Bulletin of the American Physical Society
70th Annual Gaseous Electronics Conference
Volume 62, Number 10
Monday–Friday, November 6–10, 2017; Pittsburgh, Pennsylvania
Session NW1: Poster Session II |
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Room: Salon ABC |
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NW1.00001: Electron stopping powers in H$_2$ Mark Zammit, Dmitry Fursa, Robert Threlfall, Jeremy Savage, Igor Bray Electron stopping power (STP) is an important parameter of interest in medical and environmental applications. Accurate evaluation of the electron STP in molecules requires a complete set of electron impact cross sections for all important reaction channels including excitation, ionization and dissociation. These data have recently been calculated for electron scattering on the ground state of molecular hydrogen with the convergent close-coupling (CCC) method [1,2], for incident electron energies up to 300 eV. Here we extend the CCC calculations to 2000 eV and apply the CCC collision data to calculate the electron STP in molecular hydrogen. At high energies our results are in good agreement with the Born-Bethe theory available from the NIST database [3]. Comparison with the mean excitation energy that was directly measured by Mu\'noz \textit{et al}. [4] showed excellent agreement. [1] M. C. Zammit \textit{et al}. \textit{Phys. Rev. Lett.} \textbf{116}, 233201 (2016), [2] M. C. Zammit \textit{et al}. \textit{Phys. Rev. A} \textbf{95}, 022708 (2017), [3] Stopping power and range tables for electrons \textit{http://physics.nist.gov/PhysRefData/Star/Text/method.html}, [4] A. Mu\'noz \textit{et al}. \textit{Chem. Phys. Lett}. \textbf{433}, 2614 (2007 [Preview Abstract] |
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NW1.00002: Calculation of electron scattering on silver Dmitry Fursa, Keegan McNamara, Igor Bray The relativistic convergent close-coupling (RCCC) method has been applied to study electron scattering from silver and obtain differential and integrated cross sections for elastic scattering and excitation to the $4d^{10}5p$, $4d^{10}6s$, $4d^{10}6p$, $4d^{10}5d$, $4d^{10}7s$, and combined $4d^{10}7p$, $4d^{10}6d$, and $4d^{10}4f$ states for incident electron energies up to 500 eV. In addition to the cross sections we have obtained Stokes parameters for the $(4d^{10}5p)^2P_{3/2}$ state and elastic spin asymmetries. The silver atom is described by a model of a single electron above a frozen [Kr]$4d^{10}$ core. Empirical one- and two-electron polarization potentials have been used to obtain the best representation of the target state energies and the optical oscillator strengths. To test convergence we have conducted calculations using a number of models and present results for two target states models, one consisting of 22 bound states and 28 continuum states, and the other extending the number of continuum states to 58. Good agreement was found with available experimental data for elastic scattering and $4d^{10}5p$ excitation differential cross sections. [Preview Abstract] |
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NW1.00003: Transition rates and electron impact excitation rates for O III Swaraj Tayal, Oleg Zatsarinny Transitions probabilities, electron excitation collision strengths and rate coefficients for a large number of O III lines have been calculated in the close-coupling approximation using the B-spline Breit-Pauli R-matrix method. The multiconfiguration Hartree-Fock method is employed for an accurate representation of the target wave functions. The close-coupling expansion contains 202 O III fine-structure levels comprising the 5 levels of the ground configuration 2s$^{\mathrm{2}}$2p$^{\mathrm{2}}$, 10 levels of first excited configuration 2s2p$^{\mathrm{3}}$, 4 levels of the 2p$^{\mathrm{4}}$ configuration, all levels for the 2p excitation to the 2s$^{\mathrm{2}}$2p3s, 3p, 3d, 4s, 4p, 4d, 4f, 5s configurations, and all levels for the 2s excitation to the 2s2p$^{\mathrm{3}}$3s,3p,3d configurations. The collision strengths have been calculated for the 20302 transitions between all 202 fine-structure levels. There is an overall good agreement with the recent R-matrix calculations by Storey et al. (2014) for the transitions between first 5 levels of the ground 2s$^{\mathrm{2}}$2p$^{\mathrm{2}}$ configuration, but significant discrepancies have been found with Palay et al. (2012) for transitions to the 2s$^{\mathrm{2}}$2p$^{\mathrm{2}} \quad^{\mathrm{1}}$S$_{\mathrm{0}}$ level. A fair agreement is found with the LS-coupling calculation of Aggarwal and Keenan (1999) for transitions to the 2s$^{\mathrm{2}}$2pnl states, with average discrepancies of about 30{\%}. However, rate coefficients differ by up to a factor of 10 for some transitions. The present calculations provide data sets that should allow a more detailed treatment of the available measured spectra from different space observatories. [1] P. Storey et al. \quad 2014 MNRAS \textbf{441 }3028 [2] E. Palay et al. \quad 2012 MNRAS \textbf{423 }L35 [3] K. Aggarwal and F. Keenan 1999 ApJS \textbf{123 }311 [Preview Abstract] |
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NW1.00004: Electron Impact Excitation of He, H$_{\mathrm{2}}$ and Ar. Merl Martin, Robert Wright, Leigh Hargreaves, Murtadha Khakoo Angle-differential electron impact excitation of He, Ar, H$_{\mathrm{2}}$ and H$_{\mathrm{2}}$O will be presented at low energies using a time-of-flight electron spectrometer which employs pulsing of a grid in front of the electron filament source. The data will be presented for energies close to threshold for excitation to about 20eV above threshold and will be compared to existing theory. [Preview Abstract] |
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NW1.00005: Electron Impact Excitation of the Electronic States of H$_{\mathrm{2}}$. Leigh Hargreaves, Murtadha Khakoo Differential electron scattering cross-sections for electron scattering from H$_{\mathrm{2}}$ at low energies are presented for the lowest five bound electronic states of H$_{\mathrm{2}}$. The data will be compared with the recently developed successful convergent close-coupling theory for H$_{\mathrm{2}}$. [Preview Abstract] |
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NW1.00006: Electron Impact Excitation of CO . Murtadha Khakoo, Luca Ratkovic, Logan Voorneman Extensive differential cross-sections for the electron impact excitation of CO for electronic states from 6eV to 1.5eV are presented. The data were taken for electron scattering angles from 10$^{\mathrm{o}}$ to 120$^{\mathrm{o}}$ and impact energies from 6.1eV to 20eV. The data were obtained by unfolding the energy loss spectra of CO taken t these energies and scattering angles. [Preview Abstract] |
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NW1.00007: Laser assisted free-free experiments: the search for dressed-atom effects C.M. Weaver, B.N. Kim, N.L.S. Martin, B.A. deHarak The absorption or emission of radiation during the collision of charged particles with atoms and molecules is investigated in the so-called free-free experiments. Up to now almost all such experiments have been in agreement with a simple theory which assumes that the interaction of the radiation with the atom itself has no effect on the scattering process. Very recently the first experiments to observe the unambiguous breakdown of this assumption have been carried out in xenon by Morimoto, Kanya, and Yamanouchi.\footnote{Y. Morimoto, R. Kanya, and K. Yamanouchi, Phys.\ Rev.\ Lett.\ {\bf 115}, 123201 (2015)} An estimate of the dressing of the target by the radiation's electric field may be made in terms of the electric dipole polarizability of the target. The effects in Xe were extremely difficult to measure because they occur at very small scattering angles. We have begun to carry out laser-assisted elastic scattering experiments in potassium, and laser-assisted inelastic scattering experiments in argon. In both cases we expect that dressing effects should be observed at scattering angles easily accessible to experiments, and without the need for complicated corrections. [Preview Abstract] |
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NW1.00008: Accurate Gaseous Ion Mobility Measurements Larry Viehland, Anbara Lutfullaeva, Jamiyanaa Dashdorj, Rainer Johnsen The accuracy of experimental measurements of gaseous ion mobility has not improved for decades, and it is still generally 2-5\%. It is shown that theoretical values of the mobility of atomic ions in atomic gases can be used to calibrate a drift-tube mass spectrometer, leading to subsequent measurements that are accurate to 0.6\% for He+ in He near room temperature as the ratio of the electrostatic field strength to the gas number density ranges up to 200 Td. Values of the ratio of the parallel diffusion coefficient to the mobility are also reported. [Preview Abstract] |
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NW1.00009: ABSTRACT WITHDRAWN |
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NW1.00010: Abstract Withdrawn
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NW1.00011: Abstract Withdrawn
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NW1.00012: N$_2$H$^+$ recombination with electrons in low temperature afterglow plasma Petr Dohnal, Abel Kalosi, Dmytro Shapko, Radek Plasil, Juraj Glosik, Rainer Johnsen A study on N$_2$H$^+$ recombination with electrons in afterglow plasma is presented. The cavity ring-down absorption spectroscopy in continuous wave modification was used as a principal diagnostics tool to probe number densities of several rotational states of the ground and the lowest excited vibrational state of the N$_2$H$^+$ ion. The recombination rate coefficients were measured at 300 K in afterglow of a microwave discharge ignited in a mixture of He/H$_2$/N$_2$ and of H$_2$/N$_2$ with typical number densities on the order of 10$^{17}$/10$^{14}$/10$^{14}$ cm$^{-3}$ and 10$^{17}$/10$^{14}$ cm$^{-3}$, respectively. The dependencies of the measured recombination rate coefficient on number densities of He and H$_2$ were evaluated to obtain upper limit for three body recombination rate coefficient of N$_2$H$^+$. [Preview Abstract] |
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NW1.00013: Positron scattering from helium Allan Stauffer, Robert McEachran We present scattering results for positron-helium scattering for energies from zero to 1 keV. These have been calculated using our complex optical potential method [1]. Positronium formation was calculated using the technique reported in [2]. Integrated cross sections are given for elastic, inelastic, ionization, positronium formation and total scattering. These are compared with experimental and other theoretical results and good agreement is obtained except in the case of ionization below the peak of the cross section. [1] Chen S, McEachran R P and Stauffer A D 2008 \textit{J. Phys. B} \textbf{41} 025201 [2] McEachran R P and Stauffer A D 2013 \textit{J. Phys. B} \textbf{46} 075203 [Preview Abstract] |
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NW1.00014: Imposed ordered structure in magnetized discharge Peter Hartmann First experimental findings obtained with the new Magnetized Dusty Plasma Experiment (MDPX at Auburn University) include the formation of ordered structures in high vertical magnetic fields (>1 T) imposed by the wire-grid upper horizontal electrode and visualized by micrometer dust particles levitating on top of the lower flat electrode sheath of a capacitively coupled RF discharge [E. Thomas Jr., Physics of Plasmas 23, 055701 (2016)]. Simple arguments based on charged particles being confined to helical trajectories along the magnetic field lines are not sufficient because all relevant collision processes have mean free paths well shorter than the distance between the structured electrode and the lower electrode sheath. We apply our newly implemented 2.5 dimensional GPU accelerated particle in cell (PIC) discharge simulation both for cylindrical geometry to compute global discharge parameters and with cartesian symmetry for the determination of local plasma parameters including the charging and force balance computation of the dust particles with high resolution. The PIC simulations will reveal the microscopic details of how the spatial structure of the upper electrode can migrate through the bulk plasma and influence the structure of the lower sheath region. [Preview Abstract] |
