Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Plasma Physics
Volume 54, Number 15
Monday–Friday, November 2–6, 2009; Atlanta, Georgia
Session NM9: Mini-Conference on Unsteady Reconnection in Laboratory and Nature III: 3D Reconnection and Diffusion Region |
Hide Abstracts |
Chair: Yasushi Ono, University of Tokyo Room: Regency V |
Wednesday, November 4, 2009 9:30AM - 9:55AM |
NM9.00001: Satellite observations of lower-hybrid-oscillated magnetic null and related anomalous resistivity Chijie Xiao, Xiaogang Wang, Zuyin Pu Here we report two 3D fast reconnection events with magnetic nulls, one located in the geomagnetotail and the other one in dayside magnetopause. The magnetic nulls in both events are oscillated at lower-hybrid frequencies, which imply that lower-hybrid wave may be very important at the center of reconnection current sheet. The power spectrum of the electric field around the lower-hybrid (LH) frequency is measured to compute the anomalous resistivity near the magnetic null. The anomalous resistivity due to lower-hybrid frequency turbulence is in comparison with the effective resistivity calculated from electrical field and current data. Also the fast reconnection rate is estimated from magnetic field and flow data to compare with the reconnection electrical field computed from the current data and anomalous resistivity calculation. It is found that, the anomalous resistivity induced by LH frequency turbulence is sufficient to trigger fast reconnection. [Preview Abstract] |
Wednesday, November 4, 2009 9:55AM - 10:20AM |
NM9.00002: General Method for Describing Three-Dimensional Magnetic Reconnection Viacheslav Titov, Terry Forbes, Eric Priest, Zoran Mikic, Jon Linker A general method for describing magnetic reconnection in arbitrary three-dimensional magnetic configurations is proposed. The method is based on the field-line mapping technique previously used only for the analysis of magnetic structure at a given time. This technique is extended here so as to analyze the evolution of magnetic structure. Such a generalization is made with the help of new dimensionless quantities called ``slip-squashing factors''. Their large values define the surfaces that border the reconnected or to-be-reconnected magnetic flux tubes for a given period of time during the magnetic evolution. The proposed method is universal, since it assumes only that the time sequence of evolving magnetic field and the tangential boundary flows are known. We illustrate our method for several examples and compare it with the general magnetic reconnection theory, proposed previously by Hesse and coworkers. The new method admits a straightforward numerical implementation and provides a powerful tool for the diagnostics of numerical data obtained in theoretical or experimental studies of magnetic reconnection in space and laboratory plasmas. [Preview Abstract] |
Wednesday, November 4, 2009 10:20AM - 10:40AM |
NM9.00003: Experiments on Three-Dimensional Reconnection Walter Gekelman, Eric Lawrence, Andrew Collette, Stephen Vincena Magnetic Field Line reconnection is still considered, by some, to be one of the most important topics in plasma physics and has been in this category for close to thirty years. One reason is most of the models for it are still two dimensional. We report on two very different experiments in which 3D reconnection plays a role. In the first experiment two magnetic flux ropes are generated from initially adjacent pulsed current channels in a background magnetoplasma. The currents twist about each other and merge and are observed to filament after merging. Volumetric space-time data show multiple reconnection sites with time-dependent locations. The quasi-separatrix layer (QSL) , a concept used in study of solar reconnection has been measured, and its three dimensional development will be shown. In the second experiment three-dimensional currents associated with colliding laser produced plasmas are observed. The currents in this situation are those of shear Alfv\'en waves. The wave fields are a small fraction of the background field; nevertheless, reconnection regions, multiple magnetic `X' points (which are three dimensional) and induced electric fields are observed. The role of the guide field is investigated. [Preview Abstract] |
Wednesday, November 4, 2009 10:40AM - 11:05AM |
NM9.00004: Energetics of Localized, Transient Reconnection Models in 1, 2 and 3 Dimensions Dana Longcope Fast magnetic reconnection has been proposed to explain how stored magnetic energy might be rapidly converted into other forms. The general prerequisite for local flux transfer to release significant energy is achieved most easily at some form of current sheet where fields of distinct global topologies come into close proximity. In Petschek's steady model magnetic fields are reconnected at a site of localized electric field, initiating energy release far away at standing slow mode shocks. I show that a wide variety of models, both steady and transient, agree qualitatively and quantitatively in the nature and outcome of a basic energy release scenario broadly similar to Petschek's. These include a recently-developed three-dimensional model whereby transient, localized flux transfer across a current sheet creates retracting magnetic flux tubes. This and all other models predict the same total energy release, its apportionment between thermal to kinetic forms, and the final plasma temperature. These quantities depend on initial field line angle and plasma beta and not on details of the flux-transfer electric field due to its assumed localization. [Preview Abstract] |
