A new fast reconnection model in a collisionless regime
Tsiklauri, David
2008-11-15
Based on the first principles [i.e., (i) by balancing the magnetic field advection with the term containing electron pressure tensor nongyrotropic components in the generalized Ohm's law; (ii) using the conservation of mass; and (iii) assuming that the weak magnetic field region width, where electron meandering motion supports electron pressure tensor off-diagonal (nongyrotropic) components, is of the order of electron Larmor radius] a simple model of magnetic reconnection in a collisionless regime is formulated. The model is general, resembling its collisional Sweet-Parker analog in that it is not specific to any initial configuration, e.g., Harris-type tearing unstable current sheet, X-point collapse or otherwise. In addition to its importance from the fundamental point of view, the collisionless reconnection model offers a much faster reconnection rate [M{sub c{sup '}}{sub less}=(c/{omega}{sub pe}){sup 2}/(r{sub L,e}L)] than Sweet-Parker's classical one (M{sub sp}=S{sup -1/2}). The width of the diffusion region (current sheet) in the collisionless regime is found to be {delta}{sub c{sup '}}{sub less}=(c/{omega}{sub pe}){sup 2}/r{sub L,e}, which is independent of the global reconnection scale L and is only prescribed by microphysics (electron inertial length, c/{omega}{sub pe}, and electron Larmor radius, r{sub L,e}). Amongst other issues, the fastness of the reconnection rate alleviates, e.g., the problem of interpretation of solar flares by means of reconnection, as for the typical solar coronal parameters the obtained collisionless reconnection time can be a few minutes, as opposed to Sweet-Parker's equivalent value of less than a day. The new theoretical reconnection rate is compared to the Magnetic Reconnection Experiment device experimental data by Yamada et al. [Phys. Plasmas 13, 052119 (2006)] and Ji et al. [Geophys. Res. Lett. 35, 13106 (2008)], and a good agreement is obtained.
Reversible collisionless magnetic reconnection
Ishizawa, A.; Watanabe, T.-H.
2013-10-15
Reversible magnetic reconnection is demonstrated for the first time by means of gyrokinetic numerical simulations of a collisionless magnetized plasma. Growth of a current-driven instability in a sheared magnetic field is accompanied by magnetic reconnection due to electron inertia effects. Following the instability growth, the collisionless reconnection is accelerated with development of a cross-shaped structure of current density, and then all field lines are reconnected. The fully reconnected state is followed by the secondary reconnection resulting in a weakly turbulent state. A time-reversed simulation starting from the turbulent state manifests that the collisionless reconnection process proceeds inversely leading to the initial state. During the reversed reconnection, the kinetic energy is reconverted into the original magnetic field energy. In order to understand the stability of reversed process, an external perturbation is added to the fully reconnected state, and it is found that the accelerated reconnection is reversible when the deviation of the E × B streamlines due to the perturbation is comparable with or smaller than a current layer width.
Fast collisionless reconnection and electron heating in strongly magnetized plasmas.
Loureiro, N F; Schekochihin, A A; Zocco, A
2013-07-12
Magnetic reconnection in strongly magnetized (low-beta), weakly collisional plasmas is investigated by using a novel fluid-kinetic model [Zocco and Schekochihin, Phys. Plasmas 18, 102309 (2011)] which retains nonisothermal electron kinetics. It is shown that electron heating via Landau damping (linear phase mixing) is the dominant dissipation mechanism. In time, electron heating occurs after the peak of the reconnection rate; in space, it is concentrated along the separatrices of the magnetic island. For sufficiently large systems, the peak reconnection rate is cE(∥)(max) ≈ 0.2v(A)B(y,0), where v(A) is the Alfvén speed based on the reconnecting field B(y,0). The island saturation width is the same as in magnetohydrodynamics models except for small systems, when it becomes comparable to the kinetic scales. PMID:23889411
Linear theory for fast collisionless magnetic reconnection in the lower-hybrid frequency range
NASA Astrophysics Data System (ADS)
Jovanović, D.; Shukla, P. K.
2005-05-01
A linear theory is presented for the interplay between the fast collisionless magnetic reconnection and the lower-hybrid waves that has been observed in recent computer simulations [J. F. Drake, M. Swisdak, C. Cattell et al., Science 299, 873 (2003)]. In plasma configurations with a strong guide field and anisotropic electron temperature, the electron dynamics is described within the framework of standard electron magnetohydrodynamic equations, accounting also for the effects of the electron polarization and ion motions in the presence of perpendicular electric fields. In the linear phase, we find two types of instabilities of a thin current sheet with steep edges, corresponding to its filamentation (or tearing) and bending. Using a surface-wave formalism for the perturbations whose wavelength is larger than the thickness of the current sheet, the corresponding growth rates are calculated as the contributions of singularities in the plasma dispersion function. These are governed by the electron inertia and the linear coupling of the reconnecting magnetic field with local plasma modes propagating in the perpendicular direction that are subject to the Buneman instability. The linear surface wave instability may be particularly important as a secondary instability, dissipating the thin current sheets that develop in the course of the fast reconnection in the shear-Alfvén and kinetic-Alfvén regimes, and providing the anomalous resistivity for the growth of magnetic islands beyond the shear-Alfvén and kinetic-Alfvén scales.
Collisionless reconnection in Jupiter's magnetotail
NASA Astrophysics Data System (ADS)
Zimbardo, G.
1991-04-01
Collisionless reconnection in Jupiter's magnetotail is quantitatively studied for the first time. It is proposed that the same tearing mechanism which works in the earth magnetotail also works in Jupiter's. It is shown that collisionless reconnection may occur around 60 R(J) downtail.
Nonlinear Collisionless Magnetic Reconnection
Grasso, D.; Tassi, E.; Borgogno, D.; Pegoraro, F.
2008-10-15
We review some recent results that have been obtained in the investigation of collisionless reconnection in two and three dimensional magnetic configurations with a strong guide field in regimes of interest for laboratory plasmas. First, we adopt a two-field plasma model where two distinct regimes, laminar and turbulent, can be identified. Then, we show that these regimes may combine when we consider a more general four-field model, where perturbation of the magnetic and velocity fields are allowed also along the ignorable coordinate.
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.
Recent advances in collisionless magnetic reconnection
NASA Astrophysics Data System (ADS)
Porcelli, F.; Borgogno, D.; Califano, F.; Grasso, D.; Ottaviani, M.; Pegoraro, F.
2002-12-01
One of the recurring problems in magnetic reconnection is the identification of the appropriate generalized Ohm's law. In weakly collisional plasmas with a strong magnetic guide field component, a fluid model may be adopted, where electron inertia and the electron pressure gradient play important roles. In the absence of collisions, electron inertia provides the mechanism for magnetic field-line breaking. Electron compressibility alters significantly the structure of the reconnection region and allows for faster reconnection rates, which are consistent with the fast relaxation times of sawtooth oscillations in tokamak plasmas. The Hall term may also become important when the guide field is weak. The very possibility of nonlinear, irreversible magnetic reconnection in the absence of dissipation is addressed. We show that in a collisionless plasma, magnetic islands can grow and reach a saturated state in a coarse-grained sense. Magnetic energy is transferred to kinetic energy in smaller and smaller spatial scale lengths through a phase mixing process. The same model is then applied to the interpretation of driven reconnection events in the vicinity of a magnetic X-line observed in the VTF experiment at MIT. The reconnection is driven by externally induced plasma flows in a background magnetic configuration that has a hyperbolic null in the reconnection plane and a magnetic guide field component perpendicular to that plane. In the limit where the guide field is strong, assuming the external drive to be sufficiently weak for a linear approximation to hold, a dynamic evolution of the system is obtained which does not reach a stationary state. The reconnection process develops in two phases: an initial phase, whose characteristic rate is a fraction of the Alfvén frequency, and a later one, whose rate is determined by the electron collision frequency.
Collisionless Reconnection and Electron Demagnetization
NASA Astrophysics Data System (ADS)
Scudder, J. D.
Observable, dimensionless properties of the electron diffusion region of collisionless magnetic reconnection are motivated and benchmarked in two and three dimensional Particle In Cell (PIC) simulations as appropriate for measurements with present state of the art spacecraft. The dimensionless quantities of this paper invariably trace their origin to breaking the magnetization of the thermal electrons. Several observable proxies are also motivated for the rate of frozen flux violation and a parameter \\varLambda _{\\varPhi } that when greater than unity is associated with close proximity to the analogue of the saddle point region of 2D reconnection usually called the electron diffusion region. Analogous regions to the electron diffusion region of 2D reconnection with \\varLambda _{\\varPhi } > 1 have been identified in 3D simulations. 10-20 disjoint diffusion regions are identified and the geometrical patterns of their locations illustrated. First examples of associations between local observables based on electron demagnetization and global diagnostics (like squashing) are also presented. A by product of these studies is the development of a single spacecraft determinations of gradient scales in the plasma.
Collisionless Reconnection in an Electron-Positron Plasma
Bessho, N.; Bhattacharjee, A.
2005-12-09
Electromagnetic particle-in-cell simulations of fast collisionless reconnection in a two-dimensional electron-positron plasma (without an equilibrium guide field) are presented. A generalized Ohm's law in which the Hall current cancels out exactly is given. It is suggested that the key to fast reconnection in this plasma is the localization caused by the off-diagonal components of the pressure tensors, which produce an effect analogous to a spatially localized resistivity.
Collisionless reconnection in an electron-positron plasma.
Bessho, N; Bhattacharjee, A
2005-12-01
Electromagnetic particle-in-cell simulations of fast collisionless reconnection in a two-dimensional electron-positron plasma (without an equilibrium guide field) are presented. A generalized Ohm's law in which the Hall current cancels out exactly is given. It is suggested that the key to fast reconnection in this plasma is the localization caused by the off-diagonal components of the pressure tensors, which produce an effect analogous to a spatially localized resistivity. PMID:16384388
Magnetic reconnection in collisionless plasmas - Prescribed fields
NASA Technical Reports Server (NTRS)
Burkhart, G. R.; Drake, J. F.; Chen, J.
1990-01-01
The structure of the dissipation region during magnetic reconnection in collisionless plasma is investigated by examining a prescribed two-dimensional magnetic x line configuration with an imposed inductive electric field E(y). The calculations represent an extension of recent MHD simulations of steady state reconnection (Biskamp, 1986; Lee and Fu, 1986) to the collisionless kinetic regime. It is shown that the structure of the x line reconnection configuration depends on only two parameters: a normalized inductive field and a parameter R which represents the opening angle of the magnetic x lines.
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.
New expression for collisionless magnetic reconnection rate
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.
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
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
Effects of electron inertia in collisionless magnetic reconnection
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.
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.
Accessing the new collisionless reconnection regime in laboratory experiment
NASA Astrophysics Data System (ADS)
Olson, Joseph; Egedal, Jan; Greess, Samuel; Wallace, John; Clark, Michael; Forest, Cary
2015-11-01
The Terrestrial Reconnection Experiment (TREX), the largest dedicated reconnection experiment to date, is currently in operation at the Wisconsin Plasma Astrophysics Laboratory (WiPAL). In its inaugural run, TREX demonstrated its ability to operate in what has traditionally been called the collisionless reconnection regime by observing the out-of-plane magnetic field characteristic of Hall reconnection. Additionally, TREX is projected to access even more collisionless parameters in which electron pressure anisotropy develops, greatly influencing the dynamics of the reconnection process beyond two fluid effects. For example, spacecraft observations and kinetic simulations show that large-scale current layers are driven by this pressure anisotropy. In the last year, TREX has undergone upgrades to its plasma heating, reconnection drive, and diagnostic suite in order to study these features exclusive to truly collisionless reconnection. Preliminary results from the newly optimized experimental runs will be presented. Supported in part by DoE grant DE-SC0010463.
Nonlinear gyrofluid simulations of collisionless reconnection
Grasso, D.; Tassi, E.; Waelbroeck, F. L.
2010-08-15
The Hamiltonian gyrofluid model recently derived by Waelbroeck et al. [Phys. Plasmas 16, 032109 (2009)] is used to investigate nonlinear collisionless reconnection with a strong guide field by means of numerical simulations. Finite ion Larmor radius gives rise to a cascade of the electrostatic potential to scales below both the ion gyroradius and the electron skin depth. This cascade is similar to that observed previously for the density and current in models with cold ions. In addition to density cavities, the cascades create electron beams at scales below the ion gyroradius. The presence of finite ion temperature is seen to modify, inside the magnetic island, the distribution of the velocity fields that advect two Lagrangian invariants of the system. As a consequence, the fine structure in the electron density is confined to a layer surrounding the separatrix. Finite ion Larmor radius effects produce also a different partition between the electron thermal, potential, and kinetic energy, with respect to the cold-ion case. Other aspects of the dynamics such as the reconnection rate and the stability against Kelvin-Helmholtz modes are similar to simulations with finite electron compressibility but cold ions.
Collisionless Three-dimensional Reconnection In Impulsive Solar Flares
NASA Astrophysics Data System (ADS)
Somov, Boris V.; Kosugi, Takeo; Sakao, Taro
1998-04-01
Two subclasses of impulsive solar flares, observed with the Hard X-Ray Telescope (HXT) onboard Yohkoh, have been discovered by Sakao et al. The two subclasses can be characterized as more impulsive (MI) and less impulsive (LI) flares, the former having a shorter total duration of the impulsive phase in the hard X-ray emission than the latter. We assume that in both subclasses, the collisionless three-dimensional reconnection process occurs at the separator with a longitudinal magnetic field. The high-temperature turbulent-current sheet (HTTCS), located along the separator, generates accelerated particles and fast outflows of ``superhot'' (T >= 30 MK) plasma. Powerful anomalous heat-conductive fluxes along the reconnected field lines maintain a high temperature in the superhot plasma. The difference between the LI and MI flares presumably appears because the footpoint separation (the distance between two brightest hard X-ray sources) increases in time in the LI flares, but decreases in the MI flares. According to our model, in the LI flares the three-dimensional reconnection process accompanies an increase in the longitudinal magnetic field at the separator. In contrast, in the MI flares the reconnection proceeds with a decrease of the longitudinal field; hence, the reconnection rate is higher in the MI flares. Since reconnection in the MI flares proceeds with a decrease of the longitudinal field, the reconnected field lines become shorter in this process. As the reconnected lines become shorter, accelerated electron beams arrive at the upper chromosphere faster. So, in the MI flares chromospheric evaporation begins earlier than in the LI flares. The evaporation process driven by accelerated electron beams generates upflows of ``warm'' (T <= 10 MK) plasma that interacts with downflows of superhot plasma and can switch off the accumulation of superhot plasma in the MI flares during the impulsive phase. In the LI flares, however, an observable amount of superhot
Multiscale dynamics based on kinetic simulation of collisionless magnetic reconnection
NASA Astrophysics Data System (ADS)
Fujimoto, Keizo; Takamoto, Makoto
2016-07-01
Magnetic reconnection is a natural energy converter which allows explosive energy release of the magnetic field energy into plasma kinetic energy. The reconnection processes inherently involve multi-scale process. The breaking of the field lines takes place predominantly in a small region called the diffusion region formed near the x-line, while the fast plasma jets resulting from reconnection extend to a distance far beyond the ion kinetic scales from the x-line. There has been a significant gap in understanding of macro-scale and micro-scale processes. The macro-scale model of reconnection has been developed using the magnetohydrodynamics (MHD) equations, while the micro-scale processes around the x-line have been based on kinetic equations including the ion and electron inertia. The problem is that these two kinds of model have significant discrepancies. It has been believed without any guarantee that the microscopic model near the x-line would connect to the macroscopic model far downstream of the x-line. In order to bridge the gap between the macro and micro-scale processes, we have performed large-scale particle-in-cell simulations with the adaptive mesh refinement. The simulation results suggest that the microscopic processes around the x-line do not connect to the previous MHD model even in the region far downstream of the x-line. The slow mode shocks and the associated plasma acceleration do not appear at the exhaust boundary of kinetic reconnection. Instead, the ions are accelerated due to the Speiser motion in the current layer extending to a distance beyond the kinetic scales. The different acceleration mechanisms between the ions and electrons lead to the Hall current system in broad area of the exhaust. Therefore, the previous MHD model could be inappropriate for collisionless magnetic reconnection. Ref. K. Fujimoto & M. Takamoto, Phys. Plasmas, 23, 012903 (2016).
