Bulletin of the American Physical Society
2006 Four Corners Section of the APS Fall Meeting
Friday–Saturday, October 6–7, 2006; Logan, Utah
Session D3: Plasmas and Fusion |
Hide Abstracts |
Chair: Ross Spencer, Brigham Young University Room: Eccles Conference Center Room 201/203 |
Friday, October 6, 2006 1:30PM - 1:42PM |
D3.00001: Collisional Braginskii closure vs. the integral closure and closing the fluid equations J.-Y. Ji, E.D. Held Recent calculation of the exact linearized Coulomb collision operators and the general moment equations\footnote{J.-Y. Ji and E. D. Held, Phys. Plasmas, to be published (2006). } are introduced. As an application, higher order terms for the collisional heat flux closure are derived and the limitation of the collisional Braginskii closure is evaluated quantitatively. For plasmas with general collisionality, the integral heat flux closure based on the pitch-angle scattering operator\footnote {E. D. Held {\it et al}., Phys. Plasmas {\bf 8}, 1171 (2001). } is introduced and its physical meaning is discussed in comparison with the Braginskii closure. Improvements to the derivation of general closures with a more rigorous treatment of the collision operator and a general scheme for closing the fluid equations are presented. [Preview Abstract] |
Friday, October 6, 2006 1:42PM - 1:54PM |
D3.00002: General parallel closures for tokamak plasmas M. Sharma, J.-Y. Ji, E.D. Held Analytical and numerical work is done to understand controlled magnetic fusion experiments such as tokamaks, a doughnut-shaped magnetic confinement device that may form the basis of future fusion reactors. In such systems plasma can be described in terms of transport equations obtained from the kinetic equation. We close the density, momentum and energy conservation equations by solving the drift kinetic equation and taking closure moments. A Chapman-Enskog-like approach is adopted where the distribution function is written as the sum of a dynamic Maxwellian and a kinetic distortion, $F$, expanded in Legendre polynomials $P_l (v_\| /v)$. For an accurate treatment of collisional effects, a moment approach is applied to the full, albeit linearized Coulomb collision operator. This approach leads to denumerable infinity of equations describing the system. Truncation at some suitable order permits a derivation of neoclassical closures for the parallel conductive heat fluxes and stresses. The parallel gradient operator, acting on $F$ as well as $v_\| /v$, is inverted via the Legendre-polynomial expansion and subsequent diagonalization of the differential equation system for the expansion coefficients is done. This approach allows examination of the closures in all collisionality regimes and thus aids in understanding the complex behavior of confined tokamak plasmas. [Preview Abstract] |
Friday, October 6, 2006 1:54PM - 2:06PM |
D3.00003: Implementation and Analysis of 4$^{th}$ Order CWENO Reconstruction for use in Relativisitic MHD Simulations Nicholas Nelson, David Neilsen Relativistic magneto-hydrodynamics (RMHD) is used to model astrophysical systems with magnetic fields. Numerical simulations in RMHD require high accuracy to efficiently resolve the complex features expected in the solutions. We discuss an implementation of a central 4th order CWENO method for RMHD. Preliminary results of standard test problems, including comparisons with an established CENO scheme, will be presented and discussed. [Preview Abstract] |
Friday, October 6, 2006 2:06PM - 2:18PM |
D3.00004: Non-local plasma heat flow in a perturbed magnetic field John James, Eric Held In this work, we review the derivation and implementation of a non-local closure\footnote{E. D. Held, J. D. Callen and C. C. Hegna, Phys. Plasmas 10, 3933 (2003).} for the field-aligned heat flow in the plasma fluid temperature equation. We apply the closure to a plasma embedded in a sheared slab magnetic field configuration with a single-helicity perturbation and compare derived quantities such as effective radial thermal diffusivity and on-axis plasma temperature with those obtained using a flux-limiting and a local diffusive form for the closure. A novel algorithm for rapid approximation of the heat-flow integrals involved in calculating the non-local closure is presented along with results from validity and convergence tests. [Preview Abstract] |
Friday, October 6, 2006 2:18PM - 2:30PM |
D3.00005: Effects of Generalized Ion Stress on Plasma Sound Waves Michael Addae-Kagyah, Eric Held Details of two key effects of the generalized parallel ion stress tensor ($\Pi _{\vert \vert })$ on magnetized plasmas, namely sound wave damping and viscous heating, are presented. Kinetic-based derivation of $\Pi _{\vert \vert }$, employing an expansion of the particle distribution function, forms the theoretical basis of this study. The goal of this research is to incorporate kinetic physics into the physical models of high-temperature plasmas. Here, a hybrid fluid/kinetic model is applied to the simulation of plasma systems, via the use of the generalized stress closure in the closing of fluid equations. The NIMROD code is used to run the simulations designed to highlight the finite physical effects of the generalized $\Pi _{\vert \vert }$. Runs involve scans of plasma parameters that correspond to various degrees of plasma collisionality. Analogous simulations, involving the local form of $\Pi _{\vert \vert }$, are also run for comparison. Diagnostics of the parallel viscosity, damping rates, and energies are made. It is concluded that the generalized $\Pi _{\vert \vert }$ and the local $\Pi _{\vert \vert }$models produce similar results at high collisionality, whilst the former$_{ }$predicts more realistic values at low collisionality. [Preview Abstract] |
