Bulletin of the American Physical Society
67th Annual Gaseous Electronics Conference
Volume 59, Number 16
Sunday–Friday, November 2–7, 2014; Raleigh, North Carolina
Session GT1: Poster Session I (17:30-19:30) |
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Room: Exhibit Hall |
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GT1.00001: Air mode waveguide cavity with hybrid tunable plasma switching elements for K-band microwaves Benjamin Wang, Mark Cappelli A tapered holey waveguide with an air mode cavity was designed with plasma switching elements. The propagation of microwaves in this device was investigated experimentally and computationally. Finite difference time domain (FDTD) simulations confirm unique resonance modes for plasma on and plasma off states. Integration of low-pressure plasma elements into this hybrid device allowed for controllable propagation of electromagnetic waves, showing tunable band gaps and resonance states. [Preview Abstract] |
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GT1.00002: Difference in Rotational Temperatures between Neutral Molecules and Molecular Ions of Low-Pressure Discharge N2-O2 Plasmas Hiroshi Akatsuka, Hirokazu Kawano, Koichi Naoi, Hao Tan, Atsushi Nezu, Haruaki Matsuura For a microwave discharge nitrogen plasma with its discharge pressure about 1 Torr, our OES measurement showed that the rotational temperature of N$_2^+$ B state by the first negative system (1NS) is about 1.5 times higher than that of N$_2$ C state by the second positive system (2PS). Meanwhile, it is found that the rotational temperature of O$_2^+$ b state by 1NS is almost the same as that of O$_2$ b state by the atmospheric absorption band, which is quite different from N$_2$ plasma. We consider that the rotational temperature of the ground state O$_2^+$ X ion should be higher than that of O$_2^+$ b state due to difference in the internuclear distance, where that of the O$_2^+$ b state is much larger than that of the ground state O$_2^+$ X. The angular momentum of both X and b states are almost conserved before and after the electron impact excitation due to small mass of an electron. Therefore, the rotational temperature of the X state of O$_2^+$ ion should be estimated to be about 1.3 times of that of O$_2^+$ b state. This value gives a similar result with that of nitrogen plasma, where the internuclear distances of B and X states of N$_2^+$ are almost the same. It is considered that the ground-state molecular ion has higher rotational temperature than neutral molecule. [Preview Abstract] |
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GT1.00003: Global Model of a Fast Ionization Wave in Helium Benjamin Yee, Edward Barnat, John Foster Technical challenges inhibit a complete examination of fast ionization waves via empirical means. The high-voltage pulses used to excite these waves can be on the order of nanoseconds or less. Such short timescales require instruments with exceptional sensitivity and bandwidth, but these may not be available or may not exist. In order to more completely understand the energetics of the fast ionization wave, a global model of a helium discharge was developed. We present the results of the model predictions and a comparison to experimental measurements when possible. The model follows 19 neutral helium states, helium ions, and electrons. Among the reactions included in the model are: electron impact ionization, electron (de)excitation, atomic excitation transfer, radiative decay, and radiation trapping. Comparisons demonstrate that the model can accurately predict 2$^3$S metastable densities, but discrepancies in the measured and predicted emissions indicate a greater than expected number of higher excited states. This suggests the presence of a persistent source of excitation which is believed to be the result of space charge buildup within the system. [Preview Abstract] |
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GT1.00004: Modeling the impact of magnetic field on plasma parameters in an electron beam generated argon plasma George Petrov, David Boris, Tzvetelina Petrova, Scott Walton A spatially averaged model of an electron beam generated plasma is developed to model the impact of an externally applied magnetic field on the formation of the electron energy distribution function in an argon background. The model is based on numerical solution of the electron Boltzmann equation that is self-consistently coupled to a set of rate balance equations for electrons and argon ions. The confining effect of the magnetic field is studied theoretically by calculating the electron energy distribution function, electron density and temperature as a function of the magnetic field strength in the range 0-300 Gauss. It was established that a rigorous kinetic treatment, which accounts for the impact of the magnetic field over the whole distribution of electrons, is required for accurate description of the plasma. [Preview Abstract] |
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GT1.00005: Controlling the Electron Energy Distribution Function Using an Anode Scott D. Baalrud, Edward V. Barnat, Mathew M. Hopkins Positively biased electrodes inserted into plasmas influence the electron energy distribution function (EEDF) by providing a sink for low energy electrons that would otherwise be trapped by ion sheaths at the chamber walls. We develop a model for the EEDF in a hot filament generated discharge in the presence of positively biased electrodes of various surface areas, and compare the model results with experimental Langmuir probe measurements and particle-in-cell simulations. In the absence of an anode, the EEDF is characterized by a cool trapped population at energies below the sheath energy, and a comparatively warm tail population associated with the filament primaries. Anodes that are small enough to collect a negligible fraction of the electrons exiting the plasma have little affect on the EEDF, but as the anode area approaches $\sqrt{m_e/m_i}A_w$, where $A_w$ is the chamber wall area, the anode collects most of the electrons leaving the plasma. This drastically reduces the density of the otherwise trapped population, causing an effective heating of the electrons and a corresponding density decrease. A global model is developed based on the EEDF model and current balance, which shows the interconnected nature of the electron temperature, density and the plasma potential. [Preview Abstract] |
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GT1.00006: Effect of mass and charge of ionic species on spatio-temporal evolution of transient electric field in CCP discharges Sarveshwar Sharma, Sanjay Kumar Mishra, Predhiman Kaw, Miles Turner, Shantanu Kumar Karkari The formation of capacitive sheath and existence of the transition electric field between sheath edge and bulk plasma in RF-CCP discharge is predicted by Kaganovich (PRL 89, 265006 2002); such structures are sensitive to the plasma composition. On the basis of semi-infinite particle-in-cell (PIC) simulation the effect of charge and mass of ionic species on the spatio-temporal evolution of the transient electric field and phase mixing phenomena in linear and weakly nonlinear regime has been explored. As an important feature, the simulation results predict that the maximum amplitude of the transient electric field decreases while the potential structure approaching to the electrode with increasing ionic mass and charge. The excitation of wave like structures in the transition region and efficient energy transport to the bulk region of CCP discharges in a nonlinear regime has also been predicted. \\[4pt] [1] I. D. Kaganovich, Phys. Rev. Lett. 89, 265006 (2002).\\[0pt] [2] I. D. Kaganovich, O. V. Polomarov and C. E. Theodosiou, IEEE Trans. Plasma Sci. 34, 696 (2006). [Preview Abstract] |
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GT1.00007: Tuning of Electron Energy and Density in a Double-Pulsed Argon Plasma Ricky Tang, Edward Barnat, Paul Miller The ability to tune the properties of a plasma was demonstrated with a double-pulsed positive column discharge. The plasma is generated by the first voltage pulse, which sets the peak electron density. A subsequent voltage pulse is applied during the afterglow to achieve independent tuning of the electron energy. Experiments were conducted over a range of voltage pulse amplitudes. Microwave resonant cavity (MRC) measurements of electron density and temperature demonstrated operating conditions, such as relative pulse amplitude and pulse width, where the electron temperature can be independently adjusted without affecting the density. Laser absorption measurements of the concentration of the 1S4 and 1S5 metastable states of argon corroborate the MRC measurements, demonstrating an increase in metastable density while the electron density continues its decay after the initial pulse. Electron drift velocity calculation also shows the dependence of the electron energy on the second voltage pulse. Results from the two diagnostics demonstrate the ability to tune the E/N ratio of the plasma, and hence the mean electron energy, independently of the density. This work was supported in part by the Department of Energy Office of Fusion Energy Science Contract DE-SC0001939. [Preview Abstract] |
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GT1.00008: Controlling plasma properties in a dc discharge with two anodes and a cold cathode Vladimir Demidov, Evgeny Bogdanov, Mark Koepke, Anatoly Kudryavtsev, Iya Kurlyandskaya, Olga Stepanova Understanding the interaction between sheath and contacting electrodes is important for predicting plasma kinetics and controlling plasma properties for various applications where the plasma is volumetrically confined To demonstrate controlling electron temperature in nonlocal plasma, modeling a dc discharge with cold cathode and application of different voltages to the discharge anodes has been performed. The modeling has been conducted in low-pressure argon gas discharge. It has been demonstrated that applied voltage can modify trapping within the device volume the energetic electrons arising from atomic and molecular processes in the plasma and emitted from the cathode due to ion bombarding. This leads to transformation of heating slow electrons by energetic electrons and as a result modifies the electron temperature. This also leads to modification of spatial distribution of densities of charged and excited metastable atom particles and plasma potentials. The above effects have also been experimentally demonstrated in short (without positive column) dc discharges of various constructions. [Preview Abstract] |
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GT1.00009: Experimental study of low-temperature plasma transport across a magnetic filter Romain Baude, Freddy Gaboriau, Gerjan Hagelaar Magnetized low-temperature plasmas are widely used in fields like space propulsion, materials processing or neutral beam injection. Charged particle transport in these plasmas is complex and still not fully understood. This paper presents an experimental study of plasma transport across a magnetic barrier as used in various (negative) ion sources. The aim is to obtain experimental data that are sufficiently detailed to provide direct insight into the physical principles of the cross-field transport and to validate numerical simulations. For this purpose we developed a dedicated laboratory set-up featuring an inductive argon discharge connected with a magnetic filter region. A segmented wall probe was used to measure the spatial profiles of the electron and ion current densities across the filter, while the plasma parameters were measured at different positions with a Langmuir probe. Measurements were performed for different gas pressures, magnetic field strengths, and bias voltages. The results clearly demonstrate the transition between a collisional regime where the electron current varies as 1/B2 and a bounded-drift regime with asymmetric electron temperature and 1/B current. [Preview Abstract] |