Reconnection properties in collisionless plasma with open boundary conditions
Sun, H. E.; Ma, Z. W.; Huang, J.
2014-07-15
Collisionless magnetic reconnection in a Harris current sheet with different initial thicknesses is investigated using a 21/2 -D Darwin particle-in-cell simulation with the magnetosonic open boundary condition. It is found that the thicknesses of the ion dissipation region and the reconnection current sheet, when the reconnection rate E{sub r} reaches its first peak, are independent of the initial thickness of the current sheet; while the peak reconnection rate depends on it. The peak reconnection rate increases with decrease of the current sheet thickness as E{sub r}∼a{sup −1/2}, where a is the initial current sheet half-thickness.
Electron nongyrotropy in the context of collisionless magnetic reconnection
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.
Collisionless reconnection driven bulk heating of electrons on TREX
NASA Astrophysics Data System (ADS)
Olson, Joseph; Egedal, Jan; Greess, Samuel; Wallace, John; Clark, Michael; Forest, Cary
2015-11-01
The mechanism for particle heating during magnetic reconnection is an open topic in plasma physics research. Addressing this issue is a major concern for theory, observation, and experiment alike. Recently, a new model has been proposed to explain the bulk heating of electrons during collisionless reconnection, predicting that the heating scales inversely with the plasma beta. The new Terrestrial Reconnection Experiment (TREX) aims to examine this energy partition in a laboratory plasma. By reducing the collisionality in the experiment, the upstream electron pressure should become anisotropic due to adiabatic trapping, making TREX the first reconnection experiment able to access the necessary parameters to study these plasma dynamics. Preliminary analysis from the TREX magnetic flux probe array will be presented, characterizing the electron diffusion region in for collisionless magnetic reconnection. Supported in part by DoE grant DE-SC0010463.
Bellan, Paul M.
2014-10-15
If either finite electron inertia or finite resistivity is included in 2D magnetic reconnection, the two-fluid equations become a pair of second-order differential equations coupling the out-of-plane magnetic field and vector potential to each other to form a fourth-order system. The coupling at an X-point is such that out-of-plane even-parity electric and odd-parity magnetic fields feed off each other to produce instability if the scale length on which the equilibrium magnetic field changes is less than the ion skin depth. The instability growth rate is given by an eigenvalue of the fourth-order system determined by boundary and symmetry conditions. The instability is a purely growing mode, not a wave, and has growth rate of the order of the whistler frequency. The spatial profile of both the out-of-plane electric and magnetic eigenfunctions consists of an inner concave region having extent of the order of the electron skin depth, an intermediate convex region having extent of the order of the equilibrium magnetic field scale length, and a concave outer exponentially decaying region. If finite electron inertia and resistivity are not included, the inner concave region does not exist and the coupled pair of equations reduces to a second-order differential equation having non-physical solutions at an X-point.
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.
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.
New Measure of the Dissipation Region in Collisionless Magnetic Reconnection
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.
Catastrophic onset of fast magnetic reconnection with a guide field
NASA Astrophysics Data System (ADS)
Cassak, P. A.; Drake, J. F.; Shay, M. A.
2007-05-01
It was recently shown that the slow (collisional) Sweet-Parker and the fast (collisionless) Hall magnetic reconnection solutions simultaneously exist for a wide range of resistivities; reconnection is bistable [Cassak, Shay, and Drake, Phys. Rev. Lett., 95, 235002 (2005)]. When the thickness of the dissipation region becomes smaller than a critical value, the Sweet-Parker solution disappears and fast reconnection ensues, potentially explaining how large amounts of magnetic free energy can accrue without significant release before the onset of fast reconnection. Two-fluid numerical simulations extending the previous results for anti-parallel reconnection (where the critical thickness is the ion skin depth) to component reconnection with a large guide field (where the critical thickness is the thermal ion Larmor radius) are presented. Applications to laboratory experiments of magnetic reconnection and the sawtooth crash are discussed.
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.
The role of microturbulence on collisionless reconnection. [in magnetospheric plasmas
NASA Technical Reports Server (NTRS)
Papadopoulos, K.
1980-01-01
The linear, non-linear and anomalous transport properties associated with various microinstabilities driven by cross field currents in reconnecting geometries are reviewed. An assessment of their role in collisionless tearing based on analytic theory, computer simulations and experimental evidence, supports the dominant role of lower hybrid waves. The relevance of microturbulence on macroscopic stationary and time dependent models of merging is presented. It is concluded that a fluid-numerical simulation approach that includes (at each space and time step) the effects of anomalous transport in a self consistent manner, similar to the one used for laboratory collisionless shocks, represents the best method for studying and modeling the details of the reconnection process.
Collisionless Reconnection in Global Modeling of Magnetospheric Dynamics
NASA Astrophysics Data System (ADS)
Kuznetsova, M. M.; Hesse, M.; Rastaetter, L.; Gombosi, T.; de Zeeuw, D.; Toth, G.
2006-12-01
Recent advances in small-scale kinetic modeling of magnetic reconnection significantly improved our understanding of physical mechanisms controlling the dissipation in the vicinity of the reconnection site in collisionless plasma. However the progress in studies of small-scale geometries was not very helpful for large scale simulations. Global magnetosphere simulations usually include non-ideal processes in terms of numerical dissipation and/or ad hoc anomalous resistivity. To understand the role of magnetic reconnection in global evolution of magnetosphere and to place spacecraft observations into global context it is desirable to perform global simulations with physically motivated model of dissipation that are capable to reproduce reconnection rates observed in kinetic models. In our efforts to bridge the gap between small scale kinetic modeling and global simulations we introduced an approach that allows to quantify the interaction between large-scale global magnetospheric dynamics and microphysical processes in diffusion regions near reconnection sites. We utilized the global MHD code BATSRUS and incorporate primary mechanism controlling the dissipation in the vicinity of the reconnection site in terms of non-gyrotropic corrections to the induction equation. We demonstrated that nongyrotropic effects can significantly alter the global magnetosphere evolution. Our approach allowed for the first time to model loading/unloading cycle in response to steady southward IMF driving. We will extend our approach to cases with nonzero IMF By and analyze the effects of solar wind parameters and ionospheric conductance on reconnection rate and global magnetosphere dynamics.
Collisionless Reconnection with Weak Slow Shocks Under Anisotropic MHD Approximation
NASA Astrophysics Data System (ADS)
Hirabayashi, K.; Hoshino, M.
2014-12-01
Magnetic reconnection accompanied by a pair of slow-mode shock waves, known as Petschek's theory, has been widely studied as an efficient mechanism to convert magnetically stored energy to thermal and/or kinetic energy in plasmas. Satellite observations in the Earth's magnetotail, on the other hand, report that the detection of slow shocks is rare compared with the theory. As an important step to bridge the gap between the observational fact and the Petschek-type reconnection, we performed one- and two- dimensional collisionless magnetohydrodynamic (MHD) simulations of magnetic reconnection paying special attention to the effect of temperature anisotropy. In high-beta plasmas such as a plasma sheet in the magnetotail, it is expected that even weak temperature anisotropy can greatly modify the dynamics. We demonstrate that the slow shocks do exist in the reconnection layer even under the anisotropic temperature. The resultant shocks, however, are weaker than those in isotropic MHD in terms of plasma compression. In addition, the amount of magnetic energy released across the shock is extremely small, that is, the shock is no longer switch-off type. In spite of the weakness of the shocks, the reconnection rates measured by the inflow velocities are kept at the same level as the isotropic cases. Once the slow shock forms, the downstream plasma is heated in highly anisotropic manner, and the firehose-sense anisotropy affects the wave structure in the system. In particular, it is remarkable that the sequential order of propagation of slow shocks and rotational discontinuities reverses depending upon the magnitude of a superposed guide field. Our result is consistent with the rareness of the slow shock detection in the magnetotail, and implies that shocks do not necessarily play an important role. Furthermore, a variety of wave structure of a reconnection layer shown here will help interpretation of observational data in collisionless reconnection.
Electron Force Balance in Steady Collisionless-Driven Reconnection
Li Bin; Horiuchi, Ritoku
2008-11-21
Steady collisionless-driven reconnection in an open system is investigated by means of full-particle simulations. A long thin electron current sheet extends towards the outflow direction when the system relaxes to a steady state. Although the pressure tensor term along the reconnection electric field contributes to the violation of the electron frozen-in condition, a new force balance in the inflow direction is realized between the Lorentz and electrostatic forces, which is quite different from that in Harris equilibrium. The strong electrostatic field is generated through the combined effect of the Hall term and a driving inflow. This new force balance is more evident in the three-dimensional case due to the growth of an instability along the reconnection electric field. It is also found that the normalized charge density is in proportion to the square of the electron Alfven velocity averaged over the electron dissipation region.
ONSET OF FAST MAGNETIC RECONNECTION IN PARTIALLY IONIZED GASES
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.
Toward a transport model of collisionless magnetic reconnection
NASA Astrophysics Data System (ADS)
Kuznetsova, Masha M.; Hesse, Michael; Winske, Dan
2000-04-01
An absence of theoretical justification for the magnitude of resistivity is one of the major limitations of large-scale simulations of magnetic reconnection in collisionless magnetospheric plasma. We took advantage of the results of recent progress in kinetic modeling of collisionless dissipation in the vicinity of the magnetically neutral X point aiming to find ways to represent small-scale kinetic effects in large-scale models. The study was based on a combination of hybrid and particle methods and on analytical analysis. A comprehensive hybrid simulation code which incorporates the leading terms in electron dynamics responsible for breaking the frozen magnetic flux constraint (electron bulk flow inertia and nongyrotropic pressure effects) was utilized. The results of the comprehensive hybrid model were found to be in excellent quantitative agreement with the results of full particle simulations with similar setups. Both simulations demonstrated that the actual reconnection electric field is determined primarily by kinetic quasi-viscous effects and less by electron bulk flow inertia. An analytical expression for the quasi-viscous reconnection electric field averaged over the nongyrotropic region was obtained. Similar behavior of the evaluated quasi-viscous electric field and actual reconnection electric field taken from the simulations was demonstrated. Conventional hybrid simulations with simple nongyrotropic corrections to the electric field where also performed. The model was further reduced for utilization in MHD models. Analytical expressions for the time evolution of the reconnected flux evaluated from the MHD model modified by nongyrotropic corrections appeared to be in very good agreement with the results of comprehensive kinetic simulations. The evaluated averaged quasi-viscous electric field can be substituted into large-scale simulation models.
Kinetic Vlasov simulations of collisionless magnetic reconnection
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.
Does fast magnetic reconnection exist?
NASA Technical Reports Server (NTRS)
Priest, E. R.; Forbes, T. G.
1992-01-01
The main features of the Priest-Forbes (1986) and Priest-Lee (1990) models of magnetic reconnection in astrophysical plasmas are discussed, and the Priest-Lee model is generalized to include inflow pressure gradients and thus different regimes of reconnection. It is shown that different scaling results can be obtained depending on the boundary conditions. These results are compared to the ones observed in the numerical experiments of Biskamp (1986) and Lee and Fu (1986). It is concluded that numerical experiments with suitably designed boundary conditions are likely to exhibit fast reconnection, and that such reconnection is a common process in astrophysical and space plasmas.
Scaling of magnetic reconnection in relativistic collisionless pair plasmas.
Liu, Yi-Hsin; Guo, Fan; Daughton, William; Li, Hui; Hesse, Michael
2015-03-01
Using fully kinetic simulations, we study the scaling of the inflow speed of collisionless magnetic reconnection in electron-positron plasmas from the nonrelativistic to ultrarelativistic limit. In the antiparallel configuration, the inflow speed increases with the upstream magnetization parameter σ and approaches the speed of light when σ>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 ∼0.1 in both the nonrelativistic and relativistic limits. PMID:25793820
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.
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.
Slow shock formation and temperature anisotropy in collisionless magnetic reconnection
NASA Astrophysics Data System (ADS)
Higashimori, K.; Hoshino, M.
2011-12-01
We perform a two-dimensional simulation by using an electromagnetic hybrid code to study the formation of slow-mode shocks in collisionless magnetic reconnection in low beta plasmas, and we argue that one of important agents of the formation of slow shocks is the ion temperature anisotropy enhanced at the shock downstream region. As magnetic reconnection develops, it is known that the parallel temperature along the magnetic field becomes large in association with the anisotropic PSBL ion beams, and this temperature anisotropy has a tendency to suppress the formation of slow shock. Although preceding studies on magnetic reconnection with kinetic codes have shown such ion temperature anisotropy along the reconnection layer, the direct relation between formation of slow shocks and the ion temperature anisotropy has not been investigated. Based on our simulation result, we found that the slow shock formation is suppressed due to the large temperature anisotropy near the X-type region, but the downstream ion temperature anisotropy relaxes with increasing the distance from the magnetic neutral point. As a result, two pairs of current structures, which are the strong evidence of dissipation of magnetic field in slow shocks, are formed at the distance |x| > 115 λ i from the neutral point.
On the relationship between quadrupolar magnetic field and collisionless reconnection
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.
Asymmetric evolution of magnetic reconnection in collisionless accretion disk
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.
A twenty-moment model for collisionless guide field reconnection
NASA Astrophysics Data System (ADS)
Ng, Jonathan; Hakim, Ammar; Bhattacharjee, Amitava
2015-11-01
The integration of kinetic effects in fluid models is an important problem in global simulations of the Earth's magnetosphere and space weather modelling. Here we introduce a new fluid model and closure for collisionless magnetic reconnection and more general applications. It has recently been shown that electron pressure anisotropy is important in setting the structure of the reconnection region, and a closure based on the drift kinetic equation using a distribution of trapped and passing particles has been derived. We extend the model and present a general expression for moments of the distribution function. By evolving the heat flux tensor and closing at the fourth velocity moment, we obtain a self-consistent set of fluid equations, which includes the evolution of the off-diagonal elements of the pressure tensor. The model is implemented in a two-fluid code and the results are compared to PIC simulations of guide field reconnection. This work was supported by NSF Grant No. AGS-1338944, DOE Contract DE-AC02-09CH11466.
The link between shocks, turbulence, and magnetic reconnection in collisionless plasmas
NASA Astrophysics Data System (ADS)
Karimabadi, H.; Roytershteyn, V.; Vu, H. X.; Omelchenko, Y. A.; Scudder, J.; Daughton, W.; Dimmock, A.; Nykyri, K.; Wan, M.; Sibeck, D.; Tatineni, M.; Majumdar, A.; Loring, B.; Geveci, B.
2014-06-01
Global hybrid (electron fluid, kinetic ions) and fully kinetic simulations of the magnetosphere have been used to show surprising interconnection between shocks, turbulence, and magnetic reconnection. In particular, collisionless shocks with their reflected ions that can get upstream before retransmission can generate previously unforeseen phenomena in the post shocked flows: (i) formation of reconnecting current sheets and magnetic islands with sizes up to tens of ion inertial length. (ii) Generation of large scale low frequency electromagnetic waves that are compressed and amplified as they cross the shock. These "wavefronts" maintain their integrity for tens of ion cyclotron times but eventually disrupt and dissipate their energy. (iii) Rippling of the shock front, which can in turn lead to formation of fast collimated jets extending to hundreds of ion inertial lengths downstream of the shock. The jets, which have high dynamical pressure, "stir" the downstream region, creating large scale disturbances such as vortices, sunward flows, and can trigger flux ropes along the magnetopause. This phenomenology closes the loop between shocks, turbulence, and magnetic reconnection in ways previously unrealized. These interconnections appear generic for the collisionless plasmas typical of space and are expected even at planar shocks, although they will also occur at curved shocks as occur at planets or around ejecta.
The Link Between Shocks, Turbulence, and Magnetic Reconnection in Collisionless Plasmas
NASA Technical Reports Server (NTRS)
Karimabadi, H.; Roytershteyn, V.; Vu, H. X.; Omelchenko, Y. A.; Scudder, J.; Daughton, W.; Dimmock, A.; Nykyri, K.; Wan, M.; Sibeck, D.; Tatineni, M.; Majumdar, A.; Loring, B.; Geveci, B.
