5x10$^{12}$--5x10$^{13}$ cm$^{-3})$ was also obtained. Acknowledgement- This work was supported by the Funda\c{c}\~{a}o para a Ci\^{e}ncia e a Tecnologia, Minist\'{e}rio da Ci\^{e}ncia, Tecnologia e Ensino Superior, Portugal [Preview Abstract] |
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KTP.00079: LIGHTING PLASMAS: GLOWS, ARCS, FLAT PANELS, NOVEL SOURCES, OTHERS |
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KTP.00080: UV Discharge Lamp on Distilled Water Vapor Svetlana Avtaeva, Andrij General Recently interest in sources of ultra-violet (UV) radiation in a wavelength range of 200-400 nm has increased. Therefore we have created a source of spontaneous, incoherent UV radiation on distilled water vapor excited by the low-pressure capacitive discharge (1 Torr). Spectral, temporary and energy characteristics of the spontaneous UV radiation source have been experimentally studied. In addition the electron energy distribution function (EEDF), the mean electron energy, electron transport coefficients, rate constants of elastic and inelastic electron collisions with atoms and electron energy losses have been theoretically calculated with help of the program Bolsig+. Results of the theoretical calculation are used for optimizing radiative characteristics of the radiation source. Advantages of the created lamp based on the low-pressure capacitive discharge on water vapor are: 1) inexpensive and ecologically safe working medium on the basis of hydroxyl radicals; 2) absence of electrodes in a gas-discharge zone that allows to hope for significant increasing their useful operation resource, in comparison with lamps of glow or other discharges; 3) simplicity of the lamp construction. [Preview Abstract] |
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KTP.00081: A study on the influence of operating circuit on the position of emission point of fluorescent lamp Tadao Uetsuki, Yuki Genba, Takashi Kanda High efficiency fluorescent lamp systems driven by high frequency are very popular for general lighting. Therefore it is very beneficial to be able to predict the lamp's life before the lamp dying, because people can buy a new lamp just before the lamp dying and need not have stocks. In order to judge the lifetime of a lamp it is very useful to know where the emission point is on the electrode filament. With regard to a method for grasping the emission point, it has been reported that the distance from the emission point to the end of the filament can be calculated by measuring the voltage across the filament and the currents flowing in both ends of the filament. The lamp's life can be predicted by grasping the movement of the emission point with operating time. Therefore it is very important to confirm whether the movement of the emission point changes or not when the operating circuit is changed. The authors investigated the difference in the way the emission points moved for two lamp systems which are very popular. One system had an electronic ballast having an auxiliary power source for the heating cathode. Another system had an electronic ballast with no power source, but with a capacitor connected to the lamp in parallel. In this presentation these measurement results will be reported. [Preview Abstract] |
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KTP.00082: A study on the ignition characteristics of inductively coupled electrode-less lamp Tadao Uetsuki, Masao Fujita, Motohiro Saimi, Hidenori Kakehashi Almost twenty years have passed since the first electrode-less lamp operated at 13.56MHz was put on the market. Since then, it has come to be expected that the lumen output and the efficiency of these lamp systems would be improved. The present electrode-less lamp system operated at 135kHz has higher efficiency and output than the high pressure mercury lamp system which is very popular in the market. However, the ignition mechanism of the electrode-less lamp has not yet been completely worked out. To grasp the ignition voltage and time is very important for designing this lamp system, because these influence the cost of the system. The authors investigated how to reduce the ignition time. With regard to the ignition for magnetic coupled electrode-less lamp, it was reported that there are theoretically two types of ignition, E-discharge and H-discharge. However, the definition of the ignition actually is regarded as the time when the H-discharge occurs. The authors observed the starting state of the electrode-less lamp and found that the performance of the circuit influenced the transition from E- discharge to H- discharge. The large current is necessary for the smooth transition from E- discharge to H- discharge right after the E- discharge occurs. [Preview Abstract] |
