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Sample records for 3d magnetic reconnection

  1. Particle acceleration at 3D reconnecting magnetic separators

    NASA Astrophysics Data System (ADS)

    Threlfall, James; Neukirch, Thomas; Parnell, Clare; Stevenson, Julie

    2015-04-01

    We present results of test particle orbit calculations in three different environments which model separator reconnection in three dimensions. The test particle (electron and proton) orbits are calculated using the relativistic guiding centre approximation. We investigate test particle orbits in a time-dependent (analytical) electro-magnetic field configuration [detailed in Threlfall et al. (A&A, in press); arXiv:1410.6465]. These results are also compared with orbits based upon large-scale 3D MHD simulations of both a single reconnecting magnetic separator and an observationally driven 3D model of a solar active region which contains several topological features of interest, including separators. We discuss how the test-particle orbits and the energy gain depend on the initial conditions, and how observations (for example, of solar flares) may be used to constrain model parameters.

  2. 3-D, Impulsive Magnetic Reconnection in a Laboratory Plasma (Invited)

    NASA Astrophysics Data System (ADS)

    Dorfman, S. E.; Ji, H.; Yamada, M.; Yoo, J.; Myers, C. E.; Roytershteyn, V.; Daughton, W. S.; Jara-Almonte, J.

    2013-12-01

    Magnetic reconnection is a fundamental plasma process involving the efficient conversion of magnetic field energy to plasma kinetic energy through changing field line topology. In many space and astrophysical systems, including the solar surface and the Earth's magnetotail, reconnection is not only fast, but also impulsive; in other words, a slow buildup phase is followed by a comparatively quick release of magnetic energy. An important question in the literature is if these examples of impulsive reconnection can be described by a two-dimensional model with no variation in the out-of-plane direction or if impulsive reconnection is fundamentally three-dimensional. Events observed on the Magnetic Reconnection Experiment (MRX) are characterized by large local gradients in the third direction and cannot be explained by 2-D models [1]. Detailed measurements show that the ejection of flux rope structures from the current sheet plays a key role in these events. By contrast, even though electromagnetic fluctuations in the lower hybrid frequency range are also observed concurrently with the impulsive behavior, they are not the key physics responsible. Furthermore, an important discrepancy in the layer width and force balance between the collisionless regime of MRX and kinetic simulations [2-4] persists when the fluctuations are small or absent, implying that they are not the cause of the wider electron layers observed in the experiment [5]. These wider layers may instead be due to the formation of flux ropes with a wide range of sizes; consistent with this hypothesis, flux rope signatures are observed down to the smallest scales resolved by the diagnostics. Finally, a qualitative, 3-D, two-fluid model is proposed to explain the observed disruptions. Many of the features observed in MRX including current disruptions [6], flux ropes [7], and electromagnetic fluctuations [8] have analogues in space observations. Thus, further detailed comparisons may enhance our understanding

  3. Experimental Studies on the 3D Macro- and Microphysics of Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Jara-Almonte, J.; Ji, H.; Yamada, M.; Yoo, J.; Fox, W. R., II

    2015-12-01

    Magnetic reconnection has been extensively studied in 2D geometries for many decades and considerable progress has been made in understating 2D reconnection physics, yet in real plasmas reconnection is fundamentally 3D in nature. Only recently has it become possible to study 3D reconnection using simulations, however some initial results have suggested that the inclusion of 3D effects does not strongly affect the basic properties of reconnection (e.g. reconnection rate or particle acceleration). Yet on the other hand, previous experiments, without direct 3D measurements, have implied that 3D effects could be important even in a quasi-2D system. Here we experimentally study both the (1) macro- and (2) microphysics of 3D reconnection in order to directly test the importance of 3D effects in a quasi-2D experiment. Using fully simultaneous 3D measurements, it is shown that during highly driven reconnection the macroscopic structure of the current sheet can become strongly 3D despite an essentially 2D upstream region. The correlation length along the current sheet is measured to be far shorter than suggested by kinetic simulations. Results from new experiments with stronger reconnection drive and diagnostics designed to estimate the 3D reconnection rate will be discussed. With regards to (2), the 3D microphysics, new diagnostics capable of measuring fluctuations at frequencies up to the electron cyclotron frequency (~ 300 MHz) have been developed and have identified the presence of very high frequency waves (~ 100 MHz) during asymmetric reconnection, localized to the low-density side. The detailed properties of these waves, including the measured power spectra and dispersion relation, will be discussed and compared with both previous satellite observations of high-frequency waves as well as with theoretical predictions on the generation of whistler waves during reconnection.

  4. Magnetic reconnection in 3D magnetosphere models: magnetic separators and open flux production

    NASA Astrophysics Data System (ADS)

    Glocer, A.; Dorelli, J.; Toth, G.; Komar, C. M.; Cassak, P.

    2014-12-01

    There are multiple competing definitions of magnetic reconnection in 3D (e.g., Hesse and Schindler [1988], Lau and Finn [1990], and Boozer [2002]). In this work we focus on separator reconnection. A magnetic separator can be understood as the 3D analogue of a 2D x line with a guide field, and is defined by the line corresponding to the intersection of the separatrix surfaces associated with the magnetic nulls. A separator in the magnetosphere represents the intersection of four distinct magnetic topologies: solar wind, closed, open connected to the northern hemisphere, and open connected to the southern hemisphere. The integral of the parallel electric field along the separator defines the rate of open flux production, and is one measure of the reconnection rate. We present three methods for locating magnetic separators and apply them to 3D resistive MHD simulations of the Earth's magnetosphere using the BATS-R-US code. The techniques for finding separators and determining the reconnection rate are insensitive to IMF clock angle and can in principle be applied to any magnetospheric model. The present work examines cases of high and low resistivity, for two clock angles. We also examine the separator during Flux Transfer Events (FTEs) and Kelvin-Helmholtz instability.

  5. Nonthermal Particle Acceleration in 3D Relativistic Magnetic Reconnection in Pair Plasma

    NASA Astrophysics Data System (ADS)

    Uzdensky, Dmitri; Werner, Gregory; Zhdankin, Vladimir

    2016-10-01

    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 Bz and on the simulation box length Lz 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. This work was funded by NSF, DOE, and NASA.

  6. Experimental onset threshold and magnetic pressure pileup for 3D Sweet-Parker reconnection

    SciTech Connect

    Intrator, Thomas P; Sun, Xuan; Lapenta, Giovanni; Furno, Ivo

    2008-01-01

    In space, astrophysical and laboratory plasmas, magnetic reconnect ion converts magnetic into particle energy during unsteady, explosive events. 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 Sweet-Parker type magnetic reconnection between magnetized and parallel current (flux) ropes driven by magnetohydrodynamic (MHD) attraction and 3D instability. Mutually attracting flux ropes advect and merge oppositely directed magnetic fields. Magnetic flux is annihilated, but reaches soon a threshold where magnetic flux and pressure pile up, and reconnection magnetic topology appears. This occurs when inflow speeds exceed the SweetParker speed v{sub SP} = v{sub A} / S{sup 1/2}, where v{sub A} is the Alfven speed and S is the Lundquist number for the reconnection layer, as magnetic flux arrives faster than flux annihilation can process it. Finally piled up fields generate MHD reaction forces that stall the inflow and the reconnection process.

  7. Magnetic Dissipation in Asymmetric Strong Guide 3D Simulations: Examples of Magnetic Diffusion and Reconnection

    NASA Astrophysics Data System (ADS)

    Scudder, J. D.; Karimabadi, H.; Daughton, W. S.

    2013-12-01

    Interpretations of 2D simulations of magnetic reconnection are greatly simplified by using the flux function, usually the out of plane component of the vector potential. This theoretical device is no longer available when simulations are analyzed in 3-D. We illustrate the results of determining the locale rates of flux slippage in simulations by a technique based on Maxwell's equations. The technique recovers the usual results obtained for the flux function in 2D simulations, but remains viable in 3D simulations where there is no flux function. The method has also been successfully tested for full PIC simulations where reconnection is geometrically forbiddden. While such layers possess measurable flux slippages (diffusion) their level is not as strong as recorded in known 2D PIC reconnection sites using the same methodology. This approach will be used to explore the spatial incidence and strength of flux slippages across a 3D, asymmetric, strong guide field run discussed previously in the literature. Regions of diffusive behavior are illustrated where LHDI has been previously identified out on the separatrices, while much stronger flux slippages, typical of the X-regions of 2D simulations, are shown to occur elsewhere throughout the simulation. These results suggest that reconnection requires sufficiently vigorous flux slippage to be self sustaining, while non-zero flux slippage can and does occur without being at the reconnection site. A cross check of this approach is provided by the mixing ratio of tagged simulation particles of known spatial origin discussed by Daughton et al., 2013 (this meeting); they provide an integral measure of flux slippage up to the present point in the simulation. We will discuss the correlations between our Maxwell based flux slippage rates and the inferred rates of change of this mixing ratio (as recorded in the local fluid frame).

  8. Magnetospheric Magnetic Reconnection with Southward IMF by a 3D EMPM Simulation

    NASA Technical Reports Server (NTRS)

    Nishikawa, K.-I.; Yan, X. Y.; Cai, D. S.; Lembege, B.

    2004-01-01

    We report our new simulation results on magnetospheric magnetic reconnection with southward IMF using a 3D EMPM model, with greater resolution and more particles using the parallelized 3D HPF TRISTAN code on VPP5000 supercomputer. Main parameters used in the new simulation are: domain size is 215 x 145 x 145, grid size = 0.5 Earth radius, initial particle number is 16 per cell, the IMF is southward. Arrival of southward IMF will cause reconnection in the magnetopause, thus allowing particles to enter into the inner magnetosphere. Sunward and tailward high particle flow are observed by satellites, and these phenomena are also observed in the simulation near the neutral line (X line) of the near-Earth magnetotail. This high particle flow goes along with the reconnected island. The magnetic reconnection process contributes to direct plasma entry between the magnetosheath to the inner magnetosphere and plasma sheet, in which the entry process eats the magnetosheath plasma to plasma sheet temperatures. We investigate magnetic, electric fields, density, and current during this magnetic reconnection with southward IMF. Further investigation with this simulation will provide insight into unsolved problems, such as the triggering of storms and substorms, and the storm-substorm relationship. New results will be presented at the meeting.

  9. Local and Global 3-D Effects in the Magnetic Reconnection Experiment (MRX)

    NASA Astrophysics Data System (ADS)

    Dorfman, S.; Ji, H.; Yamada, M.; Oz, E.; Yoo, J.; Daughton, W.; Roytershteyn, V.

    2009-11-01

    One of the key open questions in Magnetic Reconnection is the nature of the mechanism that governs the reconnection rate in real astrophysical and laboratory systems. Comparisons between fully kinetic 2-D simulations of the Magnetic Reconnection Experiment (MRX) and experimental data show that the 2-D, collisionless expression for the electric field due to particle dynamics [1] does not match MRX data; related to this is a factor of 3-5 discrepancy in the layer width [2,3]. Adding collisions to the simulation leads to a broadening of the layer, but the level of collisionality present in MRX may not be high enough to resolve the discrepancy. Ongoing research on MRX explores the role of fluctuations and 3-D effects in the force balance. Significant toroidal asymmetries have been found, manifested by regions of high inductive electric field moving in the electron flow direction within the layer. Electromagnetic fluctuations in the lower hybrid frequency range [4] tend to occur in discharges with high local currents and a rapid local reconnection rate. The precise relation of these phenomena to fast reconnection is actively being investigated. [1] M. Hesse, et al., Phys. Plasmas, 6:1781 (1999). [2] Y. Ren, et al., Phys. Plasmas 15, 082113 (2008). [3] S. Dorfman, et al., Phys. Plasmas 15, 102107 (2008). [4] H. Ji, et al., Phys.Rev.Lett. 92 (2004) 115001. Supported by NDSEG, DOE, NASA, and NSF.

  10. Steady state reconnection at a single 3D magnetic null point

    NASA Astrophysics Data System (ADS)

    Galsgaard, K.; Pontin, D. I.

    2011-05-01

    Aims: We systematically stress a rotationally symmetric 3D magnetic null point by advecting the opposite footpoints of the spine axis in opposite directions. This stress eventually concentrates in the vicinity of the null point, thereby forming a local current sheet through which magnetic reconnection takes place. The aim is to look for a steady state evolution of the current sheet dynamics, which may provide scaling relations for various characteristic parameters of the system. Methods: The evolution is followed by solving numerically the non-ideal MHD equations in a Cartesian domain. The null point is embedded in an initially constant density and temperature plasma. Results: It is shown that a quasi-steady reconnection process can be set up at a 3D null by continuous shear driving. It appears that a true steady state is unlikely to be realised because the current layer tends to grow until it is restricted by the geometry of the computational domain and the imposed driving profile. However, ratios between characteristic quantities clearly settle after some time to stable values, so that the evolution is quasi-steady. The experiments show a number of scaling relations, but they do not provide a clear consensus for extending to lower magnetic resistivity or faster driving velocities. More investigations are needed to fully clarify the properties of current sheets at magnetic null points.

  11. Particle energization in 3D magnetic reconnection of relativistic pair plasmas

    SciTech Connect

    Liu Wei; Yin Lin; Albright, B. J.; Bowers, K. J.; Liang, Edison P.; Li Hui

    2011-05-15

    We present large scale 3D particle-in-cell simulations to examine particle energization in magnetic reconnection of relativistic electron-positron (pair) plasmas. The initial configuration is set up as a relativistic Harris equilibrium without a guide field. These simulations are large enough to accommodate a sufficient number of tearing and kink modes. Contrary to the non-relativistic limit, the linear tearing instability is faster than the linear kink instability, at least in our specific parameters. We find that the magnetic energy dissipation is first facilitated by the tearing instability and followed by the secondary kink instability. Particles are mostly energized inside the magnetic islands during the tearing stage due to the spatially varying electric fields produced by the outflows from reconnection. Secondary kink instability leads to additional particle acceleration. Accelerated particles are, however, observed to be thermalized quickly. The large amplitude of the vertical magnetic field resulting from the tearing modes by the secondary kink modes further help thermalizing the non-thermal particles generated from the secondary kink instability. Implications of these results for astrophysics are briefly discussed.

  12. Mini-conference Poster: 3D Onset and Propagation of Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Lapenta, Giovanni; Ricci, P.; Brackbill, J. U.; Daughton, W.; Delzanno, G. L.

    2005-10-01

    A fundamental problem in reconnection physics is how to relate 2D and 3D reconnection. The great majority of studies of reconnection focus on 2D configurations. The state of affair is best described by the cave allegory of Plato. In 2D we look at the reconnection process as if we were studying the real world through its reflections on the walls of a cave [1]. We propose to turn our head away from the familiar wall and face the real world. We do 3D fully kinetic (i.e. both electrons and ions are kinetic) simulations of reconnection. We use the implicit PIC code CELESTE to achieve parameter ranges and system sizes inaccessible to traditional explicit codes. Our results will clarify the fundamental issue: if reconnection is started at one location, does it propagate in the system? How? And what coupling of microscopic and macroscopic processes causes the reconnection onset in the first place? All these effects can only be studied in 3D [2]. The crucial physics missing in 2D simulations is the role of macroscopic equilibrium changes induced by the microinstabilities [3].1) Plato, Republic, Book VII, Hackett Pub. Co., 1992. 2) P. Ricci, J.U. Brackbill, W.S. Daughton, G. Lapenta, Phys. Plasmas, 11, 4489, 2004.3) W. Daughton, G. Lapenta, P. Ricci, Phys. Rev. Lett., 93, 105004, 2004.

  13. 3D magnetic field configuration of small-scale reconnection events in the solar plasma atmosphere

    NASA Astrophysics Data System (ADS)

    Shimizu, T.

    2015-10-01

    The outer solar atmosphere, i.e., the corona and the chromosphere, is replete with small energy-release events, which are accompanied by transient brightening and jet-like ejections. These events are considered to be magnetic reconnection events in the solar plasma, and their dynamics have been studied using recent advanced observations from the Hinode spacecraft and other observatories in space and on the ground. These events occur at different locations in the solar atmosphere and vary in their morphology and amount of the released energy. The magnetic field configurations of these reconnection events are inferred based on observations of magnetic fields at the photospheric level. Observations suggest that these magnetic configurations can be classified into two groups. In the first group, two anti-parallel magnetic fields reconnect to each other, yielding a 2D emerging flux configuration. In the second group, helical or twisted magnetic flux tubes are parallel or at a relative angle to each other. Reconnection can occur only between anti-parallel components of the magnetic flux tubes and may be referred to as component reconnection. The latter configuration type may be more important for the larger class of small-scale reconnection events. The two types of magnetic configurations can be compared to counter-helicity and co-helicity configurations, respectively, in laboratory plasma collision experiments.

  14. 3D magnetic field configuration of small-scale reconnection events in the solar plasma atmosphere

    SciTech Connect

    Shimizu, T.

    2015-10-15

    The outer solar atmosphere, i.e., the corona and the chromosphere, is replete with small energy-release events, which are accompanied by transient brightening and jet-like ejections. These events are considered to be magnetic reconnection events in the solar plasma, and their dynamics have been studied using recent advanced observations from the Hinode spacecraft and other observatories in space and on the ground. These events occur at different locations in the solar atmosphere and vary in their morphology and amount of the released energy. The magnetic field configurations of these reconnection events are inferred based on observations of magnetic fields at the photospheric level. Observations suggest that these magnetic configurations can be classified into two groups. In the first group, two anti-parallel magnetic fields reconnect to each other, yielding a 2D emerging flux configuration. In the second group, helical or twisted magnetic flux tubes are parallel or at a relative angle to each other. Reconnection can occur only between anti-parallel components of the magnetic flux tubes and may be referred to as component reconnection. The latter configuration type may be more important for the larger class of small-scale reconnection events. The two types of magnetic configurations can be compared to counter-helicity and co-helicity configurations, respectively, in laboratory plasma collision experiments.

  15. Three-dimensional two-fluid investigation of 3D-localized magnetic reconnection and its relation to whistler waves

    NASA Astrophysics Data System (ADS)

    Yoon, Young Dae; Bellan, Paul M.

    2016-10-01

    A full three-dimensional computer code was developed in order to simulate a 3D-localized magnetic reconnection. We assume an incompressible two-fluid regime where the ions are stationary, and electron inertia and Hall effects are present. We solve a single dimensionless differential equation for perturbed magnetic fields with arbitrary background fields. The code has successfully reproduced both experimental and analytic solutions to resonance and Gendrin mode whistler waves in a uniform background field. The code was then modified to model 3D-localized magnetic reconnection as a 3D-localized perturbation on a hyperbolic-tangent background field. Three-dimensional properties that are asymmetric in the out-of-plane direction have been observed. These properties pertained to magnetic field lines, electron currents and their convection. Helicity and energy have also been examined, as well as the addition of a guide field.

  16. Locating magnetic reconnection x-lines in 3D PIC simulations

    NASA Astrophysics Data System (ADS)

    Olson, D. K.; Dorelli, J.; Daughton, W. S.; Karimabadi, H.

    2013-12-01

    In a three-dimensional PIC simulation of turbulent magnetic reconnection, a reconnection 'X-line' can be identified as a separator in the magnetic topology. From this x-line, it is possible to compute the reconnection rate by evaluating the line integral of the electric field along the separator. This technique is used in a reconnection simulation of a symmetric Harris sheet driven by inflow at the upstream boundaries with a strong guide field (such that the magnetic field is non-vanishing everywhere and there are no magnetic nulls). The results of this analysis are compared to the General Magnetic Reconnection theory (GMR) [Hesse and Schindler, 1998], showing that in this symmetric case GMR agrees with our topological approach to finding the location of the x-line. The parallel electric field is non-trivial along the entire length of the x-line, however, suggesting that the reconnection diffusion region cannot be identified by local measures of the breakdown of ideal MHD alone. We discuss the implications of these results for NASA's upcoming Magnetospheric Multiscale mission.

  17. Simulation of the 3-D Evolution of Electron Scale Magnetic Reconnection - Motivated by Laboratory Experiments Predictions for MMS

    NASA Astrophysics Data System (ADS)

    Buechner, J.; Jain, N.; Sharma, A.

    2013-12-01

    The four s/c of the Magnetospheric Multiscale (MMS) mission, to be launched in 2014, will use the Earth's magnetosphere as a laboratory to study the microphysics of three fundamental plasma processes. One of them is magnetic reconnection, an essentially multi-scale process. While laboratory experiments and past theoretical investigations have shown that important processes necessary to understand magnetic reconnection take place at electron scales the MMS mission for the first time will be able to resolve these scales by in space observations. For the measurement strategy of MMS it is important to make specific predictions of the behavior of current sheets with a thickness of the order of the electron skin depth which play an important role in the evolution of collisionless magnetic reconnection. Since these processes are highly nonlinear and non-local numerical simulation is needed to specify the current sheet evolution. Here we present new results about the nonlinear evolution of electron-scale current sheets starting from the linear stage and using 3-D electron-magnetohydrodynamic (EMHD) simulations. The growth rates of the simulated instabilities compared well with the growth rates obtained from linear theory. Mechanisms and conditions of the formation of flux ropes and of current filamentation will be discussed in comparison with the results of fully kinetic simulations. In 3D the X- and O-point configurations of the magnetic field formed in reconnection planes alternate along the out-of-reconnection-plane direction with the wavelength of the unstable mode. In the presence of multiple reconnection sites, the out-of-plane magnetic field can develop nested structure of quadrupoles in reconnection planes, similar to the 2-D case, but now with variations in the out-of-plane direction. The structures of the electron flow and magnetic field in 3-D simulations will be compared with those in 2-D simulations to discriminate the essentially 3D features. We also discuss

  18. Localization and propagation of the energy release during 3D kinetic magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Lapenta, Giovanni; Markidis, Stefano; Goldman, Marty; Newman, David

    2013-04-01

    Reconnection is a key processes where energy is released: magnetic field lines break, merge in a new configuration. In the process some of the energy is released. Recent work by Shay and collaborators has pointed out that energy is released far and moving fast away from the reconnection site, at a speed exceeding several times the Alfven speed. We revisit this point, considering the release of energy from reconnection and considering both laminar processes and turbulent reconnection. We analyse the energy budget and the processes of energy transfer via Poynting flux and particle flows. The results are compared with the recent findings by Shay. The effect of the guide field can be very significant at even relatively weak strength, as our recent analysis shows. The effect on the life cycle of energy is considered. The research leading to these results has received funding from the European Commission's Seventh Framework Programme (FP7/2007-2013) under the grant agreement SWIFF (project n° 263340, www.swiff.eu). [1] M. A. Shay, J. F. Drake, J. P. Eastwood, and T. D. Phan, Super-Alfvénic Propagation of Substorm Reconnection Signatures and Poynting Flux, Phys. Rev. Lett. 107, 089901, 2011. [2] M.V. Goldman, G. Lapenta, D. L. Newman, S. Markidis, H. Che, Jet Deflection by Very Weak Guide Fields during Magnetic Reconnection, Physical Review Letters, 107, 135001, 2011.

  19. Connecting Global Measures of 3D Magnetic Reconnection to Local Kinetic Physics

    SciTech Connect

    Daughton, William Scott

    2015-07-16

    After giving the motivation for the work, slides present the topic under the following headings: Description of LAPD experiment; Actual simulation setup; Simple kinetic theory of ined-tied tearing; Diagnostics to characterizing 3D reconnection; Example #1 - short-tied system; and Example #2 - long line-tied system. Colorful simulations are shown for quasipotential vs field line exponentiation, field line integrated Ohms Law, and correlation with agyrotopy & energy conversion for example #1; and evolution of current density for largest case, field exponentiation vs quasi-potential, and time evolution of magnetic field lines for example #2. To satisfy line-tied boundary conditions, there is need for superposition of oblique modes--the simple two-mode approximation works surprisingly well. For force-free layers with bg >1, the fastest growing periodic modes are oblique with kxλ ~0.5. This implies a minimum length of Ly > 2πλbg. There are strong correlations between σ → Ξ → A0e (observable with spacecraft). Electron pressure tensor is the dominant non-ideal term.

  20. 3D Hall MHD Reconnection Dynamics

    NASA Astrophysics Data System (ADS)

    Huba, J. D.; Rudakov, L.

    2002-05-01

    A 3D Hall MHD simulation code (VooDoo) has recently been developed at the Naval Research Laboratory. We present preliminary results of a fully 3D magnetic reconnection study using this code. The initial configuration of the plasma system is as follows. The ambient, reversed magnetic field is in the x-direction and is proportional to B0 tanh(y/Ly) where Ly is the scale length of the current sheet. Perturbation fields δ Bx and δ By are introduced to initiate the reconnection process. This initial configuration is similar to that used in the 2D GEM reconnection study. However, the perturbation fields are localized in the z-direction. We consider two cases: no guide field (Bz = 0) and a weak guide field (Bz = 0.1B0). We find that the reconnection process is not stationary in the z-direction but propagates in the B x ∇ n direction consistent with Hall drift physics. Hence, an asymmetric disruption of the current sheet ensues. The flow structure of the plasma in the vicinity of the X-point is complex. We find that the `neutral line' (i.e, along the z-direction) is not an ignorable coordinate and is not periodic in Hall MHD reconnection dynamics; two assumptions that are often made in reconnection studies. \\ Research supported by NASA and ONR

  1. Conceptual design of the 3D magnetic field configuration relevant to the magnetopause reconnection in the SPERF

    NASA Astrophysics Data System (ADS)

    Mao, Aohua; Ji, Hantao; Ren, Yang; E, Peng; Wang, Zhibin; Xiao, Qingmei; Xiao, Chijie

    2016-10-01

    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.

  2. Observation of Magnetic Reconnection at a 3D Null Point Associated with a Solar Eruption

    NASA Astrophysics Data System (ADS)

    Sun, J. Q.; Zhang, J.; Yang, K.; Cheng, X.; Ding, M. D.

    2016-10-01

    Magnetic null has long been recognized as a special structure serving as a preferential site for magnetic reconnection (MR). However, the direct observational study of MR at null-points is largely lacking. Here, we show the observations of MR around a magnetic null associated with an eruption that resulted in an M1.7 flare and a coronal mass ejection. The Geostationary Operational Environmental Satellites X-ray profile of the flare exhibited two peaks at ∼02:23 UT and ∼02:40 UT on 2012 November 8, respectively. Based on the imaging observations, we find that the first and also primary X-ray peak was originated from MR in the current sheet (CS) underneath the erupting magnetic flux rope (MFR). On the other hand, the second and also weaker X-ray peak was caused by MR around a null point located above the pre-eruption MFR. The interaction of the null point and the erupting MFR can be described as a two-step process. During the first step, the erupting and fast expanding MFR passed through the null point, resulting in a significant displacement of the magnetic field surrounding the null. During the second step, the displaced magnetic field started to move back, resulting in a converging inflow and subsequently the MR around the null. The null-point reconnection is a different process from the current sheet reconnection in this flare; the latter is the cause of the main peak of the flare, while the former is the cause of the secondary peak of the flare and the conspicuous high-lying cusp structure.

  3. Magnetic Reconnection

    NASA Video Gallery

    This science visualization shows a magnetospheric substorm, during which, magnetic reconnection causes energy to be rapidly released along the field lines in the magnetotail, that part of the magne...

  4. Calibrating MMS Electron Drift Instrument (EDI) Ambient Electron Flux Measurements and Characterizing 3D Electric Field Signatures of Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Shuster, J. R.; Torbert, R. B.; Vaith, H.; Argall, M. R.; Li, G.; Chen, L. J.; Ergun, R. E.; Lindqvist, P. A.; Marklund, G. T.; Khotyaintsev, Y. V.; Russell, C. T.; Magnes, W.; Le Contel, O.; Pollock, C. J.; Giles, B. L.

    2015-12-01

    The electron drift instruments (EDIs) onboard each MMS spacecraft are designed with large geometric factors (~0.01cm2 str) to facilitate detection of weak (~100 nA) electron beams fired and received by the two gun-detector units (GDUs) when EDI is in its "electric field mode" to determine the local electric and magnetic fields. A consequence of the large geometric factor is that "ambient mode" electron flux measurements (500 eV electrons having 0°, 90°, or 180° pitch angle) can vary depending on the orientation of the EDI instrument with respect to the magnetic field, a nonphysical effect that requires a correction. Here, we present determinations of the θ- and ø-dependent correction factors for the eight EDI GDUs, where θ (ø) is the polar (azimuthal) angle between the GDU symmetry axis and the local magnetic field direction, and compare the corrected fluxes with those measured by the fast plasma instrument (FPI). Using these corrected, high time resolution (~1,000 samples per second) ambient electron fluxes, combined with the unprecedentedly high resolution 3D electric field measurements taken by the spin-plane and axial double probes (SDP and ADP), we are equipped to accurately detect electron-scale current layers and electric field waves associated with the non-Maxwellian (anisotropic and agyrotropic) particle distribution functions predicted to exist in the reconnection diffusion region. We compare initial observations of the diffusion region with distributions and wave analysis from PIC simulations of asymmetric reconnection applicable for modeling reconnection at the Earth's magnetopause, where MMS will begin Science Phase 1 as of September 1, 2015.

  5. Magnetic Reconnection

    SciTech Connect

    Masaaki Yamada, Russell Kulsrud and Hantao Ji

    2009-09-17

    We review the fundamental physics of magnetic reconnection in laboratory and space plasmas, by discussing results from theory, numerical simulations, observations from space satellites, and the recent results from laboratory plasma experiments. After a brief review of the well-known early work, we discuss representative recent experimental and theoretical work and attempt to interpret the essence of significant modern findings. In the area of local reconnection physics, many significant findings have been made with regard to two- uid physics and are related to the cause of fast reconnection. Profiles of the neutral sheet, Hall currents, and the effects of guide field, collisions, and micro-turbulence are discussed to understand the fundamental processes in a local reconnection layer both in space and laboratory plasmas. While the understanding of the global reconnection dynamics is less developed, notable findings have been made on this issue through detailed documentation of magnetic self-organization phenomena in fusion plasmas. Application of magnetic reconnection physics to astrophysical plasmas is also brie y discussed.

  6. Solar Wind Heating as Revealed from the Variation of 3D Ion Velocity Distributions across the Magnetic Reconnection Exhaust Region

    NASA Astrophysics Data System (ADS)

    He, J.

    2015-12-01

    Magnetic reconnection within current sheet has been regarded as one of the crucial dissipation and heating processes of coherent structures in the solar wind turbulence. Counter-streaming of ions is an important phenomenon in the reconnection exhaust region ranged from the ion diffusion region to the extended outflow region. It has been suggested by theoretical and numerical models that the ions are going to be picked up by the ejecting magnetic field and show larger T_perpendicular than T_parallel, if the guide field is strong enough (in other word, the shear angle is relatively low). The pick-up behavior seems to favor the heating of heavy ions with high mass-to-charge ratio, since the high M/Q ions have larger gyro-period/transit-time and tend to be non-adiabatic more easily. The above statements from theoretical models have not been thoroughly testified in the solar wind observations, though the changes in total temperature and 1D reduced velocity distribution function had been studied. Until now, it remains unclear about the difference of full 3D velocity distribution for the proton and helium ions between the upstream and the exhaust regions. Here, we will analyze the plasma measurement data from WIND/3DP to explore and compare the parallel and perpendicular heating effect of different species of ions. As a preliminary result, the proton is found to show bi-directional streams in its velocity distribution in some reconnection exhaust regions. The thermalization of the counter-streaming protons will be presented. The relation between proton T_parallel/T_perpendicular and guide field strength (or shear angle) will be studied. The velocity distributions of helium ions will be illustrated, which shows the difference of heating effect between different M/Q ratios.

  7. The Effect of Dissipation Mechanism and Guide Field Strength on X-line Spreading in 3D Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Shepherd, Lucas; Cassak, P.; Drake, J.; Gosling, J.; Phan, T.; Shay, M. A.

    2013-07-01

    In two-ribbon flares, the fact that the ribbons separate in time is considered evidence of magnetic reconnection. However, in addition to the ribbons separating, they can also elongate (as seen in animations of, for example, the Bastille Day flare). The elongation is undoubtedly related to the reconnection spreading in the out-of-plane direction. Indeed, naturally occurring magnetic reconnection generally begins in a spatially localized region and spreads in the direction perpendicular to the reconnection plane as time progresses. For example, it was suggested that X-line spreading is necessary to explain the observation of X-lines extending more than 390 Earth radii (Phan et al., Nature, 404, 848, 2006), and has been seen in reconnection experiments. A sizeable out-of-plane (guide) magnetic field is present at flare sites and in the solar wind. Here, we study the effect of dissipation mechanism and the strength of the guide field has on X-line spreading. We present results from three-dimensional numerical simulations of magnetic reconnection, comparing spreading with the Hall term to spreading with anomalous resistivity. Applications to solar flares and magnetic reconnection in the solar wind will be discussed.

  8. Global Magnetospheric Modeling of 3D Reconnection

    NASA Technical Reports Server (NTRS)

    Spicer, Daniel S.

    1999-01-01

    A review of approaches to the global modeling of the terrestrial magnetosphere, how these approaches are utilized to interpret satellite data, and how these approaches have been successful at predicting magnetospheric phenomena will be presented. In addition, the importance of the ionospheric boundary and its effect on the globally topology of the magnetospheric magnetic field will be reviewed. In particular, numerical results that are rapidly changing our view of magnetospheric reconnection within the magnetospheric magnetic field will be discussed.

  9. Quantifying Reconnection in Fragmented 3D Current Layers

    NASA Astrophysics Data System (ADS)

    Wyper, Peter Fraser; Hesse, Michael

    2015-04-01

    There is growing evidence that when magnetic reconnection occurs in high Lundquist number plasmas such as in the Solar Corona or the Earth's Magnetosphere it does so within a fragmented, rather than a smooth current layer. Within the extent of these fragmented current regions the associated magnetic flux transfer and energy release occurs simultaneously in many different places. This simultaneous energy release and flux transfer has been postulated as a possible resolution to the problem of obtaining “fast” reconnection rates in such high conductivity plasmas. But how does one measure the reconnection rate in such fragmented current layers?In 2D the reconnection rate is simply given by the electric field at the dominant X-point, typically then normalized by the product of the upstream magnetic field strength and Alfven speed. However, the continuous nature of connection change in 3D makes measuring the reconnection rate much more challenging. Building on the analytical work of previous investigations (e.g. Hesse & Schindler 1988, Hesse & Birn 1993, Hesse et al. 2005) we present recently derived expressions providing, for the first time, a quantitative measure of reconnection rate in fragmented 3D current layers. We show that in 3D two measures actually characterize the rate of flux transfer; a total rate which measures the true rate at which new connections are formed and a net rate which measures the net change of connection associated with the largest value of ∫E‖dl through all of the non-ideal regions. Some simple examples will be used to illustrate how each expression may be applied and what it quantifies. This work was supported by an appointment to the NASA Postdoctoral Program and by NASA’s Magnetospheric Multiscale mission.

  10. Impulsive reconnection: 3D onset and stagnation in turbulent paradigms

    SciTech Connect

    Sears, Jason A; Intrator, Thomas P; Weber, Tom; Lapenta, Giovanni; Lazarian, Alexander

    2010-12-14

    Reconnection processes are ubiquitous in solar coronal loops, the earth's magnetotail, galactic jets, and laboratory configurations such as spheromaks and Z pinches. It is believed that reconnection dynamics are often closely linked to turbulence. In these phenomena, the bursty onset of reconnection is partly determined by a balance of macroscopic MHD forces. In a turbulent paradigm, it is reasonable to suppose that there exist many individual reconnection sites, each X-line being finite in axial extent and thus intrinsically three-dimensional (3D) in structure. The balance between MHD forces and flux pile-up continuously shifts as mutually tangled flux ropes merge or bounce. The spatial scale and thus the rate of reconnection are therefore intimately related to the turbulence statistics both in space and in time. We study intermittent 3D reconnection along spatially localized X-lines between two or more flux ropes. The threshold of MHD instability which in this case is the kink threshold is varied by modifying the line-tying boundary conditions. For fast inflow speed of approaching ropes, there is merging and magnetic reconnection which is a well known and expected consequence of the 2D coalescence instability. On the other hand, for slower inflow speed the flux ropes bounce. The threshold appears to be the Sweet Parker speed v{sub A}/S{sup 1/2}, where v{sub A} is the Alfven speed and S is the Lundquist number. Computations by collaborators at University of Wisconsin, Madison, Katholieke Universiteit Leuven, and LANL complement the experiment.

  11. Reconnection of Magnetic Fields

    NASA Technical Reports Server (NTRS)

    1984-01-01

    Spacecraft observations of steady and nonsteady reconnection at the magnetopause are reviewed. Computer simulations of three-dimensional reconnection in the geomagnetic tail are discussed. Theoretical aspects of the energization of particles in current sheets and of the microprocesses in the diffusion region are presented. Terrella experiments in which magnetospheric reconnection is simulated at both the magnetopause and in the tail are described. The possible role of reconnection in the evolution of solar magnetic fields and solar flares is discussed. A two-dimensional magnetohydrodynamic computer simulation of turbulent reconnection is examined. Results concerning reconnection in Tokamak devices are also presented.

  12. Magnetic field reconnection

    NASA Astrophysics Data System (ADS)

    Axford, W. I.

    The fundamental principles of particle acceleration by magnetic reconnection in cosmic plasmas are reviewed. The history of reconnection models is traced, and consideration is given to the Kelvin-Helmholtz theorem, the frozen-field theorem, the application of the Kelvin-Helmholtz theorem to a collisionless plasma, solutions to specific reconnection problems, and configurational instability. Diagrams and graphs are provided, and the objections raised by critics of the reconnection theory and/or its astrophysical applications are discussed.

  13. Observations of Plasma Waves in the Colliding Jet Region of a 3D Magnetic Flux Rope Flanked by Two Active Reconnection X Lines at the Subsolar Magnetopause

    NASA Astrophysics Data System (ADS)

    Oieroset, M.; Sundkvist, D. J.; Chaston, C. C.; Phan, T. D.; Mozer, F.; McFadden, J. P.; Angelopoulos, V.; Andersson, L.; Eastwood, J. P.

    2014-12-01

    We have performed a detailed analysis of plasma and wave observations in a 3D magnetic flux rope encountered by the THEMIS spacecraft at the subsolar magnetopause. The extent of the flux rope was ˜270 ion skin depths in the outflow direction, and it was flanked by two active reconnection X lines producing colliding plasma jets in the flux rope core where ion heating and suprathermal electrons were observed. The colliding jet region was highly dynamic and characterized by the presence of high-frequency waves such as ion acoustic-like waves, electron holes, and whistler mode waves near the flux rope center and low-frequency kinetic Alfvén waves over a larger region. We will discuss possible links between these waves and particle heating.

  14. Turbulent Reconnection in the Magnetic Reconnection Experiment (MRX)

    NASA Astrophysics Data System (ADS)

    Dorfman, S.; Ji, H.; Yamada, M.; Oz, E.; Yoo, J.; Daughton, W.; Roytershteyn, V.

    2009-11-01

    One of the key open questions in Magnetic Reconnection is the nature of the mechanism that governs the reconnection rate in real astrophysical and laboratory systems. For collisonless plasmas, the Hall effect removes an important bottleneck to fast reconnection as the heavier ions exit the reconnection layer over a broader region [1]. However, the Hall term cannot balance the reconnection electric field at the layer center, and the 2-D, collisionless expression for the electric field due to particle dynamics [2] has been shown to be insufficient in the Magnetic Reconnection Experiment (MRX) [1,3]. Turbulent 3-D effects such as lower hybrid frequency range fluctuations [4] may play an important role in fast reconnection in MRX. These electromagnetic fluctuations tend to be associated with high local currents and a rapid local reconnection rate. The precise relation of these fluctuations and associated 3-D asymmetries to fast reconnection is a topic of active investigations; the most up to date results will be discussed. This work was supported by NDSEG, DOE, NASA, and NSF.[4pt] [1] Y. Ren, et al., Phys. Plasmas 15, 082113 (2008). [2] M. Hesse, et al., Phys. Plasmas, 6:1781 (1999). [3] S. Dorfman, et al., Phys. Plasmas 15, 102107 (2008). [4] H. Ji, et al., Phys.Rev.Lett. 92 (2004) 115001.

  15. Perspectives on magnetic reconnection

    PubMed Central

    Yamada, Masaaki

    2016-01-01

    Magnetic reconnection is a topological rearrangement of magnetic field that occurs on time scales much faster than the global magnetic diffusion time. Since the field lines break on microscopic scales but energy is stored and the field is driven on macroscopic scales, reconnection is an inherently multi-scale process that often involves both magnetohydrodynamic (MHD) and kinetic phenomena. In this article, we begin with the MHD point of view and then describe the dynamics and energetics of reconnection using a two-fluid formulation. We also focus on the respective roles of global and local processes and how they are coupled. We conclude that the triggers for reconnection are mostly global, that the key energy conversion and dissipation processes are either local or global, and that the presence of a continuum of scales coupled from microscopic to macroscopic may be the most likely path to fast reconnection. PMID:28119547

  16. Perspectives on magnetic reconnection

    SciTech Connect

    Zweibel, Ellen G.; Yamada, Masaaki

    2016-12-07

    Magnetic reconnection is a topological rearrangement of magnetic field that occurs on time scales much faster than the global magnetic diffusion time. Since the field lines break on microscopic scales but energy is stored and the field is driven on macroscopic scales, reconnection is an inherently multi-scale process that often involves both magnetohydrodynamic (MHD) and kinetic phenomena. In this article, we begin with the MHD point of view and then describe the dynamics and energetics of reconnection using a two-fluid formulation. We also focus on the respective roles of global and local processes and how they are coupled. Here, we conclude that the triggers for reconnection are mostly global, that the key energy conversion and dissipation processes are either local or global, and that the presence of a continuum of scales coupled from microscopic to macroscopic may be the most likely path to fast reconnection.

  17. Perspectives on magnetic reconnection

    DOE PAGES

    Zweibel, Ellen G.; Yamada, Masaaki

    2016-12-07

    Magnetic reconnection is a topological rearrangement of magnetic field that occurs on time scales much faster than the global magnetic diffusion time. Since the field lines break on microscopic scales but energy is stored and the field is driven on macroscopic scales, reconnection is an inherently multi-scale process that often involves both magnetohydrodynamic (MHD) and kinetic phenomena. In this article, we begin with the MHD point of view and then describe the dynamics and energetics of reconnection using a two-fluid formulation. We also focus on the respective roles of global and local processes and how they are coupled. Here, wemore » conclude that the triggers for reconnection are mostly global, that the key energy conversion and dissipation processes are either local or global, and that the presence of a continuum of scales coupled from microscopic to macroscopic may be the most likely path to fast reconnection.« less

  18. THEMIS Sees Magnetic Reconnection

    NASA Video Gallery

    THEMIS observations confirm for the first time that magnetic reconnection in the magnetotail triggers the onset of substorms. Substorms are the sudden violent eruptions of space weather that releas...

  19. Reconnection rates in driven magnetic reconnection

    SciTech Connect

    Birn, J.; Hesse, M.

    2007-08-15

    Using resistive magnetohydrodynamic simulations, we investigate the influence of various parameters on the reconnection rate in two scenarios of magnetic reconnection. The first scenario consists of the ''Newton Challenge'' problem [Birn et al., Geophys. Res. Lett. 32, L06105 (2005)]. In this scenario, reconnection is initiated in a plane Harris-type current sheet by temporally limited, spatially varying, inflow of magnetic flux. The second scenario consists of the well-studied island coalescence problem. This scenario starts from an equilibrium containing periodic magnetic islands with parallel current filaments. Due to the attraction between parallel currents, pairs of islands may move toward each other, forming a current sheet in between. This leads to reconnection and ultimately the merging of islands. In either scenario, magnetic reconnection may be considered as being driven by external or internal forcing. Consistent with that interpretation we find that in either case the maximum reconnection rate (electric field) depends approximately linearly on the maximum driving electric field, when other parameters remain unchanged. However, this can be understood mostly from the change of characteristic background parameters; particularly, the increase of the magnetic field strength in the inflow region due to the added magnetic flux. This interpretation is consistent with the result that the maximum of the reconnection electric field is assumed significantly later (tens of Alfven times) than the maximum driving and typically does not match the instantaneous driving electric field. Furthermore, the reconnection rate also depends on the resistivity and the time scale of the driving.

  20. Experimental observation of 3-D, impulsive reconnection events in a laboratory plasma

    SciTech Connect

    Dorfman, S.; Ji, H.; Yamada, M.; Yoo, J.; Lawrence, E.; Myers, C.; Tharp, T. D.

    2014-01-15

    Fast, impulsive reconnection is commonly observed in laboratory, space, and astrophysical plasmas. In this work, impulsive, local, 3-D reconnection is identified for the first time in a laboratory current sheet. The two-fluid, impulsive reconnection events observed on the Magnetic Reconnection Experiment (MRX) [Yamada et al., Phys Plasmas 4, 1936 (1997)] cannot be explained by 2-D models and are therefore fundamentally three-dimensional. Several signatures of flux ropes are identified with these events; 3-D high current density regions with O-point structure form during a slow buildup period that precedes a fast disruption of the reconnecting current layer. The observed drop in the reconnection current and spike in the reconnection rate during the disruption are due to ejection of these flux ropes from the layer. Underscoring the 3-D nature of the events, strong out-of-plane gradients in both the density and reconnecting magnetic field are found to play a key role in this process. Electromagnetic fluctuations in the lower hybrid frequency range are observed to peak at the disruption time; however, they are not the key physics responsible for the impulsive phenomena observed. Important features of the disruption dynamics cannot be explained by an anomalous resistivity model. An important discrepancy in the layer width and force balance between the collisionless regime of MRX and kinetic simulations is also revisited. The wider layers observed in MRX may be due to the formation of flux ropes with a wide range of sizes; consistent with this hypothesis, flux rope signatures are observed down to the smallest scales resolved by the diagnostics. Finally, a 3-D two-fluid model is proposed to explain how the observed out-of-plane variation may lead to a localized region of enhanced reconnection that spreads in the direction of the out-of-plane electron flow, ejecting flux ropes from the layer in a 3-D manner.

  1. Gyrotropy During Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Swisdak, M.

    2015-12-01

    Gyrotropic particle distributions -- those that can be characterized completely by temperatures meausred parallel and perpendicular to the local magnetic field -- are the norm in many plasmas. However, near locations where magnetic topology suddenly changes, e.g., where magnetic reconnection occurs, gyrotropy can be expected to be violated. If these departures from gyrotropy are quantifiable they are useful as probes since magnetic topological changes are, in some sense, non-local while gyrotropy can be measured locally. I will discuss previously proposed measures of gyrotropy, give examples of cases where they give unphysical results, and propose a new measure. By applying this measure to particle-in-cell simulations of reconnection I will show that it does an excellent job of localizing reconnection sites. I will also show how gyrotropy can be quickly calculated in any case where the full pressure tensor is available. This has obvious applications to the interpretation of MMS data.

  2. Forced magnetic reconnection

    SciTech Connect

    Hahm, T.S.; Kulsrud, R.M.

    1984-11-01

    By studying a simple model problem, we examine the time evolution of magnetic field islands which are induced by perturbing the boundary surrounding an incompressible plasma with a resonant surface inside. We find that for sufficiently small boundary perturbations, the reconnection and island formation process occurs on the tearing mode time scale defined by Furth, Killeen, and Rosenbluth. For larger perturbations the time scale is that defined by Rutherford. The resulting asymptotic equilibrium is such that surface currents in the resonant region vanish. A detailed analytical picture of this reconnection process is presented.

  3. TURBULENT GENERAL MAGNETIC RECONNECTION

    SciTech Connect

    Eyink, G. L.

    2015-07-10

    Plasma flows with a magnetohydrodynamic (MHD)-like turbulent inertial range, such as the solar wind, require a generalization of general magnetic reconnection (GMR) theory. We introduce the slip velocity source vector per unit arclength of field line, the ratio of the curl of the non-ideal electric field in the generalized Ohm’s Law and magnetic field strength. It diverges at magnetic nulls, unifying GMR with null-point reconnection. Only under restrictive assumptions is the slip velocity related to the gradient of quasi-potential (which is the integral of parallel electric field along magnetic field lines). In a turbulent inertial range, the non-ideal field becomes tiny while its curl is large, so that line slippage occurs even while ideal MHD becomes accurate. The resolution is that ideal MHD is valid for a turbulent inertial range only in a weak sense that does not imply magnetic line freezing. The notion of weak solution is explained in terms of renormalization group (RG) type theory. The weak validity of the ideal Ohm’s law in the inertial range is shown via rigorous estimates of the terms in the generalized Ohm’s Law. All non-ideal terms are irrelevant in the RG sense and large-scale reconnection is thus governed solely by ideal dynamics. We discuss the implications for heliospheric reconnection, in particular for deviations from the Parker spiral model. Solar wind observations show that reconnection in a turbulence-broadened heliospheric current sheet, which is consistent with Lazarian–Vishniac theory, leads to slip velocities that cause field lines to lag relative to the spiral model.

  4. 3D Hall MHD Reconnection Dynamics in a Strongly Sheared System

    NASA Astrophysics Data System (ADS)

    Huba, J. D.; Rudakov, L. I.

    2002-12-01

    A 3D Hall MHD simulation code (VooDoo) has recently been developed at the Naval Research Laboratory. Recent results have demonstrated that magnetic shock-like structures [Rudakov and Huba, 2002] and a `reconnection wave' [Huba and Rudakov, 2002] can propagate in three dimensional, reversed field plasma layers. In this talk we present preliminary results of a fully 3D magnetic reconnection process in a reversed field plasma that includes a strong guide field, i.e., no magnetic nulls. The initial configuration of the plasma system is as follows. The ambient, reversed magnetic field is in the x-direction with Bx = B0 tanh(y/Ly) where Ly is the scale length of the current sheet. The ambient guide field is in the z-direction with Bz = B0. Perturbation fields δ Bx and δ By are introduced to initiate the reconnection process. This initial configuration is similar to that used in the 2D GEM reconnection study. However, the perturbation fields are localized in the z-direction. We find that the magnetic topology of the system is reconfigured via a process akin to `magnetic flipping' described by Priest and Forbes (1992). A high-density, magnetic flux-rope forms in the center of the plasma sheet. Magnetic flipping occurs between the center of the flux-tube and the boundaries in the x-direction. Associated with this magnetic flipping geometry, the reconnected magnetic field component By reverses sign 3 times in the x-direction, in contrast to only once in the no-guide field case. As in previous Hall MHD reconnection simulation studies, the system evolves asymmetrically along the current. Huba, J.D. and L.I. Rudakov, to be published in Phys. Plasmas, 2002. Priest, E.R. and T.G. Forbes, J. Geophys. Res. 97, 1521, 1992. Rudakov, L.I. and J.D. Huba, Phys. Rev. Lett. 89, 095002, 2002. Research supported by NASA and ONR.

  5. Acceleration during magnetic reconnection

    SciTech Connect

    Beresnyak, Andrey; Li, Hui

    2015-07-16

    The presentation begins with colorful depictions of solar x-ray flares and references to pulsar phenomena. Plasma reconnection is complex, could be x-point dominated or turbulent, field lines could break due to either resistivity or non-ideal effects, such as electron pressure anisotropy. Electron acceleration is sometimes observed, and sometimes not. One way to study this complex problem is to have many examples of the process (reconnection) and compare them; the other way is to simplify and come to something robust. Ideal MHD (E=0) turbulence driven by magnetic energy is assumed, and the first-order acceleration is sought. It is found that dissipation in big (length >100 ion skin depths) current sheets is universal and independent on microscopic resistivity and the mean imposed field; particles are regularly accelerated while experiencing curvature drift in flows driven by magnetic tension. One example of such flow is spontaneous reconnection. This explains hot electrons with a power-law tail in solar flares, as well as ultrashort time variability in some astrophysical sources.

  6. Magnetic reconnection launcher

    SciTech Connect

    Cowan, M.

    1989-04-04

    An electromagnetic launcher is described, which includes a plurality of electrical stages which are energized sequentially in synchrony with the passage of a projectile. Each stage of the launcher includes two or more coils which are arranged coaxially on either closed-loop or straight lines to form gaps between their ends. The projectile has an electrically conductive gap-portion that passes through all the gaps of all the stages in a direction transverse to the axes of the coils. The coils receive an electric current, store magnetic energy, and convert a significant portion of the stored magnetic energy into kinetic energy of the projectile by magnetic reconnection as the gap portion of the projectile moves through the gap. The magnetic polarity of the opposing coils is in the same direction, e.g. N-S-N-S. A gap portion of the projectile may be made from aluminum and is propelled by the reconnection of magnetic flux stored in the coils which causes accelerating forces to act upon the projectile at both the rear vertical surface of the projectile and at the horizontal surfaces of the projectile near its rear. The gap portion of the projectile may be flat, rectangular and longer than the length of the opposing coils and fit loosely within the gap between the opposing coils.

  7. Magnetic reconnection launcher

    DOEpatents

    Cowan, Maynard

    1989-01-01

    An electromagnetic launcher includes a plurality of electrical stages which are energized sequentially in synchrony with the passage of a projectile. Each stage of the launcher includes two or more coils which are arranged coaxially on either closed-loop or straight lines to form gaps between their ends. The projectile has an electrically conductive gap-portion that passes through all the gaps of all the stages in a direction transverse to the axes of the coils. The coils receive an electric current, store magnetic energy, and convert a significant portion of the stored magnetic energy into kinetic energy of the projectile by magnetic reconnection as the gap portion of the projectile moves through the gap. The magnetic polarity of the opposing coils is in the same direction, e.g. N-S-N-S. A gap portion of the projectile may be made from aluminum and is propelled by the reconnection of magnetic flux stored in the coils which causes accelerating forces to act upon the projectile at both the rear vertical surface of the projectile and at the horizontal surfaces of the projectile near its rear. The gap portion of the projectile may be flat, rectangular and longer than the length of the opposing coils and fit loosely within the gap between the opposing coils.

  8. Secondary reconnection, energisation and turbulence in dipolarisation fronts: results of a 3D kinetic simulation campaign

    NASA Astrophysics Data System (ADS)

    Lapenta, Giovanni; Goldman, Martin; Newman, David; olshevskyi, Vyacheslav; Markidis, Stefano

    2016-04-01

    Dipolarization fronts (DF) are formed by reconnection outflows interacting with the pre-existing environment. These regions are host of important energy exchanges [1], particle acceleration [2] and a complex structure and evolution [3]. Our recent work has investigated these regions via fully kinetic 3D simulations [4]. As reported recently on Nature Physics [3], based on 3D fully kinetic simulations started with a well defined x-line, we observe that in the DF reconnection transitions towards a more chaotic regime. In the fronts an instability devel- ops caused by the local gradients of the density and by the unfavourable acceleration and field line curvature. The consequence is the break up of the fronts in a fashion similar to the classical fluid Rayleigh-Taylor instability with the formation of "fingers" of plasma and embedded magnetic fields. These fingers interact and produce secondary reconnection sites. We present several different diagnostics that prove the existence of these secondary reconnection sites. Each site is surrounded by its own electron diffusion region. At the fronts the ions are generally not magnetized and considerable ion slippage is present. The discovery we present is that electrons are also slipping, forming localized diffusion regions near secondary reconnection sites [1]. The consequence of this discovery is twofold. First, the instability in the fronts has strong energetic implications. We observe that the energy transfer locally is very strong, an order of magnitude stronger than in the "X" line. However, this energy transfer is of both signs as it is natural for a wavy rippling with regions of magnetic to kinetic and regions of kinetic to magnetic energy conversion. Second, and most important for this session, is that MMS should not limit the search for electron diffusion regions to the location marked with X in all reconnection cartoons. Our simulations predict more numerous and perhaps more easily measurable electron diffusion

  9. Experimental study of 3-D, impulsive reconnection events in a laboratory plasma

    NASA Astrophysics Data System (ADS)

    Dorfman, Seth Elliot

    Fast, impulsive reconnection is commonly observed in laboratory, space and astrophysical plasmas. Many existing models of reconnection attempt to explain this behavior without including variation in the third direction. However, the impulsive reconnection events observed on the Magnetic Reconnection Experiment (MRX) which are described in this dissertation cannot be explained by 2-D models and are therefore fundamentally three-dimensional. These events include both a slow buildup phase and a fast current layer disruption phase. The buildup phase is characterized by a slow transition from collisional to collisionless reconnection and the formation of "flux rope" structures; these "flux ropes" are defined as 3-D high current density regions associated with an O point at the measurement location. In the disruption phase, the "flux ropes" are ejected from the reconnection layer as the total current drops and the reconnection rate spikes. Strong out-of-plane gradients in both the density and reconnecting magnetic field are another key feature of disruptive discharges; after finite upstream density is depleted by reconnection during the buildup phase, the out of plane magnetic field gradient flattens and this disruption spreads in the electron flow direction. Electromagnetic fluctuations in the lower hybrid frequency range are observed to peak at the disruption time; however, they are not the key physics responsible for the impulsive phenomena observed. Important features of the disruption dynamics cannot be explained by an anomalous resistivity model. Furthermore, an important discrepancy in the layer width and force balance between the collisionless regime of MRX and kinetic simulations persists when the fluctuations are small or absent, implying that they are not the cause of the wider electron layers observed in the experiment. These wider layers may instead be due to the formation of flux ropes with a wide range of sizes; consistent with this hypothesis, flux rope

  10. Observations and models of magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Barta, Miroslav

    2015-08-01

    Magnetic reconnection is now almost unanimously considered to be a key plasma process for energy release in solar and stellar flares. Recent decade have seen rapid development in the theory, simulations and searching for observational evidences of magnetic reconnection being in action in the core of flares. Modern modeling approach involves many realistic aspects of magnetic reconnection such as intrinsically 3D nature of the process and, namely, its highly dynamic character connected with violent formation of plasmoids at many scales. The cascade of plasmoid formation represents natural process of fast, turbulent energy transfer to the kinetic dissipation scale. This concept, revealed by numerical simulations, has found its ground in the theory of (ideal) plasmoid instability in current layers with high aspect ratio. The plasmoid dominated reconnection regime is capable to account for many puzzling dilemmas in the flare physics ranging from the observation-demanded energy release rate vs. standard reconnection-regime timescales, observed organized large-scale structures vs. signatures of fragmented energy release etc. The talk aims at reviewing recent theoretical and simulation development in this direction and observational support for the concept of plasmoid-driven reconnection cascade namely in solar flares.

  11. Self-generated Turbulence in Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Oishi, Jeffrey S.; Mac Low, Mordecai-Mark; Collins, David C.; Tamura, Moeko

    2015-06-01

    Classical Sweet-Parker models of reconnection predict that reconnection rates depend inversely on the resistivity, usually parameterized using the dimensionless Lundquist number (S). We describe magnetohydrodynamic (MHD) simulations using a static, nested grid that show the development of a three-dimensional (3D) instability in the plane of a current sheet between reversing field lines without a guide field. The instability leads to rapid reconnection of magnetic field lines at a rate independent of S over at least the range 3.2× {{10}3}≲ S≲ 3.2× {{10}5} resolved by the simulations. We find that this instability occurs even for cases with S≲ {{10}4} that in our models appear stable to the recently described, two-dimensional, plasmoid instability. Our results suggest that 3D, MHD processes alone produce fast (resistivity independent) reconnection without recourse to kinetic effects or external turbulence. The unstable reconnection layers provide a self-consistent environment in which the extensively studied turbulent reconnection process can occur.

  12. Relaxation and merging flux ropes and 3D effects in the Reconnection Scaling Experiment at LANL

    NASA Astrophysics Data System (ADS)

    Intrator, T.; Furno, I.; Light, A.; Madziwa-Nussinov, T.; Lapenta, G.; Ricci, P.; Hemsing, E.

    2005-12-01

    Magnetic structures are embedded in astrophysical, space, solar and laboratory plasmas. The dynamics and relaxation of these plasmas can involve flows, changes in topology, magnetic reconnection, plasma heating, and dissipation of magnetic energy. This complex behavior is intrinsically three-dimensional (3D). Current-carrying magnetic flux ropes are the fundamental building blocks for many of these cases. At Los Alamos National Laboratory, we have an experimental realization of this model. The Reconnection Scaling Experiment (RSX) is a unique facility that can create multiple current-carrying flux ropes in an MHD experiment. Plasma guns are used to inject magnetic helicity into plasma columns. We show 3D structure with camera views, along with magnetic, electric, and particle probe data. Experiments in the presence of a strong guide magnetic field (Bz/Brcxn>10) show the formation of a current sheet and electron heating during the coalescence of two flux ropes. Computed simulations of the interactions of two current ropes are shown of that predict many of the experimental characteristics. A density wave structure that propagates opposite to the current is measured in the current sheet with wavelength and speed that are consistent with a kinetic Alfven wave. The current channels acquire angular momentum and rotate about each other developing helical structures, both individually and jointly. Parallel pressure gradients (a 3D effect) appear to be an important term in the Ohm's Law.

  13. Observational Signatures of Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Savage, Sabrina

    2014-01-01

    Magnetic reconnection is often referred to as the primary source of energy release during solar flares. Directly observing reconnection occurring in the solar atmosphere, however, is not trivial considering that the scale size of the diffusion region is magnitudes smaller than the observational capabilities of current instrumentation, and coronal magnetic field measurements are not currently sufficient to capture the process. Therefore, predicting and studying observationally feasible signatures of the precursors and consequences of reconnection is necessary for guiding and verifying the simulations that dominate our understanding. I will present a set of such observations, particularly in connection with long-duration solar events, and compare them with recent simulations and theoretical predictions.

  14. Magnetic reconnection launcher

    DOEpatents

    Cowan, M.

    1987-04-06

    An electromagnetic launcher includes a plurality of electrical stages which are energized sequentially in the launcher with the passage of a projectiles. Each stage of the launcher includes two or more coils which are arranged coaxially on either closed-loop or straight lines to form gaps between their ends. The projectile has an electrically conductive gap-portion that passes through all the gaps of all the stages in a direction transverse to the axes of the coils. The coils receive an electric current, store magnetic energy, and convert a significant portion of the stored magnetic energy into kinetic energy of the projectile moves through the gap. The magnetic polarity of the opposing coils is in the same direction, e.g. N-S-N-S. A gap portion of the projectile may be made from aluminum and is propelled by the reconnection of magnetic flux stored in the coils which causes accelerating forces to act upon the projectile and at the horizontal surfaces of the projectile near its rear. The gap portion of the projectile may be flat, rectangular and longer than the length of the opposing coils. The gap portion of the projectile permits substantially unrestricted distribution of the induced currents so that current densities are only high where the useful magnetic force is high. This allows designs which permit ohmic oblation from the rear surfaces of the gap portion of the projectile allowing much high velocities to be achieved. An electric power apparatus controls the electric power supplied to the opposing coils until the gap portion of the projectile substantially occupies the gap between the coils, at which time the coils are supplied with peak current quickly. 8 figs.

  15. Properties of asymmetric magnetic reconnection

    SciTech Connect

    Birn, J.; Borovsky, J. E.; Hesse, M.

    2008-03-15

    Properties of magnetic reconnection are investigated in two-dimensional, resistive magnetohydrodynamic (MHD) simulations of current sheets separating plasmas with different magnetic field strengths and densities. Specific emphasis is on the influence of the external parameters on the reconnection rate. The effect of the dissipation in the resistive MHD model is separated from this influence by evaluating resistivity dependence together with the dependence on the background parameters. Two scenarios are considered, which may be distinguished as driven and nondriven reconnection. In either scenario, the maximum reconnection rate (electric field) is found to depend on appropriate hybrid expressions based on a magnetic field strength and an Alfven speed derived from the characteristic values in the two inflow regions. The scaling compares favorably with an analytic formula derived recently by Cassak and Shay [Phys. Plasmas 14, 102114 (2007)] applied to the regime of fast reconnection. An investigation of the energy flow and conversion in the vicinity of the reconnection site revealed a significant role of enthalpy flux generation, in addition to the expected conversion of Poynting flux to kinetic energy flux. This enthalpy flux generation results from Ohmic heating as well as adiabatic, that is, compressional heating. The latter is found more important when the magnetic field strengths in the two inflow regions are comparable in magnitude.

  16. Magnetic Reconnection in Solar Flares

    NASA Astrophysics Data System (ADS)

    Forbes, Terry G.

    2016-05-01

    Reconnection has at least three possible roles in solar flares: First, it may contribute to the build-up of magnetic energy in the solar corona prior to flare onset; second, it may directly trigger the onset of the flare; and third, it may allow the release of magnetic energy by relaxing the magnetic field configuration to a lower energy state. Although observational support for the first two roles is somewhat limited, there is now ample support for the third. Within the last few years EUV and X-ray instruments have directly observed the kind of plasma flows and heating indicative of reconnection. Continued improvements in instrumentation will greatly help to determine the detailed physics of the reconnection process in the solar atmosphere. Careful measurement of the reconnection outflows will be especially helpful in this regard. Current observations suggest that in some flares the jet outflows are accelerated within a short diffusion region that is more characteristic of Petschek-type reconnection than Sweet-Parker reconnection. Recent resistive MHD theoretical and numerical analyses predict that the length of the diffusion region should be just within the resolution range of current X-ray and EUV telescopes if the resistivity is uniform. On the other hand, if the resistivity is not uniform, the length of the diffusion region could be too short for the outflow acceleration region to be observable.

  17. Spontaneous three-dimensional magnetic reconnection in merging toroidal plasma experiment

    SciTech Connect

    Ii, Toru; Ono, Yasushi

    2013-01-15

    We investigated a new phenomenon of three-dimensional (3D) magnetic reconnection in TS-4 torus plasma merging experiments by directly measuring the 3D structures of the current sheet. Removal of all toroidal asymmetry of the device reveals that a strong external drive of reconnection inflow increases the toroidal asymmetry of the current sheet only during the reconnection. This spontaneous 3D deformation of the current sheet increases the reconnection outflow as well as the reconnection electric field, probably because local compression of the current sheet to a thickness less than the ion gyroradius triggers its strong dissipation of the current sheet, responsible for the onset of 3D reconnection. These mechanisms indicate that the 3D reconnection is a newly observed spontaneous process of fast reconnection.

  18. Improved Magnetic Reconnection Experiment at FRC Device

    NASA Astrophysics Data System (ADS)

    Xu, Ming; Zhou, Ruijie; Vasquez, Daniel; Huang, Tian-Sen; Prairie View Solar Observatory Team

    2014-10-01

    With experimental facility's improvement, magnetic reconnection has been further studied at Prairie View rotamak device. By adding one toroidal current in the central part of the rotamak device, the cutting of one magnetic field reverse configuration (FRC) as two FRCs in the experiment process becomes more obvious. Differing from the magnetic reconnection experiments conducted at other labs, where magnetic reconnection is formed with two ware-coiled currents buried in a chamber with large scale magnetic field, in our magnetic reconnection experiment the main source of the magnetic field is plasma current. Thus, the magnetic reconnection experiments conducted at rotamak device are closer to the one occurring in the space and on the sun. At the present stage, our experiments focus on the study of the change in electron temperature during the magnetic reconnection process. Furthermore, the ion temperature and plasma flow can be easily achieved from fast ion Doppler spectroscopy (IDS) diagnostic system, which makes the magnetic reconnection process more clearly.

  19. 3D Model of Slip-Running Reconnection on Solar Sigmoidal Regions

    NASA Astrophysics Data System (ADS)

    Douglas, B.; Savcheva, A. S.; DeLuca, E. E.

