Bulletin of the American Physical Society
68th Annual Gaseous Electronics Conference/9th International Conference on Reactive Plasmas/33rd Symposium on Plasma Processing
Volume 60, Number 9
Monday–Friday, October 12–16, 2015; Honolulu, Hawaii
Session HT1: Atomic and Molecular Scattering Data for Plasma and Related Applications Workshop I |
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Chair: Alisher Kadyrov, Curtin University Room: 301 B |
Tuesday, October 13, 2015 8:00PM - 8:30PM |
HT1.00001: Application of the Convergent Close-Coupling method to collisions of electrons, positrons, and protons with light atomic and molecular targets Invited Speaker: Igor Bray The Convergent Close-Coupling (CCC) method for electron-atom collisions has been applied successfully for around two decades for quasi one- and two-electron atomic targets. The underlying engine is the complete Laguerre basis for treating to convergence the target discrete and continuous spectra via a square-integrable approach, together with a formulation of the close-coupling equations in momentum space. The method has continued to be extended, and now incorporates collisions with positrons with allowance for positronium formation. This is a major advancement because it addresses the complexity associated with treating multi-center collision problems. These techniques have then been readily transferred to collisions with protons, where charge-exchange can be a substantial scattering outcome. The latter also required a move to solving the CCC equations using an impact parameter formalism. Most recently, in addition to the extension of the variety of projectiles, the collision targets have been generalized to molecules. Presently, just the H$_{2}^{+}$ and the H$_{2}$ molecules have been implemented. In the talk a broad range of applications of the CCC method will be discussed and future developments will be indicated. [Preview Abstract] |
Tuesday, October 13, 2015 8:30PM - 9:00PM |
HT1.00002: Benchmark calculations for electron collisions with complex atoms: accuracy, convergence and completeness Invited Speaker: Oleg Zatsarinny Over the past decade, we have developed a highly flexible $B$-spline $R$-matrix (BSR) method [1] that has some advantages compared to the standard $R$-matrix (close-coupling) approach. The two essential refinements are i) the capability for using the flexible term-dependent one-electron orbitals, and ii) the use of $B$-splines as a universal and effectively complete basis to generate the $R$-matrix basis. These features allow us to achieve a high accuracy in the target description, as well as a truly consistent treatment of the scattering system. The BSR code was successfully applied to many problems of electron collisions from atoms and ions, with special emphasis was placed on complex, open-shell targets. Often considerable \textit{improvement} was obtained in comparison with previous calculations. Many examples can be found in a recent Topical Review [2]. More recently, the BSR complex has been extended to i) the fully relativistic Dirac scheme and ii) intermediate energies using the continuum pseudo-state approach. These extensions allow for an accurate treatment of \textit{heavy targets} as well as a fully non-perturbative way to handle electron-impact \textit{ionization}, including such highly correlated processes as ionization plus simultaneous excitation. During the last years we developed parallel versions of our BSR and DBSR codes. They made it possible to carry out large-scale $R-$matrix with pseudo-states (RMPS) calculations and thereby provide \textit{converged} (with respect to the number of coupled states) results for electron impact excitation of individual target states. For many systems our calculations revealed dramatic reductions of the predicted excitation cross-sections at intermediate energies, due to the strong influence of coupling to the target continuum. These results raise questions about the absolute normalization in several published measurements. Our RMPS calculations represent the extensive and \textit{complete} sets of electron scattering data ready for applications. \\[4pt] [1] Zatsarinny O 2006 \textit{Comput. Phys. Commun. }\textbf{174} 273\\[0pt] [2] Zatsarinny O and Bartschat K 2013 \textit{J. Phys. B: At. Mol. Opt. Phys. }\textbf{46 } 112001 [Preview Abstract] |
Tuesday, October 13, 2015 9:00PM - 9:30PM |
HT1.00003: The Empowerment of Plasma Modeling by Fundamental Electron Scattering Data Invited Speaker: Mark J. Kushner Modeling of low temperature plasmas addresses at least 3 goals -- investigation of fundamental processes, analysis and optimization of current technologies, and prediction of performance of as yet unbuilt systems for new applications. The former modeling may be performed on somewhat idealized systems in simple gases, while the latter will likely address geometrically and electromagnetically intricate systems with complex gas mixtures, and now gases in contact with liquids. The variety of fundamental electron and ion scattering data (FSD) required for these activities increases from the former to the latter, while the accuracy required of that data probably decreases. In each case, the fidelity, depth and impact of the modeling depends on the availability of FSD. Modeling is, in fact, empowered by the availability and robustness of FSD. In this talk, examples of the impact of and requirements for FSD in plasma modeling will be discussed from each of these three perspectives using results from multidimensional and global models. The fundamental studies will focus on modeling of inductively coupled plasmas sustained in Ar/Cl$_{\mathrm{2}}$ where the electron scattering from feed gases and their fragments ultimately determine gas temperatures. Examples of the optimization of current technologies will focus on modeling of remote plasma etching of Si and Si$_{\mathrm{3}}$N$_{\mathrm{4}}$ in Ar/NF$_{\mathrm{3}}$/N$_{\mathrm{2}}$/O$_{\mathrm{2}}$ mixtures. Modeling of systems as yet unbuilt will address the interaction of atmospheric pressure plasmas with liquids [Preview Abstract] |
Tuesday, October 13, 2015 9:30PM - 10:00PM |
HT1.00004: Scaling of plane-wave Born cross sections for electron-impact excitation of neutral atoms and molecules Invited Speaker: Hiroshi Tanaka We review the scaling of plane-wave Born cross sections for electron-impact excitation of neutral atoms and molecules. The scaling method is applied to integrated cross sections for electric dipole-allowed transitions. As introduced in the BEB scaling model for ionization cross sections, this scaling replaces the incident electron energy $T$ in the first-order PWB cross sections by $T + B + E$, where $B$ is the ionization energy, or the binding energy, of the target electron, and $E$ is the excitation energy. Note in a generic form, first-order PWB cross sections are defined as $\sigma _{PWB} =$ (4$\pi a_{0}^{2}R$/$T)$ GOS$_{PWB}(T)$, where $a_{0}$ is the Bohr radius, $R$ is the Rydberg energy, and GOS is the \textit{Bethe} generalized oscillator strength. In the scaling, though two approaches, computational and experimental have been applied, the latter is presented at this meeting in which the \textit{Bethe} GOS is replaced by the \textit{apparent} GOS determined by the experiments. Representative examples show that an simple improvement scaled by $T + B + E$ extends the usage of the Born-Bethe approximation into the \textit{intermediate} region, thereby bridging the gap between the two regions categorized conventionally as slow and fast collisions. [Preview Abstract] |
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