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KTP.00083: A study on the relationship between CCFL's characteristics and gas pressure Tadao Uetsuki, Naoki Aoyama, Yuji Takeda, Hidetoshi Yano, Osamu Fukumasa A continuous improvement in the lumen output and efficacy of the cold cathode fluorescent lamps (CCFLs) used for the backlight of LC-TVs is always expected. The lumen output and efficacy can be improved by controlling the electric field intensity by changing gas pressure. Therefore it is very important to grasp the relationship between the CCFL's characteristics and gas pressure. The authors investigated the influence of gas pressure on the cathode fall voltage (CFV) and the electric field intensity of the positive column. The measurement results show mainly three points. The first is that the CFV of the Ne-Ar lamp reaches a minimum at 5.3kPa, while the CFVs of the Ne-Ar-Hg lamps decrease with a rise in gas pressure monotonously. This difference is caused by the variation of the sheath thickness arising from the presence of the mercury. The second point is that the CFV of the Ni-electrode lamp is higher than the Mo-electrode lamps' whether the mercury is present or not. This is caused by the difference of gamma coefficients between Ni and Mo. The third point is that the electric field strength increases with a rise in gas pressure whether the mercury is present or not. This is caused by the increase of the elastic collision loss between electrons and atoms. [Preview Abstract] |
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KTP.00084: UV Discharge Lamp on Alcohol Vapor Svetlana Avtaeva, Andrij Heneral The non coherent sources of UV radiation based on safe and nontoxic gaseous mixtures have good aspects for different applications. The paper reports about experimental investigations of the high voltage capacitive discharge in alcohol vapor. The time-integrated emission spectra have been studied in the wavelength interval from 200 to 400~nm at alcohol vapor pressure of 1 Torr. In the spectra the most intensive bands were vibrational bands of the \textit{CO}(\textit{b$\to $a}) transition with heads at 283.3~(0-0), 297.7~(0-1), 313.4~(0-2), 330.5~(0-3) and 349.3~nm (0-4). The (0-2)~ band of \textit{CO} molecules superimposes with (0-0) and (1-1) vibrational bands of the \textit{CH}(\textit{C$\to $X)} transition with $Q$-heads at 314.49 and 315.66~nm on the long wavelength side and with bands of $OH$ radicals with intensity maximums at 308.1 and 309.2~nm (\textit{A$\to $X} transition) on the short wavelength side. No other radiating species were detected. The emitting surface area of the lamp is 220 cm$^{2}$, average output power of the UV radiation is 70 mW and the estimated efficiency is 0.2{\%}. This source of UV radiation can be applied in photochemistry, in medicine, for disinfection of medical tools, in ecology and for purification and disinfection of water from different pathogenic microorganisms. [Preview Abstract] |
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KTP.00085: Study of the 222 nm KrCl emission produced by nanosecond pulsed arrays of microdischarges Virginie Martin, Gerard Bauville, Bernard Lacour, Vincent Puech Microdischarges operating in DC mode have been widely used for producing VUV emission from rare-gas excimers. However for biological applications, pulsed UV sources emitting in the range 200-280 nm (DNA absorption band) are required. They can be obtained from exciplex molecules produced in discharges operating in rare-gas halogen mixtures. Up to now, DBD's have been mainly used to generate these emissions. However, the use of arrays of microdischarges could be very advantageous due to a simpler geometry, a reduced operating voltage and the possibility of higher power loading. The present paper reports results obtained from arrays of microdischarges powered, in Kr/Cl2 mixtures, by nanosecond pulsed discharges operating at high repetition frequency. It will be shown that, without individual resistive ballasting, the nanosecond pulsed mode allows the simultaneously ignition of all microdischarges. As a result, an intense emission at 222 nm is obtained. Weak emissions from Cl2* at 258 nm and from krypton at 762 nm are also detected. The influence, on the intensity of these emissions, of the different experimental parameters: total pressure, chlorine concentration, energy per pulse and repetition rate frequency, was studied and the conditions allowing the optimization of the 222 nm will be reported. [Preview Abstract] |
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KTP.00086: Modeling and simulation of emitter effects at cathodes in high intensity discharge lamps Andre Bergner, Frank Scharf, Juergen Mentel The temperature of tungsten cathodes in high intensity discharge lamps may be kept down by reducing the work function $\phi$. This can be accomplished by an atomic dipole layer on the electrode surface made of a certain emitter material, e.g. thorium. If the emitter material is deposited by an ion current, $\phi$ will be reduced mainly in the center of the arc attachment area. This local reduction may cause a constricted arc attachment, called emitter spot. The power balance of the arc cathode can be simulated using the power flux density and current density as boundary conditions [1]. Both are functions of $\phi$ and the local cathode surface temperature. The emitter spot is simulated in accordance with experimental results [2] by a superposition of transfer functions for $\phi=4.55\,\mathrm{eV}$ and $\phi<4.55\,\mathrm{eV}$, weighted in dependence on temperature. \\[4pt] [1] S. Lichtenberg et al. Phys. D: Appl. Phys. {\bf 38} (2005) 3112--3127.\\[0pt] [2] G. K\"{u}hn et al., Phys. Rev. {\bf E} 75, 016406 (2007). [Preview Abstract] |