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GT1.00010: Breakdown in vapors of alcohols: methanol and ethanol Zoran Lj. Petrovic, Jelena Sivos, Nikola Skoro, Dragana Maric, Gordana Malovic Breakdown data for vapors of the two simplest alcohols -- methanol and ethanol -- are presented. The breakdown is achieved between plan-parallel electrodes, where cathode is made of copper and anode is a thin film of platinum deposited on quartz window. Diameter of electrodes is 5.4 cm and electrode gap 1.1 cm. We compare breakdown voltages (Paschen curves) for methyl and ethyl alcohol in the pressure range 0.1 - 2 Torr. In both vapors, the pressure is kept well below the vapor pressure, to prevent formation of liquid droplets. For each point of Paschen curves corresponding axial profiles of emission are recorded by ICCD camera in visual part of the spectra. Axial intensity distributions reveal important processes of excitation. Both vapors show strong emission peak near the cathode at all pd values covered by measurements, which indicates that excitation by ions and fast neutrals play important role in the discharge. Preliminary spectrally resolved measurements of the discharge structure with optical filters show that dominantly emission comes from CH band at 431 nm. There is a very low intensity of H$\alpha $ emission detected in ethanol vapor at high E/N, while it is much stronger in methanol even at lower E/N. It is interesting to note that H$\alpha $ emission in methanol exhibits exponential increase of intensity from the cathode to the anode, so it comes mainly from excitation by electrons, not heavy particles. [Preview Abstract] |
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GT1.00011: Electron heating due to coulomb collisions between slow and intermediate electrons in DC glow discharges Stepan Eliseev, Anatoliy Kudryavtsev As is known, the electrons in the cathode glow discharge plasma (negative glow and Faraday dark space) can be divided into three groups - slow, intermediate and fast electrons. Slow electrons, having maximum density, provide quasi-neutrality. They're locked in a potential well and have Maxwellian energy distribution. Fast electrons gain their energy in the cathode fall and maintain sufficient ionization in discharge. Intermediate electrons originate during ionization by fast electrons and carry current in the discharge. They have energies up to the threshold of inelastic collisions in the gas. At the same time they carry out their energy to the walls of the discharge and spend it on elastic collisions with gas atoms and Coulomb collisions with slow electrons and heat them. The amount of heating depends on the degree of ionization of gas, pressure, discharge tube size etc. The paper presents the results of a study on the impact of the heating on temperature and concentration of slow electrons in glow discharge. [Preview Abstract] |
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GT1.00012: Investigation of power dependence of electron density for various pressures June Young Kim, Dong-Hwan Kim, Ju Ho Kim, Sang-Bum Jeon, Chin-Wook Chung Experimental observation of the electron density variation in inductively coupled plasmas with the electron energy probability function was performed at various gas pressures at two RF input powers (25 W, 200 W). The measured electron energy probability functions (EEPFs) at high power discharges (200 W) showed a Maxwellian distribution, while evolution of the EEPFs from a bi-Maxwellian distribution to a Druyvesteyn-like distribution was observed at low RF powers (25 W) with increasing pressure. A discrepancy of the electron density variation between the two RF input powers was observed, and it was explained by the modified collisional loss and the Bohm velocity from the electron energy probability functions of the bi-Maxwellian distribution and the Druyvesteyn -like distribution. [Preview Abstract] |
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GT1.00013: DBCC Software as Database for Collisional Cross-Sections Daniel Moroz, Paul Moroz Interactions of species, such as atoms, radicals, molecules, electrons, and photons, in plasmas used for materials processing could be very complex, and many of them could be described in terms of collisional cross-sections. Researchers involved in plasma simulations must select reasonable cross-sections for collisional processes for implementing them into their simulation codes to be able to correctly simulate plasmas. However, collisional cross-section data are difficult to obtain, and, for some collisional processes, the cross-sections are still not known. Data on collisional cross-sections can be obtained from numerous sources including numerical calculations, experiments, journal articles, conference proceedings, scientific reports, various universities' websites, national labs and centers specifically devoted to collecting data on cross-sections. The cross-sections data received from different sources could be partial, corresponding to limited energy ranges, or could even not be in agreement. The DBCC software package was designed to help researchers in collecting, comparing, and selecting cross-sections, some of which could be constructed from others or chosen as defaults. This is important as different researchers may place trust in different cross-sections or in different sources. We will discuss the details of DBCC and demonstrate how it works and why it is beneficial to researchers working on plasma simulations. [Preview Abstract] |
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GT1.00014: Anode Sheath and Double Layer Solutions with Ionization Brett S. Scheiner, Scott D. Baalrud When an electrode in a plasma is biased more positive than the plasma potential it attracts electrons and repels ions forming a region of negative space charge (electron sheath). Ballistic electrons moving towards this anode gain energy equal to the difference in electrostatic potential energy, $\Delta \phi=\phi(x) -\phi_{plasma}$, with a maximum of $\phi_{anode}-\phi_{plasma}$. When $\phi_{anode}$ is large enough, electrons can gain enough energy to ionize neutral atoms through electron impact ionization. This leads to a layer of increased ion density near the anode, which can exceed the local electron density at large enough anode biases forming a double layer. We model the sheath potential profile using Poisson's equation with a fluid model for the electron density in the case without ionization and formulate an integral equation for the case with ionization where the ion density depends on an integral from $\phi(x)$ to $\phi_{anode}$. An analytic form of the sheath electric field is obtained for the case without ionization and we demonstrate that it asymptotically agrees with the Child-Langmuir solution. We numerically obtain double layer solutions when including ionization and show that the potential profile expands beyond that of the Child-Langmuir solution. [Preview Abstract] |
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GT1.00015: Does the Bohm Criterion have meaning for collisional plasmas? Greg Severn, Chi-Shung Yip, Sirous Nourgostar, Noah Hershkowitz Theorists view the Bohm criterion as approximately true, holding only for collisionless plasmas. The question of whether there exists a collisionally modified Bohm Criterion (CMBC) is often answered in the negative, and it is only a question of how the Bohm Criterion fails for the case of finite collisionality. The question is of importance considering that nearly all practical plasma processing applications involve plasmas of finite collisionality. There is, however, very little experimental work to help choose between competing models of how Bohm's Criterion fails. The question of critical importance is this: in plasmas of finite collisionality, do ions reach the Bohm speed at the location where the quasineutral plasma ends and where space charge appears? We have begun to examine the question experimentally in single ion species plasmas, and our goal is to vary the ion-neutral mean free path $\lambda$ within the interval $1< \lambda/\lambda_D < 10^{3}$, where $\lambda_{D}$ is the Debye length, and to present both plasma potential data and ion velocity distribution function profiles, measured by emissive probes and by LIF, respectively, to help us understand and assess the validity of theoretical claims. [Preview Abstract] |
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GT1.00016: First steps towards the reaction kinetics of HMDSO in an atmospheric pressure plasma jet in argon Detlef Loffhagen, Markus M. Becker, R\"udiger Foest, Jan Sch\"afer, Florian Sigeneger Hexamethyldisiloxane (HMDSO) is a silicon-organic compound which is often used as precursor for thin-film deposition by means of plasma polymerization because of its high deposition rate and low toxicity. To improve the physical understanding of the deposition processes, fundamental investigations have been performed to clarify the plasma-chemical reaction pathways of HMDSO and their effect on the composition and structure of the deposited film. The current contribution represents the main primary and secondary plasma-chemical processes and their reaction products in the effluent region of an argon plasma jet at atmospheric pressure. The importance of the different collision processes of electrons and heavy particles are discussed. Results of numerical modelling of the plasma jet and the Ar-HMDSO reaction kinetics indicate that the fragmentation of HMDSO is mainly initiated by collisions with molecular argon ions, while Penning ionization processes play a minor role for the reaction kinetics in the effluent region of the jet. [Preview Abstract] |
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GT1.00017: Optical emission study of ion composition in an inductively coupled oxygen plasma Nathaniel Ly, John B. Boffard, Chun C. Lin, Amy Wendt, Svetlana Radovanov, Harold Persing, Alexandre Likhanskii The success of ion implantation to precisely modify substrate properties requires control of the incident ion energies to achieve the desired depth of the implanted ions. Oxygen plasmas generally contain both O$^+$ and O$_2^+$ ions, and in plasma immersion ion implantation (PIII) of oxygen, the two will produce different concentration depth profiles due to their different energy/mass ratios. Predicting the overall profile thus requires knowledge of the relative fluxes of the two ion species. Here we combine experiment and modeling to investigate the feasibility of using non-invasive optical emission spectroscopy (OES) to monitor O$^+$ and O$_2^+$ abundances in an oxygen inductively-coupled plasma. Measurements of multiple O, O$_2$, O$^+$, and O$_2^+$ emission line intensities were made as a function of pressure (1-30~mTorr) and power (500-2000~W). While the O$_2^+$ emissions were relatively intense, the O$^+$ emissions were very weak for all conditions examined. Emissions from both ion species were highest at low pressures and at the highest power levels, but the O$^+$ / O$_2^+$ emission ratio varied little with plasma conditions. [Preview Abstract] |
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GT1.00018: Kinetic study of the NO formation in pulsed air-like low-pressure dc plasmas: measurement and numerical modelling Marko Huebner, Sergej Gorchakov, Detlef Loffhagen, Olivier Guaitella, Daniil Marinov, Antoine Rousseau, Juergen Roepcke The formation of NO has been studied measuring the temporal evolution of the density of NO, NO$_{2}$ and N$_{2}$O by high time-resolved quantum cascade laser absorption spectroscopy. The densities of these nitrous oxides have been measured in synthetic air as well as in air with an admixture of 1{\%} of NO$_{2}$ and N$_{2}$O, respectively, at a pressure of 1.33 mbar and mean currents between 50 and 150 mA. The measured time-dependent densities of NO, NO$_{2}$ and N$_{2}$O have been compared with those calculated by means of a self-consistent numerical model. The modelling approach includes the coupled solution of the time-dependent electron Boltzmann equation and a system of rate equations for various heavy particles. In general, measured and calculated results show good qualitatively agreement. In total four distinct phases of the NO density evolution during the plasma pulse and the early afterglow are found. The densities of NO$_{2}$ and N$_{2}$O decrease exponentially during the plasma pulse and remain almost constant in the afterglow. The admixture of NO$_{2}$ has a remarkable impact on the NO production during the ignition of the plasma. The dominating processes are presented and discussed. [Preview Abstract] |
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GT1.00019: Surface mechanisms during cryogenic etching of silicon with SF$_{6}$/O$_{2}$ inductively coupled plasmas Stefan Tinck, Thomas Tillocher, Annemie Bogaerts A computational and experimental study is performed to obtain better insight in the surface reactions occurring during the etching of silicon with SF$_{6}$/O$_{2}$ inductively coupled plasmas at cryogenic conditions. Cryogenic etching is a promising technique to etch ultra-high aspect ratio nanoscale trenches for fabricating microchips. During cryoetching, the substrate (i.e., a silicon wafer) is cooled down to about -100 $^{\circ}$C. Cryoetching has some advantages compared to the well-known Bosch process, like no scalloping of sidewalls and no material residues on the reactor walls. A disadvantage of cryoetching is its sensitivity to operating conditions such as substrate temperature and fraction of oxygen in the SF$_{6}$/O$_{2}$ mixture. During etching, the sidewalls of the trenches are passivated with a SiF$_{\mathrm{x}}$O$_{\mathrm{y}}$ layer which prevents lateral etching. When heating the wafer to room temperature, the passivation layer desorbs automatically, leaving a smooth and clean trench. The mechanism of the formation and desorption of this passivation layer at cryogenic temperatures is not well understood and is investigated here. A 2-dimensional hybrid Monte Carlo Fluid plasma model linked with Molecular Dynamics simulations is used for a computational investigation while results are validated by experimentally measured etch rates. The focus is on the reaction mechanisms during cryoetching in comparison with conventional room temperature etching. [Preview Abstract] |
