Bulletin of the American Physical Society
50th Annual Meeting of the Division of Plasma Physics
Volume 53, Number 14
Monday–Friday, November 17–21, 2008; Dallas, Texas
Session PO4: Magnetic Reconnection and Basic Plasma Properties |
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Chair: Troy Carter, University of California, Los Angeles Room: Reunion B |
Wednesday, November 19, 2008 2:00PM - 2:12PM |
PO4.00001: The scaling of the two-fluid resistive and collisionless tearing instability Mahboub Hosseinpour, Nickolas Bian, Grigory Vekstein The tearing instability of viscous compressible plasma which is embedded in a sheared force-free magnetic field configuration has been studied in the framework of the two-fluid model both for resistive and collisionless reconnection. In the former case, the resistivity of plasma, and in the latter one the finite electron inertia effect, which are characterized respectively by the Lundquist number$S\equiv \frac{\tau _\eta }{\tau _A }$, ($\tau _\eta ,\tau _A $ are resistive diffusion and Alfven transient time.), and electron inertial skin depth $d_e \equiv \frac{c}{\omega _{pe} }$ ($\omega _{pe}$ is the plasma frequency) are accounted for field reconnection. Under the assumption of constant-``$\psi $'' approximation, the analytical analysis of the linearized Hall-MHD equations yields three different regimes of tearing instability, each which corresponds to particular values of plasma $\beta $ and $d_i =d_e (\frac{m_i }{m_e})^{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$2$}}$, the ion inertial skin depth. All possible regimes are shown in the $d_i -\beta $ diagram. Also the transitions between these regimes are explained. [Preview Abstract] |
Wednesday, November 19, 2008 2:12PM - 2:24PM |
PO4.00002: Hall Magnetohydrodynamics near a Hyperbolic Magnetic Neutral Line Bhimsen Shivamoggi Hall magnetohydrodynamics (MHD) properties near a two-dimensional X-type magnetic neutral line in the steady state are considered. Upon viewing the steady state as the asymptotic limit of the corresponding time-dependent problem, Hall effects are shown to be or not to be able to sustain the hyperbolicity of the magnetic field (and hence a more open X-point configuration) near the neutral line depending on the initial conditions. [Preview Abstract] |
Wednesday, November 19, 2008 2:24PM - 2:36PM |
PO4.00003: Magnetic Reconnection of Super-Strong Magnetic Fields in Magnetar Magnetospheres Dmitri Uzdensky Magnetic reconnection in magnetar magnetospheres, sometimes invoked to explain SGR giant flares, involves magnetic fields exceeding $10^{14}$ Gauss. When this magnetic energy is released, the energy density is so high that electron-positron pairs are inevitably created in copious quantities. The pairs make the reconnection layer optically thick to Thomson scattering, thereby trapping $\gamma$-photons. The plasma pressure inside the layer is then dominated by radiation with a temperature $aT^4 \sim B_0^2/8\pi$. Since the timescale for radiation diffusion across the layer is still shorter than the global (along the layer) Alfven transit time, the effects of radiative cooling on the thermodynamics of the layer need to be included. In addition, the high pair density makes the reconnection layer highly collisional, essentially independent of the upstream plasma density. This makes various collisionless effects negligible, so that resistive MHD (with both Spitzer and Compton resistivity) applies, suggesting a slow, Sweet-Parker-like reconnection rate. [Preview Abstract] |
Wednesday, November 19, 2008 2:36PM - 2:48PM |
PO4.00004: Plasmoid Generation in Driven Compressible Magnetic Reconnection R. Samtaney, N. Loureiro, A. Schekochihin, D. Uzdensky, S. Cowley High Lundquist number (S) magnetic reconnection (MR) drives the formation of very intense and localized current sheets which, as evidenced both in observations and simulations, fragment and lead to the formation of plasmoids. Plasmoids have been invoked in theories of MR and related phenomena: as a plausible mechanism for accelerating reconnection; to explain the production of energetic electrons during MR; and periodic ejection of plasmoids in star-disk systems may account for the knot-like structures observed in stellar jets. A theoretical understanding of the plasmoid formation mechanism has been lacking. We present high-resolution simulations of driven compressible reconnection in which a new current sheet instability leads to the formation of plasmoid chains. This is a generalization of recent results by Loureiro et al. (PoP 14 100703, 2007) to include the effect of the reconnected field. Nonlinear simulations clearly show the break up of these current sheet into secondary islands. We quantify several characteristics (number of plasmoids etc.), their dependence on S and their effect on reconnection rate. Furthermore, we discuss the setup of boundary conditions for these numerical simulations. [Preview Abstract] |