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KTP.00087: Investigation of Ce-emitters in high intensity discharge lamps Cornelia Ruhrmann, Michael Westermeier, Jens Reinelt, Peter Awakowicz, Juergen Mentel The improvement of lifetime is a particular interest of actual research into HID lamps. It can be achieved by a reduction of the temperature of the lamp electrodes being accomplished by the so called ``emitter effect.'' It is generated by an atomic monolayer of certain emitter elements (e.g. Ce, Dy) on the tungsten electrode surface by which the work function is reduced. By means of a special optical absorption spectroscopy setup - presented in an accompanying contribution - the absorption coefficient of resonance lines is measured and the ground state atom density of the respective emitter material is determined within the plasma. Spatial and phase resolved measurements of Ce-densities and associated electrode temperatures in special research HID lamps will be presented for low and high frequencies. An emitter effect is observed not only in the cathodic but also in the anodic phase. At high frequencies the effect of the emitter material on the electrode temperature converges in both phases due to the inertia of the Ce-atoms and ions. [Preview Abstract] |
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KTP.00088: Ab initio based calculation of emission properties of Ar-AlCl$_{3}$ glow discharge Maxim Deminsky, Boris Potapkin, Stanislav Umanskii, Alexander Zaitsevskii, David Smith, Darryl Michael, Timothy Sommerer Emission properties of Ar-AlCl$_{3}$ DC glow discharge were calculated using ``Chemical Workbench'' VIBRAKIN code in frame work of quasi 1D model. Unknown properties of atoms and molecules were calculated from first principles. Potential energy curves of Al$_{x}$Cl$_{y}^{-}$ negative ions were performed by approximate quadratic coupled cluster (AQCC) and SCF methods. Potential energy curves, transition dipole moments of neutral species Al$_{x}$Cl$_{y}$ were calculated based on many-body multipartitioning perturbation theory (MPPT). These data are used for evaluation of the cross sections of the electron impact dissociative attachment and vibrational excitation for AlCl$_{3}$ and fragments of its decomposition. The cross sections of the electron impact excitation of electronic states of atoms and molecules are evaluated in frame work modified Born approximation with taking into account electron exchange. Based on calculated properties of molecular ions, the rate parameters of thermal ion-molecular reactions of molecular ions conversion were calculated. The calculation results present dependencies of the electron energy balance and the emission efficiency as a function of the plasma parameters. [Preview Abstract] |
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KTP.00089: Non Empirical Calculation of Emission Properties of Xe:Cl$_{2}$:Ar Glow Discharge Maxim Deminsky, Irina Chernysheva, Alexander Eletskii, Igor Kochetov, Andrei Zaitsevskii, Boris Potapkin, Darryl Michael, David Smith, Timothy Sommerer Emission properties of the Xe:Cl$_{2}$:Ar DC glow discharge have been calculated using the kinetic code VIBROKIN. Potential energy curves for the ground and excited states and the electronic transitions strengths of XeCl excimer molecule are calculated ab initio within the quasirelativistic many-electron intermediate Hamiltonian approach; the relativity is introduced through the relativistic pseudo-potentials of atomic cores. The cross section of the harpooning reaction responsible for formation of XeCl excimer molecule is evaluated on the basis of the asymptotic method. The similar approach was also applied for estimation of the cross section for quenching the XeCl excimer molecule and metastable Xe atoms by Cl$_{2}$ molecule. The electron impact excitation cross sections for the mixture components as well as the Cl$_{2}$ dissociation cross section were calculated using modified Born approximation, taking into account electron exchange. The calculation results present dependencies of the electron energy balance and the excimer emission efficiency as a function of the reduced electrical field strength, electron number density and gas mixture composition. [Preview Abstract] |
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KTP.00090: Parametric study of the breakdown of high intensity discharge lamps filled with xenon Martin Wendt, Manfred Kettlitz, Detlef Loffhagen, Silke Peters A parametric study of model results on the breakdown of high intensity discharge lamps filled with xenon at pressures between $0.1$ and $5$~bar is presented. The results are compared with experimental measurements of voltage and current waveforms obtained for voltage rates of increase from $5$~mV/ns to $100$~V/ns. Specially designed lamps ensure a volume breakdown of the gas. The time-dependent, spatially one-dimensional model comprises the Poisson equation, electron energy balance and species continuity equations using the drift-diffusion approximation for the fluxes. The set of equations is solved on an inhomogeneous grid using the cubic interpolated propagation scheme with an adaptive time step. The electron transport parameters were used as function of the local mean electron energy. They were determined by solving the homogeneous Boltzmann equation. The breakdown voltages obtained by the model increase with growing pressure and voltage rate and are in good agreement with the experiments. A cathode-directed ionization front is found whose velocity increases with rising voltage rate and falling pressure. [Preview Abstract] |