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GT1.00020: Sum frequency generation spectroscopy of interfacial water molecules influenced by plasma-generated radicals Takahiro Kondo, Tsuyohito Ito We report the effects of radicals generated by plasma on the structure of water molecules in the air/water interfacial region by sum frequency generation (SFG) spectroscopy. SFG spectroscopy gives molecular level information for the interfacial region. We used a visible pulse laser (wavelength: 532 nm) and a tunable IR pulse laser (wavenumber: 2850-4000 cm$^{-1}$) for SFG spectroscopy. Radicals are generated by a dielectric barrier discharge (DBD) in the air, and supplied to the water surface. We found that the peak at about 3700 cm$^{-1}$ in the SFG spectrum tends to decrease when the DBD is generated and the radicals are supplied. When the DBD is turned off, the SFG signal recovers. According to previous studies, the SFG peak at about 3700 cm$^{-1}$ is assigned to the stretch mode of free OH in interfacial water molecules. We believe that the radicals interact with the free OH and disturb the vibration, leading to a decrease of the SFG signal when the DBD is generated. When the DBD is turned off, the SFG signal recovers because there are much less radicals in the air. Details on the experimental results and discussions will be presented at the conference. [Preview Abstract] |
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GT1.00021: Effects of the Fabrication and Preparation Processes on the SEY of Niobium SRF Cavities Milos Basovic, Ana Samolov, Svetozar Popovic, Lepsha Vuskovic We are reporting progress on effects of the plasma treated surface on the Secondary Electron Yield (SEY) of Niobium (Nb) samples. Fabrication and preparation processes affect intrinsic quality factor (Q factor) to a great extent contributing to multipacting. Multipacting is a resonant phenomenon occurring as an electron buildup and degrading the maximum Q factor achievable by cavity. Apart from the initial impurities of the Nb sheet metal used for cavity fabrication, additional inclusions on the surface of the cavity are added by forming and welding of the components. Operation of the cavities is affected by these inclusions in such a way that it decreases the overall performance of the accelerators. Performance of the cavities can be improved by manipulating the parameters or by mitigating the consequences of the fabrication and preparation processes. We are testing the influence of the electron beam welding and various surface treatments on Nb samples by measuring the SEY of coin-like samples with the surface treated in several different methods. The system is designed to measure energy distribution of SEY of the samples under several incident angles. Comparison is being made between non-treated and treated surface, as well as effects of each treatment on SEY of the surface. Our aim is to show which of the surface treatments or combination of them are beneficial to reducing SEY of the cavity surface. [Preview Abstract] |
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GT1.00022: Laser-induced Fluorescence and Optical Emission Spectroscopy for the Determination of Reactive Species in the Effluent of Atmospheric Pressure Low Temperature Plasma Jets Xuekai Pei, Hamid Razavi, Xinpei Lu, Mounir Laroussi OH radicals and O atoms are important active species in various applications of room temperature atmospheric pressure plasma jet (RT-APPJ). So the determination of absolute density of OH radicals and O atoms in RT-APPJs is necessary. In this work, the time and spatially resolved OH radicals density of a RT-APPJ are measured using the laser-induced fluorescence (LIF) technology [1]. In addition, the spatial distribution of the emitting species along the axial direction of the jet is of interest and is measured using optical emission spectroscopy. The absolute OH density of the RT-APPJ is about 2.0 $\times$ 10$^{13}$ cm$^{-3}$ at 5 mm away from the plasma jet nozzle and 1 $\mu$s after the discharge. The OH density reaches a maximum when H$_{2}$O concentration in helium gas flow is about 130ppm. In order to control the OH density, the effect of voltage polarity, applied voltage magnitude, pulse frequency, pulse width on the OH density are also investigated and discussed. O atoms are investigated by TA-LIF. It is demonstrated that the O atoms density reaches a maximum when O$_{2}$ percent is about 0.3{\%} in pure He and the lifetime of O atoms in RT-APPJ is much longer (up to dozens of ms) than OH radicals. \\[4pt] [1] X. Pei, Y. Lu, S. Wu, Q. Xiong, X. Lu, Plasma Sources Science and Technology, 2013, 22(2): 0250232. [Preview Abstract] |
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GT1.00023: Measurement of Gas Temperature in Negative Hydrogen Ion Source by Wavelength-Modulated Laser Absorption Spectroscopy S. Nishiyama, K. Sasaki, H. Nakano, M. Goto, M. Kisaki, K. Tsumori Measurement of the energy distribution of hydrogen atom is important and essential to understand the production mechanism of its negative ion (H$^-$) in cesium-seeded negative ion sources. In this work, we evaluated the temperature of atomic hydrogen in the large-scale arc-discharge negative hydrogen ion source in NIFS by wavelength-modulated laser absorption spectroscopy. The laser beam was passed through the adjacent region to the grid electrode for extracting negative ions. The frequency of the laser was scanned slowly over the whole range of the Doppler width (100 GHz in 1s). A sinusoidal frequency modulation at 600 Hz with a width of 30 GHz was superposed onto the slow modulation. The transmitted laser was detected using a photodiode, and its second harmonic component of the sinusoidal modulation was amplified using a lock-in amplifier. The obtained spectrum was in good agreement with an expected spectrum of the Doppler-broadened Balmer-$\alpha$ line. The estimated temperature of atomic hydrogen was approximately 3000 K. The absorption increased with the arc-discharge power, while the temperature was roughly independent of the power. [Preview Abstract] |
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GT1.00024: Correlating Metastable-Atom Density, Reduced Electric Field, and Electron Energy Distribution in the Early Stages of a 1-Torr Argon Discharge J.B. Franek, S.H. Nogami, M.E. Koepke, V.I. Demidov, E.V. Barnat Temporal measurement of electron density, metastable-atom density, and reduced electric field are used to approximate certain reaction rate constants [1] for electron-atom collision excitation in a 1-Torr positive column of argon plasma. This allows us to relate the observed 420.1nm to 419.8nm line-intensity ratio to plasma parameters by invoking a plausible assumption regarding the shape of the electron energy distribution function (EEDF) throughout the discharge [1]. We show that these reaction rate constants agree well with experimental observations in the late stages of the pulse, but we do not emphasize the late-stage behavior here. Instead, we address discrepancies in the initiation and transient phases of the discharge. We examine three assumptions made in the model to see if the assumptions are violated in these two stages of the discharge: (1) The stepwise excitation from the 1s4 and 1s2 resonant states is negligible; (2) The numerical model designed for a 5-millitorr plasma is applicable to our 1000-millitorr plasma; and (3) The EEDF is bi-Maxwellian and is modified only slightly due to the presence of electrons or metastable-atoms in the discharge. We conclude that diagnostic signatures for electron density, metastable density, and reduced electric field can be quantitatively interpreted by this correlation at all stages of the discharge. [1] Adams et al. Phys. Plasmas 19, 023510 (2012) *also St. Petersburgh Univ. [Preview Abstract] |
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GT1.00025: Optical emission diagnostics for plasma parameters in pulse-modulated argon capacitively-coupled discharges Shicong Wang, John B. Boffard, Chun C. Lin, Amy E. Wendt Pulsing of discharge power in low pressure rf plasmas is a means to improve materials processing outcomes. Plasma-surface interactions depend on the relative fluxes of ions, reactive neutrals and photons, which can be controlled by adjusting pulse frequency and duty cycle, due their effect on plasma properties, particularly the electron energy distribution. We report on an optical emission spectroscopy (OES) based plasma diagnostic to characterize the time evolution of plasma properties within the pulse cycle for two systems: a pulsed capacitively-coupled plasma (CCP), and a pulsed CCP in combination with a continuous-wave (cw) inductively coupled plasma (ICP); Typical conditions: 30 mTorr Ar, 13.56 MHz rf power (400 W peak CCP and 500 W ICP) and 1 kHz pulse frequency. We quantify the trade off between time resolution versus uncertainty in measured OES intensities. Because only a small fraction of CCP rf power contributes to electron heating, the method is limited by relatively low {\it absolute} OES intensities for the CCP-only case, and small incremental changes in intensity when the pulsed CCP is combined with the cw ICP. Nevertheless, with sufficient signal averaging, even subtle changes in parameters induced by the CCP in the latter case can be quantified. [Preview Abstract] |
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GT1.00026: Diagnostics of nonlocal plasmas: advanced techniques Alexander Mustafaev, Artiom Grabovskiy, Anastasiya Strakhova, Vladimir Soukhomlinov This talk generalizes our recent results, obtained in different directions of plasma diagnostics. First-method of flat single-sided probe, based on expansion of the electron velocity distribution function (EVDF) in series of Legendre polynomials. It will be demonstrated, that flat probe, oriented under different angles with respect to the discharge axis, allow to determine full EVDF in nonlocal plasmas. It is also shown, that cylindrical probe is unable to determine full EVDF. We propose the solution of this problem by combined using the kinetic Boltzmann equation and experimental probe data. Second-magnetic diagnostics. This method is implemented in knudsen diode with surface ionization of atoms (KDSI) and based on measurements of the magnetic characteristics of the KDSI in presence of transverse magnetic field. Using magnetic diagnostics we can investigate the wide range of plasma processes: from scattering cross-sections of electrons to plasma-surface interactions. Third-noncontact diagnostics method for direct measurements of EVDF in remote plasma objects by combination of the flat single-sided probe technique and magnetic polarization Hanley method. [Preview Abstract] |
(Author Not Attending)
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GT1.00027: Radially resolved spectroscopic analysis of positive streamers under transient luminous events conditions Vaclav Prukner, Tomas Hoder, Milan Simek The Transient Luminous Events (TLE) are huge electrical discharges appearing at the upper atmosphere. Sufficiently spatially and temporally resolved spectroscopy is currently one of the very few methods how to get closer to the basic TLEs parameters. In this study, triggered positive streamers were operated in volume barrier discharge with 4 cm gap fed with synthetic air at pressures between 8.98 and 0.16 torr corresponding to equivalent TLE altitudes ranging from 30 to 60 km, respectively. Time resolved axial and radial emission profiles of streamer channel were collected by scanning the discharge via fast photo-multiplier and spectral band-pass filters. Depending on different streamer velocities, different widths of the streamers were measured. Obtained data were analyzed in order to estimate values of the streamer head electric field with radial resolution. [Preview Abstract] |
