Bulletin of the American Physical Society
71st Annual Gaseous Electronics Conference
Volume 63, Number 10
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session GT1: Poster Session I |
Hide Abstracts |
Room: Oregon Convention Center Exhibit Hall A1 |
|
GT1.00001: Low Energy Electron Impact Elastic and Vibrational Excitation of Acetonitrile. Mateusz Zawadzki, Grant Dolmat, Bianca Diaz, Gillian Tatreau, Borna Hlousek, Murtadha A Khakoo We present measurements of differential cross-sections for elastic scattering of low energy electrons from acetonitrile for incident energies of 0.7eV to 30eV and scattering angles of 10 to 130 degrees and for vibrational excitation of acetonitrile for 6 incident energies from 1.5eV to 5eV in the same angular range. Comparisons with available experimental and theoretical results are made. [Preview Abstract] |
|
GT1.00002: Low Energy Electron Impact Excitation of Molecular Hydrogen and Carbon Monoxide Mateusz Zawadzki, Grant Dolmat, Bianca Diaz, Gillian Tatreau, Eimon Erfanfar, Murtadha A Khakoo We present measurements of differential cross-sections for inelastic scattering of low energy electrons from molecular hydrogen and carbon monoxide for incident energies of 6 eV to 25 eV and scattering angles of 20 to 130 degrees using time-of-flight and conventional electron spectrometers. Comparisons with experimental and theoretical results are made. [Preview Abstract] |
|
GT1.00003: Ring Vortices for Positronium Formation in Positron-Hydrogen Collisions in the Ore Gap S. J. Ward, Albandari W. Alrowaily, P. Van Reeth Using the inverse Kohn variational method, we determine K-matrices, the Ps-formation scattering amplitude $f_{\rm Ps}$, and the corresponding differential cross section (DCS) for positron-hydrogen collisions in the Ore gap (6.8 to 10.2 eV) [1]. We also determine the velocity field associated with $f_{\rm Ps}$ [1]. There are two zeros in $f_{\rm Ps}$ and the Ps-formation DCS for when these quantities are functions of the magnitude of the momentum of the incident positron, ${\bf k}$, and the scattering angle of the outgoing Ps. Associated with each zero in $f_{\rm Ps}$, there is a ring vortex. By making a linear expansion of $f_{\rm Ps}$ about the vicinity of a zero, we determine for each zero the expectation value of the $y$-component of the angular momentum, $\langle L_y \rangle$, over a small area (circle or square) in the vicinity of the zero, where the $z$-axis is the direction of ${\bf k}$ and the $x$-axis is in the plane of ${\bf k}$ and the momentum of the outgoing Ps. \vskip 0.2truecm \noindent [1] A.~W.~Alrowaily, S.~J.~Ward, P.~Van Reeth, in preparation. [Preview Abstract] |
|
GT1.00004: An improved trochoidal electron gun design William Terry, Christopher Bryan, Luis Rios, Leigh Hargreaves Electron scattering experiments, for example, elastic scattering, conducted in strong magnetic fields have the potential to allow consideration of targets that are impractical in purely electrostatic experiments. A prominent example is electron scattering from biomaterials, such as uracil, data for which would allow improved simulation of electron transport in biological plasma environments. The Trochoidal Electron Monochromator (TEM) is a well-established gun design that allows for production monochromatic electron beams in magnetic fields. However, the standard design suffers from strong coupling of the energy resolution to the beam energy and typically operates in weak (\textless 50 Gauss) magnetic fields, limiting use cases to very low energies (\textless 5eV). We have designed and fabricated a modified TEM, extending the work of [1], that shows good resolution (\textless 100mev) at energies up to 50eV, in magnetic fields up to 500 Gauss, allowing for a much broader range of scattering experiments. We present both simulations of our TEM and performance data. [1] V. Grill, H. Drexel, W. Sailer, M. Lezius and T.D. Mark, Int. J. Mass. Spectrom., \textbf{205}, 209 (2001) [Preview Abstract] |
|
GT1.00005: Elastic electron scattering from levulinic acid Luis Rios, Andrea Cilliani-Mineau, Kate Nixon, Leigh Hargreaves Biofuels are a potential solution to the continued use of fossil fuels in the automotive industry. Atmospheric plasma treatment of biomass has demonstrated its potential to efficiently break down the protective lignin layer that limits ethanol production from cellulosic decomposition and is a barrier to the widespread adoption of ethanol fuels. In addition, cellulosic breakdown yields useful by-products that contribute to the financial viability of biofuels. We present elastic scattering differential cross section measurements for levulinic acid, one of the primary value-added chemicals in plasma assisted cellulosic breakdown. We present data for scattering energies less than 30eV and scattering angles from 10 degrees to 125 degrees. These data will facilitate modelling and process control improvements for plasma assisted biomass treatement. [Preview Abstract] |
|
GT1.00006: Gas diameter sensitivity in electron scattering from water molecules Luis Rios, Andrea Cilliani-Mineau, Leigh Hargreaves Water is an important target for both biological and technological applications, and its scattering cross sections have received significant attention. However, water is also a complicated target for scattering measurements that rely on knowledge of its gas diameter, primarily elastic scattering data derived from the Relative Flow Method (RFM). While water is a geometrically small molecule, it has a large dipole moment that increases its effective gas diameter, although to what extent seems unclear. RFM measurements have been reported with estimates ranging from 2.89 through to 7.25 angstroms. Disagreements between several measurements currently available are potentially attributable to this issue. We present elastic scattering differential cross sections for water at energies less than 30eV. In addition to the DCS data, we have measured the apparent gas diameter for water in our own apparatus, and conducted sensitivity measurements to investigate the variation in the final measurements to the assumed gas diameter. [Preview Abstract] |
|
GT1.00007: B-spine R-matrix with pseudostates calculations for electron-impact excitation and ionization of calcium. Oleg Zatsarinny, Klaus Bartschat The B-spline R-matrix with Pseudo-States method [1,2] was employed to treat electron collisions with calcium atoms. Predictions for elastic scattering, excitation, ionization, and ionization-excitation were obtained for all transitions between the lowest 39 states of Ca in the energy range from threshold to 100~eV. The accuracy of the results was checked by comparing them with available experimental data and checking different approximations with increasing number of coupled states. The largest scattering model included 483 states, most of which were pseudo-states that simulate the effect of the high-lying Rydberg continuum and, most importantly, the ionization continuum on the results for transitions between the discrete states of interest. This effect is particularly strong at ``intermediate'' incident energies of a few times the ionization threshold. The dataset generated from the largest model is estimated to be accurate to within a few percent for the cross sections of relevance for plasma modelling. [1] O.~Zatsarinny, Comp.\ Phys.\ Commun.~{\bf 174} (2006) 273. [2] O.~Zatsarinny and K.~Bartschat, J.~Phys.\ B~{\bf 46} (2013) 112001. [Preview Abstract] |
|
GT1.00008: Electron-impact excitation cross sections for Fe I. Kedong Wang, Oleg Zatsarinny, Klaus Bartschat Calculations are reported for electron collision strengths, rate coefficients, and transitions probabilities for a wide range of transitions in Fe I. The collision strengths were calculated using the B-spline Breit-Pauli R-matrix approach~[1]. The MCHF method in connection with adjustable configuration expansions and a semi-empirical fine-tuning procedure was employed to accurately represent the target wavefunctions. The close-coupling expansion contained 221 $LS$ states of Fe I, including all levels of the $3d^6 4s^2$, $3d^7 4s$, $3d^8$, $3d^6 4s4p$, and $3d^7 4p$ configurations. Effective collision strengths were obtained by averaging the electron collision strengths over Maxwellian speed distributions at electron temperatures from $10^2$ to $10^5$ K. The tabulated results for 24,531 transitions between all the above $LS$ terms considerably expand the few existing, sparse datasets for Fe I. They allow a more detailed analysis of the measured spectra from various space observatories and the nonlocal thermodynamic equilibrium modeling of late-type stars [2], for which large amounts of collisional data for the atomic species of interest are required. [1] O.~Zatsarinny, Comp.\ Phys.\ Commun.~{\bf 174} (2006) 273. [2] P.~S.~Barklem, A\&A~{\bf 24} (2016) 9. [Preview Abstract] |
|
GT1.00009: Building tailored chemistry sets for plasma modelling using a statistical approach embedded in an online engine. Jonathan Tennyson, Mala Virdee, Martin Hanicnec, Sebastian Mohr The Quantemol Plasma Chemistry Generator (QPCG) helps explore the vast number of potential chemical species and reactions present in plasma systems. Critical to the understanding and development of complex plasmas is the identification of important chemical species and reactions present, often a resource and time intensive endeavour. QPCG suggests chemical species, important reactions and cross-section data for a given mixture of feed gases, helping researchers to curate self-consistent sets of chemical reactions that are specific to the system of interest. First, constituent plasma species are obtained from the Quantemol Database (QDB, Tennyson et al, Plasma Sources Sci. Technol. (2017) 055014) based on the composition of the feed gases. Potential reactants and products for a hypothetical reaction are combined iteratively from these species to form sets of allowed chemical reactions. Classification of these reactions into different process types, using models of reactions already available in QDB, facilitates selection of important reactions based upon process parameters. Finally, rate coefficients and/or cross sections are obtained from QDB, where available, or by analogy with similar reactions. By reducing the time needed to assemble a chemistry set, QPCG provides quick fundamental insights into plasma chemistries, accelerating the development and optimisation of new plasma systems and their applications. Examples of generated chemistry sets will be presented. [Preview Abstract] |
|
GT1.00010: Calculated electron impact dissociation cross sections for H$_{\mathrm{2}}$O$_{\mathrm{2}}$ Andrew R. Gibson, James Hamilton, Jonathan Tennyson, Sandra Schroeter, Timo Gans, Deborah O'Connell Hydrogen peroxide (H$_{\mathrm{2}}$O$_{\mathrm{2}})$ is thought to be a key plasma produced reactive species in the context of biomedical applications. Data concerning electron collisions with H$_{\mathrm{2}}$O$_{\mathrm{2}}$, which are important for properly understanding its kinetics in plasma sources, is however, extremely limited. In this work, the UK polyatomic R-matrix method is used to calculate electron impact excitation and dissociation cross sections for H$_{\mathrm{2}}$O$_{\mathrm{2}}$. These cross sections focus on the dissociation of the O-O bond leading the formation of two OH radicals. The total electron impact dissociation cross section is calculated as the sum of the cross sections to the first 11 electronically excited states of H$_{\mathrm{2}}$O$_{\mathrm{2}}$, with the largest individual cross section corresponding to that for the lowest lying a$^{\mathrm{3}}$A state, with a threshold energy of 5.12 eV. Rate coefficients for electron impact dissociation of H$_{\mathrm{2}}$O$_{\mathrm{2}}$ for various electron temperatures and distribution function shapes will be presented. These are compared with those normally estimated for use in plasma modelling. The presented calculations significantly increase the dataset for electron impact processes with H$_{\mathrm{2}}$O$_{\mathrm{2}}$. [Preview Abstract] |
|
GT1.00011: A theoretical and experimental investigation of two-center interference effects in electron impact ionization of diatomic molecules (H$_{\mathrm{2}}$ and N$_{\mathrm{2}})$. Sadek Amami, Zehra N. Ozer, Don Madison In this work, we examine possible two-center interference effects by comparing triple differential cross sections (TDCSs) for electron impact ionization of an atom with the corresponding diatomic molecule for H2 and N$_{\mathrm{2}}$. The ratio of the TDCS for a diatomic molecule to the equivalent atomic TDCS (called the I-factor) is a sensitive test for interference effects. We will present the I-factor, for 350 eV electron impact ionization of H$_{\mathrm{2}}$ and N$_{\mathrm{2}}$, by comparing theoretical 3-body distorted wave approximation (3DW) results with experimental data measured at the e-COL laboratory. [Preview Abstract] |
|
GT1.00012: Low energy electron-impact ionization of CF4. Esam Ali, Khokon Hossen, Enliang Wang, Xueguang Ren, Chuangang Ning, Alexander Dorn, Don Madison Experimental and theoretical triple differential cross section results will be presented for 66 eV electron-impact ionization of CF4 for the three unresolved outermost orbitals - the highest, next highest, and next-next highest occupied molecular orbitals (HOMO, NHOMO, and HOMO-2). The theoretical results will be compared with experiment for in plane scattering and full perpendicular plane scattering with projectile scattering angles of 8$^{\mathrm{o}}$, 10$^{\mathrm{o}}$, 12$^{\mathrm{o}}$, 15$^{\mathrm{o}}$, and 20$^{\mathrm{o}}$ at ejected electron energies of 3, 5, 8, and 10 eV. Comparisons will be made with theoretical M3DW (molecular 3-body distorted wave) model calculations. [Preview Abstract] |
|
GT1.00013: Collision Induced Electron Auto-Detaching States of H$_2$CC$^-$ AND NO$^-$ Below 10 keV with N$_2$ and O$_2$ Guillermo Hinojosa, E. M. Hern\'andez, L. Hern\'andez, Laura Serkovic-Loli Simple molecular anions (SMA) are one of the most extravagant species in nature. Their unstable character contrasts with its common presence in cold plasma and in different atmospheric environments where higher-than-expected populations of anions have been recently confirmed. Even more, SMA have been detected in the interstellar medium (IM) where they are likely to deplete due the low matter density and radiation present in the IM. As a consequence of studying the collision induced electron detachment cross sections of SMA with two different methods, it was possible to realize about the formation of autodetaching states. For the case of the vinylidene anion, which ground state anion has a lifetime of 102 s, it was possible to derive a combined lifetime $\tau^{\beta}$ of its metastable states. While for the nitric oxide anion, which ground state has a lifetime of 15 $\mu s$, a crude derivation of $\tau^{\beta}$ indicates that the lifetime of the collision induced metastable states is shorter than those of the vinylidene anion. [Preview Abstract] |
|
GT1.00014: Photoionization Cross Sections of Phosphorus Cations: A tool for the Search of Life in the Universe Guillermo Hinojosa, S. N. Nahar, E. M. Hernandez, A. Covington, L. Hernandez, K. Chartkunchand, A. Antillon, A. Morales-Mori, O. Gonzalez-Magana, D. Hanstorp, A. Juarez Together with H, C, N, O and F, a chemical element indispensable for life is also phosphorus. The detection of astrophysical P depends on Earth-based observatories and on spacecraft equipped with spectrometers. Elements in space are ionized by ambient radiation. The most common phosphorous cations are likely P$^{+}$, P$^{2+}$ and P$^{3+}$. Photoionization (PI) measurements for P are scarce, but third generation synchrotron sources, combined with the photoion yield spectroscopy technique, have made PI data available. With this technique, we collided an intense beam of EUV photons with well-collimated beams of target P cations to measure PI cross sections and spectroscopy. The P$^{+}$ spectrum shows sharp resonances near and at the threshold. These findings may explain the high reactivity of the cation at low energy. However, at the high energy interval of this study, spectroscopic features fade out for the low lying states. [Preview Abstract] |
|
GT1.00015: Electron Vortex Beam Ionization Allison Harris, Alex Plumadore, Zoryana Smozhanyk, Victor Turpin Electron vortex beams (EVBs) carrying non-zero orbital angular momentum have only been experimentally realized in the last decade. Many unique applications and uses have been proposed, such as the control and rotation of nanoparticles and improved resolution in electron microscopy. Unfortunately, very little is known about how EVBs interact with individual atoms, and there are no experimental results yet for collisions between EVBs and atoms. There is also very little theoretical work on this topic, with only a handful of studies to date for EVB collisions with hydrogen atoms. If EVBs are to be used for any of the proposed applications, it is crucial to understand how electrons with non-zero angular momentum interact with atoms on a fundamental level. We present here the first theoretical calculations for ionization collisions between electron vortex beams and simple atoms. [Preview Abstract] |
|