2014-01-01
Global hybrid (electron fluid, kinetic ions) and fully kinetic simulations of the magnetosphere have been used to show surprising interconnection between shocks, turbulence and magnetic reconnection. In particular collisionless shocks with their reflected ions that can get upstream before retransmission can generate previously unforeseen phenomena in the post shocked flows: (i) formation of reconnecting current sheets and magnetic islands with sizes up to tens of ion inertial length. (ii) Generation of large scale low frequency electromagnetic waves that are compressed and amplified as they cross the shock. These 'wavefronts' maintain their integrity for tens of ion cyclotron times but eventually disrupt and dissipate their energy. (iii) Rippling of the shock front, which can in turn lead to formation of fast collimated jets extending to hundreds of ion inertial lengths downstream of the shock. The jets, which have high dynamical pressure, 'stir' the downstream region, creating large scale disturbances such as vortices, sunward flows, and can trigger flux ropes along the magnetopause. This phenomenology closes the loop between shocks, turbulence and magnetic reconnection in ways previously unrealized. These interconnections appear generic for the collisionless plasmas typical of space, and are expected even at planar shocks, although they will also occur at curved shocks as occur at planets or around ejecta.
The link between shocks, turbulence, and magnetic reconnection in collisionless plasmas
Karimabadi, H.; Omelchenko, Y. A.; Roytershteyn, V.; Vu, H. X.; Scudder, J.; Daughton, W.; Dimmock, A.; Nykyri, K.; Wan, M.; Sibeck, D.; Tatineni, M.; Majumdar, A.; Loring, B.; Geveci, B.
2014-06-15
Global hybrid (electron fluid, kinetic ions) and fully kinetic simulations of the magnetosphere have been used to show surprising interconnection between shocks, turbulence, and magnetic reconnection. In particular, collisionless shocks with their reflected ions that can get upstream before retransmission can generate previously unforeseen phenomena in the post shocked flows: (i) formation of reconnecting current sheets and magnetic islands with sizes up to tens of ion inertial length. (ii) Generation of large scale low frequency electromagnetic waves that are compressed and amplified as they cross the shock. These “wavefronts” maintain their integrity for tens of ion cyclotron times but eventually disrupt and dissipate their energy. (iii) Rippling of the shock front, which can in turn lead to formation of fast collimated jets extending to hundreds of ion inertial lengths downstream of the shock. The jets, which have high dynamical pressure, “stir” the downstream region, creating large scale disturbances such as vortices, sunward flows, and can trigger flux ropes along the magnetopause. This phenomenology closes the loop between shocks, turbulence, and magnetic reconnection in ways previously unrealized. These interconnections appear generic for the collisionless plasmas typical of space and are expected even at planar shocks, although they will also occur at curved shocks as occur at planets or around ejecta.
Collisionless reconnection in two-dimensional magnetotail equilibria
NASA Technical Reports Server (NTRS)
Pritchett, P. L.; Coroniti, F. V.; Pellat, R.; Karimabadi, H.
1991-01-01
A two-dimensional particle simulation model based on the Darwin approximation to Maxwell's equations for studying collisionless reconnection in the magnetotail has been developed. Simulations of the pure ion tearing mode in a thin current sheet with normal B(z) field component demonstrate that in this limit this mode grows more slowly than expected based on previous analytic estimates. The saturation level of the tearing instability greatly surpasses estimates based on a simple trapping argument. The effect of the normal field component on the evolution of the tearing instability is considered. It is found that a normal field of even a few percent on axis strongly inhibits the growth of the instability.
Do dispersive waves play a role in collisionless magnetic reconnection?
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.
Mechanisms for fast flare reconnection
NASA Technical Reports Server (NTRS)
Vanhoven, G.; Deeds, D.; Tachi, T.
1988-01-01
Normal collisional-resistivity mechanisms of magnetic reconnection have the drawback that they are too slow to explain the fast rise of solar flares. Two methods are examined which are proposed for the speed-up of the magnetic tearing instability: the anomalous enhancement of resistivity by the injection of MHD turbulence and the increase of Coulomb resistivity by radiative cooling. The results are described for nonlinear numerical simulations of these processes which show that the first does not provide the claimed effects, while the second yields impressive rates of reconnection, but low saturated energy outputs.
Physics of collisionless reconnection in a stressed X-point collapse
Tsiklauri, D.; Haruki, T.
2008-10-15
Recently, magnetic reconnection during collisionless, stressed, X-point collapse was studied using kinetic, 2.5-dimensional, fully electromagnetic, relativistic particle-in-cell numerical code [D. Tsiklauri and T. Haruki, Phys. Plasmas 14, 112905 (2007)]. Here we finalize the investigation of this topic by addressing key outstanding physical questions: (i) Which term in the generalized Ohm's law is responsible for the generation of the reconnection electric field? (ii) How does the time evolution of the reconnected flux vary with the ion-electron mass ratio? (iii) What is the exact energy budget of the reconnection process; i.e., in which proportion initial (mostly magnetic) energy is converted into other forms of energy? (iv) Are there any anisotropies in the velocity distribution of the accelerated particles? The following points have been established. (i) A reconnection electric field is generated by the electron pressure tensor off-diagonal terms, resembling to the case of tearing unstable Harris current sheet studied by the GEM reconnection challenge. (ii) For m{sub i}/m{sub e}>>1, the time evolution of the reconnected flux is independent of ion-electron mass ratio. In addition, in the case of m{sub i}/m{sub e}=1, we show that reconnection proceeds slowly as the Hall term is zero; when m{sub i}/m{sub e}>>1 (i.e., the Hall term is nonzero) reconnection is fast and we conjecture that this is due to magnetic field being frozen into electron fluid, which moves significantly faster than ion fluid. (iii) Within one Alfven time, somewhat less than half ({approx}40%) of the initial total (roughly magnetic) energy is converted into the kinetic energy of electrons, and somewhat more than half ({approx}60%) into kinetic energy of ions (similar to solar flare observations). (iv) In the strongly stressed X-point case, in about one Alfven time, a full isotropy in all three spatial directions of the velocity distribution is seen for superthermal electrons (also commensurate
NASA Astrophysics Data System (ADS)
Olson, J.; Egedal, J.; Greess, S.; Myers, R.; Clark, M.; Endrizzi, D.; Flanagan, K.; Milhone, J.; Peterson, E.; Wallace, J.; Weisberg, D.; Forest, C. B.
2016-06-01
The spontaneous formation of magnetic islands is observed in driven, antiparallel magnetic reconnection on the Terrestrial Reconnection Experiment. We here provide direct experimental evidence that the plasmoid instability is active at the electron scale inside the ion diffusion region in a low collisional regime. The experiments show the island formation occurs at a smaller system size than predicted by extended magnetohydrodynamics or fully collisionless simulations. This more effective seeding of magnetic islands emphasizes their importance to reconnection in naturally occurring 3D plasmas.
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.
Suppression of collisionless magnetic reconnection in asymmetric current sheets
NASA Astrophysics Data System (ADS)
Liu, Yi-Hsin; Hesse, Michael
2016-06-01
Using fully kinetic simulations, we study the suppression of asymmetric reconnection in the limit where the diamagnetic drift speed ≫ Alfvén 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.
FAST MAGNETIC RECONNECTION AND SPONTANEOUS STOCHASTICITY
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} .
Aunai, Nicolas; Hesse, Michael; Black, Carrie; Evans, Rebekah; Kuznetsova, Maria
2013-04-15
Numerical studies implementing different versions of the collisionless Ohm's law have shown a reconnection rate insensitive to the nature of the non-ideal mechanism occurring at the X line, as soon as the Hall effect is operating. Consequently, the dissipation mechanism occurring in the vicinity of the reconnection site in collisionless systems is usually thought not to have a dynamical role beyond the violation of the frozen-in condition. The interpretation of recent studies has, however, led to the opposite conclusion that the electron scale dissipative processes play an important dynamical role in preventing an elongation of the electron layer from throttling the reconnection rate. This work re-visits this topic with a new approach. Instead of focusing on the extensively studied symmetric configuration, we aim to investigate whether the macroscopic properties of collisionless reconnection are affected by the dissipation physics in asymmetric configurations, for which the effect of the Hall physics is substantially modified. Because it includes all the physical scales a priori important for collisionless reconnection (Hall and ion kinetic physics) and also because it allows one to change the nature of the non-ideal electron scale physics, we use a (two dimensional) hybrid model. The effects of numerical, resistive, and hyper-resistive dissipation are studied. In a first part, we perform simulations of symmetric reconnection with different non-ideal electron physics. We show that the model captures the already known properties of collisionless reconnection. In a second part, we focus on an asymmetric configuration where the magnetic field strength and the density are both asymmetric. Our results show that contrary to symmetric reconnection, the asymmetric model evolution strongly depends on the nature of the mechanism which breaks the field line connectivity. The dissipation occurring at the X line plays an important role in preventing the electron current layer
Explosive magnetic reconnection caused by an X-shaped current-vortex layer in a collisionless plasma
Hirota, M.; Hattori, Y.; Morrison, P. J.
2015-05-15
A mechanism for explosive magnetic reconnection is investigated by analyzing the nonlinear evolution of a collisionless tearing mode in a two-fluid model that includes the effects of electron inertia and temperature. These effects cooperatively enable a fast reconnection by forming an X-shaped current-vortex layer centered at the reconnection point. A high-resolution simulation of this model for an unprecedentedly small electron skin depth d{sub e} and ion-sound gyroradius ρ{sub s}, satisfying d{sub e}=ρ{sub s}, shows an explosive tendency for nonlinear growth of the tearing mode, where it is newly found that the explosive widening of the X-shaped layer occurs locally around the reconnection point with the length of the X shape being shorter than the domain length and the wavelength of the linear tearing mode. The reason for the onset of this locally enhanced reconnection is explained theoretically by developing a novel nonlinear and nonequilibrium inner solution that models the local X-shaped layer, and then matching it to an outer solution that is approximated by a linear tearing eigenmode with a shorter wavelength than the domain length. This theoretical model proves that the local reconnection can release the magnetic energy more efficiently than the global one and the estimated scaling of the explosive growth rate agrees well with the simulation results.
Wave modes facilitating fast magnetic reconnection
NASA Astrophysics Data System (ADS)
Singh, N.
2011-12-01
Whistler and kinetic Alfven waves are often invoked to explain fast magnetic reconnection in collsionless plasmas. But how these wave modes facilitate the reconnection has remained unclear. An important unanswered question deals with the meaning of the wave frequency in the context of magnetic reconnection. New measurement on a fast explosive reconnection event in the Versatile Toroidal Facility (VTF) at MIT provides an interesting example of the meaning of the wave mode and the associated frequency directly related to the time scale of the impulsive reconnection. We examine the measurements in VTF in view of the whistler wave mode, showing that the explosive growth in the reconnection is related to the thinning of the current sheet to a few electron skin depths. We further demonstrate that the fastest measured time scale (~ 3 microseconds) and the largest normalized reconnection rate (~0.35) agree with those predicted from the whistler mode dispersion relation.
NASA Astrophysics Data System (ADS)
Büchner, J.; Kuska, J.-P.
1997-01-01
Based on analytical calculations we have currently argued that spontaneous reconnection through thin collisionless current sheets is an essentially three-dimensional (3 D) process (Büchner, 1996 a, b). Since 3 D kinetic PIC codes have become available, the three dimensional nature of the collisionless current sheet decay are now illustrated by numerical simulations (Büchner and Kuska, 1996; Pritchett and Coroniti, 1996; Zhu and Winglee, 1996). While the latter two claim a coupling to a longer wavelength kink mode as a main factor, destabilizing thin current sheets in 3 D, our simulations have revealed that even shorter scale perturbations in the current direction suffice to destabilize thin sheets very quickly. Since past simulation runs, however, were limited to mass ratios near unity, the influence of the electrons was not treated adequately. We have now investigated the stability of thin collisionless current sheets including 64 times lighter negatively charged particles. We can now show that while the two-dimensional tearing instability slows down for M = M_p/m_e = 64, the three-dimensional current sheet decay is a much faster process - practically as fast as the mass ratio M = 1 3 D sheet decay, even without kinking the sheet. We further conclude that, unlike the two-dimensional tearing instability, the three-dimensional decay of thin current sheets is not controlled by the electrons. For a sheet width comparable with the ion inertial length, we also recovered signatures of the Hall effect as predicted by Vasyliunas (1975) in the mass ratio M = 64 case. The ion inertial length seems to be the critical scale at which the sheet starts to decay.
Aspects of collisionless magnetic reconnection in asymmetric systems
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.
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.
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.
Olson, J; Egedal, J; Greess, S; Myers, R; Clark, M; Endrizzi, D; Flanagan, K; Milhone, J; Peterson, E; Wallace, J; Weisberg, D; Forest, C B
2016-06-24
The spontaneous formation of magnetic islands is observed in driven, antiparallel magnetic reconnection on the Terrestrial Reconnection Experiment. We here provide direct experimental evidence that the plasmoid instability is active at the electron scale inside the ion diffusion region in a low collisional regime. The experiments show the island formation occurs at a smaller system size than predicted by extended magnetohydrodynamics or fully collisionless simulations. This more effective seeding of magnetic islands emphasizes their importance to reconnection in naturally occurring 3D plasmas. PMID:27391729
Erratum: A Simple, Analytical Model of Collisionless Magnetic Reconnection in a Pair Plasma
NASA Technical Reports Server (NTRS)
Hesse, Michael; Zenitani, Seiji; Kuznetsova, Masha; Klimas, Alex
2011-01-01
The following describes a list of errata in our paper, "A simple, analytical model of collisionless magnetic reconnection in a pair plasma." It supersedes an earlier erratum. We recently discovered an error in the derivation of the outflow-to-inflow density ratio.
Zacharias, O.; Kleiber, R.; Borchardt, M.; Comisso, L.; Grasso, D.; Hatzky, R.
2014-06-15
The first detailed comparison between gyrokinetic and gyrofluid simulations of collisionless magnetic reconnection has been carried out. Both the linear and nonlinear evolution of the collisionless tearing mode have been analyzed. In the linear regime, we have found a good agreement between the two approaches over the whole spectrum of linearly unstable wave numbers, both in the drift kinetic limit and for finite ion temperature. Nonlinearly, focusing on the small-Δ′ regime, with Δ′ indicating the standard tearing stability parameter, we have compared relevant observables such as the evolution and saturation of the island width, as well as the island oscillation frequency in the saturated phase. The results are basically the same, with small discrepancies only in the value of the saturated island width for moderately high values of Δ′. Therefore, in the regimes investigated here, the gyrofluid approach can describe the collisionless reconnection process as well as the more complete gyrokinetic model.
Hewett, D.W.; Francis, G.E.; Max, C.E.
1990-06-29
Evidence from magnetospheric and solar flare research supports the belief that collisionless magnetic reconnection can proceed on the Alfven-wave crossing timescale. Reconnection behavior that occurs this rapidly in collisionless plasmas is not well understood because underlying mechanisms depend on the details of the ion and electron distributions in the vicinity of the emerging X-points. We use the direct implicit Particle-In-Cell (PIC) code AVANTI to study the details of these distributions as they evolve in the self-consistent E and B fields of magnetic reconnection. We first consider a simple neutral sheet model. We observe rapid movement of the current-carrying electrons away from the emerging X-point. Later in time an oscillation of the trapped magnetic flux is found, superimposed upon continued linear growth due to plasma inflow at the ion sound speed. The addition of a current-aligned and a normal B field widen the scope of our studies.
Origins of effective resistivity in collisionless magnetic reconnection
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.
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.
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).;
Yoo, Jongsoo; Yamada, Masaaki; Ji, Hantao; Myers, Clayton E.
2012-12-10
The ion dynamics in a collisionless magnetic reconnection layer are studied in a laboratory plasma. The measured in-plane plasma potential profile, which is established by electrons accelerated around the electron diffusion region, shows a saddle-shaped structure that is wider and deeper towards the outflow direction. This potential structure ballistically accelerates ions near the separatrices toward the outflow direction. Ions are heated as they travel into the high pressure downstream region.