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GT1.00028: Measuring of the nonlocal EDF of penning electrons by the wall electrode in the plasma afterglow Anatoly Kudryavtsev, Kirill Kapustin, Almaz Sayfutdinov In [1] was patented ionization detector for gas analysis, based on the method of collisional electron spectroscopy (CES), which allows working at a high gas pressure. The CES method provides an opportunity to analyze energy of nonlocal electrons released during Penning ionization of atomic or molecular impurities by metastable helium atoms. In this case, the EDF of fast electrons will be narrow peaks that correspond to the energies of their appearance in Penning ionization. To realize the CES method at high (atmospheric) pressure the plasma gap must be small L \textless 0.1 mm. In this condition the traditional Langmuir probe is impossible to use for measuring the EDF. To overcome this difficulty in [1] was proposed to use afterglow plasma and one of the electrodes as a measuring probe for the registration of EDF of fast penning electrons. In this paper we simulate the afterglow of argon discharge between parallel electrodes and show that EDF and electron sources of Penning ionization are determined by the first derivative of the current to the wall electrode with respect to potential. This work was supported by RSCF and SPbSU. \\[4pt] [1] A.A.Kudryavtsev, A.B.Tsyganov. US Patent 7,309,992, issued December 18, 2007. [Preview Abstract] |
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GT1.00029: Time-resolved measurements of energy distributions for mass-identified ions in low pressure plasmas Dave Seymour, Alan Rees, Tom Russell, Claire Greenwood The direct measurement of energy distributions for mass-identified positive and negative ions arriving at target surfaces in plasma reactors has produced much useful information. The measurements have been, in the great majority of cases, of the time-averaged distributions even when the applied power to the plasma has been pulsed. Time-resolved data particularly during initiation and decay of pulsed plasmas would be advantageous. To facilitate such studies we have incorporated a Multi-Channel Scaler device into the ion detector system of a Hiden EQP instrument. Preliminary data which illustrate the capabilities of the new equipment will be presented. The data were obtained for a number of typical reactor systems. For the first of these the plasma was RF powered, typically at 20 Watts, in nitrous oxide at a pressure of 20 mTorr. The energy distributions for N2O$+$, NO$+$ and O$+$ and O- ions were measured throughout the duration of a pulsing cycle with particular emphasis on the ignition and decay of the plasma. The distributions show considerable detail and clear differences between the behaviour of the different ions which reflect differences in their production and decay mechanisms. [Preview Abstract] |
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GT1.00030: Analysis of the harmonic currents in floating probes with dielectric films Kyung-Hyun Kim, Dong-Hwan Kim, Jin-Yong Kim, Yu-Sin Kim, Chin-Wook Chung Plasma diagnostics using harmonic currents was firstly used to obtain the electron temperatures and ion densities. In this method, the electron temperature is proportional to the ratio of the harmonic currents due to the sheath non-linearity. Harmonic currents are affected by input voltage, thus calculation of exact voltage across the sheath is important; the voltage is calculated using phase analysis of the probe current. However, in the case of the dielectric deposited probe, rapid decrease of the second harmonic current than expected is observed. To explain this effect, circuit analysis including non-linear elements is adopted, and the calculations using this analysis are compared with experimental results. [Preview Abstract] |
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GT1.00031: On harmonic diagnostic method using two frequencies in a floating Langmuir probe Dong-Hwan Kim, Young-Do Kim, Sung-Won Cho, Yu-Sin Kim, Chin-Wook Chung Plasma diagnostic methods using harmonic currents analysis of floating probes were experimentally investigated. When dual-frequency voltage ($\omega_{1}, \omega_{2} )$ was applied to a probe, various harmonic currents ($\omega_{1}, 2\omega_{1}, \omega_{2}, 2\omega_{2}, \omega_{2} \pm \omega_{1}, \omega _{2} \pm 2\omega_{1} )$ were generated due to the nonlinearity of the probe sheath. The electron temperature can be obtained from the ratio of the two harmonics of the probe currents. According to the combinations of the two harmonics, the sensitivities in measurement of the electron temperature differs and this results in the difference in the electron temperature. From experiments and simulation, it is shown that the difference is caused by the random and systematic noise. [Preview Abstract] |
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GT1.00032: Tunable external RF choke filter design for single Langmuir probe in RF discharges SangBum Jeon, Yu-Sin Kim, Dong-Hwan Kim, Chin-Wook Chung The tunable external RF choke circuit was developed to compensate radio frequency (RF) fluctuation in single Langmuir probe measurement. This method consists of series circuit of each harmonic component of the driving frequency, and has high impedance at the resonance frequencies. The measured electron energy probability functions (EEPFs) from the single Langmuir probe with the external RF compensation circuit were obtained at various discharge conditions, such as gas pressures and RF powers. The EEPFs have highly populated low energy electrons with bi-Maxwellian EEPFs at low plasma density regime, compared to results from the uncompensated Langmuir probes. This method can also provide real-time tuning and thus, high quality EEPF measurement is possible even when the rf discharge condition is changed. [Preview Abstract] |
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GT1.00033: Experimental investigation of plasma parameter profiles on wafer level with discharge gap lengths in an inductively coupled plasma Ju Ho Kim, Young-Cheol Kim, June Young Kim, Chin-Wook Chung Experimental investigation of the gap length effect on plasma parameters was performed in a planar type inductively coupled plasma (ICP) at various conditions. The spatial profile (wafer level, 260 mm) of ion flux, and electron temperature were measured from a 2-D floating probe measurement system. At low pressures, the spatial profile of the ion flux rarely changed; however, at relatively high pressures, the spatial profile of the ion flux dramatically changed with different discharge gap length. [Preview Abstract] |
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GT1.00034: Inductively-coupled plasmas in pure O$_2$: measurements of densities of O atoms, electrons and vibrationally excited Omolecules Micka\"el Foucher, Emile Carbone, Jean-Paul Booth, Pascal Chabert Inductively-coupled plasmas containing O$_2$ (pure or mixtures) are widely used in materials processing. Various simulations have been developed but experimental validation is still sparse. We present here a comprehensive data set for O$_2$ plasmas over a wide range of pressure and RF power to address this need. The plasma is excited with a 4-turn planar coil through a dielectric window at 13.56 MHz in an anodized aluminium reactor. The electron density was measured with a microwave resonator hairpin probe. It increases continuously with RF power, but with pressure it passes through a broad maximum around 40 mTorr. Ground-state O atom densities were determined using Two-Photon Absorption Laser-Induced Fluorescence combined with absolute calibration using Xe TALIF. The atom density increases with gas pressure, but with RF power it first increases but progressively saturates tot about 20{\%} of the initial (no plasma) gas density. A novel high-sensitivity ultra-broad-band absorption spectroscopy setup allowed O$_2$ molecules to be detected in high vibrational states (up to v $=$ 18) via the Schumann-Runge bands. Molecular Ovibrational temperatures up to 12,000K were observed, whereas the rotational temperature did not exceed 500K. This indicates that electron-impact pumping of vibrational levels is important, whereas V-T transfer is slow. These processes must be included to accurately model the O$_2$ plasma system. [Preview Abstract] |
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GT1.00035: Study on self-bias effect in floating probe using dual frequency Il-seo Park, Hyo-Chang Lee, Yu-Sin Kim, Dong-Hwan Kim, Chin-Wook Chung A floating probe is one of the promising electrical probe for plasma diagnostics, which is using small sinusoidal signal to perturb the plasma for obtaining plasma parameters such as ion flux and electron temperature. The ac signal could be selected for the purpose of the plasma condition and its advantages, and single or dual frequency is usually used for diagnostics. When one or dual frequency is applied to the probe, a self-bias effect is observed in the capacitor in series to the floating probe. Due to the mobility difference of the ions and electrons, the self-bias effect is presented at the capacitor. In this paper, two consecutive frequencies are applied to the probe with phase differences. The result of the self-bias effect agrees with the floating probe theory, which gives a relation among electron temperature, phase difference and amplitude of the each frequency. The electron temperatures by using the relation can be obtained, and it agree with those of a Langmuir probe. [Preview Abstract] |
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GT1.00036: Measurement of the surface charge accumulation using anodic aluminum oxide(AAO) structure in an inductively coupled plasma Ji-Hwan Park, Seung-Ju Oh, Hyo-Chang Lee, Yu-Sin Kim, Young-Cheol Kim, June Young Kim, Chang-Seoung Ha, Soon-Ho Kwon, Jung-Joong Lee, Chin-Wook Chung As the critical dimension of the nano-device shrinks, an undesired etch profile occurs during plasma etch process. One of the reasons is the local electric field due to the surface charge accumulation. To demonstrate the surface charge accumulation, an anodic aluminum oxide (AAO) membrane which has high aspect ratio is used. The potential difference between top electrode and bottom electrode in an anodic aluminum oxide contact structure is measured during inductively coupled plasma exposure. The voltage difference is changed with external discharge conditions, such as gas pressure, input power, and gas species and the result is analyzed with the measured plasma parameters. [Preview Abstract] |
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GT1.00037: The effect of rf plasma fluctuation on floating harmonic probes Jaewon Lee, Kyunghyun Kim, Sangbum Jeon, Chin-Wook Chung Measurement of electron temperature, plasma density and ion flux with floating harmonic method (FHM) has several advantages for RF plasma diagnosis. In principle, RF oscillation of plasma does not distort the characteristic of the probe at a floating potential. Thus, an active or passive RF compensation is unnecessary. However, in fact, the uncompensated probe results in higher electron temperature than the rf compensated probe especially at low plasma density. Plasma parameters from the FHM and that of Langmuir probe was compared, and it shows that the measured plasma parameter from RF compensated floating probe (FHM) has great agreements with Langmuir probe. [Preview Abstract] |
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GT1.00038: In-situ measurement method of sheath capacitance in plasmas Jin-Yong Kim, Chin-Wook Chung In-situ measurement method of sheath capacitance was studied. To measure the sheath capacitance, small dual frequency sinusoidal voltage signals ($\sim$1V) are applied to floating planar probe. The sheath circuit model and capacitance of the dielectric deposition film on the probe are considered in our measurement. The experiment was performed at various discharge conditions and our results are in good agreements with other studies. This study can be helpful for plasma monitoring in industrial processing. [Preview Abstract] |
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GT1.00039: Two-photon laser-induced fluorescence imaging of atomic oxygen in an atmospheric pressure plasma jet Jacob Schmidt, Brian Sands, Waruna Kulatilaka, Sukesh Roy, James Scofield, James Gord A femtosecond two-photon absorption laser-induced fluorescence (fs-TALIF) diagnostic is applied to a nanosecond-pulsed, capillary dielectric barrier discharge (CDBD) plasma jet flowing helium with a variable oxygen admixture to produce two-dimensional images of atomic oxygen distributions. The high-peak intensity, low-average energy fs pulses, combined with increased spectral bandwidth, increase the number of photon pairs responsible for the two-photon excitation, resulting in increased TALIF signal. These features enabled imaging of absolute atomic oxygen number densities ranging from 4.07 x 10$^{15}$ cm$^{-3}$, to the single-shot detection limit of 10$^{12}$ cm$^{-3}$. Atomic oxygen imaging results are compared against traditional nanosecond diagnostics employing the same two-photon excitation scheme, including issues of experimental error, signal strengths, and quenching. Xenon calibration is used for quantification of the fluorescence signal. Imaging results show this CDBD capable of remotely generating quasi-steady-state atomic oxygen densities with a spatial distribution that depends on oxygen admixture. [Preview Abstract] |
