Bulletin of the American Physical Society
55th Annual Meeting of the APS Division of Plasma Physics
Volume 58, Number 16
Monday–Friday, November 11–15, 2013; Denver, Colorado
Session NO5: Magnetic Reconnection |
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Chair: Michael Brown, Swarthmore College Room: Governor's Square 10 |
Wednesday, November 13, 2013 9:30AM - 9:42AM |
NO5.00001: Magnetic Reconnection in highly magnetized relativistic plasmas Fan Guo, Hui Li, William Daughton, Yi-Hsin Liu Magnetic reconnection is a key mechanism that rapidly converts magnetic energy into plasma kinetic energies. It has been widely used to explain explosive release of magnetic energy in astrophysical plasmas. In many astrophysical systems such as Active Galactic Nucleus (AGN) jets and pulsar wind nebulae, the magnetization parameter (the ratio between magnetic energy and plasma kinetic energy) is expected to be very large. We explore the formation of thin current sheets and their properties in highly magnetized relativistic plasmas. Furthermore, we perform particle-in-cell simulations to investigate the efficiency of magnetic energy dissipation in these parameters. [Preview Abstract] |
Wednesday, November 13, 2013 9:42AM - 9:54AM |
NO5.00002: Kinematics of Bulk Flows Driven by Relativistic Collisionless Magnetic Reconnection Krzysztof Nalewajko, Dmitri Uzdensky, Benoit Cerutti, Gregory Werner, Mitchell Begelman In several problems of high-energy astrophysics, magnetic reconnection is considered to operate in relativistic collisionless plasmas, where the magnetic energy density dominates even the particle rest energy density, and the magnetization parameter, defined as magnetic-to-plasma enthalpy ratio, exceeds unity. In such a regime, it was proposed that ultra-relativistic bulk plasma outflows, so-called minijets, can be driven along reconnection layers. Here, 2D Particle-in-Cell numerical simulations of relativistic collisionless pair-plasma reconnection for a wide range of magnetization values, in particular for values above unity, are reported. Detailed analysis is presented for bulk flow kinematics and reconnection rate, and their dependence on the magnetization. Basic analytical predictions of the minijets model are tested numerically for the first time. A new effect of fast variation of the bulk velocity field is observed, which could explain rapid gamma-ray variability of cosmic sources such as blazars, gamma-ray bursts, and pulsar wind nebulae. [Preview Abstract] |
Wednesday, November 13, 2013 9:54AM - 10:06AM |
NO5.00003: The Effect of Mass Ratio in Relativistic, Collisionless Electron-Ion Reconnection Gregory Werner, Mitchell Begelman, Benoit Cerutti, Krzysztof Nalewajko, Dmitri Uzdensky Astrophysical relativistic magnetic reconnection can accelerate particles to high energies, yielding synchrotron and inverse Compton radiation. Thus relativistic reconnection could explain gamma rays and hard x-rays observed from such diverse sources as Pulsar Wind Nebulae, Gamma Ray Bursts, jets of Active Galactic Nuclei, and accretion disc coronas. Using 2D particle-in-cell simulations, we have obtained new results of the effect of the ion/electron mass ratio on relativistic reconnection. We focus on the regime where electrons are strongly relativistic, and ions are mildly relativistic. As ions become increasingly relativistic, the effect of the rest mass ratio diminishes. We scan a range of mass ratios to determine scalings that can be extrapolated to high mass ratios; in particular, we report on the reconnection rate, the energy fractions given to ions and electrons, and the importance of the Hall effect in the generalized Ohm's law. [Preview Abstract] |
Wednesday, November 13, 2013 10:06AM - 10:18AM |