Porkolab, Miklos; Egedal, Jan
2007-11-30
The Grant DE-FG-02-00ER54712, ?Experimental Studies of Collisionless Reconnection Processes in Plasmas?, financed within the DoE/NSF, spanned a period from September , 2003 to August, 2007. It partly supported an MIT Research scientist, two graduate students and material expenses. The grant enabled the operation of a basic plasma physics experiment (on magnetic reconnection) at the MIT Plasma Science and Fusion Center and the MIT Physics Department. A strong educational component characterized this work throughout, with the participation of a large number of graduate and undergraduate students and interns to the experimental activities. The study of the collisionless magnetic reconnection constituted the primary work carried out under this grant. The investigations utilized two magnetic configurations with distinct boundary conditions. Both configurations were based upon the Versatile Toroidal Facility (VTF). The first configuration is characterized by open boundary conditions where the magnetic field lines interface directly with the vacuum vessel walls. The reconnection dynamics for this configuration has been methodically characterized and it has been shown that kinetic effects related to trapped electron trajectories are responsible for the high rates of reconnection observed [7]. This type of reconnection has not been investigated before. Nevertheless, the results are directly relevant to observations by the Wind spacecraft of fast reconnection deep in the Earth magnetotail [9]. The second configuration was developed to be specifically relevant to numerical simulations of magnetic reconnection, allowing the magnetic field-lines to be contained inside the device. The configuration is compatible with the presence of large current sheets in the reconnection region and reconnection is observed in fast powerful bursts. These reconnection events facilitate the first experimental investigations of the physics governing the spontaneous onset of fast reconnection [12
NASA Astrophysics Data System (ADS)
Jain, Neeraj; Büchner, Jörg; Munoz Sepulveda, Patricio Alejandro
2016-07-01
In collisionless magnetic reconnection, dissipation region, where frozen-in condition of magnetic field breaks down, develops two scale structure, viz., electron current sheets embedded inside ion current sheets. Instabilities of these current sheets lead to the development of electromagnetic turbulence which can cause anomalous dissipation enhancing the reconnection rate. Laboratory experiments, e.g., Magnetic Reconnection Experiment and VINETA-II have measured fluctuations in electron current sheets in the lower hybrid frequency range. We present simulations of the electromagnetic turbulence generated by current sheet instabilities. The characteristic features of the electromagnetic turbulence, which can be used to identify the unstable modes responsible for the turbulence, will be studied. The results will be compared with the laboratory experiments.
Influence of the Hall effect and electron inertia in collisionless magnetic reconnection
NASA Astrophysics Data System (ADS)
Andrés, Nahuel; Dmitruk, Pablo; Gómez, Daniel
2016-02-01
We study the role of the Hall current and electron inertia in collisionless magnetic reconnection within the framework of full two-fluid MHD. At spatial scales smaller than the electron inertial length, a topological change of magnetic field lines exclusively due to the electron inertia becomes possible. Assuming stationary conditions, we derive a theoretical scaling for the reconnection rate, which is simply proportional to the Hall parameter. Using a pseudo-spectral code with no dissipative effects, our numerical results confirm this theoretical scaling. In particular, for a sequence of different Hall parameter values, our numerical results show that the width of the current sheet is independent of the Hall parameter, while its thickness is of the order of the electron inertial range, thus confirming that the stationary reconnection rate is proportional to the Hall parameter.
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.
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.
Graf von der Pahlen, J.; Tsiklauri, D.
2014-01-15
Works of Tsiklauri and Haruki [Phys. Plasmas 15, 102902 (2008); 14, 112905 (2007)] are extended by inclusion of the out-of-plane magnetic (guide) field. In particular, magnetic reconnection during collisionless, stressed X-point collapse for varying out-of-plane guide-fields is studied using a kinetic, 2.5D, fully electromagnetic, relativistic particle-in-cell numerical code. For zero guide-field, cases for both open and closed boundary conditions are investigated, where magnetic flux and particles are lost and conserved, respectively. It is found that reconnection rates, out-of-plane currents and density in the X-point increase more rapidly and peak sooner in the closed boundary case, but higher values are reached in the open boundary case. The normalized reconnection rate is fast: 0.10-0.25. In the open boundary case it is shown that an increase of guide-field yields later onsets in the reconnection peak rates, while in the closed boundary case initial peak rates occur sooner but are suppressed. The reconnection current changes similarly with increasing guide-field; however for low guide-fields the reconnection current increases, giving an optimal value for the guide-field between 0.1 and 0.2 times the in-plane field in both cases. Also, in the open boundary case, it is found that for guide-fields of the order of the in-plane magnetic field, the generation of electron vortices occurs. Possible causes of the vortex generation, based on the flow of decoupled particles in the diffusion region and localized plasma heating, are discussed. Before peak reconnection onset, oscillations in the out-of-plane electric field at the X-point are found, ranging in frequency from approximately 1 to 2 ω{sub pe} and coinciding with oscillatory reconnection. These oscillations are found to be part of a larger wave pattern in the simulation domain. Mapping the out-of-plane electric field along the central lines of the domain over time and applying a 2D Fourier transform reveal that
HYBRID AND HALL-MHD SIMULATIONS OF COLLISIONLESS RECONNECTION: EFFECTS OF PLASMA PRESSURE TENSOR
L. YIN; D. WINSKE; ET AL
2001-05-01
In this study we performed two-dimensional hybrid (particle ions, massless fluid electrons) and Hall-MHD simulations of collisionless reconnection in a thin current sheet. Both calculations include the full electron pressure tensor (instead of a localized resistivity) in the generalized Ohm's law to initiate reconnection, and in both an initial perturbation to the Harris equilibrium is applied. First, electron dynamics from the two calculations are compared, and we find overall agreement between the two calculations in both the reconnection rate and the global configuration. To address the issue of how kinetic treatment for the ions affects the reconnection dynamics, we compared the fluid-ion dynamics from the Hall-MHD calculation to the particle-ion dynamics obtained from the hybrid simulation. The comparison demonstrates that off-diagonal elements of the ion pressure tensor are important in correctly modeling the ion out-of-plane momentum transport from the X point. It is that these effects can be modeled efficiently using a particle Hall-MHD simulation method in which particle ions used in a predictor/corrector to implement the ion gyro-radius corrections. We also investigate the micro- macro-scale coupling in the magnetotail dynamics by using a new integrated approach in which particle Hall-MHD calculations are embedded inside a MHD simulation. Initial results of the simulation concerning current sheet thinning and reconnection dynamics are discussed.
Secondary instabilities and vortex formation in collisionless-fluid magnetic reconnection.
Del Sarto, D; Califano, F; Pegoraro, F
2003-12-01
It is shown that the pattern of current layers formed within a magnetic island in the nonlinear phase of magnetic field line reconnection in a collisionless two-dimensional fluid plasma is subject to the onset of a secondary instability, the effect of which increases with decreasing electron temperature. In the cold electron limit the saturation of the island growth is accompanied by a turbulent redistribution of the current layers and by the development of long lived fluid vortices while, in the opposite limit, the current layer structure remains regular. PMID:14683188
Werner, G. R.; Uzdensky, D. A.; Cerutti, B.; Nalewajko, K.; Begelman, M. C.
2015-12-30
Using two-dimensional particle-in-cell simulations, we characterize the energy spectra of particles accelerated by relativistic magnetic reconnection (without guide field) in collisionless electron–positron plasmas, for a wide range of upstream magnetizations σ and system sizes L. The particle spectra are well-represented by a power lawmore » $${\\gamma }^{-\\alpha }$$, with a combination of exponential and super-exponential high-energy cutoffs, proportional to σ and L, respectively. As a result, for large L and σ, the power-law index α approaches about 1.2.« less
Werner, G. R.; Uzdensky, D. A.; Cerutti, B.; Nalewajko, K.; Begelman, M. C.
2015-12-30
Using two-dimensional particle-in-cell simulations, we characterize the energy spectra of particles accelerated by relativistic magnetic reconnection (without guide field) in collisionless electron–positron plasmas, for a wide range of upstream magnetizations σ and system sizes L. The particle spectra are well-represented by a power law ${\\gamma }^{-\\alpha }$, with a combination of exponential and super-exponential high-energy cutoffs, proportional to σ and L, respectively. As a result, for large L and σ, the power-law index α approaches about 1.2.
NASA Astrophysics Data System (ADS)
Werner, G. R.; Uzdensky, D. A.; Cerutti, B.; Nalewajko, K.; Begelman, M. C.
2016-01-01
Using two-dimensional particle-in-cell simulations, we characterize the energy spectra of particles accelerated by relativistic magnetic reconnection (without guide field) in collisionless electron-positron plasmas, for a wide range of upstream magnetizations σ and system sizes L. The particle spectra are well-represented by a power law {γ }-α , with a combination of exponential and super-exponential high-energy cutoffs, proportional to σ and L, respectively. For large L and σ, the power-law index α approaches about 1.2.
Energy budgets in collisionless magnetic reconnection: Ion heating and bulk acceleration
Aunai, N.; Belmont, G.; Smets, R.
2011-12-15
This paper investigates the energy transfer in the process of collisionless antiparallel magnetic reconnection. Using two-dimensional hybrid simulations, we measure the increase of the bulk and thermal kinetic energies and compare it to the loss of magnetic energy through a contour surrounding the ion decoupling region. It is shown, for both symmetric and asymmetric configurations, that the loss of magnetic energy is not equally partitioned between heating and acceleration. The heating is found to be dominant and the partition ratio depends on the asymptotic parameters, and future investigations will be needed to understand this dependence.
Zenitani, Seiji; Hesse, Michael; Klimas, Alex; Black, Carrie; Kuznetsova, Masha
2011-12-15
It was recently proposed that the electron-frame dissipation measure, the energy transfer from the electromagnetic field to plasmas in the electron's rest frame, identifies the dissipation region of collisionless magnetic reconnection [Zenitani et al., Phys. Rev. Lett. 106, 195003 (2011)]. The measure is further applied to the electron-scale structures of antiparallel reconnection, by using two-dimensional particle-in-cell simulations. The size of the central dissipation region is controlled by the electron-ion mass ratio, suggesting that electron physics is essential. A narrow electron jet extends along the outflow direction until it reaches an electron shock. The jet region appears to be anti-dissipative. At the shock, electron heating is relevant to a magnetic cavity signature. The results are summarized to a unified picture of the single dissipation region in a Hall magnetic geometry.
Del Sarto, D.; Califano, F.; Pegoraro, F.
2005-01-01
The nonlinear phase of a magnetic field line reconnection instability in a collisionless two-dimensional cold plasma is investigated in the Hall dominated regime, described by the electron-magnetohydrodynamic equations, which corresponds to the frequency range of whistler waves. It is found that the regular pattern of current density layers that forms in the initial nonlinear phase of the reconnection instability is destroyed by the onset of a Kelvin-Helmholtz-type instability and the formation of current jets that develop into vortex rings. These processes can be interpreted in terms of a Hasegawa-Mima-type regime inside the magnetic island and lead to the creation of magnetic vortices. It is shown that electron compressibility, which is related to charge separation, tends to stabilize these processes.
Kinetic turbulence in 3D collisionless magnetic reconnection with a guide magnetic field
NASA Astrophysics Data System (ADS)
Alejandro Munoz Sepulveda, Patricio; Kilian, Patrick; Jain, Neeraj; Büchner, Jörg
2016-04-01
The features of kinetic plasma turbulence developed during non-relativistic 3D collisionless magnetic reconnection are still not fully understood. This is specially true under the influence of a strong magnetic guide field, a scenario common in space plasmas such as in the solar corona and also in laboratory experiments such as MRX or VINETA II. Therefore, we study the mechanisms and micro-instabilities leading to the development of turbulence during 3D magnetic reconnection with a fully kinetic PIC code, emphasizing the role of the guide field with an initial setup suitable for the aforementioned environments. We also clarify the relations between these processes and the generation of non-thermal populations and particle acceleration.
In-plane electric fields in magnetic islands during collisionless magnetic reconnection
Chen Lijen; Bhattacharjee, Amitava; Torbert, Roy B.; Bessho, Naoki; Daughton, William; Roytershteyn, Vadim
2012-11-15
Magnetic islands are a common feature in both the onset and nonlinear evolution of magnetic reconnection. In collisionless regimes, the onset typically occurs within ion-scale current layers leading to the formation of magnetic islands when multiple X lines are involved. The nonlinear evolution of reconnection often gives rise to extended electron current layers (ECL) which are also unstable to formation of magnetic islands. Here, we show that the excess negative charge and strong out-of-plane electron velocity in the ECL are passed on to the islands generated therein, and that the corresponding observable distinguishing the islands generated in the ECL is the strongly enhanced in-plane electric fields near the island core. The islands formed in ion-scale current layers do not have these properties of the ECL-generated islands. The above result provides a way to assess the occurrence and importance of extended ECLs that are unstable to island formation in space and laboratory plasmas.
Evidence of Magnetic Field Switch-off in Collisionless Magnetic Reconnection
NASA Astrophysics Data System (ADS)
Innocenti, M. E.; Goldman, M.; Newman, D.; Markidis, S.; Lapenta, G.
2015-09-01
The long-term evolution of large domain particle-in-cell simulations of collisionless magnetic reconnection is investigated following observations that show two possible outcomes for collisionless reconnection: toward a Petschek-like configuration or toward multiple X points. In the present simulation, a mixed scenario develops. At earlier time, plasmoids are emitted, disrupting the formation of Petschek-like structures. Later, an almost stationary monster plasmoid forms, preventing the emission of other plasmoids. A situation reminiscent of Petschek’s switch-off then ensues. Switch-off is obtained through a slow shock/rotational discontinuity compound structure. Two external slow shocks (SS) located at the separatrices reduce the in-plane tangential component of the magnetic field, but not to zero. Two transitions reminiscent of rotational discontinuities (RD) in the internal part of the exhaust then perform the final switch-off. Both the SS and the RD are characterized through analysis of their Rankine–Hugoniot jump conditions. A moderate guide field is used to suppress the development of the firehose instability in the exhaust.
Fast magnetic reconnection with large guide fields
Stanier, A.; Simakov, Andrei N.; Chacón, L.; Daughton, W.
2015-01-09
Here, we demonstrate 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. 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. Ultimately, the rate is independent of the DR physics and is in good agreement with kinetic results.
Fast magnetic reconnection with large guide fields
Stanier, A.; Simakov, Andrei N.; Chacón, L.; Daughton, W.
2015-01-09
Here, we demonstrate 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. 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. Ultimately, the rate is independentmore » of the DR physics and is in good agreement with kinetic results.« less
Jain, Neeraj; Büchner, Jörg
2014-06-15
In collisionless magnetic reconnection, electron current sheets (ECS) with thickness of the order of an electron inertial length form embedded inside ion current sheets with thickness of the order of an ion inertial length. These ECS's are susceptible to a variety of instabilities which have the potential to affect the reconnection rate and/or the structure of reconnection. We carry out a three dimensional linear eigen mode stability analysis of electron shear flow driven instabilities of an electron scale current sheet using an electron-magnetohydrodynamic plasma model. The linear growth rate of the fastest unstable mode was found to drop with the thickness of the ECS. We show how the nature of the instability depends on the thickness of the ECS. As long as the half-thickness of the ECS is close to the electron inertial length, the fastest instability is that of a translational symmetric two-dimensional (no variations along flow direction) tearing mode. For an ECS half thickness sufficiently larger or smaller than the electron inertial length, the fastest mode is not a tearing mode any more and may have finite variations along the flow direction. Therefore, the generation of plasmoids in a nonlinear evolution of ECS is likely only when the half-thickness is close to an electron inertial length.
Micro-instabilities and anomalous transport effects in collisionless guide field reconnection
NASA Astrophysics Data System (ADS)
Munoz Sepulveda, Patricio Alejandro; Büchner, Jörg; Kilian, Patrick
2016-07-01
It is often the case that magnetic reconnection takes place in collisionless plasmas with a current aligned guide magnetic field, such as in the Solar corona. The general characteristics of this process have been exhaustively analyzed with theory and numerical simulations, under different approximations, since some time ago. However, some consequences and properties of the secondary instabilities arising spontaneously -other than tearing instability-, and their dependence on the guide field strength, have not been completely understood yet. For this sake, we use the results of fully kinetic 2D PIC numerical simulations of guide field reconnection. By using a mean field approach for the Generalized Ohm's law that explains the balance of the reconnected electric field, we find that some of the cross-streaming and gradient driven instabilities -in the guide field case- produce an additional anomalous transport term. The latter can be interpreted as a result of the enhanced correlated electromagnetic fluctuations, leading to a slow down of the current carriers and kinetic scale turbulence. We characterize these processes on dependence on the guide field strength, and explore the causal relation with the source of free energy driving the mentioned instabilities. Finally, we show the main consequences that a fully 3D approach have on all those phenomena in contrast to the reduced 2D description.