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KTP.00091: Ultra High Luminance and Luminous Efficacy Mercury-free Flat Fluorescent Lamp In Woo Seo, Byung Joo Oh, Jae-Chul Jung, Ki-Woong Whang We proposed a new Mercury-free Flat Fluorescent Lamp (MFFL) as a flat light source which can be used as an alternative of conventional line-type Cold Cathode Fluorescent Lamp (CCFL) containing Mercury. The MFFL using dielectric barrier discharge with Ne-Xe gas mixtures has a pair of the parallel-running main electrodes covered by dielectric layer in a 40x40 mm size of the emission area as a unit cell. A new electrode structure and optimized driving methods have been adopted to make an effective glow discharge which shows a wide driving voltage margin. In order to realize the high luminance and luminous efficacy MFFLs, we optimized the phosphor profile to enlarge the surface area. The MFFL with the new phosphor profile shows a very wide luminance range from 2,600 to 17,000 nit with the corresponding luminous efficacy from 66 to 32.5 lm/W. The results were obtained with the color coordinate of the phosphor to be around (0.25, 0.23), which is required for LCD backlights. The work to realize improved luminance and luminous efficacy MFFLs with the color coordinate (0.32, 0.32) for daylight lighting is in progress. [Preview Abstract] |
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KTP.00092: Rapid estimates of plasma emission spectra from any atomic species David Smith, Tim Sommerer A method has been developed and implemented to provide rapid estimates of emission spectra from plasmas in atomic gases. Results from these calculations have been validated against experimental data for species with both sparse (Sn) and dense (Zr) emission spectra. The calculation relies on two profound assumptions on the atomic-plasma kinetics, namely a modified Boltzmann distribution of the excited-state densities accounting for a non-Maxwellian distribution, and a general expression for radiation trapping. The atomic density and excitation temperature are the input variables; the excitation temperature includes an additional scaling function to simulate the inelastic depletion of high-energy electrons. The model has been applied to identify Sb, Ge, Ga, Sn, Pt, and Mg as the most promising atoms for germicidal sources (excluding Hg). Additionally it has used to select species and gas phase densities of additives to avoid arc constriction in plasmas where most of the radiation comes from atoms with dense emission spectra. [Preview Abstract] |
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KTP.00093: PLASMA PROPULSION AND AERODYNAMICS |
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KTP.00094: Performance prediction of a novel microplasma thruster with microhollow cathode discharge Guangqing Xia, Genwang Mao The gas heating of microhollow cathode discharge(MHCD) is found to have a strong relation with overall discharge behavior in the theoretical and experimental investigation. It provides crucial understanding to support the application and preliminary design of MHCD plasma thruster. The hot gas heated is expanded through a Laval-type converging-diverging micro-nozzle to produce thrust. With the MHCD hole diameter 100 $\mu $m and at the pressure 50$\sim $750 Torr, input power 0.15$\sim $2 W and mass flow rate 0.15$\sim $1.5 mg/s, the thrust produced by this kind of propulsion system is preliminary expected to be in the range of several tens to several thousands $\mu $N and the specific impulse is evaluated on the order of 600$\sim $1000 N$\cdot$s/kg when using argon while on the order of 3000 N$\cdot$s/kg using helium as the propellant gas. From the main performance of the MHCD plasma thruster, it can be applied as a new microplasma propulsion system for attitude control and station keeping of nano-satellites. [Preview Abstract] |
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KTP.00095: A multi-fluid 2-D simulation of a co-axial Hall plasma discharge Aaron Knoll, Mark Cappelli A multi-fluid 2-D simulation of a co-axial E x B plasma discharge is presented, resolving the azimuthal dynamics leading to the growth and saturation of high-frequency (0.5 -- 10 MHz) azimuthally-propagating fluctuations. The simulation accounts for finite-rate ionization kinetics, with associated losses of particles and energy to the bounding ceramic walls. These discharges are typical of Hall thruster plasma accelerators, which are increasingly being used in space propulsion applications. The simulations presented are for full scale thrusters that operate in the 1 kW power levels, capturing the entire azimuthal domain. The simulations focus on the role played by these fluctuations in establishing the cross-field electron current in regions of relatively strong magnetic fields (50-200 Gauss). The time-average predictions for plasma properties are in qualitative and quantitative agreement with experiments, and the findings seem to be supportive of the experimental results that indicate that high frequency fluctuations may be more important at defining electron current at lower discharge voltages, where the azimuthal electron shear is small. [Preview Abstract] |
