Bulletin of the American Physical Society
2006 APS April Meeting
Saturday–Tuesday, April 22–25, 2006; Dallas, TX
Session P16: Sherwood III |
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Sponsoring Units: DPP Chair: Linda Sugiyama, PSFC, Massachusetts Institute of Technology Room: Hyatt Regency Dallas Landmark D |
Monday, April 24, 2006 10:45AM - 11:15AM |
P16.00001: Momentum transport from magnetic reconnection in flowing plasmas Invited Speaker: Fatima Ebrahimi Magnetic fluctuations arising from MHD instabilities can cause momentum transport both in laboratory and astrophysical plasmas. We investigate momentum transport from current-driven reconnection, likely a powerful mechanism in laboratory fusion plasmas and possibly important in astrophysical venues. Momentum transport is examined, both analytically and numerically, using the Maxwell stress associated with tearing instabilities. We study momentum transport from single tearing modes, and transport from multiple tearing modes. We find that spontaneous reconnection of a single tearing mode in a plasma with equilibrium flow can transport momentum, but that transport is substantially enhanced in the presence of multiple modes due to nonlinear mode coupling. It is shown that the major contribution of single tearing mode to momentum transport arises from the inner layer solutions. The nonlinear, 3D, resistive MHD code DEBS, with an ad-hoc term added to the momentum equation, is employed to study momentum transport from multiple tearing modes. The role of coupled spontaneous and nonlinear driven reconnection are examined. Theoretical results are compared with measurements of momentum transport and Lorentz forces in the MST reversed field pinch experiment. [Preview Abstract] |
Monday, April 24, 2006 11:15AM - 11:45AM |
P16.00002: Piecewise-Beltrami MHD equilibria Invited Speaker: Robert Dewar An algorithm for constructing 3-dimensional toroidal MHD equilibria that converged rapidly to arbitrary accuracy would be useful not only for design and experimental interpretation purposes but as a constructive solution to the fundamental mathematical existence problem [H. Grad, Phys. Fluids {\bf 10}, 137 (1967)]. A construction based on minimizing the pressure + magnetic energies cannot converge to arbitrary accuracy if ideal MHD constraints (frozen-in flux) are imposed everywhere because of the generic existence of islands and chaotic field line regions between invariant (KAM) tori. Instead we freeze the topology only on selected surfaces with irrational rotational transforms and, in between, impose only conservation of magnetic helicity, leading to piecewise-flat-pressure Beltrami ($\nabla\times {\rm B} = \mu {\rm B}$) equilibria. Little generality is lost, because, if KAM surfaces are of full measure a smooth pressure profile can be approximated with arbitrary accuracy by increasing the number of ``barrier'' surfaces. To this end, cylindrical stepped equilibria have been constructed semi-analytically, and the Beltrami field between two nested 3-D toroidal flux surfaces solved numerically using the method of lines. \newline \newline In collaboration with Matthew Hole, The Australian National University, Dept. of Theoretical Physics, RSPhysSE; and Stuart Hudson, Princeton University Plasma Physics Laboratory. [Preview Abstract] |
Monday, April 24, 2006 11:45AM - 12:15PM |
P16.00003: Pure electron plasmas in a stellarator: Theory and experiment Invited Speaker: Thomas Sunn Pedersen The confinement of non-neutral plasmas by magnetic surfaces, such as those of a tokamak or a stellarator, is a new area of plasma research. The theory of such plasmas, which range from single component to quasi-neutral, has had a rapid development in recent years. The primary focus has been on pure electron plasmas, in particular the properties of low density electron plasma equilibria. The equilibrium equation is a Poisson-Boltzmann equation for the electrostatic potential which has been solved numerically in realistic three-dimensional geometries. Pure electron plasmas confined on magnetic surfaces are now being studied in several experiments, including the recently operational Columbia Non-neutral Torus (CNT). CNT is an ultralow aspect ratio stellarator at Columbia University, which is devoted to the study of plasma confinement on magnetic surfaces over the full range of plasma neutrality: single component to quasi-neutral. These experiments have already confirmed one theoretical prediction: The existence of macroscopically stable equilibria. We will report on theoretical predictions and experimental measurements of equilibrium, stability, and confinement, and will discuss work in progress on the inclusion of a finite ion fraction and the effects of high electron densities. \newline \newline In collaboration with Allen H. Boozer, Remi G. Lefrancois, Jason P. Kremer, Quinn R. Marksteiner, and John Berkery, Columbia University. [Preview Abstract] |
Monday, April 24, 2006 12:15PM - 12:45PM |
P16.00004: Parallel closures for transport applications Invited Speaker: J.-Y. Ji We present recent advances in solving the steady-state closure problem with applications to parallel transport in magnetically confined plasmas. First, we present a treatment of the linearized Coulomb collision operator for ionized plasmas. Moment expansion of a distribution function reduces the collision operator to products of moments and speed dependent terms that include the full particle and field responses. This approach preserves the conservation properties of the collision operator for each moment and provides for quantitative, collisional transport coefficients. Next, we discuss converting ordered kinetic equations into a small set of coupled ordinary differential equations for higher-order moments. By preserving the collisionless response of free-streaming particles and the nonlinear temperature and density dependence in thermodynamic drives, we study parallel transport in the nearly collisionless core of magnetically confined plasmas and in edge plasmas where density and temperature vary significantly along magnetic field lines. Finally, we discuss the solution of the coupled higher- order moment equations in the NIMROD code and apply this solution in studies of parallel electron heat transport in the SSPX experiment\footnote{E. B. Hooper, {\it et al.}, Nucl. Fusion {\bf 39}, 863 (1999).} and large tokamaks. \newline \newline In collaboration with E.D. Held, Utah State University and C.R. Sovinec, University of Wisconsin-Madison. [Preview Abstract] |
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