GT1.00016: Role of the classical path in a quantum mechanical model Torrey Saxton, Zachary Temple, Allison Harris The path integral technique is an alternative formulation of quantum mechanics that is based on a Lagrangian approach. In its exact form, it is completely equivalent to the Hamiltonian-based Schr\"{o}dinger equation approach. We have used the path integral formalism to develop our Path Integral Quantum Trajectory (PIQTr) model for use in the study of charged particle dynamics. We will present results for several one-dimensional systems, and demonstrate the method's ability to analyze individual trajectories and their influence on the total probability amplitude. We will also show how the range of included trajectories can affect the time evolution of the wave function, resulting in interference fringes reminiscent of those observed with single slit Fresnel diffraction. [Preview Abstract] |
|
GT1.00017: Heavy-Ion Scattering using the PIQTr Model Zachary Temple, Torrey Saxton, Allison Harris Heavy-ion charged particle collisions have important applications in fields such as astrophysics, biophysics, and plasma physics, and from a fundamental standpoint, provide valuable information about the few-body problem. Current theoretical atomic collision models work well for electron projectiles, but heavy-ion projectiles continue to present a challenge for even the most advanced models. To help address these challenges, we developed the Path Integral Quantum Trajectory (PIQTr) model for the calculation of time-dependent wave functions. The method has been applied to particles moving in one dimension and was shown to work well for heavy particles. We have now extended our method to charged particles moving in two dimensions and present time-dependent numerical results for heavy-ion scattering. [Preview Abstract] |
|
GT1.00018: Bound-state models in the electron capture process Allison Harris, Alex Plumadore Electron capture processes play an important role in many physical systems, from fusion reactors to astrophysical processes. In an electron capture collision, an incident ion collides with a target atom, captures an electron, and leaves the collision as a bound state. Recent experimental results for He\textasciicircum \textbraceleft $+$\textbraceright $+$ He single electron capture show previously unobserved features in the differential cross section. Some of these features have been attributed to Fraunhofer diffraction effects, while others remain unexplained by theory. We present results from a fully quantum mechanical model and compare with experimental results. Using our model, we explore the effect of treating the projectile as either a single particle or a two-particle bound state. We also study the effect of the nuclear potential on the capture process. [Preview Abstract] |
|
GT1.00019: Fully Differential Study of Cusp Electron Production in p $+$ He, H$_{\mathrm{2}}$ Collisions Madhav Dhital, Sujan Bastola, Ahmad Hasan, Ramaz Lomsadze, Basu Lamichhane, Aaron Silvus, Brendan Boggs, Deni Cikota, Michael Schulz We have performed a kinematically complete experiment on ionization of He and H$_{\mathrm{2}}$ targets by 75 keV p impact. The momentum-analyzed scattered projectiles and recoiling target ions were measured in coincidence. The ejected electron momentum was deduced from momentum conservation. From the data we extracted fully differential cross sections (FDCS) for electrons ejected with a speed close to the projectile speed. Such electrons lead to a sharp structure in the energy spectrum known as the cusp. In terms of FDCS cusp electrons are still to a large extent unexplored. So far, only one data set on FDCS for ionization of H$_{\mathrm{2}}$ in this regime was reported$^{\mathrm{1}}$. There, a very sharp and large structure in the angular distribution was predicted by theory in the initial projectile beam direction, but this structure was almost absent in the experimental data. New data for a He target and several ejected electron energies will be reported in order to analyze the discrepancies between theory and experiment. $^{\mathrm{1}}$ A. Hasan et al., JPB \underline {49}, 04LT01 (2016). [Preview Abstract] |
|
GT1.00020: Calculation of electron emission cross sections in proton-biomolecule collisions Tom Kirchner, Marko Horbatsch, Hans Jurgen Luedde Ion collisions with biologically relevant molecules have received considerable attention in recent years, in large parts because of their relevance in biomedical and other applications. We have developed an independent-atom-model (IAM) based description of ion-molecule and ion-cluster collisions that can be applied to these problems [1,2]. The model improves on the simple Bragg additivity rule by taking geometric screening corrections due to overlapping atomic cross sections into account. A pixel counting method (PCM) is used for the (exact) calculation of the screening corrections and the method is referred to as IAM-PCM. We have used the IAM-PCM to study the proton-impact induced net ionization of a variety of target systems, including DNA/RNA nucleobases and a number of amino acids. At the conference we will present an overview of our results and specifically discuss cross section scaling relations. [1] H. J. L\"udde {\it et al.}, Eur. Phys. J. D {\bf 70}, 82 (2016). [2] H. J. L\"udde {\it et al.}, Eur. Phys. J. B {\bf 91}, 99 (2018). [Preview Abstract] |
|
GT1.00021: New cross section for reaction of O$^{\mathrm{\mathbf{+}}}$\textbf{(}$^{\mathrm{\mathbf{4}}}$\textbf{S) with N}$_{\mathrm{\mathbf{2}}}$ Rainer Johnsen, Larry Viehland Rate coefficients of the ionospheric reaction O$^{\mathrm{+}}$ ($^{\mathrm{4}}$S) $+$ N$_{\mathrm{2}} \quad \to $ NO$^{\mathrm{+}} \quad +$N that were measured 40 years ago by the flow-drift $^{\mathrm{1\thinspace }}$method are still used in ionospheric models. The reaction depends strongly on energy which makes it sensitive to the ion velocity distribution. The NOAA flow-drift data (using both helium and argon as buffer gases) were analyzed using then available interaction potentials and analytical and Monte Carlo solutions of the Boltzmann equation. More accurate ab initio potentials are now available and new approaches to deriving velocity distributions have been developed, such as the Gram Charlier method that computes the higher moments of the distribution functions (skewness, kurtosis, and correlations between the parallel and perpendicular velocity components). We have carried out extensive computations of O$^{\mathrm{+}}$ ion velocity distributions in both helium and argon, based on the Gram Charlier method and ab initio interaction potentials. We then applied the results to the O$^{\mathrm{+}} \quad +$ N$_{\mathrm{2}}$ reaction rate data. We found that the experimental data can only be reproduced if the reaction cross section is substantially changed from that in the original paper of the NOAA group. As a consequence, effective rate coefficients appropriate to the temperatures and velocity distributions in the ionosphere need to be reevaluated. $^{\mathrm{1}}$D. L. Albritton et al J. Chem. Phys. \textbf{66}, 410 (1977). [Preview Abstract] |
|
GT1.00022: Modification of the Coulomb logarithm due to electron-neutral collisions Gerjan Hagelaar, Zoltan Donko, Nikolay Dyatko We investigate the validity of the binary collision operator used to describe the effect of electron-electron Coulomb interactions in Boltzmann calculations of the electron distribution function in weakly ionized gases. In order to do this, we compare results from such Boltzmann calculations with those from particle simulations in which the electron-electron Coulomb interactions are described from first principles, via Molecular Dynamics techniques. It turns out that significant differences can arise, for example in the calculated drift velocity in xenon at low reduced electric field, because the Coulomb interactions are perturbed by electron collisions with neutral gas particles. We demonstrate that this effect can be included in the Boltzmann collision operator by a simple modification of the Coulomb logarithm, derived from elementary physical considerations. This modified Coulomb logarithm brings the Boltzmann calculations in perfect agreement with the first-principles simulations, over a wide range of conditions. [Preview Abstract] |
|
GT1.00023: Influence of electronically excited states of nitrogen and oxygen on plasma kinetics in dielectric barrier discharges. Vitaly Datsyuk, Igor Izmailov, Vadym Naumov, Vladimir Khomich, Vyacheslav Tsiolko Kinetics of non-equilibrium plasma in dielectric barrier discharges (DBD) is of great interest for science and practice [1]. But despite the advances in plasma physics, the mechanisms of plasma-chemical processes are not very clear, in particular, concerning electronically excited states (EES) of oxygen and nitrogen atoms and molecules. We tried to study this issue in detail. Experiments were done in various DBD in oxygen/nitrogen/argon mixtures, employing electrical and optical diagnostics. Measurements showed that DBD plasma processes are accompanied by the formation of EES. Computer modeling by using self-consistent 0D-kinetic and 1D-fluid models, including ionization, excitation, dissociation-recombination, vibrational relaxation, collisional quenching, and radiation revealed the most probable mechanisms of plasma-chemical transformations. Effects of metastable EES, involving singlet oxygen $O_{2}^{\ast } (a,b)$,$O^{\ast }({ }^{1}D)$ and nitrogen $N_{2}^{\ast } (A)$,$N^{\ast }({ }^{2}D)$ were examined. Our study confirmed the role of EES in the DBD plasma kinetics and indicated the way to more efficient plasma processing. [1] M.A. Lieberman, A.J. Lichtenberg, \textit{Principles of Plasma Discharges and Materials Processing}, John Wiley {\&} Sons, 2005. [Preview Abstract] |
|
GT1.00024: Emission properties of atmospheric pressure plasma jets on the basis of helium-air and argon-air operating mixtures Andrii Heneral The spectral-temporal and energy luminescence characteristics of the "cold" plasma jets generated by the atmospheric pressure barrier discharge in helium-air and argon-air mixtures were experimentally studied and analyzed. The main radiating components of the nitrogen containing low-temperature plasma were observed in radiation spectrum of the generated plasma jets outside the capillary cut-off when an operating mixture is blown through the gas-discharge radiation source, namely, nitrogen molecules N$_{\mathrm{2\thinspace }}(C\,{ }^{3}\Pi_{u} \to B\,{ }^{3}\Pi_{g} $- transition) and nitrogen ions $N_{2}^{+} (B\,{ }^{2}\Sigma_{u}^{+} \to X\,{ }^{2}\Sigma_{g}^{+} $-transition) for helium-air mixture and nitrogen molecules N$_{\mathrm{2\thinspace }}(C\,{ }^{3}\Pi_{u} \to B\,{ }^{3}\Pi _{g} $- transition) for argon-air mixture. At the same time, the radiation power of the "cold" plasma jet increased approximately in 3 times when the argon-air mixture is replaced with the helium-air mixture. The work was supported by a grant of National Academy of Sciences of Ukraine for young scientists (2017--2018). [Preview Abstract] |
|
GT1.00025: Electron desorption effect of accumulated electrons in atmospheric pressure dielectric barrier discharges Haruaki Akashi, Tomokazu Yoshinaga Recently, atmospheric dielectric barrier discharges(DBDs)are widely applied to various fields. However, in DBDs, there are many parameters which affect to plasma significantly, such as dielectric materials and its thicknesses, gas, gas pressure and applied voltage waveform, and so on. A few researchers investigatedon the interaction between plasma and dielectric surfaces but mostof phenomena is still inside the veil.Golubovskii et al[1] and Itoh et al [2] are mentioned about somesurface interactionsin DBDs. And authors also have been simulated DBDsincluding electron desorption effect. In the present paper, the electron desorption effect lead by hot gas particles have been examined inatmospheric pressure DBDs using two dimensional fluid model.The hot gas particle regions are generally formed in the vicinity of the dielectrics where the filament discharge formed. As a results, effect of electrondesorption causes stable filament discharges while hot gas temperature regions in the vicinity of the dielectrics are exist. But without hot gas regions, the filaments are randomly generated in the discharge space. [1] Y.B.Golubovskii, et al, J.Phys. D: Appl.Phys. Vol.35, pp.751-761 (2002) [2] H.Itoh et al, ESCAMPIG XXIII, Bratislava, Slovakia, p.192 (2016) [Preview Abstract] |
|
GT1.00026: Magnetization effect on secondary electron emission in a hollow cathode plasma source. Montu Bhuva The secondary electrons play a significant role in the sustenance of direct current discharges, as it contributes to a major fraction of the discharge current. The emission characteristics can be greatly influenced by choosing appropriate hollow cathode geometry and/or application of external magnetic field. In this paper, the effect of tangential/oblique magnetic field on the secondary electron emission from a cylindrical and conical hollow cathode surface has been experimentally studied and discussed. It is found that the sustenance voltage of the discharge tend to shift towards higher gas pressure as the magnetic field increases. Furthermore, the discharge transpires in to a collimated, elongated plasma column. The cathode fall thickness is visually seen to increase with the applied magnetic field. The observed phenomena have been qualitatively explained using a phenomenological model; which intrinsically takes in to account the variation in the secondary electron emission yield due to magnetic field. [Preview Abstract] |
|
GT1.00027: Comparison of low frequency ac theory to Langmuir characteristics on the same probe David Walker, David Blackwell, Richard Fernsler, Bill Amatucci The small-signal, ac impedance $Z_{ac}(V_{dc})$ of spherical probes, offers a direct means of determining plasma potential $\varphi_{p}$ when the ac frequency $\omega $ is low and the probe radius $r_{p}$ is much larger than the electron Debye length.$^{\mathrm{a,b}}$ In particular, Re($Z_{ac})$ is a minimum at low f when the dc probe bias $V_{dc}$ equals $\varphi_{p}$. Here we compare low-frequency results for Re($Z_{ac})$ given by a network analyzer to the dc slope, (d$I_{dc}$/d$V_{dc})^{\mathrm{-1}}$, obtained by using the same sphere as a Langmuir probe. The two results agree well at moderate bias over a frequency range $\omega_{\mathrm{pi}}$\textless \textless $\omega $\textless 0.3$\omega_{\mathrm{pe}}(r_{p})$, where $\omega_{\mathrm{pi}}$ and $\omega_{\mathrm{pe}}$ are the ion and electron plasma frequencies, respectively.$^{\mathrm{a}}$ However, the agreement worsens as the bias voltage becomes increasingly negative. Furthermore, because $\omega $\textgreater \textgreater $\omega _{\mathrm{pi}}$, we expect the ions to contribute only weakly to the ac current, which suggests that Re($Z_{ac})$ should be no less than (d$I_{dc}$/d$V_{dc})^{\mathrm{-1}}$. Nevertheless, just the opposite behavior was seen experimentally. We will show results both from earlier work along with recent data in which we use frequencies in the range $\omega $\textless \textless $\omega_{\mathrm{pi.}}$. $_{\mathrm{.\thinspace }}^{\mathrm{a\thinspace }}$\textit{Phys. Plasmas }\textbf{17}, 113503 (2010); $^{\mathrm{b\thinspace }}$\textit{US Patent }\textbf{8,175,827 B2}$,$(5/2012) . [Preview Abstract] |
|
GT1.00028: Abstract Withdrawn
|
|
GT1.00029: Modulation of microwaves using rotating magnetron discharges Andrea Marcovati, David Biggs, Nicolas Gascon, Mark Cappelli The frequency modulation of microwaves (1-100 GHz) with unsteady plasmas can be performed with pulsed plasma discharges that can absorb or scatter microwaves, depending on the wavelength and plasma properties. This kind of modulation is limited by the timescales of gas ionization and decay, which can limit the possible bandwidths to a few MHz or less. Here we present simulations and experiments on the feasibility of modulating microwaves using dc magnetron plasmas. In these discharges, ``spoke'' type density instabilities can develop and rotate in a circular zone where the electric and magnetic fields are perpendicular. Modulation of microwaves can be obtained with bandwidths that are depending on the number of spokes and their frequency of gyration. Different magnetron discharge and wave coupling configurations are simulated and presented using Ansys HFSS. The plasma dielectric properties are modeled as function of frequency of the microwave passing through, following the Drude model. Simulations show that such modulation is possible. In the experiments, microwaves in the range of 1 to 20 GHz are sent through a circular (19 mm diameter), low pressure (100-300 mTorr) dc magnetron discharge and the wave transmission properties are measured as function of time. [Preview Abstract] |
|
GT1.00030: Ion kinetics and long-time evolution of current-carrying instabilities in low temperature plasma sources Cameron Treece, Kentaro Hara Ion kinetics and time evolution of bulk plasma properties in the nonlinear saturation regime of a collisionless current-carrying instability are presented using a 1D Vlasov-Poisson simulation. Such instabilities are considered to be responsible for the anomalous electron transport in hollow cathode plumes, and the high-energy ions due to the generation of plasma waves can cause cathode erosion, which may limit the lifetime of space propulsion missions. The ratio of initial electron bulk velocity to initial electron thermal velocity, which we define as the electron Mach number, ranges from 1 to 2.5. Argon ions are used, and the initial electron temperature is 2 eV while the initial ion temperature is 0.2 eV. The simulation domain employs periodic boundary conditions and allows for multiple wave modes to be excited. The production of backstreaming high-energy ions is observed when the electron Mach number is greater than 1.3, which agrees with previous theories. Simulation results show that bulk plasma properties continue to evolve in time during nonlinear saturation. The data set can be used to provide kinetic corrections to existing fluid simulations of hollow cathode discharge. [Preview Abstract] |