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KTP.00096: V-I Characteristics and Power Measurements in Asymmetric Dielectric Barrier Discharges Dmitry Opaits, Mikhail Shneider, Richard Miles, Sergey Macheret Dielectric barrier discharge (DBD) plasma actuators for flow control have been under extensive studies for the last decade. It is usually driven by a sinusoidal voltage profile at up to 20 kHz frequency, although some other voltage profiles, such as square, triangular, and positive and negative sawtooth, were also used and in some cases demonstrated an improvement in performance. A voltage profile consisting of nanosecond pulses added to bias voltage was also found to be effective in generating wall jets. It was also shown that if the dielectric is coated with a semiconductive material the actuator can be driven by dc voltage only. This work will present V-I characteristics and power consumption of the plasma actuators driven by various voltage profile, including sinusoidal in wide range of frequencies, nanosecond pulses and dc, and compare their efficiency. [Preview Abstract] |
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KTP.00097: Particle Simulation of a Micro ICP Plasma Source for Miniature Ion Thruster Yoshinori Takao, Koji Eriguchi, Kouich Ono There has recently been an ongoing trend toward decreasing the mass, dimension, and overall complexity of spacecraft. Propulsion systems are no exception. We have developed an electrothermal-type microthruster so far, which can produce a relatively high thrust, and have investigated the thrust performance with an experimental and numerical approach. On the other hand, a microthruster with a high specific impulse, such as ion thruster, is also required. The micro ion thruster presented here uses a cylindrical micro ICP with a flat spiral coil for its ion source, the inner radius and the length of which are 3 mm and 6 mm, respectively. To investigate the plasma characteristics of the source, we have developed a particle simulation model (PIC/MC: Particle-in-Cell/Monte Carlo) for Ar gas as a propellant. The simulation results showed that the electron density obtained was $\sim 10^{17}$ m$^ {-3}$ at an Ar gas pressure of 4 mTorr with an absorbed power of 10 mW, producing a thrust of 50 $\mu$N and specific impulse of 7000 s. [Preview Abstract] |
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KTP.00098: Analysis of a new Extraction Aperture for the Nonambipolar Electron Source Jesse Gudmundson, Noah Hershkowitz, Lutfi Oksuz The Nonambipolar Electron Source (NES) is a radio frequency plasma-based electron source that does not rely on electron emission at a cathode. All electrons are extracted at an electron sheath through a biased ring and all ions are lost radially to a separately biased cylindrical graphite Faraday shield. Plasma density increases and electron confinement at the ring improves by the addition of an axial magnetic field. An electromagnet in the original NES has been replaced by a NdFeB magnet array. Approximately 30{\%} of the electron current was extracted using the magnet array. The remainder was lost to the ring while the electromagnet provided 90{\%} extraction efficiency. A disk with a concentric hole has replaced the ring and the hole diameter was varied to improve extraction efficiency. The disk was separated from the cylinder to prevent shorting between them and sputtering of graphite on the insulator between the ring and the cylinder seen previously. Plasma potential, plasma density, electron temperature, and electron energies in the plume measurements as well as time resolved ICCD camera images of the plume will be discussed. [Preview Abstract] |
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KTP.00099: Wall material effect on electron transport in Hall thruster discharge Yevgeny Raitses, Leonid Dorf, Igor Kaganovich, Nathaniel J. Fisch, Dmytro Sydorenko Plasma-wall interaction is studied for annular Hall thruster configurations, in which collisionless plasma is bounded by channel walls made of ceramic and graphite materials with different secondary electron emission (SEE) properties [1]. Plasma properties and discharge characteristics are measured for different discharge voltages at the same magnetic field [2]. It is shown that the electron cross-field mobility in the thruster with ceramic walls is higher than in the thruster with graphite walls. Results of analytical modeling [3] and participle-in-cell simulations [4] demonstrate that this effect is a consequence of higher SEE of ceramic materials. [1] Y. Raitses, D. Staack, A. Dunaevsky and N. J. Fisch, J. Appl. Phys. 99, 036103 (2006). [2] Y. Raitses, A. Smirnov, D. Staack, and N. J. Fisch, Phys. Plasmas 13, 014502 (2006). [3] I. Kaganovich, Y. Raitses, D. Sydorenko and A. Smolyakov, Phys. Plasmas 14, 057104 (2007). [4] D. Sydorenko, A. Smolyakov, I. Kaganovich, and Y. Raitses, Phys. Plasmas 13, 014501 (2006). [Preview Abstract] |