Wednesday, November 19, 2008 2:48PM - 3:00PM |
PO4.00005: Current sheets and filaments in relativistic collisionless plasmas: Exact solutions for a broad class of particle distributions Vladimir Kocharovsky, Vitaly Kocharovsky, Vladimir Martyanov A broad class of stationary current sheets and filaments in collisionless plasma is found analytically using integrals of particle motion in the self-consistent magnetic field. The solutions employ arbitrarily anisotropic particle distributions in both relativistic and non-relativistic plasmas, which can support magnetic structures produced, e.g., via Weibel instability. We consider the properties of newly found stationary structures and their possible applications to analysis of magnetic field configurations emerging in various astrophysical problems, including relativistic shocks and jets. In the latter cases quasistatic turbulence is present, and individual long-living filaments may be described on the basis of the obtained exact solutions. We discuss short-term stability and synchrotron radiation of such filaments, and show that their magnetic energy density can be comparable to that of particles, and the spatial scale can be arbitrary compared to typical gyroradius of the particles. [Preview Abstract] |
Wednesday, November 19, 2008 3:00PM - 3:12PM |
PO4.00006: Fast magnetic reconnection in collisionless plasmas with velocity shear Francesco Pegoraro, Matteo Faganello, Francesco Califano In plasma configurations with a velocity shear qualitatively different magnetic structures are produced depending on how fast the reconnection process develops and competes with the pairing process of the vortices produced by the Kelvin-Helmholtz instability. In a magnetized plasma if the Alfv\'en velocity associated to the in-plane magnetic field is sufficiently weak, the K-H instability generates fully rolled-up vortices which advect the magnetic field lines into a complex configuration, causing the formation of current layers along the inversion curves of the in-plane magnetic field component. We investigate the development of magnetic reconnection during the vortex pairing process and show that completely different magnetic structures are produced depending on how fast the reconnection process develops on the time scale set by the pairing process. develops on the time scale set by the pairing process. [Preview Abstract] |
Wednesday, November 19, 2008 3:12PM - 3:24PM |
PO4.00007: Towards all-optical plasma physics Jason Fleischer, Dmitry Dylov We consider the nonlinear propagation of partially-spatially-incoherent light as a photonic plasma. Using wave-kinetic theory, we interpret the speckles of statistical light as quasi-particles which can interact via the nonlinearity. We analytically derive a Bohm-Gross dispersion relation for these speckles and their Langmuir-type interaction waves, and identify an effective plasma frequency, effective Debye length, etc. Experimentally, we demonstrate this mapping by studying the nonlinear propagation of diffused (quasi-thermal) light in a self-focusing photorefractive crystal. Observed phenomena include modulation instability, two-stream and (multiple) bump-on-tail instabilities, wave collapse, and optical turbulence. By recording a hologram of the internal dynamics, we observe speckle-wave and wave-wave interactions, in both position (x) space and momentum (k) space. The results generalize ideas from plasma physics, lead to new wave dynamics in nonlinear statistical optics, and allow the experimental study of phenomena that are difficult, if not impossible, to observe in material plasma. [Preview Abstract] |
Wednesday, November 19, 2008 3:24PM - 3:36PM |
PO4.00008: Low velocity Ion Stopping in Strongly Magnetized Plasmas Claude Deutsch, Romain Popoff We focus attention on the low velocity ion slowing down(LIVSD)at projectile velocity Vp$<$Vthe in the target electron plasma with arbitrary density Ne and submitted to a steady homogeneous magnetic intensity B of any strength. In order to circumvent several basic conceptual difficulties encountered with the usual binary collisions-dielectric two-pronged approach for the specific and highly significant parallel and orthogonal orientations w.r.t magnetic field, we initiate an analytical and hydrodynamic derivation of magnetized LIVSD based on particle diffusion coefficients in arbirary magnetized one- component-plasmas(OCP). In the B=0 limit, we recover the usual expected results. We proceed to a parameter study involving B- and temperature T-dependence in two extreme cases of presently hot current interest. First, we consider the very dense and sometimes extremely magnetized hot plasms envisioned for fast ignition in ICF with B~10$^{10}$ G. Then, we turn to ultracold and highly dilute electron plasmas used for ion beam cooling at CERN. In both situations the electron Larmor radius$<$Debye length. Pertaining analytical LIVSD are presented. [Preview Abstract] |
