Bulletin of the American Physical Society
58th Annual Meeting of the APS Division of Plasma Physics
Volume 61, Number 18
Monday–Friday, October 31–November 4 2016; San Jose, California
Session NO7: Magnetic Reconnection |
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Chair: Hantao Ji, Princeton Plasma Physics Laboratory Room: 212 AB |
Wednesday, November 2, 2016 9:30AM - 9:42AM |
NO7.00001: Investigating the Dynamics of Canonical Flux Tubes Jens von der Linden, Jason Sears, Thomas Intrator, Setthivoine You Canonical flux tubes are flux tubes of the circulation of a species' canonical momentum. They provide a convenient generalization of magnetic flux tubes to regimes beyond magnetohydrodynamics (MHD). We hypothesize that hierarchies of instabilities which couple disparate scales could transfer magnetic pitch into helical flows and vice versa while conserving the total canonical helicity. This work first explores the possibility of a sausage instability existing on top of a kink as mechanism for coupling scales, then presents the evolution of canonical helicity in a gyrating kinked flux rope. Analytical and numerical stability spaces derived for magnetic flux tubes with core and skin currents indicate that, as a flux tube lengthens and collimates, it may become kink unstable with a sausage instability developing on top of the kink. A new analysis of 3D magnetic field and ion flow data on gyrating kinked magnetic flux ropes from the Reconnection Scaling Experiment tracks the evolution of canonical flux tubes and their helicity. These results and methodology are being developed as part of the Mochi experiment specifically designed to observe the dynamics of canonical flux tubes. [Preview Abstract] |
Wednesday, November 2, 2016 9:42AM - 9:54AM |
NO7.00002: Kinetic Alfv\'{e}n Waves in three-dimensional magnetic reconnection Yu Lin, Ji Liang, Jay Johnson, Xueyi Wang Alfv\'{e}nic waves are believed to be fundamentally important in magnetic reconnection. In this work, the generation and signatures of kinetic Alfv\'{e}n waves (KAWs) associated with magnetic reconnection in a current sheet is investigated using a three-dimensional (3-D) hybrid code under a zero or finite guide field. In order to understand the wave structures in the general cases of multiple X-line reconnection, cases with a single X-line of various lengths are examined. KAWs with perpendicular wave number $k_\perp \rho_i \sim 1$ (with $\rho_i$ being the ion Larmor radius) are found throughout the transient plasma bulge region and propagate outward along magnetic field lines with a super-Alfv\'{e}nic velocity. These KAWs, which coexist with the whistler structure of the ion diffusion region, are generated from the X-line and propagate along field lines, carrying parallel electric field and Poynting fluxes. The structure, energy, and damping of the KAWs are examined. [Preview Abstract] |
Wednesday, November 2, 2016 9:54AM - 10:06AM |
NO7.00003: ABSTRACT WITHDRAWN |
Wednesday, November 2, 2016 10:06AM - 10:18AM |
NO7.00004: Nonthermal Particle Acceleration in 3D Relativistic Magnetic Reconnection in Pair Plasma Dmitri Uzdensky, Gregory Werner, Vladimir Zhdankin Magnetic reconnection is a fundamental plasma process that converts magnetic energy into particle kinetic energy. ``Relativistic'' reconnection is of interest in astrophysical contexts because it can accelerate particles to relativistic energies high enough for synchrotron (or inverse Compton) emission to explain observed high-energy radiation. After several 2D particle-in-cell (PIC) simulations of reconnection in pair plasmas demonstrated power-law electron-energy spectra extending to high energies, a few 3D simulations surprisingly confirmed the robustness of nonthermal particle acceleration, despite fundamental differences, such as the development of the relativistic drift-kink instability (RDKI) in 3D. We present a comprehensive PIC study of 3D relativistic pair-plasma reconnection characterizing the effect of the third dimension. We investigate how reconnection dynamics and particle acceleration depend on guide magnetic field $B_z$ and on the simulation box length $L_z$ in the third dimension. We find that, while the RDKI does indeed grow in 3D reconnection, it does not inhibit particle acceleration, even in the absence of guide field. [Preview Abstract] |
Wednesday, November 2, 2016 10:18AM - 10:30AM |