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NW1.00015: Application of a large wall probe in a short dc discharge as a gas analytical detector for high-energy atomic and molecular processes. V. I. Demidov, S. F. Adams, M. E. Koepke, A. A. Kudryavtsev, I. P. Kurlyandskaya, J. A. Miles An approach, which is based on the measurements of the electron energy distribution function (EEDF) with a large electric wall probe in a short (without positive column) dc discharge, can lead to the development of gas analytical detectors [1]. In this work, a short dc discharge with cold cathode and conducting walls was used in experiments at gas pressures of a few Torr to measure fine structures associated with atomic and molecular plasma processes at the high-energy portion of the EEDF in the plasma. It is experimentally demonstrated that for the investigated conditions the maxima associated with plasma-chemical reactions at the EEDF are proportional to the second derivative of electron current with respect to the probe potentials. Measurements have been conducted in helium gas and helium-argon gas mixtures with content of argon from 0.002{\%} to 5{\%}. Calibration of the device for the absolute measurements of densities of plasma constituents has been demonstrated. It is shown that the presence of a specific target gas component can be monitored from the measured EEDF. [1] V. I. Demidov et al., Phys. Plasmas, 23, 2016, 103508. [Preview Abstract] |
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NW1.00016: Dielectric-directed surface flashover under atmospheric conditions. Paul Clem, Laura Biedermann, Chris Moore High-voltage arc formation near a dielectric material is a complex process by which surface charging, secondary electron emission, and photoelectron emission modify the local electric field to determine the arc path and breakdown threshold. Strong electric field enhancement at the triple-point junction of dielectric, metal, and atmosphere may act to generate initiating electrons to seed prompt formation of streamers. This study investigates the dielectric role in influencing voltage breakdown threshold and reproducibility under high voltage conditions with and without external ultraviolet stimulation. We investigate effects of varying dielectric permittivity, and whether and how field emission at triple points can minimize variance in atmospheric breakdown behavior. Using a low-inductance test-stand, 200 micron dielectric granules were placed on a planar brass electrode in dry air at 600-Torr, opposite rounded brass rod electrodes which defined 0.25mm to 1-mm gaps. Polarity-dependent breakdown measurements (V, I) and images were collected as a function of granule permittivity and voltage polarity. We will discuss data and models of how dielectric material properties impact surface charging, electron emission, and ionization, thereby directing the flashover path. [Preview Abstract] |
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NW1.00017: Pressure Effects on Double Layer Accelerated Ion Beams in Multi-Species Helicon Plasmas Evan Aguirre, Timothy Good, Earl Scime Double layers are free-standing sheath like structures that are observed to form spontaneously in expanding, high-density plasmas, thereby accelerating ions to supersonic speeds. We use laser induced fluorescence to measure the parallel ion flow speeds of multi-species helicon plasmas immediately downstream of a current free double layer. Steady state, low pressure plasmas are created with three different gas mixtures; argon and xenon, argon and helium, xenon and helium. A helium ion LIF scheme does not exist, so we are confined to measuring the ion velocity distribution functions of argon and xenon. Contrary to observations in mixed gas sheath experiments, our measurements show that adding a lighter gas does not increase the ion beam speed, In fact, the heavy ion speed decreases. Thus, we find that different ion species fall through the double layer at their own Bohm speed rather than an average of their speeds, regardless of the relative densities of the ion species. Pressure effects are the dominant factor for ion beam speed; increasing pressure slows all ion beams. [Preview Abstract] |
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NW1.00018: The Influences of the Wall Material Arrangement of Ionization Region on the Discharge Characteristics of the Hall Thruster Channel Ping Duan, Long Chen, Xingyu Bian, Xiang Hu, Wenqing Li Hall thruster plasma has strong interactions with the channel wall, which significantly affect the discharge performance of the thruster. In this work, a two-dimensional physical model is established based on the discharge process of Hall thruster discharge channel. PIC method is applied to study the influences of segmented low emission graphite electrodes with biased voltage on discharge characteristics of the Hall thruster channel. The influences of segmented electrode arranged in the ionization region on electric potential, ion number density, electron temperature, ionization rate, discharge current and impulse are discussed. The results show that, when the segmented electrode is arranged at different positions in the ionization region, the axial length of the acceleration region is obviously shortened, the potential line is perpendicular to the wall, and the channel wall corrosion decreases along with the radial velocity reduction. As the position of the segmented electrode moves towards the acceleration region, the axial peak position of electron temperature moves towards the exit. The collision frequency between the electrons and the wall increases, the ionization rate is enhanced, the discharge current declines, eventually the impulse of thruster is improved. [Preview Abstract] |
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NW1.00019: Electron Avalanche and Streamer Processes Near a Dielectric Interface with Variable Photo-Electron Emission Ashish Jindal, Chris Moore, Andrew Fierro, Roy Jorgenson The effects of secondary photo-electron emission from a dielectric surface on electron avalanche and streamer processes are modeled in air at 760 Torr via an electrostatic PIC code which simulates particle-particle collisions using the DSMC method. A quasi-neutral seed plasma is placed near the cathode end of a 2 mm gap. The air chemistry model$^{\mathrm{1}}$ includes Townsend breakdown and streamer mechanisms, tracking excited state neutrals that can either undergo quenching collisions or spontaneous photon emission transitions$^{\mathrm{2}}$.~Initial results suggest that photoemission can significantly affect streamer evolution along the dielectric$^{\mathrm{3}}$.$^{\mathrm{\thinspace }}$[1] C. Moore \textit{et al.}, ``Development of Kinetic PIC-DSMC Model for Breakdown in the Presence of a Dielectric'', ICOPS, Banff, 2016. [2] A. Fierro \textit{et al.}, ``Discrete Photon Implementation for Plasma Simulations,'' Physics of Plasma, 23, 013506, 2016. [3] A. Jindal \textit{et al.}, ``Streamer Formation Near a Dielectric Surface with Variable Quantum Efficiency'', ICOPS 2017.$\varepsilon $ [Preview Abstract] |
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NW1.00020: Study on the radical production in atmospheric pressure plasma jets operated by nanosecond pulses Youbin Seol, Byungkeun Na, Hongyoung Chang Applications of plasma discharges for bio-medical uses are rapidly growing area. Atmospheric pressure plasmas have various advantages in bio-medical applications from sterilization to coagulation or skin regeneration. Atmospheric pressure plasma jets are one of the common atmospheric pressure plasma sources, which have unique virtue in the utility and the local treatment. The radicals produced from plasma discharge have important roles in plasma - bio interactions. It can enhance the cell proliferation and also cause cell death. The pulsed operation of plasma was introduced for bio-treatment, which can reduce the heat and enhance the radical production with better power efficiency. In pulsed plasma jets, the pulse characteristics changes the plasma operation and the radical productions. Currently, using nanosecond pulses are growing with its high efficiency. The experiment was performed by changing the pulse width in nanosecond range and measuring the radical production. The effect of the pulse characteristics on the radical production was studied. The computational simulations of chemical reactions were also accomplished which supplements the experimental results. [Preview Abstract] |
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NW1.00021: The influence of the pulse duration and the duty ratio on the discharge characteristics of helium and argon atmospheric pressure plasma jets. TianYu Tang, Hyunyoung Lee, Guang-Hoon Kim, Byunghak Lee, Hae June Lee Atmospheric pressure plasma jets (APPJs) have been widely used for biomedical applications for the last couple of decades. Most of APPJs are operated with the sinusoidal driving voltage at a frequency range of tens of kHz to MHz. In this study, we present the properties of monopolar pulse-driven APPJs which show different performances from those with sinusoidal driving voltages. The pulse duration has been varied from hundred nanoseconds to hundreds of microseconds, and the duty ratio is also varied. Experimental investigation of APPJ includes optical emission spectrometry (OES) and the current-voltage characteristics. In this presentation, a global simulation model was used to compare electron temperature, electron density and electron energy density of helium and argon gas plasma jet. In the experiment, the relationship between the plasma parameters and the breakdown voltage was investigated. Also, OES was used to investigate the radical components and to calculate the electron temperature. [Preview Abstract] |
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NW1.00022: Charging characteristics of dust grains in different plasma environments Long Chen, Ping Duan, Xingyu Bian, Wenqing Li Dust particles are exist in space, earth atmosphere, industrial production and laboratory, and also charged by plasmas. Charged dust in plasma environment has been widely studied in various scientific research fields, such as the charge and discharge of dust, dust and impurities in Tokamak boundary transport, dust crystal, space debris charging and utilization etc. The charging model in the plasma environment of dust mainly used the OLM theory, but with the complicated plasma environments, relaxation process of dust particle charging and the final saturation electron quality and potential will be distinct. For example, in the tokamak dust grains are charged by plasma with a strong macro velocity; in the space environment, dust debris particles charging are not only determined by plasmas, but also by high-energy particle radiation, magnetic field, secondary electron emission, ultraviolet ray and so on. Therefore, it is of great significance to study the charge relaxation process of dust particles under different circumstances. [Preview Abstract] |
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NW1.00023: Comparison of algorithms for numerical optimization of chemical reaction rate coefficients in plasma simulation Sang-Young Chung, Deuk-Chul Kwon For a reliable plasma simulation accurate rate coefficients for chemical reactions are important. The set of the rate coefficients should include essential reactions like appearing and disappearing of main species. However, some of them are hard to achieve from literature survey, experiments or calculations. Then, researchers have been estimated the missing rate coefficients and looked for proper rate coefficients until the simulation results agree with experiments. These searching process can be done by researchers with trial and error method, but can be done by numerical optimization method with less human efforts. In this study rate coefficients were numerically optimized with several algorithms including steepest descent, Newton, modified Newton and Broyden-Fletcher-Goldfarb-Shanno algorithms. A spatially averaged global code were used to simulate plasma while numerical optimizations. The accuracy and efficiency of algorithms were compared with each other. The methods to determine initial starting point of the optimization were also discussed. [Preview Abstract] |
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NW1.00024: Comparison of Zero Dimensional Plasma Chemistry Model with Ozone Absorption Spectroscopy Measurements Ryan T. Smith, Efe Kemaneci, Bjoern Offerhaus, Friderike Kogelheide, Nikita Bibinov, Peter Awakowicz, Ralf Peter Brinkmann, Katharina Stapelmann Results from zero dimensional computer simulations are compared to absorption spectroscopy measurements of Ozone within the gas phase of a Surface Dielectric Barrier Discharge (SDBD) and a Volumetric Dielectric Barrier Discharge (VDBD). The simulation model consists of two interdependent zero dimensional models that span two time scales and spatial regimes. The model incorporates 53 reactive species and 624 reactions to simulate the chemical dynamics of an atmospheric pressure plasma discharge in humid Nitrogen/Oxygen mixtures. The separation of the reactive species into long and short lived species allows for speedy simulations of the gas phase dynamics while still being directly coupled to the discharge dynamics. Comparisons are made at varying gas mixtures, supplied voltage frequencies and amplitudes. Although the computational model does not provide spatially resolved results nor directly comparable results, generalizations can be obtained and predicted. Furthermore, this work easily leads to the expansion of the model to provide more accurate and physically representative results. [Preview Abstract] |