|
GT1.00031: A kinetic description of the effects of temperature gradients in low-temperature plasmas for space propulsion Romain Lucken, Antoine Tavant, Anne Bourdon, Pascal Chabert A common assumption in the modeling of low temperature plasma discharges consists in treating the plasma as isothermal. While this assumption is valid to estimate the main bulk plasma properties in non-magnetized discharges or magnetized plasma columns, it yields erroneous predictions of phenomena involving large electric fields, such as plasma sheaths and magnetic filters. We show here that the electron temperature can drop by one order of magnitude in the sheath, with significant consequences for example in electron induced secondary electron emission, since the emission rate strongly depends on the local temperature at the vicinity of wall. This work, based on multiple 1D and 2D particle-in-cell simulations of plasma discharges in typical conditions used for space propulsion, is a first step towards understanding the kinetic origin of heat fluxes in low-temperature low-pressure plasmas, and their role in the plasma transport and the plasma-wall interactions. [Preview Abstract] |
|
GT1.00032: Basic characteristics of low temperature DC magnetized plasmas in a weakly collisional magnetic X-point configuration Yegeon Lim, Bin Ahn, Daeho Kwon, Won-jun Lee, Se Youn Moon, Bo-sung Kim, Young-chul Ghim We have constructed a cylindrical multidipole chamber, MAXIMUS (MAgnetic X-point sIMUlator System), with a DC discharge system capable of generating variable magnetic X-point configurations. MAXIMUS is composed of two connected cylindrical chambers of 60cm in diameter and 1m long each where one chamber is grounded and the other can be electrically biased. We generate H, He or Ar discharges at working pressures between 0.1 mTorr and 100 mTorr. Plasmas are generated by energetic ionizing electrons emitted from a set of heated ThW filament wires, which can be biased up to -200V. The emitted electron current can be varied up to \textasciitilde 10A in a specific condition. Langmuir probes and emissive probes are used to measure electron temperature, plasma density and plasma potential. We use Hall probes to measure spatial profiles of magnetic fields. Typical plasma parameters generated in MAXIMUS are T$_{\mathrm{e}}$\textasciitilde 1eV, n$_{\mathrm{e}}$\textasciitilde 10$^{\mathrm{10}}$cm$^{\mathrm{-3}}$ and V$_{\mathrm{p}}$\textasciitilde 5V. The magnetic X-point is generated via parallel DC currents (up to 1kA) through two axial copper tubes in MAXIMUS. Magnetic field configurations are varied by changing relative positions and driving currents of the copper tubes independently. Influences of magnetic perturbations and neutral densities on plasmas in the X-point configuration are initially investigated. [Preview Abstract] |
|
GT1.00033: Modelling of Electrode Configurations for Nanosecond Pulsed Plasmas Nancy Isner, Prateek Gupta, Tatyana Sizyuk, Carlo Scalo, Allen Garner Nanosecond repetitively pulsed plasmas (NRPPs) can efficiently generate ionized/excited species. While studies have elucidated the impact of local flow fields [1], the influence of electrode geometry and the induced flow field remains incomplete. We hypothesize that the electrode configuration will strongly influence the electric field, plasma species generation, and the induced flow field, motivating the development of a complete model to couple these phenomena. This study couples a quasi-one dimensional model for a parallel plate geometry [2] to BOLSIG$+$ to improve plasma species characterization [3]. The implication of electrode configurations, such as pin-to-plate and pin-to-plate, on the induced electric field and generated species will be examined. The long-term incorporation of this model into a high fidelity computational fluid dynamics (CFD) model and comparison to spectroscopic results under quiescent and flowing conditions will be discussed. 1. A. V. Likhanskii, M. N. Shneider, S. O. Macheret, and R. B. Miles, J. Appl. Phys$.$ 103, 053305 (2008). 2. I. V. Adamovich, M. Nishihara, I. Choi, M. Uddi, and W. R. Lempert, Phys. Plasmas 16, 113505 (2009). 3. G. J. M. Hagelaar and L. C. Pitchford, Plasma Sources Sci. Technol$.$ 14, 722--733 (2005). [Preview Abstract] |
|
GT1.00034: Numerical study of photoionization of nitrogen by molecular and atomic helium emission Andrew Fierro, Chris Moore, Matthew Hopkins, Ed Barnat, Paul Clem This work investigates the role that molecular and atomic helium emission play on the photoionization process of molecular nitrogen. Both molecular and atomic helium emit radiation in the vacuum ultraviolet (VUV) regime ($\lambda$ $<$ 100 nm). When a plasma is formed in a helium and nitrogen mixture, there exists the possibility for photoionization. However, the atomic helium emission in this regime is radiation trapped and the molecular emission is emitted on longer timescales as compared to the atomic emission. As such, it is currently unclear if atomic or molecular helium emission dominate the photoionization process of nitrogen. Using a particle-in-cell (PIC), Direct Simulation Monte Carlo (DSMC) code, the role of atomic and molecular emission is investigated to elucidate the dominant mechanism for photoionization in a 500 torr nitrogen/helium plasma. [Preview Abstract] |
|
GT1.00035: The Inverse Mode of Thermionic Current Flow from a Hot Cathode Through a Plasma Michael Campanell Understanding the plasma and sheaths under intense thermionic current is important for modeling many hot cathode devices. The conventional view [1,2] is that when the current is space-charge limited (SCL) the cathode sheath consumes the electrode bias and an electric field proportional to the resistivity drives the current through the plasma. In our last GEC talk, we showed that SCL modes cannot exist [3]. Instead, the current-limited equilibrium of a plasma diode should have an inverse cathode sheath. Recently, the unique properties of the inverse current mode were modeled analytically and verified in simulations [4]. Unlike classical or SCL cathode sheath modes, in the inverse mode (a) plasma ions are trapped, (b) the electric field in the plasma is zero, i.e. no field from resistivity or presheath, (c) the anode sheath consumes the electrode bias. Also, the power loss and cathode sputtering can be minimized in the inverse mode, so it may be benificial to design future devices to operate in this mode. [1] S. Takamura et al., Contrib. Plasma Phys. 44, 126 (2004). [2] L. Pekker and N. Hussary, PoP 22, 083510 (2015). [3] M.D. Campanell and M.V. Umansky, PSST 26, 124002 (2017) (presented at GEC 2017 invited). [4] M.D. Campanell, Phys. Rev. E 97, 043207 (2018). [Preview Abstract] |
|
GT1.00036: An Effective RF Sheath Model that Includes Thermal and Non-harmonic Modulation Effects Laura Kroll, Schabnam Naggary, Dennis Engel, Ralf Peter Brinkmann The emergence of a boundary sheath in front of material surfaces is a universal plasma phenomenon. The characteristics of RF modulated boundary sheaths arise from the nonlinear interaction of the electrons and ions with the electric field. In order to understand the sheath behavior and the transition to the plasma, a mathematical system of equations covering the dynamics of all elements must be solved. Ab initio sheath models are particularly complex and mathematically cumbersome, because they involve coupled integro-differential equations, which can be solved only numerically. Effective models aspire to reduce the complexity of models by simplifying assumptions. Lieberman, for example, utilized the hard step model, which neglects thermal effects to arrive a compact algebraic description of a sinusoidal modulated sheath [1]. This contribution will employ the recently developed smooth step model [2] to establish a sheath model which includes also thermal effects and covers the influence of non-harmonic modulation.\\ \\ $[1] $ M. A. Lieberman 1989 \emph{IEEE Trans. Plasma Sci} \textbf{17} 338\\ $[2] $ R.P. Brinkmann 2015 \emph{Plasma Sources Sci. Technol.} \textbf{24} 064002 [Preview Abstract] |
|
GT1.00037: Experimental studies of sheath formation in multiple ion species plasma, electronegative and electropositive Greg Severn, Noah Hershkowitz Our discovery of anomalous sheath edge velocities using laser-induced fluorescence (LIF) near boundaries in multiple ion species plasma was explained by a new element of sheath formation: ion-ion streaming instabilities, which was shown to be in excellent agreement with our experimental results. No such corresponding measurements for electronegative plasma with multiple negative charge species exist. We present here experiments addressing basic questions for both electropositive and electronegative plasma: 1) What is the velocity at the sheath edge of each of the three ions in a three ion species weakly collisional electropositive plasma? We have already demonstrated that 2 of the species do not reach their individual Bohm speeds. 2) Is the Bohm Criterion (gBC), generalized for multiple positive ion species, satisfied in such plasma, and, does gBC really play the role that current theory assumes it does in sheath formation? 3a) Do the internal sheaths and double layers predicted to exist in electronegative discharges actually exit? 3b.) Is the Bohm Criterion, generalized for electronegative plasma (eBC), satisfied at these internal sheaths, and is the eBC adequate to understand sheath formation electronegative, multiple ion species plasma? [Preview Abstract] |
|
GT1.00038: Plasma chemistry as a tool for nitrogen fixation Miles Turner Nitrogen fixation is an outstanding problem of the 21st century, because the nitrate fertiliser produced by fixation is essential to agricultural productivity, but present techniques involve fossil fuel consumption with corresponding greenhouse gas emissions. A plausible alternative is a plasma process powered by renewable energy sources such as wind or solar power. Such a process aims to transform atmospheric oxygen and nitrogen initially into nitrogen oxides. The challenge is to design a process with high energy efficiency and the potential to scale to large capacity. This paper describes progress in modelling and relevant plasma chemistry and identifying the optimal conditions for operating a process. In simulation, energy efficiencies comparable to the conventional process can be achieved. The limitations of the model will be discussed, with reference to the uncertainty caused by uncertain rate constants. [Preview Abstract] |
|
GT1.00039: CRANE: a Novel MOOSE-based Open-Source tool for Plasma Chemistry Applications and Code Coupling Shane Keniley, Davide Curreli, Corey DeChant, Steven Shannon We present CRANE (Chemical ReAction NEtwork), an open-source tool for plasma chemistry applications using the MOOSE finite element framework. The tool facilitates the inclusion of a large number of chemical reactions into a MOOSE application. Adding reactions is simplified using MOOSE’s Action system, which automatically adds the necessary reaction rates, source terms, and sink terms based on the reaction equations written in the input file. Results are compared to simulations performed in the plasma chemistry freeware ZDPlasKin. The chemistry tool was also included in the low-temperature atmospheric plasma application, Zapdos, to model plasma chemistry reactions in 1D discharge systems. Zapdos, which was previously utilized to model argon ions and electrons incident on a liquid water interface, has been expanded to allow the inclusion of multiple gas species. Results of Zapdos combined with the plasma chemistry tool are compared to equivalent COMSOL simulations. [Preview Abstract] |
|
GT1.00040: Evaluation of gas phase and wall surface chemical reactions in CF$_{\mathrm{4}}$ and C$_{\mathrm{4}}$F$_{\mathrm{8}}$ plasmas Xi-Feng Wang, Yuan-Hong Song, You-Nian Wang, Igor Kaganovich A global model implanted with a set of gas phase and wall surface chemical reactions is used in this work for CF$_{\mathrm{4}}$ and C$_{\mathrm{4}}$F$_{\mathrm{8}}$ plasmas in an inductivity coupled plasma chamber. Firstly, by using the same set of chemical reactions, composition of radicals as well as ions is benchmarked. A study on contributions of gas phase and surface reactions to the production and consumption of species shows that surface chemistry plays a significant role in F, CF$_{\mathrm{3}}$ and CF$_{\mathrm{2\thinspace }}$radicals in CF$_{\mathrm{4}}$ and C$_{\mathrm{4}}$F$_{\mathrm{8}}$ plasmas, respectively. We also study the variation of plasma properties as a function of pressure and power at fixed gas inlet. Furthermore, in order to investigate impacts of electron energy distribution functions (EEDF) on plasma sources and sinks, both Maxwellian and non-Maxwellian EEDFs integrated with cross sections are used to evaluate the difference of chemical compositions in these plasmas. [Preview Abstract] |
|
GT1.00041: Influence of helium diffusion and aggregation on the variety of metal nanostructures under helium plasma irradiation Ilsu Mun, Atsushi Ito, Kenzo Ibano, Yoshio Ueda, Heun Tae Lee The formation of fiber-like nanostructures on tungsten (W) and molybdenum (Mo), known as fuzz, were observed after helium (He) plasma exposure. These nanostructures have large surface area with complete light absorption. He plasma induced structures appear to be used for various applications, but their formation mechanism has not been understood well. We proposed that the agglomeration and diffusion of He atoms in metal lattice are key phenomena of the fiber-like nanostructure formation. In this study, we have investigated variations of He binding energies between transition metals (W, Mo, tantalum (Ta), niobium (Nb), gold (Au), iridium (Ir) and hafnium (Hf)) with agglomerated He atoms by using first principle calculation based on density functional theory (DFT). As a result, we found a link between fiber-like nanostructure formation tendency and helium binding energy. Furthermore, in order to investigate the influence of the diffusion of He atoms in these metals on the variety of these nanostructures, we develop the simulation code based on a Kinetic Monte Carlo (KMC) method. The microscopic physical properties estimated by DFT has been connected to the macroscopic phenomena, which are observed in the real experimental scale, through the KMC simulation. [Preview Abstract] |
|
GT1.00042: Cryogenic Pellet Ablation Modelling in a Hot Magnetised Plasma Kyle Martin, Alasdair Wilson, Declan Diver The development of efficient refuelling schemes for tokamaks is essential for the success of fusion as an energy source. There are several techniques for replenishing the fuel, and one of the most promising is pellet injection, in which a cryogenic pellet of fuel is fired at speeds of a few 100 m/s into the tokamak plasma. This solid structure is ablated by the ambient plasma, dispersing fuel through the chamber. The ablation of this pellet creates a dense cloud of neutral particles which interacts with the background plasma, creating strong transient ionization and density gradients and making the evolution of the pellet-plasma system a complex gas-plasma problem. We attempt to model this process holistically by extending evaporative surface models (e.g. the ``$D^2$" law) and collisional plasma processes (informed by cloud profile diagnostics) in order to infer the ablation rate, density structure, cloud terminal radius and pellet size as a function of time, balancing mass-transfer and ionization rates, diffusion and sheath evolution. Fluid instabilities may play a role in the strongly sheared flows between contrasting density media. This project brings a combination of theoretical and computational modelling to bear on a fusion technology problem. [Preview Abstract] |
|
GT1.00043: Formation of the ion distribution function near a surface at a negative potential for gas discharge plasmas Alexander Mustafaev, Vladimir Sukhomlinov, Oscar Murillo The self consistent analytic solution of the Boltzmann equation for the ion distribution function (IDF) found in work [1] is used to study the perturbed wall sheath (PWS) formed near a surface at a negative potential. This sheath consists of a quasineutral presheath and a wall sheath where quasineutrality is substantially violated. The dependence of the PWS on plasma parameters and the dependence of the IDF on the charge exchange cross section and the real electron distribution function in plasma are studied. Experimental data of other authors, which had not prior interpretation, is described under the proposed model. It is shown that even in the case when in the wall sheath there are no collisions, the presheath remains experimenting collisions and that when there is no ionization in the PWS, for calculating the saturation current to a flat probe the Bohm´s criterion is not needed, while it is enough to take into account the edge effects. [1] Mustafaev A, Soukhomlinov V, Murillo O 2018 \textit{Physics of plasmas }Ion energy distribution function in the wall layer at a negative wall potential with respect to the plasma. N. 25, 013513. [Preview Abstract] |
|