NO7.00005: Synchrotron Cooling in Relativistic Magnetic Reconnection Jake Fish, Gregory Werner, Dmitri Uzdensky Radiative processes are typically unimportant to the dynamics of plasmas investigated by most magnetic reconnection studies. However, some astrophysical phenomena exhibit conditions in which radiative cooling is significant over dynamic timescales. For example, strong synchrotron cooling controls the energetics of reconnection in magnetospheres of pulsars with strong magnetic fields, including the Crab pulsar. We performed a series of simulations of reconnection in the presence of radiative cooling using the particle-in-cell code Zeltron which self-consistently includes the synchrotron radiation reaction force. We examine the resulting global particle energy distribution, which is strongly cooled by radiation over time at high energies. Basic plasma parameters, such as the average particle energy and density in the reconnection layer and at magnetic O-points, are also measured as functions of radiative cooling's importance. Our results show strong plasma cooling and compression in plasmoids due to radiation well before the reconnecting layer is significantly affected. [Preview Abstract] |
Wednesday, November 2, 2016 10:30AM - 10:42AM |
NO7.00006: Magnetic reconnection onset via disruption of a forming current sheet by the tearing instability Nuno Loureiro, Dmitri Uzdensky The recent realization that Sweet-Parker current sheets are violently unstable to the secondary tearing (plasmoid) instability implies that such current sheets cannot occur in real 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 being formed. Such an analysis is performed here in the context of nonlinear resistive magnetohydrodynamics for a generic time-dependent equilibrium representing a gradually forming current sheet. It is shown that two onset regimes, single-island and multi-island, are possible, depending on the rate of current sheet formation. A simple model is used to compute the criterion for transition between these two regimes, as well as the reconnection onset time and the current sheet parameters at that moment. For typical solar corona parameters, this model yields results consistent with observations. [Preview Abstract] |
Wednesday, November 2, 2016 10:42AM - 10:54AM |
NO7.00007: Spacecraft observations of a Maxwell Demon coating the separatrix of asymmetric magnetic reconnection with crescent-shaped electron distributions J Egedal, A Le, W Daughton, B Wetherton, PA Cassak, LJ Chen, B Lavraud, J Dorell, L Avanov, D Gershman During asymmetric magnetic reconnection in the dayside magnetopause in situ spacecraft mea- surements show that electrons from the high density inflow penetrate some distance into the low density inflow. Supported by a kinetic simulation, we present a general derivation of an exclusion energy parameter, which provides a lower kinetic energy bound for an electron to jump across the reconnection region from one inflow region to the other. As by a Maxwell Demon, only high energy electrons are permitted to cross the inner reconnection region, strongly impacting the form of the electron distribution function observed along the low density side separatrix. The dynamics produce two distinct flavors of crescent-shaped electron distributions in a thin boundary layer along the separatrix between the magnetospheric inflow and the reconnection exhaust. The analytical model presented relates these salient details of the distribution function to the electron dynamics in the inner reconnection region. [Preview Abstract] |
Wednesday, November 2, 2016 10:54AM - 11:06AM |
NO7.00008: Experimental demonstration of the role of electron pressure in fast magnetic reconnection with a guide field W. Fox, F. Sciortino, A. von Stechow, J. Jara-Almonte, J. Yoo, H. Ji, M. Yamada We report detailed laboratory observations of the structure of reconnection current sheets in a two-fluid plasma regime with a guide magnetic field, conducted on the Magnetic Reconnection Experiment. We observe in the laboratory for the first time the quadrupolar electron pressure variation in the ion-diffusion region, as originally predicted by extended MHD simulation. We quantitatively analyze the parallel and perpendicular force balance, and observe the projection of the electron pressure gradient parallel to the B field balances the parallel electric field. The resulting cross-field electron jets in the reconnection layer are diamagnetic in origin. Electron density variations are observed to dominate temperature variations and may provide a new diagnostic of reconnection with finite guide field for fusion experiments and spacecraft missions. [Preview Abstract] |
Wednesday, November 2, 2016 11:06AM - 11:18AM |