Wednesday, November 4, 2009 11:05AM - 11:30AM |
NM9.00005: Response of the Chromosphere to Penumbral Dynamics: Reconnection and Bow Shocks Margarita Ryutova, Thomas Berger, Zoe Frank, Alan Title We present observations of sunspot penumbrae obtained during the disk passage of AR 10923 (2006 November 10-20) with the SOT instrument on Hinode in 4305 A G band and Ca II H line. These observations allowed us to study new phenomena consisting in the appearance of bright elongated transients having a double structures, and abundantly pervading the entire penumbra. These transients, drifting as a whole in a direction almost perpendicular to their long axes, are clearly associated with the photospheric bright points emerging in a Y-shaped configuration formed by the reconnecting penumbral filaments. We find that a specific character of reconnection and post-reconnection dynamics in the photosphere, determined by a finite plasma beta and sharp stratification, provide necessary conditions for the formation of bow shocks generated by reconnected filaments moving upward with transsonic velocities. We present quantitative analysis, and show that calculated parameters of bow shocks, e.g. velocity, standoff distanse, height of formation, lifetime, length, etc. are in good agreement with observations. [Preview Abstract] |
Wednesday, November 4, 2009 11:30AM - 11:50AM |
NM9.00006: Unsteady 3D magnetic reconnection in the Reconnection Scaling Experiment T.P. Intrator, T.D. Olson, R.J. Oberto Magnetic reconnection changes the topology of magnetic field lines to a lower energy state. This process can liberate stored magnetic field energy and accelerate particles during unsteady, explosive events. This is one of the most important processes in astrophysical, space and laboratory plasmas. The abrupt onset and cessation has been a long standing puzzle. We show the first three-dimensional (3D) laboratory example of onset and stagnation of magnetic reconnection between magnetized and parallel current channels (flux ropes) driven by magnetohydrodynamic (MHD) attraction and an external kink mode, which is a 3D plasma current driven instability. Antiparallel magnetic field lines carried by these colliding flux ropes annihilate and drive an electric field. The inflow soon exceeds a threshold for the formation of a reconnection current layer. Magnetic flux and pressure pile up just outside this layer, and eventually become large enough to support MHD back-reaction forces that stall the inflow and stagnate the reconnection process. [Preview Abstract] |
Wednesday, November 4, 2009 11:50AM - 12:10PM |
NM9.00007: Kinetic Theory and Petascale 3D Simulations of Magnetic Reconnection with a Guide Field W. Daughton, V. Roytershteyn, L. Yin, B.J. Albright, K.J. Bowers, H. Karimabadi In the presence of a finite guide field, current sheets are unstable to a spectrum of collisionless tearing modes at resonant surfaces across the layer. Fully kinetic treatments of this problem have typically focused on the fastest growing modes with resonant surface in the center of the layer. However in large-scale systems, tearing modes can grow at resonant surfaces on both sides of the layer, corresponding to oblique angles relative to the standard 2D reconnection geometry. In hydrogen plasmas, these modes couple to the electron drift wave while in electron-positron plasmas the oblique tearing modes are purely growing. In this work, we review the Vlasov theory for this problem using an exact integro-differential treatment. The theoretical results are used to guide and interpret 3D fully kinetic simulations performed on Roadrunner, the world's first petascale supercomputer. The evolution is highly dynamic and features the formation and interaction of flux ropes over a wide range of angles consistent with linear theory. Over long time scales, new current sheets form which are unstable to additional reconnection instabilities and island (flux rope) formation. The influence of this complex evolution on the dissipation of magnetic energy and particle acceleration is explored. [Preview Abstract] |
Wednesday, November 4, 2009 12:10PM - 12:30PM |
NM9.00008: 3D Magnetic Reconnection of Relativistic Pair Plasmas Wei Liu, Lin Yin, Brian Albright, Kevin Bowers, Hui Li, Edison Liang Relativistic plasma physics plays an essential role in a number of famous and longstanding astrophysical problems. Using the ultrafast code VPIC, we present one of the largest scale 3D particle-in-cell (PIC) simulations to date to examine relativistic magnetic reconnection in pair plasmas. These simulations are large enough to accommodate a sufficient number of kink modes. It is demonstrated that multiple, patchy reconnection sites form during the initial stage and then self-organize to form an elongated diffusion region with increased system size. The secondary kinking folds the current sheet in the orthogonal direction. The interaction between kink and tearing instabilities results in plasmoids, which affect the particle acceleration and reconnection rate. The reconnection rate remains fast and time varying. The relativistic effects increase the linear kink mode wavelengths and results in almost identical growth rates for initial linear kink and tearing modes. Relativistic drift kink instability, reconnection, folding of the diffusion region due to the secondary kink and plasmoids all contribute to the particle energization. [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