NO5.00004: Two non linear dynamics plasma astrophysics experiments at LANL T.P. Intrator, T.E. Weber, Y. Feng, J.A. Sears, H. Swan, T. Hutchinson, J. Boguski, K. Gao, L. Chapdelaine, J. Dunn Two laboratory experiments at Los Alamos National Laboratory (LANL) have been built to gain access to a wide range of fundamental plasma physics issues germane astro, space, and fusion plasmas. The over arching theme is magnetized plasma dynamics that include currents, MHD forces and instabilities, sheared flows and shocks, creation and annihilation of magnetic field. The Reconnection Scaling Experiment (RSX) creates current sheets and flux ropes that exhibit fully 3D dynamics, that can kink, bounce, merge and reconnect, shred, and reform in complicated ways. The most recent movies from a large detailed data set describe the 3D magnetic structure and helicity budget of a driven and dissipative system that spontaneously self saturates a kink instability. The Magnetized Shock Experiment (MSX) uses a Field reversed configuration (FRC) that is ejected at high speed and then stagnated onto a stopping mirror field, which drives a collisionless magnetized shock. A plasmoid accelerator will also access super critical shocks at much larger Alfven Mach numbers. Unique features include access to parallel, oblique and perpendicular shocks, in regions much larger than ion gyro radius and inertial length, large magnetic and fluid Reynolds numbers, and volume for turbulence. [Preview Abstract] |
Wednesday, November 13, 2013 10:18AM - 10:30AM |
NO5.00005: Nonlinear self stabilization of a kinking plasma current channel J. Sears, Y. Feng, T.P. Intrator, H. Swan, K. Gao, L. Chapdelaine A plasma column with plasma pressure, axial magnetic field and current has helically twisted field lines that form a screw pinch. If the current density exceeds the kink threshold, this current driven ideal MHD instability is expected to grow explosively on an Alfv{\'e}n time scale and destroy the equilibrium. In the Reconnection Scaling Experiment (RSX) we use a plasma gun to generate a single plasma column which terminates on an external anode. We then drive an axial plasma current at the limit of marginal kink stability. We observe a deformation to a new dynamic equilibrium with finite gyration amplitude, where the currents and magnetic fields that support the force balance have surprising axial structure. Three dimensional measurements of magnetic field $B$, plasma density $n$, plasma potential $\varphi $, and ion flow velocity $v_{i}$ in the deformed plasma column show variation in the axial direction of the instability parameter $J\cdot B/B^{2}$ and in the momentum balance terms $J\times B$ and $\nabla p$. The field line curvature which should correspond to a restoring force and the pitch of the kink also vary along the axis. In addition there is an induced return current antiparallel to the driven plasma current that is localized in the axial direction. [Preview Abstract] |
Wednesday, November 13, 2013 10:30AM - 10:42AM |
NO5.00006: Plasma relaxation and topological aspects in Hall magnetohydrodynamics Bhimsen Shivamoggi Parker's formulation of isotopological plasma relaxation process in magnetohydrodynamics (MHD) is extended to Hall MHD (Shivamoggi [1]). The torsion coefficient $al$ in the Hall MHD Beltrami condition turns out now to be proportional to the {\it potential vorticity}. The Hall MHD Beltrami condition becomes equivalent to the {\it potential vorticity} conservation equation in two-dimensional (2D) hydrodynamics if the Hall MHD Lagrange multiplier $\beta$ is taken to be proportional to the {\it potential vorticity} as well. The winding pattern of the magnetic field lines in Hall MHD then appears to evolve in the same way as {\it potential vorticity} lines in 2D hydrodynamics.\\[4pt] [1] Shivamoggi, B. K.: {\it Phys. Plasmas} {\bf 19}, 072124, (2012). [Preview Abstract] |
Wednesday, November 13, 2013 10:42AM - 10:54AM |