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KTP.00100: Time resolved Schlieren imaging of DBD actuator flow fields Cyrus Nourgostar, Lutfi Oksuz, Noah Hershkowitz Schlieren imaging methods measure the first derivative of density in the direction of a knife-edge spatial filter. It has been used extensively in aerodynamic research to visualize the structure of flow fields. With a single barrier planer dielectric barrier discharge (DBD) actuator, Schlieren images clearly show the absence of significant vertical air flow normal to the surface, and no more than few millimeters thick induced boundary layer flow. A gated intensified CCD camera along with a Schlieren system can not only visualize the flow field induced by the actuator, but also temporarily resolve the images of the flow and plasma field. Our time resolved images with triangular applied voltage waveforms indicate that several separate discharge regimes occur during positive and negative going half cycles of single and double barrier DBD actuators. Time resolved Schlieren imaging of both single and double barrier DBDs with different applied waveforms, discharge parameters and electrode geometries reveal important information on the induced flow structure. [Preview Abstract] |
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KTP.00101: Nonequilibrium Supersonic Flow Field Measurements in a Mach 5 Plasma Wind Tunnel Munetake Nishihara, Keisuke Takashima, Naibo Jiang, Walter Lempert, Igor Adamovich, J. William Rich The effect of molecular energy transfer in nonequilibrium gas dynamic flows on supersonic/hypersonic flow field is studied using a Mach 5 nonequilibrium plasma wind tunnel. The tunnel uses a high pressure (0.5-1.0 atm) stabilized glow discharge in its plenum to load energy into internal molecular modes. The electric discharge system incorporates a repetitive nanosecond pulse discharge which weakly ionizes the flow and transverse DC discharge to load power into the vibrational energy mode of nitrogen. Translational temperature of the flow in the discharge remains low, 350-400 K, while vibrational temperature of nitrogen is up to 2,000 K. Vibration-translation (V-T) relaxation of nitrogen downstream of the discharge is accelerated by injecting hydrogen into the flow. The effect of partial vibrational relaxation of nitrogen on a shock wave stand-off distance in front of a cylinder model in a Mach 5 flow is studied by schlieren imaging and by NO Planar Laser-Induced Florescence (PLIF) using a pulse burst laser operating at a pulse repetition rate of 20 kHz. [Preview Abstract] |
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KTP.00102: DUSTY PLASMAS |
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KTP.00103: Ion-acoustic solitons in multi-components dusty plasmas Amandeep Singh Bains, Tarsem Singh Gill We have considered a hot dusty plasma system containing ions, electrons, positrons and negatively charged dust to study the solitary potential structures. Using reductive perturbation method, the Kadomtsev--Petviashvili (KP) equation has been derived. We have studied the characteristics of ion-acoustic solitary waves associated with negative/positive potential. The nonlinearity and dispersion coefficients are the function of positron to electron density ratio, dust density parameter, ion temperature and ratio of positron to electron temperature. It is observed that the amplitude and width of the solitary potential structures change with the variation of these parameters. We have explored the parametric regime for which the different type of negative/positive solitary potential structures exists. [Preview Abstract] |
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KTP.00104: Some Basic Experiments on Dusty Plasma with Negative Hydrogen Ions Generation Bipul Kumar Saikia, S.S. Kausik, B. Kakati, M. Bandyopadhyay Some parametric studies like the effect of discharge current, plasma temperature and working pressure on the charging of dust grains in hot cathode discharge plasma will be presented. The designing concepts of a novel experiment to produce negative hydrogen ions from Cesium coated dust particles and related preliminary studies with dust particles in hydrogen plasma will be presented. The aim of producing negative hydrogen ions is to devise the possibility of using such negative ions in Neutral Beam Injection Heating of Tokamak plasma. \textbf{Refs: } S.S. Kausik, M.Chakraborty, P. Dutta, M. Kakati and B.K. Saikia, \textit{Phys. Lett. A} 372, 860 (2008) [Preview Abstract] |
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KTP.00105: NEGATIVE ION PLASMAS |
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KTP.00106: WORKSHOP ON ADVANCES IN THE KINETIC DESCRIPTION OF LOW-TEMPERATURE PLASMAS: APPLICATIONS TO MODELING AND SIMULATION |