GT1.00044: Control of the mechanical stress of AlN coatings using the electrical asymmetry effect in a large-area multi- frequency CCP Stefan Ries, Lars Banko, Julian Schulze, Alfred Ludwig, Peter Awakowicz CCPs are widely used in industrial applications for deposition and etching processes. For sputtering the control of the ion bombardment energy and flux at the target and at the substrate are highly relevant for the deposition of coatings with pre-defined properties. In single frequency CCPs the energies and fluxes of the ions are coupled with each other. Also in classical dual-frequency CCPs (e. g. 2 $+$ 27 MHz) the decoupling of these parameters is limited. Using the Electrical Asymmetry Effect (EAE) a nearly ideal decoupling of the ion energy and flux can be realized, if a fundamental frequency and its second harmonic are used with the relative phase angle between the two phase-locked frequencies as a control parameter. In this work a large-area multi-frequency CCP operated at 13.56 MHz and 27.12 MHz is used to control the mechanical stress of AlN coatings by variation of the ion energy bombardment onto the growing layer based on the EAE. At the same time the ion-to-growth flux ratio is kept constant. The range of ion energy control at the substrate without additional substrate bias as well as the potential of this plasma source for reactive RF sputter deposition of ceramic films are discussed. [Preview Abstract] |
|
GT1.00045: Surface photon flux dynamics during breakdown initiation Benjamin Yee, Edward Barnat, Nicholas Roberds, Matthew Hopkins The feedback of electrons from the cathode surface is critical for Townsend breakdown events. The source of these secondary electrons can vary due to changes in the electric field [1], and thus can be expected to change over the course of breakdown as space charge alters the electric field distribution. In a helium system, VUV emissions from resonance radiation are expected to contribute significantly to the breakdown process, but how this varies with time is unknown. In this work, we present preliminary measurements of the VUV flux dynamics in a helium discharge to the cathode surface. This is compared to 1D particle in cell simulations which use a kinetic approach [2] for describing the propagation of photons in the volume. These results are then discussed in the context of how secondary electron emission changes over time in a Townsend breakdown. [1] Z. Lj. Petrovi\'{c} and A. V. Phelps. Phys. Rev. E 80.1 (2009). [2] A. S. Fierro et al. J. Phys. D: Appl. Phys. 50.6 (2017). Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525. [Preview Abstract] |
|
GT1.00046: Plasma Perturbation by Cylindrical Probe and its Effect on Probe Diagnostics Valery Godyak, Natalia Sternberg Different kinds of Langmuir (LP), magnetic (B-dot-P) and microwave (MWP) probes are widely used for plasma diagnostics. Any probe diagnostics implies that the plasma local parameters inferred from the probe measurements are not distorted by the presence of a probe. However, inserting a probe into plasma leads to local and sometime to global perturbation of the plasma parameters. This can produce erroneous diagnostic results. The criteria for undistorted probe measurement are well understood for the electron current collection by the classical Langmuir probe [1]. However, in all other types of probes, neglecting plasma perturbation caused the by probes may lead to essential errors. Here we present an analysis of plasma perturbations by a cylindrical probe, commonly found in practice, for arbitrary collisionality parameter $\beta \quad = \quad \rho $/$\lambda $i, where $\rho \quad =$ a $+$ s is the probe-sheath radius, a is the probe radius, s is the sheath width, and $\lambda $i is the ion mean free path. Our results were obtained for cylindrical probes by solving numerically a set of fluid equations for neutral plasma with cold ions, taking into account ion inertia and a nonlinear ion friction force, similarly to for a spherical probe. An analytical solution for cylindrical probe in the collisionless case, $\beta \quad =$ 0, was also found. Plasma perturbation around a cylindrical probe appeared to be significantly larger than that for a spherical probe [2]. Effects of plasma depletion around cylindrical probes is discussed for different kinds of probe (LP, B-dot and MW) diagnostics.\\ \\ $[1]$ V. Godyak and V. Demidov, J. Phys. D: Appl. Phys. 44, 233001 (2011).\newline $[2]$ N. Sternberg and V. Godyak, Phys. Plasmas 24, 093504 (2017). [Preview Abstract] |
|
GT1.00047: Laser Diagnostic for Interrogating High Electron Densities in Low Pressure Plasma Environments Brian Z. Bentz, Edward V. Barnat This communication reports methods to apply laser-collision induced fluorescence (LCIF) diagnostics in regions with high electron density in low pressure helium environments. LCIF diagnostics allow quantitative and multi-dimensional interrogation of electron densities and temperatures. However, in low pressure plasma environments with electron densities above 10$^{\mathrm{12}}$ cm$^{\mathrm{-3}}$, overcoming the collisional quenching of fluorescence emission and the reduced lifetime of excited states remains a challenge, limiting the application of LCIF for studying arc discharges. Experimental and computational aspects are considered, including the rejection of scattered excitation light and optimization procedures for determining high electron densities. Initial LCIF images of arc discharges are presented and a collisional radiative model is used to interpret results. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy National Nuclear Security Administration under contract DE-NA0003525. [Preview Abstract] |
|
GT1.00048: Detection of anisotropy in the electron velocity distribution produced by electron cyclotron resonance heating using the polarization of helium atom emission lines Taiichi Shikama, Tatsuya Teramoto, Akira Ueda, Masahiro Hasuo The deviation of the electron velocity distribution (EVD) from isotropic Maxwellian is seen in various interesting plasma phenomena, and for a better understanding of the phenomena and detailed comparisons between experiments and kinetic simulations, it is necessary to develop a method that can measure the three-dimensional EVD shape (or the two-dimensional shape assuming axisymmetry around the magnetic field). However, this has not yet been established for the existing techniques. In this study, the anisotropy in the EVD was measured using the polarization of two helium atom emission lines, 2$^1$P–3$^1$D (668 nm) and 2$^3$P–3$^3$D (588 nm), in a helium electron cyclotron resonance (ECR) discharge plasma. A small polarization degree of less than 4\% was measured by adopting a temporal modulation technique. It was found that the polarization originated locally from around the ECR layer and that the anisotropic component of the EVD produced by ECR heating had an average kinetic energy of approximately 40 eV. [Preview Abstract] |
|
GT1.00049: Density of metastable O$_{2}$ (b$^{1}$$\Sigma$$^{+}$) molecules in an O$_{2}$ DC discharge measured by vacuum ultraviolet absorption and optical emission spectroscopy Jean-Paul Booth, Abhyuday Chatterjee, Olivier Guaitella, Dmitry Lopaev, Sergey Zyryanov, Tatyana Rakhimova, Dmitry Voloshin, Yuri Mankelevich, Nelson de Oliveira, Laurent Nahon, Colin Western The number density of O$_{2}$ (b$^{1}\Sigma^{+}$) molecules in the positive column of a dc discharge in pure O$_{2}$ was determined by high-resolution vacuum ultraviolet (VUV) absorption of the (4p$\pi^{1}\Sigma_u^{+}\leftarrow$ b$^{1}\Sigma^{+}$) band at 131.3nm (using the Fourier Transform Spectrometer at the DESIRS beamline at Synchrotron Soleil) and from the absolute intensity of the A-band (b$^{1}\Sigma^{+}$v=0\rightarrow^{3}$$\Sigma_g^{-}$,v=0) emission at 760nm. The 131.3nm absorption band is the only one that is well separated from O$_{2}$ X and a absorption bands. An analysis of the rotational structure of this heavily-perturbed band is presented as well as an $ab-initio$ calculation of the (previously-unknown) transition strength. The densities obtained by the two methods agree within 20\%, confirming the accuracy of the transition strength calculation. The O$_{2}$ b density increases with O$_{2}$ pressure up 2 Torr (reaching about 1 \% of the total gas density), then decreases at higher pressure. At low pressure the b density increases with discharge current, whereas the opposite trend is observed at high pressure. These observations can be explained by O$_{2}$ b quenching by O $^3$P atoms with a rate that increases with temperature. [Preview Abstract] |
(Author Not Attending)
|
GT1.00050: MEMS based IEDF/IADF sensing: Kinetic analysis of the ion dynamics inside the sensor Kerstin Roessel, Birk Berger, Thomas Mussenbrock, Marcel Melzer, Chris Stoeckel, Sven Zimmermann Ion energy distribution functions (IEDFs) and ion angular distribution function (IADFs) are key parameters in the context of plasma based processing of materials. This holds particularly true when knowledge-based plasma processing is demanded or preferred, rather than processing which relies on trial and error. For this purpose robust, non-perturbing, and reliable IEFD and IADF sensors are asked for. Ideal would be of course a sensor which combines both, IEDF and IADF measurements. In this contribution we present an IEDF/IADF sensor based on a MEMS (microelectromechanical systems) structure. We describe the working principle and show first experimental results. Finally, a detailed analysis of the ion dynamics based on kinetic simulation is provided. The question which is intended to be answered is whether the IEDF/IADF at the orifice of the sensor is really the same as the IEDF/IADF at the current collector. [Preview Abstract] |
|
GT1.00051: Spectroscopic Measurement of Plasma Parameters in a Helium ECR Discharge Produced under a Simple Cusp Field Akira Ueda, Taiichi Shikama, Tatsuya Teramoto, Takanori Higashi, Yohei Iida, Masahiro Hasuo An electron cyclotron resonance (ECR) discharge in a simple cusp field can produce a large volume steady-state plasma with relatively high electron density and degree of ionization (DOI). We have developed a spectroscopic method for evaluating the spatial distributions of the plasma parameters in a helium discharge. In this method, we measured the local intensity ratios between specific pairs of helium atom (He I) emission lines and compared the measured ratios with the calculated ones using a collisional-radiative (CR) model [1]. We determined the two-dimensional (axial and radial) distributions of the electron temperature and density, ground and metastable state helium atom densities, and the magnitude of photoexcitation in a plasma produced using 2.45 GHz and 800 W microwaves at 67 mPa. We found that electron density and DOI reach more than 2$\times$10$^{17} \mathrm{m}^{-3}$ and 20 $\%$, respectively, inside the closed ECR surface and investigated the validity of the evaluated atomic densities and the magnitude of photoexcitation by comparing with the theoretical predictions [2]. [1] A. Ueda, et al., Phys. Plasmas 25, 054508 (2018). [2] A. Ueda, et al., Appl. Phys. Lett 111, 074101 (2017). [Preview Abstract] |
|
GT1.00052: Measurement of atomic hydrogen density in the plasma boundary region of inductively coupled plasma by VUV absorption spectroscopy Deog Gyun Cho, A-Young Moon, yongsung You, Dal Hyeon Ryu, Se Youn Moon Plasma parameters can be analyzed by applying a VUV absorption spectroscopic method to the plasma through VUV light generated by He/H2 discharge. The VUV light source can provide a variable for measuring the atomic density of hydrogen based on the absorption spectroscopy. The VUV light source based on a hollow cathode discharge was used for an intense emission of 121.56 nm (Lyman-$\alpha )$ line. For accurate measurement of the hydrogen density, the self-absorption-applied vacuum ultraviolet absorption spectroscopy (VUVAS) was employed to Ar/H2 inductively coupled plasmas (ICP). The absolute density of hydrogen atoms was investigated for various Ar/H2 gas ratio in the ICP. In this way, the absorption of the hydrogen is about 35 {\%} at 50 mTorr and 100 W in inductively coupled plasmas (ICP). The hydrogen density was varied from 10$^{\mathrm{13}}$ §¯$^{\mathrm{-3}}$ to 10$^{\mathrm{14}}$ §¯$^{\mathrm{-3}}$ with respect to gas ratios with regard to absorption. [Preview Abstract] |
|
GT1.00053: Temporally resolved optical emission spectroscopy for studies of level-to-level discharges. Keith Hernandez, Matthew Goeckner, Lawrence Overzet Phase Resolved Optical Emission Spectroscopy (PROES) is a powerful tool for the study of radio frequency (rf) discharges. In continuous wave discharges, one needs to accurately trigger against the rf cycle so as to measure the temporal variation of the emission intensity. With modern high-speed cameras, this can result in excellent time resolution within the rf cycle. Such studies become more difficult in level-to-level discharges. This is because the trigger needs to be in reference to both the rf cycle and the level-to-level transitions. In this paper we will examine some of the experimental techniques that need to be employed in order to attain temporally resolved PROES (TR-PROES) in our m-GEC system. We show that the excitation function derived from TR-PROES for the Ar 750.4 nm line is approximately a single pulse (\textasciitilde 10 ns) within the 80 ns rf cycle (12.5 MHz). Initial results indicate that essentially only the strength of this excitation function increases during the plasma transition from low to high power. [Preview Abstract] |
|
GT1.00054: A new online training course in laboratory spectroscopic diagnostics developed at Auburn University. Ivan Arnold, Stuart Loch, Ed Thomas, Shawndra Bowers, Andrew Lee, Roland DeWitt, Jeremy Roberts, Asim Ali We report on the launch of a new web-based training course, ``Introduction to Spectral Diagnostics'', developed at Auburn University as part of the Connecting the Plasma Universe to Alabama (CPU2AL) grant funded by NSF EPCSoR. The course focuses primarily on the use of optical emission spectroscopy as a tool to diagnose plasma parameters using the Generalized Collisional-Radiative method. The course is designed using education research principles. We use self-paced, web-based training modules to provide students with the necessary background physics, mathematics, laboratory techniques, and introductory coding skills to implement these skills in a laboratory setting. The course includes some training videos on spectrometer use, interactive visualization tools, and video-based worked examples. The course is also designed for future expansion into more specialized spectroscopy topics. This course can provide digital certification for industry partners. It is offered as a fee-based service, but discounts are available for educational partners. The Auburn Online course development team was instrumental in providing instructional design, graphic design, software development, video production, and deployment of this training course [Preview Abstract] |
|
GT1.00055: High frequency ion fluctuation measurements using laser-induced fluorescence R. Hood, S. D. Baalrud, R. L. Merlino, F. Skiff We present ion fluctuation spectra, resolved spatially through the presheath region of a positively biased electrode using a recently developed field programmable gate array (FPGA)-based laser-induced fluorescence (LIF) system [1]. The system is able to measure ion fluctuation spectra up to 1 MHz using a correlation function method. Digital up/down counters which are synchronized to the laser modulation frequency are used to compute the background-subtracted LIF signal in real time. Data streams are then cross-correlated and added to the average correlation function that is used to compute the fluctuation cross power spectrum. Our measurements show strong ion fluctuations near 500 kHz (about half the ion plasma frequency). [1] S. W. Mattingly and F. Skiff, Rev. Sci. Instrum. 89, 043508 (2018), \underline {https://doi.org/10.1063/1.4995971}. [Preview Abstract] |
|
GT1.00056: Correlation between spatial distribution of wafer surface temperature and plasma parameters Yeong-Min Lim, Hyundong Eo, Chin-Wook Chung The spatial distributions of wafer surface temperature and plasma parameters were measured in an inductively coupled plasma(ICP) source with different gas pressures and powers. In the plasma process, the temperature of the wafer surface is a very important parameter as well as the plasma parameters such as plasma density and electron temperature. Because if the surface temperature distribution of the wafer is not uniform, problems such as uniformity of process profile or warpage may occur. In this work, the surface temperature of the wafer was measured with a platinum resistance thermometer and the spatial temperature distribution was obtained by placing thermometers in a concentric circle. The spatial plasma density and electron temperature were measured by wafer-type two dimensional probe based on the floating harmonic method. The spatial distribution of wafer surface temperature and the distribution of plasma parameters were compared and analyzed for their correlation. [Preview Abstract] |
|
GT1.00057: Fast Sweeping Probe System for Characterization of Spokes in ExB Discharges Valentin Skoutnev, Paul Dourbal, Eduardo Rodriguez, Yevgeny Raitses We have developed a rapidly swept, back-to-back 100kHz Langmuir probe system using a variable compensating capacitor scheme to study the temporal evolution of spoke oscillations in Penning discharges, Hall Thrusters and other ExB discharges. Experimental validation of the probe system is done at low and high sweeping frequencies in a stable Penning discharge. Then application of the probe system to measurements of plasma parameter fluctuations in a low frequency (4kHz) rotating spoke and an analysis method using the Hilbert transform are shown. [1] Cross-field electron transport induced by a rotating spoke in a cylindrical Hall thruster, C. L. Ellison, Y. Raitses and N. J. Fisch, Physics of Plasmas 19, 013503 (2012). [2] Transition in electron transport in a cylindrical Hall thruster, J. B. Parker, Y. Raitses, and N. J. Fisch, Applied Physics Letters 97, 091501 (2010). [3]Particle-in-cell simulations of anomalous transport in a Penning discharge, J. Carlsson, I. Kaganovich, A. Powis, Y. Raitses, I. Romadanov, and A. Smolyakov, Physics of Plasmas 25, 061201 (2018). [Preview Abstract] |
