Bulletin of the American Physical Society
63rd Annual Gaseous Electronics Conference and 7th International Conference on Reactive Plasmas
Volume 55, Number 7
Monday–Friday, October 4–8, 2010; Paris, France
Session SF2: Electron Collisions with Atoms and Ions |
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Chair: Don Madison, Missouri University of Science and Technology Room: 262 |
Friday, October 8, 2010 8:30AM - 9:00AM |
SF2.00001: Electron-ion collisions: precision spectroscopy and plasma rate coefficients Invited Speaker: Charge-changing interactions of electrons with target ions A$^ {q+}$ are studied. Cross sections and rate coefficients are measured and the resonant excitation of the ions is employed in a new type of precision spectroscopy. Using charged particles as targets implies a number of advantages and special aspects that can be exploited in experiments. Beams of charged particles can easily be analyzed and selected with respect to the mass, the charge state and the energy of the particles. Hence, a beam of charged particles can provide a very well characterized pure target for collision and spectroscopy experiments. The determination of target density distributions is difficult but the use of energetic charged particles also offers the potential of very accurate measurements. Plasma environments, man-made or of natural origin, often contain ions in high charge states. Understanding plasma properties requires detailed and accurate knowledge of energy-dependent electron-ion cross sections specified by the charge state of the ions. Moreover, variation of the charge states of the target ions provides access to measurements along iso-electronic sequences in which the number of electrons in the system is kept constant, while the atomic number Z and the charge state q are varied. Along an iso-electronic sequence the relative importance of electron-nucleus and electron-electron interactions gradually changes, thus providing an opportunity to experimentally disentangle their influence on the structure and dynamics of the atomic system studied. Collisional spectroscopy exploiting resonance phenomena in electron-ion interactions provides an efficient new tool to test the most advanced theoretical calculations of atomic energy levels and their decay properties, to investigate the validity of quantum electrodynamics in strong fields, to understand atomic and molecular physics at the borderline to nuclear physics and to gain insights into the influence of collective effects as well as the response of a single atom on the properties of molecules or atomic clusters under the gradual increase of the number of atoms in the system. Electrons are especially fine probes for studying properties of atomic systems. High resolution measurements are possible due to the availability of very highly developed instrumentation, the possibility to exploit kinematic advantages and the selectivity of electron-ion interactions. [Preview Abstract] |
Friday, October 8, 2010 9:00AM - 9:15AM |
SF2.00002: Near threshold electron impact ionization of argon and krypton Murtadha A. Khakoo, Brent Yates, Ling Hong We report doubly differential cross-sections for the single electron impact ionization of Ar and Kr taken at 1eV above the ionization threshold up to the threshold for double ionization. The range of scattering angles are from 10 to 120 degrees, and the DDCSs are normalized to the present resonant excitation DCSs for Ar and Kr. [Preview Abstract] |
Friday, October 8, 2010 9:15AM - 9:30AM |
SF2.00003: Super-elastic scattering from atoms using visible and UV lasers Andrew Murray, Sarah Jhumka, Alex Knight-Percival, Martyn Hussey Studying excitation of atoms by electron impact to produce a full description of the collision process either requires coincidence studies between the scattered electron and photons emitted from the excited state, or uses super-elastic scattering of electrons from atoms prepared using coherent laser radiation. The latter technique adopts time reversal arguments to ascertain Atomic Collision Parameters at a rate thousands of times faster than coincidence methods. This allows measurements to be made over the complete scattering geometry with high precision. A severe limitations of the super-elastic technique is the restricted number of targets that can be excited by present lasers. These include the alkalis, and some alkali earths. This limitation arises due to a lack of UV power, where most targets have their first excited state transition. Here we discuss a new method to enhance the laser power using a resonant cavity in the apparatus. In this way we expect intensities $\sim$200mW/mm$^2$ at the interaction region for wavelengths as low as 215nm, allowing many new targets to be studied. We will also present low energy data from calcium at 12eV and below, showing the power of this technique for accurate measurements. [Preview Abstract] |
Friday, October 8, 2010 9:30AM - 9:45AM |
SF2.00004: Electron scattering from copper Oleg Zatsarinny, Klaus Bartschat We have extended our recent calculations for electron-impact excitation of the $\rm (3d^9 4s^2)^2D_{5/2,3/2}$ states in copper [1] to elastic scattering as well as other transitions, most importantly the resonance transition $\rm (3d^{10}4s)^2S_{1/2} \to 3d^{10}4p)^2P_{1/2,3/2}$. In light of the challenges associated with the Cu target, an accurate knowledge of these cross sections is of high interest as a benchmark system for atomic collision theory while at the same time being a key ingredient for modeling applications such as the copper-vapor laser, which has become a well-established source of high-power visible light. Our calculations are based upon Breit-Pauli [2] and fully relativistic [3] versions of the $B$-spline $R$-matrix (close-coupling) complex [4]. We will compare our results with those from other recent calculations [5], and also present the relevant atomic structure data, in particular oscillator strenghts for a number of transitions. [1] O.~Zatsarinny, K.~Bartschat, V.~Suvorov, P.J.O.~Teubner, and M.J.~Brunger, Phys.`Rev. A~{\bf 81} (2010), in press. [2] O.~Zatsarinny and K.~Bartschat, J. Phys.`B~{\bf 37} (2004) 2173. [3] O.~Zatsarinny and K.~Bartschat, Phys.`Rev. A~{\bf 77} (2008) 062701. [4] O.~Zatsarinny, Comp. Phys.`Commun.~{\bf 174} (2006) 273. [5] V.~Suvorov, P.J.O.~Teubner, V.~Karaganov, K.~Ratnavelu, Y.~Zhou, and M.J.~Brunger, Phys.~Rev.~A~{\bf 80} (2009) 022711. [Preview Abstract] |
Friday, October 8, 2010 9:45AM - 10:00AM |
SF2.00005: Electron-photon coincidence experiments on zinc atoms Mariusz Piwinski, Lukasz Klosowski, Darek Dziczek, Stanislaw Chwirot Atoms with two valence electrons outside relatively inert cores i.e. alkaline earths elements and associated group of atoms like Zn, Cd, Hg and Cn are challenging for both theoretical and experimental investigations of electronic collisions. Electron -- photon coincidence experiments are well known for providing more detailed information about atomic scattering than any other technique and have stimulated studies of increasingly complex collision systems. We present experimental values of the electron impact coherence parameters (EICP) and Stokes parameters for excitation of 4$^{1}$P$_{1}$ state of zinc atoms. The results have been obtained using electron -- photon coincidence technique for incident electron energy 100 eV and electron scattering angles in the range of 5$^{\circ}$ to 25$^{\circ}$. Our results are the first set of quantum-mechanically complete experimental data for zinc atoms. [Preview Abstract] |
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