Bulletin of the American Physical Society
70th Annual Gaseous Electronics Conference
Volume 62, Number 10
Monday–Friday, November 6–10, 2017; Pittsburgh, Pennsylvania
Session JW3: Antimatter and Other Processes |
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Chair: James Colgan, Los Alamos National Laboratory Room: Oakmont Junior Ballroom |
Wednesday, November 8, 2017 8:00AM - 8:30AM |
JW3.00001: Fresh Insights and Initiatives in Low Energy Scattering Processes Involving Antiparticles Invited Speaker: Michael Charlton We will review aspects of the scattering of antiparticles, and in particular processes used in the controlled formation of antihydrogen atoms with low enough kinetic energies to allow their storage in magnetic minimum neutral atom traps [1-3], an advance that has led to the first determination of some of the properties of the anti-atom [4-7]. When antihydrogen is created via the mixing of dense clouds of cold positrons and antiprotons, radial transport of the antiprotons occurs due to repeated cycles of antihydrogen formation and break-up. We will describe how simulations [8] have elucidated the underlying physics, and explore some the implications for improved antihydrogen trapping efficiencies. There is renewed interest in the use of excited state positronium to form antihydrogen. We will review recent theoretical activity in this field from which accurate data for sub-eV positronium-antiproton collisions have become available for the first time [9-12]. We describe how it may be feasible to use charge exchange in collisions of positronium with ions to create a range of cold atomic species [13], including some which, to date, have not been amenable to laser cooling. 1. G.B. Andresen \textit{et al}. (ALPHA Collaboration), Nature \textbf{468} (2010) 673 2. G.B. Andresen \textit{et al}. (ALPHA Collaboration), Nature Phys. \textbf{7} (2011) 558 3. G. Gabrielse \textit{et al.} (ATRAP Collaboration), Phys. Rev. Lett. \textbf{108} (2012) 113002 4. M. Ahmadi \textit{et al}. (ALPHA Collaboration), Nature \textbf{541} (2017) 506 5. C. Amole \textit{et al}. (ALPHA Collaboration), Nature Commun. \textbf{5} (2014) 3955 6. M. Ahmadi \textit{et al}. (ALPHA Collaboration), Nature \textbf{529} (2016) 373 7. C. Amole \textit{et al}. (ALPHA Collaboration), Nature \textbf{483} (2012) 439 8. S. Jonsell \textit{et al.}, J. Phys B: At. Mol. Opt. Phys. \textbf{49 (}2016)\textbf{ }134004 9. A.S. Kadyrov \textit{et al.}, Phys. Rev. Lett. \textbf{114} (2015) 183201 10. C.M. Rawlins \textit{et al.}, Phys. Rev. A \textbf{93} (2016) 012709 11. M. Charlton \textit{et al.}, Phys. Rev. A \textbf{94} (2016) 032701 12. I.I. Fabrikant \textit{et al.}, J. Phys B: At. Mol. Opt. Phys. \textbf{50 (}2017) 134001 13. W.A. Bertsche \textit{et al}., New J. Phys. \textbf{19} (2017) 053020 [Preview Abstract] |
Wednesday, November 8, 2017 8:30AM - 9:00AM |
JW3.00002: Gaseous Positronics -- Cross Sections, Scattering Dynamics And Applications For Low Energy Positron Interactions With Matter Invited Speaker: Stephen Buckman Intense beams of low-energy positrons with high energy resolution are now available through the use of buffer-gas (Surko) traps. These have led to measurements of interaction cross sections for a broad range of atoms and molecules, including molecules of biological interest. The increased energy resolution, and experimental techniques developed for scattering in strong magnetic fields has also enabled highly accurate measurements of discrete excitation processes such as electronic and vibrational excitation, positronium formation and ionization in a range of atomic and molecular species. This talk will review some of these measurements, including recent studies of near-threshold ionization, and discuss their application in new and sophisticated models of positron transport, with particular emphasis on potential applications in Positron Emission Tomography. This work is part of a broad collaboration between the ANU (James Sullivan, Joshua Machacek), Flinders University (Michael Brunger), James Cook University (Ronald White and co-workers) CSIC Madrid (Gustavo Garcia) and the Institute of Physics, Belgrade (Zoran Petrovic and colleagues). [Preview Abstract] |
Wednesday, November 8, 2017 9:00AM - 9:15AM |
JW3.00003: State-resolved photon-H$_2^+$ cross sections and rate coefficients Mark Zammit, Jeremy Savage, James Colgan, Dmitry Fursa, David Kilcrease, Christopher Fontes, Peter Hakel, Eddy Timmermans Studies of molecular plasmas both in local thermodynamic equilibrium (LTE) and non-LTE require state-resolved (electronic, vibrational and rotationally resolved) transition cross sections or rate coefficients to calculate populations (for non-LTE plasmas), opacities and emissivities. Here we present state-resolved results of photodissociation and radiative association of H$_2^+$ and its isotopologues (D$_2^+$, T$_2^+$, HD$^+$, HT$^+$, and DT$^+$). We note that going beyond the commonly utilized ``two-level'' approximation of H$_2^+$ could be important in models when dealing with radiation temperatures that can access photon wavelengths around 100 nm. For example at these wavelengths, and a material temperature of 8400K, the photodissociation cross section via the (second electronically excited) 2$p \pi_u$ state is over three times larger than the photodissociation cross section via the (first electronically excited) 2$p \sigma_u$ state. [Preview Abstract] |
Wednesday, November 8, 2017 9:15AM - 9:30AM |
JW3.00004: Aurora borealis' modelling in laboratory Yuliia Balkova, Oleksii Girka, Maksym Myroshnyk, Bohdan Bidenko, Oleksandr Bizyukov Basic physical mechanisms of Aurora are explained in this work: solar wind' electrons flux interacts with Earth's magnetic field in Earth's atmosphere with pressure gradient. Minimum possible size of laboratory facility is estimated in order of few centimeters on the base of the mean free path and the gyroradius values. The laboratory modeling of Earth's magnetic field shape was realized by the copper coil inside the plexiglas sphere with the titanium coating (the thickness is 3 \textmu m) deposited on sphere by vacuum-arc method. DC glow discharge serves as electron source and also it is carried out an experiment with additional hot cathode electron source to compare. Working gas (pure argon, oxygen, helium, hydrogen and air), pressure of working gas (0,08÷0,22~Torr), an impact energy of electron flux (0,6÷3 keV) and magnetic field intensity (30÷230 Oe) were varied during experiments. The thickness of ionized layer increase with magnetic field intensity; the area of ionized layer increase with the impact energy of electrons; the radiation intensity of ionized layer increase with pressure of working gas. [Preview Abstract] |
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