Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 65, Number 4
Monday–Friday, June 1–5, 2020; Portland, Oregon
Session P02: Spectroscopy of Dense PlasmasInvited Live
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Sponsoring Units: GEC Chair: Yuri Ralchenko, NIST Room: D133-134 |
Thursday, June 4, 2020 2:00PM - 2:30PM Live |
P02.00001: The Dawn of the New Age of Experimental Astrophysics at Cosmic Conditions: Astronomy becomes an experimental science Invited Speaker: Don Winget We can now achieve cosmic conditions in the laboratory. We will discuss the consequences of this relatively new circumstance for astrophysics and physics. We establish the context of the ``at-parameter'' experiments of the Wootton Center for Astrophysical Plasma Properties (WCAPP). This suite of experiments all produce macroscopic plasmas under the density and temperature conditions we find in the cosmos. Current WCAPP experiments focus on 1) stellar interior opacity, 2) atomic kinetics, x-ray heating, and temperature of photoionized plasmas, 3) accretion-powered matter and radiation, and 4) white dwarf photospheres. We will briefly summarize the results of this suite of experiments to-date, with an emphasis on the White Dwarf Photosphere Experiment (WDPE). Nearly all stars either are, or will become, white dwarf stars, giving them broad relevance. The astrophysical questions they can help us answer include the age of the universe, the age and history of star formation of our Galaxy's varied morphological components, and the evolution of stars. The compact and dense nature of these stars means that their atomic physics is not well constrained, even in the outermost layers. We briefly describe the astrophysical and physical problems associated with white dwarf photospheres and our recent progress. [Preview Abstract] |
Thursday, June 4, 2020 2:30PM - 3:00PM Live |
P02.00002: X-ray Spectroscopy and Atomic Physics of Relevance to Inertial Confinement Fusion Invited Speaker: Marilyn Schneider In inertial confinement fusion, laser energy is converted into an x-radiation drive in a high-Z cavity (“hohlraum”). The resulting thermal (~300 eV) x-rays heat a thin spherical shell of low Z material which ablates and, through a rocket-effect, drives the DT fuel inside to high enough temperature and density for fusion to occur. Many physical processes are involved in this integrated experiment, and benchmarking models for these physical processes or measuring plasma conditions is important for understanding and interpreting results. We use x-ray spectroscopy to better understand both hohlraum physics and capsule physics. We study the non-Local Thermodynamic Equilibrium (NLTE) physics of the laser deposition region with surrogate experiments (on uniform plasmas) at the OMEGA laser. We study conditions inside the capsule with high-resolution time-resolved x-ray spectroscopy plus time-integrated continuum measurements of Kr-doped fuel. Current experimental results and comparison to atomic physics models will be presented. [Preview Abstract] |
Thursday, June 4, 2020 3:00PM - 3:30PM Live |
P02.00003: Systematic measurements of opacity dependence on temperature, density, and atomic number at stellar interior conditions Invited Speaker: Taisuke Nagayama Opacity calculations for hot dense plasma are challenging due to environment effects on the atoms. In fact, modeled iron opacities are notably different from measurements performed at matter conditions similar to the boundary between the solar radiation and convection zones [J.E. Bailey et al., Nature 517, 56 (2015)]. The calculated iron opacities have narrower spectral lines, weaker quasi-continuum at short wavelength, and deeper opacity windows than the measurements. If correct, these measurements help resolve a decade old problem in solar physics. A key question is therefore: What is responsible for the model-data discrepancy? The answer is complex because the experiments are challenging and opacity theories depend on multiple entangled physical processes such as the influence of completeness and accuracy of atomic states, line broadening, and contributions from myriad transitions from excited states. To help determine the cause of this discrepancy, a systematic study of opacity variation with temperature, density, and atomic number is underway. Measurements of chromium, iron, and nickel opacities have been performed at two different temperatures and densities. The collection of measured opacities provides constraints on hypotheses to explain the discrepancy [T. Nagayama et al., Phys. Rev. Lett. 122, 235001 (2019)]. We will discuss implications of measured opacities, experimental errors, and possible opacity model refinements. [Preview Abstract] |
Thursday, June 4, 2020 3:30PM - 4:00PM Not Participating |
P02.00004: Ionization and K-shell Spectral Signatures in Dense Plasmas with non-Maxwellian Electron Distributions. Invited Speaker: Igor Golovkin Radiation-based diagnostics -- including imaging, spectroscopy, and absolute flux measurements -- are widely used to determine key features of high energy density laboratory plasmas (HEDLP). In short-pulse laser experiments, energetic particles can also be generated by intense laser fields. Spectroscopic analysis based on K$\alpha $/K$\beta $ satellite line emission can provide important information regarding characteristics of both the target plasma and the energetic electrons. The electrons travel through the dense plasma and produce K$\alpha $ and K$\beta $ emission by collisionally ionizing and exciting K-shell electrons of target ions. The subsequent refilling of the K shell by 2p$\to $1s and 3p$\to $1s transitions results in the emission of K$\alpha $ and K$\beta $ line radiation, respectively. We will present detailed analysis of time-dependent atomic kinetics in plasmas with non-Maxwellian electrons and discuss processes involved in formation of K$\alpha $/K$\beta $ composite spectral features. In particular, we will show how dense plasma effects influence plasma ionization and line shifts in experiments on Omega EP laser facility. We will also demonstrate, based on the analysis of experiments at the Zebra pulsed-power facility, that strong external magnetic fields can have a significant impact on spectroscopic observables. [Preview Abstract] |
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