Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Plasma Physics
Volume 57, Number 12
Monday–Friday, October 29–November 2 2012; Providence, Rhode Island
Session NM9: Mini-Conference: Flux Ropes and 3D Dynamics I |
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Sponsoring Units: GPAP Chair: Tom Intrator, Los Alamos National Laboratory Room: 553AB |
Wednesday, October 31, 2012 9:30AM - 9:50AM |
NM9.00001: Connected Events and their Topologies Alan Title The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) provides 24/7 full Sun coverage with a 12 second cadence, arc second resolution, and span the temperature range from 6000 to 20,000,000 K The Heliospheric and Magnetic Imager (HMI) on SDO provides doppler data every 30 seconds, line-of-sight magnetograms every 45 seconds, and vector magnetograms every 5 minutes. With the SDO data set and observations from the pair of STEREO satellites it has become apparent that many flares, filament eruptions, and CME's have causal connections. These connections often span a hemisphere or more. New numerical simulations indicates that there are several mechanisms for triggering of remote events. Maps of the magnetic topology constructed from the LOS field and a PFSS model indicates both how regions that are connected and their boundaries. Magnetic evolution can change both the shapes of the topological boundaries and the topological structure. Because of the large dynamic range of the AIA images (105) it is possible to directly map the evolution of the magnetic fields on a global scale. Movies of everts and numerical simulations will be presented as well as topological mappings that indicated the zones of connectivity. [Preview Abstract] |
Wednesday, October 31, 2012 9:50AM - 10:10AM |
NM9.00002: Reconnecting Flux Ropes Walter Gekelman, Bart Van Compernolle Magnetic flux ropes are due to helical currents and form a dense carpet of arches on the surface of the sun. Occasionally one tears loose as a coronal mass ejection and its rope structure is detected by satellites close to the earth. Current sheets can tear into filaments and these are nothing other than flux ropes. Ropes are not static, they exert mutual $\vec {J}\times \vec {B}$ forces causing them to twist about each other and merge. Kink instabilities cause them to violently smash into each other and reconnect at the point of contact. We report on experiments done in the large plasma device (LAPD) at UCLA $(L=17m,dia=60cm,0.3\le B_{0z} \le 2.5kG,n\simeq 2\times 10^{12}cm^{-3})$on three dimensional flux ropes. Two, three or more magnetic flux ropes are generated from initially adjacent pulsed current channels in a background magnetized plasma. The currents and magnetic fields form exotic shapes with no ignorable direction and no magnetic nulls. Volumetric space-time data show multiple reconnection sites with time-dependent locations. The concept of a quasi-separatrix layer (QSL), a tool to understand 3D reconnection without null points. In our experiment the QSL is a narrow ribbon-like region(s) that twists between field lines. Within the QSL(s) field lines that start close to one another rapidly diverge as they pass through one or more reconnection regions. When the field lines are tracked they are observed to slip along the QSL when reconnection occurs. The Heating and other co-existing waves will be presented. [Preview Abstract] |
Wednesday, October 31, 2012 10:10AM - 10:30AM |
NM9.00003: Magnetic Separatrices and QSLs in Solar Eruptions Viacheslav Titov, Zoran Mikic, Jon Linker, Roberto Lionello, Tibor Torok Numerical magnetohydrodynamic (MHD) simulations of the solar corona make it now possible to model dynamic evolution of realistic magnetic configurations. However, such configurations are so complex that their understanding requires development of sophisticated techniques for analyzing 3D magnetic field structure. We present the current state of the art, illustrating it with some examples from our on-going projects on modeling of solar eruptions. We emphasize the role of separatrix surfaces and quasi-separatrix layers (QSLs) in erupting magnetic flux ropes. Our techniques allow us to: (1) identify the multiple-stranded structure of these ropes; (2) determine evolving magnetic fluxes for each such strand; (3) relate certain structural features to observational features, such as H$\alpha$ flare ribbons, extreme-ultraviolet dimmings, and X-ray sigmoids in solar eruptions. The latter is particularly important, since it enables us to verify the MHD models and to understand how the coronal magnetic field opens in observed eruptions. [Preview Abstract] |
Wednesday, October 31, 2012 10:30AM - 10:50AM |
NM9.00004: Stability of magnetic flux ropes with background flow Hans Goedbloed, Rony Keppens MHD stability of magnetic flux ropes is usually studied from the view point of perturbing a static equilibrium background, whereas the significant background flow that is usually present completely modifies the stability of such systems. A new theory, based on energy conservation and self-adjoint operators, permits the computation of the full spectrum of waves and instabilities of stationary plasmas. It involves the construction of a network of curves (the spectral web) in the complex omega-plane associated with the complex complementary energy, which is the energy needed to maintain harmonic time dependence in an open system. Vanishing of that energy, at the intersections of the mentioned curves, yields the eigenvalues of the closed system. Thus, for the first time, knowledge of the full complex spectrum of modes together with a connecting structure is obtained. This theory is applied to compute the complete spectrum of waves and instabilities of flux ropes in a thin accretion disk and of the rotating magnetized jets emitted from those disks. It yields specific stability criteria in terms of the helicities of the magnetic field and of the flow velocity that may be compared with observable parameters of the flux ropes. [Preview Abstract] |
Wednesday, October 31, 2012 10:50AM - 11:10AM |