Particle-in-Cell Simulation of Collisionless Driven Reconnection with Open Boundaries
NASA Technical Reports Server (NTRS)
Kimas, Alex; Hesse, Michael; Zenitani, Seiji; Kuznetsova, Maria
2010-01-01
First results are discussed from an ongoing study of driven collisionless reconnection using a 2 1/2-dimensional electromagnetic particle-in-cell simulation model with open inflow and outflow boundaries. An extended electron diffusion region (EEDR) is defined as that region surrounding a reconnecting neutral line in which the out-of-plane nonideal electric field is positive. It is shown that the boundaries of this region in the directions of the outflow jets are at the positions where the electrons make the transition from unfrozen meandering motion in the current sheet to outward drifting with the magnetic field in the outflow jets; a turning length scale is defined to mark these positions, The initial width of the EEDR in the inflow directions is comparable to the electron bounce width. Later. as shoulders develop to form a two-scale structure. thc EEDR width expands to the ion bounce width scale. The inner portion of the EEDR or the electron diffusion region proper remains at the electron bounce width. Two methods are introduced for predicting the reconnection electric field using the dimensions of the EEDR. These results are interpreted as further evidence that the EEDR is the region that is relevant to understanding the electron role in the neutral line vicinity.
Physical processes of driven magnetic reconnection in collisionless plasmas: Zero guide field case
NASA Astrophysics Data System (ADS)
Cheng, C. Z.; Inoue, S.; Ono, Y.; Horiuchi, R.
2015-10-01
The key physical processes of the electron and ion dynamics, the structure of the electric and magnetic fields, and how particles gain energy in the driven magnetic reconnection in collisionless plasmas for the zero guide field case are presented. The key kinetic physics is the decoupling of electron and ion dynamics around the magnetic reconnection region, where the magnetic field is reversed and the electron and ion orbits are meandering, and around the separatrix region, where electrons move mainly along the field line and ions move mainly across the field line. The decoupling of the electron and ion dynamics causes charge separation to produce a pair of in-plane bipolar converging electrostatic electric field ( E→ e s ) pointing toward the neutral sheet in the magnetic field reversal region and the monopolar E→ e s around the separatrix region. A pair of electron jets emanating from the reconnection current layer generate the quadrupole out-of-plane magnetic field, which causes the parallel electric field ( E→ || ) from E→ i n d to accelerate particles along the magnetic field. We explain the electron and ion dynamics and their velocity distributions and flow structures during the time-dependent driven reconnection as they move from the upstream to the downstream. In particular, we address the following key physics issues: (1) the decoupling of electron and ion dynamics due to meandering orbits around the field reversal region and the generation of a pair of converging bipolar electrostatic electric field ( E→ e s ) around the reconnection region; (2) the slowdown of electron and ion inflow velocities due to acceleration/deceleration of electrons and ions by E→ e s as they move across the neutral sheet; (3) how the reconnection current layer is enhanced and how the orbit meandering particles are accelerated inside the reconnection region by E→ i n d ; (4) why the electron outflow velocity from the reconnection region reaches super-Alfvenic speed
NASA Astrophysics Data System (ADS)
Yun, Gunsu; Ji, Jeong-Young; Thatipamula, Shekar; Kstar Team
2015-11-01
Viscous dissipation rate of magnetic field energy due to wave-like fluctuations in collisionless magnetized plasma is obtained analytically using the exact integral closure for electron fluid viscosity [Ji, Phys. Plasmas 21 (2014)]. For typical high-temperature tokamak plasma, the viscous resistivity is several orders larger than the Spitzer (collisional) resistivity. For magnetic reconnection, it is also found that the radiative transport (i.e. Poynting flux) of the field energy of Alfven waves [Bellan, Phys. Plasmas 5, 3081 (1998)] is comparable to the viscous dissipation. The viscous dissipation is more effective for shorter wavelength fluctuation. The importance of viscous dissipation is supported by broadband emission and chirping-down phenomena observed in the ion cyclotron harmonic frequency range at the crash onset of edge-localized mode on the KSTAR tokamak. Work supported by the National Research Foundation of Korea and the Asia-Pacific Center for Theoretical Physics.
Lu, San; Lu, Quanming; Huang, Can; Wang, Shui
2013-06-15
By performing two-dimensional particle-in-cell simulations, we investigate the transfer between electron bulk kinetic and electron thermal energy in collisionless magnetic reconnection. In the vicinity of the X line, the electron bulk kinetic energy density is much larger than the electron thermal energy density. The evolution of the electron bulk kinetic energy is mainly determined by the work done by the electric field force and electron pressure gradient force. The work done by the electron gradient pressure force in the vicinity of the X line is changed to the electron enthalpy flux. In the magnetic island, the electron enthalpy flux is transferred to the electron thermal energy due to the compressibility of the plasma in the magnetic island. The compression of the plasma in the magnetic island is the consequence of the electromagnetic force acting on the plasma as the magnetic field lines release their tension after being reconnected. Therefore, we can observe that in the magnetic island the electron thermal energy density is much larger than the electron bulk kinetic energy density.
NASA Astrophysics Data System (ADS)
Higashimori, K.; Hoshino, M.
2012-01-01
We perform a two-dimensional simulation by using an electromagnetic hybrid code to study the formation of slow-mode shocks in collisionless magnetic reconnection in low beta plasmas, and we focus on the relation between the formation of slow shocks and the ion temperature anisotropy enhanced at the shock downstream region. It is known that as magnetic reconnection develops, the parallel temperature along the magnetic field becomes large in association with the anisotropic plasma sheet boundary layer ion beams, and this temperature anisotropy has a tendency to suppress the formation of slow shocks. On the basis of our simulation result, we found that the slow shock formation is suppressed due to the large temperature anisotropy near the X-type region, but the ion temperature anisotropy relaxes with increasing the distance from the magnetic neutral point. As a result, two pairs of current structures, which are the strong evidence of dissipation of magnetic field in slow shocks, are formed at the distance ∣x∣ ≥ 115 λi from the neutral point.
Plasma waves around separatrix in collisionless magnetic reconnection with weak guide field
NASA Astrophysics Data System (ADS)
Chen, Yangao; Fujimoto, Keizo; Xiao, Chijie; Ji, Hantao
2015-11-01
Electrostatic and electromagnetic waves excited by electron beam around the separatrix region are analyzed in detail during the collisionless magnetic reconnection with a weak guide field by using 2D particle-in-cell simulation with the adaptive mesh refinement. Broadband electrostatic waves are excited both in the inflow and outflow regions around the separatrices due to the electron bump-on-tail, two-stream, and Buneman instabilities. In contrast, the quasi-monochromatic electromagnetic waves are excited only in the inflow side of the separatrices due to a beam-driven Whistler instability. The localization of the Whistler waves is attributed to the non-uniformity of the out-of-plane magnetic field By. The Whistler instability is suppressed in the outflow side where By is too small for the oblique propagation. The electrostatic waves with distinct speeds can explain the in situ spacecraft observations. From the causality point of view, the waves are generated as the consequence of the electron bulk acceleration to thermalize the particles through wave-particle interactions. These simulation results provide guidance to analyze high-resolution wave observations during reconnection in the ongoing and upcoming satellite missions, as well as in dedicated laboratory experiments.
Plasma waves around separatrix in collisionless magnetic reconnection with weak guide field
NASA Astrophysics Data System (ADS)
Chen, Yangao; Fujimoto, Keizo; Xiao, Chijie; Ji, Hantao
2015-08-01
Electrostatic and electromagnetic waves excited by electron beam around the separatrix region are analyzed in detail during the collisionless magnetic reconnection with a weak guide field by using 2-D particle-in-cell simulation with the adaptive mesh refinement. Broadband electrostatic waves are excited both in the inflow and outflow regions around the separatrices due to the electron bump-on-tail, two-stream, and Buneman instabilities. In contrast, the quasi-monochromatic electromagnetic waves are excited only in the inflow side of the separatrices due to a beam-driven whistler instability. The localization of the whistler waves is attributed to the nonuniformity of the out-of-plane magnetic field By. The whistler instability is suppressed in the outflow side where By is too small for the oblique propagation. The electrostatic waves with distinct speeds can explain the in situ spacecraft observations. From the causality point of view, the waves are generated as the consequence of the electron bulk acceleration to thermalize the particles through wave-particle interactions. These simulation results provide guidance to analyze high-resolution wave observations during reconnection in the ongoing and upcoming satellite missions, as well as in dedicated laboratory experiments.
NASA Astrophysics Data System (ADS)
Hirota, Makoto; Hattori, Yuji
2014-10-01
Explosive behavior of collisionless magnetic reconnection is investigated by analyzing a two-fluid model that includes the effects of the electron inertia and the electron temperature (or compressibility). By micrifying both the electron skin depth de and the ion-sound gyroradius ρs such that ρs =de < 0 . 01 L (where L is the system size), a direct numerical simulation is performed to enlarge strongly nonlinear regime of a collisionless tearing instability. The nonlinear evolution is shown to be explosive when the inverse of the tearing index 1 /Δ' is smaller than ρs =de , whereas the maximum reconnection speed at the fully reconnected state does not significantly depend on the size of ρs =de . The singular current-vortex sheets are generated in the form of the X shape. In the explosive phase, the expansion of this X shape as well as the magnetic island occurs locally near the reconnection point. By taking an approach similar to the asymptotic matching, the dynamics of the current-vortex sheets is analyzed and the explosive reconnection speed is estimated theoretically. This work is supported by JSPS Grant-in-Aid for Young Scientists(B) (No. 25800308).
Fast Magnetic Reconnection in the Plasmoid-Dominated Regime
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.
Fast magnetic reconnection in the plasmoid-dominated regime.
Uzdensky, D A; Loureiro, N F; Schekochihin, A A
2010-12-01
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. PMID:21231473
Graf von der Pahlen, J.; Tsiklauri, D.
2014-06-15
The out-of-plane magnetic field, generated by fast magnetic reconnection, during collisionless, stressed X-point collapse, was studied with a kinetic, 2.5D, fully electromagnetic, relativistic particle-in-cell numerical code, using both closed (flux conserving) and open boundary conditions on a square grid. It was discovered that the well known quadrupolar structure in the out-of-plane magnetic field gains four additional regions of opposite magnetic polarity, emerging near the corners of the simulation box, moving towards the X-point. The emerging, outer, magnetic field structure has opposite polarity to the inner quadrupolar structure, leading to an overall octupolar structure. Using Ampere's law and integrating electron and ion currents, defined at grid cells, over the simulation domain, contributions to the out-of-plane magnetic field from electron and ion currents were determined. The emerging regions of opposite magnetic polarity were shown to be the result of ion currents. Magnetic octupolar structure is found to be a signature of X-point collapse, rather than tearing mode, and factors relating to potential discoveries in experimental scenarios or space-craft observations are discussed.
Physical conditions for fast reconnection evolution in space plasmas
Ugai, M.
2012-07-15
The present paper studies physical conditions for fast reconnection mechanism involving slow shocks to evolve spontaneously in space (high-temperature) plasmas. This is fundamental for onset mechanisms of geomagnetic substorms and solar flares. It is demonstrated that reconnection evolution strongly depends on effective resistivity available in space plasmas as well as on dimensions of initial current sheet. If a current sheet is sufficiently thin, fast reconnection spontaneously evolves only when resistivity is locally enhanced around X reconnection point. This is because in space plasmas reconnection flows cause vital current concentration locally around X point. For current-driven anomalous resistivity, the resulting resistivity is automatically localized around X point, so fast reconnection mechanism can be realized. On the other hand, for uniform or Spitzer resistivity, any fast reconnection cannot grow; in particular, Spitzer resistivity is reduced around X point because of Joule heating. Regarding reconnection simulations (either fluid or particle), unless numerical resistivities are made negligibly small, they seriously mask the effects of physical resistivity, leading to a misleading conclusion that reconnection evolution is little influenced by plasma resistivity.
NASA Astrophysics Data System (ADS)
Egedal, Jan; Le, Ari; Daughton, William
2013-06-01
From spacecraft data, it is evident that electron pressure anisotropy develops in collisionless plasmas. This is in contrast to the results of theoretical investigations, which suggest this anisotropy should be limited. Common for such theoretical studies is that the effects of electron trapping are not included; simply speaking, electron trapping is a non-linear effect and is, therefore, eliminated when utilizing the standard methods for linearizing the underlying kinetic equations. Here, we review our recent work on the anisotropy that develops when retaining the effects of electron trapping. A general analytic model is derived for the electron guiding center distribution f¯(v∥,v⊥) of an expanding flux tube. The model is consistent with anisotropic distributions observed by spacecraft, and is applied as a fluid closure yielding anisotropic equations of state for the parallel and perpendicular components (relative to the local magnetic field direction) of the electron pressure. In the context of reconnection, the new closure accounts for the strong pressure anisotropy that develops in the reconnection regions. It is shown that for generic reconnection in a collisionless plasma nearly all thermal electrons are trapped, and dominate the properties of the electron fluid. A new numerical code is developed implementing the anisotropic closure within the standard two-fluid framework. The code accurately reproduces the detailed structure of the reconnection region observed in fully kinetic simulations. These results emphasize the important role of pressure anisotropy for the reconnection process. In particular, for reconnection geometries characterized by small values of the normalized upstream electron pressure, βe∞, the pressure anisotropy becomes large with p∥≫p⊥ and strong parallel electric fields develop in conjunction with this anisotropy. The parallel electric fields can be sustained over large spatial scales and, therefore, become important for
Particle description of the electron diffusion region in collisionless magnetic reconnection
Fujimoto, Keizo; Sydora, Richard D.
2009-11-15
The present study clarifies the dissipation mechanism of collisionless magnetic reconnection in two-dimensional system based on particle dynamics. The electrons are accelerated without thermalization in the electron diffusion region, carry out the meandering oscillation, and are ejected away from the X-line. This electron behavior not only generates the electron inertia resistivity based on the particle description, but also it can be the origin of the electron viscosity resulting in the off-diagonal pressure tensor term in the generalized Ohm's law near the X-line. We derive an analytical profile for the electron pressure tensor term and confirm that the profile is consistent with the particle-in-cell simulation. The present results demonstrate that the magnetic dissipation due to the electron viscosity in the fluid picture is equivalent to that due to the inertia resistivity in the particle description. It is also suggested that the width of the electron current sheet is on the order of the electron inertia length in the case without electron scattering and thermalization, while it is expected that the width is broadened if the electron scattering occurs in the current sheet.
Collisionless Magnetic Reconnection and Dynamo Processes in a Spatially Rotating Magnetic Field
NASA Astrophysics Data System (ADS)
Choe, Gwangson; Lee, Junggi
2016-04-01
Spatially rotating magnetic fields have been observed in the solar wind and in the Earth's magnetopause as well as in reversed field pinch (RFP) devices. Such field configurations have a similarity with extended current layers having a spatially varying plasma pressure instead of the spatially varying guide field. It is thus expected that magnetic reconnection may take place in a rotating magnetic field no less than in an extended current layer. We have investigated the spontaneous evolution of a collisionless plasma system embedding a rotating magnetic field with a two-and-a-half-dimensional electromagnetic particle-in-cell (PIC) simulation. It is found that a magnetic-flux-reducing diffusion phase and a magnetic-flux-increasing dynamo phase are alternating with a certain period. The temperature of the system also varies with the same period, showing a similarity to sawtooth oscillations in tokamaks. We have shown that a modified theory of sawtooth oscillations can explain the periodic behavior observed in the simulation. A strong guide field distorts the current layer as was observed in laboratory experiments. This distortion is smoothed out as magnetic islands fade away by the O-line diffusion, but is soon strengthened by the growth of magnetic islands. These processes are all repeating with a fixed period. Our results suggest that a rotating magnetic field configuration continuously undergoes deformation and relaxation in a short time-scale although it might look rather steady in a long-term view.
NASA Astrophysics Data System (ADS)
Del Sarto, Daniele; Pucci, Fulvia; Tenerani, Anna; Velli, Marco
2016-03-01
This paper discusses the transition to fast growth of the tearing instability in thin current sheets in the collisionless limit where electron inertia drives the reconnection process. It has been previously suggested that in resistive MHD there is a natural maximum aspect ratio (ratio of sheet length and breadth to thickness) which may be reached for current sheets with a macroscopic length L, the limit being provided by the fact that the tearing mode growth time becomes of the same order as the Alfvén time calculated on the macroscopic scale. For current sheets with a smaller aspect ratio than critical the normalized growth rate tends to zero with increasing Lundquist number S, while for current sheets with an aspect ratio greater than critical the growth rate diverges with S. Here we carry out a similar analysis but with electron inertia as the term violating magnetic flux conservation: previously found scalings of critical current sheet aspect ratios with the Lundquist number are generalized to include the dependence on the ratio de2/L2, where de is the electron skin depth, and it is shown that there are limiting scalings which, as in the resistive case, result in reconnecting modes growing on ideal time scales. Finite Larmor radius effects are then included, and the rescaling argument at the basis of "ideal" reconnection is proposed to explain secondary fast reconnection regimes naturally appearing in numerical simulations of current sheet evolution.