NO5.00007: Physical Picture of Quadrupole Magnetic Field and Electrostatic Potential in 2D Magnetic Reconnection Chio Z. Cheng, Shizuo Inoue, Yasushi Ono, Ritoku Horiuchi We will present the physical picture of how the quadrupole magnetic field and the electrostatic potential are generated during reconnection of merging magnetic fields in 2-dimensional (poloidal) plane. The physical pictures are obtained based on 2-1/2 dimensional collisionless particle simulations using the PASMO code\footnote{H. Ohtani and R. Horiuchi, Plasma Fusion Res, 4, 024 (2009).} and theoretical calculations. The physical picture is different from the one presented by Uzdensky and Kulsrud.\footnote{D. A. Uzdensky and R. M. Kulsrud, Phys. Plasma, 13, 062305 (2006).} We will describe the physical picture of the reconnection process from the current sheet formation, to the initial reconnection in the electron current sheet and then the expansion of reconnection layer to the ion current sheet. In particular, we will provide the physical mechanism of how the poloidal current (including the Hall current in the downstream region) is generated and how the electrostatic potential is produced in the poloidal plane. [Preview Abstract] |
Wednesday, November 13, 2013 10:54AM - 11:06AM |
NO5.00008: Multi-Hierarchy Simulation for Magnetic Reconnection -- 2D Hierarchy-Interlocking Model Shunsuke Usami, Ritoku Horiuchi, Hiroaki Ohtani, Mitsue Den Toward the complete understanding of magnetic reconnection as a multi-hierarchy phenomenon, we have developed a multi-hierarchy simulation model which solves macro- and microscopic physics simultaneously and self-consistently. For this purpose, we pay attention to a hierarchical structure of magnetic reconnection phenomena, i.e. kinetic effects play crucial roles in the vicinity of the X point, while MHD model gives a good approximation as being away from the X point. Based on this feature, we divide a real space into macro- and microscopic domains and solve the physics in the macro- and microscopic domains with use of the MHD and PIC algorithms, respectively [1]. In 2009, with the hierarchy-interlocking model in the upstream direction, we had successfully performed multi-hierarchy simulations of magnetic reconnection. In order to apply our model to much wider systems, we have extended it to a 2D hierarchy-interlocking one, namely an interlocking in the upstream and downstream directions. In our presentation, we will show simulation results with 2D hierarchy-interlocking models and talk about the future prospect of our multi-hierarchy model.\\[4pt] [1] S. Usami, R. Horiuchi, H. Ohtani, and M. Den, Phys. Plasmas 20 (2013) 061208. [Preview Abstract] |
Wednesday, November 13, 2013 11:06AM - 11:18AM |
NO5.00009: Correlated whistlers and electron phase space holes during magnetic reconnection M.V. Goldman, D.L. Newman, G. Lapenta, L. Andersson, J.T. Gosling, S. Eriksson, S. Markidis Simulations of magnetic reconnection reveal whistler waves near the boundary of the outflow exhaust. The whistler source region is just inside the separatrix, co-located with electron phase space holes which are just beginning to disappear after propagating part way towards the x-point. The whistler wavefronts in the source region are sometimes conical and their phase velocity is on the order of the hole velocity. The whistlers are likely driven by a new mechanism: Cerenkov emission from e-holes. They propagate towards the x-pt., crossing the separatrix into the inflow region. In the source region they have higher frequencies (closer to the electron cyclotron frequency) and higher wavenumbers (greater than the inverse electron inertial length); in the inflow region they have lower frequencies and wavenumbers. Their phase velocity is surprisingly uniform throughout their trajectories, which are mapped in detail. These results can be significant for satellite detection of magnetic reconnection in the magnetotail, since whistlers in the inflow region indicate proximity to an x-point and to the electron current sheet which appears after the ambient cross-tail current sheet has torn. In addition, their location near the x-pt. may enable the whistlers to affect the reconnection rate. [Preview Abstract] |
Wednesday, November 13, 2013 11:18AM - 11:30AM |
