Bulletin of the American Physical Society
72nd Annual Gaseous Electronics Conference
Volume 64, Number 10
Monday–Friday, October 28–November 1 2019; College Station, Texas
Session PR1: Heavy Particle Collisions |
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Chair: Allison Harris, Illinois State University Room: Century I |
Thursday, October 31, 2019 10:00AM - 10:30AM |
PR1.00001: Few-body dynamics underlying post-collision effects in ionization of simple targets by 75 keV proton impact. Invited Speaker: Michael Schulz One of the most important goals of atomic scattering research is to advance our understanding of the few-body problem. The few-body dynamics is characterized by the relative importance of the first-order versus various higher-order mechanisms. One higher-order process that is particularly important in ionization is known as post-collision interaction (PCI). Here, after the primary interaction, the projectile and the electron interact with each other again in the outgoing part of the collisions. The importance of PCI is known to maximize for ejected electron velocities equal to the projectile velocity (velocity matching). We have performed kinematically complete experiments on ionization of H$_{\mathrm{2}}$ and He by 75 keV proton impact. The experiment was performed for various fixed energy losses for each target corresponding to the region around the velocity matching. Fully differential cross sections (FDCS) were analyzed for electrons ejected into the scattering plane (spanned by the initial and final projectile momenta) for various fixed scattering angles as a function of the electron emission angle. At small scattering angles the FDCS are dominated by a strong peak structure at 0$^{\mathrm{o}}$. At larger scattering angles a resolved second peak (the binary peak) is seen near the direction of the momentum transfer vector. The data were compared to two conceptually very similar calculations. Surprisingly, large differences between the experimental data and theory and between both calculations were found. This demonstrates that near the matching velocity the FDCS are very sensitive to the details of the few-body dynamics. Furthermore, significant differences between the FDCS for the two target species were found. [Preview Abstract] |
Thursday, October 31, 2019 10:30AM - 10:45AM |
PR1.00002: Stopping of proton beam in hydrogen Alisher Kadyrov, Jackson Bailey, Ilkhom Abdurakhmanov, Igor Bray, Akram Mukhamedzhanov The stopping cross section for protons passing through hydrogen is calculated for the energy range between 10 keV and 3 MeV. Both the positive and neutral charge states of the projectile are accounted for. The two-center convergent close-coupling method is used to model proton collisions with hydrogen. In this approach, electron-capture channels are explicitly included by expanding the scattering wave function in a basis of both target and projectile pseudostates. Hydrogen collisions with hydrogen are modeled using two methods: the single-center convergent close-coupling approach is used for the calculation of one-electron processes, while two-electron processes are calculated using the Born approximation. The aforementioned approaches are also applied to the calculation of the charge-state fractions. These are then used to combine the proton-hydrogen and hydrogen-hydrogen stopping cross sections to yield the total stopping cross section for protons passing through hydrogen. [Preview Abstract] |
Thursday, October 31, 2019 10:45AM - 11:00AM |
PR1.00003: Signature of s-wave scattering in atom-ion resonant charge transfer Robin Cote Collisions between an ion and its parent neutral atom can lead resonant charge transfer. This is an example of resonant exchange, a general process playing a key role in many-body dynamics and transport phenomena, such as spin, charge, or excitation diffusion. The underlying process is described by the resonant exchange cross section. We show that the s-wave scattering, generally thought to contribute mainly in the ultracold (or Wigner) regime, dictates the overall cross section (and rate coefficient) over a broad range of energies. We derive an analytical expression and explain its applicability high above the Wigner regime. In particular, we demonstrate its relationship to the classical capture (Langevin) cross section and apply it to resonant charge transfer, and explain the large variations found for different isotopes. These cannot otherwise be accounted for by the small change in mass. [Preview Abstract] |
Thursday, October 31, 2019 11:00AM - 11:15AM |
