Bulletin of the American Physical Society
2006 37th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 16–20, 2006; Knoxville, TN
Session E2: Atomic Physics for ITER and Other Next Step Fusion Experiments |
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Chair: David Schultz, Oak Ridge National Laboratory Room: Knoxville Convention Center Ballroom EFG |
Wednesday, May 17, 2006 1:30PM - 2:06PM |
E2.00001: Edge plasma simulation and AMO physics: A multi-scale problem. Invited Speaker: Plasma edge physics is one of the major challenges in fusion plasmas. The need for power and particle exhaust for any reactor inspired a lot of theoretical and experimental work. Understanding this physics requires a multi-scale ansatz bringing together also several physics and numerical models. The plasma edge of fusion experiments is characterized by atomic and molecular processes. Hydrogenic ions and neutrals hit material walls with energies from several eV up to 1000s of eV. They saturate the wall materials and due to physical or chemical processes neutrals are released from the wall, both atomic and molecular. They determine via interaction with the plasma strongly its properties. A complete physics model for the plasma-wall interaction processes alone is already rather challenging (and still missing): it requires e.g. inclusion of collision cascades, chemical formation of molecules, diffusion in strongly 3D systems. A full description needs a multi-scale model combining quite different numerical techniques like molecular dynamics, binary collisions, kinetic Monte Carlo and mixed conduction/convection equations in strongly anisotropic systems. \newline [Preview Abstract] |
Wednesday, May 17, 2006 2:06PM - 2:42PM |
E2.00002: Atomic and Surface Physics in Tokamak Edge Plasmas Invited Speaker: Material surfaces in fusion machines are subject to intense heat and particle fluxes. As a result, eroded impurities from the walls and divertor targets constitute an intrinsic component of the plasmas; understanding their production and transport relies on broad applications of atomic physics. Various materials have been used for plasma facing components, e.g., stainless steel, inconel, beryllium, tungsten, gold and graphite, and a number of these may be employed in the ITER tokamak. Because graphite tiles are widely used in present day devices, a large fraction of impurity studies have been concerned with the atomic physics of carbon. Influx rates are measured using spectral line intensities together with collisional-radiative models that are built from detailed calculations of electron excitation and ionization rates. In the cold edge region, ion temperatures and flow rates are determined from Doppler broadenings and shifts of spectral multiplets from low ionization stages, which are fitted to complex theoretical profiles that require calculating nonlinear Zeeman effects. Differentiating the mechanisms of production, such as physical sputtering, chemical sputtering, sublimation, etc., involves comparison of molecular and atomic influxes as well as detailed comparison of measured C I line shapes with those modeled for theoretical velocity distributions produced by the different mechanisms. [Preview Abstract] |
Wednesday, May 17, 2006 2:42PM - 3:18PM |
E2.00003: Computational Atomic and Molecular Physis for Transport Modelling of Fusion Plasmas Invited Speaker: M.S. Pindzola Various computational intensive non-perturbative methods are used to calculate the electron-atom, electron-molecule, and ion-atom collision processes found in high temperature fusion plasmas. The collision cross sections are benchmarked against approximate perturbative methods and experimental measurements. The baseline collision rate coefficients involving thousands of excited atomic levels are converted to generalized rate coefficients for ground and metastable atomic levels by solving collisional-radiative equations in the quasi-static equilibrium approximation, see H P Summers and M G O'Mullane in ``Nuclear Fusion Research,'' (Springer, 2005), 399-413. The derived ionization balance and radiative power loss coefficients are then used in fusion plasma modelling codes to study Li and Be transport at DIII-D and to study W wall erosion at ASDEX-Upgrade and JET. These tokamak studies are testing critical design issues for ITER. [Preview Abstract] |
Wednesday, May 17, 2006 3:18PM - 3:54PM |
E2.00004: Methane production from slow atomic and molecular D ion impact on graphite: Invited Speaker: Because of its high thermal conductivity, excellent shock resistance, absence of melting, low activation, and low atomic number, there is significant technological interest in using graphite as a plasma-facing component on present and future fusion devices. This interest extends to the use of different types of graphite or carbon fiber composites (CFC's), together with tungsten, beryllium, or other refractory metals, in the ITER divertor. Although these materials have outstanding thermo-mechanical properties, they can suffer significant chemical erosion and sputtering by low energy hydrogen ion impact, which determines in large part the carbon-based-material lifetime. Due to evolving divertor design, the interest in the erosion characteristics of the carbon surfaces is shifting to progressively lower impact energies. Results are presented of chemical sputtering yields of ATJ graphite by impact of D$^{+ }$and D$_{2}^{+}$ and D$_{3}^{+}$ in the energy range 5-250 eV/D. Our experimental approach is based on the use of a quadrupole mass spectrometer (QMS) to monitor partial pressure increases of selected mass species resulting from ion impact on the graphite surface. Due to the high D$^{+}$ currents obtainable with our ECR ion source, and the highly efficient beam deceleration optics employed at the entrance to our floating scattering chamber, comparison between same velocity atomic and molecular ion impact was possible with our apparatus at energies as low as 10 eV/D, and permitted testing of the commonly made assumption that isovelocity atomic and molecular species lead to identical sputtering yields when normalized to the D constituent number of the incident projectiles. The measurements also serve as benchmarks for new MD simulations of the chemical sputtering process that seek to incorporate more realistic many-body potentials and to expand the reaction pathway to include vibrational and/or electronic excited states. [Preview Abstract] |
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