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KTP.00107: Study of the electron kinetics in abnormal dc glow discharges in oxygen by a multiterm approach and Monte Carlo simulations Gordon K. Grubert, Detlef Loffhagen The nonequilibrium properties of the electron component in gas discharge plasmas determine decisively the behavior of the whole discharge. These properties are commonly determined by solving the electron Boltzmann equation using a multiterm approximation of the Legendre polynomial expansion of the electron momentum distribution function or by performing Monte Carlo simulations. For comparative kinetic studies of spatially inhomogeneous plasmas, consistent conditions at the spatial margins of the discharge arrangement are required. Extended boundary conditions at the electron emitting cathode are represented, which are adequate for the direct comparison of multiterm Boltzmann equation calculations and Monte Carlo simulations. First results for dc discharges in oxygen at conditions typical of abnormal glow discharges are discussed. The excellent agreement between the results of both the independent kinetic approaches verifies the extended boundary conditions deduced. [Preview Abstract] |
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KTP.00108: Verification of high voltage rf capacitive sheath models with particle-in-cell simulations Ying Wang, Michael Lieberman, John Verboncoeur Collisionless and collisional high voltage rf capacitive sheath models were developed in the late 1980's [1]. Given the external parameters of a single-frequency capacitively coupled discharge, plasma parameters including sheath width, electron and ion temperature, plasma density, power, and ion bombarding energy can be estimated. One-dimensional electrostatic PIC codes XPDP1 [2] and OOPD1 [3] are used to investigate plasma behaviors within rf sheaths and bulk plasma. Electron-neutral collisions only are considered for collisionless sheaths, while ion-neutral collisions are taken into account for collisional sheaths. The collisionless sheath model is verified very well by PIC simulations for the rf current-driven and voltage-driven cases. Results will be reported for collisional sheaths also. [1] M. A. Lieberman, IEEE Trans. Plasma Sci. 16 (1988) 638; 17 (1989) 338 [2] J. P. Verboncoeur, M. V. Alves, V. Vahedi, and C. K. Birdsall, J. Comp. Phys. 104 (1993) 321 [3] J. P. Verboncoeur, A. B. Langdon and N. T. Gladd, Comp. Phys. Comm. 87 (1995) 199 [Preview Abstract] |
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KTP.00109: On Application of Transport Coefficients in Plasma Modelling Z. Lj. Petrovic, S. Dujko, Z. Nikitovic, D. Maric, G. Malovic, R.E. Robson, R.D. White In this paper we review recent developments in the transport theory as developed to deal with the so- called swarm experiments. We analyze where and how such results can affect the outcome of the plasma models [1]. In principle it is well understood that modeling of plasmas requires representing a large number of processes, and for a large group of these one does not know all the pertinent physical processes and even more so there is a general shortage of data. In that respect insisting on purity in the representation of the charged particle, in particular electron transport seems unnecessary. Nevertheless we wish to draw attention that neglecting some aspects of electron transport may lead to neglecting some important aspects of physics. We wish to draw attention to proper representation of the transport in crossed electric and magnetic fields, differences between flux and bulk transport properties under appreciable influence of non-conservative processes, temporal development of transport coefficients, anisotropy of diffusion and anomalous longitudinal diffusion when field changes direction and many more. Finally we wish to draw attention that plasma models should be benchmarked against basic swarm test models to verify how adequate the representation of some processes is. The stage of development of plasma models has reached such sophistication that perhaps requires that all aspects should be developed at the best available level. [1] RE Robson et al. Rev.Modern Phys. 77 (4) (2005) 1303. [Preview Abstract] |
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KTP.00110: Verifying Unmatter by Experiments, More Types of Unmatter, and a Quantum Chromodynamics Formula Florentin Smarandache As shown, experiments registered unmatter: a new kind of matter whose atoms include both nucleons and anti-nucleons, while their life span was very short, no more than 10$^{-20}$ sec. Stable states of unmatter can be built on quarks and anti-quarks: applying the unmatter principle here it is obtained a quantum chromodynamics formula that gives many combinations of unmatter built on quarks and anti-quarks. [Preview Abstract] |
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KTP.00111: POST-DEADLINE ABSTRACTS |