|
GT1.00058: Particulate imaging diagnostics in a gas-discharge plasma Anton Kananovich, J. Goree A method of detecting particulates in gas-discharge plasmas is video microscopy with laser illumination. A standard approach in analyzing the video images is the moment-method of measuring the positions of particulates, which makes it possible to measure their concentrations. To also measure their velocities, as a new development in this diagnostic, we employ the Crocker-Weeks\footnote{ J. Crocker and D. Grier \textbf{J. Colloid. Interf. Sci.} 179, 298} algorithm to track particles. We demonstrate this diagnostic method in a capacitively coupled RF argon plasma, under challenging conditions when a cloud of particulates is accelerated to high velocities by the electrical sheath around a moving wire. The micron-sized particulates were electrically levitated in the sheath above the lower electrode in the plasma chamber. [Preview Abstract] |
|
GT1.00059: Detection of fast neutral species by dissociative electron attachment Nicholas Braithwaite, Ade Ayilaran Bombardment by energetic neutrals derived from sheath-accelerated ions has been proposed as a means of stimulating anisotropic etching without the charge-induced side-effects associated with using the ions directly. The energetic neutrals are presumed to inherit the energy distribution of the parent ion flux. Using a mass-resolved mass spectrometer we detected fast neutral argon atoms and oxygen molecules formed by resonant charge exchange processes in an extraction volume separated by a fine mesh from a low pressure ICP in Ar-O2 mixtures. Within the spectrometer the fast neutrals are re-ionized by electron impact, before being passed into the energy and mass analyser sections of a Hiden EQP. A combination of signals with/without the reionizing electrons is used to differntiate fast neutrals from the residual parent ion beam. Neutral distributions are found to carry the same structural features as the parent fast ions. Moreover, the effective neutralisation of oxygen molecular ions was also revealed by reionizing the neutral molecular beam component by dissociative electron attachment: the negative atomic ions were observed at exactly half the energy of the parent molecular ion distribution, the remaining energy being in the recoil neutral DEA fragments. [Preview Abstract] |
|
GT1.00060: Optical Emission Diagnostics of High Energy Electrons Injected into a Low Temperature Plasma Juan Carlos Ruiz Bello, Shicong Wang, John Boffard, Chun C. Lin, Amy Wendt Motivated by the prospect of optimization and control of technological plasmas, a model to predict plasma emission spectra has been developed as an optical emission spectroscopy (OES) diagnostic for non-Maxwellian electron energy distribution functions (EEDF) in low pressure argon inductively coupled (ICP) RF discharges with an admixture of helium and neon. The high energy range of the EEDF is of particular importance due its role in rates for ionization, excitation and gas phase chemistry, and is explored in an ICP discharge equipped with a supplemental source of energetic electrons, produced by a set of biased heated filaments. The representation of the EEDF uses a sum of two functions dominated respectively by low- and high-energy ranges with adjustable parameters use to match predicted spectra to those recorded, for plasmas with varying pressure (2.2 - 77mTorr), injected electron current (0 - 1A) and filament bias voltage (0 - 50V). The analysis uses the intensities of two different sets of emission lines as inputs in a sequential process to determine the two functions comprising the EEDF. The resulting EEDF trends will be explored for evidence of onset of the beam-plasma instability. [Preview Abstract] |
|
GT1.00061: Evaluating the effects of tungsten on CFETR phase I performance Shengyu Shi, Xiang Jian, Vincent S. Chan An integrated modeling workflow using OMFIT is constructed to evaluate the effects of tungsten (W) impurity on China Fusion Engineering Test Reactor (CFETR) performance. Self-consistent modeling of W core density profile, accounting for both turbulent and neoclassical transport contributions, is performed based on the steady-state scenario of CFETR phase I (Wan \textit{et al} 2016 IAEA and 2017 \textit{Nucl.Fusion} 57 102009). It is found that the fusion performance degrades mildly with increasing W concentration. The main challenge arises in the sustainment of H-mode operation with significant W radiation. Assuming that the power threshold of H-L back transition is approximately the same as that of L-H transition, it is found that the W fraction at the plasma boundary is not allowed to exceed 2e-5 to stay in H-mode for CFETR phase I according to the scaling law proposed by Takizuka (Takizuka etc, Plasma Phys. Control Fusion, 2004). In addition, it is found that the tolerance of W concentration decreases with increasing pedestal density through a trade-off study of pedestal density and temperature. A future step is to connect the core simulation to W wall erosion modeling. [Preview Abstract] |
|
GT1.00062: The Particle in Cell Method Does Not Always Approximate the Vlasov Equation Brett Scheiner, Patrick Adrian Recently, the theory of instability enhanced (IE) collisions [1] has been used to explain ionic transport in multi-ion species sheaths [2] and the electron transport in Hall effect thrusters (HET)[3]. In studies of both phenomenon, IE collisionality was observed in particle-in-cell simulations. However, the PIC method is well documented for its inability to capture coulomb collisions, and as such it has been stated that the PIC method approximates the Vlasov equation. These results raise a discrepancy in how PIC is able to resolve the particle-wave collisions predicted by the IE collision theory, but unable to resolve coulombic particle-particle scattering. In this work, a PIC relevant collision operator is derived, including the PIC generalization of IE collisions. This collision operator illustrates that PIC exactly captures IE behavior provided that the grid resolves the real frequency and growth rate. Furthermore, the present theory demonstrates that under such circumstances PIC self-consistently captures quasilinear behavior, with the initial electric field fluctuations being due to the collisionality of the discrete particle motion, a feature that cannot be self-consistently captured by the Vlasov equation. [1] S. D. Baalrud, C. C. Hegna, and J. D. Callen Phy. Rev. Lett. 103, 205002 (2009) [2] S. D. Baalrud, T. Lafleur, W. Fox and K. Germaschewski PSST 24, 015034 (2015) [3] T. Lafleur, S. D. Baalrud, and P. Chabert Phys. Plasmas 23, 053502 (2016) [Preview Abstract] |
|
GT1.00063: Approaches for Argon-Xenon Interaction in Low Pressure Capacitively Coupled Plasmas Maximilian Klich, Sebastian Wilczek, Ralf Peter Brinkmann, Jesper Janssen, Thomas Mussenbrock, Jan Trieschmann For the simulation of plasma processes, in particular, for industrial applications, often suitable collisional input data is not available. In particular, ion-neutral collision cross sections for ions in non-parent gases are frequently unavailable. The purpose of this contribution is to provide solution concepts to remedy this issue. In order to investigate the influence of different collisional interaction approaches on the discharge, we choose a low pressure capacitively coupled argon-xenon discharge. The main advantage of this choice is its relatively simple chemistry which leads to a feasible number of considered reactions. A PIC/MCC simulation is used with two different approaches to the ion-neutral interaction. An approach based on the Langevin formalism and its capture cross section is compared to an approach that builds on a generalized Lennard-Jones potential. We show that different approaches for the interaction between argon ions and xenon neutrals and vice versa can lead to significantly different results. It is shown that even two approaches which are based on physically sound assumptions can lead to considerably different results. It is argued that particular caution is required concerning the choice of input data in these situations. [Preview Abstract] |
|
GT1.00064: Modeling Streamer Physics in 2D and 3D Wedge Pin-to-Plane Geometries via a PIC-DSMC Code Ashish Jindal, Chris Moore, Andrew Fierro, Matthew Hopkins Streamer propagation physics is investigated in 2D and 3D pin-to-plane geometries via a PIC-DSMC code with an air model$^{\mathrm{1}}$ using Townsend breakdown and streamer mechanisms via tracking excited state neutrals that can either undergo quenching or spontaneous photon emission collisions$^{\mathrm{2}}$. A 100 $\mu $m radius 1 eV-10$^{\mathrm{18}}_{\mathrm{\thinspace }}$m$^{\mathrm{-3}}$ plasma placed at the tip of a 100 $\mu $m hemispherical pin electrode (at 6 kV) in a 600 Torr air filled gap, 1.5 mm above a planar grounded cathode, seeds the domain. Prior 2D studies have shown that E/n can significantly impact streamer evolution$^{\mathrm{3}}_{\mathrm{.}}$ We extend the analysis to 3D wedge geometries (to limit computational costs) with wedge angle swept from 10$^{\mathrm{o}}$ to 45$^{\mathrm{o}}$ to examine its effect on streamer branching, propagation, and particle noise. 1. C.Moore \textit{et al}., \textit{Development of PIC-DSMC Air Breakdown Model in the Presence of a Dielectric}, ICOPS, 2016. 2. A.Fierro \textit{et al}., \textit{Discrete Photon Implementation for Plasma Simulations}, Physics of Plasma, 23, 2016. 3. A.Jindal \textit{et al}., \textit{Streamer Formation Near a Dielectric Surface with Variable Quantum Efficiency}, ICOPS, 2017. [Preview Abstract] |
|
GT1.00065: The LisbOn Kinetics Boltzmann solver Antonio Tejero-del-Caz, Luis Alves, Vasco Guerra, Duarte Goncalves, Mario Lino da Silva, Nuno Pinhao, Luis Marques, Carlos Daniel Pintassilgo This work presents the LisbOn KInetics Boltzmann solver (LoKI-B), a simulation tool to model non-equilibrium low-temperature plasmas produced from different gas mixtures for a wide range of working conditions, discussing its current status of development, evidencing functionalities and introducing test cases along with first results of benchmarking. LoKI-B (to become open-source) provides the solution to the homogeneous and stationary two-term electron Boltzmann equation including: first and second-kind collisions, electron-electron collisions and spatial or temporal electron density growth models to account for the production of secondary electrons born in ionisation events. On output, it yields the electron energy distribution function and different electron macroscopic parameters. The simulations can be made for any gas mixture, accounting for the electronic, vibrational and rotational internal degrees of freedom of the atomic / molecular excited states present in the plasma, and it will be publicly released by the end of 2018. [Preview Abstract] |
|
GT1.00066: Kinetic Simulation of Hight Intensity Vacuum Beam Propagation Brandon Medina, Chris Moore, Matthew Bettencourt, Keith Cartwright, Timothy Pointon, Edward Phillips, Kate Bell, Jacques Gardelle, David Hebert As part of the validation effort for Sandia's new EM PIC-DSMC plasma code EMPIRE [1], we have begun to simulate high intensity vacuum beam propagation. Specifically, we are modeling the CESAR and RKA beam experiments [2], starting with vacuum propagation and proceeding to beam propagation through a low-pressure Ar background gas. EMPIRE models both charged particles and neutrals as computational particles that can move and collide with one another allowing for self-consistent evolution of the neutral gas as the e- beam propagates and interacts with the background gas. In the current work we will show comparisons for the current and beam radius to the CESEAR beam experiments. In addition, we will investigate EMPIRE's performance/scaling on multiple architectures (CPU's, MIC's, and GPU's) for the simulations. 1. Markosyan, A. et al, "Method of manufactured solutions for verification of particle-in-cell simulations'', 45$^{\mathrm{th}}$ ICOPS, June 24-28 2018. 2. Gardelle, J. et al., ``Revisiting the propagation and focusing of a high intensity electron beam in a low-pressure gas cell'', 44th ICOPS, May 21-25, 2017. [Preview Abstract] |
|
GT1.00067: Plasma Chemistry Round Robin: Progress Report Miles Turner A plasma chemistry model is usually formulated as a set of conservation equations for the number densities of species of interest, coupled in some way to a solution of the Boltzmann equation to determine the rates of electron impact processes. In isolation this is one of the most basic and widely used plasma models, but such models also form an important component of more elaborate schemes, such as multi-dimensional simulations. Consequently, solving chemistry models is a basic task of computational low-temperature plasma physics. At GEC70, a report was made on a round robin exercise comparing different solutions of an elementary plasma chemistry model. Surprising disagreement was found. This paper reports on continuing investigations into the origin of these disagreements, including comparisons of various solution schemes with an exact stationary solution of the a coupled system of the Boltzmann equation and a simple plasma chemistry model. [Preview Abstract] |
|
GT1.00068: Benchmarks for Two Dimensional Particle-in-Cell Simulations Miles Turner, Denis Eremin, Peter Hartmann, Aranka Derszi, Zoltan Donko, Romain Lucken, Pascal Chabert, Thomas Mussenbrock, Peter Stolz Code correctness is a matter of concern in any computational investigation. The strongest assurances of correctness are obtained by comparison of code calculations with exact solutions, but this approach is not yet feasible for all categories of code. An alternative in this case is benchmarking, in the sense of comparison of a number of codes solving the same problem. In this presentation, we will describe a suite of benchmarks aimed at two dimensional particle-in-cell simulations of low-temperature plasmas, in which collisional phenomena are necessarily included. The initial benchmarks address Cartesian geometries with a variety of different combinations of boundary conditions. We will describe the benchmark cases, and report on progress towards consistent solutions obtained with several independent codes. [Preview Abstract] |
|
GT1.00069: The influence of the impurities N2 in the working gas on the performance of the atmospheric pressure plasma jet surrounded by ambient N2 Jiang Yuanyuan, Wang Yanhui, Wang Dezhen A two-dimensional self-consistent fluid model is used to study the characteristics of the atmospheric pressure plasma jets under different impurities level in the working gas with a single ring electrode. A neutral gas transport model was employed to predict the molar fraction distribution of He and ambient N2 in the system. There were then used in a plasma dynamics model to investigate the characteristics of the plasma jet under different impurities molar fraction during its propagation inside the dielectric tube and outside the dielectric tube. When the molar fraction of N2 increasing from 0.001\% to 1\%, the ionization rates of electrons direct impact ionization of He increase because of the increasing of the high energy electrons in the dielectric tube. At the same time, the ionization rates of the electrons direct impact with N2 increasing because the lower ionization energy of N2 compared with He. In the tube the density of the He2+, He* decrease due to the increasing of the consuming path, which is opposite to the N2+ and N2*. The velocities of the plasma jets increase in different impurities level with the increasing of the electric field in the front of the ionization head. The plasma jets change from a circular structure to a more uniform structure. [Preview Abstract] |
|
GT1.00070: The role of electron-electrode collisions and secondary electrons in radio-frequency breakdown Marija Puac, Antonije Djordjevic, Zoran Lj Petrovic While radio-frequency (RF) plasmas have been studied in great detail, the physical foundation of the RF breakdown is less known and is the subject of this paper. Due to the alternating field, the RF breakdown can be supported by electrons only. Thereby, the voltage breakdown curve has a skewed ``U'' shape with a double-valued region at low pressures [1]. The effects at the electrodes can complement the shape of the breakdown curve by banding its left-hand side. Even a second minimum can be noticed in some gases. At the surface of the electrodes there are two groups of effects. The first group comprises electron collisions with the electrode that involve elastic reflection, inelastic reflection when electron loses a portion of its incoming energy, and electron absorption by the electrode. The second group of effects is the emission of secondary electrons by electrons or heavy particles that leads to multipacting at low pressures and high voltages. Each influence on the voltage breakdown curve has been examined separately. [1] M. Pua\v{c}, D. Mari\'{c}, M. Radmilovi\'{c}-Radjenovi\'{c}, M. \v{S}uvakov and Z. Lj Petrovi\'{c}, Plasma Sources Sci. Technol., https://doi.org/10.1088/1361-6595/aacc0c (2018). [Preview Abstract] |
|