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NW1.00025: Development of atmospheric high-speed jet pulsed plasma source for high-speed surface treatment Daisuke Ogasawara, Hiroaki Kawano, Hidekazu Miyahara, Chiaki Sato, Akitoshi Okino In recent years, atmospheric non-thermal plasmas have been widely used for surface treatment such as pretreatment for adhesion strengthening. However, in conventional remote plasma sources, many reactive species lose the surface treatment effect before they arrive to the target surface because they have short lifetime. For this reason, usual plasma sources could give the effect in short-distance of about several mm, and they have limitation in processing speed. To solve this problem, we developed an atmospheric high-speed jet pulsed plasma source. In this source, high-density plasma generated in continuous low gas flow is irradiated by high-speed short-pulsed gas flow and so reactive species arrive to the remote surface in a short time. In the experiment, a high-pressure gas valve of 0.5 MPa was opened for 0.1 s to generate the high-speed gas flow. Nitrogen plasma pulsed jet was irradiated once per second at 5 mm of working distance. The plasma gas velocity was measured by Schlieren method and the surface treatment effect was evaluated by water contact angle. Consequently, the maximum gas velocity was 490 m/s (Mach 1.4) and the hydrophilization speed had improved to twice compared to our conventional plasma source. [Preview Abstract] |
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NW1.00026: The role of secondary electron emission in capacitive rf plasmas at low pressure Birk Berger, Julian Schulze, Peter Awakowicz, Thomas Mussenbrock, Aranka Derzsi, Benedek Horv\'{a}th, Zolt\'{a}n Donk\'{o} The correct choice of the ion induced secondary electron emission coefficient, $\gamma$, is of high importance to obtain realistic results by PIC/MCC-simulations of capacitive rf plasmas. In most studies, this coefficient is set to $\gamma=0.1$ without taking into account the energy of the incident particles, the electrode material, and the surface conditions. Recently, studies showed that using a more realistic, energy dependent $\gamma$-coefficient strongly influences the outcome of computational investigations at high pressure. In CCPs used for sputtering a much lower pressure of approx. 1Pa is used. In this regime, the plasma-surface interaction can lead to a change of the surface conditions, e.g. by target poisoning. This can result in process drifts. This effect is usually linked to the change of $\gamma$ but it is not understood how $\gamma$ affects the plasma at such low pressures, where the multiplication of secondary electrons within the sheath is negligible. This work investigates the effect of different $\gamma$-coefficients on the discharge by PIC/MCC-simulations at low pressures in argon. It is found that the confinement of $\gamma$-electrons by multiple reflections at the sheaths strongly influences the ionization rate. [Preview Abstract] |
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NW1.00027: The effects of surface characteristics on the spatio-temporal excitation dynamics in capacitive RF plasmas studied by PROES Steven Brandt, Julian Schulze, Birk Berger, Mark Koepke, Douglas Keil In commercial capacitively coupled radio frequency plasmas (CCPs), surface characteristics can change as the chamber conditions drift between clean cycles. The effects of these drifts on the electron heating dynamics and, consequently, on plasma parameters are unclear. In order to clarify these effects we place aluminum discs with varying surface roughness or AlF film thickness on the powered electrode of a GEC reference cell and study their effects on the spatio-temporal electron impact excitation dynamics by Phase Resolved Optical Emission Spectroscopy (PROES). Measurements are performed in argon plasmas driven at 13.56 MHz and at different pressures as well as voltages. Special attention is paid to effects induced by a change of the secondary electron emission coefficient as a function of surface roughness and film thickness traced by monitoring the relative intensity of electron impact excitation induced by sheath expansion heating and by secondary electrons. [Preview Abstract] |
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NW1.00028: A novel cupping-assisted plasma treatment for skin disinfection. Zilan Xiong A novel plasma treatment method/plasma source called cupping-assisted plasma treatment/source for skin disinfection is introduced. The idea combines ancient Chinese 'cupping' technology with plasma sources to generate active plasma inside a reduced-pressure chamber attached to the skin. Advantages of this scheme include reducing the threshold voltage for plasma ignition and improving the spatial uniformity of the plasma treatment. In addition, the reduced pressure inside the cup should improve skin pore permeability and it simplifies attachment of the plasma device to the skin. Moreover, the plasma-generated active species are restricted inside the cup, raising local reactive species concentration and enhancing the measured surface disinfection rate. A surface micro-discharge (SMD) device is used as an example of a working plasma source. We report discharge characteristics as a function of pressure and applied voltage. When using a relatively low applied voltage, the antibacterial effect under reduced pressure showed enhanced antibacterial effects and was comparable with discharges operated at atmospheric pressure under higher voltage. [Preview Abstract] |
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NW1.00029: Kinetic treatment of plasma-material interactions utilizing dynamically-coupled Boltzmann plasma and surface erosion model Shane Keniley, Davide Curreli We present a numerical characterization of plasma-surface interaction by using a multi-species full-f Boltzmann plasma description coupled to a Binary Collision Approximation (BCA) model, Fractal-TRIDYN. The method couples a continuum Boltzmann-Poisson solver of a multi-species plasma to an improved version of the TRIDYN code including dynamic surface composition. The BCA module provides on-the-fly boundary conditions for a complete description of the dynamic feedback between the near-wall plasma and the material surface. Kernel density estimates are utilized to reconstruct continuous distributions from the discrete data predicted by the BCA model. Phenomena such as material sputtering, backscattering, and implantation, and their effect on the structure of the near-wall plasma, are are dynamically accounted for in both mono-component and multi-component targets. [Preview Abstract] |
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NW1.00030: Diagnostics of Diffuse Large Volume Plasma Generated by an External Ionization Wave Hamid Razavi, Mounir Laroussi Atmospheric pressure low temperature plasma jets are the product of guided ionization waves. Guided ionization waves can be transmitted through a dielectric material and under some conditions can ignite a discharge behind the dielectric material. We have recently reported on a novel way to produce large volume diffuse low pressure plasma inside a Pyrex chamber that does not have any electrodes or electrical energy directly applied to it. The diffuse plasma is ignited by a plasma jet located externally to the chamber. The plasma jet is placed in close proximity to the external wall/surface of the chamber or to a dielectric tubing connected to the chamber. The plasma ignited inside the chamber is diffuse, large volume and with physical and chemical characteristics that are different than the external plasma jet that ignited it. Here, we present diagnostics of the reduced pressure diffuse plasma including electron density and temperature, using Langmuir probe, fast imaging to study the propagation of the ionization wave inside the chamber and the plasma structure, and optical emission spectroscopy to identify the emitting excited species. [Preview Abstract] |
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NW1.00031: Burning modes of a bipolar pulse discharge in CO$_{\mathrm{2}}$ and nitrogen V.A. Lisovskiy, S.V. Dudin, N.N. Vusyk, A.N. Dakhov, V.D. Yegorenkov, P.A. Ogloblina This paper reports the current and voltage oscilloscope patterns of the bipolar pulsed discharge in the frequency range (from 20 to 300 kHz) with the duty cycle from 0.11 to 0.97 that have been measured in CO$_{\mathrm{2}}$ and nitrogen within the pressure range from 0.1 to 1~Torr. It has been found that varying the duty cycle may change the discharge axial structure and redistribute the potential drop across the electrodes. At large duty cycle values the discharge has been found to experience a transition from the conventional high-current mode (with cathode sheaths near both electrodes) to a low-current mode characterized by low discharge current values and a feeble glow. In this mode the ionization takes place only in the cathode sheath and the negative glow near the electrode at the time period to which the high voltage is applied. During the remaining part of the period a lower voltage is applied to the second electrode which is insufficient for the cathode sheath formation, therefore during this time one observes a decaying plasma (afterglow). The radiation spectra of the bipolar pulsed discharge in nitrogen have been measured at different duty cycle values using the optical spectrometer. It has been revealed that in a low-current mode the ionization occurs predominantly near one electrode whereas the cathode sheath is not formed near another electrode. [Preview Abstract] |
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NW1.00032: Electric field non-uniformity effect on dc low pressure gas breakdown between parallel plate electrodes V.A. Lisovskiy, R.O. Osmayev, A.V. Gapon, V.D. Yegorenkov This paper presents the results of studying the gas breakdown in a non-uniform direct current electric field. The breakdown curves have been measured in nitrogen between flat electrodes of 12 mm in diameter spaced 3 to 300 mm apart and placed inside the discharge tubes of 13 mm and 56 mm in diameter. The effects of the non-uniform distribution of the electric field inside the inter-electrode gap and of the diffusion loss of charged particles to the discharge tube walls on the gas breakdown have been studied separately. A conclusion is drawn from the experimental data that the general form of the gas breakdown criterion must be as follows $U$~$=$~$f$(\textit{pL}, $L$/$R_{el}$, $L$/$R_{tube})$ in which the $L/R_{el}$ ratio of the inter-electrode gap value to their radius describes the electric field nonuniformity inside the discharge tube whereas the $L/R_{tube}$ ratio characterizes the diffusion loss of electrons on the discharge tube walls. It has been found that the breakdown curves for different electrode radius values and a fixed gap $L$ intersect at such value of the gas pressure that corresponds to the location of the inflection point of the breakdown curve for a uniform electric field. [Preview Abstract] |
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NW1.00033: Vibrational Kinetics of Electronically Excited States in H$_2$ Discharges Gianpiero Colonna, Lucia Daniela Pietanza, Roberto Celiberto, Mario Capitelli, Annarita Laricchiuta The StS model of hydrogen plasmas has been improved, including in the kinetic scheme the vibrational levels of the relevant electronically excited singlet terms, responsible for the H$_2$ spectral emission, and correspondingly the vibrationally-resolved cross sections and the radiative decay coefficients, describing the de-excitation dynamics. Also the triplet state evolution resulting from the competition between the collisional quenching and the predissociation mechanism, both leading to dissociation, is considered. This model has been applied to repetitively pulsed nanosecond discharges. The evolution of the molecule, including excited states, atomic hydrogen and ionic species molar fractions is shown during the pulse and compared with the results obtained neglecting either the vibrational kinetics or the collisional quenching of excited singlets. The differences are discussed in the light of the modifications of the shape of the eedf and ground state vibrational distribution function, emphasizing the role of quenching at the pressures considered in the simulation. The model could be validated in low-pressure regimes, missing experimental results in high-pressure discharges. [Preview Abstract] |