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GT1.00040: High sensitivity ultra-broad-band absorption spectroscopy applied to inductively-coupled plasmas in Cl/O Micka\"el Foucher, Emile Carbone, Jean-Paul Booth, Pascal Chabert Broad-band absorption spectroscopy is a powerful diagnostic for reactive plasmas, allowing measurement of the absolute densities of numerous atoms, molecules and free radicals in ground and various excited states. Previously Xe arc lamps have been used as the continuum light source, but these suffer from spatiotemporal fluctuations which limit the sensitivity to about 10$^{-3}$ in absorption. More recently UV light-emitting diodes have been used, but these only emit over a very limited spectral range. Our new absorption spectroscopy setup uses a laser-driven plasma light source, achromatic optics and an aberration free spectrograph. This light source has ideal characteristics for absorption spectroscopy (high intensity, stability and a wide spectral range (200-1000nm)), overcoming previous limitations. Noise levels as low as 10$^{-5}$ can be achieved in single-pass absorption, covering up to 250nm in a single spectrum. Measurements were made in a 13.56 MHz inductively-coupled plasma reactor in O, Cland Cl/Omixtures. We observed absorption by Cl, Oand ClxOy molecules, and excited state atoms. Whereas the Clvibrational distribution is close to equilibrium with the gas translational temperature, Omolecules show high vibrational excitation (up to v$=$18, T$_{\mathrm{vib}}$12,000K). However, high resolution spectra of Oindicated rotational temperatures up to only 500 K. Many oxychloride molecules were detected in Cl/Omixtures. [Preview Abstract] |
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GT1.00041: Hairpin resonator probes with frequency domain boxcar operation for time resolved density measurements in pulsed RF discharges David Peterson, Theresa Kummerer, David Coumou, Steven Shannon In this work, microsecond time resolved electron density measurements in pulsed RF discharges are shown using an automated hairpin resonance probe using relatively low cost electronics, on par with normal Langmuir probe boxcar mode operation. A low cost signal generator is used to produce the applied microwave frequency and the reflected waveform is filtered to remove the RF component. The signal is then heterodyned with a simple frequency mixer to produce a dc signal read by an oscilloscope to determine the electron density. The applied microwave frequency is automatically shifted in small increments in a frequency boxcar routine through a Labview\texttrademark program to determine the resonant frequency. A simple dc sheath correction is then easily applied since the probe is fully floating, producing low cost, high fidelity, and highly reproducible electron density measurements. The measurements are made in a capacitively coupled, parallel plate configuration in a 13.56 MHz, 50-200 W RF discharge pulsed at 500 Hz, 200 W, 50{\%} duty cycle. The gas input ranged from 50-100mTorr pure Ar or with 5-10{\%} O/He mixtures. [Preview Abstract] |
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GT1.00042: Experimental Characterization of the Time-Averaged and Oscillatory Behavior of a Hall Plasma Discharge Christopher Young, Andrea Lucca Fabris, Nicolas Gascon, Mark Cappelli An extensive experimental campaign characterizes a 70 mm diameter stationary plasma thruster operating on xenon in the 200-500 W power range. This study resolves both time-averaged properties and oscillatory phenomena in the plasma discharge. Specifically, we explore the time variation of the plume ion velocity field referenced to periodic discharge current oscillations using time-synchronized laser induced fluorescence (LIF) measurements. This LIF scheme relies on a triggered signal acquisition gate locked at a given phase of the current oscillation period. The laser is modulated at a characteristic frequency and homodyne detection through a lock-in amplifier extracts the induced fluorescence signal out of the bright background emission. [Preview Abstract] |
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GT1.00043: Periodic Evolution of a Xe I Population in an Oscillatory Discharge Captured Through Time-Synchronized Laser Induced Fluorescence Techniques Andrea Lucca Fabris, Christopher Young, Mark Cappelli We track the evolution of the Xe I $6s'[1/2]_{1} - 6p'[3/2]_{2}$ (834.68 nm air) transition lineshape in a plasma discharge oscillating at 60 Hz. Two time-synchronized laser induced fluorescence techniques based on phase sensitive detection of the fluorescence signal are demonstrated, yielding consistent results. One approach used previously involves a sample-and-hold procedure that collects fluorescence signal at a particular phase in the oscillation period and holds the average value until the following sample. The second method is based on fast switching of the fluorescence signal; only the signal collected inside the acquisition gate is sent to a lock-in amplifier for processing. Both methods rely on modulating the exciting laser beam and the latter permits operation at a much higher frequency range with reduced spectral noise density. The maximum observed peak fluorescence intensity occurs at low discharge currents, although the peak intensity drops to zero at zero discharge current. The peak intensity also decreases at the discharge current maximum. Time-varying properties of the xenon neutrals are extracted from a lineshape analysis. [Preview Abstract] |
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GT1.00044: Theoretical modeling of laser-induced plasmas using the ATOMIC code James Colgan, Heather Johns, David Kilcrease, Elizabeth Judge, James Barefield II, Samuel Clegg, Kyle Hartig We report on efforts to model the emission spectra generated from laser-induced breakdown spectroscopy (LIBS). LIBS is a popular and powerful method of quickly and accurately characterizing unknown samples in a remote manner. In particular, LIBS is utilized by the ChemCam instrument on the Mars Science Laboratory. We model the LIBS plasma using the Los Alamos suite of atomic physics codes. Since LIBS plasmas generally have temperatures of somewhere between 3000~K and 12000~K, the emission spectra typically result from the neutral and singly ionized stages of the target atoms. We use the Los Alamos atomic structure and collision codes to generate sets of atomic data and use the plasma kinetics code ATOMIC to perform LTE or non-LTE calculations that generate level populations and an emission spectrum for the element of interest. In this presentation we compare the emission spectrum from ATOMIC with an Fe LIBS laboratory-generated plasma as well as spectra from the ChemCam instrument. We also discuss various physics aspects of the modeling of LIBS plasmas that are necessary for accurate characterization of the plasma, such as multi-element target composition effects, radiation transport effects, and accurate line shape treatments. [Preview Abstract] |
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GT1.00045: RF Models for Plasma-Surface Interactions in VSim Thomas G. Jenkins, D.N. Smithe, A.Y. Pankin, C.M. Roark, C.D. Zhou, P.H. Stoltz, S.E. Kruger An overview of ongoing enhancements to the Plasma Discharge (PD) module of Tech-X's VSim software tool is presented. A sub-grid kinetic sheath model, developed for the accurate computation of sheath potentials near metal and dielectric-coated walls, enables the physical effects of DC and RF sheath physics to be included in macroscopic-scale plasma simulations that need not explicitly resolve sheath scale lengths. Sheath potential evolution, together with particle behavior near the sheath, can thus be simulated in complex geometries. Generalizations of the model to include sputtering, secondary electron emission, and effects from multiple ion species and background magnetic fields are summarized; related numerical results are also presented. In addition, improved tools for plasma chemistry and IEDF/EEDF visualization and modeling are discussed, as well as our initial efforts toward the development of hybrid fluid/kinetic transition capabilities within VSim. Ultimately, we aim to establish VSimPD as a robust, efficient computational tool for modeling industrial plasma processes. [Preview Abstract] |
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GT1.00046: Electrical characteristics and energy budget of dielectric barrier discharges in argon at atmospheric pressure Markus M. Becker, Tomas Hoder, Detlef Loffhagen Recently, an asymmetric dielectric barrier discharge ignited in atmospheric pressure argon in a single filament configuration has been analysed by experiments and modelling [1,2]. A special feature of the discharge under consideration is the occurrence of two different discharge modes at different amplitudes of the sinusoidal voltage supply. At voltages below the critical voltage of 2\,kV ordinary filamentary discharges occur, while at higher voltages discharges with striated filaments emerge. In the present contribution the mode transition is investigated with respect to the electrical characteristics as well as the electron energy budget by means of numerical modelling. It is found that the mode transition caused by an increase of the voltage amplitude is accompanied by a non-linear change of the power density and a marked rise of the electron energy gain in chemo-ionization processes.\\[4pt] [1] T. Hoder et al., \textit{Phys. Rev. E} \textbf{84} (2011) 46404.\\[0pt] [2] M. M. Becker et al., \textit{J. Phys. D: Appl. Phys.} \textbf{46} (2013) 355203. [Preview Abstract] |
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GT1.00047: Modeling of filaments and gas flow in an atmospheric pressure plasma jet Florian Sigeneger, Detlef Loffhagen A non-thermal atmospheric pressure plasma jet is investigated by a combination of different approaches. The jet consists of two concentric capillaries and two ring-shaped electrodes which are twisted around the outer capillary to supply the rf power at 27.12\,MHz. One part of the model is devoted to describe one single filament as observed in the active volume between the electrodes. For this purpose a two-dimensional axisymmetric fluid model has been used which comprises continuity equations for electrons and the most important argon species, the electron energy balance equation, Poisson's equation and an equation for the surface charges at the walls of the capillaries. Furthermore, the heat balance equation is solved to determine the temperature of the gas. The inclusion of contraction mechanisms allows to describe the establishment of a constricted filament and even pronounced striations as observed in the experiments. The second part uses results of the first one to model the gas flow through the jet under the influence of local heating at the position of the filament which leads finally to an azimuthal rotation of the filaments as observed in experiments. [Preview Abstract] |
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GT1.00048: Fast 2D Fluid-Analytical Simulation of IEDs and Plasma Uniformity in Multi-frequency CCPs E. Kawamura, M.A. Lieberman, D.B. Graves A fast 2D axisymmetric fluid-analytical model using the finite elements tool COMSOL is interfaced with a 1D particle-in-cell (PIC) code to study ion energy distributions (IEDs) in multi-frequency argon capacitively coupled plasmas (CCPs). A bulk fluid plasma model which solves the time-dependent plasma fluid equations is coupled with an analytical sheath model which solves for the sheath parameters. The fluid-analytical results are used as input to a PIC simulation of the sheath region of the discharge to obtain the IEDs at the wafer electrode. Each fluid-analytical-PIC simulation on a moderate 2.2 GHz CPU workstation with 8 GB of memory took about 15--20 minutes. The 2D multi-frequency fluid-analytical model was compared to 1D PIC simulations of a symmetric parallel plate discharge, showing good agreement. Fluid-analytical simulations of a 2/60/162 MHz argon CCP with a typical asymmetric reactor geometry were also conducted. The low 2 MHz frequency controlled the sheath width and voltage while the higher frequencies controlled the plasma production. A standing wave was observable at the highest frequency of 162 MHz. Adding 2MHz power to a 60 MHz discharge or 162 MHz to a dual frequency 2MHz/60MHz discharge enhanced the plasma uniformity. [Preview Abstract] |