GT1.00071: The LisbOn Kinetics tool suit Antonio Tejero-del-Caz, Luis Alves, Vasco Guerra, Duarte Goncalves, Mario Lino da Silva, Nuno Pinhao, Luis Marques, Carlos Daniel Pintassilgo This work presents the LisbOn KInetics (LoKI) tool suit, a set of simulation tools to model non-equilibrium low-temperature plasmas, produced from different gas mixtures for a wide range of working conditions. LoKI comprises two modules: a Boltzmann solver, LoKI-B (to become open-source; see companion abstract), and a chemistry solver, LoKI-C. Both modules can run as standalone tools or coupled in a self-consistent manner. LoKI-B provides the solution to the homogeneous and stationary two-term electron Boltzmann equation, while LoKI-C gives the solution to the system of zero-dimensional (volume average) rate balance equations for the heavy species, charged and neutral, present in the plasma. For stationary discharges, when both modules are activated, the reduced maintenance electric field (or an equivalent parameter, such as the electron temperature) is self-consistently calculated as an eigenvalue solution to the problem, under the assumption of quasi-neutrality. [Preview Abstract] |
|
GT1.00072: Comparative study on atmospheric-pressure helium plasma jets driven by pulsed voltage with different polarity Wang Yanhui, Jiang Yuanyuan, Zhang Jiao, Wang Dezhen Atmospheric-pressure plasma jets, have shown immense potentials for numerous industrial and biomedical applications. To understand the physical and chemical processes taking place in plasma jet, numerous studies have been carried out, but, there are still many aspects to be explored further. In this paper,we focus on the effect of pulsed-voltage polarity on the characteristics of the atmospheric pressure helium plasma jets propagating into humid air. A two-dimensional neutral gas transport model and a plasma dynamics model are used in this study. Simulation results show that the positive jet looks like a “bullet”, but the negative jet likes a “sword” and more diffusive. The electric field in the positive jet head is much higher than the negative one, but it is reversed in plasma channel. The velocity of the negative jet in the tube is higher than the positive one, but out of the tube, the velocity of positive jet becomes higher than the negative one. The primary reactive species densities in negative jet are higher than those in positive one. The dominant physics associated with the formation and propagation of positive and negative plasma jets are analyzed. In addition, the behaviors of the second discharge at the falling edge of the voltage pulse in the both polarity plasma jet [Preview Abstract] |
|
GT1.00073: Multi-physics simulation of the COST APPJ in the MOOSE framework Corey DeChant, Shane Keniley, Davide Curreli, Katharina Stapelmann, Steven Shannon The COST atmospheric pressure plasma jet has been modelled using the Zapdos application in the MOOSE framework and compared to previous experimental and simulation efforts. The Zapdos application has been expanded to enable 2D simulation using a plurality of chemical species and time varying electrode potentials. This expanded application is combined with a Navier-Stokes fluid model to study the COST APPJ. This work focuses on expanding Zapdos to multidimensional plasma modeling by introduction more scalability of units than is currently available and incorporation of a simplified plasma chemistry module. The principle behind this method was by scaling the coefficient used in the physical equations, the values in the Jacobian matrix would be reduced resulting in a converged solution. With the proper scaling, 2D results for plasma parameters can be obtain for both a DC discharge and a sinusoidal voltage driven RF discharge. To validate these models, results will be compared to both previously published experimental data and simulation results from different frameworks. [Preview Abstract] |
|
GT1.00074: Self-Consistent Circuit Model for Pulsed Inductively Coupled Plasmas Carl Smith, Joel Brandon, Steven Shannon, Peng Tian, Mark Kushner, Sang-Ki Nam Pulsed inductively coupled plasma discharges show promise in industry due to increased chemistry control and decreased substrate damage. Coupling circuit effects from power delivery and antenna structures with a self-consistent plasma model enable an integrated design approach that includes the entire power delivery network. This model has demonstrated distinct regimes where the power delivery network can dictate transient properties moreso than the behavior of the plasma: \textit{1)} Circuit effects depress the magnitude of delivered power and the time response of $T_{e}$, and $n_{e}$ during the pulse onset. Novel approaches for power coupling optimization and plasma transient control are identified enabling passive control of \textit{dn}$_{e}$\textit{/dt} and \textit{dT}$_{e}$\textit{/dt}. \textit{2)} The influence of modest dissipative elements in the power delivery network and antenna on the plasma transient behavior are shown to demand a more detailed treatment than traditional insertion loss type models. \textit{3)} A methodology for matching steady state and transient conditions to experimental data by scaling the effective area term is used as part of an experimental validation effort and may be extended to steady state models. [Preview Abstract] |
|
GT1.00075: Speed-Limited Particle-in-Cell Modeling of Plasma Discharges Thomas G. Jenkins, Andrew M. Chap, John R. Cary, Gregory R. Werner Speed-limited particle-in-cell (SLPIC) modeling is a new simulation technique [G. R. Werner & J. R. Cary, arXiv:1511.08225 (2015)] for efficiently modeling plasmas characterized by low-velocity kinetic processes. Numerical constraints (e.g. timestep limitations associated with particle cell-crossing times) often place challenging restrictions on PIC models of these systems, since even though the physics of interest is predominantly driven by slower particles, it is the fastest particles which dictate the timestep constraint. In SLPIC, artificial speed-limiting behavior is imposed on fast particles whose kinetics do not play a meaningful role in the system dynamics. Larger simulation timesteps, and more rapid modeling of such discharges, are thus enabled. In this poster we'll demonstrate the use of SLPIC methods in a number of plasma discharge simulations using the VSim code [C. Nieter & J. R. Cary, JCP 196, 448 (2004)], including collisionless and collisional sheath formation (for which SLPIC has achieved up to 7x overall speedup and comparable accuracy) and the free expansion of plasma into vacuum (2.5x speedup/comparable accuracy). In addition, we'll discuss a potential application of SLPIC in modeling plasma opening switches, and the challenges associated with such modeling. [Preview Abstract] |
|
GT1.00076: Interface model of plasma-surface interactions using artificial neural networks Florian Krueger, Tobias Gergs, Thomas Mussenbrock, Jan Trieschmann Plasma based materials processing relies on both the direct impact of the gaseous plasma on the solid surfaces and the feedback contribution of sputtered atoms from the surfaces onto the plasma. A self consistent theoretical description of this interaction is tremendously challenging due to the intrinsic time and length scales of the systems, which span several orders of magnitudes. Therefore, direct coupling of two distinct models is infeasible. Alternative strategies are required. In this work, an interface model based on artificial neural networks is suggested and tested. A multilayer perceptron network has been trained on data of Ar sputtering an Al-Ti composite target. The data set has been obtained using TRIDYN developed by Moeller and Eckstein [1]. It is demonstrated that the trained network can be successfully exploited to predict the energy distributions and angular distributions of sputtered and reflected particles for arbitrary energy distributions of impinging particles. \newline [1] W.\ Moeller, W.\ Eckstein, Nucl.\ Instr.\ and Meth.\ B2, 814 (1984) [Preview Abstract] |
|
GT1.00077: Floating potential of emitting surfaces in plasmas with respect to the space potential Brian Kraus, Yevgeny Raitses Strongly emitting surfaces affect the plasma-wall interaction in many applications, for example in divertors and limiters in fusion devices, emissive probes, and thermionic cathodes. The potential difference between a floating emitting surface and the surrounding plasma strongly impacts particle and energy transport to the surface. A variety of sheath models describe this potential difference, including the space-charge-limited sheath, the electron sheath with high emission current, and the inverse sheath with ion trapping. Our measurements reveal that each of these methods has its own regime of validity. We determine the charge state of an emissive filament immersed in a variety of plasmas, emphasizing variations in emitted current density and neutral particle density. Depending on the regime chosen, emitting surfaces can float positively or negatively with respect to the plasma potential. [Preview Abstract] |
|
GT1.00078: An approximate Monte Carlo method for modeling radiation transport during DC plasma breakdown Nicholas A. Roberds, Matthew M. Hopkins, Andrew Fierro, Benjamin T. Yee Line emission radiation in the UV range can play an important role in Townsend-type DC plasma breakdown [1]. A Monte Carlo method can be used to model the radiation transport numerically. Monte Carlo methods make few approximating assumptions and provide very accurate results for a wide range of cases [2]. Many systems of interest are optically thick for resonance radiation (photons emitted in transitions to the ground state). The very short photon mean-free-paths (MFPs) and short time intervals ($\tau )$ between emission and absorption place severe spatial and temporal resolution constraints on explicit Monte Carlo methods. We present an explicit Monte Carlo method with additional simplifying assumptions that relax the spatial and temporal resolution requirements. The model has been implemented in Aleph, which is a particle-in-cell direct simulation Monte Carlo (PIC-DSMC) code. [1] A. Fierro, C. Moore, B. Scheiner, B. Yee and M. Hopkins, J. Phys. D 50.6 (2017), 065202. [2] A. F. Molisch and B. P. Oehry, ``Radiation Trapping in Atomic Vapours'', p. 94, Oxford University Press, Oxford, 2006. [Preview Abstract] |
|
GT1.00079: Electron-induced secondary electrons in low-pressure capacitively coupled radio-frequency plasmas Benedek Horvath, Julian Schulze, Katharina Noesges, Sebastian Wilczek, Zoltan Donko, Aranka Derzsi We investigate the effects of secondary electrons (SEs) induced by electrons on the discharge characteristics in low-pressure single-frequency capacitively coupled plasmas (CCPs) by Particle-in-Cell/Monte Carlo Collisions simulations. Such SEs ($\delta$-electrons) were found to have a remarkable influence on the plasma parameters in argon at 0.5 Pa and 6.7 cm gap between SiO$_2$ electrodes (B. Horv\'ath et al. 2017 \textit{Plasma Sources Sci. Technol.} \textbf{26} 124001). Here we study the impact of $\delta$-electrons on the ionization dynamics and plasma parameters at various pressures and voltage amplitudes, assuming different SE yields for ions ($\gamma$-coefficient). The voltage amplitude, the gas pressure and the value of the $\gamma$-coefficient affect the role of $\delta$-electrons in the ionization dynamics. While their effect is most striking at low pressures, high voltage amplitudes and high $\gamma$-coefficients, in the whole parameter regime investigated here the realistic description of the electron-surface interaction changes significantly the computed plasma parameters compared to results based on a widely used simple model for the description of the electron-surface interaction. [Preview Abstract] |
|
GT1.00080: Benchmark test cases for low temperature magnetized plasma modeling Jean-Pierre Boeuf, Andrei Smolyakov, Gerjan Hagelaar, Kentaro Hara Cross-field plasma discharges play an important role in space propulsion and material processing. Such low-temperature magnetized plasmas are typically non-equilibrium, moderately ionized, and partially magnetized, which exhibits unique physical processes compared to other plasma phenomena. Low temperature magnetized plasma modeling (LANDMARK) project [https://www.landmark-plasma.com/] has been established as a subset of the previous ExB workshops. The purpose is to offer a framework where different computational models can be tested and benchmarked against other codes. We propose three standard test cases for cross-field discharge modeling tools, including a one-dimensional (1D) azimuthal kinetic simulation of electron cyclotron drift instability (ECDI), a 2D azimuthal-axial kinetic simulation of a dc discharge in the presence of ECDI, and a 1D axial fluid model of Hall thruster discharge plasmas. In the poster presentation, the test cases and numerical results will be discussed. [Preview Abstract] |
|
GT1.00081: Verification of Collisional Models in the Aleph PIC-DSMC Code Jeremiah Boerner, Jose Pacheco, Anne Grillet Particle collisions play several important roles in plasma applications. Excitation and ionization collisions generate the plasma using kinetic energy extracted from applied electric fields. Elastic and inelastic collisions diffuse the flux of momentum and energy in charged and neutral species. Relaxation and recombination collisions often emit light, which enables a variety of experimental diagnostics. Therefore, high fidelity plasma models require accurate methods for simulating collisional dynamics. This work verifies key aspects of the collisional interaction algorithms in Aleph through a series of validation tests. Aleph is a massively parallel, 3D unstructured mesh, Particle-in-Cell (PIC) code, developed to model low temperature plasma applications. The interaction rates and particle selection methods are verified for Direct Simulation Monte Carlo (DSMC) two body interactions, three body interactions, and one body spontaneous reactions. The scattering kernels are verified for uniform isotropic and anisotropic screened Coulomb models. Favorable comparisons establish confidence in Aleph's capability to accurately model the suite of particle collisions.\\ \\Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. [Preview Abstract] |
|
GT1.00082: A multi-term Boltzmann equation based global model for low temperature plasmas Jacob Stephens This report demonstrates the application of a time-dependent multi-term Boltzmann equation (BE) model, utilized as the central construct of a global model for low temperature plasma modeling. As opposed to utilizing pre-computed solutions to the BE, this model solves the BE self-consistently with global model. This also eliminates the energy conservation equation regularly employed in global models of low temperature plasmas. As a brief demonstration, the BE based global model is utilized for the efficient prediction of high power microwave induced plasma formation over a range of experimental conditions. [Preview Abstract] |
|
GT1.00083: Monte Carlo simulations of ion energy and angular distributions at the extreme wafer edge Ananth Bhoj, Zhongmin (Andy) Xiong, Kunal Jain Plasma processing is primarily used in microelectronics fabrication to enable anisotropic etching, so the knowledge and control of ion energy and angular distributions (IEADs) is necessary to maintain the feature critical dimensions. In this work, we present a computational investigation of IEADs in a model rf-CCP resembling an industrial reactor with particular focus on the geometric details of the extreme wafer edge region. Since probes cannot access these regions, simulations may help provide insights and guide geometry and design optimization. The multiphysics modeling platform CFD-ACE$+$ used in this work contains an upgraded postprocessor Monte Carlo Module (MCM) to compute the IEADs. The procedure involves running an rf CCP plasma simulation to convergence, then restarting the solution with the MCM enabled to compute IEADs at locations of interest. In the latest improvements to the MCM, adaptive MCM meshes are automatically generated around the output locations of interest on the wafer surface. The benefits of this method include better memory usage, lower CPU solution time and visualization of IEDs in the plasma from the pre-sheath to the wafer. Trends in IEADs at the extreme wafer edge in an Ar discharge with rf bias and pressure are discussed. [Preview Abstract] |
(Author Not Attending)
|
GT1.00084: Numerical simulation and stability analysis of a spark discharge high-voltage switch. Vasily Kozhevnikov, Vladislav Igumnov, Andrey Kozyrev, Aleksandr Kokovin, Andrey Zherlitsyn, Evgeniy Kumpyak In this work, we propose the numerical theoretical model for the simulation and stability analysis of a spark-gap high-voltage switch. These devices are of particular interest as commutators of high energy in facilities intended for technological applications, mainly high-current RC-generators. For such switches, a stability problem of voltage triggering is critical. We propose an accurate theoretical model of the high-voltage high-current switch based on the drift-diffusion theory of a multicomponent discharge plasma in the atmospheric-pressure air. The simplified plasma kinetic scheme with the reduced number of components (namely, N$_{\mathrm{2}}^{\mathrm{+\thinspace }}$, O$_{\mathrm{2}}^{\mathrm{+}}$, N$_{\mathrm{4}}^{\mathrm{+}}$, O$_{\mathrm{4}}^{\mathrm{+}}$, O$_{\mathrm{2}}^{\mathrm{+}}$N$_{\mathrm{2}}$, O$_{\mathrm{2}})$ is implemented to model air discharge atmosphere. In order to investigate the stability of triggering depending on initial conditions profile first, we perform one-dimensional simplified simulation, and then the realistic two-dimensional axisymmetric model of the spark gap is studied. Within the framework of this model, the electrophysical parameters of the spark gap are calculated, which are in agreement with the available experimental observations. The developing of the proposed model opens possibility to investigate the triggering stability depending on the initial preionization profile of the gas-discharge gap. [Preview Abstract] |