NO5.00010: Implicit PIC Simulations of Magnetospheric Reconnection Initialized with Fully Kinetic Asymmetric Current-Sheet Equilibria David L. Newman, Martin V. Goldman, Giovanni Lapenta, Stefano Markidis A family of one-dimensional kinetic current sheet equilibria has been developed in which the density difference across the sheet is maintained by ambipolar electric fields (with \textbf{E} perpendicular to \textbf{J} and \textbf{B}). These electric fields can form an effective potential barrier that allows particles of one species (e.g., electrons) with the same energy to have different phase-space densities on the two sides of the current sheet, thereby breaking the symmetry. Such solutions necessarily require the inclusion of non-Maxwellian features, and share characteristics with double layers and other nonlinear electrostatic structures. Implicit PIC simulations were initialized with the electron and ion distribution functions corresponding to specific solutions of this type and were found to behave as equilibria that are subject to an asymmetric tearing-mode-like instability. As expected, the instability growth rate increases as the width of the current sheet decreases. Imposing a weak perturbation on the equilibrium allows for a controlled study of the evolution of the asymmetric reconnecting plasma. Examples will be presented of the evolution for different initial states relevant to magnetospheric reconnection, including varying values of the guide magnetic field. [Preview Abstract] |
Wednesday, November 13, 2013 11:30AM - 11:42AM |
NO5.00011: Magnetic Reconnection Onset via Disruption of a Forming Current Sheet by the Plasmoid Instability Dmitri Uzdensky, Nuno Loureiro The recent realization that thin Sweet-Parker reconnection current sheets are violently unstable to the secondary tearing (plasmoid) instability implies that such current sheets are unlikely to be realized in real natural systems. This suggests that, in order to understand the onset of magnetic reconnection, one needs to consider the growth of the tearing instability in a current layer as it is just being formed. The current sheet formation process thus leads the system directly into plasmoid-dominated reconnection regime. Such an analysis is performed here in the context of resistive MHD for generic time-dependent equilibrium representing a gradually forming current sheet. Both linear and nonlinear (Rutherford and X-point collapse) stages of the evolution of the instability are considered. It is shown that, under most conditions, the longest-wavelength mode dominates, resulting in just one or two big plasmoids produced in the immediate aftermath of current sheet formation. [Preview Abstract] |
Wednesday, November 13, 2013 11:42AM - 11:54AM |
NO5.00012: Evolution of diffusion region structures in collisionless magnetic reconnection Li-Jen Chen, Naoki Bessho, Jason Shuster, Guanlai Li, William Daughton, Roy Torbert Using a combination of measurements from space and particle-in-cell simulations, we investigate the evolution of diffusion region structures in collisionless magnetic reconnection with weak to zero guide fields. Ion outflow jets develop and reach the Alfven speed before any significant anisotropy in the electron velocity space can be discerned. The Hall fields and the inversion electric field vary significantly with phases of reconnection, and are modified as secondary magnetic islands emerge from the electron diffusion region. Highly structured electron anisotropies develop in distinct magnetic regions after the reconnection rate reaches its maximum, providing a way to delineate sub-domains of the ion diffusion region. The evolution of the electron diffusion region is strongly affected under a guide field even just a few percent of the reconnecting field. Quantitative knowledge on the evolution of the diffusion region is critical to interpreting the comparisons between space measurements, laboratory experiments, and simulations of reconnection. [Preview Abstract] |
Wednesday, November 13, 2013 11:54AM - 12:06PM |