NM9.00005: 3-D simulations of magnetic reconnection in high-energy-density laser-produced plasmas W. Fox, A. Bhattacharjee, K. Germaschewski Magnetic reconnection has recently been observed and studied in high-energy-density, laser-produced plasmas, in a regime characterized by extremely high magnetic fields, high plasma beta and strong, supersonic plasma inflow. These experiments are interesting both for obtaining fundamental data on reconnection, and may also be relevant for inertial fusion, as this magnetic reconnection geometry, with multiple, colliding, magnetized plasma bubbles occurs naturally inside ICF hohlraums. Previous 2-d particle-in-cell reconnection simulations, with parameters and geometry relevant to the experiments, identified key ingredients for obtaining the very fast reconnection rates, namely two-fluid reconnection mediated by collisionless effects (the Hall current and electron pressure tensor), and strong flux pile-up of the inflowing magnetic field [1]. We present results from extending the previous simulations to 3-d, and discuss 3-d effects in the experiments, including instabilities in the reconnection layer, the topological skeleton of null-null lines, and field-generation from the Biermann battery effect. \\[4pt] [1] W. Fox, A. Bhattacharjee, and K. Germaschewski, \textbf{PRL} 106, 215003 (2011). [Preview Abstract] |
Wednesday, October 31, 2012 11:10AM - 11:30AM |
NM9.00006: Experimental Observations of 3D Dynamics of Magnetic Flux Ropes Paul Bellan, Eve Stenson, Auna Moser Laboratory plasma experiments reveal that when electric current flows along open magnetic field lines, strong unbalanced MHD forces evolve the plasma through a sequence of distinct morphologies. The forces drive flows that convect frozen-in magnetic flux associated with the magnetic field created by the electric current so the flowing plasma effectively carries its own pinching force. The result is a self-collimating, MHD-driven plasma jet. The jet kinks at a critical length determined by the Kruskal-Shafranov kink instability. The kink can spawn a localized fine-scale, much faster instability that rips the jet apart resulting in localized explosive 3D reconnection. This secondary instability has been identified as a Rayleigh-Taylor instability and has free energy coming from the effective gravity inherent in the kink-induced jet lateral acceleration. When current flows along an arched magnetic flux tube having solar corona loop morphology, MHD forces drive plasma jets from \textit{both} ends towards the apex; these jets fill the flux tube with just the right amount of plasma to maintain constant density while the flux tube volume increases as a result of hoop-force-driven major radius expansion. [Preview Abstract] |
Wednesday, October 31, 2012 11:30AM - 11:50AM |
NM9.00007: Uncombed Penumbrae: Formation, Ongoing Reconnections and Fine Substructures Margarita Ryutova Sunspot penumbrae consist of an ``uncombed'' system of thin, interlaced magnetic flux tubes with varying physical parameters and inclinations. Recent high-resolution observations from space and ground based instruments reveal previously unobservable details in structure and dynamics of penumbra. Based on these observation we propose a mechanism that explains the fine structures of penumbra filaments, their dynamics and their formation process. The mechanism is based on the fact that the umbra itself is a dense conglomerate of twisted, interlaced flux tubes with peripheral filaments branching out from the ``trunk'' at different heights due to ongoing reconnection processes. The twist of individual filaments, and resulting distribution of magnetic fields and temperature forming sub-structure of filaments, is due to the onset of the post-reconnection screw pinch instability, the parameters and details of which are well observed and can be measured from our data. [Preview Abstract] |
Wednesday, October 31, 2012 11:50AM - 12:10PM |
NM9.00008: Magnetic Field Generation and Particle Energization in Relativistic Shear Flows Edison Liang, Markus Boettcher, Ian Smith We present Particle-in-Cell simulation results of magnetic field generation by relativistic shear flows in collisionless electron-ion (e-ion) and electron-positron (e+e-) plasmas. In the e+e- case, small current filaments are first generated at the shear interface due to streaming instabilities of the interpenetrating particles from boundary perturbations. Such current filaments create transverse magnetic fields which coalesce into larger and larger flux tubes with alternating polarity, eventually forming ordered flux ropes across the entire shear boundary layer. Particles are accelerated across field lines to form power-law tails by semi-coherent electric fields sustained by oblique Langmuir waves. In the e-ion case, a single laminar slab of transverse flux rope is formed at the shear boundary, sustained by thin current sheets on both sides due to different drift velocities of electrons and ions. The magnetic field has a single polarity for the entire boundary layer. Electrons are heated to a fraction of the ion energy, but there is no evidence of power-law tail forming in this case. [Preview Abstract] |
Wednesday, October 31, 2012 12:10PM - 12:30PM |
NM9.00009: Solar flares and magnetic reconnection in quasi-separatrix layers G. Aulanier, P. Demoulin, M. Janvier, S. Masson, E. Pariat Magnetic reconnection is a fundamental plasma physics process which is believed to be responsible for the bulk of energy release in solar flares. One the one hand, the onset of fast reconnection in high-Reynolds plasmas has long since been regarded as, perhaps, the major issue to understand. On the other hand, little attention has relatively been given to the three-dimensional nature of this phenomenon. Up to very recently, the latter has mostly been addressed by the solar physics community, presumably due to the wealth of space-borne and ground-based observations of three-dimensional solar coronal features during flares. Among other 3D concept, finite-B ``quasi-separatrix layers'' (QSLs) have been introduced in the nineties, as a generalization of the concept of true separatrices emanating from null-points. In this talk, I will show how both solar and experimental physics have revealed that these QSLs physically behave like true separatrices, in terms of current sheet formation and magnetic reconnection, albeit for the continuous slippage of field lines during the process. I will then show how this ``slip-running reconnection'' occurs in the wake of flux-ropes erupting from the solar corona towrds the heliosphere, and how it it eventually forms the observed post-flare loops in the Sun's corona. [Preview Abstract] |
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