    2015-12-01

    The structure of energy storing magnetic field lines on the Sun is very twisted and contorted. Some of the twist arises from photospheric foot point motion and some is due to currents carried into the corona as fields emerge. The stability of a region depends on both the energy stored (so-called "free" energy) and on the structure of the surrounding nearly potential fields. Free energy is usually contained in these S-shaped regions called sigmoids on the solar corona. The only way to reach lower energy state is to release this free energy, by changing its connectivity. This change in connectivity leads to flares and coronal mass ejections (CMEs) that can affect environments of nearby planets. For this project, we focus on a special kind of connectivity change called slip-running reconnection to create 3D numerical models of flare-producing magnetic fields. By comparing these numerical models to observational data from Atmospheric Imaging Assembly (AIA), we will be able to better explain the evolution of sigmoidal flares from active regions. We are studying a flare from Dudik et al 2014 paper (2012 July 12), and a flare from 2015 June 14. Using the Coronal Modeling System (CMS) software, we read the photospheric magnetogram for the specified date and time, compute the potential field, setup the 3D flux rope path, and then relax this flux rope over 60,000 iterations to create a nonlinear force-free field (NLFFF). Using these relaxed models we find the best-fit loops surrounding the flux rope. We then compare these models to the observations in AIA. We compare the magnetic field structure in our models with the observed slipping. For regions near our inserted flux rope, our models successfully correlate with this observation. Further modeling is required, but these initial results suggest that NLFFF modeling may be able to capture realistic 3-D magnetic structures associated with slipping reconnection.

  20. High-Frequency Fluctuations During Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Jara-Almonte, J.; Ji, H.; Daughton, W. S.; Roytershteyn, V.; Yamada, M.; Yoo, J.; Fox, W. R., II

    2014-12-01

    During collisionless reconnection, the decoupling of the field from the plasma is known to occur only within the localized ion and electron diffusion regions, however predictions from fully kinetic simulations do not agree with experimental observations on the size of the electron diffusion region, implying differing reconnection mechanisms. Previous experiments, along with 2D and 3D simulations, have conclusively shown that this discrepancy cannot be explained by either classical collisions or Lower-Hybrid Drift Instability (Roytershtyn 2010, 2013). Due to computational limitations, however, previous simulations were constrained to have minimal scale separation between the electron skin depth and the Debye length (de/λD ~ 10), much smaller than in experiments (de/λD ~ 300). This lack of scale-separation can drastically modify the electrostatic microphysics within the diffusion layer. Using 3D, fully explicit kinetic simulations with a realistic and unprecedentedly large separation between the Debye length and the electron skin depth, de/λD = 64, we show that high frequency electrostatic waves (ω >> ωLH) can exist within the electron diffusion region. These waves generate small-scale turbulence within the electron diffusion region which acts to broaden the layer. Anomalous resistivity is also generated by the turbulence and significantly modifies the force balance. In addition to simulation results, initial experimental measurements of high frequency fluctuations (electrostatic and electromagnetic, f ≤ 1 GHz) in the Magnetic Reconnection Experiment (MRX) will be presented.

  1. Dynamic Response of Magnetic Reconnection Due to Current Sheet Variability

    NASA Astrophysics Data System (ADS)

    George, D. E.; Jahn, J. M.; Burch, J. L.; Hesse, M.; Pollock, C. J.

    2014-12-01

    Magnetic reconnection is a process which regulates the interaction between regions of magnetized plasma. While many factors have an impact on the evolution of this process, there still remains a lack of understanding of the key behaviors involved in the triggering of fast reconnection. Despite an abundance of in-situ measurements, indicating the high degree of variability in the thickness, density and composition along the current sheet, no simulation studies exist which account for such current sheet variations. 2D and 3D simulations have a periodic boundary in the dimension along the current sheet and so tend to neglect these variations in the current sheet originating external to the modeled reconnection region. Here we focus on the effects on reconnection due to the variability in the thickness and density of the current sheet. Using 2.5D kinetic simulations of 2-species plasma, we isolate and explore the dynamic effects on reconnection associated with variations in the current sheet originating externally to the reconnection region. While periodic boundary conditions are still used, in the direction along the current sheet, a step-change perturbation in thickness or density of the current sheet is introduced once a stable reconnection rate is reached. The dynamic response of the overall system, after introducing the perturbation, is then evaluated, with a focus on the reconnection rate. When the reconnection rate is slowed significantly over time, loading of the inflow region occurs (a build-up of plasma and magnetic energy/pressure. This state is indicated by an asymptotic behavior in the reconnection rate over time. If a sudden variation in the current sheet is introduced under these conditions, a resultant triggering of fast reconnection may occur, which could lead to an episode of fast reconnection, saw-tooth-crash condition or even act as a trigger for sub-storms.

  2. Fundamental Concepts Associated with Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Gonzalez, W. D.; Parker, E. N.; Mozer, F. S.; Vasyliūnas, V. M.; Pritchett, P. L.; Karimabadi, H.; Cassak, P. A.; Scudder, J. D.; Yamada, M.; Kulsrud, R. M.; Koga, D.

    The chapter starts with a discussion about the importance of the concept of magnetic field lines in space plasmas and magnetic reconnection, followed by presentations on: (a) the meaning and validity of empirical constructs related with magnetic reconnection research, such as: "moving" magnetic field lines, "frozen-in" condition and "diffusion region" of reconnection; and (b) experimental evidence of the diffusion region and related energetics. Next, aims to link external (MHD) with internal (non-MHD) regions of reconnection are discussed in association with the so-called "Axford conjecture", followed by short presentations on: (a) global equilibria in reconnection; and (b) the role of the separatrices in global aspects of reconnection. In the last section, we present additional discussion about the concept of "diffusion region" and about the two fundamental questions associated with magnetic reconnection reviewed in this chapter.

  3. The relation between reconnected flux, the parallel electric field, and the reconnection rate in a three-dimensional kinetic simulation of magnetic reconnection

    SciTech Connect

    Wendel, D. E.; Olson, D. K.; Hesse, M.; Kuznetsova, M.; Adrian, M. L.; Aunai, N.; Karimabadi, H.; Daughton, W.

    2013-12-15

    We investigate the distribution of parallel electric fields and their relationship to the location and rate of magnetic reconnection in a large particle-in-cell simulation of 3D turbulent magnetic reconnection with open boundary conditions. The simulation's guide field geometry inhibits the formation of simple topological features such as null points. Therefore, we derive the location of potential changes in magnetic connectivity by finding the field lines that experience a large relative change between their endpoints, i.e., the quasi-separatrix layer. We find a good correspondence between the locus of changes in magnetic connectivity or the quasi-separatrix layer and the map of large gradients in the integrated parallel electric field (or quasi-potential). Furthermore, we investigate the distribution of the parallel electric field along the reconnecting field lines. We find the reconnection rate is controlled by only the low-amplitude, zeroth and first–order trends in the parallel electric field while the contribution from fluctuations of the parallel electric field, such as electron holes, is negligible. The results impact the determination of reconnection sites and reconnection rates in models and in situ spacecraft observations of 3D turbulent reconnection. It is difficult through direct observation to isolate the loci of the reconnection parallel electric field amidst the large amplitude fluctuations. However, we demonstrate that a positive slope of the running sum of the parallel electric field along the field line as a function of field line length indicates where reconnection is occurring along the field line.

  4. Slip Running Reconnection in Magnetic Flux Ropes

    NASA Astrophysics Data System (ADS)

    Gekelman, W. N.; Van Compernolle, B.; Vincena, S. T.; De Hass, T.

    2012-12-01

    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 can be 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 ěc{J}×ěc{B} forces causing them to twist about each other and eventually merge. Kink instabilities cause them to violently smash into each other and reconnect at the point of contact. We report on experiments on two adjacent ropes done in the large plasma device (LAPD) at UCLA ( ne ˜ 1012, Te ˜ 6 eV, B0z=330G, Brope}\\cong{10G,trep=1 Hz). The currents and magnetic fields form exotic shapes with no ignorable direction and no magnetic nulls. Volumetric space-time data (70,600 spatial locations) show multiple reconnection sites with time-dependent locations. The concept of a quasi-separatrix layer (QSL), a tool to understand and visualize 3D magnetic field lines reconnection without null points is introduced. Three-dimensional measurements of the QSL derived from magnetic field data are presented. Within the QSL field lines that start close to one another rapidly diverge as they pass through one or more reconnection regions. The motion of magnetic field lines are traced as reconnection proceeds and they are observed to slip through the regions of space where the QSL is largest. As the interaction proceeds we double the current in the ropes. This accompanied by intense heating as observed in uv light and plasma flows measured by Mach probes. The interaction of the ropes is clearly seen by vislaulizng magnetic field data , as well as in images from a fast framing camera. Work supported by the Dept. of Energy and The National Science Foundation, done at the Basic Plasma Science Facility at UCLA.Magnetic Field lines (measured) of three flux ropes and the plasma currents associated with them

  5. Three-dimensional outflow jets generated in collisionless magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Fujimoto, Keizo

    2016-10-01

    The present study proposes a new theoretical model generating three-dimensional (3-D) outflow jets in collisionless magnetic reconnection by means of a large-scale particle-in-cell simulation. The key mechanism is the formation of 3-D flux ropes arising in the turbulent electron current layer formed around the magnetic x line. The scale of the flux ropes along the current density is determined by the wavelength of an electron flow shear mode which is a macroscopic scale larger than the typical kinetic scales. The 3-D flux ropes are intermittently ejected from the current layer and regulates the outflow jets into three dimensions. The gross reconnection rate is sufficiently large, since reconnection takes place almost uniformly along the x line.

  6. The Development of Drift Wave Turbulence in Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    McMurtrie, L.; Drake, J. F.; Swisdak, M. M.

    2013-12-01

    An important feature in collisionless magnetic reconnection is the development of sharp discontinuities along the separatrices bounding the Alfvenic outflow. The typical scale length of these features is ρs (the Larmor radius based on the sound speed) for guide field reconnection. Temperature gradients in the inflowing plasma (as might be found in the magnetopause) can lead to instabilities at these separatrices, specifically drift wave turbulence. We present standalone 2D and 3D PIC simulations of drift wave turbulence to investigate scaling properties and growth rates. Further investigations of the relative importance of drift wave turbulence in the development of reconnection will also be considered.

  7. A Rosetta Stone for in situ Observations of Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Scudder, J. D.; Daughton, W. S.; Karimabadi, H.; Roytershteyn, V.

    2015-12-01

    Local conditions that constrain the physics of magnetic reconnection in space in 3D will be discussed, including those observable conditions presently used and new ones that enhance experimental closure. Three classes of tests will be discussed: i) proxies for unmeasurable theoretical properties II) observable properties satisfied by all layers that pass mass flux, including those of the reconnection layer, and (iii) observable kinetic tests that are increasingly peculiar to collisionless magnetic reconnection. A Rosetta Stone of state of the art observables will be proposed, including proxies for unmeasurable theoretical local rate of frozen flux violation and measures of the significance of frozen flux encountered. A suite of kinetic observables involving properties peculiar to electrons will also be demonstrated as promising litmus tests for certifying sites of collisionless magnetic reconnection.

  8. Spontaneous magnetic reconnection. Collisionless reconnection and its potential astrophysical relevance

    NASA Astrophysics Data System (ADS)

    Treumann, R. A.; Baumjohann, W.

    2015-10-01

    The present review concerns the relevance of collisionless reconnection in the astrophysical context. Emphasis is put on recent developments in theory obtained from collisionless numerical simulations in two and three dimensions. It is stressed that magnetic reconnection is a universal process of particular importance under collisionless conditions, when both collisional and anomalous dissipation are irrelevant. While collisional (resistive) reconnection is a slow, diffusive process, collisionless reconnection is spontaneous. On any astrophysical time scale, it is explosive. It sets on when electric current widths become comparable to the leptonic inertial length in the so-called lepton (electron/positron) "diffusion region", where leptons de-magnetise. Here, the magnetic field contacts its oppositely directed partner and annihilates. Spontaneous reconnection breaks the original magnetic symmetry, violently releases the stored free energy of the electric current, and causes plasma heating and particle acceleration. Ultimately, the released energy is provided by mechanical motion of either the two colliding magnetised plasmas that generate the current sheet or the internal turbulence cascading down to lepton-scale current filaments. Spontaneous reconnection in such extended current sheets that separate two colliding plasmas results in the generation of many reconnection sites (tearing modes) distributed over the current surface, each consisting of lepton exhausts and jets which are separated by plasmoids. Volume-filling factors of reconnection sites are estimated to be as large as {<}10^{-5} per current sheet. Lepton currents inside exhausts may be strong enough to excite Buneman and, for large thermal pressure anisotropy, also Weibel instabilities. They bifurcate and break off into many small-scale current filaments and magnetic flux ropes exhibiting turbulent magnetic power spectra of very flat power-law shape W_b∝ k^{-α } in wavenumber k with power becoming as

  9. Particle Acceleration Due to Coronal Non-null Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Threlfall, James; Neukirch, Thomas; Parnell, Clare Elizabeth

    2017-03-01

    Various topological features, for example magnetic null points and separators, have been inferred as likely sites of magnetic reconnection and particle acceleration in the solar atmosphere. In fact, magnetic reconnection is not constrained to solely take place at or near such topological features and may also take place in the absence of such features. Studies of particle acceleration using non-topological reconnection experiments embedded in the solar atmosphere are uncommon. We aim to investigate and characterise particle behaviour in a model of magnetic reconnection which causes an arcade of solar coronal magnetic field to twist and form an erupting flux rope, crucially in the absence of any common topological features where reconnection is often thought to occur. We use a numerical scheme that evolves the gyro-averaged orbit equations of single electrons and protons in time and space, and simulate the gyromotion of particles in a fully analytical global field model. We observe and discuss how the magnetic and electric fields of the model and the initial conditions of each orbit may lead to acceleration of protons and electrons up to 2 MeV in energy (depending on model parameters). We describe the morphology of time-dependent acceleration and impact sites for each particle species and compare our findings to those recovered by topologically based studies of three-dimensional (3D) reconnection and particle acceleration. We also broadly compare aspects of our findings to general observational features typically seen during two-ribbon flare events.

  10. Magnetic reconnection in a compressible MHD plasma

    SciTech Connect

    Hesse, Michael; Zenitani, Seiji; Birn, Joachim

    2011-04-15

    Using steady-state resistive MHD, magnetic reconnection is reinvestigated for conditions of high resistivity/low magnetic Reynolds number, when the thickness of the diffusion region is no longer small compared to its length. Implicit expressions for the reconnection rate and other reconnection parameters are derived based on the requirements of mass, momentum, and energy conservation. These expressions are solved via simple iterative procedures. Implications specifically for low Reynolds number/high resistivity are being discussed.

  11. Magnetic Reconnection in a Compressible MHD Plasma

    NASA Technical Reports Server (NTRS)

    Hesse, Michael; Birn, Joachim; Zenitani, Seiji

    2011-01-01

    Using steady-state resistive MHD, magnetic reconnection is reinvestigated for conditions of high resistivity/low magnetic Reynolds number, when the thickness of the diffusion region is no longer small compared to its length. Implicit expressions for the reconnection rate and other reconnection parameters are derived based on the requirements of mass, momentum, and energy conservation. These expressions are solved via simple iterative procedures. Implications specifically for low Reynolds number/high resistivity are being discussed

  12. The Onset of Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Daldorff, Lars K. S.; Klimchuk, James A.; van der Holst, Bart

    2015-04-01

    A fundamental question concerning magnetic energy release on the Sun is why the release occurs only after substantial stresses have been built up in the field. If reconnection were to occur readily, the released energy would be insufficient to explain coronal heating, CMEs, flares, jets, spicules, etc. How can we explain this switch-on property? What is the physical nature of the onset conditions? One idea involves the "secondary instability" of current sheets, which switches on when the rotation of the magnetic field across a current sheet reaches a critical angle. Such conditions would occur at the boundaries of flux tubes that become tangled and twisted by turbulent photospheric convection, for example. Other ideas involve a critical thickness for the current sheet. We report here on the preliminary results of our investigation of reconnect onset. Unlike our earlier work on the secondary instability (Dahlburg, Klimchuk, and Antiochos 2005), we treat the coupled chromosphere-corona system. Using the BATS-R-US MHD code, we simulate a single current sheet in a sheared magnetic field that extends from the chromosphere into the corona. Driver motions are applied at the base of the model. The configuration and chromosphere are both idealized, but capture the essential physics of the problem. The advantage of this unique approach is that it resolves the current sheet to the greatest extent possible while maintaining a realistic solar atmosphere. It thus bridges the gap between "reconnection in a box" studies and studies of large-scale systems such as active regions. One question we will address is whether onset conditions are met first in the chromosphere or corona. We will report on the work done on the project.

  13. The Onset of Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Daldorff, L. K. S.; Klimchuk, J. A.

    2015-12-01

    A fundamental question concerning magnetic energy release on the Sun is why the release occurs only after substantial stresses have been built up in the field. If reconnection were to occur readily, the released energy would be insufficient to explain coronal heating, CMEs, flares, jets, spicules, etc. How can we explain this switch-on property? What is the physical nature of the onset conditions? One idea involves the "secondary instability" of current sheets, which switches on when the rotation of the magnetic field across a current sheet reaches a critical angle. Such conditions would occur at the boundaries of flux tubes that become tangled and twisted by turbulent photospheric convection, for example. Other ideas involve a critical thickness for the current sheet. We report here on the preliminary results of our investigation of reconnect onset. Unlike our earlier work on the secondary instability (Dahlburg, Klimchuk, and Antiochos 2005), we treat the coupled chromosphere-corona system. Using the BATS-R-US MHD code, we simulate a single current sheet in a sheared magnetic field that extends from the chromosphere into the corona. Driver motions are applied at the base of the model. The configuration and chromosphere are both idealized, but capture the essential physics of the problem. The advantage of this unique approach is that it resolves the current sheet to the greatest extent possible while maintaining a realistic solar atmosphere. It thus bridges the gap between"reconnection in a box" studies and studies of large-scale systems such as active regions. One question we will address is whether onset conditions are met first in the chromosphere or corona. We will report on the work done on the project.

  14. Magnetohydrodynamic Numerical Simulations of Magnetic Reconnection in Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Tanuma, Syuniti

    2000-03-01

    In this thesis, we perform two-dimensional (2D) resistive magnetohydrodynamic (MHD) numerical simulations of the magnetic reconnection in interstellar medium. Part I is introduction. The motivation of the study is to investigate the origin of hot gas in interstellar medium. A scenario for generating X-ray gas in Galaxy is proposed, and examined by performing 2D MHD simulations with simple assumptions (Part II). The magnetic reconnection triggered by a supernova (Part III) and Parker instability (Part IV) are studied in detail, by performing 2D MHD simulations. Furthermore, the magnetic reconnection is also studied by performing three-dimensional (3D) MHD numerical simulation in (Part V). % Finally, we discuss and summarize the thesis (Parts VI and VII). Part I First, we review observation of Galactic Ridge X-ray Emission (GRXE) and its problems. Second, we describe observation of interstellar magnetic field briefly. Third, we review magnetic reconnection, theoretical models, numerical simulations, observations and experiments, and tearing instability. Forth, Parker instability (undular mode of magnetobuoyancy instability) is mentioned. Finally, we show the purpose of this thesis. Part II We present a scenario for the origin of the hot plasma in Galaxy as a model of strong X-ray emission [sim 3-10 keV; LX(2-10 keV) sim 1038 erg s-1], called GRXE, which has been observed near to the galactic plane. GRXE is thermal emission from a hot component (sim 7 keV) and a cool component (sim 0.8 keV). Observations suggest that the hot component is diffuse, and that it is not escaping away freely. Both what heats the hot component and what confines it in Galactic ridge still remain puzzling, while the cool component is believed to be created by supernovae. We propose a new scenario: the hot component is heated by magnetic reconnection, and confined by a helical magnetic field produced by magnetic reconnection. We solved 2D MHD equations numerically to study how magnetic

  15. Magnetic reconnection from a multiscale instability cascade

    NASA Astrophysics Data System (ADS)

    Moser, Auna L.; Bellan, Paul M.

    2012-02-01

    Magnetic reconnection, the process whereby magnetic field lines break and then reconnect to form a different topology, underlies critical dynamics of magnetically confined plasmas in both nature and the laboratory. Magnetic reconnection involves localized diffusion of the magnetic field across plasma, yet observed reconnection rates are typically much higher than can be accounted for using classical electrical resistivity. It is generally proposed that the field diffusion underlying fast reconnection results instead from some combination of non-magnetohydrodynamic processes that become important on the `microscopic' scale of the ion Larmor radius or the ion skin depth. A recent laboratory experiment demonstrated a transition from slow to fast magnetic reconnection when a current channel narrowed to a microscopic scale, but did not address how a macroscopic magnetohydrodynamic system accesses the microscale. Recent theoretical models and numerical simulations suggest that a macroscopic, two-dimensional magnetohydrodynamic current sheet might do this through a sequence of repetitive tearing and thinning into two-dimensional magnetized plasma structures having successively finer scales. Here we report observations demonstrating a cascade of instabilities from a distinct, macroscopic-scale magnetohydrodynamic instability to a distinct, microscopic-scale (ion skin depth) instability associated with fast magnetic reconnection. These observations resolve the full three-dimensional dynamics and give insight into the frequently impulsive nature of reconnection in space and laboratory plasmas.

  16. Frontiers for Laboratory Research of Magnetic Reconnection

    SciTech Connect

    Ji, Hantao; Guo, Fan

    2015-07-16

    Magnetic reconnection occcurs throughout heliophysical and astrophysical plasmas as well as in laboratory fusion plasmas. Two broad categories of reconnection models exist: collisional MHD and collisionless kinetic. Eight major questions with respect to magnetic connection are set down, and past and future devices for studying them in the laboratory are described. Results of some computerized simulations are compared with experiments.

  17. Imaging Observations of Magnetic Reconnection in a Solar Eruptive Flare

    NASA Astrophysics Data System (ADS)

    Li, Y.; Sun, X.; Ding, M. D.; Qiu, J.; Priest, E. R.

    2017-02-01

    Solar flares are among the most energetic events in the solar atmosphere. It is widely accepted that flares are powered by magnetic reconnection in the corona. An eruptive flare is usually accompanied by a coronal mass ejection, both of which are probably driven by the eruption of a magnetic flux rope (MFR). Here we report an eruptive flare on 2016 March 23 observed by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. The extreme-ultraviolet imaging observations exhibit the clear rise and eruption of an MFR. In particular, the observations reveal solid evidence of magnetic reconnection from both the corona and chromosphere during the flare. Moreover, weak reconnection is observed before the start of the flare. We find that the preflare weak reconnection is of tether-cutting type and helps the MFR to rise slowly. Induced by a further rise of the MFR, strong reconnection occurs in the rise phases of the flare, which is temporally related to the MFR eruption. We also find that the magnetic reconnection is more of 3D-type in the early phase, as manifested in a strong-to-weak shear transition in flare loops, and becomes more 2D-like in the later phase, as shown by the apparent rising motion of an arcade of flare loops.

  18. Gyrokinetic Studies of Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Pueschel, Moritz J.; Jenko, Frank; Told, Daniel; Buechner, Joerg

    2011-10-01

    Collisionless magnetic reconnection constitutes an effective mechanism for particle acceleration in astrophysical plasmas, in particular the solar corona. In addition, it is also of relevance to fusion experiments. Gyrokinetic simulations with the GENE code are performed to explore the temporal evolution of current sheets in two-dimensional slab geometry with a strong guide field. After successful code-code benchmarking, Extensive parameter studies are performed, covering a wide range of physical scenarios. In particular, differing findings regarding the influence of the ion temperature are explained. In its nonlinear phase, the characteristics of the reconnection process depend on whether the system is driven or decaying. Decaying turbulence sees an inverse cascade, and all energy is ultimately transferred to the largest radial scale. If driven by a Krook-type term, the system develops into a turbulent, quasi-stationary state. An important quantity to investigate in nonlinear simulations is the parallel electric field which is able to accelerate particles along the background magnetic field. The spatial structure of this field is studied for the different nonlinear cases, and its amplitude reported as a function of the drive frequency.

  19. Relativistic Magnetic Reconnection in Kerr Spacetime.

    PubMed

    Asenjo, Felipe A; Comisso, Luca

    2017-02-03

    The magnetic reconnection process is analyzed for relativistic magnetohydrodynamical plasmas around rotating black holes. A simple generalization of the Sweet-Parker model is used as a first approximation to the problem. The reconnection rate, as well as other important properties of the reconnection layer, has been calculated taking into account the effect of spacetime curvature. Azimuthal and radial current sheet configurations in the equatorial plane of the black hole have been studied, and the case of small black hole rotation rate has been analyzed. For the azimuthal configuration, it is found that the black hole rotation decreases the reconnection rate. On the other hand, in the radial configuration, it is the gravitational force created by the black hole mass that decreases the reconnection rate. These results establish a fundamental interaction between gravity and magnetic reconnection in astrophysical contexts.

  20. Relativistic Magnetic Reconnection in Kerr Spacetime

    NASA Astrophysics Data System (ADS)

    Asenjo, Felipe A.; Comisso, Luca

    2017-02-01

    The magnetic reconnection process is analyzed for relativistic magnetohydrodynamical plasmas around rotating black holes. A simple generalization of the Sweet-Parker model is used as a first approximation to the problem. The reconnection rate, as well as other important properties of the reconnection layer, has been calculated taking into account the effect of spacetime curvature. Azimuthal and radial current sheet configurations in the equatorial plane of the black hole have been studied, and the case of small black hole rotation rate has been analyzed. For the azimuthal configuration, it is found that the black hole rotation decreases the reconnection rate. On the other hand, in the radial configuration, it is the gravitational force created by the black hole mass that decreases the reconnection rate. These results establish a fundamental interaction between gravity and magnetic reconnection in astrophysical contexts.

  1. 3D instabilities connected with reconnection in full 3D PIC simulations

    NASA Astrophysics Data System (ADS)

    Lapenta, Giovanni

    2013-10-01

    Kinetic reconnection is characterized by a distinct behavior of electrons and ions with regions of strong relative speeds between the species. Electrons can flow at great speed relative to ions and can be characterized by a strong non-gyrotropy and anisotropy. When studied in full three dilensions, these electron peculiar properties can drive numerous instabilities that have been investigated by the suggested speaker and his collaborators in a number of recent published papers. Two regions have received most attention: 1) the separatrices where instabilities are caused by the electron flow and the electron phase space features, 2) the downstream fronts where an interchange instability leads to strong energy exchanges and secondary reconnection. In both situations the ions are demagnitezed but the electrons are not and their behaviour is rich in full kinetic processes. At the separatrices, two types of instabilities have been observed. The electron phase space is characterized by multiple populations at relative drifts (electron beams) and the whole electron species is drifting with respect to the ions. This condition is subject to different streaming instabilities. Additionally, the separatrices are regions of intense density and flow shear, with free energy available to drive Kelvin-Helmholtz-type instabilities. In the downstream fronts of reconnection, a density gradient develops in conditions where the acceleration is directed unfavourably for stability, leading to ballooning and interchange-type instabilities. Both cases are of great importance for the upcoming Magnetospheric Multiscale Mission that is bent on finding and analyzing the regions where the electron scale physics is dominant. The processes discussed above can provide key information for the operation of the mission and the interpretation of its results. Collaboration between the University of Colorado NASA-MMSIDS team (M. Goldman, D. Newman, L. Anderson, S. Erikson) and the KULeuven Swiff team

  2. Three-dimensional, Impulsive Magnetic Reconnection in a Laboratory Plasma

    SciTech Connect

    S Dorfman, et al

    2013-05-03

    Impulsive, local, 3-D reconnection is identified for the first time in a laboratory current sheet. The events observed in the Magnetic Reconnection Experiment (MRX) are characterized by large local gradients in the third direction and cannot be explained by 2-D models. Detailed measurements show that the ejection of flux rope structures from the current sheet plays a key role in these events. By contrast, even though electromagnetic fluctuations in the lower hybrid frequency range are also observed concurrently with the impulsive behavior, they are not the key physics responsible. A qualitative, 3-D, two-fluid model is proposed to explain the observations. The experimental results may be particularly applicable to space and astrophysical plasmas where impulsive reconnection occurs.

  3. Definitions of Reconnection Revisited: Distinction Between Magnetic Reconnection and Plasma Reconnection

    NASA Astrophysics Data System (ADS)

    Vasyliunas, V. M.

    2015-12-01

    The term "magnetic reconnection" has been used with several different meanings, and sometimes (particularly in discussions of observations) it is not clear which one of them (if any) is meant. Most common is a more or less literal definition of "cutting" and "reconnecting" two magnetic field lines (often illustrated by a sketch of field lines in two dimensions, or a perspective drawing of isolated spaghetti-like flux tubes); this concept can be formulated more precisely in terms of plasma flow across (or, equivalently, electric field in) a bounding surface (separatrix) between topologically distinct magnetic fields. The so-called "generalized reconnection" invokes only deviations from ideal MHD in a localized region; a more precise formulation is by integrals of the electric field along magnetic field lines. These two definitions can be related to two different physical processes, which I call magnetic reconnection and plasma reconnection, respectively. Magnetic reconnection involves field lines that change from one topological class to another (e.g., between open and closed). Its occurrence, requiring the presence of singular magnetic null points, can be identified (at least in principle, conceptually) from the magnetic field alone. When representing magnetic reconnection graphically, it is important to show all the singular points explicitly and to keep in mind that field lines are a continuum: between any two field lines, there is always another field line (even arbitrarily close to the singular points). Plasma reconnection involves plasma flow in which plasma elements initially located on a single field line do not remain on a field line, and this may occur without any changes in the topology or other properties of the magnetic field. To understand either one, the process must be visualized always in three dimensions and without special symmetries. Prototype of magnetic reconnection is the well-known open-magnetosphere model of Dungey (1961). Prototype of

  4. On phase diagrams of magnetic reconnection

    SciTech Connect

    Cassak, P. A.; Drake, J. F.

    2013-06-15

    Recently, “phase diagrams” of magnetic reconnection were developed to graphically organize the present knowledge of what type, or phase, of reconnection is dominant in systems with given characteristic plasma parameters. Here, a number of considerations that require caution in using the diagrams are pointed out. First, two known properties of reconnection are omitted from the diagrams: the history dependence of reconnection and the absence of reconnection for small Lundquist number. Second, the phase diagrams mask a number of features. For one, the predicted transition to Hall reconnection should be thought of as an upper bound on the Lundquist number, and it may happen for considerably smaller values. Second, reconnection is never “slow,” it is always “fast” in the sense that the normalized reconnection rate is always at least 0.01. This has important implications for reconnection onset models. Finally, the definition of the relevant Lundquist number is nuanced and may differ greatly from the value based on characteristic scales. These considerations are important for applications of the phase diagrams. This is demonstrated by example for solar flares, where it is argued that it is unlikely that collisional reconnection can occur in the corona.

  5. Synchrotron Cooling in Relativistic Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Fish, Jake; Werner, Gregory; Uzdensky, Dmitri

    2016-10-01

    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. This work is supported by DOE and NASA.

  6. Relativistic Magnetic Reconnection in the Laboratory

    NASA Astrophysics Data System (ADS)

    Krushelnick, Karl; Raymond, Anthony; Dong, Cf; McKelvey, A.; Zulick, C.; Alexander, N.; Bhattacharjee, A.; Campbell, Pt; Chen, H.; Chvykov, V.; Del Rio, E.; Fitzsimmons, P.; Fox, W.; Hou, Bx; Maksimchuk, A.; Mileham, C.; Nees, J.; Nilson, Pm; Stoekl, C.; Thomas, Agr; Wei, Ms; Yanovsky, V.; Willingale, L.

    2016-10-01

    Magnetic reconnection is a fundamental plasma process involving an exchange of magnetic energy to plasma kinetic energy through changes in the magnetic field topology. Here we present experimental measurements using the OMEGA EP laser at LLE and the HERCULES laser at the University of Michigan as well as numerical modeling which indicate that relativistic magnetic reconnection can be driven by short-pulse, high-intensity lasers that produce a relativistic plasma along with very strong magnetic fields. Evidence of magnetic reconnection was identified by the plasma's X-ray emission patterns, changes to the electron energy spectrum, and by measuring the time over which reconnection occurs. Funded by DOE Award No. DE-NA0002727.

  7. Collisionless Magnetic Reconnection in Space Plasmas

    NASA Astrophysics Data System (ADS)

    Treumann, Rudolf A.; Baumjohann, Wolfgang

    2013-12-01

    Magnetic reconnection, the merging of oppositely directed magnetic fields that leads to field reconfiguration, plasma heating, jetting and acceleration, is one of the most celebrated processes in collisionless plasmas. It requires the violation of the frozen-in condition which ties gyrating charged particles to the magnetic field inhibiting diffusion. Ongoing reconnection has been identified in near-Earth space as being responsible for the excitation of substorms, magnetic storms, generation of field aligned currents and their consequences, the wealth of auroral phenomena. Its theoretical understanding is now on the verge of being completed. Reconnection takes place in thin current sheets. Analytical concepts proceeded gradually down to the microscopic scale, the scale of the electron skin depth or inertial length, recognizing that current layers that thin do preferentially undergo spontaneous reconnection. Thick current layers start reconnecting when being forced by plasma inflow to thin. For almost half a century the physical mechanism of reconnection has remained a mystery. Spacecraft in situ observations in combination with sophisticated numerical simulations in two and three dimensions recently clarified the mist, finding that reconnection produces a specific structure of the current layer inside the electron inertial (also called electron diffusion) region around the reconnection site, the X line. Onset of reconnection is attributed to pseudo-viscous contributions of the electron pressure tensor aided by electron inertia and drag, creating a complicated structured electron current sheet, electric fields, and an electron exhaust extended along the current layer. We review the general background theory and recent developments in numerical simulation on collisionless reconnection. It is impossible to cover the entire field of reconnection in a short space-limited review. The presentation necessarily remains cursory, determined by our taste, preferences, and kn

  8. The Relation between Reconnected Flux, the Parallel Electric Field, and the Reconnection Rate in a Three-Dimensional Kinetic Simulation of Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Wendel, D. E.; Olson, D. K.; Hesse, M.; Karimabadi, H.; Daughton, W. S.

    2013-12-01

    We investigate the distribution of parallel electric fields and their relationship to the location and rate of magnetic reconnection of a large particle-in-cell simulation of 3D turbulent magnetic reconnection with open boundary conditions. The simulation's guide field geometry inhibits the formation of topological features such as separators and null points. Therefore, we derive the location of potential changes in magnetic connectivity by finding the field lines that experience a large relative change between their endpoints, i.e., the quasi-separatrix layer. We find a correspondence between the locus of changes in magnetic connectivity, or the quasi-separatrix layer, and the map of large gradients in the integrated parallel electric field (or quasi-potential). Furthermore, we compare the distribution of parallel electric fields along field lines with the reconnection rate. We find the reconnection rate is controlled by only the low-amplitude, zeroth and first-order trends in the parallel electric field, while the contribution from high amplitude parallel fluctuations, such as electron holes, is negligible. The results impact the determination of reconnection sites within models of 3D turbulent reconnection as well as the inference of reconnection rates from in situ spacecraft measurements. It is difficult through direct observation to isolate the locus of the reconnection parallel electric field amidst the large amplitude fluctuations. However, we demonstrate that a positive slope of the partial sum of the parallel electric field along the field line as a function of field line length indicates where reconnection is occurring along the field line.

  9. Three-dimensional geometry of magnetic reconnection induced by ballooning instability in a generalized Harris sheet

    NASA Astrophysics Data System (ADS)

    Zhu, Ping; Bhattacharjee, Amitava; Sangari, Arash; Wang, Zechen; Bonofiglo, Phillip

    2017-02-01

    We report for the first time the intrinsically three-dimensional (3D) geometry of the magnetic reconnection process induced by ballooning instability in a generalized Harris sheet. The spatial distribution and the structure of the quasi-separatrix layers, as well as their temporal emergence and evolution, indicate that the associated magnetic reconnection can only occur in a 3D geometry, which is irreducible to that of any two-dimensional reconnection process. Such a finding provides a new perspective to the long-standing controversy over the substorm onset problem and elucidates the combined roles of reconnection and ballooning instabilities. It also connects to the universal presence of 3D reconnection processes previously discovered in various natural and laboratory plasmas.

  10. The Role of Geometry in Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Hesse, Michael; Aunai, Nicholas; Birn, Joachim; Zenitani, Seiji

    2012-01-01

    Magnetic reconnection is arguably the most effective energy conversion and transport process in plasmas. Reconnection is subject to topological considerations in two ways. First, the process itself involves a change in topology of the combined plasma-magnetic field system. This change in topology transcends that of the magnetic field alone and accounts for flux transport relative to the motion of the plasma in the system under investigation. The second way topology is important to magnetic reconnection is through modifications of the diffUSion/dissipation physics brought about by the structure of the reconnecting system. This presentation will present an overview and summary of both past and recent results pertaining to both aspects.

  11. Electron acceleration during guide field magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Wan, Weigang; Lapenta, Giovanni; Delzanno, Gian Luca; Egedal, Jan

    2008-03-01

    Particle-in-cell simulations of the guide field intermittent magnetic reconnection are performed to study electron acceleration and pitch angle distributions. During the growing stage of reconnection, the power-law distribution function for the high-energy electrons and the pitch angle distributions of the low-energy electrons are obtained and compare favorably with observations by the Wind spacecraft. Direct evidence is found for the secondary acceleration during the later reconnection stage. A correlation between the generation of energetic electrons and the induced reconnection electric field is found. Energetic electrons are accelerated first around the X line, and then in the region outside the diffusion region, when the reconnection electric field has a bipolar structure. The physical mechanisms of these accelerations are discussed. The in-plane electrostatic field that traps the low-energy electrons and causes the anisotropic pitch angle distributions has been observed.

  12. Prospects for Fermi Particle Acceleration at Coronal Magnetic Reconnection Sites

    NASA Astrophysics Data System (ADS)

    Provornikova, E.; Laming, J. M.; Lukin, V.

    2015-12-01

    The mechanism of first order Fermi acceleration of particles interacting with the converging magnetized flows at a reconnection site was introduced recently in an attempt to predict the energy distribution of particles resulting from violent reconnection in galactic microquasars. More careful consideration of this mechanism showed that the spectral index of accelerated particles is related to the total plasma compression within a reconnection region, similar to that in the formulation for diffusive shock acceleration. In the solar context, reconnection regions producing strong compression could be the source of suprathermal "seed particles". A hard spectrum of such suprathermal particles is believed to be necessary to initiate the particle acceleration process at low Mach number coronal mass ejection shocks close to the Sun where the gradual solar energetic particle events originate. As a first step to investigate the efficiency of Fermi acceleration, we explore the degree of plasma compression that can be achieved at reconnection sites in the solar corona. This work presents a set of 2D two-temperature resistive MHD simulations of the dynamics of several magnetic configurations within a range of lower corona plasma parameters. Energy transport processes in the MHD model include anisotropic thermal conduction for electrons and ions and radiative cooling. Magnetic configurations considered are a Harris current sheet, a force-free current sheet, a flux rope sitting above an arcade of magnetic loops, and two merging flux ropes. We demonstrate that only for some magnetic topologies, corresponding in particular to 3D magnetic nulls, the compression ratio, sufficient for first order Fermi acceleration in the reconnection region, can be achieved. These represent the potential sites in the solar corona where a hard seed particle energetic spectrum could be produced.

  13. Relating magnetic reconnection to coronal heating.

    PubMed

    Longcope, D W; Tarr, L A

    2015-05-28

    It is clear that the solar corona is being heated and that coronal magnetic fields undergo reconnection all the time. Here we attempt to show that these two facts are related--i.e. coronal reconnection generates heat. This attempt must address the fact that topological change of field lines does not automatically generate heat. We present one case of flux emergence where we have measured the rate of coronal magnetic reconnection and the rate of energy dissipation in the corona. The ratio of these two, [Formula: see text], is a current comparable to the amount of current expected to flow along the boundary separating the emerged flux from the pre-existing flux overlying it. We can generalize this relation to the overall corona in quiet Sun or in active regions. Doing so yields estimates for the contribution to coronal heating from magnetic reconnection. These estimated rates are comparable to the amount required to maintain the corona at its observed temperature.

  14. Relating magnetic reconnection to coronal heating

    PubMed Central

    Longcope, D. W.; Tarr, L. A.

    2015-01-01

    It is clear that the solar corona is being heated and that coronal magnetic fields undergo reconnection all the time. Here we attempt to show that these two facts are related—i.e. coronal reconnection generates heat. This attempt must address the fact that topological change of field lines does not automatically generate heat. We present one case of flux emergence where we have measured the rate of coronal magnetic reconnection and the rate of energy dissipation in the corona. The ratio of these two, , is a current comparable to the amount of current expected to flow along the boundary separating the emerged flux from the pre-existing flux overlying it. We can generalize this relation to the overall corona in quiet Sun or in active regions. Doing so yields estimates for the contribution to coronal heating from magnetic reconnection. These estimated rates are comparable to the amount required to maintain the corona at its observed temperature. PMID:25897089

  15. Magnetic reconnection in a weakly ionized plasma

    SciTech Connect

    Leake, James E.; Lukin, Vyacheslav S.; Linton, Mark G.

    2013-06-15

    Magnetic reconnection in partially ionized plasmas is a ubiquitous phenomenon spanning the range from laboratory to intergalactic scales, yet it remains poorly understood and relatively little studied. Here, we present results from a self-consistent multi-fluid simulation of magnetic reconnection in a weakly ionized reacting plasma with a particular focus on the parameter regime of the solar chromosphere. The numerical model includes collisional transport, interaction and reactions between the species, and optically thin radiative losses. This model improves upon our previous work in Leake et al.[“Multi-fluid simulations of chromospheric magnetic reconnection in a weakly ionized reacting plasma,” Astrophys. J. 760, 109 (2012)] by considering realistic chromospheric transport coefficients, and by solving a generalized Ohm's law that accounts for finite ion-inertia and electron-neutral drag. We find that during the two dimensional reconnection of a Harris current sheet with an initial width larger than the neutral-ion collisional coupling scale, the current sheet thins until its width becomes less than this coupling scale, and the neutral and ion fluids decouple upstream from the reconnection site. During this process of decoupling, we observe reconnection faster than the single-fluid Sweet-Parker prediction, with recombination and plasma outflow both playing a role in determining the reconnection rate. As the current sheet thins further and elongates, it becomes unstable to the secondary tearing instability, and plasmoids are seen. The reconnection rate, outflows, and plasmoids observed in this simulation provide evidence that magnetic reconnection in the chromosphere could be responsible for jet-like transient phenomena such as spicules and chromospheric jets.

  16. Relaxation of flux ropes and magnetic reconnection in the Reconnection Scaling Experiment at LANL

    NASA Astrophysics Data System (ADS)

    Furno, Ivo

    2004-11-01

    Magnetic reconnection and plasma relaxation are studied in the Reconnection Scaling Experiment (RSX) with current carrying plasma columns (magnetic flux ropes). Using plasma guns, multiple flux ropes (B_pol < 100 Gauss, L=90 cm, r < 3 cm) are generated in a three-dimensional (3D) cylindrical geometry and are observed to evolve dynamically during the injection of magnetic helicity. Detailed evolution of electron density, temperature, plasma potential and magnetic field structures is reconstructed experimentally and visible light emission is captured with a fast-gated, intensified CCD camera to provide insight into the global flux rope dynamics. Experiments with two flux ropes in collisional plasmas and in a strong axial guide field (Bz / B_pol > 10) suggest that magnetic reconnection plays an important role in the initial stages of flux rope evolution. During the early stages of the applied current drive (t < 20τ_Alfven), the flux ropes are observed to twist, partially coalesce and form a thin current sheet with a scale size comparable to that of the ion sound gyro-radius. Here, non-ideal terms in a generalized Ohm's Law appear to play a significant role in the 3D reconnection process as shown by the presence of a strong axial pressure gradient in the current sheet. In addition, a density perturbation with a structure characteristic of a kinetic Alfvén wave is observed to propagate axially in the current layer, anti-parallel to the induced sheet current. Later in the evolution, when a sufficient amount of helicity is injected into the system, a critical threshold for the kink instability is exceeded and the helical twisting of each individual flux rope can dominate the dynamics of the system. This may prevent the complete coalescence of the flux ropes.

  17. Relaxation of flux ropes and magnetic reconnection in the Reconnection Scaling Experiment at LANL

    NASA Astrophysics Data System (ADS)

    Furno, I.; Intrator, T.; Hemsing, E.; Hsu, S.; Lapenta, G.; Abbate, S.

    2004-12-01

    Magnetic reconnection and plasma relaxation are studied in the Reconnection Scaling Experiment (RSX) with current carrying plasma columns (magnetic flux ropes). Using plasma guns, multiple flux ropes (Bθ ≤ 100 Gauss, L=90 cm, r≤3 cm) are generated in a three-dimensional (3D) cylindrical geometry and are observed to evolve dynamically during the injection of magnetic helicity. Detailed evolution of electron density, temperature, plasma potential and magnetic field structures is reconstructed experimentally and visible light emission is captured with a fast-gated, intensified CCD camera to provide insight into the global flux rope dynamics. Experiments with two flux ropes in collisional plasmas and in a strong axial guide field (Bz / Bθ > 10) suggest that magnetic reconnection plays an important role in the initial stages of flux rope evolution. During the early stages of the applied current drive (t≤ 20 τ Alfv´ {e}n), the flux ropes are observed to twist, partially coalesce and form a thin current sheet with a scale size comparable to that of the ion sound gyro-radius. Here, non-ideal terms in a generalized Ohm's Law appear to play a significant role in the 3D reconnection process as shown by the presence of a strong axial pressure gradient in the current sheet. In addition, a density perturbation with a structure characteristic of a kinetic Alfvén wave is observed to propagate axially in the current layer, anti-parallel to the induced sheet current. Later in the evolution, when a sufficient amount of helicity is injected into the system, a critical threshold for the kink instability is exceeded and the helical twisting of each individual flux rope can dominate the dynamics of the system. This may prevent the complete coalescence of the flux ropes.

  18. Unsteady magnetic reconnection in laboratory experiments with current sheets

    NASA Astrophysics Data System (ADS)

    Frank, Anna

    2009-11-01

    According to present notion, unsteady magnetic reconnection in current sheets (CS) is basic to dramatic natural phenomena: solar and stellar flares, substorms in the Earth and other planetary magnetospheres, as well as to disruptive instabilities in tokamak plasmas. We present a review of laboratory experiments studying evolution of CS formed in 3D and 2D magnetic configurations with an X line, in the CS-3D device. Usually CS exists during an extended period in a metastable stage, without essential changes of its structure and parameters. Under certain conditions this stage may be suddenly interrupted by unsteady phase of magnetic reconnection, which manifests itself in a rapid change of the magnetic field topology, current redistribution, excitation of pulsed electric fields, and other dynamic effects. The unsteady phase results in effective conversion of magnetic energy into the energy of plasma and accelerated particles, and may finally bring about the CS disruption. In the context of the solar flares, a metastable CS is associated with a pre-flare situation, while CS disruption -- with the flare itself. The physical mechanisms triggering the unsteady magnetic reconnection in the laboratory produced current sheets are discussed. Supported by the Russian Foundation for Basic Research (project # 09-02-00971).

  19. Magnetic reconnection, merging, and viscous interaction in the magnetosphere

    NASA Technical Reports Server (NTRS)

    Heikkila, W. J.

    1990-01-01

    This paper discusses the historical development of the reconnection theory, with consideration given to the effects of a magnetic field within the plasma and the mechanisms of magnetic reconnection, merging, and viscouslike interaction. Particular attention is given to Dungey's (1958, 1961) steady-state reconnection model of the magnetosphere and to its criticism. Observational evidence supporting the reconnection model is presented.

  20. Three-dimensional Spontaneous Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Beresnyak, Andrey

    2017-01-01

    Magnetic reconnection is best known from observations of the Sun where it causes solar flares. Observations estimate the reconnection rate as a small, but non-negligible fraction of the Alfvén speed, so-called fast reconnection. Until recently, the prevailing pictures of reconnection were either of resistivity or plasma microscopic effects, which was contradictory to the observed rates. Alternative pictures were either of reconnection due to the stochasticity of magnetic field lines in turbulence or the tearing instability of the thin current sheet. In this paper we simulate long-term three-dimensional nonlinear evolution of a thin, planar current sheet subject to a fast oblique tearing instability using direct numerical simulations of resistive-viscous magnetohydrodynamics. The late-time evolution resembles generic turbulence with a ‑5/3 power spectrum and scale-dependent anisotropy, so we conclude that the tearing-driven reconnection becomes turbulent reconnection. The turbulence is local in scale, so microscopic diffusivity should not affect large-scale quantities. This is confirmed by convergence of the reconnection rate toward ∼ 0.015{v}{{A}} with increasing Lundquist number. In this spontaneous reconnection, with mean field and without driving, the dissipation rate per unit area also converges to ∼ 0.006ρ {v}{{A}}3, and the dimensionless constants 0.015 and 0.006 are governed only by self-driven nonlinear dynamics of the sheared magnetic field. Remarkably, this also means that a thin current sheet has a universal fluid resistance depending only on its length to width ratio and to {v}{{A}}/c.

  1. Intuitive approach to magnetic reconnection

    SciTech Connect

    Kulsrud, Russell M.

    2011-11-15

    Two reconnection problems are considered. The first problem concerns global physics. The plasma in the global reconnection region is in magnetostatic equilibrium. It is shown that this equilibrium can be uniquely characterized by a set of constraints. During reconnection and independently of the local reconnection physics, these constraints can be uniquely evolved from any initial state. The second problem concerns Petschek reconnection. Petschek's model for fast reconnection, which is governed by resistive MHD equations with constant resistivity is not validated by numerical simulations. Malyshkin et al.[Phys. Plasmas 12, 102920 (2005)], showed that the reason for the discrepancy is that Petschek did not employ Ohm's law throughout the local diffusion region, but only at the X-point. A derivation of Petschek reconnection, including Ohm's law throughout the entire diffusion region, removes the discrepancy. This derivation is based largely on Petschek's original 1964 calculation [in AAS-NASA Symposium on Solar Flares (National Aeronautics and Space Administration, Washington, D.C., 1964), NASA SP50, p. 425]. A useful physical interpretation of the role which Ohm's law plays in the diffusion region is presented.

  2. Electron Layer Dissipation Mechanisms in Driven Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Dorfman, S.; Ji, H.; Yamada, M.; McGeehan, B.; Oz, E.; Schroeder, J.; Daughton, W.; Roytershteyn, V.; Ren, Y.

    2008-11-01

    An open question in magnetic reconnection is the nature of the dissipation mechanism(s) responsible for fast reconnection rates in laboratory and astrophysical plasmas. In 2-D collisionless particle in cell simulations, the off-diagonal terms in the electron pressure tensor provide the necessary force balance at the electron diffusion layer center [1]. Recent comparisons between the Magnetic Reconnection Experiment (MRX) and a well-matched PIC code have shown that this mechanism is insufficient to balance the reconnecting electric field in MRX [2,3]. Candidate mechanisms not present in the simulation are under investigation, including electromagnetic fluctuations and other 3-D effects such as layer distortions. The relationship between fluctuations and equilibrium parameters such as the outflow current and layer width is examined, and first investigations into the 3-D symmetry of the layer are presented. On the simulation side, analysis is underway to gain further insight into the nature of the off-diagonal pressure tensor terms, especially effects due to the driven nature of the simulation. [1] M. Hesse, et al., Phys. Plasmas, 6:1781 (1999). [2] S. Dorfman, et al., submitted to Phys. Plasmas (2008). [3] H. Ji, et al., Geophys. Res. Lett., 35, L13106 (2008). This work was supported by NDSEG, DOE, NASA, and NSF.

  3. New Expression for Collisionless Magnetic Reconnection Rate

    NASA Technical Reports Server (NTRS)

    Klimas, Alexander J.

    2014-01-01

    For 2D, symmetric, anti-parallel, collisionless magnetic reconnection, a new expression for the reconnection rate in the electron diffusion region is introduced. It is shown that this expression can be derived in just a few simple steps from a physically intuitive starting point; the derivation is given in its entirety and the validity of each step is confirmed. The predictions of this expression are compared to the results of several long-duration, open-boundary PIC reconnection simulations to demonstrate excellent agreement.

  4. New expression for collisionless magnetic reconnection rate

    SciTech Connect

    Klimas, Alex

    2015-04-15

    For 2D, symmetric, anti-parallel, collisionless magnetic reconnection, new expressions for the reconnection rate in the electron diffusion region are introduced. It is shown that these expressions can be derived in just a few simple steps from a physically intuitive starting point; the derivations are given in their entirety, and the validity of each step is confirmed. The predictions of these expressions are compared to the results of several long-duration, open-boundary particle-in-cell reconnection simulations to demonstrate excellent agreement.

  5. Fast Reconnection of Weak Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Zweibel, Ellen G.

    1998-01-01

    Fast magnetic reconnection refers to annihilation or topological rearrangement of magnetic fields on a timescale that is independent (or nearly independent) of the plasma resistivity. The resistivity of astrophysical plasmas is so low that reconnection is of little practical interest unless it is fast. Yet, the theory of fast magnetic reconnection is on uncertain ground, as models must avoid the tendency of magnetic fields to pile up at the reconnection layer, slowing down the flow. In this paper it is shown that these problems can be avoided to some extent if the flow is three dimensional. On the other hand, it is shown that in the limited but important case of incompressible stagnation point flows, every flow will amplify most magnetic fields. Although examples of fast magnetic reconnection abound, a weak, disordered magnetic field embedded in stagnation point flow will in general be amplified, and should eventually modify the flow. These results support recent arguments against the operation of turbulent resistivity in highly conducting fluids.

  6. RESISTIVE MAGNETOHYDRODYNAMIC SIMULATIONS OF RELATIVISTIC MAGNETIC RECONNECTION

    SciTech Connect

    Zenitani, Seiji; Hesse, Michael; Klimas, Alex

    2010-06-20

    Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to investigate the system evolution of relativistic magnetic reconnection. A time-split Harten-Lan-van Leer method is employed. Under a localized resistivity, the system exhibits a fast reconnection jet with an Alfvenic Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures are resolved in and around the plasmoid such as the post-plasmoid vertical shocks and the 'diamond-chain' structure due to multiple shock reflections. Under a uniform resistivity, Sweet-Parker-type reconnection slowly evolves. Under a current-dependent resistivity, plasmoids are repeatedly formed in an elongated current sheet. It is concluded that the resistivity model is of critical importance for RRMHD modeling of relativistic magnetic reconnection.

  7. Resistive Magnetohydrodynamic Simulations of Relativistic Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Zenitani, Seiji; Hesse, Michael; Klimas, Alex

    2010-01-01

    Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to investigate the system evolution of relativistic magnetic reconnection. A time-split Harten-Lan-van Leer method is employed. Under a localized resistivity, the system exhibits a fast reconnection jet with an Alfv enic Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures are resolved in and around the plasmoid such as the post-plasmoid vertical shocks and the "diamond-chain" structure due to multiple shock reflections. Under a uniform resistivity, Sweet-Parker-type reconnection slowly evolves. Under a current-dependent resistivity, plasmoids are repeatedly formed in an elongated current sheet. It is concluded that the resistivity model is of critical importance for RRMHD modeling of relativistic magnetic reconnection.

  8. Magnetic Reconnection Models of Prominence Formation

    NASA Astrophysics Data System (ADS)

    Welsch, B. T.; DeVore, C. R.; Antiochos, S. K.

    2005-12-01

    To investigate the hypothesis that prominences form by magnetic reconnection between initially distinct flux systems in the solar corona, we simulate coronal magnetic field evolution when two flux systems are driven together by boundary motions. In particular, we focus on configurations similar to those in the quiescent prominence formation model of Martens & Zwaan. We find that reconnection proceeds very weakly, if at all, in configurations driven with global shear flows (i.e., differential rotation); reconnection proceeds much more efficiently in similar configurations that are driven to collide directly, with converging motions along the neutral line that lead to flux cancellation; reconnected fields from this process can exhibit sheared, dipped field lines along the neutral line, consistent with prominence observations. Our field configurations do not possess the ``breakout'' topology, and eruptions are not observed, even though a substantial amount of flux is canceled in some runs.

  9. Resistive Magnetohydrodynamic Simulations of Relativistic Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Zenitani, Seiji; Hesse, Michael; Klimas, Alex

    2010-06-01

    Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to investigate the system evolution of relativistic magnetic reconnection. A time-split Harten-Lan-van Leer method is employed. Under a localized resistivity, the system exhibits a fast reconnection jet with an Alfvénic Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures are resolved in and around the plasmoid such as the post-plasmoid vertical shocks and the "diamond-chain" structure due to multiple shock reflections. Under a uniform resistivity, Sweet-Parker-type reconnection slowly evolves. Under a current-dependent resistivity, plasmoids are repeatedly formed in an elongated current sheet. It is concluded that the resistivity model is of critical importance for RRMHD modeling of relativistic magnetic reconnection.

  10. 3D meshes of carbon nanotubes guide functional reconnection of segregated spinal explants.

    PubMed

    Usmani, Sadaf; Aurand, Emily Rose; Medelin, Manuela; Fabbro, Alessandra; Scaini, Denis; Laishram, Jummi; Rosselli, Federica B; Ansuini, Alessio; Zoccolan, Davide; Scarselli, Manuela; De Crescenzi, Maurizio; Bosi, Susanna; Prato, Maurizio; Ballerini, Laura

    2016-07-01

    In modern neuroscience, significant progress in developing structural scaffolds integrated with the brain is provided by the increasing use of nanomaterials. We show that a multiwalled carbon nanotube self-standing framework, consisting of a three-dimensional (3D) mesh of interconnected, conductive, pure carbon nanotubes, can guide the formation of neural webs in vitro where the spontaneous regrowth of neurite bundles is molded into a dense random net. This morphology of the fiber regrowth shaped by the 3D structure supports the successful reconnection of segregated spinal cord segments. We further observed in vivo the adaptability of these 3D devices in a healthy physiological environment. Our study shows that 3D artificial scaffolds may drive local rewiring in vitro and hold great potential for the development of future in vivo interfaces.

  11. 3D meshes of carbon nanotubes guide functional reconnection of segregated spinal explants

    PubMed Central

    Usmani, Sadaf; Aurand, Emily Rose; Medelin, Manuela; Fabbro, Alessandra; Scaini, Denis; Laishram, Jummi; Rosselli, Federica B.; Ansuini, Alessio; Zoccolan, Davide; Scarselli, Manuela; De Crescenzi, Maurizio; Bosi, Susanna; Prato, Maurizio; Ballerini, Laura

    2016-01-01

    In modern neuroscience, significant progress in developing structural scaffolds integrated with the brain is provided by the increasing use of nanomaterials. We show that a multiwalled carbon nanotube self-standing framework, consisting of a three-dimensional (3D) mesh of interconnected, conductive, pure carbon nanotubes, can guide the formation of neural webs in vitro where the spontaneous regrowth of neurite bundles is molded into a dense random net. This morphology of the fiber regrowth shaped by the 3D structure supports the successful reconnection of segregated spinal cord segments. We further observed in vivo the adaptability of these 3D devices in a healthy physiological environment. Our study shows that 3D artificial scaffolds may drive local rewiring in vitro and hold great potential for the development of future in vivo interfaces. PMID:27453939

  12. The Diffusion Region in Collisionless Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Hesse, Michael; Neukirch, Thomas; Schindler, Karl; Kuznetsova, Masha; Zenitani, Seiji

    2011-01-01

    A review of present understanding of the dissipation region in magnetic reconnection is presented. The review focuses on results of the thermal inertia-based dissipation mechanism but alternative mechanisms are mentioned as well. For the former process, a combination of analytical theory and numerical modeling is presented. Furthermore, a new relation between the electric field expressions for anti-parallel and guide field reconnection is developed.

  13. Magnetic Properties of 3D Printed Toroids

    NASA Astrophysics Data System (ADS)

    Bollig, Lindsey; Otto, Austin; Hilpisch, Peter; Mowry, Greg; Nelson-Cheeseman, Brittany; Renewable Energy; Alternatives Lab (REAL) Team

    Transformers are ubiquitous in electronics today. Although toroidal geometries perform most efficiently, transformers are traditionally made with rectangular cross-sections due to the lower manufacturing costs. Additive manufacturing techniques (3D printing) can easily achieve toroidal geometries by building up a part through a series of 2D layers. To get strong magnetic properties in a 3D printed transformer, a composite filament is used containing Fe dispersed in a polymer matrix. How the resulting 3D printed toroid responds to a magnetic field depends on two structural factors of the printed 2D layers: fill factor (planar density) and fill pattern. In this work, we investigate how the fill factor and fill pattern affect the magnetic properties of 3D printed toroids. The magnetic properties of the printed toroids are measured by a custom circuit that produces a hysteresis loop for each toroid. Toroids with various fill factors and fill patterns are compared to determine how these two factors can affect the magnetic field the toroid can produce. These 3D printed toroids can be used for numerous applications in order to increase the efficiency of transformers by making it possible for manufacturers to make a toroidal geometry.

  14. Turbulent magnetic fluctuations in laboratory reconnection

    NASA Astrophysics Data System (ADS)

    Von Stechow, Adrian; Grulke, Olaf; Klinger, Thomas

    2016-07-01

    The role of fluctuations and turbulence is an important question in astrophysics. While direct observations in space are rare and difficult dedicated laboratory experiments provide a versatile environment for the investigation of magnetic reconnection due to their good diagnostic access and wide range of accessible plasma parameters. As such, they also provide an ideal chance for the validation of space plasma reconnection theories and numerical simulation results. In particular, we studied magnetic fluctuations within reconnecting current sheets for various reconnection parameters such as the reconnection rate, guide field, as well as plasma density and temperature. These fluctuations have been previously interpreted as signatures of current sheet plasma instabilities in space and laboratory systems. Especially in low collisionality plasmas these may provide a source of anomalous resistivity and thereby contribute a significant fraction of the reconnection rate. We present fluctuation measurements from two complementary reconnection experiments and compare them to numerical simulation results. VINETA.II (Greifswald, Germany) is a cylindrical, high guide field reconnection experiment with an open field line geometry. The reconnecting current sheet has a three-dimensional structure that is predominantly set by the magnetic pitch angle which results from the superposition of the guide field and the in-plane reconnecting field. Within this current sheet, high frequency magnetic fluctuations are observed that correlate well with the local current density and show a power law spectrum with a spectral break at the lower hybrid frequency. Their correlation lengths are found to be extremely short, but propagation is nonetheless observed with high phase velocities that match the Whistler dispersion. To date, the experiment has been run with an external driving field at frequencies higher than the ion cyclotron frequency f_{ci}, which implies that the EMHD framework applies

  15. Entropy conservation in simulations of magnetic reconnection

    SciTech Connect

    Birn, J.; Hesse, M.; Schindler, K.

    2006-09-15

    Entropy and mass conservation are investigated for the dynamic field evolution associated with fast magnetic reconnection, based on the 'Newton Challenge' problem [Birn et al., Geophys. Res. Lett. 32, L06105 (2005)]. In this problem, the formation of a thin current sheet and magnetic reconnection are initiated in a plane Harris-type current sheet by temporally limited, spatially varying, inflow of magnetic flux. Using resistive magnetohydrodynamic (MHD) and particle-in-cell (PIC) simulations, specifically the entropy and mass integrated along the magnetic flux tubes are compared between the simulations. In the MHD simulation these should be exactly conserved quantities, when slippage and Ohmic dissipation are negligible. It is shown that there is very good agreement between the conservation of these quantities in the two simulation approaches, despite the effects of dissipation, provided that the resistivity in the MHD simulation is strongly localized. This demonstrates that dissipation is highly localized in the PIC simulation also, and that heat flux across magnetic flux tubes has negligible effect as well, so that the entropy increase on a full flux tube remains small even during reconnection. The mass conservation also implies that the frozen-in flux condition of ideal MHD is a good integral approximation outside the reconnection site. This result lends support for using the entropy-conserving MHD approach not only before and after reconnection but even as a constraint connecting the two phases.

  16. Particle acceleration and plasma dynamics during magnetic reconnection in the magnetically dominated regime

    DOE PAGES

    Guo, Fan; Liu, Yi -Hsin; Daughton, William; ...

    2015-06-17

    Magnetic reconnection is thought to be the driver for many explosive phenomena in the universe. The energy release and particle acceleration during reconnection have been proposed as a mechanism for producing high-energy emissions and cosmic rays. We carry out two- and three-dimensional (3D) kinetic simulations to investigate relativistic magnetic reconnection and the associated particle acceleration. The simulations focus on electron–positron plasmas starting with a magnetically dominated, force-free current sheet (σ ≡ B2 / (4πnemec2) >> 1). For this limit, we demonstrate that relativistic reconnection is highly efficient at accelerating particles through a first-order Fermi process accomplished by the curvature driftmore » of particles along the electric field induced by the relativistic flows. This mechanism gives rise to the formation of hard power-law spectra f α (γ - 1)-p and approaches p = 1 for sufficiently large σ and system size. Eventually most of the available magnetic free energy is converted into nonthermal particle kinetic energy. An analytic model is presented to explain the key results and predict a general condition for the formation of power-law distributions. The development of reconnection in these regimes leads to relativistic inflow and outflow speeds and enhanced reconnection rates relative to nonrelativistic regimes. In the 3D simulation, the interplay between secondary kink and tearing instabilities leads to strong magnetic turbulence, but does not significantly change the energy conversion, reconnection rate, or particle acceleration. This paper suggests that relativistic reconnection sites are strong sources of nonthermal particles, which may have important implications for a variety of high-energy astrophysical problems.« less

  17. Particle acceleration and plasma dynamics during magnetic reconnection in the magnetically dominated regime

    SciTech Connect

    Guo, Fan; Liu, Yi -Hsin; Daughton, William; Li, Hui

    2015-06-17

    Magnetic reconnection is thought to be the driver for many explosive phenomena in the universe. The energy release and particle acceleration during reconnection have been proposed as a mechanism for producing high-energy emissions and cosmic rays. We carry out two- and three-dimensional (3D) kinetic simulations to investigate relativistic magnetic reconnection and the associated particle acceleration. The simulations focus on electron–positron plasmas starting with a magnetically dominated, force-free current sheet (σ ≡ B2 / (4πnemec2) >> 1). For this limit, we demonstrate that relativistic reconnection is highly efficient at accelerating particles through a first-order Fermi process accomplished by the curvature drift of particles along the electric field induced by the relativistic flows. This mechanism gives rise to the formation of hard power-law spectra f α (γ - 1)-p and approaches p = 1 for sufficiently large σ and system size. Eventually most of the available magnetic free energy is converted into nonthermal particle kinetic energy. An analytic model is presented to explain the key results and predict a general condition for the formation of power-law distributions. The development of reconnection in these regimes leads to relativistic inflow and outflow speeds and enhanced reconnection rates relative to nonrelativistic regimes. In the 3D simulation, the interplay between secondary kink and tearing instabilities leads to strong magnetic turbulence, but does not significantly change the energy conversion, reconnection rate, or particle acceleration. This paper suggests that relativistic reconnection sites are strong sources of nonthermal particles, which may have important implications for a variety of high-energy astrophysical problems.

  18. Asymmetric Magnetic Reconnection in the Solar Atmosphere

    NASA Astrophysics Data System (ADS)

    Murphy, N. A.; Miralles, M. P.; Ranquist, D. A.; Pope, C. L.; Raymond, J. C.; Lukin, V. S.; McKillop, S.; Shen, C.; Winter, H. D.; Reeves, K. K.; Lin, J.