Fast Magnetic Reconnection: Bridging Laboratory and Space Plasma Physics
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.
Fast magnetic reconnection in three-dimensional magnetohydrodynamics simulations
Pang Bijia; Pen, U.-L.; Vishniac, Ethan T.
2010-10-15
A constructive numerical example of fast magnetic reconnection in a three-dimensional periodic box is presented. Reconnection is initiated by a strong, localized perturbation to the field lines. The solution is intrinsically three-dimensional and its gross properties do not depend on the details of the simulations. {approx}30% of the magnetic energy is released in an event which lasts about one Alfven time, but only after a delay during which the field lines evolve into a critical configuration. The physical picture of the process is presented. The reconnection regions are dynamical and mutually interacting. In the comoving frame of these regions, reconnection occurs through a x-like point, analogous to Petschek reconnection. The dynamics appear to be driven by global flows, not local processes.
Fingerprints of collisionless reconnection at the separator, I, Ambipolar-Hall signatures
NASA Astrophysics Data System (ADS)
Scudder, J. D.; Mozer, F. S.; Maynard, N. C.; Russell, C. T.
2002-10-01
Plasma, electric, and magnetic field data on the Polar spacecraft have been analyzed for the 29 May 1996 magnetopause traversal searching for evidence of in situ reconnection and traversal of the separator. In this paper we confine our analysis to model-free observations and intrasensor coherence of detection of the environs of the separator. (1) We illustrate the first documented penetration of the separator of collisionless magnetic reconnection in temporal proximity to successful Walén tests with opposite slopes. (2) We present the first direct measurements of E∥ at the magnetopause. (3) We make the first empirical argument that E∥ derives from the electron pressure gradient force. (4) We document the first detection of the electron pressure ridge astride the magnetic depression that extends from the separator. (5) We provide the first empirical detection of the reconnection rate at the magnetopause with the locally sub-Alfvénic ion inflow, MAi ≃ 0.1, and trans-Alfvénic exhaust at high electron pressure of MiA ≃ 1.1-5. (6) We exhibit the first empirical detection of supra-Alfvénic electron flows parallel to B in excess of 5 in narrow sheets. (7) We illustrate the detection of heat flux sheets indicative of separatrices near, but not always in superposition, with the supra-Alfvénic parallel electron bulk flows. (8) We present the first evidence that pressure gradient scales are short enough to explain the electron fluid's measured cross-field drifts not explained by E × B drift but predicted by the measured size of E∥. (9) We illustrate that the size of the observed E∥ is well organized with the limit implied by Vasyliunas's analysis of the generalized Ohm's law of scale length ?, indicative of the intermediate scale of the diffusion region. (10) We document the first detection of departure from electron gyrotropy not only at the separator crossing but also in its vicinity, an effect presaged by [1975]. (11) We make the first reports of very
Fast sawtooth reconnection at realistic Lundquist numbers
NASA Astrophysics Data System (ADS)
Günter, S.; Yu, Q.; Lackner, K.; Bhattacharjee, A.; Huang, Y.-M.
2015-01-01
Magnetic reconnection, a ubiquitous phenomenon in astrophysics, space science and magnetic confinement research, frequently proceeds much faster than predicted by simple resistive MHD theory. Acceleration can result from the break-up of the thin Sweet-Parker current sheet into plasmoids, or from two-fluid effects decoupling mass and magnetic flux transport over the ion inertial length {{v}A}/{ωci} or the drift scale \\sqrt{{{T}e}/{{m}i}}/{ωci}, depending on the absence or presence of a strong magnetic guide field. We describe new results on the modelling of sawtooth reconnection in a simple tokamak geometry (circular cylindrical equilibrium) pushed to realistic Lundquist numbers for present day tokamaks. For the resistive MHD case, the onset criteria and the influence of plasmoids on the reconnection process agree well with earlier results found in the case of vanishing magnetic guide fields. While plasmoids are also observed in two-fluid calculations, they do not dominate the reconnection process for the range of plasma parameters considered in this study. In the two-fluid case they form as a transient phenomenon only. The reconnection times become weakly dependent on the S-value and for the most complete model—including two-fluid effects and equilibrium temperature and density gradients—agree well with those experimentally found on ASDEX Upgrade ≤ft(≤slant 100 μ s\\right).
Wang, Liang Germaschewski, K.; Hakim, Ammar H.; Bhattacharjee, A.
2015-01-15
We introduce an extensible multi-fluid moment model in the context of collisionless magnetic reconnection. This model evolves full Maxwell equations and simultaneously moments of the Vlasov-Maxwell equation for each species in the plasma. Effects like electron inertia and 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 for each species. We first demonstrate analytically and numerically that 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. 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 local closure towards a nonlocal fully three-dimensional closure are also discussed.
NASA Astrophysics Data System (ADS)
Wang, Liang; Hakim, Ammar H.; Bhattacharjee, A.; Germaschewski, K.
2015-01-01
We introduce an extensible multi-fluid moment model in the context of collisionless magnetic reconnection. This model evolves full Maxwell equations and simultaneously moments of the Vlasov-Maxwell equation for each species in the plasma. Effects like electron inertia and 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 for each species. We first demonstrate analytically and numerically that 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. 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 local closure towards a nonlocal fully three-dimensional closure are also discussed.
Trigger of Fast Reconnection via Collapsing Current Sheets
NASA Astrophysics Data System (ADS)
Tenerani, A.; Velli, M.; Rappazzo, A. F.; Pucci, F.
2015-12-01
It has been widely believed that reconnection is the underlying mechanism of many explosive processes observed both in astrophysical and laboratory plasmas. However, both the questions of how magnetic reconnection is triggered in high Lundquist (S) and Reynolds (R) number plasmas, and how it can then occur on fast, ideal, time-scales remain open. Indeed, it has been argued that fast reconnection rates could be achieved once kinetic scales are reached, or, alternatively, by the onset of the so-called plasmoid instability within Sweet-Parker current sheets. However, it has been shown recently that a tearing mode instability (the "ideal tearing") can grow on an ideal, i.e., S-independent, timescale once the width a of a current sheet becomes thin enough with respect to its macroscopic length L, a/L ~ S-1/3. This suggests that current sheet thinning down to such a threshold aspect ratio —much larger, for S>>1, than the Sweet-Parker one that scales as a/L ~ S-1/2— might provide the trigger for fast reconnection even within the fluid plasma framework. Here we discuss the transition to fast reconnection by studying with visco-resistive MHD simulations the onset and evolution of the tearing instability within a single collapsing current sheet. We indeed show that the transition to a fast tearing mode instability takes place when an inverse aspect ratio of the order of the threshold a/L ~ S-1/3 is reached, and that the secondary current sheets forming nonlinearly become the source of a succession of recursive tearing instabilities. The latter is reminiscent of the fractal reconnection model of flares, which we modify in the light of the "ideal tearing" scenario.
NASA Astrophysics Data System (ADS)
Innocenti, M. E.; Goldman, M. V.; Newman, D. L.; Markidis, S.; Lapenta, G.
2015-12-01
The long term evolution of large domain Particle In Cell simulations of collisionless magnetic reconnection is investigated following observations that show two possible outcomes for collisionless reconnection: towards a Petschek-like configuration (Gosling 2007) or towards multiple X points (Eriksson et al. 2014). In the simulations presented here and described in [Innocenti2015*], a mixed scenario develops. At earlier time, plasmoids are emitted, disrupting the formation of Petschek-like structures. Later, an almost stationary monster plasmoid forms, preventing the emission of other plasmoids. A situation reminding of Petschek's switch-off then ensues. Switch-off is obtained through a slow shock / rotational discontinuity (SS/RD) compound structure, with the rotation discontinuity downstreamthe slow shock. Two external slow shocks located in correspondence of the separatrices reduce the in plane tangential component of the magnetic field, but not to zero. Two transitions reminding of rotational discontinuities in the internal part of the exhausts then perform the final switch-off. Both the slow shocks and the rotational discontinuities are characterized as such through the analysis of their Rankine-Hugoniot jump conditions. A moderate guide field is used to suppress the development of the firehose instability in the exhaust that prevented switch off in [Liu2012]. Compound SS/RD structures, with the RD located downstream the SS, have been observed in both the solar wind and the magnetosphere in Wind and Geotail data respectively [Whang1998, Whang2004]. Ion trajectiories across the SS/RD structure are followed and the kinetic origin of the SS/RD structure is investigated. * Innocenti, Goldman, Newman, Markidis, Lapenta, Evidence of magnetic field switch-off in collisionless magnetic reconnection, accepted in Astrophysical Journal Letters, 2015 Acknowledgements: NERSC, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of
A simple, analytical model of collisionless magnetic reconnection in a pair plasma
Hesse, Michael; Zenitani, Seiji; Kuznetsova, Masha; Klimas, Alex
2009-10-15
A set of conservation equations is utilized to derive balance equations in the reconnection diffusion region of a symmetric pair plasma. The reconnection electric field is assumed to have the function to maintain the current density in the diffusion region and to impart thermal energy to the plasma by means of quasiviscous dissipation. Using these assumptions it is possible to derive a simple set of equations for diffusion region parameters in dependence on inflow conditions and on plasma compressibility. These equations are solved by means of a simple, iterative procedure. The solutions show expected features such as dominance of enthalpy flux in the reconnection outflow, as well as combination of adiabatic and quasiviscous heating. Furthermore, the model predicts a maximum reconnection electric field of E{sup *}=0.4, normalized to the parameters at the inflow edge of the diffusion region.
A Simple, Analytical Model of Collisionless Magnetic Reconnection in a Pair Plasma
NASA Technical Reports Server (NTRS)
Hesse, Michael; Zenitani, Seiji; Kuznetova, Masha; Klimas, Alex
2011-01-01
A set of conservation equations is utilized to derive balance equations in the reconnection diffusion region of a symmetric pair plasma. The reconnection electric field is assumed to have the function to maintain the current density in the diffusion region, and to impart thermal energy to the plasma by means of quasi-viscous dissipation. Using these assumptions it is possible to derive a simple set of equations for diffusion region parameters in dependence on inflow conditions and on plasma compressibility. These equations are solved by means of a simple, iterative, procedure. The solutions show expected features such as dominance of enthalpy flux in the reconnection outflow, as well as combination of adiabatic and quasi-viscous heating. Furthermore, the model predicts a maximum reconnection electric field of E(sup *)=0.4, normalized to the parameters at the inflow edge of the diffusion region.
Analysis of Fast Reconnection in MRX
NASA Astrophysics Data System (ADS)
Yamada, M.; Ji, H.; Kulsrud, R.; Kuritsyn, A.; Terry, S.
2002-11-01
In MRX (Magnetic Reconnection Experiment), the detailed magnetic field structure and the plasma profiles of the neutral sheet have been measured and evidence for non-MHD physics mechanisms has been obtained(M. Yamada et al., Phys. Plasmas, 7), 1781 (2000). As the electron-ion collision frequency is reduced, the reconnection rate has been observed to be significantly enhanced over the classical value. Both electrostatic and magnetic turbulence of lower hybrid frequency range has been observed in the low collisionality regime. The amplitude of magnetic fluctuation is the largest at the center of neutral sheet while electropotential fluctuations peak at the edge of the sheath. To describe the physics of this region, much thought has been given to the `` generalized" Ohm's law where electrons and ions are treated separately. In this `` E-MHD" region electrons but not ions are considered to be magnetized and the lower hybrid wave can be connected continuously to an obliquely propagating Whistler wave(R.L. Stenzel and J.M. Urrutia, Phys. Plasmas, 7), 4450 (2000). In this paper we examine the entire spectrum of waves from the electron cyclotron frequency down to the ion cyclotron frequency, focusing on comparisons with the recent experimental data from the MRX neutral sheet plasmas(H. Ji, et al., this meeting). The physical mechanisms of the observed enhanced resistivity due to these waves will be discussed. This work is supported by DoE, NASA and NSF.
Liu, Yi-Hsin; Drake, J. F.; Swisdak, M.
2011-09-15
Simulations of collisionless oblique propagating slow shocks have revealed the existence of a transition associated with a critical temperature anisotropy {epsilon} = 1 - {mu}{sub 0}(P{sub ||} - P{sub perpendicular})/B{sup 2} = 0.25 (Y.-H. Liu, J. F. Drake, and M. Swisdak, Phys. Plasmas 18, 062110 (2011)). An explanation for this phenomenon is proposed here based on anisotropic fluid theory, in particular, the anisotropic derivative nonlinear-Schroedinger-Burgers equation, with an intuitive model of the energy closure for the downstream counter-streaming ions. The anisotropy value of 0.25 is significant because it is closely related to the degeneracy point of the slow and intermediate modes and corresponds to the lower bound of the coplanar to non-coplanar transition that occurs inside a compound slow shock (SS)/rotational discontinuity (RD) wave. This work implies that it is a pair of compound SS/RD waves that bound the outflows in magnetic reconnection, instead of a pair of switch-off slow shocks as in Petschek's model. This fact might explain the rareness of in-situ observations of Petschek-reconnection-associated switch-off slow shocks.
NASA Astrophysics Data System (ADS)
Liu, Yi-Hsin; Drake, J. F.; Swisdak, M.
2011-09-01
Simulations of collisionless oblique propagating slow shocks have revealed the existence of a transition associated with a critical temperature anisotropy ɛ = 1 - μ0(P|| - P⊥)/B2 = 0.25 (Y.-H. Liu, J. F. Drake, and M. Swisdak, Phys. Plasmas 18, 062110 (2011)). An explanation for this phenomenon is proposed here based on anisotropic fluid theory, in particular, the anisotropic derivative nonlinear-Schrödinger-Burgers equation, with an intuitive model of the energy closure for the downstream counter-streaming ions. The anisotropy value of 0.25 is significant because it is closely related to the degeneracy point of the slow and intermediate modes and corresponds to the lower bound of the coplanar to non-coplanar transition that occurs inside a compound slow shock (SS)/rotational discontinuity (RD) wave. This work implies that it is a pair of compound SS/RD waves that bound the outflows in magnetic reconnection, instead of a pair of switch-off slow shocks as in Petschek's model. This fact might explain the rareness of in-situ observations of Petschek-reconnection-associated switch-off slow shocks.
Faganello, M; Califano, F; Pegoraro, F
2008-09-01
We give evidence for the first time of the onset of undriven fast, collisionless magnetic reconnection during the evolution of an initially homogeneous magnetic field advected in a sheared velocity field. We consider the interaction of the solar wind with the magnetospheric plasma at low latitude and show that reconnection takes place in the layer between adjacent vortices generated by the Kelvin-Helmholtz instability. This process generates coherent magnetic structures with a size comparable to the ion inertial scale, much smaller than the system dimensions but much larger than the electron inertial scale. These magnetic structures are further advected in the plasma in a complex pattern but remain stable over a time interval much longer than their formation time. These results can be crucial for the interpretation of satellite data showing coherent magnetic structures in the Earth's magnetosheath or the magnetotail. PMID:18851219
Fast magnetic reconnection due to anisotropic electron pressure
NASA Astrophysics Data System (ADS)
Cassak, Paul; Baylor, Robert; Fermo, Raymond; Beidler, Matthew; Shay, Michael; Swisdak, Marc; Drake, James; Karimabadi, Homa
2015-11-01
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.
Fast magnetic reconnection due to anisotropic electron pressure
NASA Astrophysics Data System (ADS)
Cassak, P. A.; Baylor, R. N.; Fermo, R. L.; Beidler, M. T.; Shay, M. A.; Swisdak, M.; Drake, J. F.; Karimabadi, H.
2015-02-01
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.
Fast magnetic reconnection due to anisotropic electron pressure
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.
NASA Astrophysics Data System (ADS)
Melzani, Mickaël; Walder, Rolf; Folini, Doris; Winisdoerffer, Christophe; Favre, Jean M.