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NW1.00034: Second harmonic wave generation in ununiform microwave plasma by metamaterial effect Akinori Iwai, Yoshihiro Nakamura, Osamu Sakai We performed the monitoring of plasma parameters and intensity of second harmonic (SH) wave in the composite of microwave overdense plasma and the metamaterial under the various conditions; input power, gas pressure and the position of the detection. Plasma has been dealt with the nonlinear optical material because of the inherent nonlinearity based on the complex motion of particles in plasma. Moreover, generation of ions from plasma is important for many industrial processes. However, electron density $n_{\mathrm{e}}$ provides the threshold frequency $\omega_{\mathrm{pe}}$ and the electromagnetic (EM) wave cannot penetrate into rich-$n_{\mathrm{e}}$ plasma when the frequency is under $\omega_{\mathrm{pe}}$; plasma permittivity ($\varepsilon )$ becomes negative. We introduced double-split-ring resonators (DSRRs), one of metamaterials, which macroscopically have negative permeability ($\mu )$ by the magnetic resonance, and canceled the negative $\varepsilon $. Our previous report [1] included the rough results about SH wave generation and $n_{\mathrm{e}}$ in terms of the monitoring positions. In this report, we show the relation between the propagation of the input wave (2.45 GHz), SH wave and parameters of generated plasma in detail, and clarify the microscopic effect of DSRRs [1] A. Iwai, Y. Nakamura, and O. Sakai, Phys. Rev. E, 92 (2015) 033105. [Preview Abstract] |
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NW1.00035: DC discharge sustained by repetitive nanosecond pulses in nitrogen with a single pair of electrodes Keisuke Takashima, Toshiro Kaneko To enhance the nitrogen molecule dissociation reactions with the oxygen and water, a nanosecond pulse (NS) sustained DC discharge in nitrogen is experimentally studied in a coaxially arranged discharge cell with a single pair of exposed electrodes. The DC discharge current is sustained by repetitive nanosecond pulse discharge which propagates along the discharge cell and the DC current follows the ionized channel produced by the NS discharge. The total discharge coupling power reaches nearly 1kW power loading to moderated pressure nitrogen flow with relatively low voltage across the gap. The discharge characterization on the repetitive NS discharge and the NS sustained DC discharge with the gas mixture will also be presented. [Preview Abstract] |
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NW1.00036: Variations in Plasma Parameters in the Plume of a DC Plasma Source Near a Substrate. Sophia Gershman, Yevgeny Raitses A three-electrode dc plasma source was constructed and operated in Ar at pressures of 2 -- 10 torr. The plasma source consists of two cylindrical electrodes with dimensions in the mm range and 1 mm inter-electrode distance, and a third, biased electrode/substrate, positioned in front of the cathode or in front of the anode opening. Optical and electrical measurements show that plasma at the substrate has a higher temperature (12 -- 14 eV) on the anode side than on the cathode side (4 -- 7 eV). The biased electrode offers flexibility in controlling plasma-surface interactions by extracting electrons of various energies from the discharge. This electrode exploits the non-local electron kinetics to control plasma properties in the plume from the discharge near the surface of the electrode/substrate. [Preview Abstract] |
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NW1.00037: Effects of pulse modulation on the density distributions of ions and molecules in Ar/H$_{\mathrm{2}}$ inductively coupled plasma Kwon-Sang Seo, Dong-Hyun Kim, Ho-Jun Lee Pulse modulation operation of inductively coupled plasma(ICP) and microwave plasma is an effective method for controlling plasma chemistry through active utilization of afterglow process and temporal variation of electron energy. In this work, effects of power pulsing on the neutrals and ions chemistry in Ar/H$_{\mathrm{2}}$ ICP are investigated using 2D fluid simulations. Driving frequency of ICP was 13.56 MHz and pulse frequency was varied from 10 to 20 kHz. The effects of pulse frequency, duty cycle, and gas mixture ratios have been analyzed comprehensively. For comparison with continuous mode, time average power of pulse mode was set equal to the continuous mode. The atomic ions such as Ar$^{\mathrm{+}}$ and H$^{\mathrm{+}}$, generated dominantly by electron impact reaction, increase only during the plasma on time. However, dimer and trimer ions like H$_{\mathrm{2}}^{\mathrm{+}}$, H$_{\mathrm{3}}^{\mathrm{+}}$ increase rapidly during plasma off time because important generation channels of these ions are gas phase reaction including charge transfer reaction. During the off period, ion flux toward chamber surface remains very low level due to rapid cooling of elections. These variations profoundly affect the density distributions of dimer and trimer ions. [Preview Abstract] |
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NW1.00038: Experimental characterization of a magnetized ICP source used as the first stage of an Inductive Double-stage HALL Thruster (ID-HALL) Freddy Gaboriau, Loic Dubois, Alexandre Guglielmi, Laurent Liard, Jean-Pierre Boeuf The new generation of all-electric propulsion satellites requires multimode thrusters able to provide high thrust for orbit transfer and high specific impulse for satellite station keeping. In conventional Hall thruster, the same electric field provides electron energy for ionization and controls the ion acceleration, thus thrust and specific impulse are closely linked. The concept of double-stage Hall thruster (DSHT), where ionization is separated and controlled independently from ion acceleration, allows separating thrust and specific impulse. This concept raises fundamental questions and the challenge is to obtain a high degree of ionization in the first stage and an efficient extraction of the ions from the ionization region to the acceleration stage. To address this issue, a new concept of DSHT called ID-HALL is proposed. The ionization stage is a cylindrical ICP source with a closed magnetic circuit (confining the plasma and reducing ion losses) and is magnetically connected to the standard Hall acceleration stage. Results regarding the efficiency of the ICP source with and without the closed magnetic circuit will be presented and discussed based on the determination of the electron density and the electron temperature using single and double probes. [Preview Abstract] |
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NW1.00039: Experimental investigation on the E to H transition in a dual frequency inductively coupled plasma (2MHz/13.56MHz) Ju-Ho Kim, Ho-Won Lee, Chin-Wook Chung A transition from a capacitive mode to an inductive mode is investigated in a dual frequency inductively coupled plasma. The frequency powers of 13.56 MHz and 2 MHz are applied to the two antennas, respectively. The plasma density is measured using RF compensated Langmuir probe. The density jump due to the transition with increasing power is measured at 13.56 MHz and 2 MHz respectively, and compared to dual frequency operation. The characteristics in the transition can be explained by the absorbed power and the lost power with respect to the plasma density and driving frequency difference. [Preview Abstract] |
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NW1.00040: Comparison of power transfer efficiency and plasma parameters of series and parallel antennas in inductively coupled plasmas Tae-Woo Kim, Hyun-Ju Kang, Chin-Wook Chung When the capacitive coupling between the antenna and plasma is large, it is hard to make the high density plasma due to the large ion energy losses inductively coupled plasma. Therefore, the parallel antenna structure is commonly used in plasma processing chamber to reduce the capacitive coupling. However, when a parallel antenna is used, the power transfer efficiency from the antenna to the plasma is low because the primary inductance (antenna inductance) is lower than that of the series antenna and the mutual inductance is also lower in the transformer model. In this study, the power transfer efficiency and the plasma parameters were measured to investigate the effects of the series and parallel antennas on the plasma. To compare the series and parallel antennas, both antennas were made of copper tubes of the same length and thickness. The experiment shows that the parallel antenna has good ionization efficiency and the series antenna has good power transfer efficiency as expected from the model. [Preview Abstract] |
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NW1.00041: The effect of a remote plasma generator on a direct inductively coupled plasma Se-Yeol Paek, Kyung-Hyun Kim, Ho-Won Lee, Chin-Wook Chung The electron energy distribution functions (EEDFs) were measured in a planar inductively coupled plasmas (ICP) with a remote plasma generator (RPG) using Langmuir probes. RF power frequencies of the ICP and the RPG were 13.56 MHz and 2 MHz, respectively. While the gas pressure and the argon flow rate are varied, the plasma density is changed little with the RPG, however, the electron temperature is changed remarkably. The change in electron temperature is not monotonically decreased and the pressure condition of minimum electron temperature is moved. This phenomenon can be explained by the changes in EEDFs depending on the RPG. [Preview Abstract] |
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NW1.00042: Experimental investigation of rf bias power on the plasma density and electron heating in an inductively coupled plasma. Ho-Won Lee, Ju-Ho Kim, Chin-Wook Chung Plasma densities are measured with rf bias powers at an inductively coupled plasma (ICP) using rf compensated Langmuir probe. When the ICP power is fixed, the plasma density has a maximum at a specific rf bias power. The rf bias power having maximum plasma density varies with ICP powers. This seem to be related to discharge mode transition (electron heating mode and ion acceleration mode) according to rf bias powers. These modes are determined by the power balance depending on rf bias voltages. Since the rf bias voltage decreases with ICP power, the bias power having the maximum density is shifted. This shows that electron heating and generation can be controlled by rf bias power.. [Preview Abstract] |
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NW1.00043: Electron energy distribution function measurement in a CO$_{\mathrm{2}}$/Ar inductively coupled plasma Kyung-Hyun Kim, Kwan-Yong Kim, Chin-Wook Chung Electron energy distribution functions (EEDFs) in CO$_{\mathrm{2}}$/Ar mixed plasma were measured at various fractions of the argon. Electron density increases with ratio of the argon. Electron temperature has maximum values in a pure CO$_{\mathrm{2}}$ plasma. On the other hand, the electron temperature increases with the argon ratio in CO$_{\mathrm{2}}$/Ar plasma. EEDF becomes from Maxwellian to non-Maxwellian by increasing pressure and decreasing the Ar ratio because Maxwellization of EEDF is determined by the electron-electron collision frequency and electron energy relaxation frequency. Unusual phenomenon occurs at intermediate pressure, 50 mTorr. It is the EEDF of the pure CO$_{\mathrm{2}}$ plasma is closer to the Maxwellian than those of the CO$_{\mathrm{2}}$/Ar plasma with a small proportion of Ar. This result seems to be effect of superelastic collisions determined by vibration-vibration (V-V) exchange and vibration-translation (V-T) relaxation. [Preview Abstract] |
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NW1.00044: Abstract Withdrawn
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NW1.00045: Electron density and electron temperature measurements for repetitive nanosecond pulsed discharges using Thomson scattering Jared Miles, Steven Adams, James Hornef, Chunqi Jiang Measurements of electron temperature and electron density in repetitive nanosecond pulsed plasmas provide key insight to the properties and kinetics of non-equilibrium plasmas. This work applies non-invasive Thomson scattering to spatially and temporally resolved measurements of electron temperature and electron density in repetitively pulsed plasmas in ambient air and inert gas flows. Plasmas were generated by a pin-to-pin electrode system driven by 12 ns, 6-10 kV pulses at a repetition rate up to 300 kHz. A \textless 1mm in width He/O$_{\mathrm{2}}$ plasma jet produced by a tubular electrode configuration and powered by 140 ns kilovolt pulses at 10 Hz was also used for the study. The dependence of the plasma properties including the electron temperature, electron density and gas temperature on pulse duration, pulse rise time, and gas composition are discussed here. [Preview Abstract] |
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NW1.00046: Investigation of the flow rate effect on the plasma parameters by using miniaturized plasma diagnostic device in the remote plasma. Hyun-dong Eo, Jin-youg Kim, Chin-Wook Chung Miniaturized plasma diagnostic device was developed for installing near the remote plasma source because there is a little space for the monitoring system. Miniaturized plasma diagnostic device can be used like a gauge without additional connection with measuring instrument and computer. Miniaturized plasma diagnostic device used the floating harmonic method that used for obtaining plasma parameters such as electron temperature and ion density. Experiments were conducted to measure plasma parameters in the remote source with wall probe. As increasing the flow rate of the remote source, the increase of the ion density and electron temperature is observed by using our device. [Preview Abstract] |