PR1.00004: Independent-atom-model pixel counting method calculations for ion collisions from biomolecules Tom Kirchner, Marko Horbatsch, Hans Jurgen Ludde The recently introduced independent-atom-model pixel counting method (IAM-PCM) [1,2] is used to calculate net capture and net ionization cross sections for ion-biomolecule collisions in the 10 keV to 10 MeV impact energy range. Taking advantage of the flexibility of the method we have studied a large class of target systems including nucleobases, amino acids, and nucleotides. Results are compared with experimental data and previous theoretical calculations where available. At low to intermediate energies, where experimental data are sparse, the IAM-PCM cross sections are in marked disagreement with previous perturbative and classical calculations. For the case of net ionization it is shown that they follow a scaling relation and can be parametrized in terms of a simple analytical formula. [1] H.J. L\"udde {\it et al.}, Eur. Phys. J. D \textbf{70}, 82 (2016). [2] H.J. L\"udde {\it et al.}, Eur. Phys. J. B \textbf{91}, 99 (2018). [Preview Abstract] |
Thursday, October 31, 2019 11:15AM - 11:30AM |
PR1.00005: Fully differential single ionization cross sections in 75 keV p $+$ He collisions near the velocity matching. Madhav Dhital, Sujan Bastola, Aaron Silvus, Ahmad Hasan, Basu Lamichhane, Esam Ali, Marcelo Ciappina, Ramaz Lomsadze, Don Madison We have performed a kinematically complete experiment on ionization of He by 75 keV proton impact. The momentum-analyzed scattered projectiles and recoil ions were measured in coincidence and the ejected electron momentum determined from the conservation laws. The experiment was performed for various fixed energy losses near the projectile-electron matching velocity. Fully differential cross sections (FDCS) were analyzed as a function of a) the electron emission angle and b) the ejected electron energy. Pronounced post-collision effects were found in terms of a strong peak structure in the electron angular dependence at 0$^{\mathrm{o}}$ and in terms of a cusp-shaped peak in the energy-dependence of the FDCS. Additional structures were found in the FDCS which were not observed in previous FDCS measurements for energy losses well below the velocity matching region. Such structures are also found in theoretical calculations, however, there are significant quantitative discrepancies to the experimental data. [Preview Abstract] |
Thursday, October 31, 2019 11:30AM - 12:00PM |
PR1.00006: Line Shapes of Fast Hydrogen Atoms in a Low Density Gas Discharge: Challenges and Applications Invited Speaker: Oleksandr Marchuk For many years plasma spectroscopy established itself as one the most powerful and robust technique to deliver information on the plasma parameters such as gas pressure, electron density and tempera-ture or the electric field in the plasma sheath. But could the emission spectroscopy go beyond these limits and provide the answers on new challenges of low-temperature plasma physics? One of them is to determine the optical properties of the surface exposed to a plasma. In this talk I demonstrate that in Ar-H low density gas discharges (p<1Pa) the emission of fast hydrogen or deuterium atoms in the energy range of 80-300 eV at plasma-solid interfaces replaces to a certain extent the conventional mirror laboratory. The Doppler effect observed for the Balmer-lines transfers the time-resolved measurements in the laboratory to in-situ measurements in the velocity domain. Fast atoms originate from neutralization of ions accelerated in the sheath at the surface of interest. The light emission is stimulated by collisions between these fast atoms and argon atoms. The measurements of total reflectance, polarization properties of the surface, real-time evolution of reflectance such as a transition between the specular and diffusive type and the modification of the surface morphology during the surface cleaning are only a few examples of this powerful technique which emerged recently. In contrast to the expectations based on the atomic data set for the emission cross-sections of Balmer-lines, the signal of fast atoms in other noble gases remains extremely weak. The excitation of H atoms by collisions with Kr is, for instance, a factor of five weaker than the excitation by Ar atoms although the measured cross-sections are within 20\% in the energy range of interest. It is proposed that the metastable fraction of Ar could play the dominant role in the excitation channel of Balmer-lines via an endothermal excitation transfer reaction. [Preview Abstract] |
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