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 G3: Invited Session: Line Broadening |
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Chair: Arati Dasgupta, Naval Research Laboratory Room: Grand Ballroom E |
Wednesday, June 6, 2012 8:00AM - 8:30AM |
G3.00001: Line Broadening in White Dwarf Photospheres Invited Speaker: D.E. Winget White dwarfs are the simplest stars with the simplest surface chemical compositions known. Spectroscopically we detect only hydrogen in surfaces of the vast majority of these stars. The remainders are of various types, including stars with surfaces of nearly pure helium and some apparently massive stars with carbon and oxygen at the photosphere. We will examine the potential offered by the white dwarf stars in the context of both astrophysics and physics. This potential includes studying cosmochronology--establishing the age and evolutionary history of our galaxy and an independent lower limit on the age of the universe, constraining the properties of axions and WIMPS in the context of dark matter models, constraining dark energy by establishing the properties of the massive progenitors of type Ia supernovae, studying nucleosynthesis from their internal composition structure, and crystallization in dense Coulomb plasmas, among many others. Realizing this tremendous scientific potential depends on the determination of two boundary conditions for each star: the surface gravity and effective temperature. To do this, we must establish the photospheric plasma conditions, density and temperature, using observations of the stellar absorption spectra. Our understanding of line broadening appears to be an obstacle, at present. We will discuss the evidence for past theoretical inadequacies in line broadening theory and the hope for recent and future calculations. We will discuss how the experiments underway on the Z-facility at Sandia National Laboratories --where we can create macroscopic uniform plasmas under white dwarf photospheric conditions--will provide the benchmarks for improving our understanding of line broadening under white dwarf photospheric plasma conditions. These experiments will guide future theory and improve our understanding of the white dwarf stars and, through them, the contents and evolution of the cosmos. [Preview Abstract] |
Wednesday, June 6, 2012 8:30AM - 9:00AM |
G3.00002: Broadening of Hydrogenic Spectral Lines in Magnetized Plasmas: Diagnostic Applications Invited Speaker: Eugene Oks In diagnostics based on the broadening of spectral lines in plasmas, magnetic fields are important only if their strength is relatively high -- to compete with the Stark and Doppler broadenings. Relevant examples are plasmas produced by ultrashort, high intensity lasers and edge plasmas of magnetic fusion experiments. The focus of this invited talk is at hydrogenic spectral lines. This is because the generally complicated physics of the Stark-Zeeman broadening can be best understood and used in practice for spectral lines of one-electron systems: hydrogen atoms and hydrogenlike ions. Besides, this subject is also theoretically important for two reasons. First, it deals with a deeply fundamental problem of the simplest, two-particle bound Coulomb system immersed in a multi-particle Coulomb system of free charges (plasma) exhibiting long-range interactions. Second, due to the fact that a bound two-particle Coulomb system possesses a higher algebraic symmetry than its geometrical symmetry, sophisticated analytical advances can be made into the problem of the broadening of spectral lines of such a system in a plasma, thus yielding a profound physical insight and leading to innovative diagnostic applications. [Preview Abstract] |
Wednesday, June 6, 2012 9:00AM - 9:30AM |
G3.00003: A new method for line-shape modeling of hydrogen-like and Rydberg transitions in plasma Invited Speaker: Evgeny Stambulchik Calculations of line shapes of hydrogen and hydrogen-like transitions (including Rydberg ones) are important for many topics of plasma physics and astrophysics. However, the Stark effect of the radiative transitions originating from high-$n$ levels is rather complex, making the detailed calculations of their spectral structure very cumbersome. Surprisingly, the complex structure of such transitions can be approximated, under certain assumptions, with a quasi-contiguous (QC) rectangular shape. This formed the basis of an analytical method for the calculation of line broadening\,[1], resulting in a simple expression for the full width at half-maximum of the Stark line broadening in plasma. Although the method is especially suitable for transitions with $\Delta n \gg 1$, it describes rather well even first members of the spectroscopic series with $\Delta n$ as low as 2. Recently, the QC method was extended\,[2] to analytical calculations of line {\em shapes} (not mere line {\em widths}) in plasmas. To this end, we employed a formulation\,[3] of the frequency fluctuation model. Accurate computer simulations\,[4] as well as comparison with experimental data, where available, were used to verify the validity of the method. Applications of the method to a range of physical problems are shown.\\[4pt] [1] E. Stambulchik and Y. Maron, J. Phys. B: At. Mol. Opt. Phys. {\bf 41}, 095703 (2008).\\[0pt] [2] E. Stambulchik and Y. Maron, in {\it Atomic Processes in Plasmas}, AIP Conf. Proc. (AIP, 2012) accepted for publication.\\[0pt] [3] A. Calisti, C. Moss\'{e}, S. Ferri, B. Talin, F. Rosmej, L. A. Bureyeva, and V. S. Lisitsa, Phys. Rev. E {\bf 81}, 016406 (2010); L. A. Bureeva, M. B. Kadomtsev, M. G. Levashova, V. S. Lisitsa, A. Calisti, B. Talin, and F. Rosmej, JETP Letters {\bf 90}, 647 (2010).\\[0pt] [4] E. Stambulchik and Y. Maron, J. Quant. Spectr. Rad. Transfer {\bf 99}, 730--749 (2006). [Preview Abstract] |
Wednesday, June 6, 2012 9:30AM - 10:00AM |
G3.00004: Collisional-radiative analysis of neutral beam spectra in fusion plasmas Invited Speaker: Yuri Ralchenko Powerful beams of neutral particles are extensively used in fusion devices, such as tokamaks and stellarators, to heat and diagnose magnetically confined plasmas. The spectral lines originating from the excited states of a neutral beam provide valuable information on plasma fields, particle temperatures and densities, and other parameters. I will present the recently developed collisional-radiative (CR) model for $m$-resolved parabolic states of hydrogen which has been successfully used to explain motional Stark effect (MSE) spectra from tokamak plasmas.\footnote{O. Marchuk et al., J. Phys. B 43, 011002 (2010).} \footnote{E. Delabie et al., PPCF 52, 125008 (2010).} A new method for calculation of collisional cross sections between parabolic states is developed and used to compute the required atomic data. It is shown that the $\sigma$- and $\pi$-component intensities under typical magnetic fusion conditions cannot be described by statistical (Boltzmann) distribution and therefore require a complete CR analysis. I will also discuss non-statistical behavior of parabolic state populations in a wide range of parameters including those of the ITER tokamak. The field-induced ionization of the high excited states is shown to be a strong uncompensated depopulation channel responsible for deviations from the Boltzmann distribution. [Preview Abstract] |
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