    2013-12-01

    Models of solar flares and coronal mass ejections typically predict the development of an elongated current sheet in the wake behind the rising flux rope. In reality, reconnection in these current sheets will be asymmetric along the inflow, outflow, and out-of-plane directions. We perform resistive MHD simulations to investigate the consequences of asymmetry during solar reconnection. We predict several observational signatures of asymmetric reconnection, including flare loops with a skewed candle flame shape, slow drifting of the current sheet into the strong field upstream region, asymmetric footpoint speeds and hard X-ray emission, and rolling motions within the erupting flux rope. There is net plasma flow across the magnetic field null along both the inflow and outflow directions. We compare simulations to SDO/AIA, Hinode/XRT, and STEREO observations of flare loop shapes, current sheet drifting, and rolling motions during prominence eruptions. Simulations of the plasmoid instability with different upstream magnetic fields show that the reconnection rate remains enhanced even during the asymmetric case. The islands preferentially grow into the weak field upstream region. The islands develop net vorticity because the outflow jets impact them obliquely rather than directly. Asymmetric reconnection in the chromosphere occurs when emerging flux interacts with pre-existing overlying flux. We present initial results on asymmetric reconnection in partially ionized chromospheric plasmas. Finally, we discuss how comparisons to observations are necessary to understand the role of three-dimensional effects.

  19. Asymmetric Magnetic Reconnection in the Solar Atmosphere

    NASA Astrophysics Data System (ADS)

    Murphy, N. A.; Miralles, M. P.; Ranquist, D. A.; Pope, C. L.; Raymond, J. C.; Lukin, V. S.; McKillop, S. C.; Shen, C.; Winter, H. D.; Reeves, K. K.; Lin, J.

    2013-12-01

    Models of solar flares and coronal mass ejections typically predict the development of an elongated current sheet in the wake behind the rising flux rope. In reality, reconnection in these current sheets will be asymmetric along the inflow, outflow, and out-of-plane directions. We perform resistive MHD simulations to investigate the consequences of asymmetry during solar reconnection. We predict several observational signatures of asymmetric reconnection, including flare loops with a skewed candle flame shape, slow drifting of the current sheet into the strong field upstream region, asymmetric footpoint speeds and hard X-ray emission, and rolling motions within the erupting flux rope. There is net plasma flow across the magnetic field null along both the inflow and outflow directions. We compare simulations to SDO/AIA, Hinode/XRT, and STEREO observations of flare loop shapes, current sheet drifting, and rolling motions during prominence eruptions. Simulations of the plasm! oid instability with different upstream magnetic fields show that the reconnection rate remains enhanced even during the asymmetric case. The islands preferentially grow into the weak field upstream region. The islands develop net vorticity because the outflow jets impact them obliquely rather than directly. Asymmetric reconnection in the chromosphere occurs when emerging flux interacts with pre-existing overlying flux. We present initial results on asymmetric reconnection in partially ionized chromospheric plasmas. Finally, we discuss how comparisons to observations are necessary to understand the role of three-dimensional effects.

  20. Recurrent Magnetic Reconnection in Protostellar Magnetospheres

    NASA Astrophysics Data System (ADS)

    Hayashi, Mitsuru; Shibata, K.; Matsumoto, R.

    The solar X-ray satellite Yohkoh, has found extensive evidence for magnetic reconnection in the solar corona. Here we extend the magnetic reconnection model of solar flares to hard X-ray flares observed in star forming regions. A new ingredient is a protostellar disk which can inject helicity into the magnetosphere if the disk is threaded by the dipole magnetic field of the protostar. We carried out 2.5-dimensional magnetohydrodynamical (MHD) simulations of the disk-star interaction. The closed magnetic loops connecting the central star and the disk are twisted by the rotation of the disk. In the presence of resistivity, magnetic reconnection takes place in the current sheet formed inside the expanding loops. A hot, outgoing plasmoid and hot post flare loops are formed as a result of the reconnection. Numerical results are consistent with the observed plasma temperature (107 - 108K), the length of the flaring loop (1011 - 1012cm), and the velocity of optical jets (200 - 400km/s). We use high-resolution numerical simulations to show that multiple magnetic islands are created in the current sheet due to the growth of the tearing mode instability. The magnetic islands are ejected quasi-periodically. Intermittent flaring activity continues as long as the disk matter twists the dipole magnetic field

  1. Multi-scale structures of turbulent magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Nakamura, T. K. M.; Nakamura, R.; Narita, Y.; Baumjohann, W.; Daughton, W.

    2016-05-01

    We have analyzed data from a series of 3D fully kinetic simulations of turbulent magnetic reconnection with a guide field. A new concept of the guide filed reconnection process has recently been proposed, in which the secondary tearing instability and the resulting formation of oblique, small scale flux ropes largely disturb the structure of the primary reconnection layer and lead to 3D turbulent features [W. Daughton et al., Nat. Phys. 7, 539 (2011)]. In this paper, we further investigate the multi-scale physics in this turbulent, guide field reconnection process by introducing a wave number band-pass filter (k-BPF) technique in which modes for the small scale (less than ion scale) fluctuations and the background large scale (more than ion scale) variations are separately reconstructed from the wave number domain to the spatial domain in the inverse Fourier transform process. Combining with the Fourier based analyses in the wave number domain, we successfully identify spatial and temporal development of the multi-scale structures in the turbulent reconnection process. When considering a strong guide field, the small scale tearing mode and the resulting flux ropes develop over a specific range of oblique angles mainly along the edge of the primary ion scale flux ropes and reconnection separatrix. The rapid merging of these small scale modes leads to a smooth energy spectrum connecting ion and electron scales. When the guide field is sufficiently weak, the background current sheet is strongly kinked and oblique angles for the small scale modes are widely scattered at the kinked regions. Similar approaches handling both the wave number and spatial domains will be applicable to the data from multipoint, high-resolution spacecraft observations such as the NASA magnetospheric multiscale (MMS) mission.

  2. Magnetic reconnection in the near Venusian magnetotail.

    PubMed

    Zhang, T L; Lu, Q M; Baumjohann, W; Russell, C T; Fedorov, A; Barabash, S; Coates, A J; Du, A M; Cao, J B; Nakamura, R; Teh, W L; Wang, R S; Dou, X K; Wang, S; Glassmeier, K H; Auster, H U; Balikhin, M

    2012-05-04

    Observations with the Venus Express magnetometer and low-energy particle detector revealed magnetic field and plasma behavior in the near-Venus wake that is symptomatic of magnetic reconnection, a process that occurs in Earth's magnetotail but is not expected in the magnetotail of a nonmagnetized planet such as Venus. On 15 May 2006, the plasma flow in this region was toward the planet, and the magnetic field component transverse to the flow was reversed. Magnetic reconnection is a plasma process that changes the topology of the magnetic field and results in energy exchange between the magnetic field and the plasma. Thus, the energetics of the Venus magnetotail resembles that of the terrestrial tail, where energy is stored and later released from the magnetic field to the plasma.

  3. Magnetic reconnection in a magnetohydrodynamic plasma

    SciTech Connect

    Kulsrud, R.M.

    1998-05-01

    Magnetic reconnection is important because of its connection with the topology of field lines. In general, a change in topology means a change of equilibrium, and a release of energy, such as occurs in solar flares. In the context of the solar flare two models for magnetic reconnection, the Sweet{endash}Parker and the Petschek mechanism are presented. The pros and cons of these two models are presented. The role of anomalous resistivity in the Sweet{endash}Parker model is discussed. The bearing of a laboratory experiment and a boundary layer analysis of the problem are described. {copyright} {ital 1998 American Institute of Physics.}

  4. Design of a Magnetic Reconnection Experiment in the Collisionless Regime

    NASA Astrophysics Data System (ADS)

    Egedal, J.; Le, A.; Daughton, W. S.

    2012-12-01

    A new model for effective heating of electrons during reconnection is now gaining support from spacecraft observations, theoretical considerations and kinetic simulations [1]. The key ingredient in the model is the physics of trapped electrons whose dynamics causes the electron pressure tensor to be strongly anisotropic [2]. The heating mechanism becomes highly efficient for geometries with low upstream electron pressure, conditions relevant to the magnetotail. We propose a new experiment that will be optimized for the study of kinetic reconnection including the dynamics of trapped electrons and associated pressure anisotropy. This requires an experiment that accesses plasmas with much lower collisionality and lower plasma beta than are available in present reconnection experiments. The new experiment will be designed such that a large variety of magnetic configurations can be established and tailored for continuation of our ongoing study of spontaneous 3D reconnection [3]. The flexible design will also allow for configurations suitable for the study of merging magnetic islands, which may be a source of super thermal electrons in naturally occurring plasmas. [1] Egedal J et al., Nature Physics, 8, 321 (2012). [2] Le A et al., Phys. Rev. Lett. 102, 085001 (2009). [3] Katz N et al., Phys. Rev. Lett. 104, 255004 (2010).;

  5. Forced Magnetic Reconnection In A Tokamak Plasma

    NASA Astrophysics Data System (ADS)

    Callen, J. D.; Hegna, C. C.

    2015-11-01

    The theory of forced magnetic field reconnection induced by an externally imposed resonant magnetic perturbation usually uses a sheared slab or cylindrical magnetic field model and often focuses on the potential time-asymptotic induced magnetic island state. However, tokamak plasmas have significant magnetic geometry and dynamical plasma toroidal rotation screening effects. Also, finite ion Larmor radius (FLR) and banana width (FBW) effects can damp and thus limit the width of a nascent magnetic island. A theory that is more applicable for tokamak plasmas is being developed. This new model of the dynamics of forced magnetic reconnection considers a single helicity magnetic perturbation in the tokamak magnetic field geometry, uses a kinetically-derived collisional parallel electron flow response, and employs a comprehensive dynamical equation for the plasma toroidal rotation frequency. It is being used to explore the dynamics of bifurcation into a magnetically reconnected state in the thin singular layer around the rational surface, evolution into a generalized Rutherford regime where the island width exceeds the singular layer width, and assess the island width limiting effects of FLR and FBW polarization currents. Support by DoE grants DE-FG02-86ER53218, DE-FG02-92ER54139.

  6. Nonlinear regimes of forced magnetic reconnection

    SciTech Connect

    Vekstein, G.; Kusano, K.

    2015-09-15

    This letter presents a self-consistent description of nonlinear forced magnetic reconnection in Taylor's model of this process. If external boundary perturbation is strong enough, nonlinearity in the current sheet evolution becomes important before resistive effects come into play. This terminates the current sheet shrinking that takes place at the linear stage and brings about its nonlinear equilibrium with a finite thickness. Then, in theory, this equilibrium is destroyed by a finite plasma resistivity during the skin-time, and further reconnection proceeds in the Rutherford regime. However, realization of such a scenario is unlikely because of the plasmoid instability, which is fast enough to develop before the transition to the Rutherford phase occurs. The suggested analytical theory is entirely different from all previous studies and provides proper interpretation of the presently available numerical simulations of nonlinear forced magnetic reconnection.

  7. Formation of Plasmoid Chains in Magnetic Reconnection

    SciTech Connect

    Samtaney, R.; Loureiro, N. F.; Uzdensky, D. A.; Schekochihin, A. A.; Cowley, S. C.

    2009-09-09

    A detailed numerical study of magnetic reconnection in resistive MHD for very large, previously inaccessible, Lundquist numbers (104 ≤ S ≤ 108) is reported. Large-aspect-ratio Sweet-Parker current sheets are shown to be unstable to super-Alfvenically fast formation of plasmoid (magnetic-island) chains. The plasmoid number scales as S3/8 and the instability growth rate in the linear stage as S1/4, in agreement with the theory by Loureiro et al. [Phys. Plasmas 14, 100703 (2007)]. In the nonlinear regime, plasmoids continue to grow faster than they are ejected and completely disrupt the reconnection layer. These results suggest that high-Lundquist-number reconnection is inherently time-dependent and hence call for a substantial revision of the standard Sweet-Parker quasistationary picture for S>104.

  8. Magnetic Reconnection: Theoretical and Observational Perspectives: Preface

    NASA Technical Reports Server (NTRS)

    Lewis, W. S.; Antiochos, S. K,; Drake, J. F.

    2011-01-01

    Magnetic reconnection is a fundamental plasma-physical process by which energy stored in a magnetic field is converted, often explosively, into heat and the kinetic energy of the charged particles that constitute the plasma. It occurs in a variety of astrophysical settings, ranging from the solar corona to pulsar magnetospheres and winds, as well as in laboratory fusion experiments, where it is responsible for sawtooth crashes. First proposed by R.G. Giovanelli in the late I 940s as the mechanism responsible for solar flares, magnetic reconnection was invoked at the beginning of the space age to explain not just solar flares but also the transfer of energy, mass, and momentum from the solar wind to Earth's magnetosphere and the subsequent storage and release of the transferred energy in the magnetotai\\. During the half century or so that has followed the seminal theoretical works by J.W. Dungey, P.A. Sweet, E.N. Parker, and H.E. Petschek, in-situ measurements by Earth-orbiting satellites and remote-sensing observations of the solar corona have provided a growing body of evidence for the occurrence of reconnection at the Sun, in the solar wind, and in the near-Earth space environment. The last thirty years have also seen the development of laboratory reconnection experiments at a number of institutions. In parallel with the efforts of experimentalists in both space and laboratory plasma physics, theorists have investigated, analytically and with the help of increasingly powerful MHD, hybrid, and kinetic numerical simulations, the structure of the diffusion region, the factors controlling the rate, onset, and cessation of reconnection, and the detailed physics that enables the demagnetization of the ions and electrons and the topological reconfiguration of the magnetic field. Moreover, the scope of theoretical reconnection studies has been extended well beyond solar system and laboratory plasmas to include more exotic astrophysical plasma systems whose strong (10

  9. Magnetic reconnection under anisotropic magnetohydrodynamic approximation

    SciTech Connect

    Hirabayashi, K.; Hoshino, M.

    2013-11-15

    We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one- and two-dimensional collisionless MHD codes based on the double adiabatic approximation and the Landau closure model. We bridge the gap between the Petschek-type MHD reconnection model accompanied by a pair of slow shocks and the observational evidence of the rare occasion of in-situ slow shock observations. Our results showed that once magnetic reconnection takes place, a firehose-sense (p{sub ∥}>p{sub ⊥}) pressure anisotropy arises in the downstream region, and the generated slow shocks are quite weak comparing with those in an isotropic MHD. In spite of the weakness of the shocks, however, the resultant reconnection rate is 10%–30% higher than that in an isotropic case. This result implies that the slow shock does not necessarily play an important role in the energy conversion in the reconnection system and is consistent with the satellite observation in the Earth's magnetosphere.

  10. Quantitative, comprehensive, analytical model for magnetic reconnection in Hall magnetohydrodynamics.

    PubMed

    Simakov, Andrei N; Chacón, L

    2008-09-05

    Dissipation-independent, or "fast", magnetic reconnection has been observed computationally in Hall magnetohydrodynamics (MHD) and predicted analytically in electron MHD. However, a quantitative analytical theory of reconnection valid for arbitrary ion inertial lengths, d{i}, has been lacking and is proposed here for the first time. The theory describes a two-dimensional reconnection diffusion region, provides expressions for reconnection rates, and derives a formal criterion for fast reconnection in terms of dissipation parameters and d{i}. It also confirms the electron MHD prediction that both open and elongated diffusion regions allow fast reconnection, and reveals strong dependence of the reconnection rates on d{i}.

  11. Magnetic reconnection: from MHD to QED

    NASA Astrophysics Data System (ADS)

    Bulanov, S. V.

    2017-01-01

    The paper examines the prospects of using laser plasmas for studying novel regimes of the magnetic field line reconnection and charged particle acceleration. Basic features of plasma dynamics in the three-dimensional configurations relevant to the formation of current sheets in a plasma are addressed by analyzing exact self-similar solutions of the magneto-hydrodynamics and electron magneto-hydrodynamics equations. Then the magnetic field annihilation in the ultrarelativistic limit is considered, when the opposite polarity magnetic field is generated in collisionless plasma by multiple laser pulses, in the regime with a dominant contribution of the displacement current exciting a strong large-scale electric field. This field leads to the conversion of the magnetic energy into the kinetic energy of accelerated particles inside a thin current sheet. Charged particle acceleration during magnetic field reconnection is discussed when radiation friction and quantum electrodynamics effects become dominant.

  12. Quantized Chiral Magnetic Current from Reconnections of Magnetic Flux

    DOE PAGES

    Hirono, Yuji; Kharzeev, Dmitri E.; Yin, Yi

    2016-10-20

    We introduce a new mechanism for the chiral magnetic e ect that does not require an initial chirality imbalance. The chiral magnetic current is generated by reconnections of magnetic ux that change the magnetic helicity of the system. The resulting current is entirely determined by the change of magnetic helicity, and it is quantized.

  13. VINETA II: A linear magnetic reconnection experiment

    SciTech Connect

    Bohlin, H. Von Stechow, A.; Rahbarnia, K.; Grulke, O.; Klinger, T.

    2014-02-15

    A linear experiment dedicated to the study of driven magnetic reconnection is presented. The new device (VINETA II) is suitable for investigating both collisional and near collisionless reconnection. Reconnection is achieved by externally driving magnetic field lines towards an X-point, inducing a current in the background plasma which consequently modifies the magnetic field topology. Owing to the open field line configuration of the experiment, the current is limited by the axial sheath boundary conditions. A plasma gun is used as an additional electron source in order to counterbalance the charge separation effects and supply the required current. Two drive methods are used in the device. First, an oscillating current through two parallel conductors drive the reconnection. Second, a stationary X-point topology is formed by the parallel conductors, and the drive is achieved by an oscillating current through a third conductor. In the first setup, the magnetic field of the axial plasma current dominates the field topology near the X-point throughout most of the drive. The second setup allows for the amplitude of the plasma current as well as the motion of the flux to be set independently of the X-point topology of the parallel conductors.

  14. Electron nongyrotropy in the context of collisionless magnetic reconnection

    SciTech Connect

    Aunai, Nicolas; Hesse, Michael; Kuznetsova, Maria

    2013-09-15

    Collisionless magnetized plasmas have the tendency to isotropize their velocity distribution function around the local magnetic field direction, i.e., to be gyrotropic, unless some spatial and/or temporal fluctuations develop at the particle gyroscales. Electron gyroscale inhomogeneities are well known to develop during the magnetic reconnection process. Nongyrotropic electron velocity distribution functions have been observed to play a key role in the dissipative process breaking the field line connectivity. In this paper, we present a new method to quantify the deviation of a particle population from gyrotropy. The method accounts for the full 3D shape of the distribution and its analytical formulation allows fast numerical computation. Regions associated with a significant degree of nongyrotropy are shown, as well as the kinetic origin of the nongyrotropy and the fluid signature it is associated with. Using the result of 2.5D Particle-In-Cell simulations of magnetic reconnection in symmetric and asymmetric configurations, it is found that neither the reconnection site nor the topological boundaries are generally associated with a maximized degree of nongyrotropy. Nongyrotropic regions do not correspond to a specific fluid behavior as equivalent nongyrotropy is found to extend over the electron dissipation region as well as in non-dissipative diamagnetic drift layers. The localization of highly nongyrotropic regions in numerical models and their correlation with other observable quantities can, however, improve the characterization of spatial structures explored by spacecraft missions.

  15. Kinetic simulations of collisionless magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Aunai, N.; Dargent, J.; Lavraud, B.; Ciardi, A.; Drouin, M.; Smets, R.

    2016-12-01

    This paper focuses on magnetic reconnection and its role in magnetospheric physics, where collisions are inexistant. In this context, the presence of a very cold ion population of ionospheric origin is known to have an important contribution to the particle density at the magnetopause. However, besides this mass loading effect, consequences of their extremely low temperature, and therefore of their must smaller gyroscale, have not yet been addressed from a modeling viewpoint. This study presents two fully kinetic simulations with and without cold ions in the magnetosphere and highlights how their small Larmor radius can change signatures expected to be proxy of the X line in spacecraft measurements. In a second part, this paper addresses shortly the problem of the X line orientation in an asymmetric system. Using this time hybrid kinetic simulations, we show the X line aligned with the bisector of upstream magnetic field vectors results in faster reconnection rate. This have consequences regarding where reconnection at the magnetopause, although models here do not include large scale dynamics. We conclude with perspectives regarding future developments to address multi-scale magnetic reconnection dynamics at the magnetopause.

  16. Magnetic Reconnection in Extreme Astrophysical Environments

    NASA Astrophysics Data System (ADS)

    Uzdensky, Dmitri A.

    2011-10-01

    Magnetic reconnection is a fundamental plasma physics process in which ideal-MHD's frozen-in constraints are broken and the magnetic field topology is dramatically re-arranged, which often leads to a violent release of the free magnetic energy. Most of the magnetic reconnection research done to date has been motivated by the applications to systems such as the solar corona, Earth's magnetosphere, and magnetic confinement devices for thermonuclear fusion. These environments have relatively low energy densities and the plasma is adequately described as a mixture of equal numbers of electrons and ions and where the dissipated magnetic energy always stays with the plasma. In contrast, in this paper I would like to introduce a different, new direction of research—reconnection in high energy density radiative plasmas, in which photons play as important a role as electrons and ions; in particular, in which radiation pressure and radiative cooling become dominant factors in the pressure and energy balance. This research is motivated in part by rapid theoretical and experimental advances in High Energy Density Physics, and in part by several important problems in modern high-energy astrophysics. I first discuss some astrophysical examples of high-energy-density reconnection and then identify the key physical processes that distinguish them from traditional reconnection. Among the most important of these processes are: special-relativistic effects; radiative effects (radiative cooling, radiation pressure, and radiative resistivity); and, at the most extreme end—QED effects, including pair creation. The most notable among the astrophysical applications are situations involving magnetar-strength fields (1014-1015 G, exceeding the quantum critical field B ∗≃4×1013 G). The most important examples are giant flares in soft gamma repeaters (SGRs) and magnetic models of the central engines and relativistic jets of Gamma Ray Bursts (GRBs). The magnetic energy density in

  17. Magnetic reconnection process in accretion disk systems

    NASA Astrophysics Data System (ADS)

    Piovezan, P.; de Gouveia Dal Pino, E. M.

    2009-08-01

    At the present study, we investigate the role of magnetic reconnection in three different astrophysical systems, namely young stellar objects (YSO's), microquasars, and active galactic nuclei (AGN's). In the case of microquasars and AGN's, violent reconnection episodes between the magnetic field lines of the inner disk region (which are established by a turbulent dynamo) and those anchored into the black hole are able to heat the coronal/disk gas and accelerate particles to relativistic velocities through a diffusive first-order Fermi-like process within the reconnection site that will produce relativistic blobs. The heating of the coronal/disk gas is able to produce a steep X-ray spectrum with a luminosity that is consistent with the observations and we argue that it is being produced mainly at the foot of the reconnection zone, while the Fermi-like acceleration process within the reconnection site results a power-law electron distribution with N(E) ∝ E-α, with α=5/2, and a corresponding synchrotron radio power-law spectrum with a spectral index that is compatible with that observed during the radio flares in microquasars (Sν ∝ ν-0.75). The scaling laws that we derive for AGN's indicate that the same mechanism may be occurring there. Finally, in the case of the YSO's, a similar magnetic configuration can be reached. The amount of magnetic energy that can be extracted from the inner disk region can heat the coronal gas to temperatures of the order of 10^8 K and could explain the observed X-ray flaring emission.

  18. Magnetic reconnection in Saturn's magnetotail: A comprehensive magnetic field survey.

    NASA Astrophysics Data System (ADS)

    Smith, A. W.; Jackman, C. M.; Thomsen, M. F.; Dougherty, M. K.

    2015-10-01

    Magnetic reconnection is a fundamental process throughout the solar system, significantly shaping and modulating the magnetospheres of the magnetized planets. Within planetary magnetotails reconnection can be responsible for energizing particles and potentially changing the total flux and mass contained within the magnetosphere. The Kronian magnetosphere is thought to be a middle ground between the rotationally dominated Jovian magnetosphere and the solar wind driven terrestrial magnetosphere. However, previous studies have not been able to find a statistical reconnection x-line, as has been possible at both Jupiter and Earth. Additionally the standard picture of magnetotail reconnection at Saturn, developed by Cowley et al. [2004], suggests a potential asymmetry between the dawn and dusk flanks, caused by different reconnection processes dominating. This work centers on the development of an algorithm designed to find reconnection related events in spacecraft magnetometer data, aiming to reduce the bias that manual searches could inherently introduce, thereby ensuring the validity of any statistical analysis. The algorithm primarily identifies the reconnection related events from deflections in the north-south component of the magnetic field, allowing an almost uninterrupted in-situ search (when the spacecraft is situated within the magnetotail). The new catalogue of candidate reconnection events, produced by the algorithm, enables a more complete statistical view of reconnection in the Kronian magnetotail. Well-studied data encompassing the deep magnetotail and dawn flank (particularly from orbits in 2006) were used to train the algorithm and develop reasonable criteria. The algorithm was then applied to data encompassing the dusk flank (including orbits from 2009, for which plasma data have been examined by Thomsen et al. [2014]). This combination enables a robust, and global, comparison of reconnection rates, signatures and properties in the Kronian magnetotail.

  19. Magnetic Reconnection in Different Environments: Similarities and Differences

    NASA Technical Reports Server (NTRS)

    Hesse, Michael; Aunai, Nicolas; Kuznetsova, Masha; Zenitani, Seiji; Birn, Joachim

    2014-01-01

    Depending on the specific situation, magnetic reconnection may involve symmetric or asymmetric inflow regions. Asymmetric reconnection applies, for example, to reconnection at the Earth's magnetopause, whereas reconnection in the nightside magnetotail tends to involve more symmetric geometries. A combination of review and new results pertaining to magnetic reconnection is being presented. The focus is on three aspects: A basic, MHD-based, analysis of the role magnetic reconnection plays in the transport of energy, followed by an analysis of a kinetic model of time dependent reconnection in a symmetric current sheet, similar to what is typically being encountered in the magnetotail of the Earth. The third element is a review of recent results pertaining to the orientation of the reconnection line in asymmetric geometries, which are typical for the magnetopause of the Earth, as well as likely to occur at other planets.

  20. Fast magnetic reconnection with large guide fields

    DOE PAGES

    Stanier, A.; Simakov, Andrei N.; Chacón, L.; ...

    2015-01-09

    We domonstrate, using two-fluid simulations, that low-βmagnetic reconnection remains fast, regardless of the presence of fast dispersive waves, which have been previously suggested to play a critical role. In order to understand these results, a discrete model is constructed that offers scaling relationships for the reconnection rate and dissipation region (DR) thickness in terms of the upstream magnetic field and DR length. Moreover, we verify these scalings numerically and show how the DR self-adjusts to process magnetic flux at the same rate that it is supplied to a larger region where two-fluid effects become important. The rate is therefore independentmore » of the DR physics and is in good agreement with kinetic results.« less

  1. Gyro-induced acceleration of magnetic reconnection

    SciTech Connect

    Comisso, L.; Grasso, D.; Waelbroeck, F. L.; Borgogno, D.

    2013-09-15

    The linear and nonlinear evolution of magnetic reconnection in collisionless high-temperature plasmas with a strong guide field is analyzed on the basis of a two-dimensional gyrofluid model. The linear growth rate of the reconnecting instability is compared to analytical calculations over the whole spectrum of linearly unstable wave numbers. In the strongly unstable regime (large Δ′), the nonlinear evolution of the reconnecting instability is found to undergo two distinctive acceleration phases separated by a stall phase in which the instantaneous growth rate decreases. The first acceleration phase is caused by the formation of strong electric fields close to the X-point due to ion gyration, while the second acceleration phase is driven by the development of an open Petschek-like configuration due to both ion and electron temperature effects. Furthermore, the maximum instantaneous growth rate is found to increase dramatically over its linear value for decreasing diffusion layers. This is a consequence of the fact that the peak instantaneous growth rate becomes weakly dependent on the microscopic plasma parameters if the diffusion region thickness is sufficiently smaller than the equilibrium magnetic field scale length. When this condition is satisfied, the peak reconnection rate asymptotes to a constant value.

  2. Current disruption and its spreading in collision-less magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Jain, Neeraj; Buechner, Joerg; Dorfman, Seth; Ji, Hantao; Sharma, A. Surjalal; Max-Planck/Princeton CenterPlasma Physics Collaboration

    2013-10-01

    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. This work was partially funded by the Max-Planck/Princeton Center for Plasma Physics.

  3. Magnetic diffusion and ion nonlinear dynamics in magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Zenitani, S.; Shinohara, I.; Nagai, T.; Wada, T.

    2013-12-01

    Magnetic reconnection is a fundamental process in many plasma systems, ranging from laboratory and solar-terrestrial environments to extreme astrophysical settings. The reconnection process is controlled by magnetic dissipation physics in a small-scale region near the reconnection point (X-line), and therefore the structure of the reconnection site is of strong interest. According to the standard picture of collisionless reconnection, the X-line is surrounded by a compact electron diffusion region and by an outer ion diffusion region. While the electron region has been extensively studied, much less is known about the ion region. In this work, we examine key aspects of the ion region in magnetic reconnection. First, we evaluate the ''diffusion'' of magnetic field lines, going back to the topology theorems. Unlike in the MHD, the idealness, the frozen-in, magnetic diffusion, and the energy dissiation can be all different in a kinetic plasma. We will apply these concepts to the reconnection site in two-dimensional particle-in-cell (PIC) simulations. Importantly, in the outer part of the ion region, even though the ion ideal condition is violated, the magnetic fields are frozen to plasma fluids. This raises a serious question to the widespread definition of the ion diffusion region, based on the ion nonidealness. We further examine the ion velocity distribution function in the same region. The distribution function contains multiple populations such as global Speiser ions, local Speiser ions, and trapped ions. The particle motion of the local Speiser ions in an appropriately rotated frame explains the plasma nonidealness. The trapped ions are the first demonstration of the regular orbits in Chen & Palmadesso (1986), in self-consistent PIC simulations. They would be observational signatures in the ion current layer near reconnection sites.

  4. Laboratory experiments on magnetic reconnection and current systems

    NASA Astrophysics Data System (ADS)

    Stenzel, R. L.; Urrutia, J. M.; Gekelman, W.; Pfister, H.

    After a brief review of laboratory experiments involving magnetic reconnection a series of basic physics experiments on reconnection phenomena is described. These include magnetic annihilation, transport of magnetic energy by waves, stable and unstable current sheets, energy conversion mechanisms, and the role of global current systems vs. local reconnection processes. Current systems driven by electric fields resulting in particle flows are examined. Also, the role of a magnetic field component B(y) along the separator has been investigated.

  5. Three-dimensional lattice Boltzmann model for magnetic reconnection

    SciTech Connect

    Mendoza, M.; Munoz, J. D.

    2008-02-15

    We develop a three-dimensional (3D) lattice Boltzmann model that recovers in the continuous limit the two-fluids theory for plasmas, and consequently includes the generalized Ohm's law. The model reproduces the magnetic reconnection process just by giving the right initial equilibrium conditions in the magnetotail, without any assumption on the resistivity in the diffusive region. In this model, the plasma is handled similar to two fluids with an interaction term, each one with distribution functions associated to a cubic lattice with 19 velocities (D3Q19). The electromagnetic fields are considered as a third fluid with an external force on a cubic lattice with 13 velocities (D3Q13). The model can simulate either viscous fluids in the incompressible limit or nonviscous compressible fluids, and successfully reproduces both the Hartmann flow and the magnetic reconnection in the magnetotail. The reconnection rate in the magnetotail obtained with this model lies between R=0.062 and R=0.073, in good agreement with the observations.

  6. Quantitative analytical model for magnetic reconnection in hall magnetohydrodynamics

    SciTech Connect

    Simakov, Andrei N

    2008-01-01

    Magnetic reconnection is of fundamental importance for laboratory and naturally occurring plasmas. Reconnection usually develops on time scales which are much shorter than those associated with classical collisional dissipation processes, and which are not fully understood. While such dissipation-independent (or 'fast') reconnection rates have been observed in particle and Hall magnetohydrodynamics (MHD) simulations and predicted analytically in electron MHD, a quantitative analytical theory of fast reconnection valid for arbitrary ion inertial lengths d{sub i} has been lacking. Here we propose such a theory without a guide field. The theory describes two-dimensional magnetic field diffusion regions, provides expressions for the reconnection rates, and derives a formal criterion for fast reconnection in terms of dissipation parameters and di. It also demonstrates that both open X-point and elongated diffusion regions allow dissipation-independent reconnection and reveals a possibility of strong dependence of the reconnection rates on d{sub i}.

  7. Observation of a 3D Magnetic Null Point

    NASA Astrophysics Data System (ADS)

    Romano, P.; Falco, M.; Guglielmino, S. L.; Murabito, M.

    2017-03-01

    We describe high-resolution observations of a GOES B-class flare characterized by a circular ribbon at the chromospheric level, corresponding to the network at the photospheric level. We interpret the flare as a consequence of a magnetic reconnection event that occurred at a three-dimensional (3D) coronal null point located above the supergranular cell. The potential field extrapolation of the photospheric magnetic field indicates that the circular chromospheric ribbon is cospatial with the fan footpoints, while the ribbons of the inner and outer spines look like compact kernels. We found new interesting observational aspects that need to be explained by models: (1) a loop corresponding to the outer spine became brighter a few minutes before the onset of the flare; (2) the circular ribbon was formed by several adjacent compact kernels characterized by a size of 1″–2″ (3) the kernels with a stronger intensity emission were located at the outer footpoint of the darker filaments, departing radially from the center of the supergranular cell; (4) these kernels started to brighten sequentially in clockwise direction; and (5) the site of the 3D null point and the shape of the outer spine were detected by RHESSI in the low-energy channel between 6.0 and 12.0 keV. Taking into account all these features and the length scales of the magnetic systems involved in the event, we argue that the low intensity of the flare may be ascribed to the low amount of magnetic flux and to its symmetric configuration.

  8. Magnetic Reconnection During Major Magnetospheric Storms

    NASA Astrophysics Data System (ADS)

    Hubert, B. A.; Milan, S. E.; Cowley, S. W. H.

    2014-12-01

    We combine imaging of the proton aurora from the SI12-IMAGE instrument with ionospheric convection measurement from the SuperDARN radar network to analyze the cycle of magnetic flux opening and closure of the Earth magnetosphere. Interaction between the solar wind and the Earth geomagnetic environment causes a reconfiguration of the magnetic field that connects the interplanetary magnetic field (IMF) to the geomagnetic field. This reconnection process produces open magnetic field lines (i.e. field lines of the magnetosphere that close through the interplanetary medium) that are dragged to the magnetotail by the solar wind flow, where they eventually reconnect again, back to a closed topology. The SI12 imaging of the Doppler-shifted Lyman-α emission of the proton aurora is used to estimate the location of the boundary separating open and closed field lines at ionospheric altitude. We then estimate the open magnetic flux of the Earth magnetosphere, encircled by this boundary. The rate of reconnection causing a variation of the open magnetic flux can be expressed as a voltage in application of Faraday's law. This voltage is measured along the open/closed field line boundary determined from the imaging data. The electric field associated with the voltage has two origins: motion of the boundary and the ionospheric field. We use the ionospheric electric field deduced from ionospheric convection measurement from the SuperDARN to estimate the reconnection voltage at the magnetopause (flux opening) and in the magnetotail (flux closure) accounting for the motion of the open/closed field line boundary determined from the SI12 images. The method is applied during several (strong) geomagnetic storms. These intervals are characterized by large values of open flux and reconnection rates, as a result of coupling between the solar wind and the geomagnetic environment. We present these results in terms of a magnetospheric mode that develops under strong coupling with the solar wind

  9. FAST MAGNETIC RECONNECTION AND SPONTANEOUS STOCHASTICITY

    SciTech Connect

    Eyink, Gregory L.; Lazarian, A.; Vishniac, E. T.

    2011-12-10

    Magnetic field lines in astrophysical plasmas are expected to be frozen-in at scales larger than the ion gyroradius. The rapid reconnection of magnetic-flux structures with dimensions vastly larger than the gyroradius requires a breakdown in the standard Alfven flux-freezing law. We attribute this breakdown to ubiquitous MHD plasma turbulence with power-law scaling ranges of velocity and magnetic energy spectra. Lagrangian particle trajectories in such environments become 'spontaneously stochastic', so that infinitely many magnetic field lines are advected to each point and must be averaged to obtain the resultant magnetic field. The relative distance between initial magnetic field lines which arrive at the same final point depends upon the properties of two-particle turbulent dispersion. We develop predictions based on the phenomenological Goldreich and Sridhar theory of strong MHD turbulence and on weak MHD turbulence theory. We recover the predictions of the Lazarian and Vishniac theory for the reconnection rate of large-scale magnetic structures. Lazarian and Vishniac also invoked 'spontaneous stochasticity', but of the field lines rather than of the Lagrangian trajectories. More recent theories of fast magnetic reconnection appeal to microscopic plasma processes that lead to additional terms in the generalized Ohm's law, such as the collisionless Hall term. We estimate quantitatively the effect of such processes on the inertial-range turbulence dynamics and find them to be negligible in most astrophysical environments. For example, the predictions of the Lazarian and Vishniac theory are unchanged in Hall MHD turbulence with an extended inertial range, whenever the ion skin depth {delta}{sub i} is much smaller than the turbulent integral length or injection-scale L{sub i} .

  10. Influence of Spontaneously Generated Turbulence on Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Daughton, William; Roytershteyn, Vadim; Karimabadi, Homa

    2012-10-01

    The 3D dynamics of reconnection is examined for electron-positron plasmas within Harris sheet geometry with a guide field. This configuration is unstable to tearing modes at resonant surfaces across the layer, corresponding to oblique angles relative to 2D models. Vlasov theory predicts a spectrum of oblique modes which can destroy the flux surfaces and produce interacting flux ropes. These structures coalesce to larger scales leading to the continual formation and break-up of new current sheets and the generation of turbulence. The fluctuation spectrum is highly anisotropic and is characterized by two power-laws with a break at k di˜1, where di is the inertial length. In the large 3D simulations, the dissipation rate is reduced by ˜40% relative to small 2D cases which are steady and laminar. In both limits, the reconnection remains fast (i.e. Alfv'enic), is insensitive to the system size and ultimately occurs within inertial-scale current sheets. These results imply that the physics responsible for setting the time scale is not radically altered by the turbulence. However, the results indicate that a larger fraction of the magnetic energy is accessible in 3D and that many more particles are accelerated into the high energy tails due to the turbulence.

  11. Possible Properties of Kinetic Flux Ropes Generated by Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Ng, C. S.

    2015-12-01

    We present latest results of numerical studies of a recently obtained analytic solution that can describe small-scale kinetic flux ropes. Such exact nonlinear solution of the Vlasov-Poisson-Ampere system of equations can be regarded as two-dimensional Bernstein-Greene-Kruskal (BGK) mode, generalizing from a solution in a magnetized plasma with finite magnetic field strength [Ng, Bhattacharjee, and Skiff, Phys. Plasmas 13, 055903 (2006)], with the additional effect of field-aligned current. Such solution might explain magnetic flux ropes observed to form within the diffusion region in 3D kinetic simulations of magnetic reconnection, and the 2D version of them (plasmoids, secondary islands). We will present properties of solutions based on a range of typical plasma parameters within regions of the magnetosphere where magnetic reconnection could happen. These solutions could potentially be used to compare with future Magnetospheric Multiscale Mission (MMS) observation. This work is supported by a National Science Foundation grant PHY-1004357 and the Alaska NASA EPSCoR Program (NNX13AB28A).

  12. Properties of Magnetic Reconnection as a function of magnetic shear

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Daughton, W. S.; Karimabadi, H.; Li, H.; Gary, S. P.; Guo, F.

    2013-12-01

    Observations of reconnection events at the Earth's magnetopause and in the solar wind show that reconnection occurs for a large range in magnetic shear angles extending to the very low shear limit 1. Here we report a fully kinetic study of the influence of the magnetic shear on details of reconnection such as its structure and rate. In previous work, we found that the electron diffusion region bifurcates into two or more distinct layers in regimes with weak magnetic shear2, a new feature that may be observable by NASA's up-coming Magnetospheric Multiscale mission. In this work, we have systematically extended the study to lower shear cases and found a new regime, where the reconnection electric field becomes much smaller and the properties of the reconnection changes significantly. We will discuss the role of various physics mechanisms in determining the observed scaling of the reconnection rate, including the dispersive properties of the waves in the system, the dissipation mechanisms and the tearing instability. 1 J. T. Goslings and T. D. Phan. APJL 763, L39, 2013 2 Yi-Hsin Liu et al. Phys. Rev. Lett. 110 , 265004, 2013

  13. Anisotropic heat transport in integrable and chaotic 3-D magnetic fields

    SciTech Connect

    Del-Castillo-Negrete, Diego B; Blazevski, D.; Chacon, Luis

    2012-01-01

    A study of anisotropic heat transport in 3-D chaotic magnetic fields is presented. The approach is based on the recently proposed Lagrangian-Green s function (LG) method in Ref. [1] that allows an efficient and accurate integration of the parallel transport equation applicable to general magnetic fields with local or non-local parallel flux closures. We focus on reversed shear magnetic field configurations known to exhibit separatrix reconnection and shearless transport barriers. The role of reconnection and magnetic field line chaos on temperature transport is studied. Numerical results are presented on the anomalous relaxation of radial temperature gradients in the presence of shearless Cantori partial barri- ers. Also, numerical evidence of non-local effective radial temperature transport in chaotic fields is presented. Going beyond purely parallel transport, the LG method is generalized to include finite perpendicular diffusivity, and the problem of temperature flattening inside a magnetic island is studied.

  14. Formation of current sheets in magnetic reconnection

    SciTech Connect

    Boozer, Allen H.

    2014-07-15

    An ideal evolution of magnetic fields in three spatial dimensions tends to cause neighboring field lines to increase their separation exponentially with distance ℓ along the lines, δ(ℓ)=δ(0)e{sup σ(ℓ)}. The non-ideal effects required to break magnetic field line connections scale as e{sup −σ}, so the breaking of connections is inevitable for σ sufficiently large—even though the current density need nowhere be large. When the changes in field line connections occur rapidly compared to an Alfvén transit time, the constancy of j{sub ||}/B along the magnetic field required for a force-free equilibrium is broken in the region where the change occurs, and an Alfvénic relaxation of j{sub ||}/B occurs. Independent of the original spatial distribution of j{sub ||}/B, the evolution is into a sheet current, which is stretched by a factor e{sup σ} in width and contracted by a factor e{sup σ} in thickness with the current density j{sub ||} increasing as e{sup σ}. The dissipation of these sheet currents and their associated vorticity sheets appears to be the mechanism for transferring energy from a reconnecting magnetic field to a plasma. Harris sheets, which are used in models of magnetic reconnection, are shown to break up in the direction of current flow when they have a finite width and are in a plasma in force equilibrium. The dependence of the longterm nature of magnetic reconnection in systems driven by footpoint motion can be studied in a model that allows qualitative variation in the nature of that motion: slow or fast motion compared to the Alfvén transit time and the neighboring footpoints either exponentially separating in time or not.

  15. Fluctuation dynamo based on magnetic reconnections

    NASA Astrophysics Data System (ADS)

    Baggaley, A. W.; Shukurov, A.; Barenghi, C. F.; Subramanian, K.

    2010-01-01

    We develop a new model of the fluctuation dynamo in which the magnetic field is confined to thin flux ropes advected by a multi-scale flow which models turbulence. Magnetic dissipation occurs only via reconnections of flux ropes. The model is particularly suitable for rarefied plasma, such as the solar corona or galactic halos. We investigate the kinetic energy release into heat, mediated by dynamo action, both in our model and by solving the induction equation with the same flow. We find that the flux rope dynamo is more than an order of magnitude more efficient at converting mechanical energy into heat. The probability density of the magnetic energy released during reconnections has a power-law form with the slope -3, consistent with the solar corona heating by nanoflares. We also present a nonlinear extension of the model. This shows that a plausible saturation mechanism of the fluctuation dynamo is the suppression of turbulent magnetic diffusivity, due to suppression of random stretching at the location of the flux ropes. We confirm that the probability distribution function of the magnetic line curvature has a power-law form suggested by \\citet{Sheck:2002b}. We argue, however, using our results that this does not imply a persistent folded structure of magnetic field, at least in the nonlinear stage.

  16. Visco-Resistive MHD Modeling Benchmark of Forced Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Beidler, M. T.; Hegna, C. C.; Sovinec, C. R.; Callen, J. D.; Ferraro, N. M.

    2016-10-01

    The presence of externally-applied 3D magnetic fields can affect important phenomena in tokamaks, including mode locking, disruptions, and edge localized modes. External fields penetrate into the plasma and can lead to forced magnetic reconnection (FMR), and hence magnetic islands, on resonant surfaces if the local plasma rotation relative to the external field is slow. Preliminary visco-resistive MHD simulations of FMR in a slab geometry are consistent with theory. Specifically, linear simulations exhibit proper scaling of the penetrated field with resistivity, viscosity, and flow, and nonlinear simulations exhibit a bifurcation from a flow-screened to a field-penetrated, magnetic island state as the external field is increased, due to the 3D electromagnetic force. These results will be compared to simulations of FMR in a circular cross-section, cylindrical geometry by way of a benchmark between the NIMROD and M3D-C1 extended-MHD codes. Because neither this geometry nor the MHD model has the physics of poloidal flow damping, the theory of will be expanded to include poloidal flow effects. The resulting theory will be tested with linear and nonlinear simulations that vary the resistivity, viscosity, flow, and external field. Supported by OFES DoE Grants DE-FG02-92ER54139, DE-FG02-86ER53218, DE-AC02-09CH11466, and the SciDAC Center for Extended MHD Modeling.

  17. Transition in Electron Physics of Magnetic Reconnection in Weakly Collisional Plasma

    NASA Astrophysics Data System (ADS)

    Le, A.; Roytershteyn, V.; Karimabadi, H.; Daughton, W. S.; Egedal, J.; Forest, C.

    2013-12-01

    Using self-consistent fully kinetic simulations with a Monte-Carlo treatment of the Coulomb collision operator, we explore the transition between collisional and kinetic regimes of magnetic reconnection in high-Lundquist-number current sheets. Recent research in collisionless reconnection has shown that electron kinetic physics plays a key role in the evolution. Large-scale electron current sheets may form, leading to secondary island formation and turbulent flux rope interactions in 3D. The new collisional simulations demonstrate how increasing collisionality modifies or eliminates these electron structures in the kinetic regimes. Additional basic questions that are addressed include how the reconnection rate and the release of magnetic energy into electrons and ions vary with collisionality. The numerical study provides insight into reconnection in dense regions of the solar corona, the solar wind, and upcoming laboratory experiments at MRX (Princeton) and MPDX (UW-Madison). The implications of these results for studies of turbulence dissipation in weakly collisional plasmas are discussed.

  18. Aspects of collisionless magnetic reconnection in asymmetric systems

    SciTech Connect

    Hesse, Michael; Aunai, Nicolas; Kuznetsova, Masha; Zenitani, Seiji; Birn, Joachim

    2013-06-15

    Asymmetric reconnection is being investigated by means of particle-in-cell simulations. The research has two foci: the direction of the reconnection line in configurations with nonvanishing magnetic fields; and the question why reconnection can be faster if a guide field is added to an otherwise unchanged asymmetric configuration. We find that reconnection prefers a direction, which maximizes the available magnetic energy, and show that this direction coincides with the bisection of the angle between the asymptotic magnetic fields. Regarding the difference in reconnection rates between planar and guide field models, we demonstrate that a guide field can provide essential confinement for particles in the reconnection region, which the weaker magnetic field in one of the inflow directions cannot necessarily provide.

  19. Aspects of Collisionless Magnetic Reconnection in Asymmetric Systems

    NASA Technical Reports Server (NTRS)

    Hesse, Michael; Aunai, Nicolas; Zeitani, Seiji; Kuznetsova, Masha; Birn, Joachim

    2013-01-01

    Asymmetric reconnection is being investigated by means of particle-in-cell simulations. The research has two foci: the direction of the reconnection line in configurations with non-vanishing magnetic fields; and the question why reconnection can be faster if a guide field is added to an otherwise unchanged asymmetric configuration. We find that reconnection prefers a direction, which maximizes the available magnetic energy, and show that this direction coincides with the bisection of the angle between the asymptotic magnetic fields. Regarding the difference in reconnection rates between planar and guide field models, we demonstrate that a guide field can provide essential confinement for particles in the reconnection region, which the weaker magnetic field in one of the inflow directions cannot necessarily provide.

  20. Aspects of Collisionless Magnetic Reconnection in Asymmetric Systems

    NASA Technical Reports Server (NTRS)

    Hesse, Michael; Aunai, Nicolas; Zenitani, Seiji; Kuznetsova, Masha; Birn, Joachim

    2013-01-01

    Asymmetric reconnection is being investigated by means of particle-in-cell simulations. The research has two foci: The direction of the reconnection line in configurations with nonvanishing magnetic fields; and the question why reconnection can be faster if a guide field is added to an otherwise unchanged asymmetric configuration. We find that reconnection prefers a direction, which maximizes the available magnetic energy, and show that this direction coincides with the bisection of the angle between the asymptotic magnetic fields. Regarding the difference in reconnection rates between planar and guide field models, we demonstrate that a guide field can provide essential confinement for particles in the reconnection region, which the weaker magnetic field in one of the inflow directions cannot necessarily provide.

  1. On the Location of Magnetic Reconnection at the Dayside Magnetopause

    NASA Astrophysics Data System (ADS)

    Komar, C. M.; Cassak, P.; Fermo, R. L.

    2013-12-01

    Predicting where magnetic reconnection occurs at Earth's dayside magnetopause has been the subject of studies for nearly 50 years and remains an unsolved problem. The location of dayside magnetic reconnection was originally discussed in terms of anti-parallel vs. component (guide field) reconnection, but it is now known that these descriptions are too basic to fully describe the observations. Recent models suggest that reconnection orients itself such that the local properties maximize some measure of asymmetric reconnection efficiency [Swisdak and Drake, 2007; Borovsky, 2013; Hesse, et al., 2013]. Alternatively, Trattner, et al., [2007] proposed the Maximum Magnetic Shear model, in which reconnection occurs along the curve where the shear angle between the magnetospheric and magnetosheath magnetic fields is a maximum. Each of these models is independent of the reconnection dissipation mechanism, so they should hold for any self-consistent magnetospheric model. We use global magnetospheric resistive magnetohydrodynamic simulations to identify the locus of possible magnetic reconnection sites by finding the magnetic separator where different magnetic topologies meet at the dayside magnetopause. Employing image processing techniques, we compare the separator locations with the predictions of these models to determine which, if any, accurately predict the location of reconnection.

  2. RELATIVISTIC TWO-FLUID SIMULATIONS OF GUIDE FIELD MAGNETIC RECONNECTION

    SciTech Connect

    Zenitani, Seiji; Hesse, Michael; Klimas, Alex

    2009-11-01

    The nonlinear evolution of relativistic magnetic reconnection in sheared magnetic configuration (with a guide field) is investigated by using two-dimensional relativistic two-fluid simulations. Relativistic guide field reconnection features the charge separation and the guide field compression in and around the outflow channel. As the guide field increases, the composition of the outgoing energy changes from enthalpy-dominated to Poynting-dominated. The inertial effects of the two-fluid model play an important role to sustain magnetic reconnection. Implications for the single-fluid magnetohydrodynamic approach and the physics models of relativistic reconnection are briefly addressed.

  3. Experimental study of ion heating and acceleration during magnetic reconnection

    SciTech Connect

    Hsu, S.C.

    2000-01-28

    This dissertation reports an experimental study of ion heating and acceleration during magnetic reconnection, which is the annihilation and topological rearrangement of magnetic flux in a conductive plasma. Reconnection is invoked often to explain particle heating and acceleration in both laboratory and naturally occurring plasmas. However, a simultaneous account of reconnection and its associated energy conversion has been elusive due to the extreme inaccessibility of reconnection events, e.g. in the solar corona, the Earth's magnetosphere, or in fusion research plasmas. Experiments for this work were conducted on MRX (Magnetic Reconnection Experiment), which creates a plasma environment allowing the reconnection process to be isolated, reproduced, and diagnosed in detail. Key findings of this work are the identification of local ion heating during magnetic reconnection and the determination that non-classical effects must provide the heating mechanism. Measured ion flows are sub-Alfvenic and can provide only slight viscous heating, and classical ion-electron interactions can be neglected due to the very long energy equipartition time. The plasma resistivity in the reconnection layer is seen to be enhanced over the classical value, and the ion heating is observed to scale with the enhancement factor, suggesting a relationship between the magnetic energy dissipation mechanism and the ion heating mechanism. The observation of non-classical ion heating during reconnection has significant implications for understanding the role played by non-classical dissipation mechanisms in generating fast reconnection. The findings are relevant for many areas of space and laboratory plasma research, a prime example being the currently unsolved problem of solar coronal heating. In the process of performing this work, local measurements of ion temperature and flows in a well-characterized reconnection layer were obtained for the first time in either laboratory or observational

  4. Measurements of Fast Magnetic Reconnection Driven by Relativistic Electrons

    NASA Astrophysics Data System (ADS)

    Raymond, Anthony; McKelvey, Andrew; Zulick, Calvin; Chuanfei, Dong; Maksimchuk, Anatoly; Thomas, Alexander; Yanovsky, Victor; Krushelnick, Karl; Willingale, Louise; Chykov, Vladimir; Nilson, Phil; Chen, Hui; Williams, Gerald; Bhattacharjee, Amitava; Fox, Will

    2015-11-01

    Magnetic reconnection is a process whereby opposing magnetic field lines are forced together and topologically rearrange, resulting in lower magnetic potential energy and in corresponding plasma heating. Such occurrences are ubiquitous in astrophysics as well as appearing in laboratory plasmas such as in ICF in the form of instabilities. We report measurements in the domain of ultra-fast, ultra-intense lasers, in which the mechanism responsible follows from radially expanding surface electrons with v ~ c . Results are compared from two laser facilities (HERCULES and Omega EP), both of which produced two relativistic intensity pulses focused within close proximity onto copper foils. A spherical X-ray crystal was used to image the Kα radiation induced by electron currents, revealing the midplane diffusion region wherein electrons are accelerated into the target by the electric field generated during reconnection. The characteristics of this signal are studied as a function of the focal spot separation, laser energy, and pulse duration. The results are then compared to 3D PIC simulations.

  5. Magnetic reconnection in Saturn's magnetotail: A comprehensive magnetic field survey

    NASA Astrophysics Data System (ADS)

    Smith, A. W.; Jackman, C. M.; Thomsen, M. F.

    2016-04-01

    Reconnection within planetary magnetotails is responsible for locally energizing particles and changing the magnetic topology. Its role in terms of global magnetospheric dynamics can involve changing the mass and flux content of the magnetosphere. We have identified reconnection related events in spacecraft magnetometer data recorded during Cassini's exploration of Saturn's magnetotail. The events are identified from deflections in the north-south component of the magnetic field, significant above a background level. Data were selected to provide full tail coverage, encompassing the dawn and dusk flanks as well as the deepest midnight orbits. Overall 2094 reconnection related events were identified, with an average rate of 5.0 events per day. The majority of events occur in clusters (within 3 h of other events). We examine changes in this rate in terms of local time and latitude coverage, taking seasonal effects into account. The observed reconnection rate peaks postmidnight with more infrequent but steady loss seen on the dusk flank. We estimate the mass loss from the event catalog and find it to be insufficient to balance the input from the moon Enceladus. Several reasons for this discrepancy are discussed. The reconnection X line location appears to be highly variable, though a statistical separation between events tailward and planetward of the X line is observed at a radial distance of between 20 and 30RS downtail. The small sample size at dawn prevents comprehensive statistical comparison with the dusk flank observations in terms of flux closure.

  6. Test particle acceleration in turbulent reconnecting magnetic fields

    NASA Technical Reports Server (NTRS)

    Ambrosiano, John; Matthaeus, William H.; Goldstein, Melvyn L.; Plante, Daniel

    1988-01-01

    The effect of turbulence on particle acceleration in a MHD field was investigated by computing test particle trajectories in turbulent MHD reconnecting fields, including reconnection simulations at different magnetic Reynolds numbers. The dynamics of individual particles were investigated making it possible to examine the acceleration mechanism in great detail. It was found that turbulence influences the acceleration in two ways. It enhances the reconnection electric field while producing a stochastic electric field that gives rise to momentum diffusion; and it produces magnetic 'bubbles' and other irregularities that can temporarily trap test particles in the strong reconnection electric field for times comparable to the magnetofluid characteristic time.

  7. On the relationship between quadrupolar magnetic field and collisionless reconnection

    SciTech Connect

    Smets, R. Belmont, G.; Aunai, N.; Boniface, C.

    2014-06-15

    Using hybrid simulations, we investigate the onset of fast reconnection between two cylindrical magnetic shells initially close to each other. This initial state mimics the plasma structure in High Energy Density Plasmas induced by a laser-target interaction and the associated self-generated magnetic field. We clearly observe that the classical quadrupolar structure of the out-of-plane magnetic field appears prior to the reconnection onset. Furthermore, a parametric study reveals that, with a non-coplanar initial magnetic topology, the reconnection onset is delayed and possibly suppressed. The relation between the out-of-plane magnetic field and the out-of-plane electric field is discussed.

  8. Forced magnetic reconnection in Tokamak plasmas

    NASA Astrophysics Data System (ADS)

    Cole, Andrew Joseph

    This dissertation addresses two related problems in the study of forced magnetic reconnection in Tokamak plasmas. First, a recent controversy concerning a model forced magnetic reconnection problem, the Taylor problem, has been resolved. The criticisms of Ishizawa and Tokuda [21] concerning the original analysis of Hahm and Kulsrud [17] are shown to be unwarranted, both analytically and numerically. Second, one possible reason for the discrepancy between recent experimental [29] and previous theoretical [13] scaling of the critical error-field penetration threshold with device parameters is addressed. The theory in question is entirely based on a single-fluid MHD (magnetohydrodynamical) treatment of the plasma. As is well-known, high temperature plasmas are far better modeled using the drift-MHD ordering.[18] Hence we develop a drift-MHD theory of error-field penetration. Although two new drift-MHD plasma response regimes are identified, the overall threshold scaling with device parameters is not altogether different from that predicted by single-fluid MHD.

  9. Reconnection of vorticity lines and magnetic lines

    NASA Technical Reports Server (NTRS)

    Greene, John M.

    1993-01-01

    Magnetic field and fluid vorticity share many features. First, as divergence-free vector fields they are conveniently visualized in terms of their field lines, curves that are everywhere tangent to the field. The lines indicate direction and their density indicates field strength. The question arises of the extent to which the evolution of the fields can be treated in terms of the evolution of their field lines. Newcomb (1958) derived the general conditions on the evolution of vector fields that permit the identification of field lines from one instant to the next. The equations of evolution of the vorticity field and the magnetic field fall within Newcomb's analysis. The dynamics of the flows differ between these two systems, so that geometrically similar phenomena happen in different ways in the two systems. In this paper the geometrical similarities are emphasized. Reconnection will be defined here as evolution in which it is not possible to preserve the global identification of some field lines. There is a close relation between reconnection and the topology of the vector field lines. Nontrivial topology occurs where the field has null points or there are field lines that are closed loops.

  10. Magnetic reconnection in the presence of externally driven and self-generated turbulence

    SciTech Connect

    Karimabadi, H.; Lazarian, A.

    2013-11-15

    Magnetic reconnection is an important process that violates flux freezing and induces change of magnetic field topology in conducting fluids and, as a consequence, converts magnetic field energy into particle energy. It is thought to be operative in laboratory, heliophysical, and astrophysical plasmas. These environments exhibit wide variations in collisionality, ranging from collisionless in the Earth's magnetosphere to highly collisional in molecular clouds. A common feature among these plasmas is, however, the presence of turbulence. We review the present understanding of the effects of turbulence on the reconnection rate, discussing both how strong pre-existing turbulence modifies Sweet-Parker reconnection and how turbulence may develop as a result of reconnection itself. In steady state, reconnection rate is proportional to the aspect ratio of the diffusion region. Thus, two general MHD classes of models for fast reconnection have been proposed, differing on whether they keep the aspect ratio finite by increasing the width due to turbulent broadening or shortening the length of the diffusion layer due to plasmoid instability. One of the consequences of the plasmoid instability model is the possibility that the current sheet thins down to collisionless scales where kinetic effects become dominant. As a result, kinetic effects may be of importance for many astrophysical applications which were considered to be in the realm of MHD. Whether pre-existing turbulence can significantly modify the transition to the kinetic regime is not currently known. Although most studies of turbulent reconnection have been based on MHD, recent advances in kinetic simulations are enabling 3D studies of turbulence and reconnection in the collisionless regime. A summary of these recent works, highlighting similarities and differences with the MHD models of turbulent reconnection, as well as comparison with in situ observations in the magnetosphere and in the solar wind, are presented

  11. Statistical Properties of Magnetic Reconnection in MHD turbulence

    NASA Astrophysics Data System (ADS)

    Servidio, Sergio; Matthaeus, William; Cassak, Paul; Shay, Michael; Dmitruk, Pablo

    2009-11-01

    Magnetic reconnection is an integral part of MHD turbulence[1] in that the fragmentation of magnetic eddies into smaller structures necessarily involves change of magnetic topology. To better understand this relationship, recently the properties of thousands of magnetic reconnection events in moderate Reynolds number MHD turbulence have been studied [1] using 2D spectral method simulations of compressible and incompressible MHD. Reconnection between magnetic islands, different in size and energy, occurs locally and sporadically in time. The associated reconnection rates are distributed over a wide range of values and scale with the geometry of the diffusion region. Matching classical turbulence analysis with the Sweet-Parker theory, the main statistical features of these multi-scale reconnection events are identified. Magnetic reconnection in turbulence can be described through an asymmetric Sweet-Parker model, in which the parameters that control the reconnection rates are determined by turbulence itself. This new and general perspective on reconnection is relevant in space and astrophysical systems, where plasma is generally in a fully nonlinear regime. [1] W. Matthaeus and S. Lamkin, Phys. Fluids, 29, 2513 (1986). [2] S. Servidio et al, PRL, 102, 115003 (2009).

  12. MAVEN Observations of Magnetic Reconnection on the Dayside Martian Magnetosphere

    NASA Astrophysics Data System (ADS)

    DiBraccio, Gina A.; Espley, Jared R.; Connerney, John E. P.; Brain, David A.; Halekas, Jasper S.; Mitchell, David L.; Harada, Yuki; Hara, Takuya

    2015-04-01

    The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission offers a unique opportunity to investigate the complex solar wind-planetary interaction at Mars. The Martian magnetosphere is formed as the interplanetary magnetic field (IMF) drapes around the planet's ionosphere and localized crustal magnetic fields. As the solar wind interacts with this induced magnetosphere, magnetic reconnection can occur at any location where a magnetic shear is present. Reconnection between the IMF and the induced and crustal fields facilitates a direct plasma exchange between the solar wind and the Martian ionosphere. Here we address the occurrence of magnetic reconnection on the dayside magnetosphere of Mars using MAVEN magnetic field and plasma data. When reconnection occurs on the dayside, a non-zero magnetic field component normal to the obstacle, B_N, will result. Using minimum variance analysis, we measure BN by transforming Magnetometer data into boundary-normal coordinates. Selected events are then further examined to identify plasma heating and energization, in the form of Alfvénic outflow jets, using Solar Wind Ion Analyzer measurements. Additionally, the topology of the crustal fields is validated from electron pitch angle distributions provided by the Solar Wind Electron Analyzer. To understand which parameters are responsible for the onset of reconnection, we test the dependency of the dimensionless reconnection rate, calculated from BN measurements, on magnetic field shear angle and plasma beta (the ratio of plasma pressure to magnetic pressure). We assess the global impact of reconnection on Mars' induced magnetosphere by combining analytical models with MAVEN observations to predict the regions where reconnection may occur. Using this approach we examine how IMF orientation and magnetosheath parameters affect reconnection on a global scale. With the aid of analytical models we are able to assess the role of reconnection on a global scale to better understand which

  13. Identifying magnetic reconnection events using the FOTE method

    NASA Astrophysics Data System (ADS)

    Fu, H. S.; Cao, J. B.; Vaivads, A.; Khotyaintsev, Y. V.; Andre, M.; Dunlop, M.; Liu, W. L.; Lu, H. Y.; Huang, S. Y.; Ma, Y. D.; Eriksson, E.

    2016-02-01

    A magnetic reconnection event detected by Cluster is analyzed using three methods: Single-spacecraft Inference based on Flow-reversal Sequence (SIFS), Multispacecraft Inference based on Timing a Structure (MITS), and the First-Order Taylor Expansion (FOTE). Using the SIFS method, we find that the reconnection structure is an X line; while using the MITS and FOTE methods, we find it is a magnetic island (O line). We compare the efficiency and accuracy of these three methods and find that the most efficient and accurate approach to identify a reconnection event is FOTE. In both the guide and nonguide field reconnection regimes, the FOTE method is equally applicable. This study for the first time demonstrates the capability of FOTE in identifying magnetic reconnection events; it would be useful to the forthcoming Magnetospheric Multiscale (MMS) mission.

  14. Enhanced magnetic reconnection in the presence of pressure gradients

    SciTech Connect

    Pueschel, M. J.; Terry, P. W.; Told, D.; Jenko, F.

    2015-06-15

    Magnetic reconnection in the presence of background pressure gradients is studied, with special attention to parallel (compressional) magnetic fluctuations. A process is reported that reconnects fields through coupling of drift-wave-type instabilities with current sheets. Its time scale is set not by the reconnecting field but by inhomogeneities of the background density or temperature. The observed features can be attributed to a pressure-gradient-driven linear instability which interacts with the reconnecting system but is fundamentally different from microtearing. In particular, this mode relies on parallel magnetic fluctuations and the associated drift. For turbulent reconnection, similar or even stronger enhancements are reported. In the solar corona, this yields a critical pressure gradient scale length of about 200 km below which this new process becomes dominant over the tearing instability.

  15. Electron acceleration in three-dimensional magnetic reconnection with a guide field

    SciTech Connect

    Dahlin, J. T. Swisdak, M.; Drake, J. F.

    2015-10-15

    Kinetic simulations of 3D collisionless magnetic reconnection with a guide field show a dramatic enhancement of energetic electron production when compared with 2D systems. In the 2D systems, electrons are trapped in magnetic islands that limit their energy gain, whereas in the 3D systems the filamentation of the current layer leads to a stochastic magnetic field that enables the electrons to access volume-filling acceleration regions. The dominant accelerator of the most energetic electrons is a Fermi-like mechanism associated with reflection of charged particles from contracting field lines.

  16. Electron-scale measurements of magnetic reconnection in space

    NASA Astrophysics Data System (ADS)

    Burch, J. L.; Torbert, R. B.; Phan, T. D.; Chen, L.-J.; Moore, T. E.; Ergun, R. E.; Eastwood, J. P.; Gershman, D. J.; Cassak, P. A.; Argall, M. R.; Wang, S.; Hesse, M.; Pollock, C. J.; Giles, B. L.; Nakamura, R.; Mauk, B. H.; Fuselier, S. A.; Russell, C. T.; Strangeway, R. J.; Drake, J. F.; Shay, M. A.; Khotyaintsev, Yu. V.; Lindqvist, P.-A.; Marklund, G.; Wilder, F. D.; Young, D. T.; Torkar, K.; Goldstein, J.; Dorelli, J. C.; Avanov, L. A.; Oka, M.; Baker, D. N.; Jaynes, A. N.; Goodrich, K. A.; Cohen, I. J.; Turner, D. L.; Fennell, J. F.; Blake, J. B.; Clemmons, J.; Goldman, M.; Newman, D.; Petrinec, S. M.; Trattner, K. J.; Lavraud, B.; Reiff, P. H.; Baumjohann, W.; Magnes, W.; Steller, M.; Lewis, W.; Saito, Y.; Coffey, V.; Chandler, M.

