Bulletin of the American Physical Society
73rd Annual Gaseous Electronics Virtual Conference
Volume 65, Number 10
Monday–Friday, October 5–9, 2020; Time Zone: Central Daylight Time, USA.
Session JT1: Collisional Data for Plasma ApplicationsLive
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Chair: Tom Kirchner, York |
Tuesday, October 6, 2020 1:00PM - 1:30PM Live |
JT1.00001: Overview of Modern Collisional-Radiative Modeling for Plasmas Invited Speaker: Yuri Ralchenko Collisional-radiative (CR) modeling represents the most general approach to determination of plasma emission and population kinetics parameters away from equilibrium conditions. It is heavily based on utilization of large sets of atomic data and thus puts forward demanding requirements on the quality of the data. CR modeling allows reliable treatment for low- and high-density cold and hot plasmas, non-Maxwellian electron energy distribution functions, plasma effects on atomic structure and spectra, external radiation fields, opacity effects, and other physical phenomena. I will present a broad overview of the modern techniques for generation of accurate atomic data for CR modeling, give numerous examples of CR codes and their fundamental principles, and highlight applications of CR modeling for calculation of plasma spectra under diverse conditions, covering multi-order ranges of particle temperature and densities. [Preview Abstract] |
Tuesday, October 6, 2020 1:30PM - 1:45PM Live |
JT1.00002: A collisional-radiative model benchmarking and comparative study of fusion relevant atoms Nathan A. Garland, Mark C. Zammit, Christopher J. Fontes, James Colgan, Hyun-Kyung Chung, Xian-Zhu Tang Accurate predictive capability of ion charge state and radiation profiles is a crucial input to modeling collisional, fusion-relevant discharges. With an eye to ITER operations, such applications include nitrogen injection into the cooler, collisional boundary-layer during quiescent operation, or injection of neon into a discharge experiencing a disruption event. In many of these cases, the collisionality of the discharge rapidly increases and the composition and radiative potential of the plasma must be determined. While many collisional-radiative (CR) modeling approaches have been developed over the years, it is not always clear when and why certain models, and their assumptions, should be applied to given applications. In this work we seek to provide highly accurate benchmark calculations of fusion-relevant atoms and from there, assess the strengths and limitations of decreasing model detail depending on the application at hand. In particular, we examine the requirements for producing detailed spectroscopic information, compared to more forgiving quantities such as ion stage population distributions for plasma modeling. We also comment on the time-evolution of CR systems, and detail the restrictions this imposes on using steady-state data for plasma modeling purposes. [Preview Abstract] |
Tuesday, October 6, 2020 1:45PM - 2:00PM Live |
JT1.00003: Experimental Determination of Electron-impact Rotational Excitation Rate Coefficients for CH$^+$ Abel Kalosi, K. Blaum, S. George, J. Goeck, M. Grieser, F. Grussie, R. von Hahn, N. Jain, C. Krantz, H. Kreckel, C. Meyer, D. Muell, O. Novotny, F. Nuesslein, D. Paul, S. Saurabh, D. W. Savin, V. C. Schmidt, P. Wilhelm, A. Wolf CH$^+$ has been detected in space and laboratory plasmas. Interpretation of the observed spectrum relies, in part, on radiative transfer models built on a knowledge of the relevant excitation and de-excitation processes, such as inelastic collisions with electrons. Here we present merged beams experiments of CH$^+$ with the recently implemented electron cooler at the Cryogenic Storage Ring (CSR) in Heidelberg. This experimental setup facilitates low (meV) collision energy measurements to study inelastic electron-ion collisions. We combined the collision measurements with near-threshold photodissociation to probe the populations of the lowest rotational states of the stored CH$^+$. Using a velocity-matched or slightly detuned electron beam, we can, for the first time, experimentally determine electron-impact rotational excitation and de-excitation merged beams rate coefficients for a molecular ion. Here we will present our first results. [Preview Abstract] |
Tuesday, October 6, 2020 2:00PM - 2:30PM Live |
JT1.00004: First-Principles Molecular Spectra for Air and Astrophysical Plasmas Invited Speaker: Mark Zammit Comprehensive and highly accurate rovibronic spectral measurements of molecules are critical to the modeling of low-temperature plasmas. However, with the lack of experimental data, first-principles approaches are key to generating complete molecular line lists. Here, we will discuss the methodology employed for the accurate calculation of molecular rovibronic states, and present emission, equation of state and opacity results for H$_2^+$, H$_2$, NO, and OH, which form in significant abundance in astrophysical and air plasmas. We focus on the importance of electronic excited state transitions, which are generally difficult to model, and until recently were not included in many line-lists. [Preview Abstract] |
Tuesday, October 6, 2020 2:30PM - 2:45PM Not Participating |
JT1.00005: Dissociative recombination (DR) and associative ionization (AI), N$_{\mathrm{2}}^{\mathrm{+}}+$e$^{\mathrm{-}}=$N$+$N, cross section calculations for atmospheric entry modeling Ewa Papajak, Winifred M. Huo, David W. Schwenke, Richard L. Jaffe In order to maintain desired safety margins during atmospheric entry of a space vehicle, reaction models need to accurately account for processes leading to excited species that contribute to radiative heating of the vehicle. These reactions include ionization and electron-molecule processes that ionization enables. In particular, N $+$ N AI is one of the mechanisms that can initiate production of free electrons during Earth entry. While experimental data on some of the total cross sections are available, few experiments address the need for the accurate AI cross sections starting from higher-lying atomic states and for 1,000-40,000K temperature range. In this work, theoretical cross sections and branching ratios for AI are calculated for a range of atomic states of N. We first calculate DR cross sections and then obtain AI cross sections and rate coefficients using detailed balance. For the DR calculations, we use state-of-the-art MRCI potential energy curves. The adiabatic potential curves are transformed to a diabatic representation, which is used in time-dependent wave packet calculations to describe the nuclear motion of the dissociating cation. The electron-scattering resonance widths are calculated by the R-matrix method. Based on the state distribution profiles in time, these calculations provide DR cross sections including recombination into high energy atomic states. The DR and AI rate coefficients and branching ratios are calculated and compared with the available experimental data. [Preview Abstract] |
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