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KTP.00112: Probe Diagnostics in Commercial Plasma Reactors Valery Godyak, Vladimir Nagorny, Dongsoo Lee The commercial plasma reactors are not designed for plasma diagnostics and attempts to implement methods and apparatus proved in the laboratory plasma experiments are in many cases frustrating. There are three major problems in implementing of meaningful probe diagnostics in commercial plasma reactors. They are: a) large frequency spectrum with significant amplitudes of the plasma rf potential corresponding to source and bias fundamental frequencies and their harmonics; b) contamination of the probe surface with a low conductive layer of the reaction products; and c) too high impedance between the plasma and grounded chamber due to the chamber contamination or/and an artificial protective coating. Analysis of these problems and attempts of their resolution are discussed in this presentation. Experimental measurements with different commercial probes, based on electron and ion currents of the probe characteristic, performed in commercial rf plasma processing chambers filled with both noble and molecular processing gases are presented and discussed here. Feasibility of different kinds of probe diagnostics (based on ion and electron saturation currents, as well one based on the second derivative of the probe current) in commercial plasma reactors is discussed and some recommendation are given for meaningful probe diagnostics in such devices. [Preview Abstract] |
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KTP.00113: Compilation of Electron-Neutral Collision Data in Gases Gorur Govinda Raju Data on electron-neutral interaction are required and indispensable in several areas of research including Power systems, Plasma applications, material scientists, Chemistry, and even biological processes. The data are generally classified under cross sections for various elastic and inelastic processes, swarm properties including transport parameters and growth coefficients. A large number of reviews and compilations for a limited number of gases have been previously published in the literature by other researchers. In this presentation the author has compiled, over a period of twenty years or so, data for most of the molecules, if not for all, studied for the electron energy range (0-1000 eV) For each target particle about sixteen quantities have been classified to the extent that data are available, provided in tabular and graphical formats. The data are updated on a continuous basis till publication time. [Preview Abstract] |
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KTP.00114: Performance optimisation of a neon DBD excimer light source operating in the extreme-ultraviolet (84nm) Robert Carman, B.K. Ward, D.M. Kane We have investigated the electrical and optical characteristics of a windowless dielectric barrier discharge (DBD) excimer lamp using Neon to generate output at $\sim $84nm in the extreme-ultraviolet (EUV) spectral range. A detailed comparison of Ne DBD lamp performance for both pulsed and sinusoidal voltage excitation waveforms has been undertaken using otherwise identical operating conditions. Compared to sinusoidal excitation, pulsed operation yields a $\sim $50{\%} increase in the overall electrical to EUV conversion efficiency, and also allows greater control of parameters associated with the temporal evolution of the EUV pulse shapes (risetime, peak power, pulse width) due to a synchronised breakdown of the discharge gap along the electrode length. The ability to tailor EUV pulse shapes is important for applications in materials processing and surface cleaning. The source is also found to be highly monochromatic with respect to its spectral output at $\sim $84nm which dominates the spectral emission over the wavelength range 30-550nm. The overall lamp performance, as measured by the EUV output power, electrical to EUV conversion efficiency, and spectral purity at $\sim $84nm, improves with increasing gas pressure up to 900mb with none of these parameters showing saturation characteristics. [Preview Abstract] |
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KTP.00115: A Simulation of Gas Temperature Distribution inside and outside near a Microcell Plasma in Ar H. Mitsuhashi, T. Yagisawa, T. Makabe Microcell plasmas are attractive as, for example, emission devices, conductive devices or reactive plasma sources for processes. They have intrinsic characteristics based on a high density plasma. In order to control the efficiency of plasma production, ion acceleration, wall heating etc, it is important to investigate the flow of the external electrical energy to the neutral gas molecules and surface of the microcell. We simulated the spatial gas temperature distribution in a capacitively coupled microcell plasma in Ar sustained at 13.56 MHz. We considered the energy conservation equation of gas molecules under the heat transfer on and radiation from the electrodes and walls. In our previous work, we reported the heating of the chamber wall and the feed gases by the impact of energetic ions. In the present work, we discuss the system under the circumstances of the air outside of the chamber. The dependence of the gas density on the gas heating will be discussed. [Preview Abstract] |
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