    2016-06-01

    Magnetic reconnection is a fundamental physical process in plasmas whereby stored magnetic energy is converted into heat and kinetic energy of charged particles. Reconnection occurs in many astrophysical plasma environments and in laboratory plasmas. Using measurements with very high time resolution, NASA's Magnetospheric Multiscale (MMS) mission has found direct evidence for electron demagnetization and acceleration at sites along the sunward boundary of Earth's magnetosphere where the interplanetary magnetic field reconnects with the terrestrial magnetic field. We have (i) observed the conversion of magnetic energy to particle energy; (ii) measured the electric field and current, which together cause the dissipation of magnetic energy; and (iii) identified the electron population that carries the current as a result of demagnetization and acceleration within the reconnection diffusion/dissipation region.

  17. Electron-Scale Measurements of Magnetic Reconnection in Space

    NASA Technical Reports Server (NTRS)

    Burch, J. L.; Torbert, R. B.; Phan, T. D.; Chen, L.-J.; Moore, T. E.; Ergun, R. E.; Eastwood, J. P.; Gershman, D. J.; Cassak, P. A.; Argall, M. R.; Wang, S.; Hesse, M.; Pollock, C. J.; Jiles, B. L.; Nakamura, R.; Mauk, B. H.; Fuselier, S. A.; Russell, C. T.; Strangeway, R. J.; Drake, J. F.; Shay, M. A.; Khotyaintsev, Yu. V.; Lindqvist, P.-A.; Marklund, G.; Wilder, F. D.

    2016-01-01

    Magnetic reconnection is a fundamental physical process in plasmas whereby stored magnetic energy is converted into heat and kinetic energy of charged particles. Reconnection occurs in many astrophysical plasma environments and in laboratory plasmas. Using measurements with very high time resolution, NASA's Magnetospheric Multiscale (MMS) mission has found direct evidence for electron demagnetization and acceleration at sites along the sunward boundary of Earth's magnetosphere where the interplanetary magnetic field reconnects with the terrestrial magnetic field. We have (i) observed the conversion of magnetic energy to particle energy; (ii) measured the electric field and current, which together cause the dissipation of magnetic energy; and (iii) identified the electron population that carries the current as a result of demagnetization and acceleration within the reconnection diffusion/dissipation region.

  18. Anisotropic Electron Tail Generation during Tearing Mode Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    DuBois, Ami M.; Almagri, Abdulgader F.; Anderson, Jay K.; Den Hartog, Daniel J.; Lee, John David; Sarff, John S.

    2017-02-01

    The first experimental evidence of anisotropic electron energization during magnetic reconnection that favors a direction perpendicular to the guide magnetic field in a toroidal, magnetically confined plasma is reported in this Letter. Magnetic reconnection plays an important role in particle heating, energization, and transport in space and laboratory plasmas. In toroidal devices like the Madison Symmetric Torus, discrete magnetic reconnection events release large amounts of energy from the equilibrium magnetic field. Fast x-ray measurements imply a non-Maxwellian, anisotropic energetic electron tail is formed at the time of reconnection. The tail is well described by a power-law energy dependence. The expected bremsstrahlung from an electron distribution with an anisotropic energetic tail (v⊥>v∥ ) spatially localized in the core region is consistent with x-ray emission measurements. A turbulent process related to tearing fluctuations is the most likely cause for the energetic electron tail formation.

  19. Plasma Compression in Magnetic Reconnection Regions in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Provornikova, E.; Laming, J. M.; Lukin, V. S.

    2016-07-01

    It has been proposed that particles bouncing between magnetized flows converging in a reconnection region can be accelerated by the first-order Fermi mechanism. Analytical considerations of this mechanism have shown that the spectral index of accelerated particles is related to the total plasma compression within the reconnection region, similarly to the case of the diffusive shock acceleration mechanism. As a first step to investigate the efficiency of Fermi acceleration in reconnection regions in producing hard energy spectra of particles in the solar corona, we explore the degree of plasma compression that can be achieved at reconnection sites. In particular, we aim to determine the conditions for the strong compressions to form. Using a two-dimensional resistive MHD numerical model, we consider a set of magnetic field configurations where magnetic reconnection can occur, including a Harris current sheet, a force-free current sheet, and two merging flux ropes. Plasma parameters are taken to be characteristic of the solar corona. Numerical simulations show that strong plasma compressions (≥4) in the reconnection regions can form when the plasma heating due to reconnection is efficiently removed by fast thermal conduction or the radiative cooling process. The radiative cooling process that is negligible in the typical 1 MK corona can play an important role in the low corona/transition region. It is found that plasma compression is expected to be strongest in low-beta plasma β ˜ 0.01-0.07 at reconnection magnetic nulls.

  20. Conceptual design of the three-dimensional magnetic field configuration relevant to the magnetopause reconnection in the SPERF

    NASA Astrophysics Data System (ADS)

    Aohua, MAO; Yang, REN; Hantao, JI; Peng, E.; Ke, HAN; Zhibin, WANG; Qingmei, XIAO; Liyi, LI

    2017-03-01

    A new ground-based experimental device, the Space Plasma Environment Research Facility (SPERF), is being designed at Harbin Institute of Technology in China, with Asymmetric REconnection eXperiment-3 Dimensional (AREX-3D) as one of the experimental components to study the asymmetric reconnection dynamics relevant to the interaction between the interplanetary and magnetospheric plasmas. The asymmetry in the designed magnetic reconnection process not only refers to the distinct plasma parameters designed for the two upstream regions across the current sheet, but also refers to the inhomogeneity in the direction along the current sheet resulting from the designed 3D magnetic field geometry. These two asymmetries are fundamental features of the reconnection process at the Earth’s magnetopause. In experiment, the reconnection process is driven by a set of flux cores through coil-current-ramp-up from the ‘magnetosheath-side’ to interact with a dipole magnetic field generated by the Dipole Research EXperiment (DREX) coil on the ‘magnetosphere-side’. The AREX-3D will be able to investigate a range of important reconnection issues in 3D magnetic field geometry that is relevant to the Earth’s magnetopause. A wide range of plasma parameters can be achieved through inductive plasma generation with flux cores on the ‘magnetosheath-side’ and electron cyclotron resonance (ECR) with microwave sources on the ‘magnetosphere-side’, e.g. high (low) plasma density at experimental magnetosheath (dipole) side. Different reconnection regimes and geometries can be produced by adjusting plasma parameters and coil setups as well as coil current waveforms. The three-dimensional magnetic field configurations in the SPERF relevant to the dayside magnetopause reconnection are discussed in detail.

  1. Measuring Properties of Magnetic Reconnection in Nonlinear Resistive and Two-Fluid Toroidal Simulations of Sawteeth

    NASA Astrophysics Data System (ADS)

    Beidler, Matthew; Cassak, Paul; Jardin, Stephen; Ferraro, Nathaniel

    2015-11-01

    The sawtooth crash in tokamaks limits the core temperature, harms confinement, and seeds disruptions. A predictive capability of its ramifications has been elusive. Extended-MHD physics is needed to properly analyze the magnetic reconnection that occurs during the crash phase, but it has only recently been integrated into codes using a toroidal geometry. In this study, we employ the three-dimensional toroidal, extended-MHD code M3D-C1 to study reconnection during the sawtooth crash. We study the nonlinear evolution of a test equilibrium in a non-reduced field representation for resistive-MHD and the two-fluid model. We find that the toroidal mode growth rates for the two-fluid reconnection process exhibit a nonlinear acceleration and greatly exceed that of a similar resistive MHD model, more closely in line with experimental results. Furthermore, by sampling the two-fluid simulation data in the plane perpendicular to the helical (m,n) =(1,1) mode, we present the first observation of the quadrupole out-of-plane magnetic field appearing during sawtooth reconnection with the Hall term. We also explore how reconnection as viewed in the helically perpendicular plane varies toroidally, which affects the symmetry of the reconnection geometry and the local diamagnetic effects.

  2. 3-D magnetic field calculations for wiggglers using MAGNUS-3D

    SciTech Connect

    Pissanetzky, S.; Tompkins, P.

    1988-01-01

    The recent but steady trend toward increased magnetic and geometric complexity in the design of wigglers and undulators, of which tapered wigglers, hybrid structures, laced electromagnetic wigglers, magnetic cladding, twisters and magic structures are examples, has caused a need for reliable 3-D computer models and a better understanding of the behavior of magnetic systems in three dimensions. The capabilities of the MAGNUS-3D Group of Programs are ideally suited to solve this class of problems and provide insight into 3-D effects. MAGNUS-3D can solve any problem of Magnetostatics involving permanent magnets, linear or nonlinear ferromagnetic materials and electric conductors of any shape in space. The magnetic properties of permanent magnets are described by the complete nonlinear demagnetization curve as provided by the manufacturer, or, at the user's choice, by a simpler approximation involving the coercive force, the residual induction and the direction of magnetization. The ferromagnetic materials are described by a magnetization table and an accurate interpolation relation. An internal library with properties of common industrial steels is available. The conductors are independent of the mesh and are described in terms of conductor elements from an internal library.

  3. Ion Bernstein waves in a magnetic reconnection region

    NASA Astrophysics Data System (ADS)

    Narita, Y.; Nakamura, R.; Baumjohann, W.; Glassmeier, K. H.; Motschmann, U.; Comisel, H.

    2015-12-01

    Four-dimensional energy spectra and a diagram for dispersion relations are determined for the first time in a magnetic reconnection region in the magnetotail using the four-point magnetometer data from the Cluster mission on a spatial scale of 200 km, about 0.1 ion inertial lengths. The energy spectra are anisotropic with an extension in the perpendicular direction and axially asymmetric with respect to the mean magnetic field. The dispersion diagram for the waves in the quasi-perpendicular directions in the plasma rest frame is in reasonably good agreement with the ion Bernstein waves particularly at the second harmonic of the proton gyro-frequency. Perpendicular-propagating ion Bernstein waves likely exist in an outflow region of magnetic reconnection. We discuss the causality of the Bernstein waves with magnetic reconnection with an estimate of the anomalous resistivity, and propose an observationally-driven model of turbulent magnetic reconnection.

  4. MESSENGER observations of magnetic reconnection in Mercury's magnetosphere.

    PubMed

    Slavin, James A; Acuña, Mario H; Anderson, Brian J; Baker, Daniel N; Benna, Mehdi; Boardsen, Scott A; Gloeckler, George; Gold, Robert E; Ho, George C; Korth, Haje; Krimigis, Stamatios M; McNutt, Ralph L; Raines, Jim M; Sarantos, Menelaos; Schriver, David; Solomon, Sean C; Trávnícek, Pavel; Zurbuchen, Thomas H

    2009-05-01

    Solar wind energy transfer to planetary magnetospheres and ionospheres is controlled by magnetic reconnection, a process that determines the degree of connectivity between the interplanetary magnetic field (IMF) and a planet's magnetic field. During MESSENGER's second flyby of Mercury, a steady southward IMF was observed and the magnetopause was threaded by a strong magnetic field, indicating a reconnection rate ~10 times that typical at Earth. Moreover, a large flux transfer event was observed in the magnetosheath, and a plasmoid and multiple traveling compression regions were observed in Mercury's magnetotail, all products of reconnection. These observations indicate that Mercury's magnetosphere is much more responsive to IMF direction and dominated by the effects of reconnection than that of Earth or the other magnetized planets.

  5. Local properties of magnetic reconnection in nonlinear resistive- and extended-magnetohydrodynamic toroidal simulations of the sawtooth crash

    DOE PAGES

    Beidler, M. T.; Cassak, P. A.; Jardin, S. C.; ...

    2016-12-15

    We diagnose local properties of magnetic reconnection during a sawtooth crash employing the three-dimensional toroidal, extended-magnetohydrodynamic (MHD) code M3D-C1. To do so, we sample simulation data in the plane in which reconnection occurs, the plane perpendicular to the helical (m, n) = (1, 1) mode at the q = 1 surface, where m and n are the poloidal and toroidal mode numbers and q is the safety factor. We study the nonlinear evolution of a particular test equilibrium in a non-reduced field representation using both resistive-MHD and extended-MHD models. We find growth rates for the extended-MHD reconnection process exhibit amore » nonlinear acceleration and greatly exceed that of the resistive-MHD model, as is expected from previous experimental, theoretical, and computational work. We compare the properties of reconnection in the two simulations, revealing the reconnecting current sheets are locally different in the two models and we present the first observation of the quadrupole out-of-plane Hall magnetic field that appears during extended-MHD reconnection in a 3D toroidal simulation (but not in resistive-MHD). We also explore the dependence on toroidal angle of the properties of reconnection as viewed in the plane perpendicular to the helical magnetic field, finding qualitative and quantitative effects due to changes in the symmetry of the reconnection process. Furthermore, this study is potentially important for a wide range of magnetically confined fusion applications, from confirming simulations with extended-MHD effects are sufficiently resolved to describe reconnection, to quantifying local reconnection rates for purposes of understanding and predicting transport, not only at the q = 1 rational surface for sawteeth, but also at higher order rational surfaces that play a role in disruptions and edge-confinement degradation.« less

  6. Local properties of magnetic reconnection in nonlinear resistive- and extended-magnetohydrodynamic toroidal simulations of the sawtooth crash

    SciTech Connect

    Beidler, M. T.; Cassak, P. A.; Jardin, S. C.; Ferraro, N. M.

    2016-12-15

    We diagnose local properties of magnetic reconnection during a sawtooth crash employing the three-dimensional toroidal, extended-magnetohydrodynamic (MHD) code M3D-C1. To do so, we sample simulation data in the plane in which reconnection occurs, the plane perpendicular to the helical (m, n) = (1, 1) mode at the q = 1 surface, where m and n are the poloidal and toroidal mode numbers and q is the safety factor. We study the nonlinear evolution of a particular test equilibrium in a non-reduced field representation using both resistive-MHD and extended-MHD models. We find growth rates for the extended-MHD reconnection process exhibit a nonlinear acceleration and greatly exceed that of the resistive-MHD model, as is expected from previous experimental, theoretical, and computational work. We compare the properties of reconnection in the two simulations, revealing the reconnecting current sheets are locally different in the two models and we present the first observation of the quadrupole out-of-plane Hall magnetic field that appears during extended-MHD reconnection in a 3D toroidal simulation (but not in resistive-MHD). We also explore the dependence on toroidal angle of the properties of reconnection as viewed in the plane perpendicular to the helical magnetic field, finding qualitative and quantitative effects due to changes in the symmetry of the reconnection process. Furthermore, this study is potentially important for a wide range of magnetically confined fusion applications, from confirming simulations with extended-MHD effects are sufficiently resolved to describe reconnection, to quantifying local reconnection rates for purposes of understanding and predicting transport, not only at the q = 1 rational surface for sawteeth, but also at higher order rational surfaces that play a role in disruptions and edge-confinement degradation.

  7. Local properties of magnetic reconnection in nonlinear resistive- and extended-magnetohydrodynamic toroidal simulations of the sawtooth crash

    NASA Astrophysics Data System (ADS)

    Beidler, M. T.; Cassak, P. A.; Jardin, S. C.; Ferraro, N. M.

    2017-02-01

    We diagnose local properties of magnetic reconnection during a sawtooth crash employing the three-dimensional toroidal, extended-magnetohydrodynamic (MHD) code M3D-C1. To do so, we sample simulation data in the plane in which reconnection occurs, the plane perpendicular to the helical (m,n)=(1,1) mode at the q = 1 surface, where m and n are the poloidal and toroidal mode numbers and q is the safety factor. We study the nonlinear evolution of a particular test equilibrium in a non-reduced field representation using both resistive-MHD and extended-MHD models. We find growth rates for the extended-MHD reconnection process exhibit a nonlinear acceleration and greatly exceed that of the resistive-MHD model, as is expected from previous experimental, theoretical, and computational work. We compare the properties of reconnection in the two simulations, revealing the reconnecting current sheets are locally different in the two models and we present the first observation of the quadrupole out-of-plane Hall magnetic field that appears during extended-MHD reconnection in a 3D toroidal simulation (but not in resistive-MHD). We also explore the dependence on toroidal angle of the properties of reconnection as viewed in the plane perpendicular to the helical magnetic field, finding qualitative and quantitative effects due to changes in the symmetry of the reconnection process. This study is potentially important for a wide range of magnetically confined fusion applications, from confirming simulations with extended-MHD effects are sufficiently resolved to describe reconnection, to quantifying local reconnection rates for purposes of understanding and predicting transport, not only at the q = 1 rational surface for sawteeth, but also at higher order rational surfaces that play a role in disruptions and edge-confinement degradation.

  8. Implications of RHESSI Flare Observations for Magnetic Reconnection Models

    NASA Technical Reports Server (NTRS)

    Holman, Gordon D.; Sui, Linhui; Dennis, Brian R.

    2004-01-01

    The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observations of the 2002 April 15 solar flare and related flares provide compelling evidence for the formation of a large-scale, reconnecting current sheet in at least some flares. We describe the observed evolution of the April 15 flare in terms of magnetic reconnection models. We argue that the flare most likely evolved through magnetic geometries associated with super-slow reconnection (early rise phase), fast reconnection (impulsive phase), and slow reconnection (gradual phase). We also provide evidence for X-ray brightenings within the evolving current sheet, possibly induced by the tearing mode instability. This work was supported in part by the RHESSI Program and NASA's Sun-Earth Connection Program. This work would not have been possible without the dedicated efforts of the entire RHESSI team.

  9. Efficiency of the FOTE method in identifying magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Fu, Huishan; Cao, Jinbin; Vaivads, Andris; Khotyaintsev, Yuri; Andre, Mats; Dunlop, Malcolm; Liu, Wenlong; Lu, Haoyu; Huang, Shiyong; Ma, Yuduan; Eriksson, Elin

    2016-04-01

    A magnetic reconnection event detected by Cluster is analyzed using three methods: Single-spacecraft Inference based on Flow-reversal Sequence (SIFS), Multi-spacecraft Inference based on Timing a Structure (MITS), and the First-Order Taylor Expansion (FOTE). Using the SIFS method, we find that the reconnection structure is an X-line; while using the MITS and FOTE methods, we find it is a magnetic island (O-line). We compare the efficiency and accuracy of these three methods, and find that the most efficient and accurate approach to identify a reconnection event is FOTE. Even in the guide-field reconnection, the FOTE method still works. This study for the first time demonstrates the capability of FOTE in identifying guide- and non-guide-field reconnection. It would be useful to the NASA MMS mission.

  10. Small-Scale Magnetic Reconnection at Equatorial Coronal Hole Boundaries

    NASA Astrophysics Data System (ADS)

    Lamb, Derek; DeForest, C. E.

    2011-05-01

    Coronal holes have long been known to be the source of the fast solar wind at both high and low latitudes. The equatorial extensions of polar coronal holes have long been assumed to have substantial magnetic reconnection at their boundaries, because they rotate more rigidly than the underlying photosphere. However, evidence for this reconnection has been sparse until very recently. We present some evidence that reconnection due to the evolution of small-scale magnetic fields may be sufficient to drive coronal hole boundary evolution. We hypothesize that a bias in the direction of that reconnection is sufficient to give equatorial coronal holes their rigid rotation. We discuss the prospects for investigating this using FLUX, a reconnection-controlled coronal MHD simulation framework. This work was funded by the NASA SHP-GI program.

  11. Cross-Scale Observational Signatures of Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Savage, Sabrina; Malaspina, David

    2014-01-01

    Magnetic reconnection is a significant mechanism for energy release across many astrophysical applications. In the solar atmosphere, reconnection is considered a primary contributor of flare evolution and coronal heating. Directly observing reconnection occurring in the solar atmosphere, however, is not trivial considering that the scale size of the diffusion region is magnitudes smaller than the observational capabilities of current instrumentation, and coronal magnetic field measurements are not currently sufficient to capture the process. Meanwhile, reconnection occurring in the Earth's magnetosphere transfers energy from the solar wind through a comparable process, although on vastly different scales. Magnetospheric measurements are made in situ rather than remotely; ergo, comparison of observations between the two regimes allows for potentially significant insight into reconnection as a stochastic and possibly turbulent process. We will present a set of observations from long-duration solar events and compare them to in situ measurements from the magnetosphere.

  12. Scaling of asymmetric magnetic reconnection: General theory and collisional simulations

    SciTech Connect

    Cassak, P. A.; Shay, M. A.

    2007-10-15

    A Sweet-Parker-type scaling analysis for asymmetric antiparallel reconnection (in which the reconnecting magnetic field strengths and plasma densities are different on opposite sides of the dissipation region) is performed. Scaling laws for the reconnection rate, outflow speed, the density of the outflow, and the structure of the dissipation region are derived from first principles. These results are independent of the dissipation mechanism. It is shown that a generic feature of asymmetric reconnection is that the X-line and stagnation point are not colocated, leading to a bulk flow of plasma across the X-line. The scaling laws are verified using two-dimensional resistive magnetohydrodynamics numerical simulations for the special case of asymmetric magnetic fields with symmetric density. Observational signatures and applications to reconnection in the magnetosphere are discussed.

  13. Cross-scale Observational Signatures of Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Savage, S. L.; Malaspina, D.

    2014-12-01

    Magnetic reconnection is a significant mechanism for energy release across many astrophysical applications. In the solar atmosphere, reconnection is considered a primary contributor of flare evolution and coronal heating. Directly observing reconnection occurring in the solar atmosphere, however, is not trivial considering that the scale size of the diffusion region is magnitudes smaller than the observational capabilities of current instrumentation, and coronal magnetic field measurements are not currently sufficient to capture the process. Meanwhile, reconnection occurring in the Earth's magnetosphere transfers energy from the solar wind through a comparable process, although on vastly different scales. Magnetospheric measurements are made in situ rather than remotely; ergo, comparison of observations between the two regimes allows for potentially significant insight into reconnection as a stochastic and possibly turbulent process. We will present a set of observations from long-duration solar events and compare them to in situ measurements from the magnetosphere.

  14. Dissipation in magnetic reconnection with a guide magnetic field

    SciTech Connect

    Hesse, Michael

    2006-12-15

    A combination of numerical simulation results and analytical theory is applied to the problem of magnetic reconnection in a guide magnetic field. An investigation of electron distribution functions within the electron diffusion region leads to a picture of mixing of particles with different acceleration histories on electron Larmor scales. Based on an apparent average loss of accelerated particles by field-aligned and ExB transport, it is proposed that the role of the reconnection electric field is to replenish this loss by acceleration of particles that enter the electron diffusion region. Analytic theory is employed to verify this model, and an equation is derived, which balances the average electric field force density by a diffusion term applied to the electron momentum density. The diffusion coefficient contains explicitly the electron Larmor spatial scale and a poloidal transport time scale.

  15. Connection between Magnetic Topology, Mixing and the Reconnection Rate in Asymmetric Layers

    NASA Astrophysics Data System (ADS)

    Daughton, W. S.; Nakamura, T.; Roytershteyn, V.; Karimabadi, H.; Hesse, M.; Loring, B.

    2013-12-01

    The entry of solar wind plasma into the magnetosphere occurs in thin boundary layers, which are typically asymmetric and have large magnetic and/or velocity shear across them. Magnetic reconnection is the dominant entry mechanism, but in regions with strong nearly perpendicular velocity shear, the Kelvin-Helmholtz instability dominates and can lead to vortex induced reconnection [1]. In both of these limits, recent fully kinetic simulations feature the development of 3D turbulence, characterized by electron-scale current sheets and interacting magnetic flux ropes. The 3D magnetic field, characterized by the Lyapunov exponent, reveals a chaotic structure within the reconnection layer in which neighboring field lines undergo rapid separation. In the presence of this complex 3D dynamics, defining and accurately computing the time evolving reconnection rate is a major challenge. One of the leading theoretical ideas [2] for computing the rate is based on integrating the parallel electric field. However, applying this approach is complicated by the chaotic magnetic field, which can lead to different answers on closely neighboring field lines. Furthermore, it is difficult to cleanly identify a transition back into an ideal region where the integration can be terminated. Here we explore a new approach that exploits the connection between the magnetic topology and the mixing of electrons that originate from separate sides of the asymmetric current layer. This idea is motivated by a clear correlation between the Lyapunov exponent for the magnetic field and the boundaries between mixed and unmixed regions. This correlation implies that mixing is a good proxy for quickly identifying 3D surfaces separating different topologies, and thus accurately measuring the time changing flux between topologies. The 3D reconnection rate obtained from this approach is contrasted with corresponding 2D simulations in the limits of both weak and strong velocity shear. [1] T.K.M Nakamura et al

  16. Simulation and Analysis of Magnetic Reconnection in an Experimental Geometry

    NASA Astrophysics Data System (ADS)

    Murphy, Nicholas Arnold; Sovinec, C. R.; Cassak, P. A.

    2009-01-01

    The process of magnetic reconnection is important in space, laboratory, and astrophysical plasmas. The Magnetic Reconnection Experiment (MRX) is designed to study controlled reconnection in collisional and marginally collisionless plasmas (Yamada et al. 1997). We present single and two-fluid simulations of MRX using the NIMROD extended MHD code (Sovinec et al. 2004). These simulations highlight the interrelationship between the small-scale physics of the reconnection layer and the global magnetic field geometry. The communication between small and large scales is dominated by pressure gradients that result from a pileup of reconnection outflow. Toroidicity leads to asymmetry in either the inflow direction or the outflow direction, depending on the experimental mode of operation. To explain effects observed during reconnection with asymmetry in the outflow direction, we present an extension of the Sweet-Parker model that takes into account asymmetric downstream pressure. This model is applicable to reconnection in coronal mass ejections, the Earth's magnetotail, and in circumstellar disks present in hot star winds. This research is supported by the NSF Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas.

  17. Electron acceleration in collisionless shocks and magnetic reconnection by laser-produced plasma ablation

    NASA Astrophysics Data System (ADS)

    Park, Jaehong; Spitkovksy, Anatoly; Fox, Will; Bhattacharjee, Amitava

    2016-10-01

    We perform particle-in-cell simulations of collisionless shocks and magnetic reconnection generated by ablated plasma expanding into a magnetized background plasma. We find: (1) The simulated proton radiography produces different morphology of the shock structure depending on the orientation of the magnetic field and can be used to identify a shock in the experiment. Electrons are accelerated by the whistler waves generated at oblique sites of the shock. (2) Forced collisionless magnetic reconnection is induced when the expanding plumes carry opposite magnetic polarities and interact with a background plasma. Electrons are accelerated at the reconnection X line and reveal a power-law distribution as the plasma beta is lowered, β = 0.08 . As the plasma beta is increased, β = 0.32 , the 1st order Fermi mechanism against the two plasma plumes contributes to the electron acceleration as well as the X line acceleration. Using 3-D simulations, we also explore the effect of 3-D instabilities (Weibel instability or drift-kink) on particle acceleration and magnetic field annihilation between the colliding magnetized plumes

  18. General Method for Describing Three-Dimensional Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Titov, Viacheslav; Forbes, Terry; Priest, Eric; Mikic, Zoran; Linker, Jon

    2009-11-01

    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.

  19. ASYMMETRIC MAGNETIC RECONNECTION IN WEAKLY IONIZED CHROMOSPHERIC PLASMAS

    SciTech Connect

    Murphy, Nicholas A.; Lukin, Vyacheslav S.

    2015-06-01

    Realistic models of magnetic reconnection in the solar chromosphere must take into account that the plasma is partially ionized and that plasma conditions within any two magnetic flux bundles undergoing reconnection may not be the same. Asymmetric reconnection in the chromosphere may occur when newly emerged flux interacts with pre-existing, overlying flux. We present 2.5D simulations of asymmetric reconnection in weakly ionized, reacting plasmas where the magnetic field strengths, ion and neutral densities, and temperatures are different in each upstream region. The plasma and neutral components are evolved separately to allow non-equilibrium ionization. As in previous simulations of chromospheric reconnection, the current sheet thins to the scale of the neutral–ion mean free path and the ion and neutral outflows are strongly coupled. However, the ion and neutral inflows are asymmetrically decoupled. In cases with magnetic asymmetry, a net flow of neutrals through the current sheet from the weak-field (high-density) upstream region into the strong-field upstream region results from a neutral pressure gradient. Consequently, neutrals dragged along with the outflow are more likely to originate from the weak-field region. The Hall effect leads to the development of a characteristic quadrupole magnetic field modified by asymmetry, but the X-point geometry expected during Hall reconnection does not occur. All simulations show the development of plasmoids after an initial laminar phase.

  20. TWO-FLUID MAGNETOHYDRODYNAMIC SIMULATIONS OF RELATIVISTIC MAGNETIC RECONNECTION

    SciTech Connect

    Zenitani, Seiji; Hesse, Michael; Klimas, Alex

    2009-05-10

    We investigate the large-scale evolution of a relativistic magnetic reconnection in an electron-positron pair plasma by a relativistic two-fluid magnetohydrodynamic (MHD) code. We introduce an interspecies friction force as an effective resistivity to dissipate magnetic fields. We demonstrate that magnetic reconnection successfully occurs in our two-fluid system, and that it involves Petschek-type bifurcated current layers in a later stage. We further observe a quasi-steady evolution thanks to an open boundary condition, and find that the Petschek-type structure is stable over the long time period. Simulation results and theoretical analyses exhibit that the Petschek outflow channel becomes narrower when the reconnection inflow contains more magnetic energy, as previously claimed. Meanwhile, we find that the reconnection rate goes up to {approx}1 in extreme cases, which is faster than previously thought. The role of the resistivity, implications for reconnection models in the magnetically dominated limit, and relevance to kinetic reconnection works are discussed.

  1. Magnetic reconnection in numerical simulations of the Bastille day flare

    NASA Astrophysics Data System (ADS)

    Vincent, A. P.; Charbonneau, P.

    2011-12-01

    If neither waves nor adiabatic heating due to compression are taken into account, coronal heating may be obtained in numerical simulations from current dissipation inside solar flares. To increase Joule heating locally we used a model for hyper resistivity (Klimas et al., 2004: Journal of Geophysical Research, 109, 2218-2231). Here the change in resistivity is due to small scale (less than 1Mm in our simulations) current density fluctuations. Whenever the current exceeds a cut-off value, magnetic resistivity jumps sharply to reach a maximum locally thus increasing magnetic gradients at the border of the flare. In this way, not only the current increases but also the maximum is slowly displaced and simulations of the full set of 3-D MHD equations show a progression westward as can be seen in SOHO-EIT images of the ''slinky''. In our simulations of the Bastille day flare, most of the reconnection events take place just above the transition and mostly follow the neutral line but it is Spitzer thermal diffusivity together with radiative cooling that illuminates magnetic arcades in a way similar to what can be seen in extreme ultra-violet animations of the slinky.

  2. The Role of Magnetic Reconnection in Solar Activity

    NASA Technical Reports Server (NTRS)

    Antiochos, Spiro; DeVore, C. R.

    2008-01-01

    The central challenge in solar/heliospheric physics is to understand how the emergence and transport of magnetic flux at the photosphere drives the structure and dynamics that we observe in the corona and heliosphere. This presentation focuses on the role of magnetic reconnection in determining solar/heliospheric activity. We demonstrate that two generic properties of the photospheric magnetic and velocity fields are responsible for the ubiquitous reconnection in the corona. First, the photospheric velocities are complex, which leads to the injection of energy and helicity into the coronal magnetic fields and to the efficient, formation of small-scale structure. Second, the flux distribution at the photosphere is multi-polar, which implies that topological discontinuities and, consequently, current sheets, must be present in the coronal magnetic field. We: present numerical simulations showing that photospherically-driven reconnection is responsible for the heating and dynamics of coronal plasma, and for the topology of the coronal/heliospheric magnetic field.

  3. Conversion of magnetic energy in the magnetic reconnection layer of a laboratory plasma.

    PubMed

    Yamada, Masaaki; Yoo, Jongsoo; Jara-Almonte, Jonathan; Ji, Hantao; Kulsrud, Russell M; Myers, Clayton E

    2014-09-10

    Magnetic reconnection, in which magnetic field lines break and reconnect to change their topology, occurs throughout the universe. The essential feature of reconnection is that it energizes plasma particles by converting magnetic energy. Despite the long history of reconnection research, how this energy conversion occurs remains a major unresolved problem in plasma physics. Here we report that the energy conversion in a laboratory reconnection layer occurs in a much larger region than previously considered. The mechanisms for energizing plasma particles in the reconnection layer are identified, and a quantitative inventory of the converted energy is presented for the first time in a well-defined reconnection layer; 50% of the magnetic energy is converted to particle energy, 2/3 of which transferred to ions and 1/3 to electrons. Our results are compared with simulations and space measurements, for a key step towards resolving one of the most important problems in plasma physics.

  4. Conversion of magnetic energy in the magnetic reconnection layer of a laboratory plasma

    SciTech Connect

    Yamada, Masaaki; Yoo, Jongsoo; Jara-Almonte, Jonathan; Ji, Hantao; Kulsrud, Russell M.; Myers, Clayton E.

    2014-09-10

    Magnetic reconnection, in which magnetic field lines break and reconnect to change their topology, occurs throughout the universe. The essential feature of reconnection is that it energizes plasma particles by converting magnetic energy. Despite the long history of reconnection research, how this energy conversion occurs remains a major unresolved problem in plasma physics. Here we report that the energy conversion in a laboratory reconnection layer occurs in a much larger region than previously considered. The mechanisms for energizing plasma particles in the reconnection layer are identified, and a quantitative inventory of the converted energy is presented for the first time in a well defined reconnection layer; 50% of the magnetic energy is converted to particle energy, 2/3 of which transferred to ions and 1/3 to electrons. Our results are compared with simulations and space measurements, for a key step toward resolving one of the most important problems in plasma physics.

  5. Conversion of magnetic energy in the magnetic reconnection layer of a laboratory plasma

    DOE PAGES

    Yamada, Masaaki; Yoo, Jongsoo; Jara-Almonte, Jonathan; ...

    2014-09-10

    Magnetic reconnection, in which magnetic field lines break and reconnect to change their topology, occurs throughout the universe. The essential feature of reconnection is that it energizes plasma particles by converting magnetic energy. Despite the long history of reconnection research, how this energy conversion occurs remains a major unresolved problem in plasma physics. Here we report that the energy conversion in a laboratory reconnection layer occurs in a much larger region than previously considered. The mechanisms for energizing plasma particles in the reconnection layer are identified, and a quantitative inventory of the converted energy is presented for the first timemore » in a well defined reconnection layer; 50% of the magnetic energy is converted to particle energy, 2/3 of which transferred to ions and 1/3 to electrons. Our results are compared with simulations and space measurements, for a key step toward resolving one of the most important problems in plasma physics.« less

  6. A new magnetic reconnection paradigm: Stochastic plasmoid chains

    NASA Astrophysics Data System (ADS)

    Loureiro, Nuno

    2015-11-01

    Recent analytical and numerical research in magnetic reconnection has converged on the notion that reconnection sites (current sheets) are unstable to the formation of multiple magnetic islands (plasmoids), provided that the system is sufficiently large (or, in other words, that the Lundquist number of the plasma is high). Nonlinearly, plasmoids come to define the reconnection geometry. Their nonlinear dynamics is rather complex and best thought of as new form of turbulence whose properties are determined by continuous plasmoid formation and their subsequent ejection from the sheet, as well as the interaction (coalescence) between plasmoids of different sizes. The existence of these stochastic plasmoid chains has powerful implications for several aspects of the reconnection process, from determining the reconnection rate to the details and efficiency of the energy conversion and dissipation. In addition, the plasmoid instability may also directly bear on the little understood problem of the reconnection trigger, or onset, i.e., the abrupt transition from a slow stage of energy accumulation to a fast (explosive) stage of energy release. This talk will first provide a brief overview of these recent developments in the reconnection field. I will then discuss recent work addressing the onset problem in the context of a forming current sheet which becomes progressively more unstable to the plasmoid instability. Work partially supported by Fundação para a Ciência e Tecnologia via Grants UID/FIS/50010/2013 and IF/00530/2013.

  7. Magnetic reconnection in turbulence: from Cluster to MMS and beyond

    NASA Astrophysics Data System (ADS)

    Retino, Alessandro; Sundkvist, David; Matthaeus, William; Vaivads, Andris; Califano, Francesco; Khotyaintsev, Yuri; LeContel, Olivier; Sorriso-valvo, Luca; Chasapis, Alexandros; Lavraud, Benoit; Valentini, Francesco; Servidio, Sergio; Rossi, Claudia; Camporeale, Enrico

    2016-07-01

    Magnetic reconnection is a universal energy dissipation mechanism occurring in space and astrophysical magnetized plasmas. Such plasmas are frequently in a turbulent state, raising the fundamental question of the role reconnection for energy dissipation in turbulence. Understanding reconnection in turbulence is of pivotal importance to explain phenomena such as particle acceleration in stellar atmospheres, the heating of interplanetary and interstellar media as well as particle energization in accretion disks and cosmic rays acceleration. Many numerical simulations support the role of reconnection for efficiently dissipate turbulent energy and heat and accelerated particles. Such simulations indicate that reconnection occurs in small-scale current sheets spontaneously forming within the turbulence. Yet experimental evidence of reconnection in turbulence has been provided only recently thanks to high resolution in situ measurements by modern spacecraft. Here we present ESA/Cluster and more recent NASA/MMS observations in near-Earth space showing evidence of reconnection in turbulence and its importance for energy dissipation and particle energization. We also discuss implications for upcoming spacecraft missions such as Solar Orbiter and Solar Probe Plus, as well as for missions currently under study pahse such as ESA/THOR.

  8. Plasma dynamics and heating/acceleration during driven magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Cheng, C. Z.; Inoue, Shizuo; Ono, Yasushi; Horiuchi, Ritoku

    2015-11-01

    Highlights of the plasma dynamics and energization during driven anti-parallel magnetic reconnection are presented. The MHD condition breaks down in the entire reconnection layer (the reconnection current layer, the separatrix region and the whole downstream), and the plasma dynamics is significantly different from the results of the Hall-MHD model. In particular, we explain (1) how electron and ion dynamics decouple and how the charge separation and electrostatic electric field are produced in the magnetic field reversal region (reconnection current layer and outflow exhaust) and around the separatrix regions, (2) how electrons and ions gain energy in the reconnection current layer, (3) why the electron outflow velocity in the reconnection exhaust reaches super-Alfvenic speed and the ion outflow velocity reaches Alfvenic speed and how the parallel electric field is produced, (4) how electrons are accelerated by the parallel electric field around the separatrix region, and (5) how ions gain energy when they move across the separatrix region into the downstream. Finally we show that electrons and ions gain energy mainly from the inductive reconnection driven electric field and less from the electrostatic electric field.

  9. Kinetic Vlasov simulations of collisionless magnetic reconnection

    SciTech Connect

    Schmitz, H.; Grauer, R.

    2006-09-15

    A fully kinetic Vlasov simulation of the Geospace Environment Modeling Magnetic Reconnection Challenge is presented. Good agreement is found with previous kinetic simulations using particle in cell (PIC) codes, confirming both the PIC and the Vlasov code. In the latter the complete distribution functions f{sub k} (k=i,e) are discretized on a numerical grid in phase space. In contrast to PIC simulations, the Vlasov code does not suffer from numerical noise and allows a more detailed investigation of the distribution functions. The role of the different contributions of Ohm's law are compared by calculating each of the terms from the moments of the f{sub k}. The important role of the off-diagonal elements of the electron pressure tensor could be confirmed. The inductive electric field at the X line is found to be dominated by the nongyrotropic electron pressure, while the bulk electron inertia is of minor importance. Detailed analysis of the electron distribution function within the diffusion region reveals the kinetic origin of the nongyrotropic terms.

  10. Comments on Magnetic Reconnection Models of Canceling Magnetic Features on the Sun

    NASA Astrophysics Data System (ADS)

    Litvinenko, Yuri E.

    2015-06-01

    Data analysis and theoretical arguments support magnetic reconnection in a chromospheric current sheet as the mechanism of the observed photospheric magnetic flux cancellation on the Sun. Flux pile-up reconnection in a Sweet-Parker current sheet can explain the observed properties of canceling mag-netic features, including the speeds of canceling magnetic fragments, the magnetic uxes in the fragments, and the flux cancellation rates, inferred from the data. It is discussed how more realistic chromospheric reconnection models can be developed by relaxing the assumptions of a negligible current sheet curvature and a constant height of the reconnection site above the photosphere.

  11. The role of compressibility in energy release by magnetic reconnection

    SciTech Connect

    Birn, J.; Borovsky, J. E.; Hesse, M.

    2012-08-15

    Using resistive compressible magnetohydrodynamics, we investigate the energy release and transfer by magnetic reconnection in finite (closed or periodic) systems. The emphasis is on the magnitude of energy released and transferred to plasma heating in configurations that range from highly compressible to incompressible, based on the magnitude of the background {beta} (ratio of plasma pressure over magnetic pressure) and of a guide field in two-dimensional reconnection. As expected, the system becomes more incompressible, and the role of compressional heating diminishes, with increasing {beta} or increasing guide field. Nevertheless, compressional heating may dominate over Joule heating for values of the guide field of 2 or 3 (in relation to the reconnecting magnetic field component) and {beta} of 5-10. This result stems from the strong localization of the dissipation near the reconnection site, which is modeled based on particle simulation results. Imposing uniform resistivity, corresponding to a Lundquist number of 10{sup 3} to 10{sup 4}, leads to significantly larger Ohmic heating. Increasing incompressibility greatly reduces the magnetic flux transfer and the amount of energy released, from {approx}10% of the energy associated with the reconnecting field component, for zero guide field and low {beta}, to {approx}0.2%-0.4% for large values of the guide field B{sub y0}>5 or large {beta}. The results demonstrate the importance of taking into account plasma compressibility and localization of dissipation in investigations of heating by turbulent reconnection, possibly relevant for solar wind or coronal heating.

  12. The Role of Compressibility in Energy Release by Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Birn, J.; Borovosky, J. E.; Hesse, M.

    2012-01-01

    Using resistive compressible magnetohydrodynamics, we investigate the energy release and transfer by magnetic reconnection in finite (closed or periodic) systems. The emphasis is on the magnitude of energy released and transferred to plasma heating in configurations that range from highly compressible to incompressible, based on the magnitude of the background beta (ratio of plasma pressure over magnetic pressure) and of a guide field in two-dimensional reconnection. As expected, the system becomes more incompressible, and the role of compressional heating diminishes, with increasing beta or increasing guide field. Nevertheless, compressional heating may dominate over Joule heating for values of the guide field of 2 or 3 (in relation to the reconnecting magnetic field component) and beta of 5-10. This result stems from the strong localization of the dissipation near the reconnection site, which is modeled based on particle simulation results. Imposing uniform resistivity, corresponding to a Lundquist number of 10(exp 3) to 10(exp 4), leads to significantly larger Ohmic heating. Increasing incompressibility greatly reduces the magnetic flux transfer and the amount of energy released, from approx. 10% of the energy associated with the reconnecting field component, for zero guide field and low beta, to approx. 0.2%-0.4% for large values of the guide field B(sub y0) > 5 or large beta. The results demonstrate the importance of taking into account plasma compressibility and localization of dissipation in investigations of heating by turbulent reconnection, possibly relevant for solar wind or coronal heating.

  13. New Measure of the Dissipation Region in Collisionless Magnetic Reconnection

    SciTech Connect

    Zenitani, Seiji; Hesse, Michael; Klimas, Alex; Kuznetsova, Masha

    2011-05-13

    A new measure to identify a small-scale dissipation region in collisionless magnetic reconnection is proposed. The energy transfer from the electromagnetic field to plasmas in the electron's rest frame is formulated as a Lorentz-invariant scalar quantity. The measure is tested by two-dimensional particle-in-cell simulations in typical configurations: symmetric and asymmetric reconnection, with and without the guide field. The innermost region surrounding the reconnection site is accurately located in all cases. We further discuss implications for nonideal MHD dissipation.

  14. ONSET OF FAST MAGNETIC RECONNECTION IN PARTIALLY IONIZED GASES

    SciTech Connect

    Malyshkin, Leonid M.; Zweibel, Ellen G. E-mail: zweibel@astro.wisc.edu

    2011-10-01

    We consider quasi-stationary two-dimensional magnetic reconnection in a partially ionized incompressible plasma. We find that when the plasma is weakly ionized and the collisions between the ions and the neutral particles are significant, the transition to fast collisionless reconnection due to the Hall effect in the generalized Ohm's law is expected to occur at much lower values of the Lundquist number, as compared to a fully ionized plasma case. We estimate that these conditions for fast reconnection are satisfied in molecular clouds and in protostellar disks.

  15. Magnetic Reconnection by a Self-Retreating X Line

    SciTech Connect

    Oka, M.; Nishikawa, K.-I.; Fujimoto, M.; Nakamura, T. K. M.; Shinohara, I.

    2008-11-14

    Particle-in-cell simulations of collisionless magnetic reconnection are performed to study asymmetric reconnection in which an outflow is blocked by a hard wall while leaving sufficiently large room for the outflow of the opposite direction. This condition leads to a slow, roughly constant motion of the diffusion region away from the wall, the so-called 'X-line retreat'. The typical retreat speed is {approx}0.1 times the Alfven speed. At the diffusion region, ion flow pattern shows strong asymmetry and the ion stagnation point and the X line are not collocated. A surprise, however, is that the reconnection rate remains the same unaffected by the retreat motion.

  16. New Measure of the Dissipation Region in Collisionless Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Zenitani, Seiji; Hesse, Michael; Klimas, Alex; Kuznetsova, Masha

    2012-01-01

    A new measure to identify a small-scale dissipation region in collisionless magnetic reconnection is proposed. The energy transfer from the electromagnetic field to plasmas in the electron s rest frame is formulated as a Lorentz-invariant scalar quantity. The measure is tested by two-dimensional particle-in-cell simulations in typical configurations: symmetric and asymmetric reconnection, with and without the guide field. The innermost region surrounding the reconnection site is accurately located in all cases. We further discuss implications for nonideal MHD dissipation.

  17. Does the Rate of Collisionless Magnetic Reconnection Depend on the Dissipation Mechanism?

    NASA Technical Reports Server (NTRS)

    Aunai, Nicolas; Hesse, Michael; Black, Carrie; Evans, Rebekah; Kuznetsova, Maria

    2012-01-01

    The importance of the electron dissipation effect on the reconnection rate is investigated in the general case of asymmetric collisionless magnetic reconnection. Contrary to the standard collisionless reconnection model, it is found that the reconnection rate, and the macroscopic evolution of the reconnecting system, crucially depend on the nature of the dissipation mechanism and that the Hall effect alone is not able to sustain fast reconnection.

  18. High power heating of magnetic reconnection in merging tokamak experiments

    SciTech Connect

    Ono, Y.; Tanabe, H.; Gi, K.; Watanabe, T.; Ii, T.; Yamada, T.; Gryaznevich, M.; Scannell, R.; Conway, N.; Crowley, B.; Michael, C.

    2015-05-15

    Significant ion/electron heating of magnetic reconnection up to 1.2 keV was documented in two spherical tokamak plasma merging experiment on MAST with the significantly large Reynolds number R∼10{sup 5}. Measured 1D/2D contours of ion and electron temperatures reveal clearly energy-conversion mechanisms of magnetic reconnection: huge outflow heating of ions in the downstream and localized heating of electrons at the X-point. Ions are accelerated up to the order of poloidal Alfven speed in the reconnection outflow region and are thermalized by fast shock-like density pileups formed in the downstreams, in agreement with recent solar satellite observations and PIC simulation results. The magnetic reconnection efficiently converts the reconnecting (poloidal) magnetic energy mostly into ion thermal energy through the outflow, causing the reconnection heating energy proportional to square of the reconnecting (poloidal) magnetic field B{sub rec}{sup 2}  ∼  B{sub p}{sup 2}. The guide toroidal field B{sub t} does not affect the bulk heating of ions and electrons, probably because the reconnection/outflow speeds are determined mostly by the external driven inflow by the help of another fast reconnection mechanism: intermittent sheet ejection. The localized electron heating at the X-point increases sharply with the guide toroidal field B{sub t}, probably because the toroidal field increases electron confinement and acceleration length along the X-line. 2D measurements of magnetic field and temperatures in the TS-3 tokamak merging experiment also reveal the detailed reconnection heating mechanisms mentioned above. The high-power heating of tokamak merging is useful not only for laboratory study of reconnection but also for economical startup and heating of tokamak plasmas. The MAST/TS-3 tokamak merging with B{sub p} > 0.4 T will enables us to heat the plasma to the alpha heating regime: T{sub i} > 5 keV without using any additional heating facility.

  19. Extensions of 1d Bgk Electron Solitary Wave Solutions To 3d Magnetized and Unmagnetized Plasmas

    NASA Astrophysics Data System (ADS)

    Chen, Li-Jen; Parks, George K.

    This paper will compare the key results for BGK electron solitary waves in 3D mag- netized and unmagnetized plasmas. For 3D magnetized plasmas with highly magnetic field-aligned electrons, our results predict that the parallel widths of the solitary waves can be smaller than one Debye length, the solitary waves can be large scale features of the magnetosphere, and the parallel width-amplitude relation has a dependence on the perpendicular size. We can thus obtain an estimate on the typical perpendicular size of the observed solitary waves assuming a series of consecutive solitary waves are in the same flux tude with a particular perpendicular span. In 3D unmagnetized plasma systems such as the neutral sheet and magnetic reconnection sites, our theory indi- cates that although mathematical solutions can be constructed as the time-stationary solutions for the nonlinear Vlasov-Poisson equations, there does not exist a param- eter range for the solutions to be physical. We conclude that single-humped solitary potential pulses cannot be self-consistently supported by charged particles in 3D un- magnetized plasmas.

  20. Observations of Slow Electron Holes at a Magnetic Reconnection Site

    SciTech Connect

    Khotyaintsev, Yu. V.; Vaivads, A.; Andre, M.; Fujimoto, M.; Retino, A.; Owen, C. J.

    2010-10-15

    We report in situ observations of high-frequency electrostatic waves in the vicinity of a reconnection site in the Earth's magnetotail. Two different types of waves are observed inside an ion-scale magnetic flux rope embedded in a reconnecting current sheet. Electron holes (weak double layers) produced by the Buneman instability are observed in the density minimum in the center of the flux rope. Higher frequency broadband electrostatic waves with frequencies extending up to f{sub pe} are driven by the electron beam and are observed in the denser part of the rope. Our observations demonstrate multiscale coupling during the reconnection: Electron-scale physics is induced by the dynamics of an ion-scale flux rope embedded in a yet larger-scale magnetic reconnection process.

  1. Time Scales for Energy Release in Hall Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Huba, J. D.; Rudakov, L. I.

    2004-05-01

    We present a study of the time scales for energy release in 2D Hall magnetic reconnection. We use the NRL Hall MHD code VooDoo for this study. We consider a 2D reversed field current layer with a magnetic perturbation that initiates the reconnection process. We use boundary conditions that allow inflow and outflow (i.e., not periodic) and let the system reach a steady state. We find that the system goes through three stages: a relatively long current layer thinning process, a fast reconnection phase, and a final steady state phase. We define the time scale for energy release as the fast reconnection period: from onset to steady state. Preliminary results indicate that the time for energy release scales as the initial thickness of the current layer. We apply these results to the magnetotail and magnetopause. Research supported by NASA and ONR.

  2. Relativistic magnetic reconnection driven by intense lasers in preformed plasma

    NASA Astrophysics Data System (ADS)

    Campbell, Paul; Raymond, A.; McKelvey, A.; Maksimchuk, A.; Nees, J.; Yanovsky, V.; Krushelnick, K.; Dong, C. F.; Fox, W.; Zulick, C.; Wei, M. S.; Chen, H.; Chvykov, V.; Mileham, C.; Nilson, P. M.; Stoeckl, C.; Thomas, A. G. R.; Willingale, L.

    2016-10-01

    Experiments were performed with the OMEGA EP laser system focusing the two short pulse beams to high intensities on foil targets. Relativistic electrons drive fast reconnection self-generated magnetic fields. To investigate the effects of a preformed plasma on this relativistic magnetic reconnection, a long pulse UV beam was used to ablate the front surface of layered targets. The density and reconnection dynamics in the preformed copper or CH plasma were diagnosed with a 4 ω optical probe. A spherically bent crystal imaged characteristic copper Kα emission induced by fast electrons accelerated into the target in the reconnection diffusion region. This work was supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0002727.

  3. THE ACCELERATION OF IONS IN SOLAR FLARES DURING MAGNETIC RECONNECTION

    SciTech Connect

    Knizhnik, K.; Swisdak, M.; Drake, J. F. E-mail: swisdak@umd.edu

    2011-12-20

    The acceleration of solar flare ions during magnetic reconnection is explored via particle-in-cell simulations that self-consistently and simultaneously follow the motions of both protons and {alpha} particles. We show that the dominant heating of thermal ions during guide field reconnection, the usual type in the solar corona, results from pickup behavior during the entry into reconnection exhausts. In contrast to anti-parallel reconnection, the temperature increment is dominantly transverse, rather than parallel, to the local magnetic field. A comparison of protons and {alpha} reveals a mass-to-charge (M/Q) threshold in pickup behavior that favors the heating of high-M/Q ions, which is consistent with impulsive flare observations.

  4. Evidence of 3-D Reconnection at Null Point from the Observations of Circular Flares and Homologous Jets

    NASA Astrophysics Data System (ADS)

    Wang, Haimin; Liu, C.

    2012-05-01

    In recent studies by Pariat, Antiochos and DeVore (2009, 2010), fan-separatrix topology and magnetic reconnection at the null-point were simulated and found to produce homologous jets. This motivates us to search for axisymmetric magnetic structure and associated flaring/jetting activity. Using high-resolution ( 0.15" per pixel) and high-cadence ( 15 s) H-alpha center/offband observations obtained from the recently digitized films of Big Bear Solar Observatory, we were able to identify five large circular flares with associated surges. All the events exhibit a central parasite magnetic field surrounded by opposite polarity, forming a circular polarity inversion line (PIL). Consequently, a compact flare kernel at the center is surrounded by a circular ribbon, and together with the upward ejecting dark surge, these seem to depict a dome-like magnetic structure. Very interestingly, (1) the circular ribbon brightens sequentially rather than simultaneously, (2) the central compact flare kernel shows obvious motion, and (3) a remote elongated, co-temporal flare ribbon at a region with the same polarity as the central parasite site is seen in the series of four homologous events on 1991 March 17 and 18. The remote ribbon is 120" away from the jet location. Moreover, magnetic reconnection across the circular PIL is evident from the magnetic flux cancellation. These rarely observed homologous surges with circular as well as central and remote flare ribbons provide valuable evidence concerning the dynamics of magnetic reconnection in a null-point topology. This study is dedicated to Professor Hal Zirin, the founder of Big Bear Solar Observatory, who passed away on January 3, 2012.

  5. Experimental study of energy conversion in the magnetic reconnection layer

    NASA Astrophysics Data System (ADS)

    Yamada, Masaaki

    2014-10-01

    Magnetic reconnection, in which magnetic field lines break and reconnect to change their topology, occurs throughout the universe: in solar flares, the earth's magnetosphere, star forming galaxies, and laboratory fusion plasmas. The essential feature of reconnection is that it energizes plasma particles by converting magnetic energy to particle energy; this process both accelerates and heats the plasma particles. Despite the recent advances of reconnection research, the exact mechanisms for bulk plasma heating, particle acceleration, and energy flow channels remain unresolved. In this work, the mechanisms responsible for the energization of plasma particles in the magnetic reconnection layer are investigated in the MRX device together with a quantitative evaluation of the conversion of magnetic energy to ions and electrons. A comprehensive analysis of the reconnection layer is made in terms of two-fluid physics based on the measurements of two-dimensional profiles of 1) electric potential, 2) flow vectors of electrons and ions, and 3) the electron temperature, Te and the ion temperature, Ti in the layer. It is experimentally verified that a saddle shaped electrostatic electric potential profile is formed in the reconnection plane. Ions are accelerated across the separatrices by the strong electrostatic field and enter the exhaust region where they become thermalized. Electron heating is observed to extend beyond the electron diffusion region, and non-classical heating mechanisms associated with high frequency fluctuations is found to play a role. Our quantitative analysis of the energy transport processes and energy inventory concludes that more than 50% of magnetic energy is converted to plasma particles, of which 2/3 transferred to ions and 1/3 to electrons. The results which demonstrate that conversion of magnetic energy occurs in a significantly larger region than theoretically considered before, are compared with the two-fluid simulations and the recent space

  6. The local dayside reconnection rate for oblique interplanetary magnetic fields

    NASA Astrophysics Data System (ADS)

    Komar, C. M.; Cassak, P. A.

    2016-06-01

    We present an analysis of local properties of magnetic reconnection at the dayside magnetopause for various interplanetary magnetic field (IMF) orientations in global magnetospheric simulations. This has heretofore not been practical because it is difficult to locate where reconnection occurs for oblique IMF, but new techniques make this possible. The approach is to identify magnetic separators, the curves separating four regions of differing magnetic topology, which map the reconnection X line. The electric field parallel to the X line is the local reconnection rate. We compare results to a simple model of local two-dimensional asymmetric reconnection. To do so, we find the plasma parameters that locally drive reconnection in the magnetosheath and magnetosphere in planes perpendicular to the X line at a large number of points along the X line. The global magnetohydrodynamic simulations are from the three-dimensional Block-Adaptive, Tree Solarwind Roe-type Upwind Scheme (BATS-R-US) code with a uniform resistivity, although the techniques described here are extensible to any global magnetospheric simulation model. We find that the predicted local reconnection rates scale well with the measured values for all simulations, being nearly exact for due southward IMF. However, the absolute predictions differ by an undetermined constant of proportionality, whose magnitude increases as the IMF clock angle changes from southward to northward. We also show similar scaling agreement in a simulation with oblique southward IMF and a dipole tilt. The present results will be an important component of a full understanding of the local and global properties of dayside reconnection.

  7. 3D print of polymer bonded rare-earth magnets, and 3D magnetic field scanning with an end-user 3D printer

    NASA Astrophysics Data System (ADS)

    Huber, C.; Abert, C.; Bruckner, F.; Groenefeld, M.; Muthsam, O.; Schuschnigg, S.; Sirak, K.; Thanhoffer, R.; Teliban, I.; Vogler, C.; Windl, R.; Suess, D.

    2016-10-01

    3D print is a recently developed technique, for single-unit production, and for structures that have been impossible to build previously. The current work presents a method to 3D print polymer bonded isotropic hard magnets with a low-cost, end-user 3D printer. Commercially available isotropic NdFeB powder inside a PA11 matrix is characterized, and prepared for the printing process. An example of a printed magnet with a complex shape that was designed to generate a specific stray field is presented, and compared with finite element simulation solving the macroscopic Maxwell equations. For magnetic characterization, and comparing 3D printed structures with injection molded parts, hysteresis measurements are performed. To measure the stray field outside the magnet, the printer is upgraded to a 3D magnetic flux density measurement system. To skip an elaborate adjusting of the sensor, a simulation is used to calibrate the angles, sensitivity, and the offset of the sensor. With this setup, a measurement resolution of 0.05 mm along the z-axes is achievable. The effectiveness of our calibration method is shown. With our setup, we are able to print polymer bonded magnetic systems with the freedom of having a specific complex shape with locally tailored magnetic properties. The 3D scanning setup is easy to mount, and with our calibration method we are able to get accurate measuring results of the stray field.

  8. Momentum transport near a magnetic X line in collisionless reconnection

    NASA Technical Reports Server (NTRS)

    Cai, H. J.; Ding, D. Q.; Lee, L. C.

    1994-01-01

    Plasma dynamics and momentum transport near an X line during time-dependent magnetic reconnection in a collisionless plasma are investigated based on two-dimensional particle simulations. We find that a weakly skewed velocity distribution is formed near the magnetic X line, leading to the presence of off-diagonal elements of the plasma pressure tensor. Let the reconnection electric field be in the y direction. The gradients of the off-diagonal elements of the pressure tensor can provide a transport of the y momentum. During the normal magnetic reconnection, the momentum transport associated with the off-diagonal terms of the pressure tensor mediates a transfer of the y momentum from the region near the X line to regions outside the X line. A period of 'reverse magnetic reconnection,' during which the plasma kinetic energy is converted into magnetic energy, is also observed in the simulation. When reverse reconnection occurs, the gradients of the off-diagonal pressure tensor elements can mediate a transfer of y momentum into the X line. It is found that the inertial term also plays a significant role in the force balance near the magnetic X line. An explanation for the origin of the off-diagonal pressure terms is also given in this paper.

  9. Effects of guide field in driven magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Cheng, C. Z.; Inoue, S.; Horiuchi, R.; Ono, Y.; Guo, X.

    2016-10-01

    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. 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.

  10. Understanding Magnetic Reconnection: The Physical Mechanism Driving Space Weather

    NASA Astrophysics Data System (ADS)

    Black, Carrie; Antiochos, Spiro K.; Karpen, Judith T.; Germaschewski, Kai; Bessho, Naoki

    2015-04-01

    The explosive energy release in solar eruptive events is believed to be due to magnetic reconnection. In the standard model for coronal mass ejections (CME) and/or solar flares, the free energy for the event resides in the strongly sheared magnetic field of a filament channel. The pre-eruption force balance consists of an upward force due to the magnetic pressure of the sheared field countered by the downward tension of the overlying unsheared field. Magnetic reconnection disrupts this force balance. Therefore, to understand CME/flare initiation, it is critical to model the onset of reconnection driven by the build-up of magnetic shear. In MHD simulations, the application of a magnetic-field shear is trivial. However, kinetic effects are important in the diffusion region and thus, it is important to examine this process with PIC simulations as well. The implementation of such a driver in PIC methods is nontrivial, however, and indicates the necessity of a true multiscale model for such processes in the solar environment. The field must be sheared self-consistently and indirectly to prevent the generation of waves that destroy the desired system. In the work presented here, we show reconnection in an X-Point geometry due to a velocity shear driver perpendicular to the plane of reconnection.This material is based upon work supported by the National Science Foundation under Award No. AGS-1331356 and NASA's Living With a Star Targeted Research and Technology program.

  11. Plasmoid instability in high-Lundquist-number magnetic reconnection

    SciTech Connect

    Huang, Yi-Min; Bhattacharjee, A.

    2013-05-15

    Our understanding of magnetic reconnection in resistive magnetohydrodynamics has gone through a fundamental change in recent years. The conventional wisdom is that magnetic reconnection mediated by resistivity is slow in laminar high Lundquist (S) plasmas, constrained by the scaling of the reconnection rate predicted by Sweet-Parker theory. However, recent studies have shown that when S exceeds a critical value ∼10{sup 4}, the Sweet-Parker current sheet is unstable to a super-Alfvénic plasmoid instability, with a linear growth rate that scales as S{sup 1/4}. In the fully developed statistical steady state of two-dimensional resistive magnetohydrodynamic simulations, the normalized average reconnection rate is approximately 0.01, nearly independent of S, and the distribution function f(ψ) of plasmoid magnetic flux ψ follows a power law f(ψ)∼ψ{sup −1}. When Hall effects are included, the plasmoid instability may trigger onset of Hall reconnection even when the conventional criterion for onset is not satisfied. The rich variety of possible reconnection dynamics is organized in the framework of a phase diagram.

  12. Vlasov simulations of collisionless magnetic reconnection without background density

    NASA Astrophysics Data System (ADS)

    Schmitz, H.; Grauer, R.

    2008-02-01

    A standard starting point for the simulation of collisionless reconnection is the Harris equilibrium which is made up of a current sheet that separates two regions of opposing magnetic field. Magnetohydrodynamic simulations of collisionless reconnection usually include a homogeneous background density for reasons of numerical stability. While, in some cases, this is a realistic assumption, the background density may introduce new effects both due to the more involved structure of the distribution function or due to the fact that the Alfvèn speed remains finite far away from the current sheet. We present a fully kinetic Vlasov simulation of the perturbed Harris equilibrium using a Vlasov code. Parameters are chosen to match the Geospace Environment Modeling (GEM) Magnetic Reconnection Challenge but excluding the background density. This allows to compare with earlier simulations [Schmitz H, Grauer R. Kinetic Vlasov simulations of collisionless magnetic reconnection. Phys Plasmas 2006;13:092309] which include the background density. It is found that the absence of a background density causes the reconnection rate to be higher. On the other hand, the time until the onset of reconnection is hardly affected. Again the off diagonal elements of the pressure tensor are found to be important on the X-line but with modified importance for the individual terms.

  13. Experimental Study of Current-Driven Turbulence During Magnetic Reconnection

    SciTech Connect

    Porkolab, Miklos; Egedal-Pedersen, Jan; Fox, William

    2010-08-31

    CMPD Final Report Experimental Study of Current-Driven Turbulence During Magnetic Reconnection Miklos Porkolab, PI, Jan Egedal, co-PI, William Fox, graduate student. This is the final report for Grant DE-FC02-04ER54786, MIT Participation in the Center for Multiscale Plasma Dynamics, which was active from 8/1/2004 to 7/31/2010. This Grant supported the thesis work of one MIT graduate student, William Fox, The thesis research consisted of an experimental study of the fluctuations arising during magnetic reconnection in plasmas on the Versatile Toroidal Facility (VTF) at MIT Plasma Science and Fusion Center (PSFC). The thesis was submitted and accepted by the MIT physics Department,. Fox, Experimental Study of Current-Driven Turbulence During Magnetic Reconnection, Ph.D. Thesis, MIT (2009). In the VTF experiment reconnection and current-sheet formation is driven by quickly changing currents in a specially arranged set of internal conductors. Previous work on this device [Egedal, et al, PRL 98, 015003, (2007)] identified a spontaneous reconnection regime. In this work fluctuations were studied using impedance-matched, high-bandwidth Langmuir probes. Strong, broadband fluctuations, with frequencies extending from near the lower-hybrid frequency [fLH = (fcefci)1/2] to the electron cyclotron frequency fce were found to arise during the reconnection events. Based on frequency and wavelength measurements, lower-hybrid waves and Trivelpiece-Gould waves were identified. The lower-hybrid waves are easiest to drive with strong perpendicular drifts or gradients which arise due to the reconnection events; an appealing possibility is strong temperature gradients. The Trivelpiece-Gould modes can result from kinetic, bump-on-tail instability of a runaway electron population energized by the reconnection events. We also observed that the turbulence is often spiky, consisting of discrete positive-potential spikes, which were identified as electron phase-space holes, a class of

  14. Magnetic reconnection in incompressible fluids. [of solar atmosphere and interior

    NASA Technical Reports Server (NTRS)

    Deluca, Edward E.; Craig, Ian J.

    1992-01-01

    The paper investigates the dynamical relaxation of a disturbed X-type magnetic neutral point in a periodic geometry, with an ignorable coordinate, for an incompressible fluid. It is found that the properties of the current sheet cannot be understood in terms of steady state reconnection theory or more recent linear dynamical solutions. Accordingly, a new scaling law for magnetic reconnection is presented, consistent with fast energy dissipation (i.e., the dissipation rate at current maximum is approximately independent of magnetic diffusivity (eta)). The flux annihilation rate, however, scales at eta exp 1/4, faster than the Sweet-Parker rate of sq rt eta but asymptotically much slower than the dissipation rate. These results suggest a flux pile-up regime in which the bulk of the free magnetic energy is released as heat rather than as kinetic energy of mass motion. The implications of our results for reconnection in the solar atmosphere and interior are discussed.