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GT1.00049: Transport Parameters of $F^{(-)}$ Ions in Mixtures Ar/B$F_3$ Zeljka Nikitovic, Vladimir Stojanovic, Zoran Raspopovic, Jasmina Jovanovic, Zoran Lj. Petrovic Transport parameters of $F^{(-)}$ ions in mixtures Ar/B$F_3$ in DC fields were calculated by using Monte Carlo simulation technique. The scattering cross-section set for $F^{(-)}$ in B$F_3$ is assembled on the basis of Nanbu's technique separating elastic from reactive collisions. In this work we present transport coefficients for the conditions of low and moderate reduced electric fields E/N (E-electric field, N-gas density) accounting for the non-conservative collisions. This mixture is usual in plasma etching applications. [Preview Abstract] |
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GT1.00050: The Influence of Anode Size on Bulk Plasma State: Simulation, Theory, and Experiment Matthew Hopkins, Benjamin Yee, Edward Barnat, Scott Baalrud We present recent PIC modeling results in pursuit of identifying the relationship between bulk plasma characteristics and a biased anodic surface. In the limit of small anode size we expect the anode to operate as an ideal probe and exhibit no significant influence on the bulk plasma state. In the other limit of a large anode size we expect the bulk plasma to ``lock'' onto the anode potential and the plasma state to be heavily influenced by the anode potential. Our investigations include the plasma-anode interface (sheath) structure, plasma potential, and plasma electron energy distribution function modification. The basis for our investigation lies in the plasma-anode interface model from Baalrud, et al.\footnote{Baalrud, Hershkowitz, Longmier, ``Global nonambipolar flow: Plasma confinement where all electrons are lost to one boundary and all positive ions to another boundary,'' Phys. Plasmas \textbf{14}, 014109 (2007).} In particular, we target the transition from ion-rich sheaths to electron-rich sheaths at the anode. The theoretical model predicts a transition as a function of the anode-to-wall area ratio, $A_A/A_W$. Comparisons are made between the simulation model, theoretical model, and experimental results. Considerations specific to modeling are also presented. [Preview Abstract] |
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GT1.00051: A kinetic electron-neutral collision model for particle-in-cell plasma simulation Timothy Pointon, Keith Cartwright Details of a kinetic electron-neutral collision model for particle-in-cell plasma simulation codes are presented. The model uses an efficient scheme to randomly select collision events -- elastic, excitation and ionization -- with the appropriate probability [H. Sugawara, \textit{et al}., J. Comput. Phys. \textbf{223}, 298 (2007).] Ionization events create electron-ion pairs, and the secondary electrons can themselves ionize the gas. To maintain a manageable particle count, a particle merger algorithm can be used to periodically replace all particles of a given species in a cell with a new, smaller set that conserves charge, momentum, and energy [D. R. Welch, \textit{et al}., J. Comput. Phys. \textbf{227}, 143 (2007).] Small-scale tests show that results with the merger are in good agreement with non-merged runs. Large simulations can only be done with the merger on, and typically show excellent merger efficiency (\textgreater 90{\%}). [Preview Abstract] |
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GT1.00052: Numerical simulation of capacitively coupled RF plasma flowing through a tube for the synthesis of silicon nanocrystals Romain Le Picard, Sang-Heon Song, David Porter, Mark Kushner, Steven Girshick Silicon nanocrystals (SiNCs) are of interest for applications in the photonics, electronics, and biomedical areas. Nonthermal plasmas offer several potential advantages for synthesizing SiNCs. In this work, we have developed a numerical model of a capacitively coupled RF plasma used for the synthesis of SiNCs. The plasma, consisting of silane diluted in argon at a total pressure of about 2 Torr, flows through a narrow quartz tube with two ring electrodes. The numerical model is 2D, assuming axisymmetry. An aerosol sectional model is added to the Hybrid Plasma Equipment Model developed by Kushner and coworkers. The aerosol module solves for aerosol size distributions and size-dependent charge distributions. A detailed chemical kinetic mechanism considering silicon hydride species containing up to 5 Si atoms is used to model particle nucleation and surface growth. The sectional model calculates coagulation, particle transport by electric force, neutral drag and ion drag, and particle charging using orbital motion limited theory. Simulation results are presented for selected operating conditions, and are compared to experimental results. [Preview Abstract] |
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GT1.00053: Numerical optimization of collisional cross sections for plasma simulation by Broyden-Fletcher-Goldfarb-Shanno method Sang-Young Chung, Deuk-Chul Kwon, Mi-Young Song, Jung-Sik Yoon For reliable plasma simulation an accurate full-set data of collision cross sections between each species participated in the plasma is required. However, the full-set of the reaction data is hard to achieve and estimated data have been used for the missing. To achieve reliable reaction data researchers have tuned the estimated reaction data so that the simulation results with the data agree with experimental results. However, as the number of data to be tuned is increased it becomes very hard work for researchers. In this study, we developed a code to optimize the data numerically based on the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm and adopted with a 0-dimensional global simulator for semiconductor processing plasma. BFGS algorithm is a type of a quasi-Newton method. The second derivatives are used for a next estimation like Newton method but are calculated by iterations from first derivatives and previous second derivatives. So the function is called (i.e. the simulator is executed) much smaller times than Newton method. Parallel algorithm was applied to the code to save time. In the serial code the calculation time for each iteration were proportional to the number of unknown variables but it became independent of the number of the variables in the parallel code. [Preview Abstract] |
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GT1.00054: Transport Properties of Negative Ions in HBR Plasmas Vladimir Stojanovic, Nenad Ivanovic, Marija Radmilovic-Radjenovic, Zoran Raspopovic, Aleksandar Bojarov, Zoran Petrovic Low temperature plasma in halogenated gases is standard environment for dry etching of semiconductors. Amount of negative ions in HBr plasmas determines electronegativity so modeling etching devices requires data for anion transport properties. In this work we present cross section set for Br$^{-}$ ions in HBr assembled by using Denpoh-Nanbu theory [1]. The threshold energy values were calculated by known heats of formation. The calculated total cross section accounts for ion-induced-dipole and ion-permanent-dipole interaction by using the local-dipole model. The total cross section was corrected to fit the reduced mobility obtained by SACM (Statistical Adiabatic Channel Model) approximation. Existing cross section measurements [2] were used to scale calculated cross sections. Finally, we used Monte Carlo method to determine transport parameters for Br$^{-}$ as a function of reduced electric fields that can be \textit{used in fluid and hybrid} plasma models. \\[4pt] [1] K. Denpoh and K. Nanbu, J. Vac. Sci. Technol. A (1998) 16 1201-1206.\\[0pt] [2] R. L. Champion, L.D. Doverspike, M.S. Huq, D. Scott and Y. Wang, J.Chem.Phys. (1988) 88(9) 5475. [Preview Abstract] |
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GT1.00055: Extended dielectric relaxation scheme for fluid transport simulations of high density plasma discharges Deuk-Chul Kwon, Mi-Young Song, Jung-Sik Yoon It is well known that the dielectric relaxation scheme (DRS) can efficiently overcome the limitation on the simulation time step for fluid transport simulations of high density plasma discharges. By imitating a realistic and physical shielding process of electric field perturbation, the DRS overcomes the dielectric limitation on time step. However, the electric field was obtained with assuming the drift-diffusion approximation. Although the drift-diffusion expressions are good approximations for both the electrons and ions at high pressure, the inertial term cannot be neglected in the ion momentum equation for low pressure. Therefore, in this work, we developed the extended DRS by introducing an effective electric field. To compare the extended DRS with the previous method, two-dimensional fluid simulations for inductively coupled plasma discharges were performed. [Preview Abstract] |
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GT1.00056: PLASIMO model of micro-plasma jet for biomedical applications Diana Mihailova, Ana Sobota, Wouter Graef, Jan van Dijk, Gerjan Hagelaar Non-equilibrium atmospheric pressure micro-plasma jets are widely studied for use in biotechnology, including treatment of human tissue. The setup under study consists of capillary powered electrode through which helium gas flows and a grounded ring electrode placed a distance of few mm in front of the capillary. The discharge is excited by sinusoidal voltage with amplitude of 2kV and 30KHz repetition rate. The plume emanating from the jet, or the plasma bullets, propagates through a Pyrex tube and the gas phase channel of helium into the surrounding air.aim of this work is to get insight into the plasma constituents that can affect directly or indirectly living tissue. This includes radicals (OH, NO, O,), ions and electrons, UV radiation, electrical fields. PLASIMO modelling toolkit is used to simulate the capillary plasma-jet in order to quantify the delivery of fluxes and fields to the treated tissue. Verification is made by comparing results obtained with the PLASIMO and MAGMA codes (developed at LAPLACE, Toulouse) for the same input specifications. Both models are validated by comparison with experimental observations at various operating parameters. [Preview Abstract] |
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GT1.00057: Fluid model of magnetic drifts and instabilities in magnetized low-temperature plasma sources Gerjan Hagelaar, Romain Futtersack, Romain Baude This paper presents a self-consistent fluid model of low-temperature plasma transport across a magnetic field, designed in particular to describe magnetic drifts and instabilities in the plane perpendicular to the field lines. The model is based on electron and ion continuity equations and full momentum equations and an electron energy equation, without a priori assumptions on the ordering of physical scales (Larmor radii, mean free paths, geometrical dimensions) so that it can cover a wide range of conditions, from non-magnetized collisional plasmas to tokamak edge plasmas. The model is applied to different basic configurations of immediate interest for applications such as ion negative sources. We show that in a typical magnetic filter configuration (e.g. in the ITER negative ion source or Pegases thruster), the magnetic drift is obstructed by the chamber walls which induces an asymmetric electron flux across the filter, scaling as 1/B. These results have been confirmed by experimental data from an in-house laboratory set-up. We also present model results on the Cybele ion source featuring a magnetized plasma column, in which the transport is governed by rotating instabilities and very sensitive to the boundary conditions at the end of the column. [Preview Abstract] |
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GT1.00058: Propagation of a positive streamer discharge along a dielectric rod Anna Dubinova, Ute Ebert, Jannis Teunissen We simulate positive streamer discharges developing in artificial air near dielectric and conductive materials. This research is important, for example, in the high voltage technology where surface flashovers are to beavoided. We designed an axially symmetric model in which a positive streamer develops at the tip of the needle electrode (parameterized as a spheroid) and propagates towards and then along a dielectric rod (a cylinder). Our model includes field modification due to the polarization effect, photoionization, charge accumulation on the dielectric surface and photoelectron emission. We describe a numerical method (a generalized Ghost Fluid Method) which allowed us to include dielectric interfaces into our streamer model, in an accurate and fast manner. Finally, we measure the velocity of a positive streamer propagating along the dielectric rod and compare it with experiments. We discuss the importance of the surface photoelectron emission as an intrinsically non-local source of free electrons for streamer propagation. [Preview Abstract] |