2014-10-01
Magnetic reconnection is a leading mechanism for magnetic energy conversion and high-energy non-thermal particle production in a variety of high-energy astrophysical objects, including ones with relativistic ion-electron plasmas (e.g., microquasars or AGNs), a regime where first principle studies are scarce. We present 2D particle-in-cell (PIC) simulations of low β ion-electron plasmas under relativistic conditions, i.e., with inflow magnetic energy exceeding the plasma restmass energy. We identify outstanding properties: (i) For relativistic inflow magnetizations (here 10 ≤ σe ≤ 360), the reconnection outflows are dominated by thermal agitation instead of bulk kinetic energy. (ii) At high inflow electron magnetization (σe ≥ 80), the reconnection electric field is sustained more by bulk inertia than by thermal inertia. It challenges the thermal-inertia paradigm and its implications. (iii) The inflows feature sharp transitions at the entrance of the diffusion zones. These are not shocks but results from particle ballistic motions, all bouncing at the same location, provided that the thermal velocity in the inflow is far lower than the inflow E × B bulk velocity. (iv) Island centers are magnetically isolated from the rest of the flow and can present a density depletion at their center. (v) The reconnection rates are slightly higher than in non-relativistic studies. They are best normalized by the inflow relativistic Alfvén speed projected in the outflow direction, which then leads to rates in a close range (0.14-0.25), thus allowing for an easy estimation of the reconnection electric field.
NASA Astrophysics Data System (ADS)
Zelenyi, Lev M.; Artemyev, Anton V.
2016-02-01
In this paper we revisit the paradigm of space science turbulent dissipation traditionally considered as myth (Coroniti, Space Sci. Rev., vol. 42, 1985, pp. 399-410). We demonstrate that due to approach introduced by Pitaevskii (Sov. J. Expl Theor. Phys., vol. 44, 1963, pp. 969-979 (in Russian)) (the effect of a finite Larmor radius on a classical collision integral) dissipation induced by effective interaction with microturbulence produces a significant effect on plasma dynamics, especially in the vicinity of the reconnection region. We estimate the multiplication factor of collision frequency in the collision integral for short wavelength perturbations. For waves propagating transverse to the background magnetic field, this factor is approximately ρekx)2 an electron gyroradius and where kx a transverse wavenumber. We consider recent spacecraft observations in the Earth's magnetotail reconnection region to the estimate possible impact of this multiplication factor. For small-scale reconnection regions this factor can significantly increase the effective collision frequency produced both by lower-hybrid drift turbulence and by kinetic Alfvén waves. We discuss the possibility that the Pitaevskii's effect may be responsible for the excitation of a resistive electron tearing mode in thin current sheets formed in the outflow region of the primary X-line.
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.
Fast magnetic reconnection with plasmoid / current sheet ejection events in laboratory experiments
NASA Astrophysics Data System (ADS)
Inomoto, Michiaki; Ono, Yasushi; Hayashi, Yoshinori
2012-07-01
Non-steady and fast magnetic reconnections due to plasmoid or current sheet ejection events have been investigated in laboratory experiments using TS-3, TS-4 and UTST plasma merging devices in the University of Tokyo. In these devices, magnetic reconnection is induced by two different schemes, a) push reconnection driven by flux injection from the upstream region, b) pull reconnection driven by flux extraction to the downstream region. Current sheet or plasmoid ejection events are observed in these reconnection experiments particularly with strong guide magnetic field parallel to the reconnection electric field. In push reconnection experiments, anomalous resistivity is induced by the ion's kinetic effect (meandering motion) when the current sheet width is compressed shorter than the ion gyroradius by the strongly injected inflow flux. This fast reconnection regime does not involve plasmoid / current sheet ejection events. On the other hand, the guide field reduces the ion gyroradius and suppresses the onset of the anomalous resistivity, providing slow and steady magnetic reconnection. Impulsive fast reconnection with strong guide field develops, nevertheless, due to plasmoid / current sheet ejection events in pull and push reconnection experiments with extremely large external driving forces. In such a situation, the inflow flux is forcedly pushed into the reconnection region even faster than the maximal reconnection rate, resulting in flux pile up in front of the diffusion region. This piled flux induces large current density inside the current sheet in which plasmoid structure with closed flux surface is formed in pull reconnection case. The induced large current density or plasmoid is then ejected from the diffusion region with significant increase of reconnection electric field. As a result, magnetic reconnection condition with even larger reconnection rate than that obtained by anomalous resistivity was achieved under strong guide field and large external
Models of coronal heating, turbulence and fast reconnection.
Velli, M; Pucci, F; Rappazzo, F; Tenerani, A
2015-05-28
Coronal heating is at the origin of the EUV and X-ray emission and mass loss from the sun and many other stars. While different scenarios have been proposed to explain the heating of magnetically confined and open regions of the corona, they must all rely on the transfer, storage and dissipation of the abundant energy present in photospheric motions, which, coupled to magnetic fields, give rise to the complex phenomenology seen at the chromosphere and transition region (i.e. spicules, jets, 'tornadoes'). Here we discuss models and numerical simulations which rely on magnetic fields and electric currents both for energy transfer and for storage in the corona. We will revisit the sources and frequency spectrum of kinetic and electromagnetic energies, the role of boundary conditions, and the routes to small scales required for effective dissipation. Because reconnection in current sheets has been, and still is, one of the most important processes for coronal heating, we will also discuss recent aspects concerning the triggering of reconnection instabilities and the transition to fast reconnection. PMID:25897086
Models of coronal heating, turbulence and fast reconnection
NASA Astrophysics Data System (ADS)
Velli, M.; Pucci, F.; Rappazzo, F.; Tenerani, A.
2015-04-01
Coronal heating is at the origin of the EUV and X-ray emission and mass loss from the sun and many other stars. While different scenarios have been proposed to explain the heating of magnetically confined and open regions of the corona, they must all rely on the transfer, storage and dissipation of the abundant energy present in photospheric motions, which, coupled to magnetic fields, give rise to the complex phenomenology seen at the chromosphere and transition region (i.e. spicules, jets, 'tornadoes'). Here we discuss models and numerical simulations which rely on magnetic fields and electric currents both for energy transfer and for storage in the corona. We will revisit the sources and frequency spectrum of kinetic and electromagnetic energies, the role of boundary conditions, and the routes to small scales required for effective dissipation. Because reconnection in current sheets has been, and still is, one of the most important processes for coronal heating, we will also discuss recent aspects concerning the triggering of reconnection instabilities and the transition to fast reconnection.
NASA Astrophysics Data System (ADS)
Innocenti, Maria Elena; Lapenta, Giovanni; Goldman, Martin; Newman, David; Markidis, Stefano
2015-04-01
In Petschek's model for magnetic reconnection, switch-off (SO) condition is achieved through back-to-back slow mode shocks (SS). No rotational discontinuity (RD) is needed, unless in specific cases detailed in [Vasyliunas 1975]. Decades of simulations with different models (MHD, Hall MHD, hybrid, PIC) have yielded contradictory results regarding the achievement of the SO condition during magnetic reconnection events. It has been recently argued that the formation of Petschek's SO-SS is inhibited by the development of the firehose instability, which provokes the flapping of the magnetic field in the reconnection exhausts (Liu et al., 2012). We report here on the formation of localized switch-off areas in simulations of collisionless magnetic reconnection in extremely large domains (hundreds of ion skin depths) for extremely long times (hundreds of inverse ion cyclotron frequency). A guide field (a magnetic field in the direction perpendicular to the reconnection plane) prevents the development of the firehose instability. The switch-off areas are marked by magnetic field line bending (in a way closely resembling the textbook description of RDs), by the formation of a nozzle-like structure in the in-plane projection of the ion and electron velocities perpendicular to the magnetic field direction and by a reduced rate of plasmoid formation. We use Rankine-Hugoniot conditions to characterize the transitions as Rotational Discontinuities and we comment on their origin. Priest, E. and Forbes, T. (2007). Magnetic reconnection. Magnetic Reconnection, by Eric Priest, Terry Forbes, Cambridge, UK: Cambridge University Press, 2007, 1. Vasyliunas V. (1975). Theoretical models of magnetic field line merging. Review of Geophysics and Space Phsyics, 1975. Liu, Y.-H., Drake, J. F., and Swisdak, M. (2012). The structure of the magnetic reconnection exhaust boundary. Physics of Plasmas (1994-present), 19(2):-.
Fast reconnection in relativistic plasmas: the magnetohydrodynamics tearing instability revisited
NASA Astrophysics Data System (ADS)
Del Zanna, L.; Papini, E.; Landi, S.; Bugli, M.; Bucciantini, N.
2016-08-01
Fast reconnection operating in magnetically dominated plasmas is often invoked in models for magnetar giant flares, for magnetic dissipation in pulsar winds, or to explain the gamma-ray flares observed in the Crab nebula, hence its investigation is of paramount importance in high-energy astrophysics. Here we study, by means of two dimensional numerical simulations, the linear phase and the subsequent nonlinear evolution of the tearing instability within the framework of relativistic resistive magnetohydrodynamics, as appropriate in situations where the Alfven velocity approaches the speed of light. It is found that the linear phase of the instability closely matches the analysis in classical MHD, where the growth rate scales with the Lundquist number S as S^-1/2, with the only exception of an enhanced inertial term due to the thermal and magnetic energy contributions. In addition, when thin current sheets of inverse aspect ratio scaling as S^-1/3 are considered, the so-called "ideal" tearing regime is retrieved, with modes growing independently on S and extremely fast, on only a few light crossing times of the sheet length. The overall growth of fluctuations is seen to solely depend on the value of the background Alfven velocity. In the fully nonlinear stage we observe an inverse cascade towards the fundamental mode, with Petschek-type supersonic jets propagating at the external Alfven speed from the X-point, and a fast reconnection rate at the predicted value R~(ln S)^-1.
Characteristics of a current sheet shear mode in collisionless magnetic reconnection
NASA Astrophysics Data System (ADS)
Fujimoto, Keizo
2016-05-01
The current study shows the characteristics of the kink-type electromagnetic mode excited in the thin current layer formed around the x-line during the quasi-steady phase of magnetic reconnection. The linear wave analyses are carried out for the realistic current sheet profile which differs significantly from the Harris current sheet. It is found that the peak growth rate is very sensitive to the current sheet width even though the relative drift velocity at the center of the current sheet is fixed. This indicates that the mode is excited by the velocity shear rather than the relative drift velocity. Thus, the mode is termed here a current sheet shear mode. It is also shown that the wavenumber ky has a clear mass ratio dependency as ky λi ∝ (mi /me )1/4, implying the coupling of the ion and electron dynamics, where λi is the ion inertia length.
NASA Astrophysics Data System (ADS)
Scudder, J. D.; Daughton, W.; Karimabadi, H.
2006-12-01
Many researchers are "looking" for "the" electron diffusion region layers with in situ data. Some publish papers about the statistics of such regions operationally "defined" to be electron diffusion regions, pending contradiction. Theorists also use a variety of recipes to identify diffusion regions in their numerical simulations. For example, some would say that the electron diffusion region is wherever E ≠ -U_e×B where U_e is the electron fluid velocity. Others in the "diffusion region hunt" identify the (ion) "diffusion region" as a proxy for the detection of the "electron diffusion region", in spite of the fact that any current carrying layer in space is an "ion diffusion region", whether it is attached to the reconnection site or not! Some observationalists insist that E∥ \
Global Extended MHD Studies of Fast Magnetic Reconnection
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.
Fast reconnection in relativistic plasmas: the magnetohydrodynamics tearing instability revisited
NASA Astrophysics Data System (ADS)
Del Zanna, L.; Papini, E.; Landi, S.; Bugli, M.; Bucciantini, N.
2016-08-01
Fast reconnection operating in magnetically dominated plasmas is often invoked in models for magnetar giant flares, for magnetic dissipation in pulsar winds, or to explain the gamma-ray flares observed in the Crab nebula; hence, its investigation is of paramount importance in high-energy astrophysics. Here we study, by means of two-dimensional numerical simulations, the linear phase and the subsequent non-linear evolution of the tearing instability within the framework of relativistic resistive magnetohydrodynamics (MHD), as appropriate in situations where the Alfvén velocity approaches the speed of light. It is found that the linear phase of the instability closely matches the analysis in classical MHD, where the growth rate scales with the Lundquist number S as S-1/2, with the only exception of an enhanced inertial term due to the thermal and magnetic energy contributions. In addition, when thin current sheets of inverse aspect ratio scaling as S-1/3 are considered, the so-called ideal tearing regime is retrieved, with modes growing independently of S and extremely fast, on only a few light crossing times of the sheet length. The overall growth of fluctuations is seen to solely depend on the value of the background Alfvén velocity. In the fully non-linear stage, we observe an inverse cascade towards the fundamental mode, with Petschek-type supersonic jets propagating at the external Alfvén speed from the X-point, and a fast reconnection rate at the predicted value {R}˜ (ln S)^{-1}.
Three-dimensional fast magnetic reconnection driven by relativistic ultraintense femtosecond lasers.
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. PMID:24730781
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.
Fast magnetic reconnection supported by sporadic small-scale Petschek-type shocks
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.
PARTICLE ACCELERATION DURING MAGNETOROTATIONAL INSTABILITY IN A COLLISIONLESS ACCRETION DISK
Hoshino, Masahiro
2013-08-20
Particle acceleration during the magnetorotational instability (MRI) in a collisionless accretion disk was investigated by using a particle-in-cell simulation. We discuss the important role that magnetic reconnection plays not only on the saturation of MRI but also on the relativistic particle generation. The plasma pressure anisotropy of p > p{sub ||} induced by the action of MRI dynamo leads to rapid growth in magnetic reconnection, resulting in the fast generation of nonthermal particles with a hard power-law spectrum. This efficient particle acceleration mechanism involved in a collisionless accretion disk may be a possible model to explain the origin of high-energy particles observed around massive black holes.
Fast magnetic reconnection in low-density electron-positron plasmas
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.
Comparison of Secondary Islands in Collisional Reconnection to Hall Reconnection
Shepherd, L. S.; Cassak, P. A.
2010-07-02
Large-scale resistive Hall-magnetohydrodynamic simulations of the transition from Sweet-Parker (collisional) to Hall (collisionless) magnetic reconnection are presented; the first to separate secondary islands from collisionless effects. Three main results are described. There exists a regime with secondary islands but without collisionless effects, and the reconnection rate is faster than Sweet-Parker, but significantly slower than Hall reconnection. This implies that secondary islands do not cause the fastest reconnection rates. The onset of Hall reconnection ejects secondary islands from the vicinity of the X line, implying that energy is released more rapidly during Hall reconnection. Coronal applications are discussed.
Direct evidence for kinetic effects associated with solar wind reconnection.