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NW1.00047: Picosecond TALIF to quantify collisional quenching of laser-excited states in atmospheric pressure plasmas Sandra Schroeter, Jerome Bredin, Kari Niemi, Timo Gans, Deborah O'Connell The accurate quantification of reactive oxygen species produced in atmospheric pressure plasmas is of great interest in various applications, such as surface modification and biomedicine. A technique commonly used for the detection of atomic ground state species is Two-photon Absorption Laser Induced Fluorescence (TALIF). For the measurement of absolute species densities, this technique relies on the knowledge of the laser-excited state lifetime. However, typical TALIF systems operate on timescales of nanoseconds, which is in the same order as the lifetimes of the laser-excited states due to their enhanced collisional de-excitation (quenching) at atmospheric pressure. Therefore, the effective lifetimes have to be calculated using quenching coefficients from the literature and an estimate of the gas mixture, which is particularly challenging taking into account complex gas mixing with ambient air in the plasma effluent region. In this work, we present measurements of the decay rates of the laser-excited states in the effluent of an rf atmospheric pressure plasma operated in helium with small molecular admixtures using TALIF with a sub-nanosecond temporal resolution. Quenching coefficients of the excited state O(3p $^{\mathrm{3}}$P$_{\mathrm{1,2,0}})$ with various gases such as Ar, O$_{\mathrm{2}}$, N$_{\mathrm{2}}$, CO$_{\mathrm{2}}$, and H$_{\mathrm{2}}$O are measured and compared to literature values. The active measurement of decay rates is used to map the gas entrainment of ambient air into the plasma effluent region. [Preview Abstract] |
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NW1.00048: Passive Optical Emission Spectroscopy for the electric field measurements in DC and RF sheaths in IShTAR Ana Kostic, Kristel Crombe, Rudolphe D'Inca, Jonathan Jacquot, Roman Ochoukov, Anton Nikiforov, Jean-Marie Noterdaeme Direct, non-intrusive measurements of the electric field are essential for the progress in understanding the RF sheath physics. This is especially true in the case of the ICRF antenna - plasma edge interaction in fusion devices. Here the rectification of the RF fields near the plasma-facing components of the antenna leads to the development of DC electric fields. These DC fields accelerate the ions from the plasma towards the antenna’s plasma-facing components thereby enhancing physical sputtering and release of impurities. IShTAR is a device dedicated to the investigation of the edge plasma-antenna interactions in tokamak edge-like conditions. It is equipped with a helicon plasma source and a single-strap ICRF antenna. We present here our initial approach to measure the electric fields - the passive optical emission spectroscopy concentrating on the changes of the He-I spectral line profiles introduced with the external electrical field, i.e. the Stark effect. To be able to fully control the operating parameters, at the first stage of the study the measurements are conducted on a simple electrode installed in the IShTAR plasma source at the centre of the plasma column. At the second stage of the study, the measurements are preformed in the vicinity of the ICRF antenna of IShTAR.\\ \\ The views and opinions expressed herein do not necessarily reflect those of the European Commission. [Preview Abstract] |
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NW1.00049: Electron temperature of an RF discharge in argon up to atmospheric pressure Antoine Durocher-Jean, Jean-Sebastien Boisvert, Joelle Margot, Luc Stafford A cold argon plasma is generated inside a dielectric tube (inner diameter of 2 mm) using two long linear electrodes painted on diametrically opposed sides of the tube. The optical emission spectra from Ar 4p-to-4s transitions were compared to the predictions of a collisional-radiative model using the electron temperature T$_e$ (assuming a Maxwellian EEDF) and the Ar 1s$_2$ level number density as the only adjustable parameters. T$_e$ was deduced from the best fit between measured and simulated line emission intensities. At 760 Torr, the best fit is obtained for T$_e$=1.28 eV. When the power density increases from 4.2 to 7.0 W cm$^{-3}$, T$_e$ remains constant while $n_e$ (estimated from electrical measurements) increases from 3.7 to $8.8\times10^{11}$ cm$^{-3}$. In this range of power density, the discharge remains in the $\Omega$ mode with a maximum of the light emission (dominated by a continuum in the UV-VIS range) at the center of the tube. By reducing the pressure to 90 Torr, the best fit is achieved for a higher T$_e$ of 1.50 eV. On the other hand, the power density, $n_e$ and the continuum intensity decrease with decreasing pressure. In contrast with a helium discharge in the same range of discharge current, the argon discharge does not switch to the $\gamma$ mode. [Preview Abstract] |
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NW1.00050: Measurement of effective electron collision frequency in low pressure RF plasmas by the microwave resonator Viktor Zheltukhin, Ildar Gafarov, Vadim Galeev, Anastasia Golyaeva, Alexander Tovstopyat Results of the experimental studying of effective electron collision frequency $\nu_{\mathrm{c}}$ with heavy particles in RF plasmas at pressure range from 13.3 up to 332.5 Pa is presented. The plasmas were created in a cylindrical quartz tubes from 20 up 40 mm by the diameter. The discharge power was varying from 100 up to 1000 W. RF frequency $f_{\mathrm{RF}}$ was varying from 1 up to 18 MHz. Diagnostics of the discharge was carried out by microwave resonators in UHF and microwave ranges. The probing signal frequency was varying from 5 to 12 GHz. The wave of $Å_{oso}$ type was excited in a cylindrical resonator. Average collision frequency and electron density $n_{e}$ in the discharge gap were measured. The collision frequency varies almost linearly in full range of $f_{\mathrm{RF\thinspace }}$varying. The collision frequency exceeds 10$^{\mathrm{10}}$ s$^{\mathrm{-1}}$ when p \textgreater 150 -- 180 Pa. Electron density $n_{e}$ is increased depending on voltage by linear low at low-power mode, and is increased approximately by square-law at high current mode. [Preview Abstract] |
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NW1.00051: A monolithic cavity-enhanced absorption spectrometer for NO2 detection in the ppb concentration levels. A. Lozano Fontalvo, A. M. Ju\'arez, Thomas Siegel In the past decade, many diagnostic techniques have been developed to detect and quantify the concentration of pollutants such a NOx. Among them, Incoherent broad-band cavity-enhanced absorption spectroscopy (IBBCEAS) which employs a LED as a radiation source and an optical cavity to enhance the absorption of the LED light is one of the simplest. The relatively wide spectrum of wavelengths provided by LEDs allows this technique to simultaneously detect many pollutants such as NO$_{\mathrm{2}}$ and NO$_{\mathrm{3}}$ with enhanced sensitivity. In this work we report the development of a spectrometer which implements an IBBCEAS set-up which uses a LED centered at 634 nm, for the detection of NO$_{\mathrm{2}}$. The optimal averaging acquisition time for this instrument, as evaluated using Allan variance, is found to be of 500s. For this acquisition time, the smallest detectable absorption is 1.01x10$^{\mathrm{-9}}$ cm$^{\mathrm{-1}}$, which corresponds to a detection limit of 3.36ppb. The monolithic design presented in this work, does not require the alignment of mirrors, making it very practical and easy to handle. This compact and inexpensive instrument is a promising tool for monitoring air quality among many other applications including the generation of traces in plasmas and molecular biological processes. [Preview Abstract] |
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NW1.00052: Modelling of capacitive coupled RF discharge in wide pressure range Viktor Zheltukhin, Violetta Chebakova A model of capacitive coupled RF discharge in argon at both atmospheriñ and low pressures between two parallel plate is described. Various approaches to simulate the RF discharge depending on pressure rates are used. A nonlocal approximation is used simulating the capacitive coupled RF discharge at low pressure. A local approximation considering both dimers and molecular ions is used for simulating the discharge at high pressure. Results are in agree with experimental data. [Preview Abstract] |
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NW1.00053: Modeling and Simulation of Rarefied~ RF~ Plasma~ Flow Viktor Zheltukhin, Alexander Shemakhin A hybrid mathematical model of the rarefied RF plasma flow in transition regime at Knudsen 0.03 \textless Kn\textless 3 for the carrier gas is described. The model based on both the statistical approach to the ground-state atom and the continuum model for electron, ion, and metastables. The results of plasma flow calculations are described. The upwarming effect on the bound of the plasma stream near the input is found in some mode. The effect is confirmed by comparison with experimental data. [Preview Abstract] |
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NW1.00054: Simulation of low energy ion bombardment of alkane in low pressure RF plasmas Viktor Zheltukhin, Albina Azanova, Igor Borodaev, Aidogdy Shakhyrov Results of molecular dynamics simulation of low energy (up to 100 eV) ion bombardment of both crystalline and amorphous alkanes in low pressure RF plasmas are described. An united-atom model of alkane chains where each site represents a CH2 group or a CH3 end group is used. The covalent bond between adjacent sites is modeled by a Dreiding potential. The interaction between the sites in different chains, as well as between argon and alkane sites is described by a LJ potential. A classical molecular dynamics code LAMMPS is used. [Preview Abstract] |
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NW1.00055: Comparison of Particle-in-Cell and Fluid Simulations on Ion Energy Distribution Function and Mobility in intermediate Pressure Capacitively Coupled Plasmas. YoonHo Lee, SeHun Oh, JinSeok Kim, HaeJune Lee The variation of the ion energy and angle distribution functions in the capacitively coupled plasma is changing rapidly with the variation of gas pressure because of the increase of ion-neutral collisions with increasing gas pressure. ~In general, it has been accepted that fluid models work well in high pressure discharges where the drift-diffusion approximation is valid, while the non-local property of low pressure discharges can be analyzed correctly with a particle-in-cell (PIC) model. In this study, the mean ion velocity in the sheath is investigated for an intermediate gas pressure of a few Torr, which shows~a~significant discrepancy between the PIC results and the fluid results for different phases of an RF-cycle.~In this regime, the discrepancy between two models is mainly caused by the ion momentum equation in the sheath regions due to the intrinsic properties of fluid equations. Especially, we found out that the mobility obtained from the PIC model and the mobility used in the fluid model are significantly different. We are suggesting an improved model in order to estimate the ion mobility reflecting the results of the PIC model. Finally, the results of the improved fluid model that utilizes this mobility are demonstrated and compared with the PIC simulation results. [Preview Abstract] |
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NW1.00056: Simulation of mist-containing low-temperature plasma in atmospheric-pressure helium Fumiyoshi Tochikubo, Fumiya Murayama, Satoshi Uchida Plasma-liquid interaction is a hot topic in the application of atmospheric-pressure plasma (APP). Using mist will be the efficient method to increase the effective area for plasma-liquid interaction. When mist is introduced to the APP, each droplet will be charged negatively, therefore, reductive reaction is expected at the surface of droplet. The evaporation of mist will change the gas composition. The aim of this work is to clarify the physics of mist-containing APP by numerical modeling. First, the evaporation process of the droplet was modeled by the conservation laws of mass and energy for droplets and surrounding gases. Second, the dust plasma in atmospheric-pressure helium was calculated by fluid model with heat equation for gas as parameters of particle’s diameter and concentration. The APP modeled in this work is dc glow discharge and dielectric barrier discharge. The charge of particle with diameter of 1 $¥mu$m in APP ranges from 10$^3$ to 10$^4$ of elementary charge. At particle concentration greater than 10$^7$ cm$^{-3}$, the particles influences the plasma structure as a strong loss term for electrons and ions although the charge density itself is much lower than the plasma density. The simulation with mist is ongoing by combining the above two models. [Preview Abstract] |