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GT1.00059: Modeling DC-circuit-breakers for long distance electricity transmission Ashutosh Agnihotri, Ute Ebert, Willem Hundsdorfer Modeling a circuit-breaker is a multiple timescale problem which involves a cascade of physical processes from avalanche phase to streamer, spark and post discharge phase, with a transition phase between each pair of processes. In particular, Jin Zhang and Bert van Heesch at Eindhoven University of Technology investigate now whether the conventional SF6 can be replaced by supercritical nitrogen. We focus on modeling space charge effects, gas heating and secondary electron emission from cathode. We develop a two-dimensional drift-diffusion model for streamers coupled to the Euler equations for the gas to study the related phenomena. We perform simulations to capture thermal shocks and induced pressure waves caused by the electrical breakdown of the surrounding gas. We include heat exchange mechanisms between the electrons/ions and the surrounding gas. [Preview Abstract] |
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GT1.00060: 2D streamer simulations using the high order fluid model Aram Markosyan, Sasha Dujko, Ute Ebert In 1D, the recently derived high order fluid model [Dujko et al, J. Phys. D, 46:5202, 2013] shows promising performance and accuracy compared to the classical first order model using the local field approximation [Markosyan et al, J. Phys. D, 46:5203, 2013]. Here we simulate cylindrically symmetric streamers between two planar electrodes with the high order fluid model. The system is discretized using finite volume spatial discretization (high-resolution scheme) and explicit time stepping. We discuss the results and compare with previous work. [Preview Abstract] |
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GT1.00061: Simulating the inception of pulsed discharges around needle electrodes Jannis Teunissen, She Chen, Luuk Heijmans, Rong Zeng, Sander Nijdam, Ute Ebert When a positive voltage pulse is applied to a sharp electrode, an \emph{inception cloud} can form around the electrode tip. This is an almost spherically expanding ionized region. As recently demonstrated in experiments by S. Chen, L. Heijmans and S. Nijdam, the properties of these inception clouds depend on the gas mixture and on the voltage pulse. We present a 3D particle model to simulate the initial stage of pulsed discharges near needle electrodes. With this model, we investigate how the properties of inception clouds (growth velocity, maximum size, time of destabilization) depend on the gas mixture and voltage pulse, and we compare with the experiments mentioned above. [Preview Abstract] |
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GT1.00062: Application of ILDM Technique for Simplifying Complex Plasma Chemistry Tafizur Rehman, Kim Peerenboom, Efe Kemaneci, Wouter Graef, Jan vanDijk Complete numerical description of plasma involves solving complex set of space and time dependent conservation and rate equations. Solution of this large set of equations induces a high computational load on the system. Combustion research is another branch of science that deals with the same issue. To overcome the difficulty, combustion community employs various Chemical Reduction Techniques(CRT). The CRT simply uses the fact that, due to wildly varying time scales, reaction system is not evenly sensitive to all the reactions but some reactions are fast and attain steady state in short interval of time. Hence, fast time scale variation becomes less important and the full description of the system can be given by the slow time scales without any significant loss in chemical kinetics description. The chemical reduction technique we employed is ILDM (Intrinsic Low Dimensional Manifold). This technique finds the low dimensional space inside a complete state space such that after a short interval of time the fast time scales of the system will quickly move onto this low dimensional manifold and the full system description can be given by this lower dimensional manifold. One can use these techniques of combustion research to simplify the complex chemistry in plasma simulation. [Preview Abstract] |
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GT1.00063: Parametric calculations of plasma jets generated by microdischarges M. Foletto, J.P. Boeuf, L.C. Pitchford ``Guided streamers'' or ``plasma jets'' can be generated in open air by applying rf or impulse voltages to a microdischarge through which there is a flow of helium. For flow conditions such that a helium column surrounded by air extends some distance (centimeters) past the exit of the microdischarge, a plasma jet can be initiated. Previous works have shown that this is essentially a streamer propagating in the easily-ionized helium column and impeded from branching by the surrounding air. For many applications, it is of interest to understand the parameters controlling the properties of the plasma jet. To this end, we present results from a series of parametric calculations using our previously published model [1] to identify the influence of the microdischarge configuration on the generation, propagation, and properties of the plasma jet. We focus mainly on a geometry with hollow, concentric electrodes separated by a dielectric tube corresponding to the experiments of Douat et al [2], and we vary the dimensions and relative off-set of the electrodes, applying an impulse voltage or the experimental waveform to the inner electrode. For the same applied voltage waveform, parameters which influence the electric field and electron density in the plasma jet are the dielectric permittivity, the tube diameter, and the dielectric length. \\[4pt] [1] JP Boeuf, et al, J. Phys. D: Appl. Phys. (2013) 46 015201.\\[0pt] [2] C. Douat et al, Plasma Sources Sci. Technol. (2012) 21, 034010. [Preview Abstract] |
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GT1.00064: A PLASIMO global model for plasma assisted CO$_2$ conversion Wouter Graef, Tafizur Rehman, Diana Mihailova, Jan van Dijk Conversion of CO$_2$ has become a major challenge of our time as it is of interest for the reduction of greenhouse gases in our atmosphere, but also to store energy thereby relieving the supply and demand discrepancy of many alternative forms of energy. Plasma assisted CO$_2$ conversion is heavily investigated as an efficient method to achieve this goal. Numerical modeling is an important aspect of this investigation, but is difficult due to the complex chemistry. A global model has been constructed to focus on the CO$_2$ chemistry including its vibrational kinetics. The model has been realized using the global model module of PLASIMO, a highly modular plasma modeling framework. It is based on another model\footnote{Tom\'{a}\v{s} Koz\'{a}k and Annemie Bogaerts, submitted to Plasma Sources Sci. Tech.} that was constructed using the well-established code Global\_kin. The aim of the model is therefore twofold. First, to study the chemistry and identify the most important species and reactions and perform parametric studies. The knowledge gained can be applied to other, spatially resolved models. Second, by implementing the same chemistry in the two different global model codes, a cross validation can be performed, a vital scientific process often overlooked in practice. [Preview Abstract] |
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GT1.00065: Magneto-hydrodynamic simulation of hypervelocity neutral plasma jets and their interactions with materials generating extreme conditions Vivek Subramaniam, Laxminarayan Raja, Hariswaran Sitaraman The development of a Magneto-hydrodynamics (MHD) numerical tool to study high density thermal plasma in a co-axial plasma gun is presented. The MHD governing equations are numerically solved using a matrix free implicit scheme in an unstructured grid finite volume framework. The MHD model is used to characterize the high energy jet which emanates from the accelerator. The solver is then used to predict the conditions created at the surface of a flat plate placed at a fixed distance from the exit of the gun. The model parameters are adjusted so that the energy density of the jet impacting the plate is of the same order of magnitude as that of the Edge Localized Mode (ELM) disruptions in thermonuclear fusion reactors. The idea is to use the pressure and temperature on the plate surface to obtain an estimate of the stress created on the plate due to jet impact. The model is used to quantify damage caused by ELM disruptions on the confining material surface. \\[4pt] [1] H Sitaraman and L.L Raja. ``Magneto-hydrodynamics simulation study of deflagration mode in co-axial plasma accelerators.'' \textit{Physics of Plasmas,} 21:012104, 2014 [Preview Abstract] |
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GT1.00066: Computational modelling of plasma control using electron injection from electrode surfaces Premkumar PanneerChelvam, Laxminarayan Raja A common property of gamma-mode discharge is the importance of electron emission from surfaces in establishing the overall discharge structure. The secondary electron emission (SEE) from the cathode surface plays a key role in sustaining direct current glow discharges. Active control of SEE could be used to realize control over discharge properties. Chen and Eden [1] control surface electron emission in a tri-electrode microdischarge to realize gain properties in a plasma transistor device. This work discusses a computational model of a plasma transistor microdischarge device. It includes description of active surface electron emission from one of the electrode surfaces. Gain properties in the plasma by controllable injection of electrons from the surface is shown. The non-linear processes in the plasma that realize rapid increase in the plasma density and current as a function of the electron injection from the electrode is studied using the model.\\[4pt] [1] K.F. Chen and J.G. Eden, ``The Plasma transistor: A microcavity plasma device coupled with low voltage, controllable electron emitter,'' \textit{Applied Physics Letter}s 93, 161501 (2008). [Preview Abstract] |
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GT1.00067: Validation of RF CCP Discharge Model against Experimental Data using PIC Method Casey Icenhour, Theresa Kummerer, David L. Green, David Smithe, Steven Shannon The particle-in-cell (PIC) simulation method is a well-known standard for the simulation of laboratory plasma discharges. Using parallel computation on the Titan supercomputer at Oak Ridge National Laboratory (ORNL), this research is concerned with validation of a radio-frequency (RF) capacitively-coupled plasma (CCP) discharge PIC model against previously obtained experimental data. The plasma sources under simulation are 10-100 mTorr argon plasmas with a 13 MHz source and 27 MHz source operating at 50-200 W in both pulse and constant power conditions. Plasma parameters of interest in the validation include peak electron density, electron temperature, and RF plasma sheath voltages and thicknesses. The plasma is modeled utilizing the VSim plasma simulation tool, developed by the Tech-X Corporation. The implementation used here is a two-dimensional electromagnetic model, with corresponding external circuit model of the experimental setup. The goal of this study is to develop models for more complex RF plasma systems utilizing highly parallel computing technologies and methodology. [Preview Abstract] |
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GT1.00068: Particle-In-Cell Simulation and Experimental Characterization of a Cylindrical Cusped Field Plasma Thruster Andrea Lucca Fabris, Christopher Young, Marco Manente, Daniele Pavarin, Mark Cappelli This work aims to provide new insight into the physical mechanisms occurring in the discharge channel and acceleration region of a cusped field plasma thruster through a combined experimental and computational approach. Simulations are performed using the 3D particle-in-cell code F3MPIC, comprised of a PIC core coupled with a finite element electrostatic field solver over an unstructured mesh of tetrahedra. The cusped field structure is also included to resolve magnetized particle dynamics. We perform simulations with two ionization schemes: one where constant particle source rates are assigned to certain regions, and a more rigorous approach based on Monte Carlo collision events. The simulation results reveal correlations between the particle density distributions, electrostatic potential, and magnetic field topology inside the thruster discharge channel that are confirmed through experiments. Laser induced fluorescence measurements have resolved xenon ion velocities at several points near the thruster exit plane. Faraday and floating emissive probe measurements indicate this velocity field is correlated with the measured ion beam current profile and electrostatic potential field. [Preview Abstract] |