|
GT1.00085: Comparison of PIC-MCC and fluid simulations for the description of ccrf discharges Hanno Kaehlert, Michael Bonitz, Markus Becker, Detlef Loffhagen We compare the results of Particle-in-Cell simulations with Monte-Carlo collisions (PIC-MCC) with different fluid models for the description of capacitively coupled radio-frequency (ccrf) discharges. Fluid models have the advantage of being computationally much less expensive than PIC-MCC simulations but are potentially less accurate in their predictions for the discharge physics. Compared to the classical fluid model, a novel fluid description with an improved drift-diffusion approximation for the electrons yields results that are in good agreement with the PIC-MCC data~[1]. Here, the applicability range of the fluid models is explored for an extended parameter regime.\\ $[1]$ M. M. Becker, H. K\"ahlert, A. Sun, M. Bonitz, and D. Loffhagen, PSST \textbf{26}, 044001 (2017) [Preview Abstract] |
|
GT1.00086: Approaches for Modeling Self Organization in Plasmas. Luis Martinez, Akash Dhruv, Elias Balaras, Michael Keidar Self-organization of plasmas has been reported for various applications in which plasmas interact with media. Our current work investigates interactions of cold atmospheric plasma (CAP) with biological media which occur when a CAP jet impinges onto the surface of interest. As part of our research, we study the principle drivers of non-equilibrium which lead to plasma self-organization, both by conducting experiments and by modeling plasma-media interactions. To test parameters of interest, experiments vary media targets, gas types and flow rates, voltages, electrode configurations, and gaps between jet nozzle and target. The model simulates the geometry and evolution of these experiments by solving a coupled system of transient Navier-Stokes and species transport equations accounting for diffusion, advection, reaction, generation, and supply for each species of interest on a PARAMESH block-structured adaptive mesh refinement (AMR) grid. Additionally, a mechanism for streamer contact spot advection on a target's surface is proposed and simulated by using a level-set technique which defines the boundary between streamers and targets. Preliminary results indicate that experimental parameters change the frequency of ionization wave fronts in the discharge column, spectrum of reactive oxygen and nitrogen species, and electric fields induced on the media from the accumulation of charges. [Preview Abstract] |
|
GT1.00087: Two-dimension numerical simulation of a micro plasma electron source at moderate pressure C Lan, A Khrabrov, I. D. Kaganovich, S Gershman, Y Raitses A micro plasma electron source, which consists of a flat cathode and a 1 mm apart cylindrical anode [1], is modeled and studied by two-dimension particle-in-cell simulations. The discharge is based on a cold cathode glow discharge (GD) operating in a dc steady-state mode at a moderate pressure around 2 Torr. The simulations mainly focus on the two-dimensional features of the discharge and two anodes of different length are compared. The simulation results confirm the non-equilibrium nature of this micro discharge downstream the anode, and the electron flux with an enhanced high energy tail (\textgreater 5 eV) is observed downstream.~The simulation results also show that compared with short anode, long anode absorbs much more high energy electrons striking on the anode surface, leading to the reduction of the fraction of high energy electrons.~A detailed comparison between simulations and experimental results will be presented. ~[1]~S. Gershman~and~Y. Raitses,~J. Phys. D: Appl. Phys.~51,~235202 (2018) [Preview Abstract] |
|
GT1.00088: A New Compact Surface Wave Plasma Source for Multiple Plasma Source Setup Aimed for Depositing Large-area Diamond. Hyun Jong You, Oleksii Girka The large size and high quality diamond production has been one of the most challenging tasks for the diamond industry. A compact surface wave plasma source is newly developed as a part of multiple plasma source setup for large-area microwave (MW) plasma generation. The large-area MW multiple plasma source setup will be used for the large size diamond CVD. The single source is made to be compact and efficiently generate plasma in wide range of operating gases' compositions and pressures. In this source, the microwave can be fed by a waveguide or by a coaxial structure, forming an intense microwave field at the plasma generation region by a water-cooled coupling rod. Alumina plasma region of a conical crucible-type is surrounded by an aluminium nitride (AlN) cover. The AlN cover and downstream plasma region are cooled by the coupling rod and a tightly fitted aluminium (Al) water jacket. Efficient microwave coupling is significant advantage of the source since microwave electric field does not interact with any obstacles like cooling media as it is in surfaguide sources. The aim of the work is to present the new source design, results of microwave simulation, plasma generation and characterization for the CVD process of diamond films. [Preview Abstract] |
|
GT1.00089: Multi-point microwave discharge in methane-air gases induced by pulsed microwave power Cheng Liu, Guixin Zhang, Hong Xie Application of microwave plasma offers a promising method to induce faster combustion in internal combustion engine. In this study, microwave multi-point discharge and ignition had been confirmed via high-speed schlieren imaging technique in methane-air gases. The experiment was implemented with the microwave resonant ignition system and the schlieren optical system. 2ms-3000W-2.45GHz microwave pulse was employed as the ignition energy source to produce micro-discharge and initial flame kernel in the combustion chamber. The reflected schlieren imaging was used to present the flame development process with a high speed camera. A quartz glass coated with indium tin oxide (ITO), which ensured the sufficient microwave reflection characteristics and light transmission respectively, was used as the bottom of the microwave resonant chamber. Ignition experiments were conducted at high pressure of 2 bars of stoichiometric methane-air gases. It can be seen that in schlieren images that flame kernels were generated at more than one location simultaneously and flame propagated with different speeds in the combustion chamber. And, the number and the location of discharge was investigated in the experiment. [Preview Abstract] |
|
GT1.00090: DC glow discharge investigation in CO2 by optical emission spectroscopy V.A. Lisovskiy, H.H. Krol, S.D. Dudin, P.A. Ogloblina In the present work a glow discharge in carbon dioxide gas was studied by optical emission spectroscopy. Particular attention is paid to the processes occurring in the negative glow, the positive column and the anode glow -- the most bright parts of the discharge. It is shown that in the negative glow bright emission lines of both atoms and molecules and their ions are observed: atomic oxygen 777 nm, 844 nm and 926 nm; lines of atomic oxygen ions O$^{\mathrm{+}}$ (391 nm); bright lines of CO (the Angstrom system) and O$_{\mathrm{2}}$ (Schumann-Runge system) molecules; lines of the molecular ion CO$^{\mathrm{+}}$ (427 nm, Comet-tail system). Also, the molecular continuum (approximately 350 nm to 800 nm) is clearly pronounced. In the positive column, the lines of ions and atoms disappear, against the background of a weak continuum, only the emission of CO$_{\mathrm{2}}$, CO and O$_{\mathrm{2}}$ molecules is seen. However, in the anode glow the intensity of the continuum, the molecular and atomic lines increase significantly and may even exceed the corresponding intensities in the negative glow. Axial intensity profiles of a number of characteristic emission lines have been measured for the entire interval between the cathode and the anode. [Preview Abstract] |
|
GT1.00091: DC glow discharge in nitrogen with hollow cathode or anode V.A. Lisovskiy, R.O. Osmayev, D.I. Khilko, V.D. Yegorenkov This paper reports the experiments we have performed with a ``hollow cathode and a flat anode'' and a ``hollow anode and a flat cathode''. The discharge with a hollow cathode may burn at low pressure (below 0.1 Torr) in the high voltage mode with an electron beam that can attain the anode. With the gas pressure increasing the electron beam does not leave the cavity, and the discharge is burning in the glow mode. But with the voltage increasing a ``hollow'' mode sets in when the cathode cavity is filled with the negative glow. The transition between the ``glow'' and ``hollow'' modes possesses a hysteresis pattern. At still higher nitrogen pressure (above 0.5 Torr) the total thickness of two cathode sheaths comprises only a small part of the cathode cavity, the negative glow in the form of a thin film covers the cathode surface, the ``hollow'' mode ceases to play a remarkable role. When we have employed a hollow anode and a flat cathode the flow of fast electrons comes only out of the flat cathode sheath. As the area of the flat cathode is much less than one of the hollow cathode, then using the flat cathode and the hollow anode one can get the discharge current less than one with the hollow cathode. [Preview Abstract] |
|
GT1.00092: Controll of microwave propagation in and around cylindrical plasma with additional anisotropic layers Yuki Kabe, Akinori Iwai, Alexandre Bambina, Shigeyuki Miyagi, Osamu Sakai Microwaves are used for wireless communication though the range of frequencies, but their propagation paths are limited with poor controllability, which causes confusion between antennas. Cloaking effects which reduces scattering waves [1] were demonstrated by using solid metamaterials whose anisotropic and space-gradient refractive index was critical. However, the property of cloaking is fix by the design. To control the propagation path of microwaves dynamically using a plasma generated in a glass column, we observed to reduce the reception intensity of the antenna surrounded by the plasma by 80 {\%} for 2.4 GHz waves. We found that the capacitively coupled plasma (CCP) enhanced reduction rate better than our previous result [2], and confirmed reduction of scattering waves by insertion of metamaterials with anisotropic permeability by the numerical simulation [3]. We confirmed experimentally significant reduction of the scattering waves in the combination of the CCP and metamaterials. [1] R. A. Shelby, D. R. Smith, S. Schultz, Science 292, 77 (2001). [2] O. Sakai, S. Yamaguchi, A. Bambina, A. Iwai, Y. Nakamura, Y. Tamayama and S. Miyagi, Plasma Phys. Control. Fusion 59, 014042 (2017). [3] A. Bambina, S. Yamaguchi, A. Iwai, S. Miyagi, and O. Sakai, AIP Advance 8, 015309 (2018). [Preview Abstract] |
|
GT1.00093: Pseudospark discharge as a sheet electron beam source for mm-wave generation K Ronald, H Yin, A Cross, L Zhang, W He, A Phelps, G Shu, J Zhao, G Liu, Y Yin A pseudospark discharge supports extremely high currents with short rise times through its hollow cathode structure [1]. An electron beam generated during the discharge process possesses high current density and brightness, and may propagate through sub-millimeter planar structures via ion channel focusing. This makes it an attractive electron beam source for millimeter-wave generation [2]. A 32 kV, 5 A pseudospark-sourced sheet electron beam has been used to drive a planar slow wave extended interaction oscillator (EIO) structure [3]. The EIO produced \textasciitilde 1.2 kW peak output power at 105 GHz, an increase of six times in the measured power compared with a W-band EIO based on a pseudospark-sourced pencil electron beam [4]. Such a methodology offers a promising solution for portable, low-cost and powerful millimeter-wave and terahertz-wave radiation sources. Results from the experimental demonstration of this novel radiation source will be presented. [1] H. Yin, et al., J. Appl. Phys., 90, 2001, 3212-3218, [2] W. He, et al., Appl. Phys. Lett., 107, 2015, 133501, [3] G. X. Shu, et al, IEEE Trans. Electron Devices, 63, 2016, 4955-4960, [4] J. Zhao, et al, Phys. Plasmas, 24, 2017, 060703. [Preview Abstract] |
|
GT1.00094: Design and measurement of a Penning discharge plasma K Ronald, T Heelis, M King, S McConville, D Speirs, K Wilson, C Robertson, A Phelps, M Koepke To enable experiments investigating beam-plasma interactions [1,2] plasma columns from 20cm to over 1m in length were required in cylindrical waveguides of diameters 5-8 cm. Penning discharges operating up to 10$^{\mathrm{-3}}$mB with bias voltages from 500 V to a few kV and currents up to a few 10's mA were created to address this requirement. Langmuir probes modify the discharge behavior, whilst the magnetic field made interpretation of the probe IV characteristic difficult, complicating diagnostics. The plasma density at the end of the column was inferred by observing the spectrum of plasma oscillations detected by a small electric dipole antenna polarized along the bias magnetic field. With a 20mA current the plasma density at the end of the trap was estimated to be 1x10$^{\mathrm{16}}$m$^{\mathrm{-3}}$. The density averaged along the length of the plasma column was measured by a microwave interferometric technique around 9.5GHz. At 20mA the average density was estimated to be approaching 4x10$^{\mathrm{16}}$m$^{\mathrm{-3}}$. [1] S.L. McConville et al, Plasma Phys. and Control. Fusion, 50, 2008, 074010, [2] K Ronald et al, Plasma Phys. and Control. Fusion, 53, 2011, 074015. [Preview Abstract] |
|
GT1.00095: Nonlocal and nonlinear dynamics in low pressure capacitively coupled radio frequency discharges Sebastian Wilczek, Jan Trieschmann, Julian Schulze, Ralf Peter Brinkmann, Zoltan Donko, Thomas Mussenbrock In capacitively coupled radio frequency (CCRF) discharges at low pressures, the electron power gain is dominated by electron interaction with the plasma sheath. During sheath expansion a bunch of energetic electrons is accelerated into the bulk region and carries energy to sustain the discharge via ionization. Additionally, the penetration of these beam-like electrons into the plasma bulk can lead to a local electric field reversal which leads to a nonlinear interplay between bulk electrons and the expanding sheath. The consequences are higher order oscillations in the RF current as well as the excitation of electrostatic waves. Particularly at low pressures, the electron mean free path is frequently larger than the gap size. In this nonlocal regime, the nonlinear sheath dynamics at one electrode influence the behavior in front of the opposite electrode, i.e., energetic electrons traverse through the discharge almost collisionlessly and interact with the opposing sheath at different phases. In this work, nonlinear and nonlocal dynamics, in particular the electron power gain, are investigated by means of 1d3v PIC simulations of CCRF discharges. [Preview Abstract] |
|
GT1.00096: Symmetry Breaking in a High Frequency, Low Pressure, Symmetric Capacitive Coupled Plasma (CCP) Reactor E. Kawamura, M.A. Lieberman, A.J. Lichtenberg Radially propagating surface wave modes in symmetric (equal electrode areas) CCP's can be either symmetric or anti-symmetric. In the former, the upper and lower axial sheath fields ($E_z$) are aligned, while in the latter, they are opposed. At high frequencies, the radial wavelengths of either mode can become comparable to the reactor dimensions, leading to standing waves. We use a fast 2D axisymmetric fluid-analytical code to study the discharge equilibrium, including the electromagnetic (EM) effects, in a low pressure (7.5 mTorr argon), low density ($\sim 3\times 10^{15}$ m$^{-3}$) symmetric capacitively coupled plasma (CCP) reactor in the frequency range of 55 to 100 MHz, which encompasses the first anti-symmetric spatial resonance, but is well below the first symmetric spatial resonance. At frequencies below the resonances, the symmetric discharge is in a stable symmetric equilibrium. At higher frequencies, near or above the antisymmetric resonance, a non-symmetric equilibrium appears, which can be stable or unstable. We develop a nonlinear lumped circuit model of the CCP to better understand the various discharge equilibria. The circuit model results agree well with the fluid simulation results, indicating that the stable non-symmetric equilibria consist of a combination of [Preview Abstract] |
|
GT1.00097: Nonlocal Dynamics of Secondary Electrons in Low Pressure Capacitively Coupled Plasmas Katharina Noesges, Aranka Derzsi, Benedek Horvath, Thomas Mussenbrock, Ralf Peter Brinkmann, Julian Schulze, Sebastian Wilczek The generation of secondary electrons in low pressure capacitively coupled radio frequency discharges is one part of the plasma surface interaction which strongly affects the electron dynamics. However, secondary electrons, in particular electron induced secondary electron emission (eiSEE), are frequently neglected in theory and simulations. Especially at high sheath voltages, previous work [1] has shown that eiSEEs contribute to the ionization process and can significantly increase the plasma density. The generation of eiSEE generally depends on the dynamics of ion induced secondary electron emission (iiSEE) due to their very high energies. Therefore, it is important to consider the dynamics of the different electrons (eiSEE and iiSEE) separately. With this separation, the electron power gain as well as the generation of each species can be understood on a nanosecond timescale. In this work, different parameters (gap size, pressures) are varied by means of PIC/MCC simulations and the impact of iiSEE and eiSEE on the discharge is investigated by using a realistic implementation of surface coefficients.\\ [1] B. Horv\'{a}th et al. 2017 \emph{Plasma Sources Sci. Technol.} \textbf{26} 124001 [Preview Abstract] |