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NW1.00057: Abstract GEC17-2017-000352 moved to GT1.14 |
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NW1.00058: Grid-based kinetic simulations of ladder climbing by electron plasma waves Kentaro Hara, Ido Barth, Erez Kaminski, Ilya Dodin, Nathaniel Fisch Wave-plasma interactions have been well studied in collisionless plasmas and the grid-based kinetic model is a promising tool to accurately model phase space structures in plasmas. It was recently proposed by Barth et al. [Phys. Rev. Lett. \textbf{115}, 075001 (2015)] that the energy of plasma waves can be moved up and down the spectrum using chirped modulations of plasma parameters. Depending on whether the wave spectrum is discrete (bounded plasma) or continuous (boundless plasma), this phenomenon is called ladder climbing or autoresonant acceleration of plasmons. In this talk, ladder climbing of electron plasma waves is investigated by applying a chirped external electric field using a fully nonlinear Vlasov-Poisson simulation of collisionless bounded plasma. It is shown that, in agreement with the basic theory, plasmons survive substantial transformations of the spectrum, i.e., Landau-Zener transitions, and are destroyed only when their wave numbers become large enough to trigger Landau damping. [Preview Abstract] |
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NW1.00059: SPECT3D, Imaging and Spectral Analysis Package. Igor Golovkin, Joseph MacFarlane, Viktoriya Golovkina SPECT3D is a collisional-radiative spectral analysis package designed to compute detailed emission, absorption, or x-ray scattering spectra, filtered images, XRD signals, and other synthetic diagnostics. The spectra and images are computed for virtual detectors by post-processing the results of hydrodynamics simulations in 1D, 2D, and 3D geometries. SPECT3D can account for a variety of instrumental response effects so that direct comparisons between simulations and experimental measurements can be made. We will present new features of SPECT3D and highlight their application to the analysis of HEDP experiments. We will discuss a newly implemented capability to simulate scattering signatures from realistic experimental configurations, which include the influence of plasma non-uniformities and collecting scattered x-rays from a range of angles. Other improvements include support for a wider range of hydrodynamics codes and improved lineshape models for spectral lines from neutral atoms. [Preview Abstract] |
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NW1.00060: Effect of surface protrusion on plasma sheath properties in DC microdischarges. Yangyang Fu, Peng Zhang, John Verboncoeur, Andrew Christlieb The electric field enhancement due to the presence of cathode surface protrusion is investigated in the atmospheric DC microdischarges with the goal of identifying the plasma sheath properties. The electric field enhancement of a semi-ellipsoidal protrusion is examined by adjusting the semi-major axis, $a$, and the~semi-minor axis,$ b$, of the ellipsoid. It is found that the cathode electric field enhancement depends strongly (weakly) on the aspect ratio (size) of the protrusion, when it is much smaller than the discharge gap distance. In particular, when the protrusion is spherical ($a=b)$, the cathode electric field enhancement in vacuum, as well as inside the plasma, are found to be almost constant against the radius of the hemispherical protrusion. The corresponding plasma sheath thickness is also nearly a constant with different radius. When the protrusion is ellipsoidal ($a\ne b)$, the electric field enhancement decreases and the sheath thickness increases, when the semi-minor axis $b$ increases. However, the ratio of the cathode electric field in vacuum to that in the steady-state plasma is found to be nearly a constant. The results indicate that effects of surface protrusions on plasma sheath properties are correlated with their vacuum electric field distributions. [Preview Abstract] |
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NW1.00061: The PLASIMO plasma modeling framework Wouter Graef, Diana Mihailova, Jan van Dijk, Gerrit Kroesen PLASIMO is a plasma modeling framework that has been under continuous development in the EPG plasma group at the Applied Physics Department of Eindhoven University of Technology since the 1990s. Since its initial form, aimed at modeling Inductively Coupled Plasmas and Cascaded Arcs, it has gained much functionality catering to a plethora of plasma applications: LTE and non-LTE, steady state and transient, flowing and non-flowing, with and without space charges, and from zero dimensional Global Models to full 3D simulations. The platform, which is developed in C++, is characterized by a high degree of modularization, offers a user friendly Graphical User Interface, and is available on multiple platforms, including Linux, Windows, and macOS. We present assorted applications where PLASIMO has been successfully employed, concentrating on recently added capabilities of the platform and their use cases. [Preview Abstract] |
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NW1.00062: Simulation of a laser triggered vacuum switch Andrew Fierro, Christopher Moore, Weng Chow, Laura Biedermann, Matthew Hopkins Laser triggered vacuum switches (LTVS) use input laser energy to inject electrons, ions, and neutral material from a trigger target into an electrically stressed vacuum gap. The reliability, power, and high output power of lasers make the LTVS an appealing approach for low-jitter, high voltage switching applications. Modeling of a LTVS allows for optimization of both laser and trigger material parameters for efficient operation. Essential to the laser triggering process is the injection of charged and neutral species at the trigger material surface. As such, a material supply model has been developed and is a function of the input laser intensity, wavelength, and pulse shape. This material model serves as an input flux boundary condition for into a particle-in-cell (PIC), direct simulation Monte Carlo (DSMC) code which simulates plasma growth and gap closure. Two hemispherical electrodes with a gap distance of 500 micron are simulated with the laser propagating axially towards the cathode through a small hole in the anode. An applied potential of several kV establishes an electrostatic potential. Plasma formation for various laser energies and wavelengths are compared to establish general trends of the LTVS. [Preview Abstract] |
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NW1.00063: The Design of Raw Data Management System for Plasma Surface Reaction Modeling and Simulation Jun-Hyoung Park, Won-Seok Chang, Mi-Young Song Plasma-based process technology is an important technology in semiconductor manufacturing process. By using the data of the surface reaction utilizing the plasma chemical reaction, it is possible to control the gas mixing ratio or the discharge variable necessary for the process and the material characteristics. In this method, the yield of semiconductors can be improved and highly precise processing becomes possible. In order to apply it not only to the semiconductor field but also to various industries and research, experiments on multiple plasma surface reactions are being conducted. In particular, physical and chemical analysis is necessary to solve the problem of process yield and improvement of yield of semiconductor process. However, basic plasma surface reaction data necessary for related simulation and modeling is not managed / provided efficiently. DCPP of the NFRI provides research data such as plasma collision and thermodynamics to industries and researchers as a data center that collects and disseminates experimental / research data on plasma physical properties. We are trying to design a system that can manage and provide related experiments and research data to provide data related to plasma surface reactions via database systems in the data center. [Preview Abstract] |
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NW1.00064: Modification of adhesion ability of carbon fabrics for composite materials Viktor Zheltukhin, Aidar Garifullin, Mars Shaekhof Modification of the carbon fabrics by RF capacitive coupled discharge at low pressure (13-130 Pa) is studied. The plasma treatment leads to increasing of surfaces area of the carbon fibers, to creation of active radicals, and to decreasing of wetting angle. The cumulative impact of these factors leads to increasing of wettability of technical textiles. It is established that carbonyl and hydroxyl functional groups are formed after RF plasma treating. Regulation of carbon fabrics properties by RF capacitive coupled plasma allow us to create composite materials which have strength values by 15-20{\%} higher than control samples. [Preview Abstract] |
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NW1.00065: Regulation of properties of hollow fiber membranes by low-temperature plasma Viktor Zheltukhin, Rustam Ibragimov Hollow fiber polysulfone membranes with an internal selective layer were treated by low-pressure air RF plasmas. It is found that oxygen-containing functional groups on the internal surface of membranes is formed due to RF plasma action. The mean arithmetic deviation of the roughness profile (Ra) and the height of the irregularities (Rz) of the surface microrelief the membrane is decreased. The pore diameter in the membrane is equalized. The cumulative influence of these factors leads to significant increasing of hydrophilization of the selective membrane layer. [Preview Abstract] |
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NW1.00066: Analysis of mechanical and physical properties of metal cutting tools processed by low pressure RF plasmas Viktor Zheltukhin, Albert Khubatkhuzin Physical and mechanical characteristics of metal cutting tools treated by capacitive coupled RF plasma are investigated. Topography, roughness, hardness, wear resistance, modulus of elasticity, elastic recovery coefficient and the thickness of the modified layer in a single instrument was studied. Gas saturation (carbonizing) of surface layers of metals and alloys at a depth of 1 micron during to 40 minutes processing was obtained, resulting in an increase of strength properties, durability and lifetime of the products. Research of wear resistance was carried out by experiments on field trials of "Northwest trunk pipelines". Results are showed that lifetime increases in the range from 140 up to 230{\%}. The complex approach to the study of surfaces with the use of methods to measure. [Preview Abstract] |
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NW1.00067: Numerical study of atomic layer precision control for SiO2 etching Zhang Saiqian, Dai Zhongling, Wang Younian In semiconductor fabrication industry, the application of 3D structures makes profile, damage and selectivity control more difficult. Atomic layer etching (ALE) becomes a potential way to achieve high precision control of etching. In ALE, cyclic passivation and removal of the passivated layer are performed and the self-limiting nature guarantees the 1ML/cycle in ideal case. But throughput issue arises from purge step limits the application, many study try to achieve the ALE or ALE-like precision control with less time or equipment costs by compromising the precision. In this study, a multi-dimensional model is built to simulate the SiO2 etching in fluorocarbon plasmas. First, global and sheath model are used to get energetic particle fluxes. Then particles are traced in the trench model and finally a surface Monte Carlo method is used to consider surface reactions. Results show that by cyclic control of high and low ion energies, better precision control is achieved compared to conventional etching, even without alternating the feed gas. But non-ideal etching like micro-trenching, sidewall slope exists. Control of ion energy distribution and duty ratio of energy modulation can be used to optimize the profile and selectivity control. [Preview Abstract] |
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NW1.00068: Abstract Withdrawn