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GT1.00069: Simulation of Neutral Particle Transport During HiPIMS Jan Trieschmann, Sara Gallian, Ralf Peter Brinkmann, Thomas Mussenbrock In this work the importance of the knowledge of the spatial distribution, its temporal evolution as well as their energy distribution of heavy particles within sputtering processes is discussed. To describe these discharges -- typically operated at very low pressures below 1~Pa -- specific modeling approaches are required. Our approach comprises a three-dimensional kinetic Lagrangian description of neutral particles. A modified version of the direct simulation Monte Carlo (DSMC) code \textit{dsmcFoam} [1] is used, with the aim to describe the evolution of background and sputtered particles of a High Power Impulse Magnetron Sputtering (HiPIMS) process in a research reactor. Emphasize is put on the influence of the initial angular distribution of sputtered particles, as well as their energy distribution and its angular dependence. Based on the work of Stepanova and Dew [2] a modified Thompson energy distribution [3] is used. Differently distributed sputtered particles provide densities and fluxes concerning the corresponding film formation.\\[1ex] [1] T.J. Scanlon \textit{et al.}, Computers and Fluids \textbf{39}, 2078--2089 (2010).\\[0ex] [2] M. Stepanova, S.K. Dew, J. Vac. Sci. Technol. A \textbf{19}, 2805 (2001).\\[0ex] [3] M.W. Thompson, Phil. Mag. \textbf{18}, 377--414 (1968). [Preview Abstract] |
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GT1.00070: Numerical simulation of quantum systems using the Particle-In-Cell method Sven Dirkmann, Ziad Youssef, Torben Hemke, Thomas Mussenbrock The Particle-In-Cell (PIC) method is a very powerful method for studying the dynamics of plasmas. It has been primarily developed for tracking the charged particle trajectories subject to selfconsistent and external electromagnetic fields. Exploiting the power of modern computers, one is able to track the classical paths of tens of millions of particles at the same time. In the late 1980th, it was Dawson (and later Dauger) who had the idea to apply the PIC method to the classical part in the semiclassical approach to quantum systems via path integral methods. One could estimate that if a thousands of classical paths are sufficient to describe the dynamics of one quantum particle, then millions classical paths could describe the dynamics of a quantum particle system. A PIC code in the frame of a semiclassical approach would therefore enable the investigation of a number of quantum phenomena, e.g., optical properties, electrical properties, and, ultimately, chemical reactions. In this contribution we explain the use of the PIC code \emph{yapic} (developed by the authors) in the frame of the path integral method and discuss the numerical results for simple quantum phenomena, i.e., the quantum harmonic oscillator and quantum tunneling. [Preview Abstract] |
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GT1.00071: Simulation of Saddle Coil and Helical Winding Magnetic Field Perturbation in the IR-T1 Tokamak Younes Adltalab, Pejman Khorshid, Elham Abizi Moghadam The magnetic field of a set of saddle coils compared to the magnetic field of the helical winding coil on IR-T1 tokamak in a simulation method. The equation of helical windings that they mounted on vacuum chamber in a spiral modes (L$=$2, n$=$1) and (L$=$3,n$=$1), where L represents the number of toroidal rounds, and n represents the direction of the poloidal round, using Green function has been calculated, too. The coordinate system defined on a torus and an electric current applied to create a magnetic field and the magnetic field of resonant helical magnetic field disorders of the confinement were calculated in the whole space. In this study, the shape and structure of the Saddle coils has been defined toroidally and then poloidally configuration. The resulting simulation code is used to predict the position and structure of saddle coil that has same magnetic field generation with respect to Helical winding. [Preview Abstract] |
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GT1.00072: Space -- time evolution of low-pressure H2 plasma induced by runaway photoelectrons produced by KrF laser pulse Alexey Zotovich, Andrey Volynets, Dmitry Lopaev, Sergey Zyryanov, Dmitry Astakhov, Vladimir Krivtsun, Konstantin Koshelev Extreme Ultraviolet Lithography (EUVL) at 13.5 nm is expected to provide the next generation of ULSI. One of hot EUVL problems is contamination of EUV multilayer optics that compels to search methods of in-situ cleaning. The most promising method is to apply H2 plasma generated over the mirror surface by EUV radiation itself. Therefore investigations of EUV-induced plasma are of great interest for such cleaning technology developing. To model evolution of EUV-induced plasma, the study of H2 plasma induced by photoelectrons extracted from a surface by KrF laser pulse has been done. The experiment was carried out by the space-time resolved probe technique while the analysis was made with using plasma model based on 2D PIC MC code for both electrons and ions. Comparison of experimental and calculated evolution of probe characteristics provides correct applicability of the probe theory and allows one to reveal key mechanisms and parameters which control the evolution of photoelectrons-induced plasma. [Preview Abstract] |
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GT1.00073: Effect of cathode design on dc gas breakdown Valeriy Lisovskiy, Ruslan Osmayev, Vladimir Yegorenkov This paper reports dc breakdown curves we registered between a flat anode and cathodes of various design (a flat one, two types of steps with different height, a cathode possessing a bump or an indentation at its center, cones of different height), the least inter-electrode distance was kept constant. We observed that the minima and the right-hand branches of breakdown curves coincided practically whereas the left-hand ones did not. At lower pressure a divergence of left-hand branches of breakdown curves was registered for cathodes of different design. For the step-wise cathodes near to or to the right of the breakdown curve minimum the gas breakdown occurs within the smallest gap between the upper part of the cathode and the flat anode. With the gas pressure lowering the breakdown occurs between the flat anode and the lateral surface of the step-wise cathode, and then its lower flat part. For conical cathodes the breakdown occurs either near its sharp edge or at the lateral surface of the cone at some distance from its edge. [Preview Abstract] |
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GT1.00074: Effect of inter-electrode gap on dc cathode sheath characteristics Valeriy Lisovskiy, Ekaterina Artushenko, Vladimir Yegorenkov We found in experiment that increasing the inter-electrode distance with the current fixed first leads to the growth of the voltage drop $U$ across the cathode sheath as well as of its thickness $d$. This phenomenon is observed when the anode is located in the negative glow of the dc discharge. With longer distances when the anode is located in the dark Faraday space or positive column, the quantities $U$ and $d$ approach their saturation values and then remain unchanged. The current through the negative glow is supported by fast electrons generated in the cathode sheath where they also gained energy as well as by a diffusion flow. The anode departure from the cathode within the negative glow leads to a decrease of the fast electron flow, therefore a higher voltage $U$ is required to support a fixed current what is accompanied by the cathode sheath thickness $d$ growth. This phenomenon is clearly manifested in argon and nitrogen whereas it is expressed much weaker in electronegative gases (N$_{\mathrm{2}}$O, O$_{\mathrm{2}})$. An analytical model is proposed describing the phenomenon outlined. [Preview Abstract] |
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GT1.00075: Investigation of a cylindrical transparent cathode discharge Mark Bowden, Tom Hardiment The term Transparent Cathode Discharge (TCD) refers to a low-pressure electrical discharge also known as an Inertial Electrostatic Confinement (IEC) plasma. A defining characteristic is that the discharge is generated by a hollow, grid-constructed cathode and an outer, concentrically-arranged anode. Ions and electrons are accelerated by a large potential applied between the grids, with plasma being generated in different parts of the system depending on operating conditions. This project aims to study this device in order to assess its suitability for development as a reactive plasma source. A TCD device with concentric, cylindrical, mesh electrodes was operated in noble and molecular gases, and the discharge observed with a combination of emission imaging, emission spectroscopy and electrical probe diagnostic techniques. Preliminary measurements indicate that the alignment of the apertures in the inner and outer grid electrodes plays key role in determining discharge behaviour. [Preview Abstract] |
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GT1.00076: Second-harmonic generation in composite of microwave plasma and cm-order metamaterial Akinori Iwai, Yoshihiro Nakamura, Osamu Sakai Second-harmonic generation was observed by high-power microwave propagation in composite space of plasma and cm-order metamaterial. In principle, high-power electromagnetic waves induce nonlinear polarization and harmonic-wave generation in plasma, because plasma is nonlinear dielectric medium. However, plasma frequency dispersion prevents propagation of fundamental waves; the increase in electron density leads to the evolution of plasma frequency that behaves as a cut-off frequency, and plasma dielectric constant for fundamental waves becomes negative. To remove this difficulty, our setup combines plasma and double-split-ring resonator(DSRR) or another metamaterial, whose negative permeability has been verified theoretically and experimentally [1] in order to cancel out the cutoff property of negative permittivity using negative permeability: refractive index becomes a real and negative value. By enabling electromagnetic waves to propagate into high-density plasma, intense harmonic generation occurs. Our has reported unique properties of plasma metamaterial [2]. In this study, we experimentally observed second harmonic generation (at 4.9 GHz) in plasma space with DSRR at incident microwave frequency of 2.45 GHz.\\[4pt] [1] J. B. Pendry \textit{et al.}, IEEE Trans. Microw. Theory Tech. \textbf{47} (1999) 2075.\\[0pt] [2] O. Sakai \textit{et al}., Plasma Sources Sci. Technol., \textbf{21} (2012) 013001. [Preview Abstract] |
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GT1.00077: Sustenance of electronegative plasma column in the presence of electron temperature gradient in linear magnetized plasma device Shantanu Kumar Karkari, Mimansa Shastri, Hasmukh Kabariya, Sanjay Mishra, Nishant Sirse Electronegative plasmas are widely popular in semiconductor processing industries as well as for the production of hydrogen neutral beams for plasma heating in fusion devices. This paper describes about the sustenance of electro-negative oxygen plasma in the presence of electron temperature gradient in magnetized plasma column of the linear plasma device. The electron temperature is self-consistently created in the discharge by the energy filtering of electrons across the magnetic field in conjunction with axial losses of energetic electrons at the grounded end plate. Detail measurements of radial plasma parameters performed using planar Langmuir probe finds substantial decrement in the negative to positive saturation current ratio as observed in the central region of the plasma column, characterized by low electron temperature. The negative ion fraction obtained from these measurements are based on a qualitative model that considers the modified Bohm speed in the presence of negative ions including the attenuation of thermal electron current to the probe due to the presence of external magnetic field. [Preview Abstract] |
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GT1.00078: Boundary Conditions and Heat Flux to the Walls in Two-Temperature L. Pekker N. Hussary . [Preview Abstract] |
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