NO5.00013: Current disruption and its spreading in collision-less magnetic reconnection Neeraj Jain, Joerg Buechner, Seth Dorfman, Hantao Ji, A. Surjalal Sharma Recent magnetic reconnection experiments (MRX) [Dorfman et al., Geophys. Res. Lett. 40, 233 (2012)] have disclosed current disruption in the absence of guide field. During current disruption in MRX, current density and total out-of-reconnection-plane current drop simultaneous with a rise in out-of-reconnection-plane electric field. Here we show that current disruption is an intrinsic property of dynamic formation of X-point configuration of magnetic field in magnetic reconnection, independent of the model used for plasma description and of dimensionality (2-D or 3-D) of reconnection. An analytic expression for the current drop is derived from Ampere's equation and its predictions are verified by 2-D and 3-D electron-magnetohydrodynamic (EMHD) simulations. Three dimensional EMHD simulations show that the current disruption due to localized reconnection spreads along the direction of electron flow with a speed which depends on the wave number of the perturbation. The implications of these results for MRX and other reconnection experiments will be presented. [Preview Abstract] |
Wednesday, November 13, 2013 12:06PM - 12:18PM |
NO5.00014: Relaxed MHD model for island formation by forced reconnection in a rippled-boundary plasma slab Robert Dewar, Zensho Yoshida, Shingo Emoto, Amitava Bhattacharjee Ideal MHD motions are strongly constrained by an infinite number of microscopic constraints or \textit{Casimir invariants}. To generalize Taylor relaxation theory [1] we retain a subset of these constraints on isolated surfaces (current sheets or \textit{singular Casimirs} [2]) that prevent total relaxation. We call this approach \textit{Relaxed MHD }(RXMHD), and when the current sheet surfaces partition the plasma into disjoint regions we call this \textit{MultiRegion Relaxed MHD} (MRXMHD). E.g. in the SPEC 3-D equilibrium code [3] these current sheets are taken to be tori. Another application is to the shielding current sheets formed in resonant forced reconnection, which are most simply examined in the Hahm--Kulsrud--Taylor [4] model. Recently [5] a sequence of analytic ``plasmoid'' equilibria continuously connecting the two solutions found in [4] have been found. By imposing conservation of toroidal flux and helicity on these new solutions we construct a sequence of intermediate states arising as gaps open up in the initially continuous shielding current sheet on the $y$-axis and an island forms. [1] J. B. Taylor \textit{Rev. Mod. Phys.} \textbf{58} 741 (1986) [2] Z. Yoshida {\&} R.~L. Dewar\textit{ J. Phys. A: Math. Gen. }\textbf{45 }365502 (2012) [3] S. R. Hudson, R. L. Dewar, G. Dennis, M. J. Hole, M. McGann, G. von Nessi, {\&} S. Lazerson \textit{Phys. Plasmas} \textbf{19} 112502 (2012) [4] T. S. Hahm {\&} R. M. Kulsrud \textit{Phys. Fluids} \textbf{28} 2412 (1985) [5] R.~L. Dewar, A. Bhattacharjee, R.~M. Kulsrud {\&} A.~M. Wright, \underline {arxiv:1304.6273} (accepted Phys. Plasmas 2013) [Preview Abstract] |
Wednesday, November 13, 2013 12:18PM - 12:30PM |
NO5.00015: Study of Local Plasma Heating during Magnetic Reconnection by Tomographic Ion Doppler Spectroscopy in TS-3, TS-4 and MAST Hiroshi Tanabe, Akihiro Kuwahata, Takuma Yamada, Takenori Watanabe, Keii Gi, Masanobu Annoura, Kazutake Kadowaki, Yasuhiro Kaminou, Hideya Koike, Kento Nishida, Michiaki Inomoto, Setthivoine You, Brendan Crowley, Neil Conway, Rory Scannel, Mikhail Gryaznevich, Yasushi Ono For the past decade, local plasma heating during magnetic reconnection has been investigated in TS-3 and TS-4 by use of 2D Doppler tomography and in-situ probe diagnostics. Our merging experiments revealed significant ion heating in the outflow region and electron heating around X point. The reconnection heating energy scales with the square of reconnecting field B$_{rec}$ and reaches $\sim$200eV at maximum with B$_{rec}$ $\sim$0.1T. As a promising CS-less spherical tokamak startup technique, the reconnection/merging startup in MAST achieved the maximum ions and electron temperatures over 1keV. The high-resolution Thomson scattering with 130 chords reveals direct electron heating at the X-point and electron density pile-up in the downstream. The 32 chords Doppler tomography system was installed on the midplane of MAST for the purpose of measuring the radial profile of ion temperature. The measured triple peaks of ion temperature indicate the ion heating in the downstream as well as that in the current sheet with and without the assist of centre solenoid coil. [Preview Abstract] |
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