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NW1.00069: 3D Feature Profile Simulation of Cyclic Fluorocarbon Atomic Layer Etching Process SangHeon Song, Yeoung Geun Yook, Hae Sung You, Yeon Ho Im Recently, a great deal of attention has been placed on atomic layer etching (ALE) processes as semiconductor features continue to shrink below 10 nm. ALE is a technique for removing a few monolayers of material using sequential reaction steps that are self-limiting. A cyclic plasma-enhanced fluorocarbon ALE process has attracted much interest for its selective etching and atomic-level control. A Lam Research Corp. etch system enabling this process has been qualified for manufacturing of logic devices. To build upon Lam's achievement it requires more feasibility studies for wide applications on various 3D nanoscale patterns. To address this issue, we've performed 3D topography simulations coupled with a realistic surface reaction model for the cyclic fluorocarbon ALE process for silicon oxide. In this work, 3D topography simulations were performed for a multiple 3D-level-set-based moving algorithm, a 3D ballistic transport of chemical species coupled with zero-D bulk plasma simulation, and a surface reaction module. This work can lead to a better understanding of the cyclic fluorocarbon ALE process and its application to next-generation sub-10 nm devices. [Preview Abstract] |
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NW1.00070: Efficiency technique of in-situ dry cleaning process in etch chamber Yusin Kim, Junghwan Um In order to achieve the same process results in one chamber, it is very important to keep the wall condition constant at all times. Therefore the in-situ dry clean process (ISD) is performed after each wafer is processed. End point detection (EPD) technique, which is traditionally used in the process, is applied to vary the ISD time according to the chamber wall conditions. As a result of applying the appropriate EPD algorithm according to the type of ISD gas, the minute change of the chamber is observed with the EPD time of ISD. In addition, plasma simulations were performed to find the ISD condition to minimize the surface damage caused by the plasma generated during ISD. As a result of applying the conditions derived from the simulation and the EPD technique, process defects due to particles falling off the surface are reduced. [Preview Abstract] |
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NW1.00071: New developments in Nb surface modification using a cylindrically symmetric capacitive discharge Jeremy Peshl, Milka Nikolic, Janardan Upadhyay, Svetozar Popovic, Alexander Godunov, Leposava Vuskovic We performed the ion-assisted reactive ion etching of a single cell Superconducting Radio Frequency (SRF) cavity made of pure Niobium (Nb) in a capacitive rf Ar/Cl$_{\mathrm{2}}$ discharge with cylindrical symmetry. The first rf test of a plasma etched SRF cavity at cryogenic temperature has shown no field emission, which did not increase even after multiple chemical cleanings and testing. The absence of field emission is interpreted by the effect of plasma wake field on the SRF cavity walls. In addition, we will present effects of the etching parameters on the surface roughness of cavity grade Nb. Efforts on the development of plasma diagnostics employing different line intensity ratio techniques to evaluate emission spectroscopy data and deduct plasma parameters will be presented. A comparison of the spectral data from an Ar plasma and an Ar/Cl$_{\mathrm{2}}$ plasma show an interesting influence of DC bias -- a necessary parameter in the etching of the larger surface electrode -- on the electronegative characteristics of the Ar/Cl$_{\mathrm{2}}$ plasma. [Preview Abstract] |
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NW1.00072: Simulation of Large Area Inductively Coupled Plasmas using CF4/O2 Gas for Dry Etching of a Flat Panel Display Geonwoo Park, Min Young Hur, Changrok Choi, Hoonbae Kim, M. J. Kushner, Hae June Lee As the demand for larger area display increases, the plasma uniformity is required in a chamber size of 2200 mm by 2500 mm (the 8th generation) or larger. The fluid simulation of a large area inductively coupled plasma (ICP) source is presented for the investigation of etch profiles and for the analysis of uniformity control. The plasma is produced by three by three ICP sources for the 8th generation flat panel display. The substrate is also biased with an RF source of 13.56 MHz in order to get high etching rate. Hybrid Plasma Equipment Model (HPEM) code is used for the simulation of CF4/O2 gas mixture, and the results are compared with experimental measurement of etch profiles. The generation and the transport of each species are analyzed for the variation of the input power and the bias voltage. Finally, the ratio of ion fluxes to neutral fluxes is compared with the etching profiles obtained by experiment. [Preview Abstract] |
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NW1.00073: Designing microscale gas discharges to enhance thermionic energy conversion John Haase, David Go Thermionic energy converters (TECs) are devices that convert heat directly to electricity via thermionic emission. In a TEC, a hot cathode emits electrons that are then collected by a cold anode, and when passed through a load, produces electrical work. However, the emitted electrons can build-up between the electrodes, retarding the current. Two strategies to combat the build-up negative space charge are to reduce the interelectrode gap, preferably to the micron-scale, or to introduce a positive space charge, a plasma. Previously [1], we showed that microscale inert gas plasmas could perform this role, and enhance thermionic emission, under steady state conditions. However, because energy must be injected to ignite the inert gap plasma, a microplasma-enhanced TEC device must be operated in a pulsed mode in order to achieve net power generation. In this work, we use the plasma modeling software Zapdos [2] to model an inert gas (argon) microplasma-enhanced TEC. We explore the effect of various system parameters on the net power produced by these TECs, and optimize the system parameters to maximize power output. [1] J. R. Haase and D. B. Go, J. Phys. D. Appl. Phys. 49, 55206 (2016). [2] A. D. Lindsay, D. B. Graves, and S. C. Shannon, J. Phys. D. Appl. Phys. 49, 235204 (2016). [Preview Abstract] |
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NW1.00074: The Role of Vibrational Energy on the Catalytic Production of Ammonia in Non-Equilibrium Atmospheric-Pressure Plasma Francisco Herrera, Paul Rumbach, Patrick Barboun, Jongsik Kim, Jason Hicks, David Go Plasma-catalytic nitrogen fixation to produce ammonia from nitrogen and hydrogen feedstock has been investigated as a potential alternative to the conventional Haber-Bosch process because it can be operated under less extreme conditions and potentially more energy efficiently. However, the fundamental mechanisms behind this process are not fully understood. In this work, we use optical emission spectroscopy (OES), which is a non-invasive technique for estimating relative relevant parameters of the plasma, to correlate plasma behavior with measured nitrogen conversion in a plasma-catalytic reactor. Using OES, we have performed several measurements of nitrogen-hydrogen atmospheric pressure dielectric barrier discharges (DBD) at different controlled operational conditions. We extract the vibrational and rotational temperatures of the DBD by comparing our spectroscopic measurements with a modelled optical emission. We find that the vibrational temperature is strongly dependent on the gas composition and power, and we correlate this behavior to measurements of nitrogen conversion using the same DBDs in conjunction with oxide-supported metal catalysts. [Preview Abstract] |
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NW1.00075: Abstract GEC17-2017-000356 moved to GT1.80 |
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NW1.00076: PFC Abatement Using Microwave plasma source with annular-shaped slot antenna at sub-torr pressure Seungil PARK, Sung-young Yoon, Changho Yi, Seong Bong Kim, Seungmin Ryu, Jaesung Oh, Suk Jae Yoo We present a feasibility study of a microwave plasma source with annular-shaped slot antenna for abatement of PFCs gas from semiconductor manufacturing processes. According to the company's requirements, the concept of this plasma source could be designed to have a cylinder-shaped metal reactor with quartz tube, an annular-ring resonator with an annular-shaped slot antenna, and a microwave components. In order to investigate the concept of this source, the prototype device was designed to maximize an electric field in the reactor for the breakdown using the 3D finite element method (FEM) code and fabricated with the inner diameter of 100 mm. The argon plasma was generated in the pressure range from 0.04 to 4 torr by the commercial magnetron with the power of 1 kW and the frequency of 2.45 GHz. The plasma properties such as the argon metastable density and the gas temperature have been measured by a tunable diode laser absorption spectroscopy (TDLAS). By using this plasma, destruction and removal efficiencies (DRE) over 90{\%} for CF4 were achieved with the additive gases by a quadrupole mass spectrometry (QMS). In this paper, the initial design and the preliminary experimental results of a new microwave plasma source would be discussed [Preview Abstract] |
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NW1.00077: Visible light effects in plasma plume ignition Lanlan Nie The breakdown delay time of a closed plasma plume excited by a high-voltage pulse is investigated. The visible monochromatic light of 404, 532, and 662 nm wavelength and narrow-waveband light at a central wavelength of 400, 430, 450, 470, 500, 530, 570, 610, and 630 nm are used to pre-ionize the gas. It is found that the breakdown delay time decreases when the visible light illuminates the discharge tube. The light is most effective when it is applied at the position near the high-voltage electrode. The effect of visible light is found to inversely relate to the wavelength, manifested by the longer breakdown delay times for longer wavelengths. With increasing the frequency and the pulse width of the voltage, the visible light shortens the delay time more effectively. These observations can be explained by the visible light-enhanced generation of free electrons before the ignition. The proposed mechanisms of free-electron generation are the optically stimulated exoelectron emission from the inner surface of the discharge tube wall and the vibrational excitation of nitrogen molecules. The effects of visible light weaken with the addition of oxygen as a result of electron affinity to oxygen. [Preview Abstract] |
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NW1.00078: Instabilities in fluid simulations of ExB plasmas Gerjan Hagelaar, Sarah Sadouni The operation of magnetized low-temperature plasma devices such as Hall thrusters and magnetrons involves various types of plasma instabilities, generally causing anomalous electron transport across the magnetic field lines. This paper demonstrates that fluid models of these plasma devices, when solved properly in the 2D plane perpendicular to the magnetic field lines, intrinsically produce some of such plasma instabilities and anomalous transport, whose behavior may or may not be realistic, depending on the configuration and conditions. Results are shown from a self-consistent fluid code developed at LAPLACE based on standard fluid equations for continuity, momentum and energy of (partially) magnetized electrons and ions, for different simple ExB plasma configurations. These results are compared with PIC simulations, checked against a linear instability analysis and interpreted in terms of basic instability types known in the literature. [Preview Abstract] |
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NW1.00079: Nanosecond-pulsed DBD in atmospheric air and methane-nitrogen mixtures Danil Dobrynin, Chong Liu, Alexander Fridman Dielectric barrier discharges (DBDs) are non-equilibrium low-temperature discharges. Uniform dielectric barrier discharges have many potentially transformative industrial applications, including uniform thin-film deposition, surface modification of polymers, sterilization of biological samples, treatment of living tissues and cells for their advantages of low gas temperature, moderate power density, uniform energy distribution, controllability of chemical composition and so on. Uniform DBDs are traditionally generated at special conditions (e.g., low pressure, rare gases), and in atmospheric air are of filamentary nature. Recent developments in pulsed power generation technology allowed controllable application of fast-rising short (nanosecond) high voltage pulses for generation of pulsed discharges. In our preliminary studies we have been able to perform fast imaging of the discharge development on nanosecond time scales in atmospheric air, and show transition of DBD from filamentary to uniform mode. We show that the discharge uniformity may be achieved in the case of strong overvoltage (provided by fast rise times), when anode-directed streamers are formed. Here we present our results on fast ICCD imaging of DBD in atmospheric air and methane-nitrogen mixtures for uniformity analysis, as well as temperature and local electric filed measurements using OES. [Preview Abstract] |
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NW1.00080: ABSTRACT WITHDRAWN |
