Bulletin of the American Physical Society
43rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 57, Number 5
Monday–Friday, June 4–8, 2012; Orange County, California
Session J3: Invited Session: Gaseous Electronics |
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Chair: Michael Brunger, Flinders University Room: Grand Ballroom E |
Wednesday, June 6, 2012 2:00PM - 2:30PM |
J3.00001: Differential cross sections for ionization and excitation of laser-aligned atoms by electron impact Invited Speaker: Andrew Murray Differential cross section measurements will be presented for electron impact ionization and excitation of atoms prepared using high resolution continuous wave laser radiation. In the case of ionization, low energy coplanar asymmetric (e,2e) experiments were performed from laser excited Mg atoms that were aligned using radiation around 285nm. The atoms were subjected to linearly polarized radiation whose polarization vector was varied from in the plane to perpendicular to the scattering plane. Ionization measurements were then conducted from the laser-excited 3P state, and the differential cross section determined. By careful analysis of the laser pumping, these measurements were directly compared to those from the ground state. Such experiments provide valuable information on the ionization of aligned targets. In the second experiment to be described here, a resonant enhancement cavity has been placed around the interaction region and super-elastic scattering measurements have been carried out from laser-excited atoms inside the cavity. This new technique opens up many new targets for study, since the cavity increases the effective intensity of the laser radiation that is exciting the atoms by a factor of up to 50. As such, new ionization and excitation measurements are possible using deep UV radiation where the laser power is only a few mW. Results from calcium will be presented, and progress towards studies from silver, copper and gold will be discussed. We are also advancing this new technique to allow simultaneous excitation from the hyperfine levels of different targets (such as Rb), which will allow the method to be adopted in different fields, such as laser cooling and trapping. [Preview Abstract] |
Wednesday, June 6, 2012 2:30PM - 3:00PM |
J3.00002: Two dimensional laser-collision induced fluorescence measurements in low pressure plasmas Invited Speaker: Ed Barnat Diagnostic techniques that enable the measurement of the temporal and spatial evolution of a plasma discharge provide insight into the mechanisms governing the behavior of a plasma discharge. In this presentation, the development and implementation of a two-dimensional laser diagnostic known as laser-collision induced fluorescence (2D-LCIF) is described. The technique relates the redistribution of laser excited population into nearby states to the electron density and electron energy via a collisional-radiative model (CRM) also described in this work. Central to the successful implementation of this technique is proper knowledge of the energy dependence of electron impact excitation between the various levels of the atomic or molecular system probed. Emphasis is placed on the ability of the technique to provide two dimensional maps of the electron densities in a plasma discharge. Discussion is also offered on the techniques ability to characterize the ``effective temperature'' of the electrons by observing relative changes in the excitation rates across a plasma discharge. Application of the 2D-LCIF technique to structurally interesting plasmas is demonstrated. While earlier studies have focused on helium, effort is underway to extend the technique to other systems such as argon. This work was supported by the Department of Energy Office of Fusion Energy Science Contract DE-SC0001939 [Preview Abstract] |
Wednesday, June 6, 2012 3:00PM - 3:30PM |
J3.00003: Transport and collisional processes for electrons in gases and their application to study non-equilibrium plasmas Invited Speaker: Sasa Dujko As atomic and molecular collisions critically shape distributions and rates in low temperature plasmas the advancements in modern day technology associated with the non-equilibrium plasma discharges are critically dependent on accurate modeling of the underlying collision and transport processes for charged particles in gases. To meet these challenges, we have undertaken a program to understand the kinetic behavior of charged particles under the combined action of electric and magnetic fields in neutral gases. A multi term theory for solving the Boltzmann equation has been developed and used to calculate transport coefficients of charged-particle swarms in neutral gases. In this talk, I will focus on non-equilibrium magnetized plasma discharges where the electric and magnetic fields can vary in space, time and orientation depending on the type of discharge and where attention must be paid to the correct treatment of temporal and spatial non-locality within the discharge. In particular, I will highlight the duality of transport coefficients arising from the explicit effects of non-conservative collisions. As an example of fluid modeling, I will discuss the recently developed high order fluid model for streamer discharges. Starting from the cross sections for electron scattering, it will be shown how the corresponding transport data required as input in fluid model should be calculated under conditions when the local field approximation is not applicable. Comparison between the temporal evolution of electron number density and electric field from the classical first order and that from high order model are made and differences will be addressed using physical arguments. [Preview Abstract] |
Wednesday, June 6, 2012 3:30PM - 4:00PM |
J3.00004: Benchmark Calculations of Atomic Data for Modelling Applications Invited Speaker: Klaus Bartschat In recent years, much progress has been achieved in calculating reliable cross-section datasets for electron scattering from atoms and ions, in particular quasi-one and quasi-two electron systems such as H, He, the alkalis, and the alkaline-earth metals. Until recently, however, accurate calculations of electron collisions with more complex targets, such as the heavy noble gases Ne$-$Xe, have remained a significant challenge to theory. In this talk, we will illustrate with a few examples how the $B$-spline $R$-matrix (BSR) method with non-orthogonal orbitals~[1-3] has been able to dramatically improve the quality of theoretical datasets for oscillator strengths~[4] as well as electron collisions with numerous targets, including the heavy noble gases~[5], and how these data were used successfully in modelling applications~[6]. The most recent extension of the method, the $B$-spline $R$-matrix with Pseudo-States (BSRMPS) approach, includes a large number of pseudostates in the close-coupling expansion, thereby allowing for the fully non-perturbative treatment of highly correlated processes such as ionization and even ionization with simultaneous excitation~[7]. \\[4pt] [1] O. Zatsarinny and K. Bartschat, J.~Phys. B~{\bf 37} (2004), 2173 and 4693. \\[0pt] [2] O. Zatsarinny, Comp. Phys. Commun. {\bf 174} (2006) 273.\\[0pt] [3] O. Zatsarinny and K. Bartschat, Phys. Rev. A {\bf 77} (2008) 062701.\\[0pt] [4] O. Zatsarinny and K. Bartschat, Phys. Scr. Rev. {\bf T134} (2009) 014020.\\[0pt] [5] K. Bartschat and O. Zatsarinny, Plasma Sources Sci. Technol. {\bf 20} (2011) 024012.\\[0pt] [6] D. Dodt, A. Dinklage, K. Bartschat, and O. Zatsarinny, New Journal of Physics {\bf 12} (2010) 073018.\\[0pt] [7] O. Zatsarinny and K. Bartschat, Phys. Rev. Lett. {\bf 107} (2011) 023203. [Preview Abstract] |
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