|
GT1.00098: Numerical simulation of electromagnetic effects in very high frequency capacitively coupled plasma Jian-Kai Liu, De-Qi Wen, Yu-Ru Zhang, Yong-Xin Liu, You-Nian Wang A two-dimensional (2D) fluid model, coupled with Maxwell equations and an equivalent circuit model, is developed to understand the electromagnetic (EM) effects in large-area capacitively coupled plasmas (CCP) driven at very high frequency (VHF). In our study, we discussed the effects of two distinct surface wave modes, namely the z-symmetric radially propagating standing wave mode and the z-antisymmetric mode, on these EM effects in asymmetric reactors. At low driving frequencies and low gas pressures, the${\rm {\bf E}}_{r} $of z-antisymmetric mode dominates the spatial distribution of the electron deposition power density, leading to an edge-high electron density profile, which is also called the telegraph effect in experiments. As the frequency increases at constant rf power and gas pressure, the${\rm {\bf E}}_{z} $of z-symmetric mode becomes increasingly significant on the electron deposition power density, and meanwhile the surface wave wavelength decreases. Therefore, the electron density peak shifts to the radial center, namely the standing wave effect. Furthermore, the influences of gas pressure and rf power on the EM effects are also investigated in this work. [Preview Abstract] |
|
GT1.00099: Effects of charged particle dynamics, process control, and surface characteristics on spatio-temporal behavior in capacitive RF plasmas S. Brandt, M. Koepke, A. Derzsi, Z. Donko, B. Berger, J. Schulze, D. Keil Our simulations and experimental studies have analyzed the spatio-temporal excitation, ionization, and power absorption dynamics in an electronegative CF$_4$ radio-frequency capacitively coupled discharge driven by various tailored-voltage waveforms using up to three harmonics of a fundamental frequency of 13.56 MHz. The influence of electronegativity on the discharge was observed through a variation of the mixture ratio of CF$_4$ and Ar gases. Phase-resolved optical emission spectroscopy (PROES) allowed tracing of the development of the electrical asymmetry effect. The dependence of the discharge dynamics on the secondary electron emission coefficient (SEEC) was investigated using PROES in an electropositive gas (Ar) for plasma-facing aluminum electrodes with variable surface roughness, with and without an aluminum oxide film deposited on the electrode. The alpha-to-gamma mode transition was found to be modified by the dependence of the SEEC on both surface roughness and film thickness. These results aid the understanding of the effects of an incident-energy-dependent SEEC for deposition and etching applications in plasma processing, where electronegative gas admixtures and substrate contamination are highly influential. [Preview Abstract] |
|
GT1.00100: Experimental study of the electromagnetic effect in large-area, very-high-frequency capacitively coupled plasmas Dao-Man Han, Yong-Xin Liu, Fei Gao, You-Nian Wang Large-area very-high-frequency capacitive discharges have been attracting much attention due to their wide applications in material etching and thin film deposition. However, in this regime electromagnetic effect becomes a major limitation for plasma material processing uniformity. In this work, measurements were carried out in a large-area cylindrical reactor (45 cm in electrode diameter) driven over a wide range of frequencies (27--100 MHz). We utilized a fiber Bragg grating sensor and a probe (hairpin probe or double probe) to measure the radial profiles of neutral gas temperature and plasma density, respectively. Influences of the RF power, the working pressure and the driving frequency on the evolution of the electromagnetic effect were studied. [Preview Abstract] |
|
GT1.00101: The excitation of the Bernstein waves in magnetized capacitive helium discharge. Shali Yang, Alexander Khrabrov, sarvesh sharma, Wei Jiang, Philip Efthimion, Igor Kaganovich The Bernstein waves are short wavelength electrostatic waves in the magnetized plasma, which have been widely studied in fusion plasma physics. In this work, we present the numerical evidence of the excitation of the Bernstein waves in low-temperature capacitively coupled plasmas. Our simulations have been performed with a 1D implicit PIC/MC code. Oscillation structures can be clearly observed in the spatio-temporal profiles of the electron current density at the magnetic field of 5-30G. This can be understood as the excitation of the Bernstein waves, because the signature of the excitation of Bernstein waves is that they are excited at multiple of the cyclotron frequency by nonlinear resonances with the RF frequency( n$\omega_{\mathrm{c}}=$ m$\omega )$, where n, m are the integer numbers. We also verified that the necessary condition of excitation of the Bernstein waves is that the electron collision frequency is lower than the electron cyclotron frequency. Besides, the electron energy distribution function (EEDF) profiles at the dischrge center show that the component of high-energy electrons is increased when the Bernstein waves exist, which revealing that the Bernstein waves will heat the electrons effectively. [Preview Abstract] |
|
GT1.00102: Control of spatial distribution of plasma density by series inductence in a capacitively coupled plasma Ho-Jun Moon, Chin-Wook Chung In the plasma processing, the control of the spatial distribution of plasma parameters is very important to obtain the uniform processing result. The spatial distributions of the plasma density were measured in an asymmetric capacitively coupled plasma (CCP) source. An inductor and a variable capacitor are connected to the grounded electrode of the CCP to control the voltage distribution on the electrodes. When the capacitance of the variable capacitor is turned, the voltages at each electrode are changed and then the spatial distribution of the electric field in the plasma is changed. The spatial distribution of the plasma density is changed by adjusting the variable capacitor and the uniformity of the plasma density is improved when the balance voltage is applied. [Preview Abstract] |
|
GT1.00103: Experimental investigation of the generation of multiple electron beams during the sheath expansion phase in capacitive RF plasmas Birk Berger, Kwang-Ho You, Hyo-Chang Lee, Thomas Mussenbrock, Peter Awakowicz, Julian Schulze The fundamental investigation of different plasma heating modes is important in order to fully understand their physical nature, as well as to optimize technological applications of plasmas. We operate a geometrically symmetric capacitively coupled radio-frequency discharge in a regime of comparably low plasma density. Phase Resolved Optical Emission Spectroscopy provides insights into the electron power absorption dynamics under these conditions. By reducing the applied voltage amplitude, we observe additional electron beams, which are generated within a single phase of sheath expansion at a given electrode. This effect has been predicted by Particle in Cell simulations before and contradicts existing models that assume the generation of a single beam per sheath expansion phase by stochastic heating. Here, a systematic experimental study of the effect is presented. [Preview Abstract] |
|
GT1.00104: Correlation between electron temperature and plasma power in inductively coupled plasma Hyo-Chang Lee, J. H. Kim, D. J. Seong, K. H. You, ChaeHo Shin, Deuk-Chul Kwon, B. H. Seo, S. J. Oh, C.-W. Chung It is generally recognized that the electron temperature T$_{\mathrm{e}}$ either remains constant or decreases slightly with plasma power (plasma density). This trend can be simply verified using a single-step or multi-step fluid global model. In this work, however, we observed the abnormal behavior of T$_{\mathrm{e}}$ in ICP. In the low RF power or plasma density region, T$_{\mathrm{e}}$ decreased, while it increased in the high RF power region. It was also demonstrated from the laser Rayleigh scattering measurement that gas temperature slightly increased with low RF powers, and it significantly increased in the high RF power region. The kinetic model, which considers stepwise ionization and gas heating, was developed to analyze the change in T$_{\mathrm{e}}$. From the kinetic model analysis, the apparently abnormal trend in Te can be understood by the contrasting effects of stepwise ionization and gas heating. It should be noted that the original notion was that Te is decoupled (or weakly coupled) to the plasma power or plasma density, and thus, Te must remain constant (or slightly decrease) with plasma density in the conventional global model. However, our experiments and improved modeling show that Te has a much stronger relationship with plasma power than we initially expected, and the gas heating effect should be considered [1]. [1] Lee et al., Appl. Phys. Lett. 110, 014106 (2017). [Preview Abstract] |
|
GT1.00105: Mode transition and bistable hysteresis physics in inductively coupled plasmas Hyo-Chang Lee Many different gas discharges and plasmas exhibit bistable states under a given set of conditions, and the history-dependent hysteresis that is manifested by intensive quantities of the system upon variation of an external parameter has been observed in inductively coupled plasmas (ICPs) [1]. The fundamental understanding of the mode transitions and hysteresis is essential and highly important owing to the widespread use of ICPs and if, in such applications, plasma undergoes a mode transition and hysteresis occurs in response to external perturbations, the process result will be strongly affected. Due to these reasons, this work comprehensively compares possible effects (stepwise ionization, impedance matching, and electron energy distribution (EEDF)), which can cause the hysteresis [1-3]. It is revealed that, as a new aspect, the evolution of the EEDF can creates the hysteresis [1, 2]. Because electrons are not in a thermal equilibrium in most plasma discharges, this EEDF-effect on the hysteresis may be generalized to a universal phenomenon in gas discharge plasmas. [1] H-C Lee, Applied Physics Reviews 5, 011108 (2018). [2] H-C Lee et al., Scientific Reports 5, 15254 (2015). [3] H-C Lee et al., Applied Physics Letters 102, 234104 (2013). [Preview Abstract] |
|
GT1.00106: The dynamics of the electron impact excitation in pulse-modulated Ar/O2 inductive coupled plasmas. Fei Gao, Chan Xue, Yu-Ru Zhang, You-Nian Wang It is well known that there exists E mode and H mode in ICP. In E mode, the temporal evolution of the electron impact excitation rate shows single peak structure, while it displays bimodal structure in H mode over one rf cycle. Therefore, the peak numbers of the electron impact excitation rate can be used for determination of the E-H mode transition. In this paper, an intensified charge-coupled device camera is applied to investigate this dynamics of the electron impact excitation in pulse-modulated rf Ar/O$_{\mathrm{2}}$ ICP, and the end time of the E-H mode transition at the beginning of the pulse is investigated for the first time. It is founded that the end time of the E-H mode transition at the initial stage of a pulse period decreases with increasing the duty cycle or gas pressure, but increases with the source power increasing. This means that the effects of the E-mode at the beginning of a pulse can be weakened to some extent by adjusting the discharge parameters. In addition, we also examined the spatial-temporal distributions of the electron impact excitation rate all over the whole pulse period (with microsecond time-resolution) and especially in the steady state at H mode. The measurements reveal that the axial distribution of the electron impact excitation rate concentrates closer to the quartz window with increasing the O$_{\mathrm{2}}$ content/pressure during H mode operation. Meanwhile, the bimodal structure becomes more prominent at higher O$_{\mathrm{2}}$ content/pressure. [Preview Abstract] |
|
GT1.00107: Three-dimensional Measurements of plasma properties in an industrial etch tool Walter Gekelman, Jia Han, Patrick Pribyl, Alex Paterson, Mark Kushner, Steve Lantham A computer controlled probe drive capable of moving in three dimensions has been installed on an industrial plasma etch tool modified for accessibility. The plasma was generated by pulsing a current ( $t_{plasma} \ge 500 $ ms, $t_{rep}$ : variable, $ f_{coil}$ = 2 MHz) in a 3 turn antenna mounted above a ceramic lid. In this set of experiments there was no RF bias on the wafer. The vector magnetic field was measured at over 15,000 locations throughout the plasma volume. Data was acquired at temporal intervals of 2 ns. A swept Langmuir probe was used to measured plasma parameters ($n$,$T_e$,$V_p$) at the same spatial locations as $\vec B$. The density measurement was calibrated with a 96 GHz interferometer. Measurements presented are in steady state, H mode operation. During an RF cycle the 3D current (derived from $\vec B(x,y,z,t)$) initially just below the coil, moves down towards the center of the device. Isosurfaces of current are nearly symmetric toroids. The density evolution is similar to the current, however the electron temperature is spatially uniform. The 3D electric field is derived from the data along with Poynting flux. Input power is compared to internal $\vec J \cdot \vec E$. Laboratory data will be compared to a computer simulation. [Preview Abstract] |
|
GT1.00108: Time dependent Volumetric measurements of key plasma parameters during pulsed plasma operation Jia Han, Patrick Pribyl, Walter Gekelman, Alex Paterson Volumetric measurements are done in an industrial plasma etch tool modified for accessibility using a computer-controlled probe drive. Plasma is generated by a three-turn stove-top type circular antenna mounted on a ceramic lid on the top of the device. A 2 MHz RF generator powers the antenna. Plasma is pulsed on/off at different repetition rates. The 3D magnetic field is measured using a three-axis magnetic probe. A swept Langmuir probe measures $n$ and $T_e$ as functions of time over the 3D volume. An emissive probe is used to measure the plasma potential, and the space charge field (-$\nabla V_p$) is derived. The bulk electron density forms under the antenna, with its peak eventually migrating to the middle of the machine. The antenna current turns on in less than 100 microseconds. However, it takes 2 to 5 milliseconds for the density to reach steady state. Spatial and temporal dependence of the current density inside the plasma are derived from the magnetic field measurements using $\nabla \times \vec B = \mu_0 \vec J$. The bulk plasma current forms close to the antenna, then diffuses into the plasma volume. This work describes evolution of these quantities toward steady state during the pulse. [Preview Abstract] |
|
GT1.00109: Benchmarking and validation of global model code for negative hydrogen ion sources. Wei Yang, Sergey Averkin, Alexander Khrabrov, Igor Kaganovich, You-Nian Wang Benchmarking can provide an evidence of the accuracy of computer simulations accompanied by the estimation of relevant errors, which is thus increasingly being recognized. We develop a global model for negative hydrogen ion sources (GMNIS) and perform the benchmarking of the code with global enhanced vibrational kinetic model (GEVKM). The VDF and the $\mbox{H}^{-} $ number density obtained from two codes are in good agreement with each other. The small discrepancies can be attributed to the differences in the electron temperature and electron number density caused by different solution procedures and transport properties utilized in each code. In addition, the GMNIS is validated with experimental measurements operated in an ECR discharge. The model qualitatively or even quantitatively reproduces the experimental $\mbox{H}^{-} $ number density. Benchmarking and validation of codes are presented here with the goal of making codes to become a reliable predictive tool and ultimately aiding in developing optimized negative ion beams for ITER. [Preview Abstract] |
|
GT1.00110: Investigation of tunable Dirac cones and flat bands in two dimensional plasma photonic crystals Benjamin Wang, Jesse A. Rodriguez, Mark Cappelli We present finite difference time domain (FDTD) simulations of the response of a two-dimensional plasma photonic crystal to incident TE electromagnetic waves that span regions both above and below the plasma frequency, $\omega _{\mathrm{p\thinspace }}$and investigate the Dirac cone dispersion with double degeneracy near both $\Gamma $ and X symmetry points. Additionally, flat bands due to surface plasmon modes are investigated at frequencies below the plasma frequency. Experimentally, the transmission properties are characterized for a 7 by 7 2D plasma photonics crystal, with spatial E field mapping and transmission measurements completed on the test crystal. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700