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 SR1: Heavy Particle CollisionsLive
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Chair: Yuri Ralchenko, NIST |
Thursday, October 8, 2020 8:00AM - 8:30AM Live |
SR1.00001: Atomic processes gaseous media: Ion and secondary-electron transport from swift ion precipitation into the Jovian upper atmosphere Invited Speaker: David Schultz Understanding of plasma and gaseous environments, such as those in astrophysical environments, technical plasmas, and fusion energy devices, rests in large part on modeling and diagnostics based on fundamental atomic processes. Here a description is given of work to provide a wide and detailed range of atomic data for inelastic processes in the interaction of swift ions precipitating into the atmosphere of Jupiter. In fact, a rich ion population exists in the magnetosphere of Jupiter, with species originating from the Galilean moons and as well from the solar wind. These populations give rise to precipitation of ions, accelerated by Jupiter's prodigious magnetic field, into the planet's upper atmosphere. Evidence of this precipitation comes directly from observations of auroral x-ray line emission in the polar regions coming from radiative de-excitation following charge transfer between the precipitating ions and atmospheric molecules Results of work to produce and utilize in simulations data describing secondary-electron production in keV to MeV O$^{\mathrm{q+}}$ (q$=$0-8) and S$^{\mathrm{q+}}$ (q$=$0-16) $+$ H$_{\mathrm{2}}$ collisions is described [1,2]. O and S ions slow down in their passage through the atmosphere, produce secondary electrons, heat atmospheric molecules, lead to dissociation of H$_{\mathrm{2}}$, and contribute to the atmospheric currents, linking the Jovian ionosphere and atmosphere. Incorporation of such data into models has been timely considering the arrival of the NASA Juno probe at Jupiter in July 2016 with the unique orbital characteristics to enable observations of the precipitating ion populations and their interactions with the upper atmosphere. [1] Schultz, Ozak, Cravens, and Gharibnejad, At. Data Nucl. Data Tables, 113, 1 (2017); Schultz, Gharibnejad, Cravens, and Houston, At. Data Nucl. Data Tables 126, 1 (2019) [2] Houston, Cravens, Schultz, Gharibnejad, Dunn, Haggerty, Rymer, Mauk, Gladstone, and Ozak, J. Geophys. Res.: Space Physics 125, e2019JA02700 (2019). [Preview Abstract] |
Thursday, October 8, 2020 8:30AM - 8:45AM Live |
SR1.00002: Student Excellence Award Finalist: Ejected Electron-Energy and Angular Dependence of Fully Differential Ionization Cross Sections in Proton Collisions with He and H$_{\mathrm{2}}$ Madhav Dhital, Sujan Bastola, Aaron Silvus, Jacob Davis, Basu Lamichhane, Esam Ali, Marcelo Ciappina, Ramaz Lomsadze, Ahmad Hasan, Don Madison, Michael Schulz We have measured fully momentum-analyzed recoil ions and scattered projectiles, produced in ionizing collisions between protons and He and H$_{\mathrm{2}}$, in coincidence. The momentum of the ejected electron was then deduced from momentum conservation. From the data we extracted fully differential ionization cross sections (FDCS) for a large number of ejected electron energies ranging from well below to well above the projectile -- electron velocity matching regime. Furthermore, for each electron energy data were obtained for four different projectile scattering angles. Various signatures of the post-collision interaction were identified in the electron energy- and angular dependence of the FDCS and systematically analyzed. The data were compared to two different, but conceptually very similar distorted wave calculations. This comparison demonstrates the limitations of perturbative models under conditions where the post-collision interaction is strong and thus the need for non-perturbative methods in order to advance our understanding of the underlying few-body dynamics. Furthermore, our results show that the post-collision interaction is surprisingly strong even for electrons not ejected in the forward direction. [Preview Abstract] |
Thursday, October 8, 2020 8:45AM - 9:00AM Live |
SR1.00003: Single-center technique for rearrangement processes Alisher Kadyrov, Ilkhom Abdurakhmanov, Igor Bray Recently, we developed a two-center convergent close-coupling (CCC) approach to ion-atom collisions. The approach requires large computing power since the rearrangement matrix elements describing the electron-capture channels demand more computational recourses. This fact somewhat limits the applicability of the two-center formalism to more complex targets. For such targets the formalism requires calculations of many different types of direct and rearrangement matrix elements and, as a result, becomes very challenging. Therefore, complex collision systems require the development of simpler but at the same time robust numerical methods. We present a simple approach to rearrangement collisions based on the computationally more convenient one-center formalism. To calculate electron-capture cross sections, we start from the exact definition of the electron-capture amplitude in terms of the total scattering wave function. However, we approximate the total scattering wave function with the one obtained from the one-center CCC approach. This way the total and state-resolved electron-capture cross sections can be calculated. Then the total ionization cross section can be obtained by subtracting the total electron-capture cross section from the total electron-loss cross section. [Preview Abstract] |
Thursday, October 8, 2020 9:00AM - 9:15AM Live |
SR1.00004: A parabolic quasi-Sturmian approach to quantum scattering by Coulomb-like potentials. Lorenzo Ugo Ancarani, A.S. Zaytsev, S.A. Zaytsev, K.A. Kouzakov We propose a computational method in parabolic coordinates to treat the scattering of a charged particle from both spherically and axially symmetric Coulomb-like potentials. Specifically, the short-range part of the Hamiltonian is approximated by a Sturmian L2-basis-set truncated expansion while the long-range part is represented in parabolic quasi-Sturmian basis functions. The latter are derived in closed form making use of a convenient analytical representation of the Green's function. Taking advantage of the adequate built-in Coulomb asymptotic behavior of the quasi-Sturmian functions, scattering amplitudes are extracted as simple analytical sums that can be easily computed. The scheme provides scattering solution in the entire space. It proves to be numerically efficient and robust as illustrated with converged results for three different scattering potentials, one of spherical and two of axial symmetry. Applications to realistic electron-atom or electron-molecule scattering are being investigated. [Preview Abstract] |
Thursday, October 8, 2020 9:15AM - 9:45AM Live |
SR1.00005: Ionization of complex biomolecules studied with an independent atom model including geometric screening corrections Invited Speaker: Tom Kirchner A thorough understanding of the radiation damage of biological tissue begins with data for the fundamental ionization processes of molecules in the gas/vapor phase. A growing body of experimental and theoretical work for photon, electron and heavy-particle impact is addressing this need. This talk focuses on ion-impact collisions and reports on cross-section results for target molecules such as water and the DNA/RNA nucleobases adenine and uracil obtained from independent-atom-model (IAM) based calculations. In the simplest version of the IAM the ionization or electron transfer cross sections of the atoms that make up the molecule are added up. We have recently shown that this naive Bragg additivity rule can be significantly improved by taking the overlapping nature of effective cross-sectional areas into account [1]. A pixel counting method is used to calculate the overlaps and the model is referred to as IAM-PCM. It is demonstrated that IAM-PCM net ionization results for projectile charges Q=2,3 can be reproduced by scaled proton-impact (Q=1) cross sections over a wide range of collision energies. We also show how based on this scaling model the available experimental data can be reduced to effective Q=1 cross sections and present a comparison of those results with proton impact data [2].\\ \\The work presented in this paper has been carried out in collaboration with Hans J\"urgen L\"udde (Goethe University Frankfurt) and Marko Horbatsch (York University).1] H. J. L\"udde {\it et al.}, Eur. Phys. J. D \textbf{73}, 249 (2019). [2] H. J. L\"udde {\it et al.}, Phys. Rev. A (accepted for publication). [Preview Abstract] |
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