  15. First MMS Observations of High Time Resolution 3D Electric and Magnetic fields at the Dayside Magnetopause.

    NASA Astrophysics Data System (ADS)

    Torbert, R. B.; Burch, J. L.; Russell, C. T.; Magnes, W.; Ergun, R. E.; Lindqvist, P. A.; Le Contel, O.; Vaith, H.; Macri, J.; Myers, S.; Rau, D.; Needell, J.; King, B.; Granoff, M.; Chutter, M.; Dors, I.; Argall, M. R.; Shuster, J. R.; Olsson, G.; Marklund, G. T.; Khotyaintsev, Y. V.; Eriksson, A. I.; Kletzing, C.; Bounds, S. R.; Anderson, B. J.; Baumjohann, W.; Steller, M.; Bromund, K. R.; Le, G.; Nakamura, R.; Strangeway, R. J.; Leinweber, H. K.; Tucker, S.; Westfall, J.; Fischer, D.; Plaschke, F.; Pollock, C. J.; Giles, B. L.; Moore, T. E.; Mauk, B.; Fuselier, S. A.

    2015-12-01

    The electrodynamics at the magnetopause is key to our understanding of ion and electron acceleration within reconnection regions. The Magnetospheric Multiscale (MMS) fleet of four spacecraft was launched into its Phase-1 equatorial orbit of 12 Re apogee specifically to investigate these regions at the Earth's magnetopause. In addition to a comprehensive suite of particle measurements, MMS makes very high time resolution 3D electric and magnetic field measurements of high accuracy using flux-gate, search coil, 3-axis double probe, and electron drift sensors. In September 2015, the MMS fleet will begin to encounter the dusk-side magnetopause in its initial configuration of approximately 160 km separation, allowing investigation of the spatial and temporal characteristics of important electrodynamics during reconnection. Using these field and particle measurements, we present first observations of 3D magnetic and electric fields (including their parallel component), and inferred current sheets, during active magnetopause crossings using the highest time resolution data available on MMS.

  16. Observations of Magnetic Reconnection and Plasma Dynamics in Mercury's Magnetosphere

    NASA Astrophysics Data System (ADS)

    DiBraccio, Gina A.

    Mercury's magnetosphere is formed as a result of the supersonic solar wind interacting with the planet's intrinsic magnetic field. The combination of the weak planetary dipole moment and intense solar wind forcing of the inner heliosphere creates a unique space environment, which can teach us about planetary magnetospheres. In this work, we analyze the first in situ orbital observations at Mercury, provided by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. Magnetic reconnection and the transport of plasma and magnetic flux are investigated using MESSENGER Magnetometer and Fast Imaging Plasma Spectrometer measurements. Here, we report our results on the effect of magnetic reconnection and plasma dynamics on Mercury's space environment: (1) Mercury's magnetosphere is driven by frequent, intense magnetic reconnection observed in the form of magnetic field components normal to the magnetopause, BN, and as helical bundles of flux, called magnetic flux ropes, in the cross-tail current sheet. The high reconnection rates are determined to be a direct consequence of the low plasma beta, the ratio of plasma to magnetic pressure, in the inner heliosphere. (2) As upstream solar wind conditions vary, we find that reconnection occurs at Mercury's magnetopause for all orientations of the interplanetary magnetic field, independent of shear angle. During the most extreme solar wind forcing events, the influence of induction fields generated within Mercury's highly conducting core are negated by erosion due to persistent magnetopause reconnection. (3) We present the first observations of Mercury's plasma mantle, which forms as a result of magnetopause reconnection and allows solar wind plasma to enter into the high-latitude magnetotail through the dayside cusps. The energy dispersion observed in the plasma mantle protons is used to infer the cross-magnetosphere electric field, providing a direct measurement of solar wind momentum

  17. Full Two-Fluid Collisionless Magnetic Reconnection Simulations

    NASA Astrophysics Data System (ADS)

    Gomez, D. O.; Andres, N.; Dmitruk, P.

    2015-12-01

    Magnetic reconnection is an important energy conversion process in space environments such as the solar corona or planetary magnetospheres. At the theoretical level of resistive one-fluid MHD, the Sweet-Parker model leads to extremely low reconnection rates for virtually all space physics applications. Kinetic plasma effects introduce new spatial and temporal scales into the theoretical description, which are expected to increase the reconnection rates. Within the theoretical framework of two-fluid MHD, we retain the effects of the Hall current and electron inertia and neglect dissipative effects such as viscosity and electric resistivity. This level of description brings two new spatial scales into play, namely, the ion and electron inertial scales. In absence of resistive dissipation, reconnection can only be attained by the action of electron inertia. We performed 2.5D two-fluid simulations using a pseudo-spectral code which yields exact conservation (to round-off errors) of the ideal invariants. Our simulations show that when the effects of electron inertia are retained, magnetic reconnection takes place. In a stationary regime, the reconnection rate is simply proportional to the ion inertial length, as also emerges from a scaling law derived from dimensional arguments.

  18. Fast Magnetic Reconnection: Bridging Laboratory and Space Plasma Physics

    SciTech Connect

    Bhattacharjee, Amitava

    2012-02-16

    Recent developments in experimental and theoretical studies of magnetic reconnection hold promise for providing solutions to outstanding problems in laboratory and space plasma physics. Examples include sawtooth crashes in tokamaks, substorms in the Earth’s Magnetosphere, eruptive solar flares, and more recently, fast reconnection in laser-produced high energy density plasmas. In each of these examples, a common and long-standing challenge has been to explain why fast reconnection proceeds rapidly from a relatively quiescent state. In this talk, we demonstrate the advantages of viewing these problems and their solutions from a common perspective. We focus on some recent, surprising discoveries regarding the role of secondary plasmoid instabilities of thin current sheets. Nonlinearly, these instabilities lead to fast reconnection rates that are very weakly dependent on the Lundquist number of the plasma.

  19. Magnetic reconnection in Hall-MHD including electron inertia

    NASA Astrophysics Data System (ADS)

    Gomez, D. O.; Andres, N.; Martin, L. N.; Dmitruk, P.

    2013-12-01

    Magnetic reconnection is an important energy conversion process in highly conducting plasmas, such as those present in the solar corona or in planetary magnetospheres. Within the framework of resistive one-fluid MHD, the Sweet-Parker model leads to extremely low reconnection rates for virtually all space physics applications. Kinetic plasma effects introduce new spatial and temporal scales into the theoretical description, which might significantly increase the reconnection rates. Within the more general framework of two-fluid MHD for a fully ionized hydrogen plasma, we retain the effects of the Hall current and electron inertia. We performed 2.5D Hall MHD simulations including electron inertia using a pseudo-spectral code which yields exact conservation (to round-off errors) of all the ideal invariants. We obtain finite reconnection rates even in the case of zero resistivity, thus showing the important influence of the electron inertia.

  20. Laboratory study of ion and electron dynamics during asymmetric magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Yoo, J.; Jara-Almonte, J.; Yamada, M.; Ji, H.; Fox, W. R., II; Chen, L. J.; Roytershteyn, V.; Na, B.

    2015-12-01

    Magnetic reconnection at the dayside magnetopause has a large density asymmetry across the current sheet. To study effects of the density asymmetry on the ion and electron dynamics, plasmas with a significant (~10) density asymmetry are created in the Magnetic Reconnection Experiment (MRX) [1]. The density asymmetry affects the ion flow pattern by changing the in-plane electrostatic field such that the potential decrease on the high-density side becomes much smaller than that on the low-density side [2]. The ion inflow stagnation point is shifted toward the low-density side and the maximum ion outflow velocity is observed on the low-density side. The density asymmetry also makes the electron temperature profile asymmetric, which has a higher temperature near the low-density-side separatrices. The bulk electron heating is proportional to the total incoming magnetic energy per particle. The electron energization process during asymmetric reconnection is studied via numerical simulations. By comparing 2D simulations with corresponding 3D simulations, we find that the overall energization process does not depend on variations along the third dimension. Where and how electrons are energized during asymmetric reconnection will be discussed by using data from 2D numerical simulations. Finally, the scaling of the reconnection rate and the ion outflow speed given by the Cassak and Shay 2007 [3] is tested by systematically varying the density ratio. The measured ion outflow speed is about 40% of the theoretical values and the measured reconnection rate agrees with the scaling only with the measured density in the exhaust region. [1] M. Yamada et al., Phys. Plasmas 4, 1936 (1997). [2] J. Yoo et al., Phys. Rev. Lett. 113, 095002 (2014). [3] P. Cassak and M. Shay, Phys. Plasmas 14, 102114 (2007).

  1. Evidence for magnetic field reconnection at the Earth's magnetopause

    NASA Technical Reports Server (NTRS)

    Sonnerup, B. U. O.; Paschmann, G.; Papamastorakis, I.; Sckopke, N.; Haerendel, G.; Bame, S. J.; Asbridge, J. R.; Gosling, J. T.; Russell, C. T.

    1981-01-01

    Eleven passes of the ISEE satellites through the frontside terrestrial magnetopause were identified, where the plasma velocity in the magnetopause and boundary layer was substantially larger than in the magnetosheath. The nature of the plasma flow, magnetic field, and energetic particle fluxes in these regions were examined, with a view to determining whether the velocity enhancements can be explained by magnetic field reconnection.

  2. The Impact of Geometrical Constraints on Collisionless Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Hesse, Michael; Aunai, Nico; Kuznetsova, Masha; Frolov, Rebekah; Black, Carrrie

    2012-01-01

    One of the most often cited features associated with collisionless magnetic reconnection is a Hall-type magnetic field, which leads, in antiparallel geometries, to a quadrupolar magnetic field signature. The combination of this out of plane magnetic field with the reconnection in-plane magnetic field leads to angling of magnetic flux tubes out of the plane defined by the incoming magnetic flux. Because it is propagated by Whistler waves, the quadrupolar field can extend over large distances in relatively short amounts of time - in fact, it will extend to the boundary of any modeling domain. In reality, however, the surrounding plasma and magnetic field geometry, defined, for example, by the overall solar wind flow, will in practice limit the extend over which a flux tube can be angled out of the main plain. This poses the question to what extent geometric constraints limit or control the reconnection process and this is the question investigated in this presentation. The investigation will involve a comparison of calculations, where open boundary conditions are set up to mimic either free or constrained geometries. We will compare momentum transport, the geometry of the reconnection regions, and the acceleration if ions and electrons to provide the current sheet in the outflow jet.

  3. Evolution of field line helicity during magnetic reconnection

    SciTech Connect

    Russell, A. J. B. Hornig, G.; Wilmot-Smith, A. L.; Yeates, A. R.

    2015-03-15

    We investigate the evolution of field line helicity for magnetic fields that connect two boundaries without null points, with emphasis on localized finite-B magnetic reconnection. Total (relative) magnetic helicity is already recognized as an important topological constraint on magnetohydrodynamic processes. Field line helicity offers further advantages because it preserves all topological information and can distinguish between different magnetic fields with the same total helicity. Magnetic reconnection changes field connectivity and field line helicity reflects these changes; the goal of this paper is to characterize that evolution. We start by deriving the evolution equation for field line helicity and examining its terms, also obtaining a simplified form for cases where dynamics are localized within the domain. The main result, which we support using kinematic examples, is that during localized reconnection in a complex magnetic field, the evolution of field line helicity is dominated by a work-like term that is evaluated at the field line endpoints, namely, the scalar product of the generalized field line velocity and the vector potential. Furthermore, the flux integral of this term over certain areas is very small compared to the integral of the unsigned quantity, which indicates that changes of field line helicity happen in a well-organized pairwise manner. It follows that reconnection is very efficient at redistributing helicity in complex magnetic fields despite having little effect on the total helicity.

  4. Evolution of field line helicity during magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Russell, A. J. B.; Yeates, A. R.; Hornig, G.; Wilmot-Smith, A. L.

    2015-03-01

    We investigate the evolution of field line helicity for magnetic fields that connect two boundaries without null points, with emphasis on localized finite-B magnetic reconnection. Total (relative) magnetic helicity is already recognized as an important topological constraint on magnetohydrodynamic processes. Field line helicity offers further advantages because it preserves all topological information and can distinguish between different magnetic fields with the same total helicity. Magnetic reconnection changes field connectivity and field line helicity reflects these changes; the goal of this paper is to characterize that evolution. We start by deriving the evolution equation for field line helicity and examining its terms, also obtaining a simplified form for cases where dynamics are localized within the domain. The main result, which we support using kinematic examples, is that during localized reconnection in a complex magnetic field, the evolution of field line helicity is dominated by a work-like term that is evaluated at the field line endpoints, namely, the scalar product of the generalized field line velocity and the vector potential. Furthermore, the flux integral of this term over certain areas is very small compared to the integral of the unsigned quantity, which indicates that changes of field line helicity happen in a well-organized pairwise manner. It follows that reconnection is very efficient at redistributing helicity in complex magnetic fields despite having little effect on the total helicity.

  5. The plasmoid instability during asymmetric inflow magnetic reconnection

    SciTech Connect

    Murphy, Nicholas A.; Young, Aleida K.; Shen, Chengcai; Lin, Jun; Ni, Lei

    2013-06-15

    Theoretical studies of the plasmoid instability generally assume that the reconnecting magnetic fields are symmetric. We relax this assumption by performing two-dimensional resistive magnetohydrodynamic simulations of the plasmoid instability during asymmetric inflow magnetic reconnection. Magnetic asymmetry modifies the onset, scaling, and dynamics of this instability. Magnetic islands develop preferentially into the weak magnetic field upstream region. Outflow jets from individual X-points impact plasmoids obliquely rather than directly as in the symmetric case. Consequently, deposition of momentum by the outflow jets into the plasmoids is less efficient, the plasmoids develop net vorticity, and shear flow slows down secondary merging between islands. Secondary merging events have asymmetry along both the inflow and outflow directions. Downstream plasma is more turbulent in cases with magnetic asymmetry because islands are able to roll around each other after exiting the current sheet. As in the symmetric case, plasmoid formation facilitates faster reconnection for at least small and moderate magnetic asymmetries. However, when the upstream magnetic field strengths differ by a factor of 4, the reconnection rate plateaus at a lower value than expected from scaling the symmetric results. We perform a parameter study to investigate the onset of the plasmoid instability as a function of magnetic asymmetry and domain size. There exist domain sizes for which symmetric simulations are stable but asymmetric simulations are unstable, suggesting that moderate magnetic asymmetry is somewhat destabilizing. We discuss the implications for plasmoid and flux rope formation in solar eruptions, laboratory reconnection experiments, and space plasmas. The differences between symmetric and asymmetric simulations provide some hints regarding the nature of the three-dimensional plasmoid instability.

  6. Particle-in-cell simulations of Magnetic Field Generation, Evolution, and Reconnection in Laser-driven Plasmas

    NASA Astrophysics Data System (ADS)

    Matteucci, Jack; Moissard, Clément; Fox, Will; Bhattacharjee, Amitava

    2016-10-01

    The advent of high-energy-density physics facilities has introduced the opportunity to experimentally investigate magnetic field dynamics relevant to both ICF and astrophysical plasmas. Recent experiments have demonstrated magnetic reconnection between colliding plasma plumes, where the reconnecting magnetic fields were self-generated in the plasma by the Biermann battery effect. In this study, we simulate these experiments from first principles using 2-D and 3-D particle-in-cell simulations. Simulations self-consistently demonstrate magnetic field generation by the Biermann battery effect, followed by advection by the Hall effect and ion flow. In 2-D simulations, we find in both the collisionless case and the semi-collisional case, defined by eVi × B >> Rei /ne (where Rei is the electron ion momentum transfer) that quantitative agreement with the generalized Ohm's law is only obtained with the inclusion of the pressure tensor. Finally, we document that significant field is destroyed at the reconnection site by the Biermann term, an inverse, `anti-Biermann' effect, which has not been considered previously in analysis of the experiment. The role of the anti-Biermann effect will be compared to standard reconnection mechanisms in 3-D reconnection simulations. This research used resources of the ORLC Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. DoE under Contract No. DE-AC05-00OR22725.

  7. The Effect of Dissipation Mechanism on X-line Spreading in 3D Magnetic

    NASA Astrophysics Data System (ADS)

    Shepherd, L. S.; Cassak, P.; Phan, T.; Shay, M. A.; Gosling, J. T.

    2012-12-01

    Naturally occurring magnetic reconnection generally begins in a spatially localized region and spreads in the direction perpendicular to the reconnection plane as time progresses. Reconnection spreading is associated with dawn-dusk asymmetries during substorms in the magnetotail and has been observed in two-ribbon flares (such as the Bastille Day flare) and laboratory experiments at the Versatile Toroidal Facility (VTF) and the Magnetic Reconnection eXperiment (MRX). It was suggested that X-line spreading is necessary to explain the existence of X-lines extending more than 390 Earth radii (Phan et al., Nature, 404, 848, 2006). Previous numerical studies exploring the spreading of localized magnetic reconnection exclusively addressed collisionless (Hall) reconnection. Here, we address the effect of dissipation mechanism has on X-line spreading with and without a guide field. We compare previous results with simulations using three alternate phases of reconnection - Sweet-Parker reconnection, collisional reconnection with secondary islands, and reconnection with anomalous resistivity. We present results from three-dimensional resistive magnetohydrodynamic numerical simulations to address the nature of X-line spreading. Applications to reconnection in the solar wind and corona will be discussed.

  8. Magnetic Reconnection: A Fundamental Process in Space Plasmas

    NASA Technical Reports Server (NTRS)

    Hesse, Michael

    2010-01-01

    For many years, collisionless magnetic reconnect ion has been recognized as a fundamental process, which facilitates plasma transport and energy release in systems ranging from the astrophysical plasmas to magnetospheres and even laboratory plasma. Beginning with work addressing solar dynamics, it has been understood that reconnection is essential to explain solar eruptions, the interaction of the solar wind with the magnetosphere, and the dynamics of the magnetosphere. Accordingly, the process of magnetic reconnection has been and remains a prime target for space-based and laboratory studies, as well as for theoretical research. Much progress has been made throughout the years, beginning with indirect verifications by studies of processes enabled by reconnection, such as Coronal Mass Ejections, Flux Transfer Events, and Plasmoids. Theoretical advances have accompanied these observations, moving knowledge beyond the Sweet-Parker theory to the recognition that other, collisionless, effects are available and likely to support much faster reconnect ion rates. At the present time we are therefore near a break-through in our understanding of how collisionless reconnect ion works. Theory and modeling have advanced to the point that two competing theories are considered leading candidates for explaining the microphysics of this process. Both theories predict very small spatial and temporal scales. which are. to date, inaccessible to space-based or laboratory measurements. The need to understand magnetic reconnect ion has led NASA to begin the implementation of a tailored mission, Magnetospheric MultiScale (MMS), a four spacecraft cluster equipped to resolve all relevant spatial and temporal scales. In this presentation, we present an overview of current knowledge as well as an outlook towards measurements provided by MMS.

  9. Multimaterial magnetically assisted 3D printing of composite materials

    PubMed Central

    Kokkinis, Dimitri; Schaffner, Manuel; Studart, André R.

    2015-01-01

    3D printing has become commonplace for the manufacturing of objects with unusual geometries. Recent developments that enabled printing of multiple materials indicate that the technology can potentially offer a much wider design space beyond unusual shaping. Here we show that a new dimension in this design space can be exploited through the control of the orientation of anisotropic particles used as building blocks during a direct ink-writing process. Particle orientation control is demonstrated by applying low magnetic fields on deposited inks pre-loaded with magnetized stiff platelets. Multimaterial dispensers and a two-component mixing unit provide additional control over the local composition of the printed material. The five-dimensional design space covered by the proposed multimaterial magnetically assisted 3D printing platform (MM-3D printing) opens the way towards the manufacturing of functional heterogeneous materials with exquisite microstructural features thus far only accessible by biological materials grown in nature. PMID:26494528

  10. Multimaterial magnetically assisted 3D printing of composite materials

    NASA Astrophysics Data System (ADS)

    Kokkinis, Dimitri; Schaffner, Manuel; Studart, André R.

    2015-10-01

    3D printing has become commonplace for the manufacturing of objects with unusual geometries. Recent developments that enabled printing of multiple materials indicate that the technology can potentially offer a much wider design space beyond unusual shaping. Here we show that a new dimension in this design space can be exploited through the control of the orientation of anisotropic particles used as building blocks during a direct ink-writing process. Particle orientation control is demonstrated by applying low magnetic fields on deposited inks pre-loaded with magnetized stiff platelets. Multimaterial dispensers and a two-component mixing unit provide additional control over the local composition of the printed material. The five-dimensional design space covered by the proposed multimaterial magnetically assisted 3D printing platform (MM-3D printing) opens the way towards the manufacturing of functional heterogeneous materials with exquisite microstructural features thus far only accessible by biological materials grown in nature.

  11. Flux Rope Acceleration and Enhanced Magnetic Reconnection Rate

    SciTech Connect

    C.Z. Cheng; Y. Ren; G.S. Choe; Y.-J. Moon

    2003-03-25

    A physical mechanism of flares, in particular for the flare rise phase, has emerged from our 2-1/2-dimensional resistive MHD simulations. The dynamical evolution of current-sheet formation and magnetic reconnection and flux-rope acceleration subject to continuous, slow increase of magnetic shear in the arcade are studied by employing a non-uniform anomalous resistivity in the reconnecting current sheet under gravity. The simulation results directly relate the flux rope's accelerated rising motion with an enhanced magnetic reconnection rate and thus an enhanced reconnection electric field in the current sheet during the flare rise phase. The simulation results provide good quantitative agreements with observations of the acceleration of flux rope, which manifests in the form of SXR ejecta or erupting filament or CMEs, in the low corona. Moreover, for the X-class flare events studied in this paper the peak reconnection electric field is about O(10{sup 2} V/m) or larger, enough to accelerate p articles to over 100 keV in a field-aligned distance of 10 km. Nonthermal electrons thus generated can produce hard X-rays, consistent with impulsive HXR emission observed during the flare rise phase.

  12. Free-Standing Magnetic Nanopillars for 3D Nanomagnet Logic

    PubMed Central

    2014-01-01

    Nanomagnet logic (NML) is a relatively new computation technology that uses arrays of shape-controlled nanomagnets to enable digital processing. Currently, conventional resist-based lithographic processes limit the design of NML circuitry to planar nanostructures with homogeneous thicknesses. Here, we demonstrate the focused electron beam induced deposition of Fe-based nanomaterial for magnetic in-plane nanowires and out-of-plane nanopillars. Three-dimensional (3D) NML was achieved based on the magnetic coupling between nanowires and nanopillars in a 3D array. Additionally, the same Fe-based nanomaterial was used to produce tilt-corrected high-aspect-ratio probes for the accurate magnetic force microscopy (MFM) analysis of the fabricated 3D NML gate arrays. The interpretation of the MFM measurements was supported by magnetic simulations using the Object Oriented MicroMagnetic Framework. Introducing vertical out-of-plane nanopillars not only increases the packing density of 3D NML but also introduces an extra magnetic degree of freedom, offering a new approach to input/output and processing functionalities in nanomagnetic computing. PMID:25296008

  13. Origins of effective resistivity in collisionless magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Singh, Nagendra

    2014-07-01

    The mechanisms that provide effective resistivity for supporting collisonless magnetic reconnection have remained unsettled despite numerous studies. Some of these studies demonstrated that the electron pressure nongyrotropy generates the resistivity (ηnpg) in the electron diffusion region (EDR). We derive an analytical relation for the effective resistivity (ηkin) by momentum balance in a control volume in the EDR. Both ηnpg and ηkin mutually compare well and they also compare well with the resistivity required to support reconnection electric field Erec in multi-dimensional particle-in-cell simulations as well as in satellite observations when reconnection occurs in an EDR. But they are about an order of magnitude or so smaller than that required when the reconnection occurred in a much wider reconnecting current sheet (RCS) of half width (w) of the order of the ion skin depth (di), observed in the Earth magnetosphere. The chaos-induced resistivity reported in the literature is found to be even more deficient. We find that for reconnection in RCS with w ˜ di, anomalous diffusion, such as the universal Bhom diffusion and/or that arising from kinetic Alfven waves, could fairly well account for the required resistivity.

  14. Origins of effective resistivity in collisionless magnetic reconnection

    SciTech Connect

    Singh, Nagendra

    2014-07-15

    The mechanisms that provide effective resistivity for supporting collisonless magnetic reconnection have remained unsettled despite numerous studies. Some of these studies demonstrated that the electron pressure nongyrotropy generates the resistivity (η{sub npg}) in the electron diffusion region (EDR). We derive an analytical relation for the effective resistivity (η{sub kin}) by momentum balance in a control volume in the EDR. Both η{sub npg} and η{sub kin} mutually compare well and they also compare well with the resistivity required to support reconnection electric field E{sub rec} in multi-dimensional particle-in-cell simulations as well as in satellite observations when reconnection occurs in an EDR. But they are about an order of magnitude or so smaller than that required when the reconnection occurred in a much wider reconnecting current sheet (RCS) of half width (w) of the order of the ion skin depth (d{sub i}), observed in the Earth magnetosphere. The chaos-induced resistivity reported in the literature is found to be even more deficient. We find that for reconnection in RCS with w ∼ d{sub i}, anomalous diffusion, such as the universal Bhom diffusion and/or that arising from kinetic Alfven waves, could fairly well account for the required resistivity.

  15. Magnetic Reconnection in the Interior of Interplanetary Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Fermo, R. L.; Opher, M.; Drake, J. F.

    2014-07-01

    Recent in situ observations of interplanetary coronal mass ejections (ICMEs) found signatures of reconnection exhausts in their interior or trailing edge. Whereas reconnection on the leading edge of an ICME would indicate an interaction with the coronal or interplanetary environment, this result suggests that the internal magnetic field reconnects with itself. In light of this data, we consider the stability properties of flux ropes first developed in the context of astrophysics, then further elaborated upon in the context of reversed field pinches (RFPs). It was shown that the lowest energy state of a flux rope corresponds to ∇×B=λB with λ a constant, the so-called Taylor state. Variations from this state will result in the magnetic field trying to reorient itself into the Taylor state solution, subject to the constraints that the toroidal flux and magnetic helicity are invariant. In reversed field pinches, this relaxation is mediated by the reconnection of the magnetic field, resulting in a sawtooth crash. If we likewise treat the ICME as a flux rope, any deviation from the Taylor state will result in reconnection within the interior of the flux tube, in agreement with the observations by Gosling et al. Such a departure from the Taylor state takes place as the flux tube cross section expands in the latitudinal direction, as seen in magnetohydrodynamic (MHD) simulations of flux tubes propagating through the interplanetary medium. We show analytically that this elongation results in a state which is no longer in the minimum energy Taylor state. We then present magnetohydrodynamic simulations of an elongated flux tube which has evolved away from the Taylor state and show that reconnection at many surfaces produces a complex stochastic magnetic field as the system evolves back to a minimum energy state configuration.

  16. Magnetic Reconnection Onset and Energy Release at Current Sheets

    NASA Astrophysics Data System (ADS)

    DeVore, C. R.; Antiochos, Spiro K.

    2015-04-01

    Reconnection and energy release at current sheets are important at the Sun (coronal heating, coronal mass ejections, flares, and jets) and at the Earth (magnetopause flux transfer events and magnetotail substorms) and other magnetized planets, and occur also at the interface between the Heliosphere and the interstellar medium, the heliopause. The consequences range from relatively quiescent heating of the ambient plasma to highly explosive releases of energy and accelerated particles. We use the Adaptively Refined Magnetohydrodynamics Solver (ARMS) model to investigate the self-consistent formation and reconnection of current sheets in an initially potential 2D magnetic field containing a magnetic null point. Unequal stresses applied to the four quadrants bounded by the X-line separatrix distort the potential null into a double-Y-type current sheet. We find that this distortion eventually leads to onset of fast magnetic reconnection across the sheet, with copious production, merging, and ejection of magnetic islands due to plasmoid instability. In the absence of a mechanism for ideal instability or loss of equilibrium of the global structure, however, this reconnection leads to minimal energy release. Essentially, the current sheet oscillates about its force-free equilibrium configuration. When the structure is susceptible to a large-scale rearrangement of the magnetic field, on the other hand, the energy release becomes explosive. We identify the conditions required for reconnection to transform rapidly a large fraction of the magnetic free energy into kinetic and other forms of plasma energy, and to restructure the current sheet and its surrounding magnetic field dramatically. We discuss the implications of our results for understanding heliophysical activity, particularly eruptions, flares, and jets in the corona.Our research was supported by NASA’s Heliophysics Supporting Research and Living With a Star Targeted Research and Technology programs.

  17. Asymmetric evolution of magnetic reconnection in collisionless accretion disk

    SciTech Connect

    Shirakawa, Keisuke Hoshino, Masahiro

    2014-05-15

    An evolution of a magnetic reconnection in a collisionless accretion disk is investigated using a 2.5 dimensional hybrid code simulation. In astrophysical disks, magnetorotational instability (MRI) is considered to play an important role by generating turbulence in the disk and contributes to an effective angular momentum transport through a turbulent viscosity. Magnetic reconnection, on the other hand, also plays an important role on the evolution of the disk through a dissipation of a magnetic field enhanced by a dynamo effect of MRI. In this study, we developed a hybrid code to calculate an evolution of a differentially rotating system. With this code, we first confirmed a linear growth of MRI. We also investigated a behavior of a particular structure of a current sheet, which would exist in the turbulence in the disk. From the calculation of the magnetic reconnection, we found an asymmetric structure in the out-of-plane magnetic field during the evolution of reconnection, which can be understood by a coupling of the Hall effect and the differential rotation. We also found a migration of X-point whose direction is determined only by an initial sign of J{sub 0}×Ω{sub 0}, where J{sub 0} is the initial current density in the neutral sheet and Ω{sub 0} is the rotational vector of the background Keplerian rotation. Associated with the migration of X-point, we also found a significant enhancement of the perpendicular magnetic field compared to an ordinary MRI. MRI-Magnetic reconnection coupling and the resulting magnetic field enhancement can be an effective process to sustain a strong turbulence in the accretion disk and to a transport of angular momentum.

  18. Asymmetric evolution of magnetic reconnection in collisionless accretion disk

    NASA Astrophysics Data System (ADS)

    Shirakawa, Keisuke; Hoshino, Masahiro

    2014-05-01

    An evolution of a magnetic reconnection in a collisionless accretion disk is investigated using a 2.5 dimensional hybrid code simulation. In astrophysical disks, magnetorotational instability (MRI) is considered to play an important role by generating turbulence in the disk and contributes to an effective angular momentum transport through a turbulent viscosity. Magnetic reconnection, on the other hand, also plays an important role on the evolution of the disk through a dissipation of a magnetic field enhanced by a dynamo effect of MRI. In this study, we developed a hybrid code to calculate an evolution of a differentially rotating system. With this code, we first confirmed a linear growth of MRI. We also investigated a behavior of a particular structure of a current sheet, which would exist in the turbulence in the disk. From the calculation of the magnetic reconnection, we found an asymmetric structure in the out-of-plane magnetic field during the evolution of reconnection, which can be understood by a coupling of the Hall effect and the differential rotation. We also found a migration of X-point whose direction is determined only by an initial sign of J0×Ω0, where J0 is the initial current density in the neutral sheet and Ω0 is the rotational vector of the background Keplerian rotation. Associated with the migration of X-point, we also found a significant enhancement of the perpendicular magnetic field compared to an ordinary MRI. MRI-Magnetic reconnection coupling and the resulting magnetic field enhancement can be an effective process to sustain a strong turbulence in the accretion disk and to a transport of angular momentum.

  19. Kinetic PIC simulations of reconnection signal propagation parallel to magnetic field lines: Implifications for substorms

    NASA Astrophysics Data System (ADS)

    Shay, M. A.; Drake, J. F.

    2009-12-01

    In a recent substorm case study using THEMIS data [1], it was inferred that auroral intensification occurred 96 seconds after reconnection onset initiated a substorm in the magnetotail. These conclusions have been the subject of some controversy [2,3]. The time delay between reconnection and auroral intensification requires a propagation speed significantly faster than can be explained by Alfvén waves. Kinetic Alfvén waves, however, can be much faster and could possibly explain the time lag. To test this possiblity, we simulate large scale reconnection events with the kinetic PIC code P3D and examine the disturbances on a magnetic field line as it propagates through a reconnection region. In the regions near the separatrices but relatively far from the x-line, the propagation physics is expected to be governed by the physics of kinetic Alfvén waves. Indeed, we find that the propagation speed of the magnetic disturbance roughly scales with kinetic Alfvén speeds. We also examine energization of electrons due to this disturbance. Consequences for our understanding of substorms will be discussed. [1] Angelopoulos, V. et al., Science, 321, 931, 2008. [2] Lui, A. T. Y., Science, 324, 1391-b, 2009. [3] Angelopoulos, V. et al., Science, 324, 1391-c, 2009.

  20. Effects of electron inertia in collisionless magnetic reconnection

    SciTech Connect

    Andrés, Nahuel Gómez, Daniel; Martin, Luis; Dmitruk, Pablo

    2014-07-15

    We present a study of collisionless magnetic reconnection within the framework of full two-fluid MHD for a completely ionized hydrogen plasma, retaining the effects of the Hall current, electron pressure and electron inertia. We performed 2.5D simulations using a pseudo-spectral code with no dissipative effects. We check that the ideal invariants of the problem are conserved down to round-off errors. Our numerical results confirm that the change in the topology of the magnetic field lines is exclusively due to the presence of electron inertia. The computed reconnection rates remain a fair fraction of the Alfvén velocity, which therefore qualifies as fast reconnection.

  1. Three-Dimensional Modeling of Guide-Field Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Hesse, Michael

    2005-01-01

    The dissipation mechanism of guide field magnetic reconnection remains a subject of intense scientific interest. On one hand, one set of recent studies have shown that particle inertia-based processes, which include thermal and bulk inertial effects, provide the reconnection electric field in the diffusion region. On the other hand, a second set of studies emphasizes the role of wave-particle interactions in providing anomalous resistivity in the diffusion region. In this presentation, we analyze three-dimensional PIC simulations of guide-field magnetic reconnection. Specific emphasis will be on the question whether thermal-inertia processes, mediated by the electron pressure tensor, remain a viable dissipation mechanism in fully three-dimensional systems.

  2. Effects of electron inertia in collisionless magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Andrés, Nahuel; Martin, Luis; Dmitruk, Pablo; Gómez, Daniel

    2014-07-01

    We present a study of collisionless magnetic reconnection within the framework of full two-fluid MHD for a completely ionized hydrogen plasma, retaining the effects of the Hall current, electron pressure and electron inertia. We performed 2.5D simulations using a pseudo-spectral code with no dissipative effects. We check that the ideal invariants of the problem are conserved down to round-off errors. Our numerical results confirm that the change in the topology of the magnetic field lines is exclusively due to the presence of electron inertia. The computed reconnection rates remain a fair fraction of the Alfvén velocity, which therefore qualifies as fast reconnection.

  3. Plasma Heating During Magnetic Reconnection: Implications for Turbulent Dissipation

    NASA Astrophysics Data System (ADS)

    Shay, M. A.; Parashar, T.; Matthaeus, W. H.; Haggerty, C. C.

    2015-12-01

    Current sheets and associated intermittency are known to be prevalent in many turbulent plasmas and have been shown to be correlated with heating in observations of solar wind turbulence [1] and dissipation in kinetic particle-in-cell simulations [5]. Most intriguing, recent PIC simulations have found that the relative ion to electron heating ratio is strongly dependent on the turbulence amplitude [3]. An important question is whether magnetic reconnection is an important mechanism responsible for this heating. Studies focused on laminar reconnection have made significant progress recently on the magnitude and physics responsible for heating during magnetic reconnection [2,4]. The ambient Alfven speed of plasma flowing into the reconnection region plays a critical role, with heating initially taking the form of counterstreaming beams generated by non-local acceleration mechanism. However, there are significant uncertainties with how to link this basic reconnection heating with generic heating in a turbulent plasma. In this presentation, our current understanding of heating due to reconnection will be reviewed, and the factors determining the applicability of this heating to turbulent dissipation and heating will be discussed. These ideas will be explored through the comparison of kinetic PIC simulations of turbulence with reconnection heating models. Key aspects that will be examined are the effect of differing turbulent conditions on the magnitude and anisotropy of the heating, as well as the ion to electron heating ratio. [1] Osman et al., ApJ Letters, 727, L11, 2011. [2] Phan, et al., GRL, 40, 50917, 2013. [3] Wu et al., ApJ Letters, 763, L30, 2013. [4] Shay et al., Phys. Plasmas, 21, 122902, 2014. [5] Wan et al., PRL, 114, 175002, 2015.

  4. The Onset of Magnetic Reconnection in Tail-Like Equilibria

    NASA Technical Reports Server (NTRS)

    Hesse, Michael; Birn, Joachim; Kuznetsova, Masha

    1999-01-01

    Magnetic reconnection is a fundamental mode of dynamics in the magnetotail, and is recognized as the basic mechanisms converting stored magnetic energy into kinetic energy of plasma particles. The effects of the reconnection process are well documented by spacecraft observations of plasmoids in the distant magnetotail, or bursty bulk flows, and magnetic field dipolarizations in the near Earth region. Theoretical and numerical analyses have, in recent years, shed new light on the way reconnection operates, and, in particular, which microscopic mechanism supports the dissipative electric field in the associated diffusion region. Despite this progress, however. the question of how magnetic reconnection initiates in a tail-like magnetic field with finite flux threading the current i.sheet remains unanswered. Instead, theoretical studies supported by numerical simulations support the point-of-view that such plasma and current sheets are stable with respect to collisionless tearing mode. In this paper, we will further investigate this conclusion, with emphasis on the question whether it remains valid in plasma sheets with embedded thin current sheets. For this purpose, we perform particle-in-cell simulations of the driven formation of thin current sheets, and their subsequent evolution either to equilibrium or to instability of a tearing-type mode. In the latter case we will pay particular attention to the nature of the electric field contribution which unmagnetizes the electrons.

  5. Effect of electron inertia in two-fluid magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Gomez, Daniel; Dmitruk, Pablo; Andrés, Nahuel

    2016-07-01

    In space plasmas, magnetic reconnection is an important energy conversion process. Within the traditional one-fluid resistive MHD description, the Sweet-Parker model leads to extremely low reconnection rates for virtually all space physics applications. Within the theoretical framework of two-fluid MHD, we retain the effects of the Hall current and electron inertia and neglect dissipative effects such as viscosity and electric resistivity. This description brings two new spatial scales into play, such as the ion and electron inertial lengths. In absence of resistive dissipation, reconnection can only be attained by the action of electron inertia. We performed two-fluid simulations using a pseudo-spectral code which yields exact conservation (to round-off errors) of the ideal invariants. Our simulations show that when the effects of electron inertia are retained, magnetic reconnection takes place. Moreover, in a stationary regime the reconnection rate is simply proportional to the ion inertial length, as also emerges from a scaling law derived from dimensional arguments.

  6. The plasmoid instability and Hall effect during chromospheric magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Murphy, Nicholas Arnold; Lukin, Vyacheslav

    2016-01-01

    Magnetic reconnection is a ubiquitous process in the partially ionized solar chromosphere. Recent two-dimensional simulations have shown that the plasmoid instability onsets during partially ionized reconnection [1-4]. We use the plasma-neutral module of the HiFi framework to simulate the nonlinear evolution of the plasmoid instability during symmetric and asymmetric reconnection. These simulations model the plasma and neutrals as separate fluids and include ionization, recombination, charge exchange, thermal conduction, and the Hall effect. The Hall effect leads to the development of significant out-of-plane magnetic fields in the current sheet region in the laminar phase, but we do not observe shortening of the current sheet or significant acceleration of the reconnection rate as a result. After the onset of the plasmoid instability, structure develops on scales comparable to the ion inertial length. We compare simulations of the plasmoid instability with and without the Hall effect to determine its impact on the reconnection process. Finally, we discuss ongoing efforts to connect these simulations with solar observations and laboratory experiments.[1] Leake et al. 2012, ApJ, 760, 109 [2] Leake et al. 2013, PhPl, 20, 062102 [3] Ni et al. 2015, ApJ, 799, 79 [4] Murphy & Lukin 2015, ApJ, 805, 134

  7. Kinetic simulation of magnetic reconnection in the presence of shear

    SciTech Connect

    Francis, G.E.; Hewett, D.W.; Max, C.E.

    1988-09-05

    The basic physical processes associated with collisionless magnetic reconnection are investigated using the implicit PIC code AVANTI. The code is based on a 2.5-D fully electromagnetic direct implicit algorithm which has proven stable for arbitrary time step. This stability makes it possible to separate out the respective roles of the highly magnetized electrons and the un-magnetized ions for large ion-electron mass ratios. It is found that the inclusion of a guide magnetic field (magnetic shear) severely slows the initial stages of reconnection and damps out the electrostatic ringing if local values of the guide field are above a threshold determined by questions of electron mobility. 9 refs., 6 figs.

  8. Energy conversion during magnetic reconnection for magnetotail-like equilibria

    SciTech Connect

    Yoon, P. H.; Lui, A. T. Y.

    2006-10-15

    The principle of magnetic field-to-particle energy conversion for magnetic reconnection, originally developed by the authors for Harris-Fadeev equilibria, is extended to include a finite north-south (normal) component of the magnetic field, which is typical of the Earth's magnetotail environment. On the basis of the exact conservation laws derived from the nonlinear Vlasov equation, it is demonstrated that a small portion of the energy stored in the magnetic field is released and converted to particle thermal energy as a result of the magnetic field topological transformation, i.e., reconnection. It is also found that the normal field component has a minimal impact on the efficacy of the energy exchange.

  9. Magnetism In 3d Transition Metals at High Pressures

    SciTech Connect

    Iota, V

    2006-02-09

    This research project examined the changes in electronic and magnetic properties of transition metals and oxides under applied pressures, focusing on complex relationship between magnetism and phase stability in these correlated electron systems. As part of this LDRD project, we developed new measurement techniques and adapted synchrotron-based electronic and magnetic measurements for use in the diamond anvil cell. We have performed state-of-the-art X-ray spectroscopy experiments at the dedicated high-pressure beamline HP-CAT (Sector 16 Advanced Photon Source, Argonne National Laboratory), maintained in collaboration with of University of Nevada, Las Vegas and Geophysical Laboratory of The Carnegie Institution of Washington. Using these advanced measurements, we determined the evolution of the magnetic order in the ferromagnetic 3d transition metals (Fe, Co and Ni) under pressure, and found that at high densities, 3d band broadening results in diminished long range magnetic coupling. Our experiments have allowed us to paint a unified picture of the effects of pressure on the evolution of magnetic spin in 3d electron systems. The technical and scientific advances made during this LDRD project have been reported at a number of scientific meetings and conferences, and have been submitted for publication in technical journals. Both the technical advances and the physical understanding of correlated systems derived from this LDRD are being applied to research on the 4f and 5f electron systems under pressure.

  10. Magnetic reconnection in the solar atmosphere: from proposal to paradigm

    NASA Astrophysics Data System (ADS)

    Cargill, Peter; Parnell, Clare; Browning, Philippa; de Moortel, Ineke; Hood, Alan

    2010-06-01

    MEETING REPORT On 13 November 2009, the RAS hosted a discussion meeting to commemorate the formal retirement of Prof. Eric Priest. Here Peter Cargill, Clare Parnell, Philippa Browning, Ineke de Moortel and Alan Hood examine how magnetic reconnection has evolved over the past 50 years from an important but controversial proposal, to a general paradigm.

  11. Voltage controlled magnetism in 3d transitional metals

    NASA Astrophysics Data System (ADS)

    Wang, Weigang

    2015-03-01

    Despite having attracted much attention in multiferroic materials and diluted magnetic semiconductors, the impact of an electric field on the magnetic properties remains largely unknown in 3d transitional ferromagnets (FMs) until recent years. A great deal of effort has been focused on the voltage-controlled magnetic anisotropy (VCMA) effect where the modulation of anisotropy field is understood by the change of electron density among different d orbitals of FMs in the presence of an electric field. Here we demonstrate another approach to alter the magnetism by electrically controlling the oxidation state of the 3d FM at the FM/oxide interface. The thin FM film sandwiched between a heavy metal layer and a gate oxide can be reversibly changed from an optimally-oxidized state with a strong perpendicular magnetic anisotropy to a metallic state with an in-plane magnetic anisotropy, or to a fully-oxidized state with nearly zero magnetization, depending on the polarity and time duration of the applied electric fields. This is a voltage controlled magnetism (VCM) effect, where both the saturation magnetization and anisotropy field of the 3d FM layer can be simultaneously controlled by voltage in a non-volatile fashion. We will also discuss the impact of this VCM effect on magnetic tunnel junctions and spin Hall switching experiments. This work, in collaboration with C. Bi, Y.H. Liu, T. Newhouse-Illige, M. Xu, M. Rosales, J.W. Freeland, O. Mryasov, S. Zhang, and S.G.E. te Velthuis, was supported in part by NSF (ECCS-1310338) and by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA.

  12. Effects of Magnetic Reconnection Processes in the Near Magnetosphere

    NASA Astrophysics Data System (ADS)

    Coppi, B.; Fletcher, A.

    2016-10-01

    Magnetic reconnection processes in collisionless plasmas on the Earth's dayside and nightside are shown to be capable of producing high energy populations of both ions and electrons. These particles can interact with the Radiation Belts and reach the regions close to the Earth where auroral substorms can be produced. The main theoretical issues faced in identifying plasma modes with realistic characteristics, given the scale distances and time scales, that can be responsible for the needed reconnection processes are pointed out. Solution of relevant equations obtained by a combined analytical and numerical approach. Sponsored in part by the U.S. D.O.E. and the N.S.F.

  13. Solar flares as cascades of reconnecting magnetic loops.

    PubMed

    Hughes, D; Paczuski, M; Dendy, R O; Helander, P; McClements, K G

    2003-04-04

    A model for the solar coronal magnetic field is proposed where multiple directed loops evolve in space and time. Loops injected at small scales are anchored by footpoints of opposite polarity moving randomly on a surface. Nearby footpoints of the same polarity aggregate, and loops can reconnect when they collide. This may trigger a cascade of further reconnection, representing a solar flare. Numerical simulations show that a power law distribution of flare energies emerges, associated with a scale-free network of loops, indicating self-organized criticality.

  14. Fast Magnetic Reconnection in the Plasmoid-Dominated Regime

    SciTech Connect

    Uzdensky, D. A.; Loureiro, N. F.; Schekochihin, A. A.

    2010-12-03

    A conceptual model of resistive magnetic reconnection via a stochastic plasmoid chain is proposed. The global reconnection rate is shown to be independent of the Lundquist number. The distribution of fluxes in the plasmoids is shown to be an inverse-square law. It is argued that there is a finite probability of emergence of abnormally large plasmoids, which can disrupt the chain (and may be responsible for observable large abrupt events in solar flares and sawtooth crashes). A criterion for the transition from the resistive magnetohydrodynamic to the collisionless regime is provided.

  15. A New Electric Field in Asymmetric Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Malakit, K.; Shay, M. A.; Cassak, P.; Ruffolo, D. J.

    2013-12-01

    Magnetic reconnection is an important plasma process that drives the dynamics of the plasma in the magnetosphere and plays a crucial role in the interaction between magnetospheric and magnetosheath plasma. It has been shown that when a reconnection occurs in a collisionless plasma, it exhibits the Hall electric field, an in-plane electric field structure pointing toward the X-line. In this work, we show that when the reconnection has asymmetric inflow conditions such as the reconnection at the day-side magnetopause, a new in-plane electric field structure can exist. This electric field points away from the X-line and is distinct from the known Hall electric field. We argue that the origin of the electric field is associated with the physics of finite Larmor radius. A theory and predictions of the electric field properties are presented and backed up by results from fully kinetic particle-in-cell simulations of asymmetric reconnection with various inflow conditions. Under normal day-side reconnection inflow conditions, the electric field is expected to occur on the magnetospheric side of the X-line pointing Earthward. Hence, it has a potential to be used as a signature for satellites, such as the upcoming Magnetospheric Multi-Scale (MMS) mission, to locate the reconnection sites at the day-side magnetopause. This research was supported by the postdoctoral research sponsorship of Mahidol University (KM), NSF grants ATM-0645271 - Career Award (MAS) and AGS-0953463 (PAC), NASA grants NNX08A083G - MMS IDS, NNX11AD69G, and NNX13AD72G (MAS) and NNX10AN08A (PAC), and the Thailand Research Fund (DR).

  16. Kinetic shielding of magnetic islands in 3-D equilibria

    NASA Astrophysics Data System (ADS)

    Hegna, C. C.

    2010-11-01

    Kinetic theory is employed to calculate corrections to analytic predictions of saturated magnetic islands due to pressure gradients in 3-D magnetic configurations. The theory calculates the dominant trapped particle response to 3-D field induced net bounce averaged radial drifts. The associated kinetic response describes plasma currents that flow within magnetic surfaces. In general, these currents have a component that resonates with the helical angle of the magnetic island and affect saturated island sizes through the parallel currents generated to satisfy quasineutrality. The resulting kinetic response generally opposes the effects of singular Pfirsch-Schlüter currents that arise at the rational surfaces of general 3-D MHD equilibria. Accounting for both the MHD and kinetic responses, self-consistent magnetic island widths are calculated using Ampere's law. The kinetic effect is largest at lowest collisionality suggesting high-β stellarators are more resilient to retaining flux surface integrity at high-temperatures than predictions from conventional MHD based theory would imply.

  17. Localized electron heating during magnetic reconnection in MAST

    NASA Astrophysics Data System (ADS)

    Yamada, T.; Tanabe, H.; Watanabe, T. G.; Hayashi, Y.; Imazawa, R.; Inomoto, M.; Ono, Y.; Gryaznevich, M.; Scannell, R.; Michael, C.; The MAST Team

    2016-10-01

    Significant increase in the plasma temperature above 1 keV was measured during the kilogauss magnetic field reconnection of two merging toroidal plasmas under the high-guide field and collision-less conditions. The electron temperature was observed to peak significantly at the X-point inside the current sheet, indicating Joule heating caused by the toroidal electric field along the X-line. This peaked temperature increases significantly with the guide field, in agreement with the electron mean-free path calculation. The slow electron heating in the downstream suggests energy conversion from ions to electrons through ion-electron collisions in the bulk plasma as the second electron heating mechanism in the bulk plasma. The electron density profile clearly reveals the electron density pile-up / fast shock structures in the downstream of reconnection, suggesting energy conversion from ion flow energy to ion thermal energy as well as significant ion heating by reconnection outflow.

  18. Fast magnetic reconnection due to anisotropic electron pressure

    SciTech Connect

    Cassak, P. A.; Baylor, R. N.; Fermo, R. L.; Beidler, M. T.; Shay, M. A.; Swisdak, M.; Drake, J. F.; Karimabadi, H.

    2015-02-15

    A new regime of fast magnetic reconnection with an out-of-plane (guide) magnetic field is reported in which the key role is played by an electron pressure anisotropy described by the Chew-Goldberger-Low gyrotropic equations of state in the generalized Ohm's law, which even dominates the Hall term. A description of the physical cause of this behavior is provided and two-dimensional fluid simulations are used to confirm the results. The electron pressure anisotropy causes the out-of-plane magnetic field to develop a quadrupole structure of opposite polarity to the Hall magnetic field and gives rise to dispersive waves. In addition to being important for understanding what causes reconnection to be fast, this mechanism should dominate in plasmas with low plasma beta and a high in-plane plasma beta with electron temperature comparable to or larger than ion temperature, so it could be relevant in the solar wind and some tokamaks.

  19. Observational Signatures of Magnetic Reconnection in the Extended Corona

    NASA Technical Reports Server (NTRS)

    Savage, Sabrina; West, Matthew J.; Seaton, Daniel B.; Kobelski, Adam

    2016-01-01

    Observational signatures of reconnection have been studied extensively in the lower corona for decades, successfully providing insight into energy release mechanisms in the region above post-flare arcade loops and below 1.5 solar radii. During large eruptive events, however, energy release continues to occur well beyond the presence of reconnection signatures at these low heights. Supra-Arcade Downflows (SADs) and Supra-Arcade Downflowing Loops (SADLs) are particularly useful measures of continual reconnection in the corona as they may indicate the presence and path of retracting post-reconnection loops. SADs and SADLs have been faintly observed up to 18 hours beyond the passage of coronas mass ejections through the SOHO/LASCO field of view, but a recent event from 2014 October 14 associated with giant arches provides very clear observations of these downflows for days after the initial eruption. We report on this unique event and compare these findings with observational signatures of magnetic reconnection in the extended corona for more typical eruptions.

  20. Observational Signatures of Magnetic Reconnection in the Extended Corona

    NASA Technical Reports Server (NTRS)

    Savage, Sabrina; West, Matthew J.; Seaton, Danial B.; Kobelski, Adam

    2016-01-01

    Observational signatures of reconnection have been studied extensively in the lower corona for decades, successfully providing insight into energy release mechanisms in the region above post-flare arcade loops and below 1.5 solar radii. During large eruptive events, however, energy release continues to occur well beyond the presence of reconnection signatures at these low heights. Supra-Arcade Downflows (SADs) and Supra-Arcade Downflowing Loops (SADLs) are particularly useful measures of continual reconnection in the corona as they may indicate the presence and path of retracting post-reconnection loops. SADs and SADLs have been faintly observed up to 18 hours beyond the passage of corona mass ejections through the SOHO/LASCO field of view, but a recent event from 2014 October 14 associated with giant arches provides very clear observations of these downflows for days after the initial eruption. We report on this unique event and compare these findings with observational signatures of magnetic reconnection in the extended corona for more typical eruptions.

  1. Magnetic reconnection process in transient coaxial helicity injection

    SciTech Connect

    Ebrahimi, F.; Hooper, E. B.; Sovinec, C. R.; Raman, R.

    2013-09-15

    The physics of magnetic reconnection and fast flux closure in transient coaxial helicity injection experiments in NSTX is examined using resistive MHD simulations. These simulations have been performed using the NIMROD code with fixed boundary flux (including NSTX poloidal coil currents) in the NSTX experimental geometry. Simulations show that an X point is formed in the injector region, followed by formation of closed flux surfaces within 0.5 ms after the driven injector voltage and injector current begin to rapidly decrease. As the injector voltage is turned off, the field lines tend to untwist in the toroidal direction and magnetic field compression exerts a radial J × B force and generates a bi-directional radial E{sub toroidal}×B{sub poloidal} pinch flow to bring oppositely directed field lines closer together to reconnect. At sufficiently low magnetic diffusivity (high Lundquist number), and with a sufficiently narrow injector flux footprint width, the oppositely directed field lines have sufficient time to reconnect (before dissipating), leading to the formation of closed flux surfaces. The reconnection process is shown to have transient Sweet-Parker characteristics.

  2. Turbulent reconnection of magnetic bipoles in stratified turbulence

    NASA Astrophysics Data System (ADS)

    Jabbari, S.; Brandenburg, A.; Mitra, Dhrubaditya; Kleeorin, N.; Rogachevskii, I.

    2016-07-01

    We consider strongly stratified forced turbulence in a plane-parallel layer with helicity and corresponding large-scale dynamo action in the lower part and non-helical turbulence in the upper. The magnetic field is found to develop strongly concentrated bipolar structures near the surface. They form elongated bands with a sharp interface between opposite polarities. Unlike earlier experiments with imposed magnetic field, the inclusion of rotation does not strongly suppress the formation of these structures. We perform a systematic numerical study of this phenomenon by varying magnetic Reynolds number, scale-separation ratio, and Coriolis number. We focus on the formation of a current sheet between bipolar regions where reconnection of oppositely oriented field lines occurs. We determine the reconnection rate by measuring either the inflow velocity in the vicinity of the current sheet or by measuring the electric field in the reconnection region. We demonstrate that for large Lundquist numbers, S > 103, the reconnection rate is nearly independent of S in agreement with results of recent numerical simulations performed by other groups in simpler settings.

  3. 3D Magnetic inversion and remanence: solving the problem

    NASA Astrophysics Data System (ADS)

    Thomson, V.; Morris, W.

    2003-04-01

    3D inversion of surface magnetic data is a common processing technique when used in mineral exploration. The major drawback of most 3D inversion algorithms is that they assume that the surface magnetic anomaly is produced by induced magnetization and that there are no remanent magnetization or demagnetization effects present. This has a significant impact when modeling magnetic data that has remanent magnetization. The magnetic anomaly produced by a dipping subsurface body will be identical for a consistent relationship between the dip of the body and the dip of the magnetic vector, regardless of the actual dip of the magnetic body. For example, in the case where a subsurface body is dipping, such as a dipping dike, the dip estimated by the inversion routine will be correct only if induced magnetization is present. This has serious implications for mineral exploration. A solution to the remanence problem is to model the surface magnetic anomaly using a constrained 2D approach rather than 3D. Using a priori information on dip and strike length of a source body, it is possible to approximate the remanence direction and intensity. The 2D solutions can then be rendered into a 3D imaging package to create a model in 3D. A case study was performed on a mafic-ultramafic layered igneous intrusion located in Big Trout Lake, northwestern Ontario, Canada. Large layered igneous intrusions are known to have significant remanence. Like many other layered igneous intrusions such as the Bushveld Complex in South Africa, the Big Trout Lake Complex is highly prospective for Platinum Group Elements (PGEs). Intruded during Archean time, the Big Trout Lake Complex has been subsequently folded and faulted to near vertical. As a consequence of limited surface exposures, knowledge of layering within the pluton and the extent of deformation of the pluton is very limited. Newly acquired high-resolution aeromagnetic data shows a strongly mineralized horizon within the intrusion that

  4. Slipping magnetic reconnection during an X-class solar flare observed by SDO/AIA

    SciTech Connect

    Dudík, J.; Del Zanna, G.; Mason, H. E.; Janvier, M.; Aulanier, G.; Schmieder, B.; Karlický, M. E-mail: mjanvier@maths.dundee.ac.uk

    2014-04-01

    We present SDO/AIA observations of an eruptive X-class flare of 2012 July 12, and compare its evolution with the predictions of a three-dimensional (3D) numerical simulation. We focus on the dynamics of flare loops that are seen to undergo slipping reconnection during the flare. In the Atmospheric Imaging Assembly (AIA) 131 Å observations, lower parts of 10 MK flare loops exhibit an apparent motion with velocities of several tens of km s{sup –1} along the developing flare ribbons. In the early stages of the flare, flare ribbons consist of compact, localized bright transition-region emission from the footpoints of the flare loops. A differential emission measure analysis shows that the flare loops have temperatures up to the formation of Fe XXIV. A series of very long, S-shaped loops erupt, leading to a coronal mass ejection observed by STEREO. The observed dynamics are compared with the evolution of magnetic structures in the 'standard solar flare model in 3D.' This model matches the observations well, reproducing the apparently slipping flare loops, S-shaped erupting loops, and the evolution of flare ribbons. All of these processes are explained via 3D reconnection mechanisms resulting from the expansion of a torus-unstable flux rope. The AIA observations and the numerical model are complemented by radio observations showing a noise storm in the metric range. Dm-drifting pulsation structures occurring during the eruption indicate plasmoid ejection and enhancement of the reconnection rate. The bursty nature of radio emission shows that the slipping reconnection is still intermittent, although it is observed to persist for more than an hour.

  5. Model of magnetic reconnection in space and astrophysical plasmas

    SciTech Connect

    Boozer, Allen H.

    2013-03-15

    Maxwell's equations imply that exponentially smaller non-ideal effects than commonly assumed can give rapid magnetic reconnection in space and astrophysical plasmas. In an ideal evolution, magnetic field lines act as stretchable strings, which can become ever more entangled but cannot be cut. High entanglement makes the lines exponentially sensitive to small non-ideal changes in the magnetic field. The cause is well known in popular culture as the butterfly effect and in the theory of deterministic dynamical systems as a sensitive dependence on initial conditions, but the importance to magnetic reconnection is not generally recognized. Two-coordinate models are too constrained geometrically for the required entanglement, but otherwise the effect is general and can be studied in simple models. A simple model is introduced, which is periodic in the x and y Cartesian coordinates and bounded by perfectly conducting planes in z. Starting from a constant magnetic field in the z direction, reconnection is driven by a spatially smooth, bounded force. The model is complete and could be used to study the impulsive transfer of energy between the magnetic field and the ions and electrons using a kinetic plasma model.

  6. 3-D Display Of Magnetic Resonance Imaging Of The Spine

    NASA Astrophysics Data System (ADS)

    Nelson, Alan C.; Kim, Yongmin; Haralick, Robert M.; Anderson, Paul A.; Johnson, Roger H.; DeSoto, Larry A.

    1988-06-01

    The original data is produced through standard magnetic resonance imaging (MRI) procedures with a surface coil applied to the lower back of a normal human subject. The 3-D spine image data consists of twenty-six contiguous slices with 256 x 256 pixels per slice. Two methods for visualization of the 3-D spine are explored. One method utilizes a verifocal mirror system which creates a true 3-D virtual picture of the object. Another method uses a standard high resolution monitor to simultaneously show the three orthogonal sections which intersect at any user-selected point within the object volume. We discuss the application of these systems in assessment of low back pain.

  7. MESSENGER Observations of Magnetic Reconnection in Mercury's Magnetosphere

    NASA Technical Reports Server (NTRS)

    Slavin. James A.

    2009-01-01

    During MESSENGER'S second flyby of Mercury on October 6,2008, very intense reconnection was observed between the planet's magnetic field and a steady southward interplanetary magnetic field (IMF). The dawn magnetopause was threaded by a strong magnetic field normal to its surface, approx.14 nT, that implies a rate of reconnection approx.10 times the typical rate at Earth and a cross-magnetospheric electric potential drop of approx.30 kV. The highest magnetic field observed during this second flyby, approx.160 nT, was found at the core of a large dayside flux transfer event (FTE). This FTE is estimated to contain magnetic flux equal to approx.5% that of Mercury's magnetic tail or approximately one order of magnitude higher fraction of the tail flux than is typically found for FTEs at Earth. Plasmoid and traveling compression region (TCR) signatures were observed throughout MESSENGER'S traversal of Mercury's magnetotail with a repetition rate comparable to the Dungey cycle time of approx.2 min. The TCR signatures changed from south-north, indicating tailward motion, to north-south, indicating sunward motion, at a distance approx.2.6 RM (where RM is Mercury's radius) behind the terminator indicating that the near-Mercury magnetotail neutral line was crossed at that point. Overall, these new MESSENGER observations suggest that magnetic reconnection at the dayside magnetopause is very intense relative to what is found at Earth and other planets, while reconnection in Mercury's tail is similar to that in other planetary magnetospheres, but with a very short Dungey cycle time.

  8. SIGNATURES OF MAGNETIC RECONNECTION AT BOUNDARIES OF INTERPLANETARY SMALL-SCALE MAGNETIC FLUX ROPES

    SciTech Connect

    Tian Hui; Yao Shuo; Zong Qiugang; Qi Yu; He Jiansen

    2010-09-01

    The interaction between interplanetary small-scale magnetic flux ropes and the magnetic field in the ambient solar wind is an important topic in the understanding of the evolution of magnetic structures in the heliosphere. Through a survey of 125 previously reported small flux ropes from 1995 to 2005, we find that 44 of them reveal clear signatures of Alfvenic fluctuations and thus classify them as Alfven wave trains rather than flux ropes. Signatures of magnetic reconnection, generally including a plasma jet of {approx}30 km s{sup -1} within a magnetic field rotational region, are clearly present at boundaries of about 42% of the flux ropes and 14% of the wave trains. The reconnection exhausts are often observed to show a local increase in the proton temperature, density, and plasma beta. About 66% of the reconnection events at flux rope boundaries are associated with a magnetic field shear angle larger than 90{sup 0} and 73% of them reveal a decrease of 20% or more in the magnetic field magnitude, suggesting a dominance of anti-parallel reconnection at flux rope boundaries. The occurrence rate of magnetic reconnection at flux rope boundaries through the years 1995-2005 is also investigated and we find that it is relatively low around the solar maximum and much higher when approaching solar minima. The average magnetic field depression and shear angle for reconnection events at flux rope boundaries also reveal a similar trend from 1995 to 2005. Our results demonstrate for the first time that boundaries of a substantial fraction of small-scale flux ropes have properties similar to those of magnetic clouds, in the sense that both of them exhibit signatures of magnetic reconnection. The observed reconnection signatures could be related either to the formation of small flux ropes or to the interaction between flux ropes and the interplanetary magnetic fields.

  9. The Pressure Limitations on Flux Pile-Up Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Litvinenko, Y. E.

    1999-05-01

    Flux pile-up magnetic reconnection was thought to be able to provide fast energy dissipation a strongly magnetized plasma, for example, in solar flares. We examine the problem of the plasma pressure limitations on the rapidity of flux pile-up reconnection. It is shown that for a two-dimensional stagnation point flow with nonzero vorticity the magnetic merging rate cannot exceed the Sweet-Parker scaling in a low-beta plasma, which is too slow to explain flares. Moreover, the solution has some undesireable properties such as a diffusion layer at the external boundary and the massively increasing inflow speed. The pressure limitation appears to be somewhat less restrictive for three-dimensional flux pile-up. This work was supported by NSF grant ATM-9813933.

  10. Ion Bernstein waves in the magnetic reconnection region

    NASA Astrophysics Data System (ADS)

    Narita, Y.; Nakamura, R.; Baumjohann, W.; Glassmeier, K.-H.; Motschmann, U.; Comişel, H.

    2016-01-01

    Four-dimensional energy spectra and a diagram for dispersion relations are determined for the first time in a magnetic reconnection region in the magnetotail using data from four-spacecraft measurements by the Cluster mission on a spatial scale of 200 km, about 0.1 ion inertial lengths. The energy spectra are anisotropic with an extension in the perpendicular direction and axially asymmetric with respect to the mean magnetic field. The dispersion diagram in the plasma rest frame is in reasonably good agreement with the ion Bernstein waves at the second and higher harmonics of the proton gyrofrequency. Perpendicular-propagating ion Bernstein waves likely exist in an outflow region of magnetic reconnection, which may contribute to bifurcation of the current sheet in the outflow region.

  11. Do dispersive waves play a role in collisionless magnetic reconnection?

    SciTech Connect

    Liu, Yi-Hsin; Daughton, W.; Li, H.; Karimabadi, H.; Peter Gary, S.

    2014-02-15

    Using fully kinetic simulations, we demonstrate that the properly normalized reconnection rate is fast ∼0.1 for guide fields up to 80× larger than the reconnecting field and is insensitive to both the system size and the ion to electron mass ratio. These results challenge conventional explanations of reconnection based on fast dispersive waves, which are completely absent for sufficiently strong guide fields. In this regime, the thickness of the diffusion layer is set predominantly by the electron inertial length with an inner sublayer that is controlled by finite gyro-radius effects. As the Alfvén velocity becomes relativistic for very strong guide fields, the displacement current becomes important and strong deviations from charge neutrality occur, resulting in the build-up of intense electric fields which absorb a portion of the magnetic energy release. Over longer time scales, secondary magnetic islands are generated near the active x-line while an electron inertial scale Kelvin-Helmholtz instability is driven within the outflow. These secondary instabilities give rise to time variations in the reconnection rate but do not alter the average value.

  12. Magnetic Reconnection with Strong Synchrotron Cooling in Pulsar Magnetospheres

    NASA Astrophysics Data System (ADS)

    Uzdensky, Dmitri; Spitkovsky, Anatoly

    2012-10-01

    The magnetosphere of a rotating pulsar naturally develops a current sheet beyond the light cylinder (LC). Magnetic reconnection in this current sheet inevitably dissipates a nontrivial fraction of the pulsar spin-down power within a few LC radii. In this presentation, a basic physical picture of reconnection in this environment is developed. It is shown that reconnection proceeds in the plasmoid-dominated regime, via an hierarchical chain of multiple secondary islands/flux ropes. The inter-plasmoid reconnection layers are subject to strong synchrotron cooling, leading to significant plasma compression. The basic parameters of these current layers --- temperature, density, and layer thickness --- are estimated in terms of the upstream magnetic field. It is argued that, after accounting for the bulk Doppler boosting, the synchrotron and inverse-Compton emission mechanisms can explain the observed pulsed high-energy (GeV) and VHE (˜ 100 GeV) radiation, respectively. The motions of the secondary plasmoids may contribute to the pulsar's radio emission.

