Bulletin of the American Physical Society
42nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 56, Number 5
Monday–Friday, June 13–17, 2011; Atlanta, Georgia
Session B1: The X-ray Universe |
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Chair: Phillip Stancil, University of Georgia Room: A601 |
Tuesday, June 14, 2011 10:30AM - 11:00AM |
B1.00001: Laboratory Spectroscopy for Interpreting Astrophysical Spectra Invited Speaker: We have been using electron beam ion traps and a variety of spectrometers to isolate and study atomic processes taking place in astrophysical sources and to provide calibrated X-ray line emission and absorption diagnostics for use by the astrophysics community. Studies of electron impact excitation and photoexcitation and ionization cross sections and transition energies have been conducted. Photoexcitation and ionization studies have been completed by employing a transportable electron beam ion trap, provided by the Max-Plank-Institute for Kernphysik, at various advanced light sources including the BESSY-II synchrotron, the FLASH free electron laser, and most recently, the Linac Coherent Light Source free electron laser. Various recent results will be discussed. \\[4pt] This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Tuesday, June 14, 2011 11:00AM - 11:30AM |
B1.00002: Photonic and electronic interactions of ions Invited Speaker: Merged-beam techniques are used to study electron-ion recombination as well as photoionization and photofragmentation of ions. Time reversal symmetry relates photoionization to electron-ion recombination and measurements addressing both processes can provide new detailed insight into the role of specific reaction pathways in both channels. Beams of mass and charge state analyzed accelerated ions provide well defined, clean targets for studying electron-ion and photon-ion interactions. Complete collection at high selectivity and efficient detection of product ions is ensured by the directionality of the incident energetic ion beam and, thus, absolute cross sections can be determined with good accuracy. Employing monochromatized photons and cold electron beams together with well prepared ion beams facilitates the measurement of high-resolution resonance spectra and delivers detailed spectroscopic information about singly and multiply excited states of the ions. Plasma rate coefficients derived from such measurements are required to model astrophysical and laboratory plasmas and their emission and absorption characteristics. Besides atomic ions, also fullerene ions and endohedral fullerenes with encapsulated atomic ions are addressed in photon-ion merged-beams experiments. A particularly interesting subject of such studies is the response of endohedral fullerenes to photoabsorption by the atom encaged inside a carbon sphere. Plasmon resonances, redistribution of oscillator strengths and containment resonances are exciting topics for studies of these exotic nano-scale objects. [Preview Abstract] |
Tuesday, June 14, 2011 11:30AM - 12:00PM |
B1.00003: The X-ray Sun Invited Speaker: The X-ray emission of the Sun is one of the main avenues through which we can make progress in our understanding of the physical processes that drive solar activity, heat and accelerate solar coronal plasmas, and influence the interplanetary environment and the Earth itself. The last decade has seen the launch of several space missions carrying X-ray instrumentation, that have helped us to greatly advance our understanding of our star. These missions have also boosted our need of accurate atomic data for the interpretation of the observations. In this talk I will review the main results delivered by X-ray solar missions, and will highlight the challenges that still lie ahead of us and the atomic data we need to face them. [Preview Abstract] |
Tuesday, June 14, 2011 12:00PM - 12:30PM |
B1.00004: X-ray photoionization and resonant scattering of highly charged ions in the laboratory Invited Speaker: Photoionizing highly charged ions, which are characteristic of AGNs and x-ray binaries, has become possible in the laboratory by combining an electron beam ion trap (EBIT) with powerful x-ray sources. The method consists of superimposing the photon beam with a tight ensemble of trapped ions, that have been prepared in well defined charge states through electron impact ionization, and by subsequently analyzing their charge state evolution upon interaction with photons of varying energy. The EBIT ion areal density of 10$^{10}$ ions/cm$^{2}$ is sufficient to allow for measurements of direct photoionization cross sections down to only 0.1 Mbarn. The energy determination of strong resonant transitions is possible to within 0.1 eV at 1 keV photon energy, limited by the current x-ray calibration standards in use, but statistical uncertainties of few ppm have been achieved for FeXIV and FeXV photoabsorption. Another feature of this technique is the possibility to extend resonant laser spectroscopy into the x-ray region through the use of free-electron lasers (FELs) reaching into this spectral range. Following EBIT investigations of the $2s-2p$ transitions in Li-like FeXXIV at FLASH, the soft x ray FEL at DESY in Hamburg, Germany, we have carried out work into the keV region utilizing synchrotron radiation at BESSY II, HZB, Germany, and also performed experiments at LCLS, SLAC, Stanford. The superior peak flux of FELs suppresses background by orders of magnitude, and gives access to photonic interactions of highly charged ions in a spectral region hitherto beyond reach. [Preview Abstract] |
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