NO7.00009: Magnetic reconnection in multispecies plasmas investigated by a kinetic fluid code. Chuanfei Dong, Liang Wang, Amitava Bhattacharjee, Ammar Hakim, Yi-Min Huang, Kai Germaschewski We first study the reconnection process in multispecies plasmas by using Gkeyll, which is a kinetic fluid code solving the continuity, momentum and energy equations of each species, and the full Maxwell equations. Thus, there is no assumption by solving the generalized ohm{\&}{\#}39;s law in Gkeyll. We studied the reconnection processes in the plasma consisting of electrons, protons and oxygen ions. If time allows, we also plan to show some preliminary results of magnetic reconnection in dusty plasmas with negatively charged dust. [Preview Abstract] |
Wednesday, November 2, 2016 11:18AM - 11:30AM |
NO7.00010: Observations of Plasmoids in Pulse-Power Driven Magnetic Reconnection Experiments Jack D Hare, Lee Suttle, Sergey Lebedev, Guy Burdiak, Jeremy Chittenden, Thomas Clayson, Catalina Garcia, Nicolas Niasse, Timothy Robinson, Roland Smith, Nicolas Stuart, Francisco Suzuki-Vidal, George Swadling, Andrea Ciardi, Nuno Loureiro, Jiming Ma, Jian Wu, Qingguo Yang We present a detailed study of magnetic reconnection in a quasi-two-dimensional pulsed-power driven laboratory experiment. Oppositely directed magnetic fields, advected by supersonic and sub-Alfv\'enic carbon plasma flows, are brought together and mutually annihilate inside a thin current layer. Temporally and spatially resolved non-perturbative diagnostics allow us to determine the structure and dynamics of this layer, the nature of the inflows and outflows and details of the energy conversion by the reconnection process. We find evidence for anomalous resistivity inside the layer, and for the presence of two fluid effects in the form of density depletion regions. We observe plasmoids, consistent with the predictions of semi-collisional plasmoid instability theory, which may cause enhanced viscous heating of the ions. [Preview Abstract] |
Wednesday, November 2, 2016 11:30AM - 11:42AM |
NO7.00011: Secondary fast reconnecting instability in the sawtooth crash Daniele Del Sarto, Maurizio Ottaviani We consider magnetic reconnection in thin current sheets with both resistive and electron inertia effects. By analysis of secondary instabilities we show that, when the current sheet is produced by a primary instability of the internal kink type (large ∆′), reconnection proceeds on a time scale much shorter than the primary instability characteristic time. We find that in the purely resistive regime our estimates agree with the numerical results obtained by [Q. Yu, S. Gunter, K. Lackner, Nucl. Fusion 54, 072005 (2014)] for the internal kink instability in a cylindrical tokamak. We also find that, in the case of a sawtooth crash, non-collisional physics becomes important above a value of the Lundquist number which scales like $S ∼ (R/d_e)^{12/5}$, in terms of the tokamak major radius $R$ and of the electron skin depth $d_e$. This value is commonly achieved in present day devices. As collisionality is further reduced, the characteristic rate increases, approaching Alfvenic values when the primary instability approaches the collisionless regime. All these results have been recently discussed in Ref.[D. Del Sarto, M. Ottaviani, arXiv preprint, arXiv:1603.00276 (2016)]. [Preview Abstract] |
Wednesday, November 2, 2016 11:42AM - 11:54AM |
NO7.00012: Development of High-Field ST Merging Experiment: TS-U for High Power Reconnection Heating Y. Ono, H. Koike, H. Tanabe, S. Himeno, S. Ishida, K. Kimura, M. Kawanami, M. Narita, Y. Takahata, T. Yokoyama, M. Inomoto, C. Z. Cheng We are developing high-magnetic field ST merging/ reconnection experiment TS-U with B$_{\mathrm{rec}}=$ 0.3-0.5T, based on our scaling law of reconnection heating energy proportional to square of the reconnecting (poloidal) magnetic field B$_{\mathrm{rec}}$ [1-3]. This scaling law indicates that the high-B$_{\mathrm{rec}}$ ST merging will heat ions to the burning plasma regime without using any additional heating facility. Its mechanism is that the reconnection outflow accelerates mainly ions up to the poloidal Alfven speed like the Sweet-Parker model [1]. The shock-like density pileups thermalize the accelerated ions in the down-streams in agreement with recent solar satellite observations and PIC simulation results [2,3]. We already documented significant ion heating of spheromak and ST mergings up to 0.25keV in TS-3 [1-3] and 1.2keV in MAST [2,3], leading us to the high-B$_{\mathrm{rec}}$ merging experiment TS-U. It is noted that high-resolution (\textgreater 500 channel) 2D measurements of ion and electron temperatures is being developed for the purpose of solving all acceleration and heating effects of magnetic reconnection, such as the huge outflow heating of ions in the downstream and electron heating localized at the X-point [1-3]. [1] Y. Ono et al., Phys. Rev. Lett. 107, 185001 (2011), [2] Y. Ono et al., Plasma Phys. Cont. Fus. 54 124039, (2012), [3] Y. Ono et al., Phys. Plasmas 22, 055708 (2015). [Preview Abstract] |