  13. The mechanisms of electron heating and acceleration during magnetic reconnection

    SciTech Connect

    Dahlin, J. T. Swisdak, M.; Drake, J. F.

    2014-09-15

    The heating of electrons in collisionless magnetic reconnection is explored in particle-in-cell simulations with non-zero guide fields so that electrons remain magnetized. In this regime, electric fields parallel to B accelerate particles directly, while those perpendicular to B do so through gradient-B and curvature drifts. The curvature drift drives parallel heating through Fermi reflection, while the gradient B drift changes the perpendicular energy through betatron acceleration. We present simulations in which we evaluate each of these mechanisms in space and time in order to quantify their role in electron heating. For a case with a small guide field (20% of the magnitude of the reconnecting component), the curvature drift is the dominant source of electron heating. However, for a larger guide field (equal to the magnitude of the reconnecting component) electron acceleration by the curvature drift is comparable to that of the parallel electric field. In both cases, the heating by the gradient B drift is negligible in magnitude. It produces net cooling because the conservation of the magnetic moment and the drop of B during reconnection produce a decrease in the perpendicular electron energy. Heating by the curvature drift dominates in the outflow exhausts where bent field lines expand to relax their tension and is therefore distributed over a large area. In contrast, the parallel electric field is localized near X-lines. This suggests that acceleration by parallel electric fields may play a smaller role in large systems where the X-line occupies a vanishing fraction of the system. The curvature drift and the parallel electric field dominate the dynamics and drive parallel heating. A consequence is that the electron energy spectrum becomes extremely anisotropic at late time, which has important implications for quantifying the limits of electron acceleration due to synchrotron emission. An upper limit on electron energy gain that is substantially higher than

  14. Three-dimensional MHD Magnetic Reconnection Simulations with a Finite Guide Field: Proposal of the Shock-evoking Positive-feedback Model

    NASA Astrophysics Data System (ADS)

    Wang, Shuoyang; Yokoyama, Takaaki; Isobe, Hiroaki

    2015-09-01

    Using a three-dimensional (3D) magnetohydrodynamic model, we simulate the magnetic reconnection in a single current sheet. We assume a finite guide field, a random perturbation on the velocity field, and uniform resistivity. Our model enhances the reconnection rate relative to the classical Sweet-Parker model in the same configuration. The efficiency of magnetic energy conversion is increased by interactions between the multiple tearing layers coexisting in the global current sheet. This interaction, which forms a positive-feedback system, arises from coupling of the inflow and outflow regions in different layers across the current sheet. The coupling accelerates the elementary reconnection events, thereby enhancing the global reconnection rate. The reconnection establishes flux tubes along each tearing layer. Slow-mode shocks gradually form along the outer boundaries of these tubes, further accelerating the magnetic energy conversion. Such a positive-feedback system is absent in two-dimensional simulations, 3D reconnection without a guide field, and reconnection under a single perturbation mode. We refer to our model as the “shock-evoking positive-feedback” model.

  15. THREE-DIMENSIONAL MHD MAGNETIC RECONNECTION SIMULATIONS WITH A FINITE GUIDE FIELD: PROPOSAL OF THE SHOCK-EVOKING POSITIVE-FEEDBACK MODEL

    SciTech Connect

    Wang, Shuoyang; Yokoyama, Takaaki; Isobe, Hiroaki

    2015-09-20

    Using a three-dimensional (3D) magnetohydrodynamic model, we simulate the magnetic reconnection in a single current sheet. We assume a finite guide field, a random perturbation on the velocity field, and uniform resistivity. Our model enhances the reconnection rate relative to the classical Sweet–Parker model in the same configuration. The efficiency of magnetic energy conversion is increased by interactions between the multiple tearing layers coexisting in the global current sheet. This interaction, which forms a positive-feedback system, arises from coupling of the inflow and outflow regions in different layers across the current sheet. The coupling accelerates the elementary reconnection events, thereby enhancing the global reconnection rate. The reconnection establishes flux tubes along each tearing layer. Slow-mode shocks gradually form along the outer boundaries of these tubes, further accelerating the magnetic energy conversion. Such a positive-feedback system is absent in two-dimensional simulations, 3D reconnection without a guide field, and reconnection under a single perturbation mode. We refer to our model as the “shock-evoking positive-feedback” model.

  16. Reciprocatory magnetic reconnection in a coronal bright point

    NASA Astrophysics Data System (ADS)

    Zhang, Q. M.; Chen, P. F.; Ding, M. D.; Ji, H. S.

    2014-08-01

    Context. Coronal bright points (CBPs) are small-scale and long-duration brightenings in the lower solar corona. They are often explained in terms of magnetic reconnection. Aims: We aim to study the substructures of a CBP and clarify the relationship among the brightenings of different patches inside the CBP. Methods: The event was observed by the X-ray Telescope (XRT) aboard the Hinode spacecraft on 2009 August 22-23. Results: The CBP showed repeated brightenings (or CBP flashes). During each of the two successive CBP flashes, that is, weak and strong flashes that were separated by ~2 hr, the XRT images revealed that the CBP was composed of two chambers, patches A and B. During the weak flash, patch A brightened first, and patch B brightened ~2 min later. During the transition, the right leg of a large-scale coronal loop drifted from the right side of the CBP to the left side. During the strong flash, patch B brightened first, and patch A brightened ~2 min later. During the transition, the right leg of the large-scale coronal loop drifted from the left side of the CBP to the right side. In each flash, the rapid change of the connectivity of the large-scale coronal loop is strongly suggestive of the interchange reconnection. Conclusions: For the first time we found reciprocatory reconnection in the CBP, which means that reconnected loops in the outflow region of the first reconnection process serve as the inflow of the second reconnection process. Movies associated with Figs. 2 and 5 are available in electronic form at http://www.aanda.org

  17. Three-dimensional fast magnetic reconnection driven by relativistic ultraintense femtosecond lasers.

    PubMed

    Ping, Y L; Zhong, J Y; Sheng, Z M; Wang, X G; Liu, B; Li, Y T; Yan, X Q; He, X T; Zhang, J; Zhao, G

    2014-03-01

    Three-dimensional fast magnetic reconnection driven by two ultraintense femtosecond laser pulses is investigated by relativistic particle-in-cell simulation, where the two paralleled incident laser beams are shot into a near-critical plasma layer to form a magnetic reconnection configuration in self-generated magnetic fields. A reconnection X point and out-of-plane quadrupole field structures associated with magnetic reconnection are formed. The reconnection rate is found to be faster than that found in previous two-dimensional Hall magnetohydrodynamic simulations and electrostatic turbulence contribution to the reconnection electric field plays an essential role. Both in-plane and out-of-plane electron and ion accelerations up to a few MeV due to the magnetic reconnection process are also obtained.

  18. Note: 3D printed spheroid for uniform magnetic field generation

    NASA Astrophysics Data System (ADS)

    Öztürk, Y.; Aktaş, B.

    2016-10-01

    This article is focused on a novel and practical production method for a uniform magnetic field generator. The method involves building of a surface coil template using a desktop 3D printer and winding of a conducting wire onto the structure using surface grooves as a guide. Groove pattern was based on the parametric spheroidal helical coil formula. The coil was driven by a current source and the magnetic field inside was measured using a Hall probe placed into the holes on the printed structure. The measurements are found to be in good agreement with our finite element analysis results and indicate a fairly uniform field inside.

  19. OBSERVATIONS OF A SMALL INTERPLANETARY MAGNETIC FLUX ROPE ASSOCIATED WITH A MAGNETIC RECONNECTION EXHAUST

    SciTech Connect

    Feng, H. Q.; Wu, D. J.

    2009-11-10

    A small interplanetary magnetic flux rope prior to an X-line magnetic reconnection exhaust was observed on 1998 March 25 at 1 AU. The X-line magnetic reconnection exhaust has been identified and reported by Gosling et al. The duration of this small magnetic flux rope is about 2 hr. We fitted the constant alpha force-free model to the observed magnetic fields. The model fitting results show that the spacecraft crosses the magnetic flux rope well away from the axis, with d {sub 0}/R {sub 0} being 0.76. The fitting results also show that its magnetic configuration is a right-handed helical flux rope, that the estimated field intensity at the axis is 16.3 nT, and that its diameter is 0.0190 AU. In addition, the axial direction of this rope is (theta = 6 deg., phi = 214 deg.), namely, this magnetic flux rope is lying nearly in the ecliptic plane. According to the geometric relation of the small flux rope and the reconnection exhaust, it is very possible that the small magnetic flux rope has a larger scale initially and comes from the corona; its magnetic fields are peeled off when moving from the Sun to the Earth and at last it reaches a small scale. Though magnetic reconnection can produce a flux-rope topology, in this case the X-line magnetic reconnection is destroying rather than generating the small magnetic flux rope.

  20. Undriven magnetic reconnection in magnetohydrodynamics and Hall magnetohydrodynamics

    NASA Astrophysics Data System (ADS)

    Lottermoser, R.-F.; Scholer, M.

    1997-03-01

    Undriven magnetic reconnection in a one-dimensional current sheet is investigated by means of a two-dimensional compressible and resistive Hall MHD (HMHD) code. Reconnection is set up by applying a spatially limited resistivity in the center of an isothermal Harris sheet. Although the magnetic fields on the two sides of the initial current sheet are equal and exactly antiparallel, both magnetic field and flow velocity components out of the simulation plane are self-consistently generated in the course of the reconnection process. The quasi steady state exhibits all features of Petschek-like reconnection, such as two pairs of shock waves attached to the diffusion region, a strongly converging flow toward the field line reversal region, and a weak fast mode expansion of the inflowing plasma. The reconnection rate measured in terms of the Alfvén Mach number well upstream of the diffusion region is within the analytic limits for compressible Petschek reconnection and slightly higher than in the corresponding MHD case. In contrast to MHD, the shock in HMHD is a subfast, strong (2->4), intermediate shock; the thickness is ~=10ion inertial lengths, and the shocks exhibit an internal structure. The trailing left-handed slow mode wave train predicted from the integration of the stationary one-dimensional Hall MHD equations is not found. This is probably due to the fact that waves downstream of the shock are smeared out along the shock layer by the fast outflow jet. The shock waves generated during the decay of a current sheet are studied by a one-dimensional (1-D) Hall MHD simulation. In the 1-D case, the shocks are of slow mode type, and thus a left-handed intermediate mode wave train can form upstream of the shocks. The shock thickness is estimated to be at least a factor of 3 thicker than in 2-D HMHD fast reconnection. The intermediate shock in the 2-D HMHD simulation as well as the slow shock in the 1-D HMHD simulation exhibit an S-shaped hodogram. When starting the

  1. Magnetism in a graphene-4 f -3 d hybrid system

    NASA Astrophysics Data System (ADS)

    Huttmann, Felix; Klar, David; Atodiresei, Nicolae; Schmitz-Antoniak, Carolin; Smekhova, Alevtina; Martínez-Galera, Antonio J.; Caciuc, Vasile; Bihlmayer, Gustav; Blügel, Stefan; Michely, Thomas; Wende, Heiko

    2017-02-01

    We create an interface of graphene with a metallic and magnetic support that leaves its electronic structure largely intact. This is achieved by exposing epitaxial graphene on ferromagnetic thin films of Co and Ni to vapor of the rare earth metal Eu at elevated temperatures, resulting in the intercalation of an Eu monolayer in between graphene and its substrate. The system is atomically well defined, with the Eu monolayer forming a (√{3 }×√{3 }) R 30∘ superstructure with respect to the graphene lattice. Thereby, we avoid the strong hybridization with the (Ni,Co) substrate 3 d states that otherwise drastically modify the electronic structure of graphene. This picture is suggested by our x-ray absorption spectroscopy measurements which show that after Eu intercalation the empty 2 p states of C atoms resemble more the ones measured for graphite in contrast to graphene directly bound to 3 d ferromagnetic substrates. We use x-ray magnetic circular dichroism at the Co and Ni L2 ,3 and Eu M4 ,5 as an element-specific probe to investigate magnetism in these systems. An antiferromagnetic coupling between Eu and Co/Ni moments is found, which is so strong that a magnetic moment of the Eu layer can be detected at room temperature. Density functional theory calculations confirm the antiferromagnetic coupling and provide an atomic insight into the magnetic coupling mechanism.

  2. Relativistic jets shine through shocks or magnetic reconnection?

    NASA Astrophysics Data System (ADS)

    Sironi, Lorenzo; Petropoulou, Maria; Giannios, Dimitrios

    2015-06-01

    Observations of gamma-ray-bursts and jets from active galactic nuclei reveal that the jet flow is characterized by a high radiative efficiency and that the dissipative mechanism must be a powerful accelerator of non-thermal particles. Shocks and magnetic reconnection have long been considered as possible candidates for powering the jet emission. Recent progress via fully-kinetic particle-in-cell simulations allows us to revisit this issue on firm physical grounds. We show that shock models are unlikely to account for the jet emission. In fact, when shocks are efficient at dissipating energy, they typically do not accelerate particles far beyond the thermal energy, and vice versa. In contrast, we show that magnetic reconnection can deposit more than 50 per cent of the dissipated energy into non-thermal leptons as long as the energy density of the magnetic field in the bulk flow is larger than the rest-mass energy density. The emitting region, i.e. the reconnection downstream, is characterized by a rough energy equipartition between magnetic fields and radiating particles, which naturally accounts for a commonly observed property of blazar jets.

  3. Frozen flux violation, electron demagnetization and magnetic reconnection

    SciTech Connect

    Scudder, J. D.; Karimabadi, H.; Roytershteyn, V.; Daughton, W.

    2015-10-15

    We argue that the analogue in collisionless plasma of the collisional diffusion region of magnetic reconnection is properly defined in terms of the demagnetization of the plasma electrons that enable “frozen flux” slippage to occur. This condition differs from the violation of the “frozen-in” condition, which only implies that two fluid effects are involved, rather than the necessary slippage of magnetic flux as viewed in the electron frame. Using 2D Particle In Cell (PIC) simulations, this approach properly finds the saddle point region of the flux function. Our demagnetization conditions are the dimensionless guiding center approximation expansion parameters for electrons which we show are observable and determined locally by the ratio of non-ideal electric to magnetic field strengths. Proxies for frozen flux slippage are developed that (a) are measurable on a single spacecraft, (b) are dimensionless with theoretically justified threshold values of significance, and (c) are shown in 2D simulations to recover distinctions theoretically possible with the (unmeasurable) flux function. A new potentially observable dimensionless frozen flux rate, Λ{sub Φ}, differentiates significant from anecdotal frozen flux slippage. A single spacecraft observable, ϒ, is shown with PIC simulations to be essentially proportional to the unobservable local Maxwell frozen flux rate. This relationship theoretically establishes electron demagnetization in 3D as the general cause of frozen flux slippage. In simple 2D cases with an isolated central diffusion region surrounded by separatrices, these diagnostics uniquely identify the traditional diffusion region (without confusing it with the two fluid “ion-diffusion” region) and clarify the role of the separatrices where frozen flux violations do occur but are not substantial. In the more complicated guide and asymmetric 2D cases, substantial flux slippage regions extend out along, but inside of, the preferred separatrices

  4. Magnetic flipping - Reconnection in three dimensions without null points

    NASA Technical Reports Server (NTRS)

    Priest, E. R.; Forbes, T. G.

    1992-01-01

    In three dimensions, magnetic reconnection may take place in a sheared magnetic field at any singular field line, where the nearby field has X-type topology in planes perpendicular to the field line and where an electric field is present parallel to the field line. In the ideal region around the singular line there will, in general, be singularities in the plasma flow and electric field, both at the singular line and at 'magnetic flipping layers', which are remnants of local magnetic separatrices. In the absence of a three-dimensional magnetic neutral point or null point, reconnection of field lines can still occur by a process of magnetic flipping, in which the plasma crosses the flipping layers but the field lines rapidly flip along them by magnetic diffusion. Depending on the boundary conditions, there may be two or four flipping layers which converge on the singular line. A boundary layer analysis of a flipping layer is given, in which the magnetic field parallel to the layer decreases as one crosses it while the plasma pressure (or magnetic pressure associated with the field along the singular line) increases. The width of the flipping layer decreases with distance from the singular line.

  5. Onset and Evolution of Magnetic Reconnection in Line-Tied Systems

    NASA Astrophysics Data System (ADS)

    Daughton, W. S.; Akcay, C.; Billey, Z.; Finn, J.; Zweibel, E.; Gekelman, W. N.

    2014-12-01

    In space and astrophysical plasmas, current sheets arise spontaneously from the interaction of large-scale flows or magnetic structures. As these current layers approach kinetic scales, they may become unstable to the collisionless tearing instability, resulting in the formation and interaction of magnetic flux ropes. While theoretical treatments of the tearing instability have largely focused on 1D equilibria with periodic boundary conditions, current sheets in nature have a finite spatial extent and are embedded within larger open systems. In many applications, the field boundary conditions are line-tied as in the case of flux ropes on the dayside magnetopause where the ionosphere acts as a conducting surface. To assess the applicability of existing tearing theory to these more realistic configurations, we consider a series of 3D kinetic simulations of initially force-free current layers with line-tied boundary conditions for the fields, and open boundaries for the particles. The geometry and plasma parameters are motivated by a new laboratory experiment on the Large Plasma Device at UCLA. For sufficiently long systems, we demonstrate that key aspects of the theory remain valid, and a threshold condition is derived for the onset of reconnection in line-tied systems. To gain additional insight into the nonlinear evolution, field-line mapping diagnostics are employed to characterize the 3D structure of the magnetic field, the nonlinear reconnection rate and the dominant non-ideal terms in the generalized Ohm's law.

  6. Simulation study of magnetic reconnection in high magnetic Reynolds number plasmas

    NASA Astrophysics Data System (ADS)

    Nakabo, T.; Kusano, K.; Miyoshi, T.; Vekstein, G.

    2013-12-01

    Magnetic reconnection is an important process for dynamics in space and laboratory plasmas. Magnetic reconnection is basically dominated by magnetic diffusion at thin current sheet as proposed by Sweet (1958) and Parker (1963). According to their theory, the reconnection rate must be inversely proportional to the square root of the magnetic Reynolds number (S). In magnetosphere and the solar corona, however, in spite of high magnetic Reynolds number (>10^12), reconnection rate is measured to be about 10^-2 that is much higher than the Sweet and Parker's prediction. Although Petschek proposed that the slow mode shock may accelerate reconnection, numerical simulations suggested that the Petschek's type reconnection cannot be sustained with uniform resistivity. On the other hand, it is pointed out that in high magnetic Reynolds number, the thin current sheet becomes unstable to the so-called secondary tearing instability, which generates many plasmoids and drives a sort of fast reconnection. Although Baty (2012) recently investigated the possibility of Petschek-like structure in relatively high-S (~10^4) regime, it is still unclear whether and how the magnetic reconnection is able to be accelerated in higher-S regime (S>10^5). In this paper, we developed the high-resolution magnetohydrodynamics (MHD) simulation of magnetic reconnection for very high-S (S~10^4-10^6) aiming at revealing the acceleration mechanism of magnetic reconnection. We applied the HLLD Riemann solver, which was developed by Miyoshi and Kusano (2005), to the high resolution two-dimensional MHD simulation of current sheet dynamics. In our model, the initial state is given by the Harris sheet equilibrium plus perturbation. As a result, in the case for S=10^5, multiple X-line reconnection appears as a result of the secondary tearing instability and magnetic reconnection is accelerated through the formation of multiple magnetic islands as pointed out by the previous studies. Furthermore, we found that

  7. Scaling of Magnetic Reconnection in Relativistic Collisionless Pair Plasmas

    NASA Technical Reports Server (NTRS)

    Liu, Yi-Hsin; Guo, Fan; Daughton, William; Li, Hui; Hesse, Michael

    2015-01-01

    Using fully kinetic simulations, we study the scaling of the inflow speed of collisionless magnetic reconnection in electron-positron plasmas from the non-relativistic to ultra-relativistic limit. In the anti-parallel configuration, the inflow speed increases with the upstream magnetization parameter sigma and approaches the speed of light when sigma is greater than O(100), leading to an enhanced reconnection rate. In all regimes, the divergence of the pressure tensor is the dominant term responsible for breaking the frozen-in condition at the x-line. The observed scaling agrees well with a simple model that accounts for the Lorentz contraction of the plasma passing through the diffusion region. The results demonstrate that the aspect ratio of the diffusion region, modified by the compression factor of proper density, remains approximately 0.1 in both the non-relativistic and relativistic limits.

  8. New Kind of Magnetic Reconnection in Neutral Sheet Configurations

    NASA Astrophysics Data System (ADS)

    Fletcher, Alex; Coppi, Bruno

    2016-10-01

    Neutral Sheet configurations are relatively simple models of the plasma and field configuration found in space physics that lend themselves to investigate the onset of relevant reconnection processes. In weakly collisional regimes these are shown to be intrinsically different from those occurring in plasma current sheets where the magnetic field is sheared but does not vanish. Considering an inhomogenous electron temperature profile with finite curvature at the center of the sheet, and anisotropic thermal conductivities one of the two kinds of mode that can produce magnetic reconnection is localized over a layer that remains significant when the macroscopic scale distances involved are very large as is the case in space and astrophysics. This mode lends itself to produce high-energy particle populations through a realistic combination of mode-particle resonances. Sponsored in part by the U.S. D.O.E. and the N.S.F.

  9. Suppression of Collisionless Magnetic Reconnection in Asymmetric Current Sheets

    NASA Technical Reports Server (NTRS)

    Liu, Yi-Hsin; Hesse, Michael

    2016-01-01

    Using fully kinetic simulations, we study the suppression of asymmetric reconnection in the limit where the diamagnetic drift speed >> Alfven speed and the magnetic shear angle is moderate. We demonstrate that the slippage between electrons and the magnetic flux mitigates the suppression and can even result in fast reconnection that lacks one of the outflow jets. Through comparing a case where the diamagnetic drift is supported by the temperature gradient with a companion case that has a density gradient instead, we identify a robust suppression mechanism. The drift of the x-line is slowed down locally by the asymmetric nature of the x-line, and then the x-line is run over and swallowed by the faster-moving following flux.

  10. Localized electron heating by strong guide-field magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Guo, Xuehan; Inomoto, Michiaki; Sugawara, Takumichi; Yamasaki, Kotaro; Ushiki, Tomohiko; Ono, Yasushi

    2015-10-01

    Localized electron heating of magnetic reconnection was studied under strong guide-field using two merging spherical tokamak plasmas in the University of Tokyo Spherical Tokamak experiment. Our new slide-type two-dimensional Thomson scattering system is documented for the first time the electron heating localized around the X-point. Shape of the high electron temperature area does not agree with that of energy dissipation term Et.jt . If we include a guide-field effect term Bt/(Bp+αBt) for Et.jt , the energy dissipation area becomes localized around the X-point, suggesting that the electrons are accelerated by the reconnection electric field parallel to the magnetic field and thermalized around the X-point.

  11. New models for fast steady state magnetic reconnection

    NASA Technical Reports Server (NTRS)

    Priest, E. R.; Forbes, T. G.

    1986-01-01

    A new unified family of models for incompressible, steady-state magnetic reconnection in a finite region is presented. The models are obtained by expanding in powers of the Alfven Mach number and may be used to elucidate some of the puzzling properties of numerical experiments on reconnection which are not present in the classical models. The conditions imposed on the inflow boundary of the finite region determine which member of the family occurs. Petscheklien and Sonnerup like solutions are particular members. The Sonneruplike regime is a special case of a weak slow mode expansion in the inflow region, and it separates two classes of members with reversed currents. The Petscheklike regime is a singular case of a weak fast mode expansion, and it separates the hybrid regime from a regime of slow mode compressions. Care should be taken in deciding which type of reconnection is operating in a numerical experiment. Indeed, no experiment to date has used boundary conditions appropriate for demonstrating steady state Petschek reconnection.

  12. Particle acceleration in laser-driven magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Totorica, Samuel; Abel, Tom; Fiuza, Frederico

    2016-10-01

    Particle acceleration induced by magnetic reconnection is a promising candidate for producing the nonthermal emissions associated with explosive astrophysical phenomena. We have used two- and three-dimensional particle-in-cell simulations to explore the possibility of studying particle acceleration from reconnection in laser-driven plasma experiments. For current experimental conditions, we show that nonthermal electrons can be accelerated to energies up to two orders of magnitude larger than the initial thermal energy. The nonthermal electrons gain energy primarily by the reconnection electric field near the X-points, and particle injection into the reconnection layer and escape from the finite system establishes a distribution of energies resembling a power-law spectrum. Energetic electrons can also become trapped inside the plasmoids that form in the current layer and gain additional energy from the electric field arising from the motion of the plasmoid. Based on our findings, we provide an analytical estimate of the maximum electron energy and threshold condition for suprathermal electron acceleration in terms of experimentally tunable parameters. Finally, we investigate future experiments with a more energetic laser drive and larger system size. We discuss the influence of plasmoids on the particle acceleration, and the use of proton radiography to probe plasmoids. This work was supported by the DOE Office of Science, Fusion Energy Science (FWP 100182).

  13. The kinetic scale structure of the Plasma Sheet Boundary Layer: Implications of collisionless magnetic reconnection and first MMS observations

    NASA Astrophysics Data System (ADS)

    Dorelli, J.; Gershman, D. J.; Avanov, L. A.; Pollock, C. J.; Giles, B. L.; Nakamura, R.; Chen, L. J.; Torbert, R. B.; Gliese, U.; Barrie, A. C.; Holland, M. P.; Chandler, M. O.; Coffey, V. N.; MacDonald, E.; Salo, C.; Dickson, C.; Saito, Y.; Russell, C. T.; Baumjohann, W.; Burch, J. L.

    2015-12-01

    The relationship between magnetic reconnection and the Plasma Sheet Boundary Layer (PSBL) is still an open problem in magnetospheric physics. While one can understand observed PSBL velocity distributions on the basis of a simple steady state drift-kinetic model with prescribed electric and magnetic fields (e.g., Onsager et al. [1990,1991]), such models do not incorporate the kinetic scale dynamics at the reconnection site. For example, Shay et al. [2011] have argued that the out-of-plane quadrupole magnetic field pattern at the reconnection site can be viewed as an obliquely propagating kinetic Alfvén wave with very large parallel group velocity, the implication being that the field-aligned current structure should quickly become global, though still confined to field lines connected to the ion diffusion region at the reconnection site. This raises the very interesting question: How would such a global wave structure appear in the PSBL on the kinetic scale? Here, we present some first observations of the PSBL by NASA's Magnetospheric Multiscale (MMS) mission where Fast Plasma Investigation (FPI) Burst Data (30 ms and 150 ms resolution for 3D electron and ion velocity distributions, respectively) is available during intervals where lower resolution (4.5 s) Fast Survey distributions showed evidence of connection to a remote reconnection site. This allows us to test for the first time whether the quadrupole magnetic field structure near the reconnection site -- a local structure already observed by previous spacecraft -- does indeed support a global field-aligned current pattern around the magnetic separatrix. We will also probe for the first time the electron kinetic scale sub-structure of the PSBL and compare with electron-scale features observed near the magnetic separatrix at the dayside magnetopause.

  14. Magnetic reconnection driven by Gekko XII lasers with a Helmholtz capacitor-coil target

    NASA Astrophysics Data System (ADS)

    Pei, X. X.; Zhong, J. Y.; Sakawa, Y.; Zhang, Z.; Zhang, K.; Wei, H. G.; Li, Y. T.; Li, Y. F.; Zhu, B. J.; Sano, T.; Hara, Y.; Kondo, S.; Fujioka, S.; Liang, G. Y.; Wang, F. L.; Zhao, G.

    2016-03-01

    We demonstrate a novel plasma device for magnetic reconnection, driven by Gekko XII lasers irradiating a double-turn Helmholtz capacitor-coil target. Optical probing revealed an accumulated plasma plume near the magnetic reconnection outflow. The background electron density and magnetic field were measured to be approximately 1018 cm-3 and 60 T by using Nomarski interferometry and the Faraday effect, respectively. In contrast with experiments on magnetic reconnection constructed by the Biermann battery effect, which produced high beta values, our beta value was much lower than one, which greatly extends the parameter regime of laser-driven magnetic reconnection and reveals its potential in astrophysical plasma applications.

  15. Generation of Alfvenic Waves and Turbulence in Magnetic Reconnection Jets

    NASA Astrophysics Data System (ADS)

    Hoshino, M.

    2014-12-01

    The magneto-hydro-dynamic (MHD) linear stability for the plasma sheet with a localized bulk plasma flow parallel to the neutral sheet is investigated. We find three different unstable modes propagating parallel to the anti-parallel magnetic field line, and we call them as "streaming tearing'', "streaming sausage'', and "streaming kink'' mode. The streaming tearing and sausage modes have the tearing mode-like structure with symmetric density fluctuation to the neutral sheet, and the streaming kink mode has the asymmetric fluctuation. The growth rate of the streaming tearing mode decreases with increasing the magnetic Reynolds number, while those of the streaming sausage and kink modes do not strongly depend on the Reynolds number. The wavelengths of these unstable modes are of the order of the thickness of plasma sheet, which behavior is almost same as the standard tearing mode with no bulk flow. Roughly speaking the growth rates of three modes become faster than the standard tearing mode. The situation of the plasma sheet with the bulk flow can be realized in the reconnection exhaust with the Alfvenic reconnection jet, and the unstable modes may be regarded as one of the generation processes of Alfvenic turbulence in the plasma sheet during magnetic reconnection.

  16. Extreme ultraviolet imaging of three-dimensional magnetic reconnection in a solar eruption.

    PubMed

    Sun, J Q; Cheng, X; Ding, M D; Guo, Y; Priest, E R; Parnell, C E; Edwards, S J; Zhang, J; Chen, P F; Fang, C

    2015-06-26

    Magnetic reconnection, a change of magnetic field connectivity, is a fundamental physical process in which magnetic energy is released explosively, and it is responsible for various eruptive phenomena in the universe. However, this process is difficult to observe directly. Here, the magnetic topology associated with a solar reconnection event is studied in three dimensions using the combined perspectives of two spacecraft. The sequence of extreme ultraviolet images clearly shows that two groups of oppositely directed and non-coplanar magnetic loops gradually approach each other, forming a separator or quasi-separator and then reconnecting. The plasma near the reconnection site is subsequently heated from ∼1 to ≥5 MK. Shortly afterwards, warm flare loops (∼3 MK) appear underneath the hot plasma. Other observational signatures of reconnection, including plasma inflows and downflows, are unambiguously revealed and quantitatively measured. These observations provide direct evidence of magnetic reconnection in a three-dimensional configuration and reveal its origin.

  17. Observation of Two Slow Shocks Associated with Magnetic Reconnection Exhausts in the Interplanetary Space

    NASA Astrophysics Data System (ADS)

    Feng, HengQiang; Li, QiuHuan; Wang, JieMin; Zhao, GuoQing

    2017-04-01

    In the Petschek magnetic reconnection model, two groups of slow shocks play an important role in the energy release. In the past half century, a large number of slow shocks were observed in the geomagnetic tail, and many slow shocks were associated with magnetic reconnection events in the geomagnetic tail. Slow shocks in the interplanetary space are rarer than in the geomagnetic tail. We investigated whether slow shocks associated with interplanetary reconnection exhausts are rare. We examined the boundaries of 50 reconnection exhausts reported by Phan, Gosling, and Davis (Geophys. Res. Lett. 36:L09108, 2009) in interplanetary space to identify slow shocks by fitting the Rankine-Hugoniot relations. Two slow shocks associated with magnetic reconnection exhausts were found and evaluated using observations from Wind and the Advanced Composition Explorer. The observed slow shocks associated with interplanetary reconnection exhausts are rarer than the observed slow shocks associated with geomagnetic tail reconnection exhausts.

  18. Explosive Turbulent Magnetic Reconnection: A New Approach of MHD-Turbulent Simulation

    NASA Astrophysics Data System (ADS)

    Hoshino, Masahiro; Yokoi, Nobumitsu; Higashimori, Katsuaki

    2013-04-01

    Turbulent flows are often observed in association with magnetic reconnection in space and astrophysical plasmas, and it is often hypothesized that the turbulence can contribute to the fast magnetic reconnection through the enhancement of magnetic dissipation. In this presentation, we demonstrate that an explosive turbulent reconnection can happen by using a new turbulent MHD simulation, in which the evolution of the turbulent transport coefficients are self-consistently solved together with the standard MHD equations. In our model, the turbulent electromotive force defined by the correlation of turbulent fluctuations between v and B is added to the Ohm's law. We discuss that the level of turbulent can control the topology of reconnection, namely the transition from the Sweet-Parker reconnection to the Petscheck reconnection occurs when the level of fluctuations becomes of order of the ambient physical quantities, and show that the growth of the turbulent Petscheck reconnection becomes much faster than the conventional one.

  19. Distinct characteristics of asymmetric magnetic reconnections: Observational results from the exhaust region at the dayside magnetopause

    NASA Astrophysics Data System (ADS)

    Zhang, Y. C.

    2016-06-01

    Magnetic reconnection plays a key role in the conversion of magnetic energy into the thermal and kinetic energy of plasma. On either side of the diffusion region in space plasma, the conditions for the occurrence of reconnections are usually not symmetric. Previous theoretical studies have predicted that reconnections under asymmetric conditions will bear different features compared with those of symmetric reconnections, and numerical simulations have verified these distinct features. However, to date, the features of asymmetric reconnections have not been thoroughly investigated using in situ observations; thus, some results from theoretical studies and simulations have not been tested with observations sufficiently well. Here, spacecraft observations are used in a statistical investigation of asymmetric magnetic reconnection exhaust at the dayside magnetopause. The resulting observational features are consistent with the theoretical predictions. The results presented here advance our understanding of the development of reconnections under asymmetric conditions.

  20. Distinct characteristics of asymmetric magnetic reconnections: Observational results from the exhaust region at the dayside magnetopause

    PubMed Central

    Zhang, Y. C.

    2016-01-01

    Magnetic reconnection plays a key role in the conversion of magnetic energy into the thermal and kinetic energy of plasma. On either side of the diffusion region in space plasma, the conditions for the occurrence of reconnections are usually not symmetric. Previous theoretical studies have predicted that reconnections under asymmetric conditions will bear different features compared with those of symmetric reconnections, and numerical simulations have verified these distinct features. However, to date, the features of asymmetric reconnections have not been thoroughly investigated using in situ observations; thus, some results from theoretical studies and simulations have not been tested with observations sufficiently well. Here, spacecraft observations are used in a statistical investigation of asymmetric magnetic reconnection exhaust at the dayside magnetopause. The resulting observational features are consistent with the theoretical predictions. The results presented here advance our understanding of the development of reconnections under asymmetric conditions. PMID:27270685

  1. Supramolecular 3d-4f single-molecule magnet architectures.

    PubMed

    Schmitz, Sebastian; van Leusen, Jan; Izarova, Natalya V; Lan, Yanhua; Wernsdorfer, Wolfgang; Kögerler, Paul; Monakhov, Kirill Yu

    2016-10-18

    The nanosized self-assemblies {[{Ln(III)}{H2O⊂CrLn}]2(H2O)} (Ln = Dy, 1 and Tb, 2) based on new 3d-4f mixed-metal coordination topologies are formed via extensive intramolecular hydrogen bonding that is directed by enclosed water molecules. Compounds 1 and 2 show single-molecule magnet characteristics manifested by hysteresis loops up to 1.6 K (Ueff = 8.3 cm(-1)) and 1 K (Ueff = 3.4 cm(-1)), respectively.

  2. Observation of Magnetic Reconnection Driven by Granular Scale Advection

    NASA Astrophysics Data System (ADS)

    Zeng, Zhichen; Cao, W.; Ji, H.

    2013-07-01

    We report the first evidence of magnetic reconnection driven by advection in a rapidly developing large granule, using high spatial resolution observations of a small surge event (base size 4‧‧ by 4‧‧) with the 1.6 meter aperture New Solar Telescope (NST) at Big Bear Solar Observatory. The observations were carried out in narrow-band (0.5 Å) Helium I 10830 Å and broad-band (10 Å) TiO 7057 Å. Since He I 10830 Å triplet has very high excitation level and is optically thin, its filtergrams enable us to investigate the surge from the photosphere through the chromosphere into the lower corona. Simultaneous space data from Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) were used in the analysis. It is shown that the surge is spatio-temporally associated with magnetic flux emergence in the rapidly developing large granule. During the development of the granule, its advecting flow ( 2 km/ s) squeezed the magnetic flux into an intergranular lane area, where a magnetic flux concentration was formed and the neighboring flux with opposite magnetic polarity was cancelled. During the cancellation, the surge was produced as absorption in He I 10830 Å filtergrams while simultaneous EUV brightening occurred at its base. The observations clearly indicate evidence of finest-scale reconnection process driven by the granule’s motion.

  3. Observation of Magnetic Reconnection Driven by Granular Scale Advection

    NASA Astrophysics Data System (ADS)

    Zeng, Zhicheng; Cao, Wenda; Ji, Haisheng

    2013-06-01

    We report the first evidence of magnetic reconnection driven by advection in a rapidly developing large granule using high spatial resolution observations of a small surge event (base size ~ 4'' × 4'') with the 1.6 m aperture New Solar Telescope at the Big Bear Solar Observatory. The observations were carried out in narrowband (0.5 Å) He I 10830 Å and broadband (10 Å) TiO 7057 Å. Since He I 10830 Å triplet has a very high excitation level and is optically thin, its filtergrams enable us to investigate the surge from the photosphere through the chromosphere into the lower corona. Simultaneous space data from the Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory were used in the analysis. It is shown that the surge is spatio-temporally associated with magnetic flux emergence in the rapidly developing large granule. During the development of the granule, its advecting flow (~2 km s-1) squeezed the magnetic flux into an intergranular lane area, where a magnetic flux concentration was formed and the neighboring flux with opposite magnetic polarity was canceled. During the cancellation, the surge was produced as absorption in He I 10830 Å filtergrams while simultaneous EUV brightening occurred at its base. The observations clearly indicate evidence of a finest-scale reconnection process driven by the granule's motion.

  4. The Structure of the Separatix in Collisionless Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Daughton, W.; Scudder, J.; Karimabadi, H.

    2005-12-01

    Recent kinetic simulations of magnetic reconnection indicate the formation of intense electrostatic fields that start at the x-point and form sheet-like structures that extend outward for large distances along the separatrices. In the presence of a significant guide field, the characteristic thickness of these layers is on the order of the local electron gyroradius and there are significant deviations from charge neutrality within the layer. The resulting electrostatic fields are primarily perpendicular and may exceed the reconnection electric field by a factor of 20. A serious impediment to understanding the possible role of these structures is the use of periodic boundary conditions typically employed in kinetic simulations. In particular, the strong outward electron flow generated along one leg of a separatrix is allowed to circulate back through the system along the opposite side. This recirculation may artificially enhance beam driven instabilities and/or strongly modify the structure of the separatrix. In this work, we describe initial efforts to employ open boundary conditions in 2D fully kinetic PIC simulations, with the goal of better understanding the structure and role of the separatrix in collisionless magnetic reconnection.

  5. A multi-model plasma simulation of collisionless magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Datta, I. A. M.; Shumlak, U.; Ho, A.; Miller, S. T.

    2016-10-01

    Collisionless magnetic reconnection is a process relevant to many areas of plasma physics in which energy stored in magnetic fields within highly conductive plasmas is rapidly converted to plasma energy. A full understanding of this phenomenon, however, is currently incomplete as models developed to date have difficulty explaining the fast reconnection rates often seen in nature, such as in the case of solar flares. Therefore, this behavior represents an area of much research in which various plasma models have been tested in order to understand the proper physics explaining the reconnection process. In this research, the WARPXM code developed at the University of Washington is used to study the problem using a hybrid multi-model simulation employing Hall-MHD and two-fluid plasma models. The simulation is performed on a decomposed domain where different plasma models are solved in different regions, depending on a trade-off between each model's physical accuracy and associated computational expense in each region. The code employs a discontinuous Galerkin (DG) finite element spatial discretization coupled with a Runge-Kutta scheme for time advancement and uses boundary conditions to couple the different plasma models. This work is supported by a Grant from the United States Air Force Office of Scientific Research.

  6. Structures of diffusion regions in collisionless magnetic reconnection

    SciTech Connect

    Umeda, Takayuki; Togano, Kentaro; Ogino, Tatsuki

    2010-05-15

    Detailed structures of diffusion regions in two-dimensional collisionless magnetic reconnection are studied by using an electromagnetic Vlasov simulation. It has been well known that plasma number density decreases near the X-point of the reconnection. However, numerical thermal fluctuations exist in particle-in-cell simulations, and there is a possibility that detailed structures near the X-point diffuse numerically when the number of particles per cell is not enough. In the present study, a high-resolution two-dimensional Vlasov simulation is performed. It is found that electron number density in the electron diffusion region decreases to a hundredth of the initial value. Structures of electron diffusion region are determined by the local electron inertial length.

  7. MAGNETIC RECONNECTION BETWEEN SMALL-SCALE LOOPS OBSERVED WITH THE NEW VACUUM SOLAR TELESCOPE

    SciTech Connect

    Yang, Shuhong; Zhang, Jun; Xiang, Yongyuan

    2015-01-01

    Using the high tempo-spatial resolution Hα images observed with the New Vacuum Solar Telescope, we report solid observational evidence of magnetic reconnection between two sets of small-scale, anti-parallel loops with an X-shaped topology. The reconnection process contains two steps: a slow step with a duration of more than several tens of minutes, and a rapid step lasting for only about three minutes. During the slow reconnection, two sets of anti-parallel loops gradually reconnect, and new loops are formed and stacked together. During the rapid reconnection, the anti-parallel loops approach each other quickly, and then rapid reconnection takes place, resulting in the disappearance of the former loops. In the meantime, new loops are formed and separate. The region between the approaching loops is brightened, and the thickness and length of this region are determined to be about 420 km and 1.4 Mm, respectively. During the rapid reconnection process, obvious brightenings at the reconnection site and apparent material ejections outward along reconnected loops are observed. These observed signatures are consistent with predictions by reconnection models. We suggest that the successive slow reconnection changes the conditions around the reconnection site and triggers instabilities, thus leading to the rapid approach of the anti-parallel loops and resulting in the rapid reconnection.

  8. Magnetically Defined Qubits on 3D Topological Insulators

    NASA Astrophysics Data System (ADS)

    Ferreira, Gerson J.; Loss, Daniel

    2013-09-01

    We explore potentials that break time-reversal symmetry to confine the surface states of 3D topological insulators into quantum wires and quantum dots. A magnetic domain wall on a ferromagnet insulator cap layer provides interfacial states predicted to show the quantum anomalous Hall effect (QAHE). Here, we show that confinement can also occur at magnetic domain heterostructures, with states extended in the inner domain, as well as interfacial QAHE states at the surrounding domain walls. The proposed geometry allows the isolation of the wire and dot from spurious circumventing surface states. For the quantum dots, we find that highly spin-polarized quantized QAHE states at the dot edge constitute a promising candidate for quantum computing qubits.

  9. Beaming of Particles and Synchrotron Radiation in Relativistic Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Kagan, Daniel; Nakar, Ehud; Piran, Tsvi

    2016-08-01

    Relativistic reconnection has been invoked as a mechanism for particle acceleration in numerous astrophysical systems. According to idealized analytical models, reconnection produces a bulk relativistic outflow emerging from the reconnection sites (X-points). The resulting radiation is therefore highly beamed. Using two-dimensional particle-in-cell simulations, we investigate particle and radiation beaming, finding a very different picture. Instead of having a relativistic average bulk motion with an isotropic electron velocity distribution in its rest frame, we find that the bulk motion of the particles in X-points is similar to their Lorentz factor γ, and the particles are beamed within ˜ 5/γ . On the way from the X-point to the magnetic islands, particles turn in the magnetic field, forming a fan confined to the current sheet. Once they reach the islands they isotropize after completing a full Larmor gyration and their radiation is no longer strongly beamed. The radiation pattern at a given frequency depends on where the corresponding emitting electrons radiate their energy. Lower-energy particles that cool slowly spend most of their time in the islands and their radiation is not highly beamed. Only particles that quickly cool at the edge of the X-points generate a highly beamed fan-like radiation pattern. The radiation emerging from these fast cooling particles is above the burn-off limit (˜100 MeV in the overall rest frame of the reconnecting plasma). This has significant implications for models of gamma-ray bursts and active galactic nuclei that invoke beaming in that frame at much lower energies.

  10. Magnetically Defined Qubits on 3D Topological Insulators

    NASA Astrophysics Data System (ADS)

    Ferreira, Gerson J.; Loss, Daniel

    2014-03-01

    We explore potentials that break time-reversal symmetry to confine the surface states of 3D topological insulators into quantum wires and quantum dots. A magnetic domain wall on a ferromagnet insulator cap layer provides interfacial states predicted to show the quantum anomalous Hall effect. Here, we show that confinement can also occur at magnetic domain heterostructures, with states extended in the inner domain, as well as interfacial QAHE states at the surrounding domain walls. The proposed geometry allows the isolation of the wire and dot from spurious circumventing surface states. For the quantum dots, we find that highly spin-polarized quantized QAHE states at the dot edge constitute a promising candidate for quantum computing qubits. See [Ferreira and Loss, Phys. Rev. Lett. 111, 106802 (2013)]. We explore potentials that break time-reversal symmetry to confine the surface states of 3D topological insulators into quantum wires and quantum dots. A magnetic domain wall on a ferromagnet insulator cap layer provides interfacial states predicted to show the quantum anomalous Hall effect. Here, we show that confinement can also occur at magnetic domain heterostructures, with states extended in the inner domain, as well as interfacial QAHE states at the surrounding domain walls. The proposed geometry allows the isolation of the wire and dot from spurious circumventing surface states. For the quantum dots, we find that highly spin-polarized quantized QAHE states at the dot edge constitute a promising candidate for quantum computing qubits. See [Ferreira and Loss, Phys. Rev. Lett. 111, 106802 (2013)]. We acknowledge support from the Swiss NSF, NCCR Nanoscience, NCCR QSIT, and the Brazillian Research Support Center Initiative (NAP Q-NANO) from Pró-Reitoria de Pesquisa (PRP/USP).

  11. Observations of an X-shaped Ribbon Flare and Its Three-dimensional Magnetic Reconnection with IRIS and SDO

    NASA Astrophysics Data System (ADS)

    Li, Ying; Qiu, Jiong; Longcope, Dana; Ding, Mingde

    2016-05-01

    We report evolution of an atypical X-shaped flare ribbon which provides novel observational evidence of three-dimensional (3D) magnetic reconnection at a separator. The flare occurred on 2014 November 9, and high-resolution slit-jaw 1330 images from IRIS reveal four chromospheric flare ribbons that converge and form an X-shape. These four ribbons are located in a quadrupolar magnetic field. Reconstruction of magnetic topology in the active region suggests the presence of a separator connecting to the X-point outlined by the ribbons. The inward motion of flare ribbons, as well as coronal loops observed by the SDO/AIA, indicates 3D magnetic reconnection between two sets of non-coplanar loops that approach laterally, and the reconnection proceeds downward to a very low height. We also study spectra of Si IV, C II, and Mg II observed with the IRIS slit, which cuts across the flare ribbons near the X-point. We have found two distinct types of line profiles. At the flare ribbon, all the lines show evident redshifts with a velocity up to 50 km/s, and the redshifts are well correlated with the line intensity and width. These redshifts suggest chromospheric condensation caused by impulsive energy deposition from the separator reconnection. While right outside the flare ribbon, the lines exhibit unshifted, symmetric, yet broadened profiles; in particular, the Si IV line is significantly broadened at the far wing. The line broadening persists for 20 minutes till after the end of the flare. The distinct spectral features near the X-point indicate different dynamics associated with the separator reconnection.

  12. The influence of intense electric fields on three-dimensional asymmetric magnetic reconnection

    SciTech Connect

    Pritchett, P. L.

    2013-06-15

    A three-dimensional particle-in-cell simulation of magnetic reconnection in an asymmetric configuration without a guide field and with temperature ratio T{sub i}/T{sub e}>1 demonstrates that intense perpendicular electric fields are produced on the low-density side of the current layer where there is a strong gradient in the plasma density. The simulation shows that the 3-D reconnection rate is unaffected by these intense electric fields, that the electron current layer near the X line remains coherent and does not break up, but that localized regions of strong energy dissipation exist along the low-density separatrices. Near the X line the dominant term in the generalized Ohm's law for the reconnection electric field remains the off-diagonal electron pressure gradient ∂P{sub exy}/∂x. On the low-beta separatrix, however, the anomalous drag −<δnδE{sub y}>/ makes an equally important contribution to that of the pressure gradient to the average E{sub y} field.

  13. Defining and identifying three-dimensional magnetic reconnection in resistive magnetohydrodynamic simulations of Earth's magnetosphere

    SciTech Connect

    Dorelli, John C.; Bhattacharjee, A.

    2008-05-15

    Magnetic reconnection is thought to be the primary mode by which the solar wind couples to the terrestrial magnetosphere, driving phenomena such as magnetic storms and aurorae. While the theory of two-dimensional reconnection is well developed and has been applied with great success to axisymmetric and toroidal systems such as laboratory plasma experiments and fusion devices, it is difficult to justify the application of two-dimensional theory to nontoroidal plasma systems such as Earth's magnetosphere. Unfortunately, the theory of three-dimensional magnetic reconnection is much less well developed, and even defining magnetic reconnection has turned out to be controversial. In this paper, recent progress in the use of magnetohydrodynamics (MHD) to address the physics of three-dimensional reconnection in Earth's magnetosphere is reviewed. The paper consists of two parts. In the first part, various definitions of three-dimensional reconnection are reviewed, with the goal of mapping these definitions to sets of physical phenomena that have been identified as 'reconnection' in various contexts. In the second part of the paper, MHD simulation results for the magnetosphere are presented, and two qualitatively distinct types of reconnection phenomena are identified: (1) Steady separator reconnection under generic northward interplanetary magnetic field (IMF) conditions, involving plasma flow across magnetic separatrices, and (2) time-dependent reconnection under generic southward IMF conditions, involving a locally detectable change in the magnetic field topology. It is concluded that magnetic reconnection phenomena at Earth's dayside magnetopause are adequately captured by two distinct definitions: The Vasyliunas definition [V. M. Vasyliunas, Rev. Geophys 13, 303 (1975)], which identifies magnetic reconnection with plasma flow across magnetic separatrices, and the Greene definition [J. Greene, Phys. Fluids B 5, 2355 (1993)], which identifies magnetic reconnection with a

  14. Electron heating during magnetic reconnection: A simulation scaling study

    SciTech Connect

    Shay, M. A. Haggerty, C. C.; Phan, T. D.; Oieroset, M.; Drake, J. F.; Swisdak, M.; Cassak, P. A.; Wu, P.; Malakit, K.

    2014-12-15

    Electron bulk heating during magnetic reconnection with symmetric inflow conditions is examined using kinetic particle-in-cell simulations. Inflowing plasma parameters are varied over a wide range of conditions, and the increase in electron temperature is measured in the exhaust well downstream of the x-line. The degree of electron heating is well correlated with the inflowing Alfvén speed c{sub Ar} based on the reconnecting magnetic field through the relation ΔT{sub e}=0.033 m{sub i} c{sub Ar}{sup 2}, where ΔT{sub e} is the increase in electron temperature. For the range of simulations performed, the heating shows almost no correlation with inflow total temperature T{sub tot}=T{sub i}+T{sub e} or plasma β. An out-of-plane (guide) magnetic field of similar magnitude to the reconnecting field does not affect the total heating, but it does quench perpendicular heating, with almost all heating being in the parallel direction. These results are qualitatively consistent with a recent statistical survey of electron heating in the dayside magnetopause (Phan et al., Geophys. Res. Lett. 40, 4475, 2013), which also found that ΔT{sub e} was proportional to the inflowing Alfvén speed. The net electron heating varies very little with distance downstream of the x-line. The simulations show at most a very weak dependence of electron heating on the ion to electron mass ratio. In the antiparallel reconnection case, the largely parallel heating is eventually isotropized downstream due a scattering mechanism, such as stochastic particle motion or instabilities. The simulation size is large enough to be directly relevant to reconnection in the Earth's magnetosphere, and the present findings may prove to be universal in nature with applications to the solar wind, the solar corona, and other astrophysical plasmas. The study highlights key properties that must be satisfied by an electron heating mechanism: (1) preferential heating in the parallel direction; (2) heating

  15. Fully Kinetic Simulations of Asymmetric Magnetic Reconnection at the Magnetopause with Different Configurations

    NASA Astrophysics Data System (ADS)

    Cazzola, Emanuele; Lapenta, Giovanni

    2015-04-01

    reconnection is tought to begin. Finally, further analysis focus on studying whether any relevant interaction between the two layers may occur, given the overall compression generated by the asymmetric plasmoid swelling towards the low magnetic field region in between, as well as on the eventual presence of electron holes signatures in one or both reconnecting layers. All simulations were perfomed by using the Fully Kinetic Implicit Particle-in-Cell Code iPIC3D (Markidis et al. 2010), whose implicitness allows us to no longer consider costraints between temporal scales and spatial resolutions. This work has received funding from the European Unions Seventh Programme for Research, Technological Development and Demonstration under Grant Agreement No 284461 - Project eHeroes (www.eheroes.eu) and from the Interuniversity Attraction Poles Programme initiated by the Belgian Science Policy Office (IAP P7/08 CHARM). The simulations were conducted on the computational resources provided by the PRACE Tier-0 2013091928 (SuperMUC supercomputer).

  16. Propagation and Damping of Kinetic Alfven Waves Generated During Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Sharma, P.; Shay, M. A.; Haggerty, C. C.; Parashar, T.

    2015-12-01

    Magnetospheric waves have the potential to convert to Kinetic Alfven Waves (KAW) at scales close to the ion larmor radius and the electron inertial length. At this length scale, it is observed that KAW generated at reconnection propagates super-Alfvenically and the wave is responsible for the parallel propagation of the Hall magnetic field near the separatrice from the magnetotial region. The pointing flux associated with this Hall magnetic field is also consistent with observed Cluster data observations [1]. An important question is whether this KAW energy will be able to propagate all the way to the Earth, creating aurora associated with a substorm. If this KAW propagation can be well understood, then this will provide valuable insight as to the relative timing of substorm onset versus reconnection onset in the magnetotail. The difficulty currently is that the nonlinear damping of KAW is not well understood even in a homogenous system, let alone more realistic magnetotail geometries including changes to density, magnetic field strength, and magnetic orientation. We study the propagation, dispersion, and damping of these KAWs using P3D, a kinetic particle-in-cell (PIC) simulation code. Travelling waves are initialized based on a fluid model and allowed to propagate for substantial time periods. Damping of the waves are compared with Landau damping predictions. The waves are simulated in both homogenous and varying equilibrium meant to determine the effect on propagation. Implications for energetic electron production and Poynting flux input into the ionosphere are discussed. [1] Shay, M. A., J. F. Drake, J. P. Eastwood, and T. D. Phan, Super-Alfvenic propagation of substorm reconnection signatures and Poynting flux,, Physics Review Letters, Vol. 107, 065001, 2011.

  17. Spreading of Magnetic Reconnection X-lines in Three Dimensions

    NASA Astrophysics Data System (ADS)

    Cassak, Paul; Shepherd, Lucas

    2012-03-01

    Naturally occurring magnetic reconnection often begins in a spatially localized region and spreads in the out-of-plane direction in time. A number of authors have studied this problem for magnetotail applications such as substorms and bursty bulk flows, for which the out-of-plane (guide) field is typically small. However, spreading also occurs in laboratory experiments and two-ribbon solar flares (such as the Bastille Day flare), and is inferred to occur at the dayside magnetopause. The reconnection site in each of these settings is known or thought to have a significant guide field. With no guide field, it was shown that the reconnection spreading is controlled by the species that carries the current. However, laboratory experiments with a large guide field (Katz et al., Phys. Rev. Lett., 104, 255004, 2010) revealed that spreading takes place in both directions at the Alfven speed based on the guide field. This implies a qualitative change of behavior as the guide field varies. We present a scaling argument for the condition on the guide field at which the nature of the spreading switches from being caused by current carriers to Alfven waves. Further, we show results of three-dimensional two-fluid simulations that agree with the theory. We discuss applications to observations.

  18. Transient Magnetic Reconnection and Dipolarization Fronts in the Terrestrial Magnetotail

    NASA Astrophysics Data System (ADS)

    Zhou, Meng; Deng, Xiaohua; Pang, Ye; Xu, Xiaojun; Huang, Shiyong; Tang, Rongxin; Yuan, Zhigang

    2015-04-01

    We report a Cluster observation of transient magnetic reconnection in the Earth's magnetotail at the location of [Xgsm~ -17.2 RE, Ygsm~ -4.5 RE and Zgsm~ 0]. The reconnection X-line retreated tailward with a speed of 34 km/s based on multi-spacecraft analysis. An ion diffusion region with a weak guide field (~10% of lobe field) was encountered during the flow reversal. A flux rope was embedded in the tailward flow. Transient suprathermal electron beams, which directed away from the X-line, were detected repeatedly around the separatrix region with periods of about 60s during the tailward flow bursts. On the earthward side of X-line, multiple earthward-propagating dipolarization fronts were observed quasi-periodically at the edge of the ion diffusion region with time period of 60s-90s. Particle and wave characteristics also show distinct signatures at different stages of the transient reconnection. The implications of this observation will be discussed.

  19. MagicFinger: 3D Magnetic Fingerprints for Indoor Location

    PubMed Central

    Carrillo, Daniel; Moreno, Victoria; Úbeda, Benito; Skarmeta, Antonio F.

    2015-01-01

    Given the indispensable role of mobile phones in everyday life, phone-centric sensing systems are ideal candidates for ubiquitous observation purposes. This paper presents a novel approach for mobile phone-centric observation applied to indoor location. The approach involves a location fingerprinting methodology that takes advantage of the presence of magnetic field anomalies inside buildings. Unlike existing work on the subject, which uses the intensity of magnetic field for fingerprinting, our approach uses all three components of the measured magnetic field vectors to improve accuracy. By using adequate soft computing techniques, it is possible to adequately balance the constraints of common solutions. The resulting system does not rely on any infrastructure devices and therefore is easy to manage and deploy. The proposed system consists of two phases: the offline phase and the online phase. In the offline phase, magnetic field measurements are taken throughout the building, and 3D maps are generated. Then, during the online phase, the user's location is estimated through the best estimator for each zone of the building. Experimental evaluations carried out in two different buildings confirm the satisfactory performance of indoor location based on magnetic field vectors. These evaluations provided an error of (11.34 m, 4.78 m) in the (x, y) components of the estimated positions in the first building where the experiments were carried out, with a standard deviation of (3.41 m, 4.68 m); and in the second building, an error of (4 m, 2.98 m) with a deviation of (2.64 m, 2.33 m). PMID:26184230

  20. Designing bioinspired composite reinforcement architectures via 3D magnetic printing

    NASA Astrophysics Data System (ADS)

    Martin, Joshua J.; Fiore, Brad E.; Erb, Randall M.

    2015-10-01

    Discontinuous fibre composites represent a class of materials that are strong, lightweight and have remarkable fracture toughness. These advantages partially explain the abundance and variety of discontinuous fibre composites that have evolved in the natural world. Many natural structures out-perform the conventional synthetic counterparts due, in part, to the more elaborate reinforcement architectures that occur in natural composites. Here we present an additive manufacturing approach that combines real-time colloidal assembly with existing additive manufacturing technologies to create highly programmable discontinuous fibre composites. This technology, termed as `3D magnetic printing', has enabled us to recreate complex bioinspired reinforcement architectures that deliver enhanced material performance compared with monolithic structures. Further, we demonstrate that we can now design and evolve elaborate reinforcement architectures that are not found in nature, demonstrating a high level of possible customization in discontinuous fibre composites with arbitrary geometries.

  1. Unsupervised fuzzy segmentation of 3D magnetic resonance brain images

    NASA Astrophysics Data System (ADS)

    Velthuizen, Robert P.; Hall, Lawrence O.; Clarke, Laurence P.; Bensaid, Amine M.; Arrington, J. A.; Silbiger, Martin L.

    1993-07-01

    Unsupervised fuzzy methods are proposed for segmentation of 3D Magnetic Resonance images of the brain. Fuzzy c-means (FCM) has shown promising results for segmentation of single slices. FCM has been investigated for volume segmentations, both by combining results of single slices and by segmenting the full volume. Different strategies and initializations have been tried. In particular, two approaches have been used: (1) a method by which, iteratively, the furthest sample is split off to form a new cluster center, and (2) the traditional FCM in which the membership grade matrix is initialized in some way. Results have been compared with volume segmentations by k-means and with two supervised methods, k-nearest neighbors and region growing. Results of individual segmentations are presented as well as comparisons on the application of the different methods to a number of tumor patient data sets.

  2. Designing bioinspired composite reinforcement architectures via 3D magnetic printing

    PubMed Central

    Martin, Joshua J.; Fiore, Brad E.; Erb, Randall M.

    2015-01-01

    Discontinuous fibre composites represent a class of materials that are strong, lightweight and have remarkable fracture toughness. These advantages partially explain the abundance and variety of discontinuous fibre composites that have evolved in the natural world. Many natural structures out-perform the conventional synthetic counterparts due, in part, to the more elaborate reinforcement architectures that occur in natural composites. Here we present an additive manufacturing approach that combines real-time colloidal assembly with existing additive manufacturing technologies to create highly programmable discontinuous fibre composites. This technology, termed as ‘3D magnetic printing', has enabled us to recreate complex bioinspired reinforcement architectures that deliver enhanced material performance compared with monolithic structures. Further, we demonstrate that we can now design and evolve elaborate reinforcement architectures that are not found in nature, demonstrating a high level of possible customization in discontinuous fibre composites with arbitrary geometries. PMID:26494282

  3. Genesis of Interplanetary Intermittent Turbulence: A Case Study of Rope&enrope Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Chian, Abraham C.-L.; Feng, Heng Q.; Hu, Qiang; Loew, Murray H.; Miranda, Rodrigo A.; Muñoz, Pablo R.; Sibeck, David G.; Wu, De J.

    2016-12-01

    In a recent paper, the relation between current sheet, magnetic reconnection, and turbulence at the leading edge of an interplanetary coronal mass ejection was studied. We report here the observation of magnetic reconnection at the interface region of two interplanetary magnetic flux ropes. The front and rear boundary layers of three interplanetary magnetic flux ropes are identified, and the structures of magnetic flux ropes are reconstructed by the Grad-Shafranov method. A quantitative analysis of the reconnection condition and the degree of intermittency reveals that rope-rope magnetic reconnection is the most likely site for genesis of interplanetary intermittency turbulence in this event. The dynamic pressure pulse resulting from this reconnection triggers the onset of a geomagnetic storm.

  4. The magnetic topology of the plasmoid flux rope in a MHD-simulation of magnetotail reconnection

    NASA Astrophysics Data System (ADS)

    Birn, J.; Hesse, M.

    On the basis of a 3D MHD simulation, the magnetic topology of a plasmoid that forms by a localized reconnection process in a magnetotail configuration (including a net dawn-dusk magnetic field component B sub y N is discussed. As a consequence of B sub y N not equalling 0, the plasmoid assumes a helical flux rope structure rather than an isolated island or bubble structure. Initially all field lines of the plasmoid flux rope remain connected with the earth, while at later times a gradually increasing amount of flux tubes becomes separated, connecting to either the distant boundary or to the flank boundaries. In this stage, topologically different flux tubes become tangled and wrapped around each other, consistent with predictions on the basis of an ad hoc plasmoid model.

  5. Global Extended MHD Studies of Fast Magnetic Reconnection

    SciTech Connect

    Breslau J.A.; Jardin, S.C.

    2002-09-18

    Recent experimental and theoretical results have led to two lines of thought regarding the physical processes underlying fast magnetic reconnection. One is based on the traditional Sweet-Parker model but replaces the Spitzer resistivity with an enhanced resistivity caused by electron scattering by ion acoustic turbulence. The other includes the finite gyroradius effects that enter Ohm's law through the Hall and electron pressure gradient terms. A 2-D numerical study, conducted with a new implicit parallel two-fluid code, has helped to clarify the similarities and differences in predictions between these two models and provides some insight into their respective ranges of validity.

  6. Energetic electrons associated with magnetic reconnection in the magnetic cloud boundary layer.

    PubMed

    Wang, Y; Wei, F S; Feng, X S; Zhang, S H; Zuo, P B; Sun, T R

    2010-11-05

    Here is reported in situ observation of energetic electrons (∼100-500 keV) associated with magnetic reconnection in the solar wind by the ACE and Wind spacecraft. The properties of this magnetic cloud driving reconnection and the associated energetic electron acceleration problem are discussed. Further analyses indicate that the electric field acceleration and Fermi-type mechanism are two fundamental elements in the electron acceleration processes and the trapping effect of the specific magnetic field configuration maintains the acceleration status that increases the totally gained energy.

  7. Localized Electron Heating by Strong Guide-Field Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Guo, Xuehan; Sugawara, Takumichi; Inomoto, Michiaki; Yamasaki, Kotaro; Ono, Yasushi; UTST Team

    2015-11-01

    Localized electron heating of magnetic reconnection was studied under strong guide-field (typically Bt 15Bp) using two merging spherical tokamak plasmas in Univ. Tokyo Spherical Tokamak (UTST) experiment. Our new slide-type two-dimensional Thomson scattering system documented for the first time the electron heating localized around the X-point. The region of high electron temperature, which is perpendicular to the magnetic field, was found to have a round shape with radius of 2 [cm]. Also, it was localized around the X-point and does not agree with that of energy dissipation term Et .jt . When we include a guide-field effect term Bt / (Bp + αBt) for Et .jt where α =√{ (vin2 +vout2) /v∥2 } , the energy dissipation area becomes localized around the X-point, suggesting that the electrons are accelerated by the reconnection electric field parallel to the magnetic field and thermalized around the X-point. This work was supported by JSPS A3 Foresight Program ``Innovative Tokamak Plasma Startup and Current Drive in Spherical Torus,'' a Grant-in-Aid from the Japan Society for the Promotion of Science (JSPS) Fellows 15J03758.

  8. Double layer electric fields aiding the production of superthermal electrons within magnetic reconnection exhausts

    NASA Astrophysics Data System (ADS)

    Egedal, Jan; Daughton, William; Le, Ari

    2015-11-01

    Using a kinetic simulation of magnetic reconnection it was recently shown that parallel electric fields (E∥) can be present over large spatial scales in reconnection exhausts. The largest values of E∥ are observed within double layers, which form through large parallel streaming of electrons into the reconnection region. The electron confinement, provided in part by the structure in E∥, allows sustained energization by perpendicular electric fields (E⊥). The energization is a consequence of the confined electrons' chaotic orbital motion that includes drifts aligned with the reconnection electric field. The mechanism is effective in an extended region of the reconnection exhaust allowing for the generation of superthermal electrons in reconnection scenarios, including those with only a single x-line. The numerical and analytical results agree with detailed spacecraft observations recorded during reconnection events in the Earth's magnetotail. Supported by NSF GEM award 1405166 and NASA grant NNX14AC68G.