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NW1.00081: Discharge modes in oil submerged spark gap with gas injection. Kunpeng Wang, Xin Tang, David Staack Electrical discharge in submerged spark gap with gas injection was experimentally studied with two different commonly used electric circuits. One RC circuit with constant voltage and a double spark gap circuit were used. The charging time of the RC circuit before breakdown was comparable with the bubble residence time in the spark gap, while the second circuit with double spark gap finished charging and discharging on the second capacitor two orders of magnitude faster than the bubble rising time. Consequently, bubble dynamics are relatively independent of the applied electric field if we use the second circuit. Three different discharge mechanisms were proposed. The first breakdown mechanism is believed to happen in the gas phase only when the entire spark gap was enclosed in a gas bubble. Breakdown occurs first on the electrode tips where a stronger electric field is present. The second discharge mechanism is initiated by contaminates in the liquid. When contaminates get charged from one electrode and move in the electric field towards the second electrode, breakdown happens during this process. The third discharge mechanism we proposed is due to the interactions between either charged bubbles or charged bubbles and electrode. [Preview Abstract] |
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NW1.00082: Nonlinear ECDI and anomalous transport in E$\times$B discharges Salomon Janhunen, Andrei Smolyakov, Oleksandr Chapurin, Dmytro Sydorenko, Igor Kaganovich, Yevgeni Raitses Cross-field anomalous transport is an important feature affecting the operation and performance of $E\times{B}$ discharges. Instabilities excited by $E\times{B}$ flow cause anomalous current to develop, characterized in the nonlinear regime by a large amplitude coherent wave driven by the energy input from the unstable cyclotron resonances. A persistent train of soliton-like waves characterized by the fundamental cyclotron wavelength appears in ion density. Simultaneously, there is inverse energy cascade toward long wavelength which is manifested by the formation of the long wavelength envelope of the wave train. It is shown that the long wavelength part of the turbulent spectrum provides a dominant contribution to anomalous electron transport. We present results from 1D3V and 2D3V PIC simulations, with finite boundaries in 2D. Influence of inhomogeneities in density and magnetic field on the development of the $E\times{B}$ drift cyclotron instability is investigated, as well as the non-linear mechanisms behind the coherent structures and their interactions. [Preview Abstract] |
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NW1.00083: A UV Lamp Power Supply and Method for Improved UV Lamp Performance in Vertical Applications Brett Skinner, Darrin Leonhardt, Charles Wood UV Lamps are ubiquitous in the curing of industrial coatings, inks, and adhesives. Most applications, such as printing, require the lamps to be oriented horizontally. Yet many applications like optical fiber require the lamp to be vertical. First-generation, ferroresonant power supplies, with their aggressive ripple, allowed lamps to be operated both vertically and horizontally. Then, DC power supplies were implemented into horizontal applications due to their numerous advantages over their precursor: higher efficiency, lighter weight, lower risk of slot arcing and magnetron internal moding, and more. However, the lack of turbulence in the plasma yielded an unsymmetrical distribution of the bulb fill along the bulb length in additive bulbs when not horizontal. As a result, significantly decreased overall UV output occurs along with increased peak temperatures that can reduce the lifetime of the bulb, precluding the use of DC power supplies in vertical applications. In order to study the effects that the waveform driving both engines in the power supply has on the bulb, a special power supply was built which allows all aspects of the waveform to be controlled: duty cycle, fall time, rise time, frequency, phase delay, and peak current. Years of testing these parameters have produced a waveform that provides the benefits of both DC and ferroresonant power supplies without the drawbacks inherent in both. This paper examines the impact that each waveform parameter has on vertical bulb performance. [Preview Abstract] |
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NW1.00084: Conversion of Lignin to Valuable Compounds Induced by Discharge Plasma at Gas/Liquid Interface Shigenori Takahashi, Masami Bito, Masahiro Tokuda, Wahyu diono, Noriharu Takada, Hideki Kanda, Motonobu Goto This work focused on the pulsed discharge plasma as oxidation process of lignin obtained from wood. The pulsed discharge plasma is a low-cost process because the process is performed under normal conditions. The objective of this study is to convert lignin into value-added products induced by pulsed discharge plasma, such as vanillin. Lignin that used as a starting material was extracted from the wood powder of Japanese cedar by dissolving it in sodium hydroxide solution. Experiments were conducted using a batch type reactor and DC pulsed discharge plasma power supply unit. The DC pulsed voltages at 10 -- 18 kV were introduced on the extracted lignin solution via the copper electrode under atmospheric pressure air or argon. The electrode was set at distance of 2 mm from the lignin solution surface. The products from the conversion of lignin in the aqueous solution were identified and quantified by HPLC. The results showed that the production of vanillin during discharge in air environment was larger than in argon environment due to expectedly abundant reactive oxygen species formation. However, the production of vanillin after discharge in argon environment was more rapid than in air environment following by the low molecular weight of lignin derived compounds. [Preview Abstract] |
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NW1.00085: Controlling the Directional Motion of Water Droplet on Polymer by Titled Nanopillar Fabrication by rf PECVD Lan Phan, Myoung-Woon Moon In this work, we used plasma in radio frequency plasma enhance chemical vapor deposition ( rf PECVD) to fabricate the slanted nanopillars with diameter around tens of nm on PET polymer, control the angle of tilted nanopillars on the substrate using Faraday cage. The top-view and cross-view of SEM show that the mushroom-liked nanopillar formation was created thank to the etching of O2 gas plasma under the shading effect of metal cluster come from electrode and metallic cage under the bombardment of ion. The XRD result with high density of metallic oxide from stainless steel confirms the assumption. A directional motion of water droplet on nanopillar layer show the specific function of this nanostructure. The work could activate lots of potential applications by its high surface ratio and other specific purposes such as control the cell motion, directional water condense, and so. [Preview Abstract] |
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NW1.00086: Vibrational excitation of CO2 by Nanosecond Repetitively Pulsed sparks Erwan Pannier, Valentin Baillard, Christophe Laux CO$_{\mathrm{2}}$ can be used as a feedstock for synthetic gas (syngas) production, both for ground and space (Mars settlement) applications. In these processes, CO$_{\mathrm{2}}$ splitting into CO and O$_{\mathrm{2}}$ is the most energy consuming step. Previous studies have shown that nonequilibrium plasma discharges can perform this dissociation with a maximum energy efficiency through the excitation of vibrational levels of CO$_{\mathrm{2}}$ in a process known as the ladder-climbing mechanism. In this work, we investigate the contribution of vibrational excitation in CO$_{\mathrm{2}}$ dissociation with nanosecond repetitively pulsed discharges (NRP). In particular, we investigate the potential of the high repetition frequency (10 - 20 kHz) to yield a synergetic effect that increases the vibrational temperature over several pulses. The vibrational excitation of CO$_{\mathrm{2}}$ is measured with time-resolved, phase-locked IR emission spectroscopy in the 4.2um asymmetric stretch band. The vibrational temperature is inferred from a comparison with non-equilibrium spectra calculated with the CDSD-HITEMP database. Populations of vibrationally excited states are compared with results from a 0D vibrationally-specific kinetic code to study the synergetic effect of successive discharges. [Preview Abstract] |
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NW1.00087: Growth and characterization of graphene films by halogen based plasma etching of 6H-SiC Charter Stinespring, Andrew Graves, Saurabh Chaudhari, Srikanth Raghavan The synthesis of graphene has received considerable attention due to its remarkable properties. We have developed a novel plasma based method for producing graphene films on silicon carbide. Specifically, CF$_{\mathrm{4\thinspace }}$and Cl$_{\mathrm{2}}$ based inductively coupled-reactive ion etching is used to selectively remove Si from the near surface layers of 6H-SiC(0001). The graphene film is then formed by rapid thermal annealing of this carbon rich layer at 970$^{\mathrm{o}}$C under atmospheric pressure argon or ultrahigh vacuum conditions. The composition, structure, and thickness of these films have been characterized using x-ray photoelectron spectroscopy, reflection high energy electron diffraction, Raman spectroscopy, and atomic force microscopy. The results indicate that the films are epitaxial with a thermally stable defects which buckle the graphene surface. The plasma parameters, most notably the bias voltage, are used to control the number of graphene layers. This allows reproducible synthesis of one, two, and three layer graphene films. Metal-graphene-metal structures have been characterized using simple current-voltage measurements. These exhibit Schottky type behavior. We believe this may be due to semiconducting behavior produced by the observed defect structures. [Preview Abstract] |
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NW1.00088: Argon Plasma Generated By High Repetition Rate, Nanosecond Pulses: Time-Resolved Measurements of Voltage, Current, and Electron Number Density Vladlen Podolsky, Andrei Khomenko, Sergey Macheret Weakly ionized plasmas sustained by high repetition rate nanosecond pulses have shown promise for a number of applications due to the low power budget, efficient ionization, and enhanced production of excited species. To study the dynamics of such plasmas, time-resolved probe measurements of voltage and current as well as microwave interferometry measurements of the spatially-averaged electron density were conducted in argon at a pressure of several Torr and parallel-plate electrode spacing of several centimeters. From the measured electron density decay between the pulses, the recombination rate coefficients were inferred. This provided an insight into the recombination mechanisms. In particular, the dimer ions Ar2$+$ were found to be dominant, so the recombination was primarily dissociative. The relaxation time of the electron temperature was also determined and found to be much shorter than the recombination time. Since the time interval between the pulses is much longer than the pulse duration and the electron temperature relaxation time, most of the time the plasma has a relatively high electron density but low electron temperature and hence low Johnson-Nyquist noise. Such plasmas could thus be useful in radio-frequency electronics. [Preview Abstract] |
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NW1.00089: Atomic data of low-charged Sn ions for lithography applications James Colgan, D. P. Kilcrease, J. Abdallah, M. E. Sherrill, C. J. Fontes, P. Hakel Sn is one of the most promising materials that has been investigated to date in the quest to make intense radiation sources for EUV lithography. Sn plasma readily produces an intense, narrow, emission band around 13.5~nm, a feature that has long been studied in efforts to exploit this useful property. The efforts to predict the properties of Sn that produce these intense emission features are complicated by the complex atomic structure of the Sn ions in question. We have begun investigations into the opacity of Sn at low temperatures. We have explored the accuracy of some approximations used in opacity models for Sn. The use of intermediate-coupling, as compared to full configuration-interaction (CI), is not adequate to obtain accurate line positions of the important bound-bound transitions in Sn. One requires full CI to properly describe the strong mixing between the various n=4 sub-shells that give rise to the $\Delta$n=0 transitions that dominate the opacity spectrum at low temperatures. Calculations that include full CI for large numbers of configurations quickly become computationally prohibitive, so we have explored hybrid calculations, in which full CI is retained only for the most important transitions [1]. [1] J. Colgan et al, HEDP {\bf 23}, 133 (2017). [Preview Abstract] |
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