Wednesday, November 2, 2016 11:54AM - 12:06PM |
NO7.00013: Self-organizing Knotted Magnetic Structures in Plasma Christopher Berg Smiet, Simon Candelaresi, Amy Violet Thompson, Joe Swearngin, Jan Willem Dalhuisen, Dirk Bouwmeester Magnetic helicity, which can be seen as the self- and interlinking of magnetic field lines is approximately conserved in a resistive plasma. Using full-MHD simulations we investigate the evolution of linked and/or twisted rings of magnetic flux, and observe how the initial linking gives rise to a structure where magnetic field lines lie on nested toroidal surfaces. This structure is an hydrostatic equilibrium charaterized by a lowered pressure in the toroidal region around the innermost of the nested tori. The magnetic field in this structure is highly localized and the rotational transform varies slowly from surface to surface, giving rise to magnetic islands at rational surfaces. The higher the helicity in the initial linked configuration, the more energy is retained in this knotted quasi-stable magnetic structure. We relate the ordered, toroidal structure of the magnetic field to the linked fiber structures that naturally arise in maps from the hypersphere $S^3$ to the sphere $S^2$such as the Hopf fibration. [Preview Abstract] |
Wednesday, November 2, 2016 12:06PM - 12:18PM |
NO7.00014: Conceptual design of the 3D magnetic field configuration relevant to the magnetopause reconnection in the SPERF. Aohua Mao, Hantao Ji, Yang Ren, Peng E, Zhibin Wang, Qingmei Xiao, Chijie Xiao A new terrella device, the Space Plasma Environment Research Facility (SPERF), is designed and under construction in China, with Asymmetric Reconnection EXperiment (AREX) as one component to study the interaction between the magnetosheath and magnetosphere plasmas. AREX will provide a unique platform for studying asymmetric magnetic reconnection relevant to the magnetopause, via a set of coils for simulating ``solar-wind-side'' magnetosheath field and a dipole field on the ``magnetosphere-side''. Thus it could be able to investigate a range of important issues in the magnetosphere geometry, such as the electron and ion-scale dynamics in the current sheet, particle and energy transfer from magnetosheath to magnetosphere, particle energization/heating during magnetic reconnection, 3D and asymmetric effects in fast reconnection, and so on. The plasma is generated by two flux cores at the ``magnetosheath-side'' and one electron cyclotron resonance source at the ``magnetosphere-side''. Different kinds of coils with specific current driven functions, as well as advanced diagnostics are designed. Motivation, overview of the AREX design and reconnection scenarios will be discussed. [Preview Abstract] |
Wednesday, November 2, 2016 12:18PM - 12:30PM |
NO7.00015: Effects of guide field in driven magnetic reconnection C. Z. Cheng, S. Inoue, R. Horiuchi, Y. Ono, X. Guo Decoupling of electron and ion dynamics is the key physical process in the magnetic reconnection layer. It leads to the generation of parallel E-field and in-plane electrostatic E-field, and determines how particles gain energy. For antiparallel magnetic reconnection (zero guide field case), the electron and ion dynamics decoupling is due to meandering particle (unmagnetized) orbits in the field reversal region and particle acceleration by parallel electric field in the separatrix region$^{\mathrm{1}}$.$^{\mathrm{\thinspace }}$The parallel E-field is produced mainly from the driven inductive E-field due to the quadrupole out-of-plane magnetic field generation. The decoupling of electron and ion dynamics causes charge separation which produces the in-plane electrostatic E-field. If the guide field is stronger than the reconnecting magnetic field, both electrons and ions are magnetized in the entire magnetic reconnection domain, and the electron-ion dynamics decoupling process changes from the zero guide field case. Then, the structure of parallel and electrostatic E-fields, and thus how electrons/ions gain energy also changes. We will explain the physical mechanisms of electron-ion dynamics decoupling on the E-field generation, and how electron and ion are heated/accelerated based on the driven reconnection simulation results. \begin{enumerate} \item C. Z. Cheng et al., Phys. Plasmas 22, 101205 (2015). \end{enumerate} [Preview Abstract] |
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