Wednesday, November 19, 2008 3:36PM - 3:48PM |
PO4.00009: Enhancing Laser Induced Plasma Emissions using Various Excitation Modalities Lewis Johnson, Charlemagne Akpovo, Samson Gebreegziabher, Jorge Martinez Jr. Detection of hazardous materials with Laser Induced Breakdown Spectroscopy (LIBS) requires a detailed understanding of the sample matrix as well as the surrounding environment. We report on our efforts to understand and manipulate the continuum and atmospheric levels while enhancing surface and substrate material identifications. Comparisons are made between: single pulse (SP) nanosecond (ns); SP femtosecond (fs); SP fs-self-channeled (fs-sc); Dual pulse (DP) ns; DP ns -- fs; and DP ns fs-sc; and multi--pulse Continuous Wave (CW) plasmas formed on the sample surface. Plasma emission spectra from atmospheric oxygen and nitrogen, as well as aluminum and Copper substrates, and hazardous oxygen and nitrogen rich materials residues are analyzed. [Preview Abstract] |
Wednesday, November 19, 2008 3:48PM - 4:00PM |
PO4.00010: Helium Spectroscopy Studies on Anomalous Turbulent Lines using a Mach 50 Arc-Driven Shock Tube James Titus, Chavis Raynor, Kyron Williams, Richard Appartaim, Joseph Johnson, III In astrophysical and fusion plasmas, there are anomalous spectral behaviors that are outside the normal predictions from quantum mechanics. To study these phenomena, we have built a Stainless-Steel Shock Tube capable of producing Mach 50 shock waves. Our diagnostics include pressure transducers and laser diodes for velocity measurements, 10 GHz sampling for good time resolution in neutral and ion density fluctuations along with streak spectra sampling as fast as one spectrum every 40ns. With these, we trace the evolution of changes in the optical spectra with turbulence. In our analysis, we are using the most recent techniques in turbulent physics from the quantum mechanics of many body systems to explain the influence of turbulence on optical spectra. [Preview Abstract] |
Wednesday, November 19, 2008 4:00PM - 4:12PM |
PO4.00011: Molecular Dynamics (MD) simulations of electron-ion temperature relaxation in a classical Coulomb plasma Guy Dimonte, Jerome Daligault Molecular dynamics (MD) simulations are used to investigate temperature relaxation between electrons and ions in a fully ionized, classical Coulomb plasma with minimal assumptions. Recombination is avoided by using like charges. The relaxation rate is in excellent agreement with theory in the weak coupling limit (g $\equiv $ potential/kinetic energy $<<$ 1) whereas it saturates at g $>$ 1 due to correlation effects. The `Coulomb log' is found to be independent of the ion charge and mass ratio $>$ 25. [Preview Abstract] |
Wednesday, November 19, 2008 4:12PM - 4:24PM |
PO4.00012: Numerical Calculations of Diffusion Coefficients for Plasmas Confined by Magnetic Fields Alhashmi Alabyad Bilal, Mohamed Mansor, Maulud Elaharsh, Najeeb Khalifa The collisions of electrons with other particles and with each other is an important process in plasma in general in connection with excitation, ionization, diffusion, heat and electrical conduction to name a few. In this work, the position of the guiding center is calculated from the numerical solution of the equations of motion of two electrons interacting under the effect of magnetic field. Particle orbits for various types of particles will be shown and some of the peculiarities of the scattering processes will be emphasized. Results of calculations of difusion coefficients for electrons of plasma confined in a magnetic field will be presented. The diffusion coefficients for electrons are calculated as the average of the square of the random translations of the guiding centers during collisions. The diffusion rates calculated in this way are orders of magnitude higher than their corresponding classical values which raises a question about the classical theory. [Preview Abstract] |
Wednesday, November 19, 2008 4:24PM - 4:36PM |
PO4.00013: ABSTRACT WITHDRAWN |
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