  9. Three-dimensional magnetic reconnection and its application to solar flares

    NASA Astrophysics Data System (ADS)

    Janvier, Miho

    2017-02-01

    Solar flares are powerful radiations occurring in the Sun's atmosphere. They are powered by magnetic reconnection, a phenomenon that can convert magnetic energy into other forms of energy such as heat and kinetic energy, and which is believed to be ubiquitous in the universe. With the ever increasing spatial and temporal resolutions of solar observations, as well as numerical simulations benefiting from increasing computer power, we can now probe into the nature and the characteristics of magnetic reconnection in three dimensions to better understand the phenomenon's consequences during eruptive flares in our star's atmosphere. We review in the following the efforts made on different fronts to approach the problem of magnetic reconnection. In particular, we will see how understanding the magnetic topology in three dimensions helps in locating the most probable regions for reconnection to occur, how the current layer evolves in three dimensions and how reconnection leads to the formation of flux ropes, plasmoids and flaring loops.

  10. Study of Magnetic Reconnection in Plasma: how it works and energizes plasma particles

    NASA Astrophysics Data System (ADS)

    Yamada, Masaaki

    2015-11-01

    Magnetic reconnection is a phenomenon of nature in which magnetic field lines change their topology in plasma and convert magnetic energy to plasma particles by acceleration and heating. It is a fundamental process at work in laboratory, space and astrophysical plasmas. Magnetic reconnection occurs throughout the Universe: in star forming galaxies; around supernovae; in solar flares; in the earth's magnetosphere; and in fusion plasmas. One of the great challenges in reconnection research has been to understand why reconnection occurs so much faster than predicted by MHD theory. This talk begins with a review of recent discoveries and findings in the research of fast magnetic reconnection in laboratory plasmas and space astrophysical plasmas. I compare the experimental results and space observations with theory and numerical simulations. The collaboration between space and laboratory scientists in reconnection research has reached a point where we can directly compare measurements of the reconnection layer using recently-advanced numerical simulations. In spite of the huge difference in physical scales, we find remarkable commonality between the characteristics of the magnetic reconnection in laboratory and space-astrophysical plasmas. In this talk, I will focus especially on the energy flow, a key feature of reconnection process. We have recently reported our results on the energy conversion and partitioning in a laboratory reconnection layer. In Magnetic Reconnection Experiment (MRX) the mechanisms of ion acceleration and heating are identified and a systematic study of the quantitative inventory of converted energy within a reconnection layer has been made with a well-defined but variable boundary. The measured energy partition in a reconnection region of similar effective size (L ~ 3 ion skin depth) of the Earth's magneto-tail is remarkably consistent with the laboratory results. A more comprehensive study is proposed using MMS satellites very recently put into

  11. Laboratory Experiment of Magnetic Reconnection between Merging Flux Tubes with Strong Guide FIeld

    NASA Astrophysics Data System (ADS)

    Inomoto, M.; Kamio, S.; Kuwahata, A.; Ono, Y.

    2013-12-01

    Magnetic reconnection governs variety of energy release events in the universe, such as solar flares, geomagnetic substorms, and sawtooth crash in laboratory nuclear fusion experiments. Differently from the classical steady reconnection models, non-steady behavior of magnetic reconnection is often observed. In solar flares, intermittent enhancement of HXR emission is observed synchronously with multiple ejection of plammoids [1]. In laboratory reconnection experiments, the existence of the guide field, that is perpendicular to the reconnection field, makes significant changes on reconnection process. Generally the guide field will slow down the reconnection rate due to the increased magnetic pressure inside the current sheet. It also brings about asymmetric structure of the separatrices or effective particle acceleration in collisionless conditions. We have conducted laboratory experiments to study the behavior of the guide-field magnetic reconnection using plasma merging technique (push reconnection). Under substantial guide field even larger than the reconnection field, the reconnection generally exhibits non-steady feature which involves intermittent detachment of X-point and reconnection current center[2]. Transient enhancement of reconnection rate is observed simultaneously with the X-point motion[3]. We found two distinct phenomena associated with the guide-field non-steady reconnection. The one is the temporal and localized He II emission from X-point region, suggesting the production of energetic electrons which could excite the He ions in the vicinity of the X-point. The other is the excitation of large-amplitude electromagnetic waves which have similar properties with kinetic Alfven waves, whose amplitude show positive correlation with the enhancement of the reconnection electric field[4]. Electron beam instability caused by the energetic electrons accelerated to more than twice of the electron thermal velocity could be a potential driver of the

  12. Relativistic MHD simulations of core-collapse GRB jets: 3D instabilities and magnetic dissipation

    NASA Astrophysics Data System (ADS)

    Bromberg, Omer; Tchekhovskoy, Alexander

    2016-02-01

    Relativistic jets are associated with extreme astrophysical phenomena, like the core collapse of massive stars in gamma-ray bursts (GRBs) and the accretion on to supermassive black holes in active galactic nuclei. It is generally accepted that these jets are powered electromagnetically, by the magnetized rotation of a central compact object (black hole or neutron star). However, how the jets produce the observed emission and survive the propagation for many orders of magnitude in distance without being disrupted by current-driven instabilities is the subject of active debate. We carry out time-dependent 3D relativistic magnetohydrodynamic (MHD) simulations of relativistic, Poynting-flux-dominated jets. The jets are launched self-consistently by the rotation of a strongly magnetized central object. This determines the natural degree of azimuthal magnetic field winding, a crucial factor that controls jet stability. We find that the jets are susceptible to two types of instability: (i) a global, external kink mode that grows on long time-scales. It bodily twists the jet, reducing its propagation velocity. We show analytically that in flat density profiles, like the ones associated with galactic cores, the external mode grows and may stall the jet. In the steep profiles of stellar envelopes the external kink weakens as the jet propagates outward. (ii) a local, internal kink mode that grows over short time-scales and causes small-angle magnetic reconnection and conversion of about half of the jet electromagnetic energy flux into heat. We suggest that internal kink instability is the main dissipation mechanism responsible for powering GRB prompt emission.

  13. Development of Turbulent Magnetic Reconnection in a Magnetic Island

    NASA Astrophysics Data System (ADS)

    Huang, Can; Lu, Quanming; Wang, Rongsheng; Guo, Fan; Wu, Mingyu; Lu, San; Wang, Shui

    2017-02-01

    In this paper, with two-dimensional particle-in-cell simulations, we report that the electron Kelvin–Helmholtz instability is unstable in the current layer associated with a large-scale magnetic island, which is formed in multiple X-line guide field reconnections. The current sheet is fragmented into many small current sheets with widths down to the order of the electron inertial length. Secondary magnetic reconnection then occurs in these fragmented current sheets, which leads to a turbulent state. The electrons are highly energized in such a process.

  14. Magnetic reconnection in multispecies plasmas investigated by a kinetic fluid code

    NASA Astrophysics Data System (ADS)

    Dong, Chuanfei; Wang, Liang; Bhattacharjee, Amitava; Hakim, Ammar; Huang, Yi-Min; Germaschewski, Kai

    2016-10-01

    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'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.

  15. Simulating Magnetic Reconnection Experiment (MRX) with a Guide Field using Fluid Code, HiFi

    NASA Astrophysics Data System (ADS)

    Budner, Tamas; Chen, Yangao; Meier, Eric; Ji, Hantao; MRX Team

    2015-11-01

    Magnetic reconnection is a phenomenon that occurs in plasmas when magnetic field lines effectively ``break'' and reconnect resulting in a different topological configuration. In this process, energy that was once stored in the magnetic field is transfered into the thermal velocity of the particles, effectively heating the plasma. MRX at the Princeton Plasma Physics Laboratory creates the conditions under which reconnection can occur by initially ramping the current in two adjacent coils and then rapidly decreasing with and without a guide magnetic field along the reconnecting current. We simulate this experiment using a fluid code called HiFi, an implicit and adaptive high order spectral element modeling framework, and compare our results to experimental data from MRX. The purpose is to identify physics behind the observed reconnection process for the field line break and the resultant plasma heating.

  16. Two Types of Magnetic Reconnection in Coronal Bright Points and the Corresponding Magnetic Configuration

    NASA Astrophysics Data System (ADS)

    Zhang, Q. M.; Chen, P. F.; Guo, Y.; Fang, C.; Ding, M. D.

    2012-02-01

    Coronal bright points (CBPs) are long-lived small-scale brightenings in the solar corona. They are generally explained by magnetic reconnection. However, the corresponding magnetic configurations are not well understood. We carry out a detailed multi-wavelength analysis of two neighboring CBPs on 2007 March 16, observed in soft X-ray (SXR) and EUV channels. It is seen that the SXR light curves present quasi-periodic flashes with an interval of ~1 hr superposed over the long-lived mild brightenings, suggesting that the SXR brightenings of this type of CBPs might consist of two components: one is the gentle brightenings and the other is the CBP flashes. It is found that the strong flashes of the bigger CBP are always accompanied by SXR jets. The potential field extrapolation indicates that both CBPs are covered by a dome-like separatrix surface, with a magnetic null point above. We propose that the repetitive CBP flashes, as well as the recurrent SXR jets, result from the impulsive null-point reconnection, while the long-lived brightenings are due to the interchange reconnection along the separatrix surface. Although the EUV images at high-temperature lines resemble the SXR appearance, the 171 Å and 195 Å channels reveal that the blurry CBP in SXR consists of a cusp-shaped loop and several separate bright patches, which are explained to be due to the null-point reconnection and the separatrix reconnection, respectively.

  17. TWO TYPES OF MAGNETIC RECONNECTION IN CORONAL BRIGHT POINTS AND THE CORRESPONDING MAGNETIC CONFIGURATION

    SciTech Connect

    Zhang, Q. M.; Chen, P. F.; Guo, Y.; Fang, C.; Ding, M. D.

    2012-02-10

    Coronal bright points (CBPs) are long-lived small-scale brightenings in the solar corona. They are generally explained by magnetic reconnection. However, the corresponding magnetic configurations are not well understood. We carry out a detailed multi-wavelength analysis of two neighboring CBPs on 2007 March 16, observed in soft X-ray (SXR) and EUV channels. It is seen that the SXR light curves present quasi-periodic flashes with an interval of {approx}1 hr superposed over the long-lived mild brightenings, suggesting that the SXR brightenings of this type of CBPs might consist of two components: one is the gentle brightenings and the other is the CBP flashes. It is found that the strong flashes of the bigger CBP are always accompanied by SXR jets. The potential field extrapolation indicates that both CBPs are covered by a dome-like separatrix surface, with a magnetic null point above. We propose that the repetitive CBP flashes, as well as the recurrent SXR jets, result from the impulsive null-point reconnection, while the long-lived brightenings are due to the interchange reconnection along the separatrix surface. Although the EUV images at high-temperature lines resemble the SXR appearance, the 171 Angstrom-Sign and 195 Angstrom-Sign channels reveal that the blurry CBP in SXR consists of a cusp-shaped loop and several separate bright patches, which are explained to be due to the null-point reconnection and the separatrix reconnection, respectively.

  18. Measurement of the current sheet during magnetic reconnection in a toroidal plasma.

    PubMed

    Crocker, N A; Fiksel, G; Prager, S C; Sarff, J S

    2003-01-24

    The current and magnetic-field fluctuations associated with magnetic-field-line reconnection have been measured in the reversed field pinch plasma configuration. The current sheet resulting from this reconnection has been measured. The current layer is radially broad, comparable to a magnetic-island width, as may be expected from current transport along magnetic-field lines. It is much larger than that predicted by resistive MHD for linear tearing modes and larger than prediction from two-fluid linear theory.

  19. Particle-in-cell simulations of electron energization in laser-driven magnetic reconnection

    DOE PAGES

    Lu, San; Lu, Quanming; Guo, Fan; ...

    2016-01-25

    Electrons can be energized during laser-driven magnetic reconnection, and the energized electrons form three super-Alfvénic electron jets in the outflow region (Lu et al 2014 New J. Phys. 16 083021). In this paper, by performing two-dimensional particle-in-cell simulations, we find that the electrons can also be significantly energized before magnetic reconnection occurs. When two plasma bubbles with toroidal magnetic fields expand and squeeze each other, the electrons in the magnetic ribbons are energized through betatron acceleration due to the enhancement of the magnetic field, and an electron temperature anisotropymore » $${T}_{{\\rm{e}}\\perp }\\gt {T}_{{\\rm{e}}| | }$$ develops. Meanwhile, some electrons are trapped and bounced repeatedly between the two expanding/approaching bubbles and get energized through a Fermi-like process. Furthermore, the energization before magnetic reconnection is more significant (or important) than that during magnetic reconnection.« less

  20. Particle-in-cell simulations of electron energization in laser-driven magnetic reconnection

    SciTech Connect

    Lu, San; Lu, Quanming; Guo, Fan; Sheng, Zhengming; Wang, Huanyu; Wang, Shui

    2016-01-25

    Electrons can be energized during laser-driven magnetic reconnection, and the energized electrons form three super-Alfvénic electron jets in the outflow region (Lu et al 2014 New J. Phys. 16 083021). In this paper, by performing two-dimensional particle-in-cell simulations, we find that the electrons can also be significantly energized before magnetic reconnection occurs. When two plasma bubbles with toroidal magnetic fields expand and squeeze each other, the electrons in the magnetic ribbons are energized through betatron acceleration due to the enhancement of the magnetic field, and an electron temperature anisotropy ${T}_{{\\rm{e}}\\perp }\\gt {T}_{{\\rm{e}}| | }$ develops. Meanwhile, some electrons are trapped and bounced repeatedly between the two expanding/approaching bubbles and get energized through a Fermi-like process. Furthermore, the energization before magnetic reconnection is more significant (or important) than that during magnetic reconnection.

  1. Slip-Squashing Factors as a Measure of Three-Dimensional Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Titov, V. S.; Forbes, T. G.; Priest, E. R.; Mikić, Z.; Linker, J. A.

    2009-03-01

    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 a magnetic structure at a given time. This technique is extended here so as to analyze the evolution of a 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. The application of the method is illustrated for simple examples, one of which was considered previously by Hesse and coworkers in the framework of the general magnetic reconnection theory. The examples help us to compare these two approaches; it reveals also that, just as for magnetic null points, hyperbolic and cusp minimum points of a magnetic field serve as favorable sites for magnetic reconnection. The new method admits a straightforward numerical implementation and provides a powerful tool for the diagnostics of magnetic reconnection in numerical models of solar-flare-like phenomena in space and laboratory plasmas.

  2. Slip-Squashing Factors as a Measure of Three-Dimensional Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Titov, V. S.; Forbes, T. G.; Priest, E. R.; Mikic, Z.; Linker, J. A.

    2008-12-01

    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 the evolving magnetic field and the tangential boundary flows are known. The application of the method is illustrated for simple examples, one of which was considered previously by Hesse and coworkers in the framework of the general magnetic reconnection theory. The examples help to compare these two approaches; they reveal also that, just as for magnetic null points, hyperbolic and cusp minimum points of a magnetic field may serve as favorable sites for magnetic reconnection. The new method admits a straightforward numerical implementation and provides a powerful tool for the diagnostics of magnetic reconnection in numerical models of solar-flare-like phenomena in space and laboratory plasmas. Research partially supported by NASA and NSF.

  3. Electrodynamics in a Very Thin Current Sheet Leading to Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Singh, Nagendra; Deverapalli, Chakri; Khazanov, George

    2006-01-01

    We study the formation of a very thin current sheet (CS) and associated plasma electrodynamics using three-dimensional (3-D) particle-in-cell simulations with ion to electron mass ratio M/m=1836. The CS is driven by imposed anti-parallel magnetic fields. The noteworthy features of the temporal evolution of the CS are the following: (i) Steepening of the magnetic field profile B,(z) in the central part of the CS, (ii) Generation of three-peak current distribution with the largest peak in the CS center as B,(z) steepens, (iii) Generation of converging electric fields forming a potential well in the CS center in which ions are accelerated. (iv) Electron and ion heating in the central part of the CS by current-driven instabilities (CDI). (v) Re-broadening of the CS due to increased kinetic plasma pressure in the CS center. (vi) Generation of electron temperature anisotropy with temperature perpendicular to the magnetic field being larger than the parallel one. (vii) Current disruption by electron trapping in an explosively growing electrostatic instability (EGEI) and electron tearing instability (ETI). (viii)The onset of EGEI coincides with an increase in the electron temperature above the temperature of the initially hot ions as well as the appearance of new shear in the electron drift velocity. (ix) Bifurcation of the central CS by the current disruption. (x) Magnetic reconnection (MR) beginning near the null in B, and spreading outward. (xi) Generation of highly energized electrons reaching relativistic speeds and having isotropic pitch-angle distribution in the region of reconnected magnetic fields. We compare some of these features of the current sheet with results from laboratory and space experiments.

  4. Combined registration of 3D tibia and femur implant models in 3D magnetic resonance images

    NASA Astrophysics Data System (ADS)

    Englmeier, Karl-Hans; Siebert, Markus; von Eisenhart-Rothe, Ruediger; Graichen, Heiko

    2008-03-01

    The most frequent reasons for revision of total knee arthroplasty are loosening and abnormal axial alignment leading to an unphysiological kinematic of the knee implant. To get an idea about the postoperative kinematic of the implant, it is essential to determine the position and orientation of the tibial and femoral prosthesis. Therefore we developed a registration method for fitting 3D CAD-models of knee joint prostheses into an 3D MR image. This rigid registration is the basis for a quantitative analysis of the kinematics of knee implants. Firstly the surface data of the prostheses models are converted into a voxel representation; a recursive algorithm determines all boundary voxels of the original triangular surface data. Secondly an initial preconfiguration of the implants by the user is still necessary for the following step: The user has to perform a rough preconfiguration of both remaining prostheses models, so that the fine matching process gets a reasonable starting point. After that an automated gradient-based fine matching process determines the best absolute position and orientation: This iterative process changes all 6 parameters (3 rotational- and 3 translational parameters) of a model by a minimal amount until a maximum value of the matching function is reached. To examine the spread of the final solutions of the registration, the interobserver variability was measured in a group of testers. This variability, calculated by the relative standard deviation, improved from about 50% (pure manual registration) to 0.5% (rough manual preconfiguration and subsequent fine registration with the automatic fine matching process).

  5. Magnetic reconnection mediated by hyper-resistive plasmoid instability

    SciTech Connect

    Huang, Yi-Min; Bhattacharjee, A.; Forbes, Terry G.

    2013-08-15

    Magnetic reconnection mediated by the hyper-resistive plasmoid instability is studied with both linear analysis and nonlinear simulations. The linear growth rate is found to scale as S{sub H}{sup 1/6} with respect to the hyper-resistive Lundquist number S{sub H}≡L{sup 3}V{sub A}/η{sub H}, where L is the system size, V{sub A} is the Alfvén velocity, and η{sub H} is the hyper-resistivity. In the nonlinear regime, reconnection rate becomes nearly independent of S{sub H}, the number of plasmoids scales as S{sub H}{sup 1/2}, and the secondary current sheet length and width both scale as S{sub H}{sup −1/2}. These scalings are consistent with a heuristic argument assuming secondary current sheets are close to marginal stability. The distribution of plasmoids as a function of the enclosed flux ψ is found to obey a ψ{sup −1} power law over an extended range, followed by a rapid fall off for large plasmoids. These results are compared with those from resistive magnetohydrodynamic studies.

  6. Analyses of Magnetic Structures of Active Region 11117 Evolution using a 3D Data-Driven Magnetohydrodynamic Model

    NASA Astrophysics Data System (ADS)

    Wu, Shi; Jiang, Chaowei; Feng, Xueshang

    We use the photospheric vector magnetograms obtained by Helioseismic and Magnetic Image (HMI) on-board the Solar Dynamic Observatory (SDO) as the boundary conditions for a Data-Driven CESE-MHD model (Jiang et al. 2012) to investigate the physical characteristics and evolution of magnetic field configurations in the corona before and after a solar eruptive event. Specifically, the evolution of AR11117 characteristics such as length of magnetic shear along the neutral line, current helicity, magnetic free energy and the energy flux across the photosphere due to flux emergence and surface flow are presented. The computed 3D magnetic field configuration are compared with AIA (Atmosphere Image Assembly) which shows remarkable resemblance. A topological analyses reveals that the small flare is correlated with a bald patch (BP, where the magnetic field is tangent to the photosphere), suggesting that the energy release of the flare is caused by magnetic reconnection associated with the BP separatrices. The total magnetic flux and energy keep increasing slightly in spite of flare, while the computed magnetic free energy drops during the flare by 10 (30) ergs which is adequate in providing the energy budget of a minor C-class confined flare as observed. Jiang, Chaowei, Xueshang, Feng, S. T Wu and Qiang Hu, Ap. J., 759:85, 2012 Nov 10

  7. A comparison of analytical and numerical models for steadily driven magnetic reconnection

    NASA Technical Reports Server (NTRS)

    Forbes, T. G.; Priest, E. R.

    1987-01-01

    The effect of boundary conditions in both analytical and numerical solutions of steadily driven reconnection on the reconnection of antiparallel magnetic fields is considered, with special attention given to the mathematical problem of properly specifying boundary conditions for the MHD equation. A unified formulation developed by Priest and Forbes (1986) for steady state reconnection, which includes the Petschek solution and the Sonnerup (1970) solution as special cases, is used to reinterpret the previous numerical experiments of steadily driven reconnection. It is shown that many contradictory features of these experiments were caused by the use of boundary conditions which are different from those required by Petschek's (1964) theory.

  8. Jet Formation in Solar Atmosphere due to Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    González-Avilés, J. J.; Guzmán, F. S.; Fedun, V.

    2017-02-01

    Using numerical simulations, we show that jets with features of type II spicules and cool coronal jets corresponding to temperatures of 104 K can be formed as a result of magnetic reconnection in a scenario with magnetic resistivity. For this, we model the low chromosphere–corona region using the C7 equilibrium solar atmosphere model, assuming that resistive MHD rules the dynamics of the plasma. The magnetic field configurations we analyze correspond to two neighboring loops with opposite polarity. The formation of a high-speed and sharp structure depends on the separation of the loops’ feet. We analyze the cases where the magnetic field strength of the two loops is equal and different. In the first case, with a symmetric configuration the jets rise vertically, whereas in an asymmetric configuration the structure shows an inclination. With a number of simulations carried out under a 2.5D approach, we explore various properties of the excited jets, namely, inclination, lifetime, and velocity. The parameter space involves a magnetic field strength between 20 and 40 G, and the resistivity is assumed to be uniform with a constant value of the order {10}-2{{Ω }}\\cdot m.

  9. Fundamental limitation of a two-dimensional description of magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Firpo, Marie-Christine

    2014-10-01

    For magnetic reconnection to be possible, the electrons have at some point to ``get free from magnetic slavery,'' according to von Steiger's formulation. Stochasticity may be considered as one possible ingredient through which this may be realized in the magnetic reconnection process. It will be argued that non-ideal effects may be considered as a ``hidden'' way to introduce stochasticity. Then it will be shown that there exists a generic intrinsic stochasticity of magnetic field lines that does not require the invocation of non-ideal effects but cannot show up in effective two-dimensional models of magnetic reconnection. Possible implications will be discussed in the frame of tokamak sawteeth that form a laboratory prototype of magnetic reconnection.

  10. Multifractal dissipation of intermittent turbulence generated by the magnetic reconnection in the solar wind

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Wei, F.; Feng, X.

    2013-12-01

    Recent observations revealed a scale-invariant dissipation process in the fast ambient solar wind, while numerical simulations indicated that the dissipation process in collisionless reconnection was multifractal. Here, we investigate the properties of turbulent fluctuations in the magnetic reconnection prevailed region. It is found that there are large magnetic field shear angle and obvious intermittent structures in these regions. The deduced scaling exponents in the dissipation subrange show a multifractal scaling. In comparison, in the nearby region where magnetic reconnection is less prevailed, we find smaller magnetic field shear angle, less intermittent structures, and most importantly, a monofractal dissipation process. These results provide additionally observational evidence for previous observation and simulation work, and they also imply that magnetic dissipation in the solar wind magnetic reconnection might be caused by the intermittent cascade as multifractal processes.

  11. Fast magnetic reconnection supported by sporadic small-scale Petschek-type shocks

    SciTech Connect

    Shibayama, Takuya Nakabou, Takashi; Kusano, Kanya; Miyoshi, Takahiro; Vekstein, Grigory

    2015-10-15

    Standard magnetohydrodynamic (MHD) theory predicts reconnection rate that is far too slow to account for a wide variety of reconnection events observed in space and laboratory plasmas. Therefore, it was commonly accepted that some non-MHD (kinetic) effects play a crucial role in fast reconnection. A recently renewed interest in simple MHD models is associated with the so-called plasmoid instability of reconnecting current sheets. Although it is now evident that this effect can significantly enhance the rate of reconnection, many details of the underlying multiple-plasmoid process still remain controversial. Here, we report results of a high-resolution computer simulation which demonstrate that fast albeit intermittent magnetic reconnection is sustained by numerous small-scale Petschek-type shocks spontaneously formed in the current sheet due to its plasmoid instability.

  12. The onset of ion heating during magnetic reconnection with a strong guide field

    SciTech Connect

    Drake, J. F.; Swisdak, M.

    2014-07-15

    The onset of the acceleration of ions during magnetic reconnection is explored via particle-in-cell simulations in the limit of a strong ambient guide field that self-consistently and simultaneously follow the motions of protons and α particles. Heating parallel to the local magnetic field during reconnection with a guide field is strongly reduced compared with the reconnection of anti-parallel magnetic fields. The dominant heating of thermal ions during guide field reconnection results from pickup behavior of ions during their entry into reconnection exhausts and dominantly produces heating perpendicular rather than parallel to the local magnetic field. Pickup behavior requires that the ion transit time across the exhaust boundary (with a transverse scale of the order of the ion sound Larmor radius) be short compared with the ion cyclotron period. This translates into a threshold in the strength of reconnecting magnetic field that favors the heating of ions with high mass-to-charge. A simulation with a broad initial current layer produces a reconnecting system in which the amplitude of the reconnecting magnetic field just upstream of the dissipation region increases with time as reconnection proceeds. The sharp onset of perpendicular heating when the pickup threshold is crossed is documented. A comparison of the time variation of the parallel and perpendicular ion heating with that predicted based on the strength of the reconnecting field establishes the scaling of ion heating with ambient parameters both below and above the pickup threshold. The relevance to observations of ion heating in the solar corona is discussed.

  13. Cassini in situ observations of long-duration magnetic reconnection in Saturn’s magnetotail

    NASA Astrophysics Data System (ADS)

    Arridge, C. S.; Eastwood, J. P.; Jackman, C. M.; Poh, G.-K.; Slavin, J. A.; Thomsen, M. F.; André, N.; Jia, X.; Kidder, A.; Lamy, L.; Radioti, A.; Reisenfeld, D. B.; Sergis, N.; Volwerk, M.; Walsh, A. P.; Zarka, P.; Coates, A. J.; Dougherty, M. K.

    2016-03-01

    Magnetic reconnection is a fundamental process in solar system and astrophysical plasmas, through which stored magnetic energy associated with current sheets is converted into thermal, kinetic and wave energy. Magnetic reconnection is also thought to be a key process involved in shedding internally produced plasma from the giant magnetospheres at Jupiter and Saturn through topological reconfiguration of the magnetic field. The region where magnetic fields reconnect is known as the diffusion region and in this letter we report on the first encounter of the Cassini spacecraft with a diffusion region in Saturn’s magnetotail. The data also show evidence of magnetic reconnection over a period of 19 h revealing that reconnection can, in fact, act for prolonged intervals in a rapidly rotating magnetosphere. We show that reconnection can be a significant pathway for internal plasma loss at Saturn. This counters the view of reconnection as a transient method of internal plasma loss at Saturn. These results, although directly relating to the magnetosphere of Saturn, have applications in the understanding of other rapidly rotating magnetospheres, including that of Jupiter and other astrophysical bodies.

  14. Asymmetric magnetic reconnection with out-of-plane shear flows in a two dimensional hybrid model

    SciTech Connect

    Wang, Lin; Wang, Xiao-Gang; Wang, Xian-Qu; Liu, Yue

    2015-05-15

    Effects of out-of-plane shear flows on asymmetric magnetic reconnect are investigated in a two-dimensional (2D) hybrid model with an initial Harris sheet equilibrium. It is found that the out-of-plane flow with an in-plane shear can significantly change the asymmetric reconnection process as well as the related geometry. The magnetic flux, out-of-plane magnetic field, in-plane flow vorticity, plasma density, and the reconnection rate are discussed in detail. The results are in comparison with the cases without the shear flows to further understand the effect.

  15. On the magnetic reconnection of resistive tearing mode with the dynamic flow effects

    SciTech Connect

    Ali, A.; Li, Jiquan Kishimoto, Y.

    2015-04-15

    Magnetic reconnection usually occurs in turbulent environments, which may not only provide anomalous resistivity to enhance reconnection rates but also significantly modify the reconnection process through direct nonlinear interaction with magnetic islands. This study presents numerical simulations investigating the effects of an imposed dynamic flow on magnetic reconnection, based on a two-dimensional reduced resistive MHD model. Results show that while the linear stability properties of the resistive tearing mode are moderately affected by the dynamic flow, nonlinear evolution is significantly modified by radial parity, amplitude, and frequency of the dynamic flow. After the slowly evolving nonlinear Rutherford stage, the reconnection process is found to progress in two phases by including the dynamic flow. A Sweet-Parker like current sheet is formed in the first phase. Afterwards, plasmoid instability is triggered in the second phase, where multiple plasmoids are continuously generated and ejected along the current sheet, leading to an impulsive bursty reconnection. The reconnection rate is considerably enhanced in the range of low resistivity as compared to without flow. We found that plasmoid instability onset and evolution are strongly influenced by the frequency and radial parity of the dynamic flows. The scaling of effective reconnection rates with the flow is found to be independent of resistivity.

  16. High-frequency Plasma Waves Associated with Magnetic Reconnection in the Solar Wind

    NASA Astrophysics Data System (ADS)

    Wang, Y.

    2015-12-01

    Activities of high-frequency plasma waves associated with magnetic reconnection in the solar wind observed by Time Domain Sampler (TDS) experiments on STEREO/WAVES are preliminarily analyzed. The TDS instrument can provide burst mode electric fields data with as long as 16384 sample points at 250 kHz sampling rate. In all 1120 suspected reconnection events, it is found that the most commonly occurred waves are neither ion acoustic waves, electrostatic solitary waves, nor Langmuir/upper hybrid waves, but Bernstein-like waves with harmonics of the electron cyclotron frequency. In addition, to each type of waves, Langmuir/upper hybrid waves reveal the largest occurrence rate in the reconnection region than in the ambient solar wind. These results indicate that Bernstein-like waves and Langmuir/upper hybrid waves might play important roles in the reconnection associated particle heating processes and they might also influence the dissipation of magnetic reconnection.

  17. Observations of Ion Signatures of Magnetic Reconnection for Northward IMF

    NASA Technical Reports Server (NTRS)

    Chandler, Michael O.; Moore, Thomas E.; Fuselier, S.; Lockwood, Michael

    1998-01-01

    Magnetic merging at Earth's magnetopause produces distinct mixtures of ions and electrons as well as signatures in their distribution functions. High resolution measurements allow for the separation of the different distributions and quantification of their characteristics. This provides details on the temporal and spatial nature of the merging site and the resulting history of the merged fields. The event of May 29, 1996 resulted in remote observations of the effects of reconnection on both magnetosheath and magnetosphere populations for a period of approximately three hours. Three-dimensional ion distributions obtained by the Thermal Ion Dynamics Experiment on the Polar spacecraft show that field lines threading the spacecraft's location in the northern cusp region contained a mix of D-shaped ions from the magnetosheath and accelerated magnetospheric ions both moving parallel to the local magnetic field. This mix of ions resulted from transmission of magnetosheath ions across the magnetopause at speeds greater than the de-Hoffman-Teller speed and the reflection of cold, slow-moving plasmasphere-like ions at the magnetopause. These observations are used to conclude that these field lines were connected to the ionosphere in the northern hemisphere and, southward of the spacecraft, the interplanetary magnetic field and crossed the magnetopause in the equatorial region southward of the spacecraft.

  18. Reconnection layer dynamics in the Reconnection Scaling Experiment at LANL

    NASA Astrophysics Data System (ADS)

    Furno, Ivo; Intrator, Thomas; Hemsing, Erik; Hsu, Scott; Lapenta, Giovanni; Ricci, Paolo

    2003-10-01

    Using the Reconnection Scaling Experiment (RSX) at Los Alamos National Laboratory, we are studying quasi-2D magnetic reconnection in a 3D linear geometry. RSX is a linear plasma device that relies on plasma gun technology to generate high density (>10^14 cm-3), high current (J 200A/cm^2) ohmically heated (Te 15eV) hydrogen plasma channels ( 2 cm radius). In RSX, magnetic reconnection is induced during the current ramp-up between two axially directed parallel current channels generating a reconnection magnetic field, B_rec, up to 40 Gauss. A set of 12 magnet coils induces an axial guide magnetic field Bz of up to 0.1 T allowing the reconnection field B_rec to be independently scaled from the guiding field B_z. Plasma collisionality can also be independently scaled by varying the plasma gun fill pressure. The formation and dynamics of the current sheet is studied using time and space resolved magnetic field measurements. To date, preliminary experiments in the collisional regime and in the presence of a strong guide magnetic field (B_z/B_rec>10) show the formation of a Sweet-Parker like Y-shaped current sheet. The axial electric field, as inferred from the measured magnetic flux annihilation rate, is also consistent with Sweet-Parker magnetic reconnection. In future experiments, more collisionless regimes will be explored, and the influence of the guide magnetic field on the dynamics of the current sheet and the reconnection rate will be investigated in truly 3D geometry.

  19. INFFTM: Fast evaluation of 3d Fourier series in MATLAB with an application to quantum vortex reconnections

    NASA Astrophysics Data System (ADS)

    Caliari, Marco; Zuccher, Simone

    2017-04-01

    Although Fourier series approximation is ubiquitous in computational physics owing to the Fast Fourier Transform (FFT) algorithm, efficient techniques for the fast evaluation of a three-dimensional truncated Fourier series at a set of arbitrary points are quite rare, especially in MATLAB language. Here we employ the Nonequispaced Fast Fourier Transform (NFFT, by J. Keiner, S. Kunis, and D. Potts), a C library designed for this purpose, and provide a Matlab® and GNU Octave interface that makes NFFT easily available to the Numerical Analysis community. We test the effectiveness of our package in the framework of quantum vortex reconnections, where pseudospectral Fourier methods are commonly used and local high resolution is required in the post-processing stage. We show that the efficient evaluation of a truncated Fourier series at arbitrary points provides excellent results at a computational cost much smaller than carrying out a numerical simulation of the problem on a sufficiently fine regular grid that can reproduce comparable details of the reconnecting vortices.

  20. Integrating kinetic effects in fluid models for magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Wang, Liang

    The integration of kinetic effects in global fluid models is a grand challenge in space plasma physics, and has implication for our ability to model space weather in collisionless plasma environments such as the Earth's magnetosphere. We propose an extensible multi-fluid moment model, with focus on the physics of magnetic reconnection. This model evolves the full Maxwell equations, and simultaneously moments of the Vlasov-Maxwell equation for each species in the plasma. Effects like the Hall effect, the electron inertia, and the pressure gradient are self-consistently embedded in the resulting multi-fluid moment equations, without the need to explicitly solving a generalized Ohm's law. Two limits of the multi-fluid moment model are discussed, namely, the five-moment limit that evolves a scalar pressures for each species, and the ten-moment limit that evolves the full anisotropic, non-gyrotropic pressure tensor. Particularly, the five-moment model reduces to the widely used Hall Magnetohydrodynamics (Hall MHD) model under the assumptions of vanishing electron inertia, infinite speed of light, and quasi-neutrality. In this thesis, we first numerically confirm the reduction of five-moment to Hall MHD under the limit of vanishing electron inertia. Then, we compare ten-moment and fully kinetic Particle-In-Cell (PIC) simulations of a large scale Harris sheet reconnection problem, where the ten-moment equations are closed with a local linear collisionless approximation for the heat flux. The ten-moment simulation gives reasonable agreement with the PIC results, regarding the structures and magnitudes of the electron flows, the polarities and magnitudes of elements of the electron pressure tensor, and the decomposition of the generalized Ohm's law. Possible ways to improve the simple closure towards a non-local, fully three-dimensional description are also discussed.

  1. Integrating kinetic effects in fluid models for magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Wang, L.; Hakim, A.; Bhattacharjee, A.; Germaschewski, K.

    2014-12-01

    The integration of kinetic effects in global fluid models is a grand challenge in space plasma physics, and has implication for our ability to model space weather in collisionless plasma environments such as the Earth's magnetosphere. We propose an extensible multi-fluid moment model, with focus on the physics of magnetic reconnection. This model evolves the full Maxwell equations, and simultaneously moments of the Vlasov-Maxwell equation for each species in the plasma. Effects like the Hall effect, the electron inertia, and the pressure gradient are self-consistently embedded in the resulting multi-fluid moment equations, without the need to explicitly solving a generalized Ohm's law. Two limits of the multi-fluid moment model are discussed, namely, the five-moment limit that evolves a scalar pressure for each species, and the ten-moment limit that evolves the full anisotropic, non-gyrotropic pressure tensor. Particularly, the five-moment model reduces to the widely used Hall Magnetohydrodynamics (Hall MHD) model under the assumptions of vanishing electron inertia, infinite speed of light, and quasi-neutrality. In this presentation, we first compare ten-moment and fully kinetic Particle-In-Cell (PIC) simulations of a large scale Harris sheet reconnection problem, where the ten-moment equations are closed with a local linear collisionless approximation for the heat flux. The ten-moment simulation gives reasonable agreement with the PIC results, regarding the structures and magnitudes of the electron flows, the polarities and magnitudes of elements of the electron pressure tensor, and the decomposition of the generalized Ohm's law. Preliminary results of application of the multi-fluid moment model to Ganymede are also discussed.

  2. "Smoking-Gun" Observables of Magnetic Reconnection: Spatiotemporal Evolution of Electron Characteristics Throughout the Diffusion Region

    NASA Astrophysics Data System (ADS)

    Shuster, Jason R.

    How does magnetic reconnection happen in a collisionless plasma? Knowledge of electron-scale dynamics is necessary to answer this outstanding question of plasma physics. Based on fully kinetic particle-in-cell (PIC) simulations of symmetric reconnection, the spatiotemporal evolution of velocity distribution functions in and around the electron diffusion region (EDR) elucidates how electrons are accelerated and heated by the cooperating reconnection electric and normal magnetic fields. The discrete, triangular structures characteristic of EDR distributions rotate and gyrotropize in velocity space as electrons remagnetize, forming multicomponent arc and ring structures. Further downstream, exhaust electrons are found to exhibit highly structured, time-dependent anisotropies that can be used to infer the temporal stage of reconnection. Cluster spacecraft measurements from a magnetotail reconnection exhaust region agree with these simulation predictions. In PIC simulations of asymmetric reconnection, EDR distributions acquire crescent-shaped populations, indicative of accelerated magnetosheath electrons mixing with electrons of magnetospheric origin. NASA's successfully launched Magnetospheric Multiscale (MMS) mission caught an EDR at the magnetopause and confirmed the signature crescent electron populations. A virtual spacecraft trajectory through the PIC domain is determined quantitatively by inputting MMS magnetic field measurements into an algorithm that outputs a trajectory along which the input measurements are matched. The crescent structures observed by MMS in the EDR are consistent with the simulation distributions at the corresponding time along the computed trajectory. This work demonstrates that electron characteristics can serve as "smoking-gun" observables of the EDR at the heart of the magnetic reconnection mystery.

  3. The role of guide field in magnetic reconnection driven by island coalescence

    NASA Astrophysics Data System (ADS)

    Stanier, A.; Daughton, W.; Simakov, Andrei N.; Chacón, L.; Le, A.; Karimabadi, H.; Ng, Jonathan; Bhattacharjee, A.

    2017-02-01

    A number of studies have considered how the rate of magnetic reconnection scales in large and weakly collisional systems by the modelling of long reconnecting current sheets. However, this set-up neglects both the formation of the current sheet and the coupling between the diffusion region and a larger system that supplies the magnetic flux. Recent studies of magnetic island merging, which naturally include these features, have found that ion kinetic physics is crucial to describe the reconnection rate and global evolution of such systems. In this paper, the effect of a guide field on reconnection during island merging is considered. In contrast to the earlier current sheet studies, we identify a limited range of guide fields for which the reconnection rate, outflow velocity, and pile-up magnetic field increase in magnitude as the guide field increases. The Hall-MHD fluid model is found to reproduce kinetic reconnection rates only for a sufficiently strong guide field, for which ion inertia breaks the frozen-in condition and the outflow becomes Alfvénic in the kinetic system. The merging of large islands occurs on a longer timescale in the zero guide field limit, which may in part be due to a mirror-like instability that occurs upstream of the reconnection region.

  4. COLLISION-INDUCED MAGNETIC RECONNECTION AND A UNIFIED INTERPRETATION OF POLARIZATION PROPERTIES OF GRBs AND BLAZARS

    DOE PAGES

    Deng; Zhang; Zhang; ...

    2016-04-11

    The jet composition and energy dissipation mechanism of gamma-ray bursts (GRBs) and blazars are fundamental questions that remain not fully understood. One plausible model is to interpret the γ-ray emission of GRBs and optical emission of blazars as synchrotron radiation of electrons accelerated from the collision-induced magnetic dissipation regions in Poynting-flux-dominated jets. The polarization observation is an important and independent information to test this model. Based on our recent 3D relativistic MHD simulations of collision-induced magnetic dissipation of magnetically dominated blobs, here we perform calculations of the polarization properties of the emission in the dissipation region and apply the resultsmore » to model the polarization observational data of GRB prompt emission and blazar optical emission. In this article, we show that the same numerical model with different input parameters can reproduce well the observational data of both GRBs and blazars, especially the 90° polarization angle (PA) change in GRB 100826A and the 180° PA swing in blazar 3C279. This supports a unified model for GRB and blazar jets, suggesting that collision-induced magnetic reconnection is a common physical mechanism to power the relativistic jet emission from events with very different black hole masses.« less

  5. COLLISION-INDUCED MAGNETIC RECONNECTION AND A UNIFIED INTERPRETATION OF POLARIZATION PROPERTIES OF GRBs AND BLAZARS

    SciTech Connect

    Deng, Wei; Zhang, Bing; Zhang, Haocheng; Li, Hui E-mail: zhang@physics.unlv.edu E-mail: hz193909@ohio.edu

    2016-04-10

    The jet composition and energy dissipation mechanism of gamma-ray bursts (GRBs) and blazars are fundamental questions that remain not fully understood. One plausible model is to interpret the γ-ray emission of GRBs and optical emission of blazars as synchrotron radiation of electrons accelerated from the collision-induced magnetic dissipation regions in Poynting-flux-dominated jets. The polarization observation is an important and independent information to test this model. Based on our recent 3D relativistic MHD simulations of collision-induced magnetic dissipation of magnetically dominated blobs, here we perform calculations of the polarization properties of the emission in the dissipation region and apply the results to model the polarization observational data of GRB prompt emission and blazar optical emission. We show that the same numerical model with different input parameters can reproduce well the observational data of both GRBs and blazars, especially the 90° polarization angle (PA) change in GRB 100826A and the 180° PA swing in blazar 3C279. This supports a unified model for GRB and blazar jets, suggesting that collision-induced magnetic reconnection is a common physical mechanism to power the relativistic jet emission from events with very different black hole masses.

  6. COLLISION-INDUCED MAGNETIC RECONNECTION AND A UNIFIED INTERPRETATION OF POLARIZATION PROPERTIES OF GRBs AND BLAZARS

    SciTech Connect

    Deng , Wei; Zhang , Haocheng; Zhang , Bing; Li , Hui

    2016-04-11

    The jet composition and energy dissipation mechanism of gamma-ray bursts (GRBs) and blazars are fundamental questions that remain not fully understood. One plausible model is to interpret the γ-ray emission of GRBs and optical emission of blazars as synchrotron radiation of electrons accelerated from the collision-induced magnetic dissipation regions in Poynting-flux-dominated jets. The polarization observation is an important and independent information to test this model. Based on our recent 3D relativistic MHD simulations of collision-induced magnetic dissipation of magnetically dominated blobs, here we perform calculations of the polarization properties of the emission in the dissipation region and apply the results to model the polarization observational data of GRB prompt emission and blazar optical emission. In this article, we show that the same numerical model with different input parameters can reproduce well the observational data of both GRBs and blazars, especially the 90° polarization angle (PA) change in GRB 100826A and the 180° PA swing in blazar 3C279. This supports a unified model for GRB and blazar jets, suggesting that collision-induced magnetic reconnection is a common physical mechanism to power the relativistic jet emission from events with very different black hole masses.

  7. Three-dimensional modeling of electron quasiviscous dissipation in guide-field magnetic reconnection

    SciTech Connect

    Hesse, Michael; Kuznetsova, Masha; Schindler, Karl; Birn, Joachim

    2005-10-01

    A numerical study of guide-field magnetic reconnection in a three-dimensional model is presented. Starting from an initial, perturbed, force-free current sheet, it is shown that reconnection develops to an almost translationally invariant state, where magnetic perturbations are aligned primarily along the main current flow direction. An analysis of guide-field and electron flow signatures indicates behavior that is very similar to earlier, albeit not three-dimensional, simulations. Furthermore, a detailed investigation of electron pressure nongyrotropies in the central diffusion region confirms the major role the associated dissipation process plays in establishing the reconnection electric field.

  8. The role of magnetic reconnection on astrophysical jets launching and particle acceleration

    NASA Astrophysics Data System (ADS)

    De Gouveia Dal Pino, Elisabete

    2012-07-01

    Magnetic reconnection events like those associated to solar flares can be also a very powerful mechanism operating on accretion disk/jet systems. We have recently found that the magnetic power released in fast reconnection flares is more than sufficient to accelerate relativistic plasmons and produce the observed radio luminosity of the nuclear jets associated both to galactic stellar mass black holes and low luminous active galactic nuclei (AGNs). The famous observed correlation between the radio luminosity and the black hole mass of these sources, spanning ^10^9 orders of magnitude in mass, can be naturally explained in this model as simply due to the magnetic reconnection activity at the jet launching region of the accretion disk coronae of these sources. A similar process may explain the observed x-ray flares in young stars (YSOs) as well. In this talk, we review this mechanism and show results of numerical MHD tests of its validity. Also, particle acceleration in the magnetic reconnection sites of these sources can be rather efficient . In this talk, we will also discuss this acceleration process showing the energy distribution evolution of several thousands of test particles injected in a three-dimensional MHD domain of magnetic reconnection with embedded turbulence. The particle acceleration rate, which depends on the reconnection rate, is highly enhanced in this case. This is because reconnection becomes fast and independent of magnetic resistivity in the presence of turbulence and allows the formation of a thick volume in the current sheet filled with multiple, simultaneously reconnecting magnetic fluxes. The particles trapped within this volume then suffer several head-on scatterings with the contracting magnetic fluctuations in a first-order Fermi process. Particles are thus exponentially accelerated to energies which are several orders of magnitude larger than their injected energy.

  9. Joint inversions of two VTEM surveys using quasi-3D TDEM and 3D magnetic inversion algorithms

    NASA Astrophysics Data System (ADS)

    Kaminski, Vlad; Di Massa, Domenico; Viezzoli, Andrea

    2016-05-01

    In the current paper, we present results of a joint quasi-three-dimensional (quasi-3D) inversion of two versatile time domain electromagnetic (VTEM) datasets, as well as a joint 3D inversion of associated aeromagnetic datasets, from two surveys flown six years apart from one another (2007 and 2013) over a volcanogenic massive sulphide gold (VMS-Au) prospect in northern Ontario, Canada. The time domain electromagnetic (TDEM) data were inverted jointly using the spatially constrained inversion (SCI) approach. In order to increase the coherency in the model space, a calibration parameter was added. This was followed by a joint inversion of the total magnetic intensity (TMI) data extracted from the two surveys. The results of the inversions have been studied and matched with the known geology, adding some new valuable information to the ongoing mineral exploration initiative.

  10. Extreme ultraviolet imaging of three-dimensional magnetic reconnection in a solar eruption

    PubMed Central

    Sun, J. Q.; Cheng, X.; Ding, M. D.; Guo, Y.; Priest, E. R.; Parnell, C. E.; Edwards, S. J.; Zhang, J.; Chen, P. F.; Fang, C.

    2015-01-01

    Magnetic reconnection, a change of magnetic field connectivity, is a fundamental physical process in which magnetic energy is released explosively, and it is responsible for various eruptive phenomena in the universe. However, this process is difficult to observe directly. Here, the magnetic topology associated with a solar reconnection event is studied in three dimensions using the combined perspectives of two spacecraft. The sequence of extreme ultraviolet images clearly shows that two groups of oppositely directed and non-coplanar magnetic loops gradually approach each other, forming a separator or quasi-separator and then reconnecting. The plasma near the reconnection site is subsequently heated from ∼1 to ≥5 MK. Shortly afterwards, warm flare loops (∼3 MK) appear underneath the hot plasma. Other observational signatures of reconnection, including plasma inflows and downflows, are unambiguously revealed and quantitatively measured. These observations provide direct evidence of magnetic reconnection in a three-dimensional configuration and reveal its origin. PMID:26113464

  11. BIDIRECTIONAL OUTFLOWS AS EVIDENCE OF MAGNETIC RECONNECTION LEADING TO A SOLAR MICROFLARE

    SciTech Connect

    Hong, Jie; Ding, M. D.; Li, Ying; Yang, Kai; Cheng, Xin; Fang, Cheng; Chen, Feng; Cao, Wenda

    2016-03-20

    Magnetic reconnection is a rapid energy release process that is believed to be responsible for flares on the Sun and stars. Nevertheless, such flare-related reconnection is mostly detected to occur in the corona, while there have been few studies concerning the reconnection in the chromosphere or photosphere. Here, we present both spectroscopic and imaging observations of magnetic reconnection in the chromosphere leading to a microflare. During the flare peak time, chromospheric line profiles show significant blueshifted/redshifted components on the two sides of the flaring site, corresponding to upflows and downflows with velocities of ±(70–80) km s{sup −1}, comparable with the local Alfvén speed as expected by the reconnection in the chromosphere. The three-dimensional nonlinear force-free field configuration further discloses twisted field lines (a flux rope) at a low altitude, cospatial with the dark threads in He i 10830 Å images. The instability of the flux rope may initiate the flare-related reconnection. These observations provide clear evidence of magnetic reconnection in the chromosphere and show the similar mechanisms of a microflare to those of major flares.

  12. Three Dimensional Dynamics of Magnetic Reconnection in Large-Scale Pair Plasmas

    NASA Astrophysics Data System (ADS)

    Yin, L.; Daughton, W.; Albright, B. J.; Bowers, K. J.; Karimabad, H.; Roytershteyn, V.

    2009-05-01

    Using the largest three dimensional particle-in-cell simulations to date, collisionless magnetic reconnection in large-scale electron-positron plasmas without a guide field is shown to involve complex interaction of tearing and kink modes. The reconnection onset is patchy and occurs at multiple sites which self-organize to form a single, large diffusion region. The diffusion region further expands in both outflow direction and current direction and become unstable to secondary kinking and formation of "plasmoid-rope" structures. The secondary kink leads to folding of the reconnection current layer, while plasmoid ropes at times follow the folding of the current layer. The interplay among these secondary instabilities plays a key role in controlling the time dependent reconnection rate in large-scale systems. These dynamics found in collisionless reconnection are compared with those in the collisional regime.

  13. Experimental Verification of the Role of Electron Pressure in Fast Magnetic Reconnection with a Guide Field.

    PubMed

    Fox, W; Sciortino, F; V Stechow, A; Jara-Almonte, J; Yoo, J; Ji, H; Yamada, M

    2017-03-24

    We report detailed laboratory observations of the structure of a reconnection current sheet in a two-fluid plasma regime with a guide magnetic field. We observe and quantitatively analyze the quadrupolar electron pressure variation in the ion-diffusion region, as originally predicted by extended magnetohydrodynamics simulations. The projection of the electron pressure gradient parallel to the magnetic field contributes significantly to balancing the parallel electric field, and the resulting cross-field electron jets in the reconnection layer are diamagnetic in origin. These results demonstrate how parallel and perpendicular force balance are coupled in guide field reconnection and confirm basic theoretical models of the importance of electron pressure gradients for obtaining fast magnetic reconnection.

  14. Particle-in-Cell Simulations of Collisionless Magnetic Reconnection with a Non-Uniform Guide Field

    NASA Astrophysics Data System (ADS)

    Wilson, Fiona; Neukirch, Thomas; Hesse, Michael

    2016-04-01

    Results are presented of a first study of collisionless magnetic reconnection starting from a recently found exact nonlinear force-free Vlasov-Maxwell equilibrium. The initial state has a Harris sheet magnetic field profile in one direction and a non-uniform guide field in a second direction, resulting in a spatially constant magnetic field strength as well as a constant initial plasma density and plasma pressure. It is found that the reconnection process initially resembles guide field reconnection, but that a gradual transition to anti-parallel reconnection happens as the system evolves. The time evolution of a number of plasma parameters is investigated, and the results are compared with simulations starting from a Harris sheet equilibrium and a Harris sheet plus constant guide field equilibrium.

  15. Particle-in-cell simulations of collisionless magnetic reconnection with a non-uniform guide field

    NASA Astrophysics Data System (ADS)

    Wilson, F.; Neukirch, T.; Hesse, M.; Harrison, M. G.; Stark, C. R.

    2016-03-01

    Results are presented of a first study of collisionless magnetic reconnection starting from a recently found exact nonlinear force-free Vlasov-Maxwell equilibrium. The initial state has a Harris sheet magnetic field profile in one direction and a non-uniform guide field in a second direction, resulting in a spatially constant magnetic field strength as well as a constant initial plasma density and plasma pressure. It is found that the reconnection process initially resembles guide field reconnection, but that a gradual transition to anti-parallel reconnection happens as the system evolves. The time evolution of a number of plasma parameters is investigated, and the results are compared with simulations starting from a Harris sheet equilibrium and a Harris sheet plus constant guide field equilibrium.

  16. Experimental Verification of the Role of Electron Pressure in Fast Magnetic Reconnection with a Guide Field

    NASA Astrophysics Data System (ADS)

    Fox, W.; Sciortino, F.; Stechow, A. V.; Jara-Almonte, J.; Yoo, J.; Ji, H.; Yamada, M.

    2017-03-01

    We report detailed laboratory observations of the structure of a reconnection current sheet in a two-fluid plasma regime with a guide magnetic field. We observe and quantitatively analyze the quadrupolar electron pressure variation in the ion-diffusion region, as originally predicted by extended magnetohydrodynamics simulations. The projection of the electron pressure gradient parallel to the magnetic field contributes significantly to balancing the parallel electric field, and the resulting cross-field electron jets in the reconnection layer are diamagnetic in origin. These results demonstrate how parallel and perpendicular force balance are coupled in guide field reconnection and confirm basic theoretical models of the importance of electron pressure gradients for obtaining fast magnetic reconnection.

  17. Observing the release of twist by magnetic reconnection in a solar filament eruption

    PubMed Central

    Xue, Zhike; Yan, Xiaoli; Cheng, Xin; Yang, Liheng; Su, Yingna; Kliem, Bernhard; Zhang, Jun; Liu, Zhong; Bi, Yi; Xiang, Yongyuan; Yang, Kai; Zhao, Li

    2016-01-01

    Magnetic reconnection is a fundamental process of topology change and energy release, taking place in plasmas on the Sun, in space, in astrophysical objects and in the laboratory. However, observational evidence has been relatively rare and typically only partial. Here we present evidence of fast reconnection in a solar filament eruption using high-resolution H-alpha images from the New Vacuum Solar Telescope, supplemented by extreme ultraviolet observations. The reconnection is seen to occur between a set of ambient chromospheric fibrils and the filament itself. This allows for the relaxation of magnetic tension in the filament by an untwisting motion, demonstrating a flux rope structure. The topology change and untwisting are also found through nonlinear force-free field modelling of the active region in combination with magnetohydrodynamic simulation. These results demonstrate a new role for reconnection in solar eruptions: the release of magnetic twist. PMID:27306479

  18. Magnetotail Current Sheet Thinning and Magnetic Reconnection Dynamics in Global Modeling of Substorms

    NASA Technical Reports Server (NTRS)

    Kuznetsova, M. M.; Hesse, M.; Rastaetter, L.; Toth, G.; DeZeeuw, D. L.; Gombosi, T. I.

    2008-01-01

    Magnetotail current sheet thinning and magnetic reconnection are key elements of magnetospheric substorms. We utilized the global MHD model BATS-R-US with Adaptive Mesh Refinement developed at the University of Michigan to investigate the formation and dynamic evolution of the magnetotail thin current sheet. The BATSRUS adaptive grid structure allows resolving magnetotail regions with increased current density up to ion kinetic scales. We investigated dynamics of magnetotail current sheet thinning in response to southwards IMF turning. Gradual slow current sheet thinning during the early growth phase become exponentially fast during the last few minutes prior to nightside reconnection onset. The later stage of current sheet thinning is accompanied by earthward flows and rapid suppression of normal magnetic field component $B-z$. Current sheet thinning set the stage for near-earth magnetic reconnection. In collisionless magnetospheric plasma, the primary mechanism controlling the dissipation in the vicinity of the reconnection site is non-gyrotropic effects with spatial scales comparable with the particle Larmor radius. One of the major challenges in global MHD modeling of the magnetotail magnetic reconnection is to reproduce fast reconnection rates typically observed in smallscale kinetic simulations. Bursts of fast reconnection cause fast magnetic field reconfiguration typical for magnetospheric substorms. To incorporate nongyritropic effects in diffusion regions we developed an algorithm to search for magnetotail reconnection sites, specifically where the magnetic field components perpendicular to the local current direction approaches zero and form an X-type configuration. Spatial scales of the diffusion region and magnitude of the reconnection electric field are calculated self-consistently using MHD plasma and field parameters in the vicinity of the reconnection site. The location of the reconnection sites and spatial scales of the diffusion region are updated

  19. Optimization of a Hybrid Magnetic Bearing for a Magnetically Levitated Blood Pump via 3-D FEA

    PubMed Central

    Cheng, Shanbao; Olles, Mark W.; Burger, Aaron F.; Day, Steven W.

    2011-01-01

    In order to improve the performance of a magnetically levitated (maglev) axial flow blood pump, three-dimensional (3-D) finite element analysis (FEA) was used to optimize the design of a hybrid magnetic bearing (HMB). Radial, axial, and current stiffness of multiple design variations of the HMB were calculated using a 3-D FEA package and verified by experimental results. As compared with the original design, the optimized HMB had twice the axial stiffness with the resulting increase of negative radial stiffness partially compensated for by increased current stiffness. Accordingly, the performance of the maglev axial flow blood pump with the optimized HMBs was improved: the maximum pump speed was increased from 6000 rpm to 9000 rpm (50%). The radial, axial and current stiffness of the HMB was found to be linear at nominal operational position from both 3-D FEA and empirical measurements. Stiffness values determined by FEA and empirical measurements agreed well with one another. The magnetic flux density distribution and flux loop of the HMB were also visualized via 3-D FEA which confirms the designers’ initial assumption about the function of this HMB. PMID:22065892

  20. Optimization of a Hybrid Magnetic Bearing for a Magnetically Levitated Blood Pump via 3-D FEA.

    PubMed

    Cheng, Shanbao; Olles, Mark W; Burger, Aaron F; Day, Steven W

    2011-10-01

    In order to improve the performance of a magnetically levitated (maglev) axial flow blood pump, three-dimensional (3-D) finite element analysis (FEA) was used to optimize the design of a hybrid magnetic bearing (HMB). Radial, axial, and current stiffness of multiple design variations of the HMB were calculated using a 3-D FEA package and verified by experimental results. As compared with the original design, the optimized HMB had twice the axial stiffness with the resulting increase of negative radial stiffness partially compensated for by increased current stiffness. Accordingly, the performance of the maglev axial flow blood pump with the optimized HMBs was improved: the maximum pump speed was increased from 6000 rpm to 9000 rpm (50%). The radial, axial and current stiffness of the HMB was found to be linear at nominal operational position from both 3-D FEA and empirical measurements. Stiffness values determined by FEA and empirical measurements agreed well with one another. The magnetic flux density distribution and flux loop of the HMB were also visualized via 3-D FEA which confirms the designers' initial assumption about the function of this HMB.

  1. What is the role of dayside magnetic reconnection in solar wind-magnetosphere coupling?

    NASA Astrophysics Data System (ADS)

    Dorelli, J. C.

    2008-05-01

    Our current understanding of magnetic storm triggering invokes magnetic reconnection as the basic solar wind- magnetosphere coupling mechanism. It is clear that the storm time ring current enhancement cannot be understood as a simple superposition of substorm injections (e.g., McPherron [AGU monograph 98, 131, 1998]). Instead, the storm time ring current is now thought to be produced by the global convection electric field which results from a prolonged southward IMF and the associated enhanced dayside reconnection rate. Gonzalez [Planet. Space. Sci., 38, 627, 1990]) has reviewed various solar wind magnetosphere coupling functions which have appeared in the literature, arguing that they are all special cases of a general expression (e.g., Sonnerup [J. Geophys. Res., 79, 1546, 1974]) for the rate of component reconnection at the dayside magnetopause. Sonnerup [1974] assumed that the dayside reconnection X line is parallel to the local current density, so that there is a critical IMF clock angle below which reconnection is geometrically impossible. Further, in the special case for which the magnitudes of the IMF and magnetospheric magnetic fields are equal, the reconnection electric field is proportional to sin2(θc/2), where θc is the IMF clock angle. Thus, the Sonnerup [1974] formula seems to explain the rapid decrease in solar wind magnetosphere coupling efficiency with decreasing IMF clock angle. In this talk, we revisit the role of dayside magnetic reconnection in the triggering of magnetic storms, taking into account the global, three-dimensional nature of the magnetopause magnetic field topology. We find that in contrast to the Sonnerup [1974] model -- in which two-dimensional reconnection theory is applied to a local patch of the magnetopause -- the three-dimensional X line is not parallel to the local current density. Further, we argue that the magnetopause has a null-null separator topology for all northward IMF clock angles (save due north, when the

  2. Fast ion generation and runaway through magnetic reconnection events in MST

    NASA Astrophysics Data System (ADS)

    Kim, Jungha; Anderson, Jay; Capecchi, William; Bonofiglo, Phillip; Sears, Stephanie

    2016-10-01

    Fokker-Planck and full orbit modeling are used to investigate how global reconnection events in MST plasmas generate an anisotropic fast ion distribution. A multi-step process is hypothesized. First, thermal ions are heated by a perpendicular heating mechanism, possibly a stochastic process that relies on turbulent diffusion and strong radial electric fields, or ion cyclotron damping in the tearing-driven turbulent cascade. Second, a small fraction of the heated ions have sufficient speed to develop substantial guiding center drifts that are relatively immune to stochastic magnetic transport. In the RFP, these fast ion drift orbits are favorable to confinement. Finally, these fast ions are accelerated by a parallel inductive electric field (up to 80 V/m) associated with the abruptly changing magnetic equilibrium. This strong impulsive field does not include any magnetic-fluctuation-based contribution as experienced by thermal particles or electrons, which do not run away like fast ions. CQL3D, a Fokker-Planck solver, and RIO, a full orbit tracing code, are used to model this multi-step process that is responsible for anisotropy in fast ion distribution in MST. Work supported by US DOE. Supported by US DOE.

  3. Coronal magnetic reconnection driven by CME expansion—the 2011 June 7 event

    SciTech Connect

    Van Driel-Gesztelyi, L.; Baker, D.; Green, L. M.; Williams, D. R.; Carlyle, J.; Kliem, B.; Long, D. M.; Matthews, S. A.; Török, T.; Pariat, E.; Valori, G.; Démoulin, P.; Malherbe, J.-M.

    2014-06-10

    Coronal mass ejections (CMEs) erupt and expand in a magnetically structured solar corona. Various indirect observational pieces of evidence have shown that the magnetic field of CMEs reconnects with surrounding magnetic fields, forming, e.g., dimming regions distant from the CME source regions. Analyzing Solar Dynamics Observatory (SDO) observations of the eruption from AR 11226 on 2011 June 7, we present the first direct evidence of coronal magnetic reconnection between the fields of two adjacent active regions during a CME. The observations are presented jointly with a data-constrained numerical simulation, demonstrating the formation/intensification of current sheets along a hyperbolic flux tube at the interface between the CME and the neighboring AR 11227. Reconnection resulted in the formation of new magnetic connections between the erupting magnetic structure from AR 11226 and the neighboring active region AR 11227 about 200 Mm from the eruption site. The onset of reconnection first becomes apparent in the SDO/AIA images when filament plasma, originally contained within the erupting flux rope, is redirected toward remote areas in AR 11227, tracing the change of large-scale magnetic connectivity. The location of the coronal reconnection region becomes bright and directly observable at SDO/AIA wavelengths, owing to the presence of down-flowing cool, dense (10{sup 10} cm{sup –3}) filament plasma in its vicinity. The high-density plasma around the reconnection region is heated to coronal temperatures, presumably by slow-mode shocks and Coulomb collisions. These results provide the first direct observational evidence that CMEs reconnect with surrounding magnetic structures, leading to a large-scale reconfiguration of the coronal magnetic field.

  4. Plasmoid Instabilities Mediated Three-Dimensional Magnetohydrodynamic Turbulent Reconnection

    SciTech Connect

    Huang, Yi-min; Guo, Fan

    2015-07-21

    After some introductory remarks on fast reconnection in resistive MHD due to plasmoid instability, oblique tearing modes in 3D, and previous studies on 3D turbulent reconnection, the subject is presented under the following topics: 3D simulation setup, time evolution of the 3D simulation, comparison with Sweet-Parker and 2D plasmoid reconnection, and diagnostics of the turbulent state (decomposition of mean fields and fluctuations, power spectra of energy fluctuations, structure function and eddy anisotropy with respect to local magnetic field). Three primary conclusions were reached: (1) The results suggest that 3D plasmoid instabilities can lead to self-generated turbulent reconnection (evidence of energy cascade and development of inertial range, energy fluctuations preferentially align with the local magnetic field, which is one of the characteristics of MHD turbulence); (2) The turbulence is highly inhomogeneous, due to the presence of magnetic shear and outflow jets (conventional MHD turbulence theories or phenomenologies may not be applicable – e.g. scale-dependent anisotropy as predicted by Goldreich & Sridhar is not found); (3) 3D turbulent reconnection is different from 2D plasmoid-dominated reconnection in many aspects. However, in fully developed state, reconnection rates in 2D and 3D are comparable — this result needs to be further checked in higher S.

  5. Study of Electron-scale Dissipation near the X-line During Magnetic Reconnection in a Laboratory Plasma

    NASA Astrophysics Data System (ADS)

    Ji, H.; Yoo, J.; Dorfman, S. E.; Jara-Almonte, J.; Yamada, M.; Swanson, C.; Daughton, W. S.; Roytershteyn, V.; Kuwahata, A.; Ii, T.; Inomoto, M.; Ono, Y.; von Stechow, A.; Grulke, O.; Phan, T.; Mozer, F.; Bale, S. D.