Friday, October 6, 2006 2:30PM - 2:42PM |
D3.00006: Construction of a Low-energy Single-wire Z-pinch Apparatus for Metal-catalyzed Fusion Studies Shannon Walch, Steven Jones, John Ellsworth Numerous beam and foil experiments have been undertaken in an effort to explore fusion enhanced by condensed matter and have produced substantial evidence for the catalyzing effect of metals and the variation in effectiveness of different types of metal. A group at Brigham Young University studying low energy nuclear reactions is currently building a low-energy single-wire z-pinch apparatus to test it as a tool for producing such reactions. If useful, it will expedite our studying the relationships between the type of metal used and the number of emitted particles, and it will assist in the development of a theory for this type of reaction, as no current theory can predict the outcomes of these experiments. [Preview Abstract] |
Friday, October 6, 2006 2:42PM - 2:54PM |
D3.00007: Hollow Plasma Instability: Theory vs. Experiment Melissa Powell, Grant Mason, Ross Spencer A Malmberg-Penning trap is a cylindrical apparatus which confines non-neutral plasma (electrons only) with an axial magnetic field and negative electric potentials on both ends. It is a simple system for studying basic plasma behavior, so simple that theory and experiment ought to agree. Theory predicts that a hollow plasma density profile is unstable, and experiments agree. However, the experimental growth rate of the instability is much larger than the theoretical growth rate, by a factor of around 2-4. We are collaborating with Travis Mitchell's experimental research group at the University of Delaware to find the cause for this discrepancy by recreating their Malmberg-Penning trap in our computer simulation. The growth rates of our simulation test cases have remained roughly half that of Mitchell's experiments. We will report the results of investigating several possible causes for this discrepancy, including asymmetry, resistive connections to confining rings, a non-Maxwellian particle distribution function, the initial perturbation, and the polarization drift. [Preview Abstract] |
Friday, October 6, 2006 2:54PM - 3:06PM |
D3.00008: Evidence of New Plasma Equilibrium State Sought William Edwards, Eric Held, Ajay Singh, Jeremy Bishop A recently reported plasma equilibrium state, derived by minimizing the total system energy without imposing the quasi neutrality condition [1], offers a new possibility for designing a magnetic confinement device for thermonuclear fusion. Utah State University has acquired a small tokamak from the University of Saskatchewan in Canada. This machine is being modified in an attempt to experimentally verify the existence of the state and to determine a procedure whereby a gas at room temperature can be heated to thermonuclear fusion temperatures while held in the new state by magnetic and electrostatic fields. Conditions on size of vessel, gas fill pressure, magnetic field magnitudes, and plasma beta are restricted. A fusion device will be compact leading to the possibility of applications such as production of neutron beams for examination of luggage in airports, search for unexploded land mines, cancer diagnosis, activation of thorium for fission energy, etc. \newline \textbf{Reference} \newline [1] W. F. Edwards and E. D. Held, \textit{Phys ,Rev. Lett., }\textbf{11}, 255001 (2004) [Preview Abstract] |
Friday, October 6, 2006 3:06PM - 3:18PM |
D3.00009: Generalized Stationary States for Fusion Plasmas E.D. Held, W.F. Edwards, A. Kullberg The subject of minimum energy states for magnetically confined plasmas dates back to pioneering work by Woltjer\footnote{L. Woltjer, {\em Proc. Natl. Acad. Sci. U.S.A.} {\bf 44}, 489 (1958); {\bf 44}, 833 (1958); {\bf 45}, 769 (1959)} and Chandrashekar\footnote{S. Chandrasekhar, {\em Proc. Natl. Acad. Sci. U.S.A.} {\bf 44}, 842 (1958); {\bf 42}, 273 (1956)}. After decades of work in this area, a novel theory\footnote{W. F.\ Edwards and E. D.\ Held, {\em Phys. Rev. Lett.,} {\bf 11}, 255001 (2004)} has been developed which includes all of the terms in the energy integral and adjoins local constraint equations that avoid the common assumption of quasineutrality. In this talk, we discuss a complimentary version of this recent theory which replaces the local constraints of plasma fluid and Maxwell's equations with the constraints of globally conserved generalized helicities. Comparison is made between the stationary states predicted by these theories for the problems of cylindrical Z-pinch, ${\Theta}$-pinch and screw pinch plasmas. Importantly, both theories predict that substantial electrostatic fields due to charge separation play a critical role in confinement. We conclude by discussing the application of the theory in toroidal geometry which is relevant to the problem of confining fusion plasmas in laboratory experiments. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700