    2013-12-01

    Despite its disruptive influences on the large-scale structures of space and solar plasmas, the crucial topological changes and associated dissipation during magnetic reconnection take place only near an X-line within thin singular layers. In the modern collisionless models where electrons and ions are allowed to move separately, it has been predicted that ions exhaust efficiently through a thicker, ion-scale dissipative layer while mobile electrons can evacuate through a thinner, electron-scale dissipation layer, allowing for efficient release of magnetic energy. While ion dissipation layers have been frequently detected, the existence of election layers near the X-line and the associated dissipation structures and mechanisms are still an open question, and will be a main subject of the coming MMS mission. In this presentation, we will summarize our efforts in the past a few years to study electron-scale dissipation in a well-controlled and well-diagnosed reconnecting current sheet in a laboratory plasma, with close comparisons with the state-of-the-art, 2D and 3D fully kinetic simulations. Key results include: (1) positive identification of electromagnetic waves detected at the current sheet center as long wave-length, lower-hybrid drift instabilities (EM-LHDI), (2) however, there is strong evidence that this EM-LHDI cannot provide the required force to support the reconnection electric field, (3) detection of 3D flux-rope-like magnetic structures during impulsive reconnection events, and (4) electrons are heated through non-classical mechanisms near the X-line with a small but clear temperature anisotropy. These results, unfortunately, do not resolve the outstanding discrepancies on electron layer thickness between best available experiments and fully kinetic simulations. To make further progress, we are continuously pushing in the both experimental and numerical frontiers. Experimentally, we started investigations on EM-LHDI and electron heating as a function

  6. On the Electrons Dynamics during Rapid Island Coalescence in Asymmetric Magnetic Reconnection: Case With and With No Guide Field

    NASA Astrophysics Data System (ADS)

    Cazzola, E.; Innocenti, M. E.; Markidis, S.; Goldman, M. V.; Newman, D. L.; Lapenta, G.

    2015-12-01

    We present a set of fully kinetic 2.5D simulations of electron dynamics during rapid magnetic islands coalescence in asymmetric conditions. Simulations are performed using the massively parallel fully kinetic implicit moment method code iPIC3D (Markidis et al. 2010). The domain is a double periodic box with two current sheets initially representing two different reconnection conditions with the same asymmetric ratio. In the upper sheet the conventional hyperbolic continuous functions for magnetic field and density are initialised across the layer (e.g. Pritchett 2008). In the lower layer the same asymmetric conditions are used the presence of an extremely steep gradient describing a pure tangential discontinuity.Cases with and without guide field are compared. While the upper layer shows the typical reconnection evolution of an asymmetric configuration, the lower layer very soon develops not-uniformly distributed multiple reconnection points which rapidly evolve in a series of magnetic islands. Quick islands coalescence follows. Even though the electrons dynamics during island merging has been studied in both symmetric and asymmetric conditions (e.g. Pritchett 2007, 2008b, Drake et al. 2006, Oka et al. 2010, Huang et al. 2014), these simulations show new interesting features such as the presence of three distinct regions, here named X, M and D, with very different properties. Regions X and M manifest typical signatures of ongoing reconnection, distinguishable thanks to the direct comparison with the outcomes of the upper layer. In particular, M-type regions are different because reconnection occurs between two merging islands in a vertical fashion with respect to the direction of the current sheets initially set. In contrast, regions D present a quite diverse features, not showing the typical signatures of a occurring reconnection. The present work is supported by the NASA MMS Grant NNX08AO84G. Additional support for the KULeuven team is provided by the European

  7. Effects of 3D Toroidally Asymmetric Magnetic Field on Tokamak Magnetic Surfaces

    NASA Astrophysics Data System (ADS)

    Lao, L. L.

    2005-10-01

    The effects of 3D error magnetic field on magnetic surfaces are investigated using the DIII-D internal coils (I-Coils). Slowly rotating n=1 traveling waves at 5 Hz and various amplitudes were applied to systematically perturb the edge surfaces by programming the I-Coil currents. The vertical separatrix location difference between EFIT magnetic reconstructions that assumes toroidal symmetry and Thomson scattering Te measurements responds in phase to the applied perturbed field. The oscillation amplitudes increase with the strength of the applied field but are much smaller than those expected from the applied field alone. The results indicate that plasma response is important. Various plasma response models based on results from the MHD codes MARS and GATO are being developed and compared to the experimental observations. To more accurately evaluate the effects of magnetic measurement errors, a new form of the magnetic uncertainty matrix is also being implemented into EFIT. Details will be presented.

  8. DIII-D Equilibrium Reconstructions with New 3D Magnetic Probes

    NASA Astrophysics Data System (ADS)

    Lao, Lang; Strait, E. J.; Ferraro, N. M.; Ferron, J. R.; King, J. D.; Lee, X.; Meneghini, O.; Turnbull, A. D.; Huang, Y.; Qian, J. G.; Wingen, A.

    2015-11-01

    DIII-D equilibrium reconstructions with the recently installed new 3D magnetic diagnostic are presented. In addition to providing information to allow more accurate 2D reconstructions, the new 3D probes also provide useful information to guide computation of 3D perturbed equilibria. A new more comprehensive magnetic compensation has been implemented. Algorithms are being developed to allow EFIT to reconstruct 3D perturbed equilibria making use of the new 3D probes and plasma responses from 3D MHD codes such as GATO and M3D-C1. To improve the computation efficiency, all inactive probes in one of the toroidal planes in EFIT have been replaced with new probes from other planes. Other 3D efforts include testing of 3D reconstructions using V3FIT and a new 3D variational moment equilibrium code VMOM3D. Other EFIT developments include a GPU EFIT version and new safety factor and MSE-LS constraints. The accuracy and limitation of the new probes for 3D reconstructions will be discussed. Supported by US DOE under DE-FC02-04ER54698 and DE-FG02-95ER54309.

  9. Nonlinear instability and intermittent nature of magnetic reconnection in solar chromosphere

    NASA Astrophysics Data System (ADS)

    Singh, K. A. P.; Hillier, Andrew; Isobe, Hiroaki; Shibata, Kazunari

    2015-10-01

    The recent observations of Singh et al. (2012, ApJ, 759, 33) have shown multiple plasma ejections and the intermittent nature of magnetic reconnection in the solar chromosphere, highlighting the need for fast reconnection to occur in highly collisional plasma. However, the physical process through which fast magnetic reconnection occurs in partially ionized plasma, like the solar chromosphere, is still poorly understood. It has been shown that for sufficiently high magnetic Reynolds numbers, Sweet-Parker current sheets can become unstable leading to tearing mode instability and plasmoid formation, but when dealing with a partially ionized plasma the strength of coupling between the ions and neutrals plays a fundamental role in determining the dynamics of the system. We propose that as the reconnecting current sheet thins and the tearing instability develops, plasmoid formation passes through strongly, intermediately, and weakly coupled (or decoupled) regimes, with the time scale for the tearing mode instability depending on the frictional coupling between ions and neutrals. We present calculations for the relevant time scales for fractal tearing in all three regimes. We show that as a result of the tearing mode instability and the subsequent non-linear instability due to the plasmoid-dominated reconnection, the Sweet-Parker current sheet tends to have a fractal-like structure, and when the chromospheric magnetic field is sufficiently strong the tearing instability can reach down to kinetic scales, which are hypothesized to be necessary for fast reconnection.

  10. Magnetospheric Multiscale Satellites Observations of Parallel Electric Fields Associated with Magnetic Reconnection.

    PubMed

    Ergun, R E; Goodrich, K A; Wilder, F D; Holmes, J C; Stawarz, J E; Eriksson, S; Sturner, A P; Malaspina, D M; Usanova, M E; Torbert, R B; Lindqvist, P-A; Khotyaintsev, Y; Burch, J L; Strangeway, R J; Russell, C T; Pollock, C J; Giles, B L; Hesse, M; Chen, L J; Lapenta, G; Goldman, M V; Newman, D L; Schwartz, S J; Eastwood, J P; Phan, T D; Mozer, F S; Drake, J; Shay, M A; Cassak, P A; Nakamura, R; Marklund, G

    2016-06-10

    We report observations from the Magnetospheric Multiscale satellites of parallel electric fields (E_{∥}) associated with magnetic reconnection in the subsolar region of the Earth's magnetopause. E_{∥} events near the electron diffusion region have amplitudes on the order of 100  mV/m, which are significantly larger than those predicted for an antiparallel reconnection electric field. This Letter addresses specific types of E_{∥} events, which appear as large-amplitude, near unipolar spikes that are associated with tangled, reconnected magnetic fields. These E_{∥} events are primarily in or near a current layer near the separatrix and are interpreted to be double layers that may be responsible for secondary reconnection in tangled magnetic fields or flux ropes. These results are telling of the three-dimensional nature of magnetopause reconnection and indicate that magnetopause reconnection may be often patchy and/or drive turbulence along the separatrix that results in flux ropes and/or tangled magnetic fields.

  11. A Parallel Two-fluid Code for Global Magnetic Reconnection Studies

    SciTech Connect

    J.A. Breslau; S.C. Jardin

    2001-08-09

    This paper describes a new algorithm for the computation of two-dimensional resistive magnetohydrodynamic (MHD) and two-fluid studies of magnetic reconnection in plasmas. It has been implemented on several parallel platforms and shows good scalability up to 32 CPUs for reasonable problem sizes. A fixed, nonuniform rectangular mesh is used to resolve the different spatial scales in the reconnection problem. The resistive MHD version of the code uses an implicit/explicit hybrid method, while the two-fluid version uses an alternating-direction implicit (ADI) method. The technique has proven useful for comparing several different theories of collisional and collisionless reconnection.

  12. Development of a new experimental device for long-duration magnetic reconnection in weakly ionized plasma

    NASA Astrophysics Data System (ADS)

    Yanai, Ryoma; Kaminou, Yasuhiro; Nishida, Kento; Inomoto, Michiaki

    2016-10-01

    Magnetic reconnection is a universal phenomenon which determines global structure and energy conversion in magnetized plasmas. Many experimental studies have been carried out to explore the physics of magnetic reconnection in fully ionized condition. However, it is predicted that the behavior of magnetic reconnection in weakly ionized plasmas such as solar chromosphere plasma will show different behavior such as ambipolar diffusion caused by interaction with neutral particles. In this research, we are developing a new experimental device to uncover the importance of ambipolar diffusion during magnetic reconnection in weakly ionized plasmas. We employ an inverter-driven rotating magnetic fields technique, which is used for generating steady azimuthal plasma current, to establish long-duration ( 1 ms) anti-parallel reconnection with magnetic field of 5 mT in weakly ionized plasma. We will present development status and initial results from the new experimental setup. This work was supported by JSPS A3 Foresight Program ``Innovative Tokamak Plasma Startup and Current Drive in Spherical Torus'', Giant-in Aid for Scientific Research (KAKENHI) 15H05750, 15K14279, 26287143 and the NIFS Collaboration Research program (NIFS14KNWP004).

  13. Fast 3D fluid registration of brain magnetic resonance images

    NASA Astrophysics Data System (ADS)

    Leporé, Natasha; Chou, Yi-Yu; Lopez, Oscar L.; Aizenstein, Howard J.; Becker, James T.; Toga, Arthur W.; Thompson, Paul M.

    2008-03-01

    Fluid registration is widely used in medical imaging to track anatomical changes, to correct image distortions, and to integrate multi-modality data. Fluid mappings guarantee that the template image deforms smoothly into the target, without tearing or folding, even when large deformations are required for accurate matching. Here we implemented an intensity-based fluid registration algorithm, accelerated by using a filter designed by Bro-Nielsen and Gramkow. We validated the algorithm on 2D and 3D geometric phantoms using the mean square difference between the final registered image and target as a measure of the accuracy of the registration. In tests on phantom images with different levels of overlap, varying amounts of Gaussian noise, and different intensity gradients, the fluid method outperformed a more commonly used elastic registration method, both in terms of accuracy and in avoiding topological errors during deformation. We also studied the effect of varying the viscosity coefficients in the viscous fluid equation, to optimize registration accuracy. Finally, we applied the fluid registration algorithm to a dataset of 2D binary corpus callosum images and 3D volumetric brain MRIs from 14 healthy individuals to assess its accuracy and robustness.

  14. Contiguous 3 d and 4 f Magnetism: Strongly Correlated 3 d Electrons in YbFe2Al10

    NASA Astrophysics Data System (ADS)

    Khuntia, P.; Peratheepan, P.; Strydom, A. M.; Utsumi, Y.; Ko, K.-T.; Tsuei, K.-D.; Tjeng, L. H.; Steglich, F.; Baenitz, M.

    2014-11-01

    We present magnetization, specific heat, and Al 27 NMR investigations on YbFe2Al10 over a wide range in temperature and magnetic field. The magnetic susceptibility at low temperatures is strongly enhanced at weak magnetic fields, accompanied by a ln (T0/T ) divergence of the low-T specific heat coefficient in zero field, which indicates a ground state of correlated electrons. From our hard-x-ray photoemission spectroscopy study, the Yb valence at 50 K is evaluated to be 2.38. The system displays valence fluctuating behavior in the low to intermediate temperature range, whereas above 400 K, Yb3 + carries a full and stable moment, and Fe carries a moment of about 3.1 μB. The enhanced value of the Sommerfeld-Wilson ratio and the dynamic scaling of the spin-lattice relaxation rate divided by T [(1 /T1T ) 27 ] with static susceptibility suggests admixed ferromagnetic correlations. (1 /T1T ) 27 simultaneously tracks the valence fluctuations from the 4 f Yb ions in the high temperature range and field dependent antiferromagnetic correlations among partially Kondo screened Fe 3 d moments at low temperature; the latter evolve out of an Yb 4 f admixed conduction band.

  15. A 3D Current Loop Model of Magnetic Clouds

    NASA Astrophysics Data System (ADS)

    Chen, James

    1992-05-01

    A magnetohydrodynamic (MHD) model is developed to study magnetic clouds (Burlaga et al. 1981). In this model, magnetic clouds observed near 1 AU are treated as a consequence of eruptive solar current loops. It is shown that current loops intially in MHD equilibrium can be triggered to rise rapidly, propelling material of up to 10(16) g at up to ~ 1000 km s(-1) and dissipating ~ 10(32) erg of magnetic energy in tens of minutes. The initial rise profile is consistent with observed height-time profiles of erupting filaments (Kahler et al. 1988). Two triggering mechanisms for eruption are suggested: (1)subphotospheric energy storage and trigger and (2) in situ (coronal) energy storage and trigger. In the former, eruption occurs as a result of changes in the subphotospheric magnetic topology and subsequent relaxation to a new equilibrium. In the latter, the current loop can evolve to exceed a local maximum in the magnetic potential associated with the ambient magnetic fields. The former scenario leads to more energetic and longer-lasting eruption than the latter. Burlaga, L. F., Sittler, E., Mariani, F., and Schwenn, R. 1981, J. Geophys. Res., 86, 6673. Kahler, S. W., Moore, R. L., Kane, S. R., and Zirin, H. 1988, Ap. J., 328, 824.

  16. 3D stochastic joint inversion of gravity and magnetic data

    NASA Astrophysics Data System (ADS)

    Shamsipour, Pejman; Marcotte, Denis; Chouteau, Michel

    2012-04-01

    A novel stochastic joint inversion method based on cokriging is applied to estimate density and magnetic susceptibility distributions from gravity and total magnetic field data. The method fully integrates the physical relations between density-gravity, on one hand, and magnetic susceptibility-total magnetic field, on the other hand. As a consequence, when the data are considered noise-free, the responses from the inverted density and susceptibility data exactly reproduce the observed data. The required density and magnetic susceptibility auto- and cross covariance are assumed to follow a linear model of coregionalization (LCM). The parameters of the LCM are estimated from v-v plot fitting of the gravity and total magnetic experimental covariances. The model is tested on two synthetic cases and one real data set, the Perseverance mine (Quebec, Canada). Joint inversions are compared to separate inversions. The joint inversions better recover the known models in the synthetic cases. With the real data set, better definition and location of the mineralized lenses are achieved by joint inversion.

  17. Experimental demonstration of the role of electron pressure in fast magnetic reconnection with a guide field

    NASA Astrophysics Data System (ADS)

    Fox, W.; Sciortino, F.; von Stechow, A.; Jara-Almonte, J.; Yoo, J.; Ji, H.; Yamada, M.

    2016-10-01

    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. Supported by Max-Planck Princeton Center for Plasma Physics.

  18. A symmetric, triply interlaced 3-D anionic MOF that exhibits both magnetic order and SMM behaviour.

    PubMed

    Campo, J; Falvello, L R; Forcén-Vázquez, E; Sáenz de Pipaón, C; Palacio, F; Tomás, M

    2016-11-14

    A newly prepared 3-D polymer of cobalt citrate cubanes bridged by high-spin Co(ii) centres displays both single-molecule magnet (SMM) behaviour and magnetic ordering. Triple interpenetration of the 3-D diamondoid polymers yields a crystalline solid with channels that host cations and free water molecules, with the SMM behaviour of the Co4O4 cores preserved. The octahedrally coordinated Co(ii) bridges are implicated in the onset of magnetic order at an experimentally accessible temperature.

  19. Scaling the energy conversion rate from magnetic field reconnection to different bodies

    SciTech Connect

    Mozer, F. S.; Hull, A.

    2010-10-15

    Magnetic field reconnection is often invoked to explain electromagnetic energy conversion in planetary magnetospheres, stellar coronae, and other astrophysical objects. Because of the huge dynamic range of magnetic fields in these bodies, it is important to understand energy conversion as a function of magnetic field strength and related parameters. It is conjectured theoretically and shown experimentally that the energy conversion rate per unit area in reconnection scales as the cube of an appropriately weighted magnetic field strength divided by the square root of an appropriately weighted density. With this functional dependence, the energy release in flares on the Sun, the large and rapid variation of the magnetic flux in the tail of Mercury, and the apparent absence of reconnection on Jupiter and Saturn, may be understood. Electric fields at the perihelion of the Solar Probe Plus mission may be tens of V/m.

  20. Geo-effectiveness and radial dependence of magnetic cloud erosion by magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Lavraud, Benoit; Ruffenach, Alexis; Rouillard, Alexis P.; Kajdic, Primoz; Manchester, Ward B.; Lugaz, Noé

    2014-01-01

    flux erosion by magnetic reconnection occurs at the front of at least some magnetic clouds (MCs). We first investigate how erosion influences the geo-effectiveness of MCs in a general sense and using a south-north magnetic polarity MC observed on 18-20 October 1995. Although the magnetic shear at its front may not be known during propagation, measurements at 1 AU show signatures of local reconnection. Using a standard MC model, an empirical model of the geomagnetic response (Dst), and an observational estimate of the magnetic flux erosion, we find that the strength of the observed ensuing storm was ~30% lower than if no erosion had occurred. We then discuss the interplay between adiabatic compression and magnetic erosion at the front of MCs. We conclude that the most geo-effective configuration for a south-north polarity MC is to be preceded by a solar wind with southward IMF. This stems not only from the formation of a geo-effective sheath ahead of it but also from the adiabatic compression and reduced (or lack thereof) magnetic erosion which constructively conspire for the structure to be more geo-effective. Finally, assuming simple semiempirical and theoretical Alfvén speed profiles expected from expansion to 1 AU, we provide first-order estimates of the erosion process radial evolution. We find that the expected reconnection rates during propagation allow for significant erosion, on the order of those reported. Calculations also suggest that most of the erosion should occur in the inner heliosphere, and up to ~50% may yet occur beyond Mercury's orbit.

  1. MMS observations of large guide field symmetric reconnection between colliding reconnection jets at the center of a magnetic flux rope at the magnetopause

    NASA Astrophysics Data System (ADS)

    Øieroset, M.; Phan, T. D.; Haggerty, C.; Shay, M. A.; Eastwood, J. P.; Gershman, D. J.; Drake, J. F.; Fujimoto, M.; Ergun, R. E.; Mozer, F. S.; Oka, M.; Torbert, R. B.; Burch, J. L.; Wang, S.; Chen, L. J.; Swisdak, M.; Pollock, C.; Dorelli, J. C.; Fuselier, S. A.; Lavraud, B.; Giles, B. L.; Moore, T. E.; Saito, Y.; Avanov, L. A.; Paterson, W.; Strangeway, R. J.; Russell, C. T.; Khotyaintsev, Y.; Lindqvist, P. A.; Malakit, K.

    2016-06-01

    We report evidence for reconnection between colliding reconnection jets in a compressed current sheet at the center of a magnetic flux rope at Earth's magnetopause. The reconnection involved nearly symmetric inflow boundary conditions with a strong guide field of two. The thin (2.5 ion-skin depth (di) width) current sheet (at ~12 di downstream of the X line) was well resolved by MMS, which revealed large asymmetries in plasma and field structures in the exhaust. Ion perpendicular heating, electron parallel heating, and density compression occurred on one side of the exhaust, while ion parallel heating and density depression were shifted to the other side. The normal electric field and double out-of-plane (bifurcated) currents spanned almost the entire exhaust. These observations are in good agreement with a kinetic simulation for similar boundary conditions, demonstrating in new detail that the structure of large guide field symmetric reconnection is distinctly different from antiparallel reconnection.

  2. Sub-grid-scale description of turbulent magnetic reconnection in magnetohydrodynamics

    NASA Astrophysics Data System (ADS)

    Widmer, F.; Büchner, J.; Yokoi, N.

    2016-04-01

    Magnetic reconnection requires, at least locally, a non-ideal plasma response. In collisionless space and astrophysical plasmas, turbulence could transport energy from large to small scales where binary particle collisions are rare. We have investigated the influence of small scale magnetohydrodynamics (MHD) turbulence on the reconnection rate in the framework of a compressible MHD approach including sub-grid-scale (SGS) turbulence. For this sake, we considered Harris-type and force-free current sheets with finite guide magnetic fields directed out of the reconnection plane. The goal is to find out whether unresolved by conventional simulations MHD turbulence can enhance the reconnection process in high-Reynolds-number astrophysical plasmas. Together with the MHD equations, we solve evolution equations for the SGS energy and cross-helicity due to turbulence according to a Reynolds-averaged turbulence model. The SGS turbulence is self-generated and -sustained through the inhomogeneities of the mean fields. By this way, the feedback of the unresolved turbulence into the MHD reconnection process is taken into account. It is shown that the turbulence controls the regimes of reconnection by its characteristic timescale τt. The dependence on resistivity was investigated for large-Reynolds-number plasmas for Harris-type as well as force-free current sheets with guide field. We found that magnetic reconnection depends on the relation between the molecular and apparent effective turbulent resistivity. We found that the turbulence timescale τt decides whether fast reconnection takes place or whether the stored energy is just diffused away to small scale turbulence. If the amount of energy transferred from large to small scales is enhanced, fast reconnection can take place. Energy spectra allowed us to characterize the different regimes of reconnection. It was found that reconnection is even faster for larger Reynolds numbers controlled by the molecular resistivity η, as

  3. A Magnetic Diagnostic Code for 3D Fusion Equilibria

    SciTech Connect

    Samuel A. Lazerson, S. Sakakibara and Y. Suzuki

    2013-03-12

    A synthetic magnetic diagnostics code for fusion equilibria is presented. This code calculates the response of various magnetic diagnostics to the equilibria produced by the VMEC and PIES codes. This allows for treatment of equilibria with both good nested flux surfaces and those with stochastic regions. DIAGNO v2.0 builds upon previous codes through the implementation of a virtual casing principle. The code is validated against a vacuum shot on the Large Helical Device (LHD) where the vertical field was ramped. As an exercise of the code, the diagnostic response for various equilibria are calculated on the LHD.

  4. Pulsating Magnetic Reconnection Driven by Three-Dimensional Flux-Rope Interactions

    NASA Astrophysics Data System (ADS)

    Gekelman, W.; De Haas, T.; Daughton, W.; Van Compernolle, B.; Intrator, T.; Vincena, S.

    2016-06-01

    The dynamics of magnetic reconnection is investigated in a laboratory experiment consisting of two magnetic flux ropes, with currents slightly above the threshold for the kink instability. The evolution features periodic bursts of magnetic reconnection. To diagnose this complex evolution, volumetric three-dimensional data were acquired for both the magnetic and electric fields, allowing key field-line mapping quantities to be directly evaluated for the first time with experimental data. The ropes interact by rotating about each other and periodically bouncing at the kink frequency. During each reconnection event, the formation of a quasiseparatrix layer (QSL) is observed in the magnetic field between the flux ropes. Furthermore, a clear correlation is demonstrated between the quasiseparatrix layer and enhanced values of the quasipotential computed by integrating the parallel electric field along magnetic field lines. These results provide clear evidence that field lines passing through the quasiseparatrix layer are undergoing reconnection and give a direct measure of the nonlinear reconnection rate. The measurements suggest that the parallel electric field within the QSL is supported predominantly by electron pressure; however, resistivity may play a role.

  5. Pulsating Magnetic Reconnection Driven by Three-Dimensional Flux-Rope Interactions.

    PubMed

    Gekelman, W; De Haas, T; Daughton, W; Van Compernolle, B; Intrator, T; Vincena, S

    2016-06-10

    The dynamics of magnetic reconnection is investigated in a laboratory experiment consisting of two magnetic flux ropes, with currents slightly above the threshold for the kink instability. The evolution features periodic bursts of magnetic reconnection. To diagnose this complex evolution, volumetric three-dimensional data were acquired for both the magnetic and electric fields, allowing key field-line mapping quantities to be directly evaluated for the first time with experimental data. The ropes interact by rotating about each other and periodically bouncing at the kink frequency. During each reconnection event, the formation of a quasiseparatrix layer (QSL) is observed in the magnetic field between the flux ropes. Furthermore, a clear correlation is demonstrated between the quasiseparatrix layer and enhanced values of the quasipotential computed by integrating the parallel electric field along magnetic field lines. These results provide clear evidence that field lines passing through the quasiseparatrix layer are undergoing reconnection and give a direct measure of the nonlinear reconnection rate. The measurements suggest that the parallel electric field within the QSL is supported predominantly by electron pressure; however, resistivity may play a role.

  6. A LABORATORY EXPERIMENT OF MAGNETIC RECONNECTION: OUTFLOWS, HEATING, AND WAVES IN CHROMOSPHERIC JETS

    SciTech Connect

    Nishizuka, N.; Shimizu, T.; Hayashi, Y.; Tanabe, H.; Kuwahata, A.; Kaminou, Y.; Ono, Y.; Inomoto, M.

    2012-09-10

    Hinode observations have revealed intermittent recurrent plasma ejections/jets in the chromosphere. These are interpreted as a result of non-perfectly anti-parallel magnetic reconnection, i.e., component reconnection, between a twisted magnetic flux tube and the pre-existing coronal/chromospheric magnetic field, though the fundamental physics of component reconnection is not revealed. In this paper, we experimentally reproduced the magnetic configuration and investigated the dynamics of plasma ejections, heating, and wave generation triggered by component reconnection in the chromosphere. We set plasma parameters as in the chromosphere (density 10{sup 14} cm{sup -3}, temperature 5-10 eV, i.e., (5-10) Multiplication-Sign 10{sup 4} K, and reconnection magnetic field 200 G) using argon plasma. Our experiment shows bi-directional outflows with the speed of 5 km s{sup -1} at maximum, ion heating in the downstream area over 30 eV, and magnetic fluctuations mainly at 5-10 {mu}s period. We succeeded in qualitatively reproducing chromospheric jets, but quantitatively, we still have some differences between observations and experiments such as in jet velocity, total energy, and wave frequency. Some of them can be explained by the scale gap between solar and laboratory plasma, while the others are probably due to the difference in microscopy and macroscopy, collisionality, and the degree of ionization, which have not been achieved in our experiment.

  7. Final Report for the project “The Electron Diffusion Region in 3D Spontaneous Magnetic Reconnection”

    SciTech Connect

    Egedal-Pedersen, Jan

    2016-01-19

    The DOE award, Grant ER55099, supported in part three graduate students (now Drs. A. Le, O. Ohia and A Vrublenski) and material expenses. The grant enabled these students to operate a basic plasma physics experiment on magnetic reconnection at the MIT Plasma Science and Fusion Center. The experimental investigations utilized the Versatile Toroidal Facility (VTF) in various magnetic geometries. In addition, based in part on the experimental results, new theoretical models were developed for the reconnection process.

  8. Multiscale Modeling Techniques for Plasmas: 1D Scaling Results and Application to Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Shay, M. A.; Dorland, B.; Drake, J. F.; Stantchev, G.

    2005-12-01

    We examine a novel simulation scheme called "equation free projective integration"[1] which has the potential to allow global simulations which still include microscale physics, a necessary ingredient in order to model multiscale problems. Such codes could be used to examine the global effects of reconnection and turbulence in the Earth's magnetosphere, and the solar corona, as well as in laboratory Tokamaks. Using this method to simulate the propagation and steepening of a 1D ion acoustic wave, we have already achieved excellent agreement between full particle codes and equation free with a factor of 20 speed-up. This speedup appears to scale linearly with system size, so large scale 2D and 3D simulations using this method will show a speedup of 100 or more. In this method of simulation, the global plasma variables stepped forward in time are not time-integrated directly using dynamical differential equations, hence the name "equation free." Instead, these variables are represented on a microgrid using a kinetic simulation. This microsimulation is integrated forward long enough to determine the time derivatives of the global plasma variables, which are then used to integrate forward the global variables with much larger timesteps. Results will be presented of the successful application of equation free to 1-D ion acoustic wave steepening with a PIC code serving as the underlying kinetic model. Initial results of this technique applied to magnetic reconnection will also be discussed. 1 I. G. Kevrekidis et. al., Equation-free multiscale computation: Enabling microscopic simulators to perform system-level tasks, arXiv:physics/0209043.

  9. Impact of Magnetic Draping, Convection, and Field Line Tying on Magnetopause Reconnection Under Northward IMF

    NASA Technical Reports Server (NTRS)

    Wendel, Deirdre E.; Reiff, Patricia H.; Goldstein, Melvyn L.

    2010-01-01

    We simulate a northward IMF cusp reconnection event at the magnetopause using the OpenGGCM resistive MHD code. The ACE input data, solar wind parameters, and dipole tilt belong to a 2002 reconnection event observed by IMAGE and Cluster. Based on a fully three-dimensional skeleton separators, nulls, and parallel electric fields, we show magnetic draping, convection, ionospheric field line tying play a role in producing a series of locally reconnecting nulls with flux ropes. The flux ropes in the cusp along the global separator line of symmetry. In 2D projection, the flux ropes the appearance of a tearing mode with a series of 'x's' and 'o's' but bearing a kind of 'guide field' that exists only within the magnetopause. The reconnecting field lines in the string of ropes involve IMF and both open and closed Earth magnetic field lines. The observed magnetic geometry reproduces the findings of a superposed epoch impact parameter study derived from the Cluster magnetometer data for the same event. The observed geometry has repercussions for spacecraft observations of cusp reconnection and for the imposed boundary conditions reconnection simulations.

  10. Study of energy conversion and partitioning in the magnetic reconnection layer of a laboratory plasma

    SciTech Connect

    Yamada, Masaaki; Yoo, Jongsoo; Jara-Almonte, Jonathan; Daughton, William; Ji, Hantao; Kulsrud, Russell M.; Myers, Clayton E.

    2015-05-15

    The most important feature of magnetic reconnection is that it energizes plasma particles by converting magnetic energy to particle energy, the exact mechanisms by which this happens are yet to be determined despite a long history of reconnection research. Recently, we have reported our results on the energy conversion and partitioning in a laboratory reconnection layer in a short communication [Yamada et al., Nat. Commun. 5, 4474 (2014)]. The present paper is a detailed elaboration of this report together with an additional dataset with different boundary sizes. Our experimental study of the reconnection layer is carried out in the two-fluid physics regime where ions and electrons move quite differently. We have observed that the conversion of magnetic energy occurs across a region significantly larger than the narrow electron diffusion region. A saddle shaped electrostatic potential profile exists in the reconnection plane, and ions are accelerated by the resulting electric field at the separatrices. These accelerated ions are then thermalized by re-magnetization in the downstream region. A quantitative inventory of the converted energy is presented in a reconnection layer with a well-defined, variable boundary. We also carried out a systematic study of the effects of boundary conditions on the energy inventory. This study concludes that about 50% of the inflowing magnetic energy is converted to particle energy, 2/3 of which is ultimately transferred to ions and 1/3 to electrons. When assisted by another set of magnetic reconnection experiment data and numerical simulations with different sizes of monitoring box, it is also observed that the observed features of energy conversion and partitioning do not depend on the size of monitoring boundary across the range of sizes tested from 1.5 to 4 ion skin depths.

  11. Study of energy conversion and partitioning in the magnetic reconnection layer of a laboratory plasma

    DOE PAGES

    Yamada, Masaaki; Yoo, Jongsoo; Jara-Almonte, Jonathan; ...

    2015-05-15

    The most important feature of magnetic reconnection is that it energizes plasma particles by converting magnetic energy to particle energy, the exact mechanisms by which this happens are yet to be determined despite a long history of reconnection research. Recently, we have reported our results on the energy conversion and partitioning in a laboratory reconnection layer in a short communication [Yamada et al., Nat. Commun. 5, 4474 (2014)]. The present paper is a detailed elaboration of this report together with an additional dataset with different boundary sizes. Our experimental study of the reconnection layer is carried out in the two-fluidmore » physics regime where ions and electrons move quite differently. We have observed that the conversion of magnetic energy occurs across a region significantly larger than the narrow electron diffusion region. A saddle shaped electrostatic potential profile exists in the reconnection plane, and ions are accelerated by the resulting electric field at the separatrices. These accelerated ions are then thermalized by re-magnetization in the downstream region. A quantitative inventory of the converted energy is presented in a reconnection layer with a well-defined, variable boundary. We also carried out a systematic study of the effects of boundary conditions on the energy inventory. This study concludes that about 50% of the inflowing magnetic energy is converted to particle energy, 2/3 of which is ultimately transferred to ions and 1/3 to electrons. When assisted by another set of magnetic reconnection experiment data and numerical simulations with different sizes of monitoring box, it is also observed that the observed features of energy conversion and partitioning do not depend on the size of monitoring boundary across the range of sizes tested from 1.5 to 4 ion skin depths.« less

  12. Why does Steady-State Magnetic Reconnection have a Maximum Local Rate of Order 0.1?

    NASA Astrophysics Data System (ADS)

    Liu, Yi-Hsin; Hesse, M.; Guo, F.; Daughton, W.; Li, H.; Cassak, P. A.; Shay, M. A.

    2017-02-01

    Simulations suggest collisionless steady-state magnetic reconnection of Harris-type current sheets proceeds with a rate of order 0.1, independent of dissipation mechanism. We argue this long-standing puzzle is a result of constraints at the magnetohydrodynamic (MHD) scale. We predict the reconnection rate as a function of the opening angle made by the upstream magnetic fields, finding a maximum reconnection rate close to 0.2. The predictions compare favorably to particle-in-cell simulations of relativistic electron-positron and nonrelativistic electron-proton reconnection. The fact that simulated reconnection rates are close to the predicted maximum suggests reconnection proceeds near the most efficient state allowed at the MHD scale. The rate near the maximum is relatively insensitive to the opening angle, potentially explaining why reconnection has a similar fast rate in differing models.

  13. Magnetic Field Shear in Kinetic Models Steps Toward Understanding Magnetic Reconnection Drivers

    NASA Astrophysics Data System (ADS)

    Black, Carrie; Antiochos, Spiro; DeVore, Rick; Karpen, Judith

    2015-11-01

    In the standard model for coronal mass ejections (CME) and/or solar flares, the free energy for the eruptive event resides in a strongly sheared magnetic. A pre-eruption force balance consists of an upward force due to the magnetic pressure of the sheared field and a downward tension due to overlying unsheared field. Magnetic reconnection disrupts this force balance; therefore, it is critical for understanding CME/flare initiation, to model the onset of reconnection driven by the build-up of magnetic shear. In MHD simulations, the application of a magnetic-field shear is a trivial matter. However, kinetic effects are dominant in the diffusion region and thus, it is important to examine this process with PIC simulations as well. The implementation of such a driver in PIC methods is challenging, however, and indicates the necessity of a true multiscale model for such processes in the solar environment. The field must be sheared self-consistently and indirectly to prevent the generation of waves that destroy the desired system. Plasma instabilities can arise nonetheless. Here, we show that we can control this instability and generate a predicted out-of-plane magnetic flux. This material is based upon work supported by the National Science Foundation under Award No. AGS-1331356.

  14. How Does Collisionless Magnetic Reconnection Work in the Presence of a Guide Magnetic Field?

    NASA Technical Reports Server (NTRS)

    Hesse, Michael

    2006-01-01

    The dissipation mechanism of guide field magnetic reconnection remains a subject of intense scientific interest. On one hand, one set of recent studies have shown that particle inertia-based processes, which include thermal and bulk inertial effects, provide the reconnection electric field in the diffusion region. On the other hand, a second set of studies emphasizes the role of wave-particle interactions in providing anomalous resistivity in the diffusion region. In this presentation, we present analytical theory results, as well as 2.5 and three-dimensional PIC simulations of guide-field magnetic reconnection. We will show that diffusion region scale sizes in moderate and large guide field cases are determined by electron Larmor radii, and that analytical estimates of diffusion region dimensions need to include description of the heat flux tensor. The dominant electron dissipation process appears to be based on thermal electron inertia, expressed through nongyrotropic electron pressure tensors. We will argue that this process remains viable in three dimensions by means of a detailed comparison of high resolution particle-in-cell simulations.

  15. The role of magnetic reconnection on jet/accretion disk systems

    NASA Astrophysics Data System (ADS)

    de Gouveia Dal Pino, E. M.; Piovezan, P. P.; Kadowaki, L. H. S.

    2010-07-01

    Context. It was proposed earlier that the relativistic ejections observed in microquasars could be produced by violent magnetic reconnection episodes at the inner disk coronal region (de Gouveia Dal Pino & Lazarian 2005). Aims: Here we revisit this model, which employs a standard accretion disk description and fast magnetic reconnection theory, and discuss the role of magnetic reconnection and associated heating and particle acceleration in different jet/disk accretion systems, namely young stellar objects (YSOs), microquasars, and active galactic nuclei (AGNs). Methods: In microquasars and AGNs, violent reconnection episodes between the magnetic field lines of the inner disk region and those that are anchored in the black hole are able to heat the coronal/disk gas and accelerate the plasma to relativistic velocities through a diffusive first-order Fermi-like process within the reconnection site that will produce intermittent relativistic ejections or plasmons. Results: The resulting power-law electron distribution is compatible with the synchrotron radio spectrum observed during the outbursts of these sources. A diagram of the magnetic energy rate released by violent reconnection as a function of the black hole (BH) mass spanning 109 orders of magnitude shows that the magnetic reconnection power is more than sufficient to explain the observed radio luminosities of the outbursts from microquasars to low luminous AGNs. In addition, the magnetic reconnection events cause the heating of the coronal gas, which can be conducted back to the disk to enhance its thermal soft X-ray emission as observed during outbursts in microquasars. The decay of the hard X-ray emission right after a radio flare could also be explained in this model due to the escape of relativistic electrons with the evolving jet outburst. In the case of YSOs a similar magnetic configuration can be reached that could possibly produce observed X-ray flares in some sources and provide the heating at the

  16. 3D and 4D magnetic susceptibility tomography based on complex MR images

    DOEpatents

    Chen, Zikuan; Calhoun, Vince D

    2014-11-11

    Magnetic susceptibility is the physical property for T2*-weighted magnetic resonance imaging (T2*MRI). The invention relates to methods for reconstructing an internal distribution (3D map) of magnetic susceptibility values, .chi. (x,y,z), of an object, from 3D T2*MRI phase images, by using Computed Inverse Magnetic Resonance Imaging (CIMRI) tomography. The CIMRI technique solves the inverse problem of the 3D convolution by executing a 3D Total Variation (TV) regularized iterative convolution scheme, using a split Bregman iteration algorithm. The reconstruction of .chi. (x,y,z) can be designed for low-pass, band-pass, and high-pass features by using a convolution kernel that is modified from the standard dipole kernel. Multiple reconstructions can be implemented in parallel, and averaging the reconstructions can suppress noise. 4D dynamic magnetic susceptibility tomography can be implemented by reconstructing a 3D susceptibility volume from a 3D phase volume by performing 3D CIMRI magnetic susceptibility tomography at each snapshot time.

  17. On the ions acceleration via collisionless magnetic reconnection in laboratory plasmas

    NASA Astrophysics Data System (ADS)

    Cazzola, E.; Curreli, D.; Markidis, S.; Lapenta, G.

    2016-11-01

    This work presents an analysis of the ion outflow from magnetic reconnection throughout fully kinetic simulations with typical laboratory plasma values. A symmetric initial configuration for the density and magnetic field is considered across the current sheet. After analyzing the behavior of a set of nine simulations with a reduced mass ratio and with a permuted value of three initial electron temperatures and magnetic field intensity, the best ion acceleration scenario is further studied with a realistic mass ratio in terms of the ion dynamics and energy budget. Interestingly, a series of shock wave structures are observed in the outflow, resembling the shock discontinuities found in recent magnetohydrodynamic simulations. An analysis of the ion outflow at several distances from the reconnection point is presented, in light of possible laboratory applications. The analysis suggests that magnetic reconnection could be used as a tool for plasma acceleration, with applications ranging from electric propulsion to production of ion thermal beams.

  18. GPU-accelerated denoising of 3D magnetic resonance images

    SciTech Connect

    Howison, Mark; Wes Bethel, E.

    2014-05-29

    The raw computational power of GPU accelerators enables fast denoising of 3D MR images using bilateral filtering, anisotropic diffusion, and non-local means. In practice, applying these filtering operations requires setting multiple parameters. This study was designed to provide better guidance to practitioners for choosing the most appropriate parameters by answering two questions: what parameters yield the best denoising results in practice? And what tuning is necessary to achieve optimal performance on a modern GPU? To answer the first question, we use two different metrics, mean squared error (MSE) and mean structural similarity (MSSIM), to compare denoising quality against a reference image. Surprisingly, the best improvement in structural similarity with the bilateral filter is achieved with a small stencil size that lies within the range of real-time execution on an NVIDIA Tesla M2050 GPU. Moreover, inappropriate choices for parameters, especially scaling parameters, can yield very poor denoising performance. To answer the second question, we perform an autotuning study to empirically determine optimal memory tiling on the GPU. The variation in these results suggests that such tuning is an essential step in achieving real-time performance. These results have important implications for the real-time application of denoising to MR images in clinical settings that require fast turn-around times.

  19. The Effect of Cooling on Particle Trajectories and Acceleration in Relativistic Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Kagan, Daniel; Nakar, Ehud; Piran, Tsvi

    2016-12-01

    The maximum synchrotron burnoff limit of 160 MeV represents a fundamental limit to radiation resulting from electromagnetic particle acceleration in one-zone ideal plasmas. In magnetic reconnection, however, particle acceleration and radiation are decoupled because the electric field is larger than the magnetic field in the diffusion region. We carry out two-dimensional particle-in-cell simulations to determine the extent to which magnetic reconnection can produce synchrotron radiation above the burnoff limit. We use the test particle comparison (TPC) method to isolate the effects of cooling by comparing the trajectories and acceleration efficiencies of test particles incident on such a reconnection region with and without cooling them. We find that the cooled and uncooled particle trajectories are typically similar during acceleration in the reconnection region, and derive an effective limit on particle acceleration that is inversely proportional to the average magnetic field experienced by the particle during acceleration. Using the calculated distribution of this average magnetic field as a function of uncooled final particle energy, we find analytically that cooling does not affect power-law particle energy spectra except at energies far above the synchrotron burnoff limit. Finally, we compare fully cooled and uncooled simulations of reconnection, confirming that the synchrotron burnoff limit does not produce a cutoff in the particle energy spectrum. Our results indicate that the TPC method accurately predicts the effects of cooling on particle acceleration in relativistic reconnection, and that, even far above the burnoff limit, the synchrotron energy of radiation produced in reconnection is not limited by cooling.

  20. Chaos-induced resistivity of collisionless magnetic reconnection in the presence of a guide field

    NASA Astrophysics Data System (ADS)

    Shang, Meng; Wu, De-Jin; Chen, Ling; Chen, Peng-Fei

    2017-01-01

    One of the most puzzling problems in astrophysics is to understand the anomalous resistivity in collisionless magnetic reconnection that is believed extensively to be responsible for the energy release in various eruptive phenomena. The magnetic null point in the reconnecting current sheet, acting as a scattering center, can lead to chaotic motions of particles in the current sheet, which is one of the possible mechanisms for anomalous resistivity and is called chaos-induced resistivity. In many interesting cases, however, instead of the magnetic null point, there is a nonzero magnetic field perpendicular to the merging field lines, usually called the guide field, whose effect on chaos-induced resistivity has been an open problem. By use of the test particle simulation method and statistical analysis, we investigate chaos-induced resistivity in the presence of a constant guide field. The characteristics of particle motion in the reconnecting region, in particular, the chaotic behavior of particle orbits and evolving statistical features, are analyzed. The results show that as the guide field increases, the radius of the chaos region increases and the Lyapunov index decreases. However, the effective collision frequency, and hence the chaos-induced resistivity, reach their peak values when the guide field approaches half of the characteristic strength of the reconnection magnetic field. The presence of a guide field can significantly influence the chaos of the particle orbits and hence the chaos-induced resistivity in the reconnection sheet, which decides the collisionless reconnection rate. The present result is helpful for us to understand the microphysics of anomalous resistivity in collisionless reconnection with a guide field.

  1. MAGNETIZATION OF CLOUD CORES AND ENVELOPES AND OTHER OBSERVATIONAL CONSEQUENCES OF RECONNECTION DIFFUSION

    SciTech Connect

    Lazarian, A.; Esquivel, A.; Crutcher, R.

    2012-10-01

    Recent observational results for magnetic fields in molecular clouds reviewed by Crutcher seem to be inconsistent with the predictions of the ambipolar diffusion theory of star formation. These include the measured decrease in mass to flux ratio between envelopes and cores, the failure to detect any self-gravitating magnetically subcritical clouds, the determination of the flat probability distribution function (PDF) of the total magnetic field strengths implying that there are many clouds with very weak magnetic fields, and the observed scaling B{proportional_to}{rho}{sup 2/3} that implies gravitational contraction with weak magnetic fields. We consider the problem of magnetic field evolution in turbulent molecular clouds and discuss the process of magnetic field diffusion mediated by magnetic reconnection. For this process that we termed 'reconnection diffusion', we provide a simple physical model and explain that this process is inevitable in view of the present-day understanding of MHD turbulence. We address the issue of the expected magnetization of cores and envelopes in the process of star formation and show that reconnection diffusion provides an efficient removal of magnetic flux that depends only on the properties of MHD turbulence in the core and the envelope. We show that as the amplitude of turbulence as well as the scale of turbulent motions decrease from the envelope to the core of the cloud, the diffusion of the magnetic field is faster in the envelope. As a result, the magnetic flux trapped during the collapse in the envelope is being released faster than the flux trapped in the core, resulting in much weaker fields in envelopes than in cores, as observed. We provide simple semi-analytical model calculations which support this conclusion and qualitatively agree with the observational results. Magnetic reconnection is also consistent with the lack of subcritical self-gravitating clouds, with the observed flat PDF of field strengths, and with the

  2. Signatures of complex magnetic topologies from multiple reconnection sites induced by Kelvin-Helmholtz instability

    NASA Astrophysics Data System (ADS)

    Vernisse, Y.; Lavraud, B.; Eriksson, S.; Gershman, D. J.; Dorelli, J.; Pollock, C.; Giles, B.; Aunai, N.; Avanov, L.; Burch, J.; Chandler, M.; Coffey, V.; Dargent, J.; Ergun, R. E.; Farrugia, C. J.; Génot, V.; Graham, D. B.; Hasegawa, H.; Jacquey, C.; Kacem, I.; Khotyaintsev, Y.; Li, W.; Magnes, W.; Marchaudon, A.; Moore, T.; Paterson, W.; Penou, E.; Phan, T. D.; Retino, A.; Russell, C. T.; Saito, Y.; Sauvaud, J.-A.; Torbert, R.; Wilder, F. D.; Yokota, S.

    2016-10-01

    The Magnetospheric Multiscale mission has demonstrated the frequent presence of reconnection exhausts at thin current sheets within Kelvin-Helmholtz (KH) waves at the flank magnetopause. Motivated by these recent observations, we performed a statistical analysis of the boundary layers on the magnetosheath side of all KH current sheets on 8 September 2015. We show 86% consistency between the exhaust flows and particle leakage in the magnetosheath boundary layers but further highlight the very frequent presence of additional boundary layer signatures that do not come from the locally observed reconnection exhausts. These additional electron and ion boundary layers, of various durations and at various positions with respect to the leading and trailing boundaries of the KH waves, signal connections to reconnection sites at other locations. Based on the directionality and extent of these layers, we provide an interpretation whereby complex magnetic topologies can arise within KH waves from the combination of reconnection in the equatorial plane and at midlatitudes in the Southern and Northern Hemispheres, where additional reconnection sites are expected to be triggered by the three-dimensional field lines interweaving induced by the KH waves at the flanks (owing to differential flow and magnetic field shear with latitude). The present event demonstrates that the three-dimensional development of KH waves can induce plasma entry (through reconnection at both midlatitude and equatorial regions) already sunward of the terminator where the instability remains in its linear stage.

  3. Secondary island formation in collisional and collisionless kinetic simulations of magnetic reconnection

    SciTech Connect

    Dayton, William S; Roytershteyn, Vadim; Gary, Peter; Yin, L; Albright, B J; Bowers, K J; Karimabadi, H

    2009-01-01

    The evolution of magnetic reconnection in large-scale systems often gives rise to extended current layers that are unstable to the formation of secondary magnetic islands. The role of these islands in the reconnection process and the conditions under which they form remains a subject of debate. In this work, we benchmark two different kinetic particle-in-cell codes to address the formation of secondary islands for several types of global boundary conditions. The influence on reconnection is examined for a range of conditions and collisionality limits. Although secondary islands are observed in all cases, their influence on reconnection may be different depending on the regime. In the collisional limit, the secondary islands playa key role in breaking away from the Sweet-Parker scaling and enabling faster reconnection. In the collisionless limit, their formation is one mechanism for controlling the length of the diffusion region. In both limits, the onset of secondary islands leads to a time dependent behavior in the reconnection rate. In all cases considered, the number of secondary islands increases for larger systems.

  4. Plasma and Energetic Particle Behaviors During Asymmetric Magnetic Reconnection at the Magnetopause

    NASA Technical Reports Server (NTRS)

    Lee, S. H.; Zhang, H.; Zong, Q.-G.; Otto, A.; Sibeck, D. G.; Wang, Y.; Glassmeier, K.-H.; Daly, P.W.; Reme, H.

    2014-01-01

    The factors controlling asymmetric reconnection and the role of the cold plasma population in the reconnection process are two outstanding questions. We present a case study of multipoint Cluster observations demonstrating that the separatrix and flow boundary angles are greater on the magnetosheath than on the magnetospheric side of the magnetopause, probably due to the stronger density than magnetic field asymmetry at this boundary. The motion of cold plasmaspheric ions entering the reconnection region differs from that of warmer magnetosheath and magnetospheric ions. In contrast to the warmer ions, which are probably accelerated by reconnection in the diffusion region near the subsolar magnetopause, the colder ions are simply entrained by ??×?? drifts at high latitudes on the recently reconnected magnetic field lines. This indicates that plasmaspheric ions can sometimes play only a very limited role in asymmetric reconnection, in contrast to previous simulation studies. Three cold ion populations (probably H+, He+, and O+) appear in the energy spectrum, consistent with ion acceleration to a common velocity.

  5. Fast magnetic reconnection in low-density electron-positron plasmas

    SciTech Connect

    Bessho, Naoki; Bhattacharjee, A.

    2010-10-15

    Two-dimensional particle-in-cell simulations have been performed to study magnetic reconnection in low-density electron-positron plasmas without a guide magnetic field. Impulsive reconnection rates become of the order of unity when the background density is much smaller than 10% of the density in the initial current layer. It is demonstrated that the outflow speed is less than the upstream Alfven speed, and that the time derivative of the density must be taken into account in the definition of the reconnection rate. The reconnection electric fields in the low-density regime become much larger than the ones in the high-density regime, and it is possible to accelerate the particles to high energies more efficiently. The inertial term in the generalized Ohm's law is the most dominant term that supports a large reconnection electric field. An effective collisionless resistivity is produced and tracks the extension of the diffusion region in the late stage of the reconnection dynamics, and significant broadening of the diffusion region is observed. Because of the broadening of the diffusion region, no secondary islands, which have been considered to play a role to limit the diffusion region, are generated during the extension of the diffusion region in the outflow direction.

  6. Evidence of "Tether-Cutting" Reconnection in the Onset of a Quadrupolar Solar Magnetic Eruption

    NASA Technical Reports Server (NTRS)

    Choudhary, Debi Prasad; Sterling, Alphonse C.; Moore, Ronald L.; Yurchyshyn, Vasyl

    2004-01-01

    Extensive study of the near-limb solar filament eruption event on 2000 February 26, involving coronal images from YOHKOH, SOHO EIT and photospheric magnetogram from MID have shown that that both "runaway-tether-cutting-type reconnection" and "fast breakout-type reconnection" may have occurred early in the fast phase of the eruption and may have played an important role in unleashing the explosion (Sterling & Moore 2004). That study did not identify which or if either of these types of reconnection actually triggered the fast phase. Here, together with a magnetogram and He1 10830 A filtergram from NSO/KP, we present Halpha filtergrams from Big Bear Solar Observatory, that show evidence of "tether-cutting-type reconnection" before and during the eruption of the southern filament, situated at one of the neutral lines of the quadrupole magnetic structure.

  7. Three Dimensional Dynamics of Collisionless Magnetic Reconnection in Large-Scale Pair Plasmas

    NASA Astrophysics Data System (ADS)

    Yin, L.; Daughton, W.; Karimabadi, H.; Albright, B. J.; Bowers, K. J.; Margulies, J.

    2008-12-01

    Using the largest three dimensional particle-in-cell simulations to date, collisionless magnetic reconnection in large-scale electron-positron plasmas without a guide field is shown to involve complex interaction of tearing and kink modes. The reconnection onset is patchy and occurs at multiple sites which self-organize to form a single, large diffusion region. There is a basic tendency for the diffusion region to further elongate in the outflow direction and become unstable to secondary kinking and formation of "plasmoid-rope" structures with finite extent in the current direction. The secondary kink leads to folding of the reconnection current layer, while plasmoid ropes at times follow the folding of the current layer. The interplay among these secondary instabilities plays a key role in controlling the time dependent reconnection rate in large-scale systems.

  8. Magnetic reconnection and stochastic plasmoid chains in high-Lundquist-number plasmas

    NASA Astrophysics Data System (ADS)

    Loureiro, N. F.; Samtaney, R.; Schekochihin, A. A.; Uzdensky, D. A.

    2012-04-01

    A numerical study of magnetic reconnection in the large-Lundquist-number (S), plasmoid-dominated regime is carried out for S up to 107. The theoretical model of Uzdensky et al. [Phys. Rev. Lett. 105, 235002 (2010)] is confirmed and partially amended. The normalized reconnection rate is E~eff~0.02 independently of S for S>>104. The plasmoid flux (Ψ) and half-width (wx) distribution functions scale as f(Ψ)~Ψ-2 and f(wx)~wx-2. The joint distribution of Ψ and wx shows that plasmoids populate a triangular region wx>~Ψ/B0, where B0 is the reconnecting field. It is argued that this feature is due to plasmoid coalescence. Macroscopic ``monster'' plasmoids with wx~10% of the system size are shown to emerge in just a few Alfvén times, independently of S, suggesting that large disruptive events are an inevitable feature of large-S reconnection.

  9. Direct-write 3D printing of NdFeB bonded magnets

    DOE PAGES

    Compton, Brett Gibson; Kemp, James William; Novikov, Timofei V.; ...

    2016-08-17

    We report a method to fabricate Nd-Fe-B bonded magnets of complex shape via extrusion-based additive manufacturing (AM), also known as 3D-printing. We have successfully formulated a 3D-printable epoxy-based ink for direct-write AM with anisotropic MQA NdFeB magnet particles that can be deposited at room temperature. The new feedstocks contain up to 40 vol.% MQA anisotropic Nd-Fe-B magnet particles, and they are shown to remain uniformly dispersed in the thermoset matrix throughout the deposition process. Ring, bar, and horseshoe-type 3D magnet structures were printed and cured in air at 100°C without degrading the magnetic properties. Lastly, this study provides a newmore » pathway for fabricating Nd-Fe-B bonded magnets with complex geometry at low temperature, and presents new opportunities for fabricating multifunctional hybrid structures and devices.« less

  10. Direct-write 3D printing of NdFeB bonded magnets

    SciTech Connect

    Compton, Brett Gibson; Kemp, James William; Novikov, Timofei V.; Pack, Robert Cody; Nlebedim, Cajetan I.; Duty, Chad Edward; Rios, Orlando; Paranthaman, M. Parans

    2016-08-17

    We report a method to fabricate Nd-Fe-B bonded magnets of complex shape via extrusion-based additive manufacturing (AM), also known as 3D-printing. We have successfully formulated a 3D-printable epoxy-based ink for direct-write AM with anisotropic MQA NdFeB magnet particles that can be deposited at room temperature. The new feedstocks contain up to 40 vol.% MQA anisotropic Nd-Fe-B magnet particles, and they are shown to remain uniformly dispersed in the thermoset matrix throughout the deposition process. Ring, bar, and horseshoe-type 3D magnet structures were printed and cured in air at 100°C without degrading the magnetic properties. Lastly, this study provides a new pathway for fabricating Nd-Fe-B bonded magnets with complex geometry at low temperature, and presents new opportunities for fabricating multifunctional hybrid structures and devices.

  11. Statistical Flux Tube Properties of 3D Magnetic Carpet Fields

    NASA Astrophysics Data System (ADS)

    Close, R. M.; Parnell, C. E.; Mackay, D. H.; Priest, E. R.

    2003-02-01

    The quiet-Sun photosphere consists of numerous magnetic flux fragments of both polarities that evolve with granular and supergranular flow fields. These concentrations give rise to a web of intermingled magnetic flux tubes which characterise the coronal magnetic field. Here, the nature of these flux tubes is studied. The photosphere is taken to be the source plane and each photospheric fragment is represented by a series of point sources. By analysing the potential field produced by these sources, it is found that the distribution of flux tube lengths obtained by (i) integrating forward from positive sources and (ii) tracing back from negative sources is highly dependent on the total flux imbalance within the region of interest. It is established that the relation between the footpoint separation of a flux tube and its height cannot be assumed to be linear. Where there is a significant imbalance of flux within a region, it is found that fragments of the dominant polarity will have noticeably more connections, on average, than the minority polarity fragments. Despite this difference, the flux from a single fragment of either polarity is typically divided such that (i) 60-70% connects to one opposite-polarity fragment, (ii) 25-30% goes to a further 1 to 2 opposite-polarity fragments, and (iii) any remaining flux may connect to as many as another 50 or more other opposite-polarity fragments. This is true regardless of any flux imbalance within the region. It is found that fragments connect preferentially to their nearest neighbours, with, on average, around 60-70% of flux closing down within 10 Mm of a typical fragment. Only 50% of the flux in a quiet region extends higher than 2.5 Mm above the solar surface and 5-10% extends higher than 25 Mm. The fragments that contribute to the field above this height cover a range of sizes, with even the smallest of fragments contributing to the field at heights of over 50 Mm.

  12. Imaging solar coronal magnetic structures in 3D

    NASA Astrophysics Data System (ADS)

    Cartledge, N. P.

    The study of solar coronal structures and, in particular prominences, is a key part of understanding the highly complex physical mechanisms occurring in the Sun's atmosphere. Solar prominences are important in their own right and some of the most puzzling questions in solar theory have arisen through their study. For example, how do they form and how is their mass continuously replenished? How can the magnetic field provide their continuous support against gravity over time periods of several months? How can such cool, dense material exist in thermal equilibrium in the surrounding coronal environment? Why do they erupt? A study of their structure and that of the surrounding medium is important in determining the nature of the coronal plasma and magnetic field. Also, prominences are closely associated with other key phenomena such as coronal mass ejections and eruptive solar flares which occur as a prominence loses equilibrium and rises from the solar surface. Our current understanding of these fascinating structures is extremely limited and we know very little about their basic global structure. In fact, recent prominence observations have caused our basic paradigms to be challenged (Priest, 1996) and so we must set up new models in order to gain even a fundamental understanding. Prominences are highly nonlinear, three-dimensional structures. Large feet (or barbs) reach out from the main body of a prominence and reach down to the photosphere where the dense material continuously drains away. These provide a real clue to the three-dimensional nature of the coronal field and its relation to the photospheric field. It is important, therefore, to make stereographic observations of prominences in order to gain a basic understanding of their essentially three-dimensional nature and attempt to formulate new paradigms for their structure and evolution. There is no doubt that the study of prominences in three dimensions is a crucial exercise if we are to develop a better

  13. Online reconstruction of 3D magnetic particle imaging data

    NASA Astrophysics Data System (ADS)

    Knopp, T.; Hofmann, M.

    2016-06-01

    Magnetic particle imaging is a quantitative functional imaging technique that allows imaging of the spatial distribution of super-paramagnetic iron oxide particles at high temporal resolution. The raw data acquisition can be performed at frame rates of more than 40 volumes s-1. However, to date image reconstruction is performed in an offline step and thus no direct feedback is available during the experiment. Considering potential interventional applications such direct feedback would be mandatory. In this work, an online reconstruction framework is implemented that allows direct visualization of the particle distribution on the screen of the acquisition computer with a latency of about 2 s. The reconstruction process is adaptive and performs block-averaging in order to optimize the signal quality for a given amount of reconstruction time.

  14. Nonthermally dominated electron acceleration during magnetic reconnection in a low-β plasma

    DOE PAGES

    Li, Xiaocan; Guo, Fan; Li, Hui; ...

    2015-09-24

    By means of fully kinetic simulations, we investigate electron acceleration during magnetic reconnection in a nonrelativistic proton–electron plasma with conditions similar to solar corona and flares. We demonstrate that reconnection leads to a nonthermally dominated electron acceleration with a power-law energy distribution in the nonrelativistic low-β regime but not in the high-β regime, where β is the ratio of the plasma thermal pressure and the magnetic pressure. The accelerated electrons contain most of the dissipated magnetic energy in the low-β regime. A guiding-center current description is used to reveal the role of electron drift motions during the bulk nonthermal energization.more » We find that the main acceleration mechanism is a Fermi-type acceleration accomplished by the particle curvature drift motion along the electric field induced by the reconnection outflows. Although the acceleration mechanism is similar for different plasma β, low-β reconnection drives fast acceleration on Alfvénic timescales and develops power laws out of thermal distribution. Thus, the nonthermally dominated acceleration resulting from magnetic reconnection in low-β plasma may have strong implications for the highly efficient electron acceleration in solar flares and other astrophysical systems.« less

  15. Nonthermally dominated electron acceleration during magnetic reconnection in a low-β plasma

    SciTech Connect

    Li, Xiaocan; Guo, Fan; Li, Hui; Li, Gang

    2015-09-24

    By means of fully kinetic simulations, we investigate electron acceleration during magnetic reconnection in a nonrelativistic proton–electron plasma with conditions similar to solar corona and flares. We demonstrate that reconnection leads to a nonthermally dominated electron acceleration with a power-law energy distribution in the nonrelativistic low-β regime but not in the high-β regime, where β is the ratio of the plasma thermal pressure and the magnetic pressure. The accelerated electrons contain most of the dissipated magnetic energy in the low-β regime. A guiding-center current description is used to reveal the role of electron drift motions during the bulk nonthermal energization. We find that the main acceleration mechanism is a Fermi-type acceleration accomplished by the particle curvature drift motion along the electric field induced by the reconnection outflows. Although the acceleration mechanism is similar for different plasma β, low-β reconnection drives fast acceleration on Alfvénic timescales and develops power laws out of thermal distribution. Thus, the nonthermally dominated acceleration resulting from magnetic reconnection in low-β plasma may have strong implications for the highly efficient electron acceleration in solar flares and other astrophysical systems.

  16. Global impact of collisionless magnetic reconnection on the structure of planetary magnetospheres

    NASA Astrophysics Data System (ADS)

    Dorelli, J.; Glocer, A.; Collinson, G.; Toth, G.

    2014-12-01

    While the local physics of collisionless magnetic reconnection has been well studied, the consequences for global magnetospheric structure remain largely unexplored. It is well known, for example, that Hall electric fields generate a new system of field-aligned currents propagating from the reconnection site along the magnetic separatrices; but it is not known how these currents contribute to the global region 1 and region 2 current systems or to auroral substorm features. In this presentation, we show that collisionless reconnection has a significant impact on the large scale structure of planetary magnetospheres. Using global Hall MHD simulations, we demonstrate that field-aligned currents generated at the reconnection sites (and carried by whistler or kinetic Alfven waves) extend all the way down to the surface of the magnetized body and must therefore be included in the magnetosphere-ionosphere coupling physics (e.g., Harang-like discontinuities in the ionospheric convection pattern -- absent in MHD -- are introduced, and the current densities are large enough to produce auroral emission). More surprisingly, ions and electrons pick up magnetic drifts (due to JxB forces in the ion diffusion regions) that significantly alter the global magnetospheric convection pattern. Ions in the plasma sheet drift duskward while electrons drift dawnward, producing large asymmetries in the plasma sheet structure even in the absense of solar wind asymmetry, asymmetric ionospheric conductance or co-rotation. We discuss the implications of these effects for the reconnection-driven magnetospheres of Ganymede, Mercury and Earth.

  17. NONTHERMALLY DOMINATED ELECTRON ACCELERATION DURING MAGNETIC RECONNECTION IN A LOW-β PLASMA

    SciTech Connect

    Li, Xiaocan; Li, Gang; Guo, Fan; Li, Hui

    2015-10-01

    By means of fully kinetic simulations, we investigate electron acceleration during magnetic reconnection in a nonrelativistic proton–electron plasma with conditions similar to solar corona and flares. We demonstrate that reconnection leads to a nonthermally dominated electron acceleration with a power-law energy distribution in the nonrelativistic low-β regime but not in the high-β regime, where β is the ratio of the plasma thermal pressure and the magnetic pressure. The accelerated electrons contain most of the dissipated magnetic energy in the low-β regime. A guiding-center current description is used to reveal the role of electron drift motions during the bulk nonthermal energization. We find that the main acceleration mechanism is a Fermi-type acceleration accomplished by the particle curvature drift motion along the electric field induced by the reconnection outflows. Although the acceleration mechanism is similar for different plasma β, low-β reconnection drives fast acceleration on Alfvénic timescales and develops power laws out of thermal distribution. The nonthermally dominated acceleration resulting from magnetic reconnection in low-β plasma may have strong implications for the  highly efficient electron acceleration in solar flares and other astrophysical systems.

  18. Acceleration of charged particles in magnetic reconnection Solar flares, the magnetosphere, and solar wind

    NASA Technical Reports Server (NTRS)

    Goldstein, M. L.; Matthaeus, W. H.; Ambrosiano, J. J.

    1986-01-01

    A possible source of free energy available for accelerating charged particles is conversion of magnetic energy to particle energy in reconnecting magnetic fields. Recent simulations using test particles suggests that reconnection may efficiently accelerate particles to the maximum energies that are observed in several astrophysical contexts. A simple analytic formula is used in conjunction with the simulation results to predict the maximum energy achievable in a particular plasma environment with the result that in solar flares reconnection is capable of accelerating particles to several GeV. In magnetospheric substorms the predicted maximum can reach several hundred keV, and near magnetic sector crossings in the solar wind the maximum energy can approach 100 keV.

  19. Laboratory Study Of Magnetic Reconnection With A Density Asymmetry Across The Current Sheet

    SciTech Connect

    Yoo, Joseph; Yamada, Massaaki; Ji, Hantao; Meyers,, Clayton E.; Jara-Almonte,; Chen, Li-Jen

    2014-04-18

    The effects of an upstream density asymmetry on magnetic reconnection are studied systematically in a laboratory plasma. Despite a significant upstream density asymmetry of up to 10, the reconnecting magnetic field pro file is not signifi cantly changed. On the other hand, the out-of-plane magnetic field profile is considerably modified; it is almost bipolar in structure with the density asymmetry, as compared to the quadrupolar structure in the symmetric configura