Xu, Xiaojun; Wang, Yi; Wei, Fengsi; Feng, Xueshang; Deng, Xiaohua; Ma, Yonghui; Zhou, Meng; Pang, Ye; Wong, Hon-Cheng
2015-01-01
Kinetic effects resulting from the two-fluid physics play a crucial role in the fast collisionless reconnection, which is a process to explosively release massive energy stored in magnetic fields in space and astrophysical plasmas. In-situ observations in the Earth's magnetosphere provide solid consistence with theoretical models on the point that kinetic effects are required in the collisionless reconnection. However, all the observations associated with solar wind reconnection have been analyzed in the context of magnetohydrodynamics (MHD) although a lot of solar wind reconnection exhausts have been reported. Because of the absence of kinetic effects and substantial heating, whether the reconnections are still ongoing when they are detected in the solar wind remains unknown. Here, by dual-spacecraft observations, we report a solar wind reconnection with clear Hall magnetic fields. Its corresponding Alfvenic electron outflow jet, derived from the decouple between ions and electrons, is identified, showing direct evidence for kinetic effects that dominate the collisionless reconnection. The turbulence associated with the exhaust is a kind of background solar wind turbulence, implying that the reconnection generated turbulence has not much developed. PMID:25628139
Direct evidence for kinetic effects associated with solar wind reconnection
Xu, Xiaojun; Wang, Yi; Wei, Fengsi; Feng, Xueshang; Deng, Xiaohua; Ma, Yonghui; Zhou, Meng; Pang, Ye; Wong, Hon-Cheng
2015-01-01
Kinetic effects resulting from the two-fluid physics play a crucial role in the fast collisionless reconnection, which is a process to explosively release massive energy stored in magnetic fields in space and astrophysical plasmas. In-situ observations in the Earth's magnetosphere provide solid consistence with theoretical models on the point that kinetic effects are required in the collisionless reconnection. However, all the observations associated with solar wind reconnection have been analyzed in the context of magnetohydrodynamics (MHD) although a lot of solar wind reconnection exhausts have been reported. Because of the absence of kinetic effects and substantial heating, whether the reconnections are still ongoing when they are detected in the solar wind remains unknown. Here, by dual-spacecraft observations, we report a solar wind reconnection with clear Hall magnetic fields. Its corresponding Alfvenic electron outflow jet, derived from the decouple between ions and electrons, is identified, showing direct evidence for kinetic effects that dominate the collisionless reconnection. The turbulence associated with the exhaust is a kind of background solar wind turbulence, implying that the reconnection generated turbulence has not much developed. PMID:25628139
Zhou, Fushun; Huang, Can Lu, Quanming; Wang, Shui; Xie, Jinlin
2015-09-15
Two-dimensional particle-in-cell simulation is performed to investigate magnetic reconnection in a force-free current sheet. The results show that the evolution of the ion diffusion region has two different phases. In the first phase, the electrons flow toward the X line along one pair of separatrices and away from the X line along the other pair of separatrices. Therefore, in the ion diffusion region, a distorted quadrupole structure of the out-of-plane magnetic field is formed, which is similar to that of a typical guide field reconnection in the Harris current sheet. In the second phase, the electrons move toward the X line along the separatrices and then flow away from the X line at the inner side of the separatrices. In the ion diffusion region, the out-of-plane magnetic field exhibits a characteristic quadrupole pattern with a good symmetry, which is similar to that of antiparallel reconnection in the Harris current sheet.
On the noncoplanarity of the magnetic field within a fast collisionless shock
NASA Technical Reports Server (NTRS)
Thomsen, M. F.; Gosling, J. T.; Bame, S. J.; Quest, K. B.; Winske, D.
1987-01-01
Within the magnetic ramp of fast collisionless plasma shocks observed with spacecraft instruments and simulated numerically, the magnetic field undergoes an excursion out of the plane of coplanarity. This rotation is consistently in the direction such that the electrostatic potential jump across the shock, as measured in the de Hoffman-Teller frame of the reference (HTF), is about 2-6 times smaller than the electrostatic potential jump measured in the normal incidence frame. The preferred direction is consistent with a basic whistler mode transition between the upstream and downstream orientations. The potential jump in the HTF is considerably smaller than the change in bulk flow energy across the shock, confirming the recent suggestion that magnetic forces contribute importantly to the slowing of the plasma in that frame. A further consequence is that suprathermal particles leaking back into the upstream region across the shock do not gain much energy from the cross-shock electric field.
Scudder, Jack
2011-02-04
The final years of this grant have been dedicated to diagnosing the observable properties of Collisionless Magnetic Reconnection (CMR) as disclosed by the open boundary condition PIC simulations developed under this grant. Particular attention has focussed on identifying the Electron Diffusion Region (EDR), the short scale domain where the process is thought to be enabled. The critical issue has been the need for experimental closure for CMR that is widely invoked in astrophysics, but has actually rather little direct, incontrovertible evidence for its involvement. This difficulty arises because CMR is about topology change of the magnetic field - a concept that is not conducive to single, or even few point correlations as are beginning to be possible with spacecraft armada, like Cluster or the planned Magnetospheric Multi-Scale (MMS) mission to be launched in 2014. Alternate formulations about the time rate of magnetic flux inventoried by a moving observer, reformulate the needed evidence in terms of the curl of various weak vector fields, such as E+UexB, that is zero in ideal MHD. To sense E+UexB from space measurements is already a heroic task. The curl of such a small vector field is outside the domain of the possible.
ON THE ROLE OF FAST MAGNETIC RECONNECTION IN ACCRETING BLACK HOLE SOURCES
Singh, C. B.; De Gouveia Dal Pino, E. M.; Kadowaki, L. H. S. E-mail: dalpino@iag.usp.br
2015-01-30
We attempt to explain the observed radio and gamma-ray emission produced in the surroundings of black holes by employing a magnetically dominated accretion flow model and fast magnetic reconnection triggered by turbulence. In earlier work, a standard disk model was used and we refine the model by focusing on the sub-Eddington regime to address the fundamental plane of black hole activity. The results do not change substantially with regard to previous work, ensuring that the details of accretion physics are not relevant in the magnetic reconnection process occurring in the corona. Rather, our work puts fast magnetic reconnection events as a powerful mechanism operating in the core region near the jet base of black hole sources on more solid ground. For microquasars and low-luminosity active galactic nuclei, the observed correlation between radio emission and the mass of the sources can be explained by this process. The corresponding gamma-ray emission also seems to be produced in the same core region. On the other hand, emission from blazars and gamma-ray bursts cannot be correlated to core emission based on fast reconnection.
NASA Astrophysics Data System (ADS)
Shimizu, Tohru; Torii, Hiroyuki; Kondoh, Koji
2016-05-01
The 3D instability of spontaneous fast magnetic reconnection process is studied with magnetohydrodynamic simulations, where 2D model of the spontaneous fast magnetic reconnection process is destabilized in three dimensions. In this 3D instability, the spontaneous fast magnetic reconnection process is intermittently and randomly caused in 3D. In this paper, as a typical event study, a single 3D fast magnetic reconnection process often observed in the 3D instability is studied in detail. As a remarkable feature, it is reported that, when the 3D fast magnetic reconnection process starts, plasma inflows along the magnetic neutral line are observed, which are driven by plasma static pressure gradient along the neutral line. The plasma inflow speed reaches about 15 in the upstream field region. The unmagnetized inflow tends to prevent the 3D reconnection process; nevertheless, the 3D reconnection process is intermittently maintained. Such high-speed plasma inflows along the neutral line may be observed as dawn-dusk flows in space satellite observations of magnetotail's bursty bulk flows.
Fast Reconnection Rates Based on Group Velocity Cones: Whistler Regime and Pair Plasmas
NASA Astrophysics Data System (ADS)
Singh, N.
2009-05-01
Based on the group velocity vector of the whistler mode, we predict the range of whistler-regime reconnection rate depending on the half width (w) of the current sheet (CS. During the reconnection process electromagnetic perturbations (EMPs) are generated in the localized diffusion region (DR, which acts like an antenna and radiates whistler waves for certain range of CS widths. The reconnection structure (exhaust) is approximately the radiation pattern of the DR antenna and it is determined by the group velocity directions. Since the whistler waves originate from the electromagnetic perturbations (EMPs) localized in the DR, we calculate R over a range of the discrete values of the perpendicular wave number (k'') contained in the Fourier spectrum of the EMPs. We have used such calculations to determine the reconnection rates
Ugai, M.
2009-11-15
It is well known that magnetic pulsations of long periods impulsively occur in accordance with the sudden onset of geomagnetic substorms and drastic enhancement of electrojets in the ionosphere. On the basis of the spontaneous fast reconnection model, the present paper examines the physical mechanism by which both magnetic pulsations and strong electrojets are impulsively driven by the fast (Alfvenic) reconnection jet. When a large-scale plasmoid [or traveling compression region (TCR)], directly caused by the fast reconnection jet, collides with the magnetic loop footpoint, strong electrojets are impulsively driven in a finite extent in the loop footpoint in accordance with the evolution of the current wedge and the generator current circuit. Simultaneously, magnetohydrodynamic (Alfven) waves, accompanied by the TCR, are reflected from the electrojet layer, leading to impulsive magnetic pulsations ahead of the loop footpoint because of the interaction (or resonance) between the reflected waves and the waves traveling toward the footpoint. The pulsations propagate outward in all directions from the source region of the wave reflection, and the pulsation periods are typically estimated to be of several tens of seconds.
Fast-shock formation in line-tied magnetic reconnection models of solar flares
NASA Technical Reports Server (NTRS)
Forbes, T. G.
1986-01-01
In a previous study by the author, an approximately stationary fast shock was tentatively identified in a numerical experiment designed to study line-tied magnetic reconnection. Here the evidence for the occurrence of a stationary fast shock is reexamined, and the previous identification is confirmed. In the numerical experiment, line-tied reconnection is modeled by a configuration which produces two supermagnetosonic outflow jets - one directed upward, away from the photosphere, and one directed downward, toward an arcade of closed magnetic loops tied to the photosphere. The fast shock occurs when the downward-directed jet encounters the obstacle formed by the closed loops. Although the existence of a stationary, or nearly stationary, fast shock is confirmed, the transition from the supermagnetosonic flow region upstream of the shock to the nearly static region downstream of the shock is more complicated than was previously thought. Immediately downstream of the shock, there exists a deflection sheath in which the submagnetosonic flow coming out of the shock is diverted around the region of static closed loops. The MHD jump conditions are used to investigate the characteristics of the fast shock and to show that a stationary shock cannot exist unless accompanied by a deflection sheath. Analysis of the shock's location and dimensions suggests that such fast shocks may contribute to particle acceleration and to thermal condensation in flares.
FAST MAGNETIC RECONNECTION IN THE SOLAR CHROMOSPHERE MEDIATED BY THE PLASMOID INSTABILITY
Ni, Lei; Kliem, Bernhard; Lin, Jun; Wu, Ning
2015-01-20
Magnetic reconnection in the partially ionized solar chromosphere is studied in 2.5 dimensional magnetohydrodynamic simulations including radiative cooling and ambipolar diffusion. A Harris current sheet with and without a guide field is considered. Characteristic values of the parameters in the middle chromosphere imply a high magnetic Reynolds number of ∼10{sup 6}-10{sup 7} in the present simulations. Fast magnetic reconnection then develops as a consequence of the plasmoid instability without the need to invoke anomalous resistivity enhancements. Multiple levels of the instability are followed as it cascades to smaller scales, which approach the ion inertial length. The reconnection rate, normalized to the asymptotic values of magnetic field and Alfvén velocity in the inflow region, reaches values in the range ∼0.01-0.03 throughout the cascading plasmoid formation and for zero as well as for strong guide field. The outflow velocity reaches ≈40 km s{sup –1}. Slow-mode shocks extend from the X-points, heating the plasmoids up to ∼8 × 10{sup 4} K. In the case of zero guide field, the inclusion of both ambipolar diffusion and radiative cooling causes a rapid thinning of the current sheet (down to ∼30 m) and early formation of secondary islands. Both of these processes have very little effect on the plasmoid instability for a strong guide field. The reconnection rates, temperature enhancements, and upward outflow velocities from the vertical current sheet correspond well to their characteristic values in chromospheric jets.
Bessho, Naoki; Bhattacharjee, A.
2012-05-10
Magnetic reconnection and particle acceleration in relativistic Harris sheets in low-density electron-positron plasmas with no guide field have been studied by means of two-dimensional particle-in-cell simulations. Reconnection rates are of the order of one when the background density in a Harris sheet is of the order of 1% of the density in the current sheet, which is consistent with previous results in the non-relativistic regime. It has been demonstrated that the increase of the Lorentz factors of accelerated particles significantly enhances the collisionless resistivity needed to sustain a large reconnection electric field. It is shown analytically and numerically that the energy spectrum of accelerated particles near the X-line is the product of a power law and an exponential function of energy, {gamma}{sup -1/4}exp (- a{gamma}{sup 1/2}), where {gamma} is the Lorentz factor and a is a constant. However, in the low-density regime, while the most energetic particles are produced near X-lines, many more particles are energized within magnetic islands. Particles are energized in contracting islands by multiple reflection, but the mechanism is different from Fermi acceleration in magnetic islands for magnetized particles in the presence of a guide field. In magnetic islands, strong core fields are generated and plasma beta values are reduced. As a consequence, the fire-hose instability condition is not satisfied in most of the island region, and island contraction and particle acceleration can continue. In island coalescence, reconnection between two islands can accelerate some particles, however, many particles are decelerated and cooled, which is contrary to what has been discussed in the literature on particle acceleration due to reconnection in non-relativistic hydrogen plasmas.
Experimental Study of Lower-hybrid Drift Turbulence in a Reconnecting Current Sheet
Carter, T. A.; Yamada, M.; Ji, H.; Kulsrud, R. M.; Trintchouck, F.
2002-06-18
The role of turbulence in the process of magnetic reconnection has been the subject of a great deal of study and debate in the theoretical literature. At issue in this debate is whether turbulence is essential for fast magnetic reconnection to occur in collisionless current sheets. Some theories claim it is necessary in order to provide anomalous resistivity, while others present a laminar fast reconnection mechanism based on the Hall term in the generalized Ohm's law. In this work, a thorough study of electrostatic potential fluctuations in the current sheet of the Magnetic Reconnection Experiment (MRX) [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)] was performed in order to ascertain the importance of turbulence in a laboratory reconnection experiment. Using amplified floating Langmuir probes, broadband fluctuations in the lower hybrid frequency range (fLH approximately 5-15 MHz) were measured which arise with the formation of the current sheet in MRX. The frequency spectrum, spatial amplitude profile, and spatial correlation characteristics of the measured turbulence were examined carefully, finding consistency with theories of the lower-hybrid drift instability (LHDI). The LHDI and its role in magnetic reconnection has been studied theoretically for decades, but this work represents the first detection and detailed study of the LHDI in a laboratory current sheet. The observation of the LHDI in MRX has provided the unique opportunity to uncover the role of this instability in collisionless reconnection. It was found that: (1) the LHDI fluctuations are confined to the low-beta edge of current sheets in MRX; (2) the LHDI amplitude does not correlate well in time or space with the reconnection electric field, which is directly related to the rate of reconnection; and (3) significant LHDI amplitude persists in high collisionality current sheets where the reconnection rate is classical. These findings suggest that the measured LHDI fluctuations do not play an
Dissipation mechanism in 3D magnetic reconnection
Fujimoto, Keizo
2011-11-15
Dissipation processes responsible for fast magnetic reconnection in collisionless plasmas are investigated using 3D electromagnetic particle-in-cell simulations. The present study revisits the two simulation runs performed in the previous study (Fujimoto, Phys. Plasmas 16, 042103 (2009)); one with small system size in the current density direction, and the other with larger system size. In the case with small system size, the reconnection processes are almost the same as those in 2D reconnection, while in the other case a kink mode evolves along the current density and deforms the current sheet structure drastically. Although fast reconnection is achieved in both the cases, the dissipation mechanism is very different between them. In the case without kink mode, the electrons transit the electron diffusion region without thermalization, so that the magnetic dissipation is supported by the inertia resistivity alone. On the other hand, in the kinked current sheet, the electrons are not only accelerated in bulk, but they are also partly scattered and thermalized by the kink mode, which results in the anomalous resistivity in addition to the inertia resistivity. It is demonstrated that in 3D reconnection the thickness of the electron current sheet becomes larger than the local electron inertia length, consistent with the theoretical prediction in Fujimoto and Sydora (Phys. Plasmas 16, 112309 (2009)).
NASA Astrophysics Data System (ADS)
Chai, Kil-Byoung; Zhai, Xiang; Bellan, Paul M.
2016-03-01
A spatially localized energetic extreme ultra-violet (EUV) burst is imaged at the presumed position of fast magnetic reconnection in a plasma jet produced by a coaxial helicity injection source; this EUV burst indicates strong localized electron heating. A circularly polarized high frequency magnetic field perturbation is simultaneously observed at some distance from the reconnection region indicating that the reconnection emits whistler waves and that Hall dynamics likely governs the reconnection. Spectroscopic measurement shows simultaneous fast ion heating. The electron heating is consistent with Ohmic dissipation, while the ion heating is consistent with ion trajectories becoming stochastic.
Does the resistive tearing instability nonlinearly evolve to a fast reconnection mode
NASA Technical Reports Server (NTRS)
Steinolfson, R. S.
1988-01-01
A fundamental problem in applying linear tearing instability theory to the rapid processes (particle acceleration, heating) in flares was the characteristically slow rate of reconnection. This problem can be at least partially overcome if the tearin mode nonlinearly evolves to a regime in which the reconnection rate is substantially enhanced, such as that for the Petschek configuration. This possibility was often suggested, and some numerical simulations appear to provide support for such a view. Numerical simulation are used to study the nonlinear evolution of the tearing stability and show that a fast Petschek-like regime may not be achieved. This conclusion follows when there are sufficient grid points within the diffusion region to completely resolve the nonlinear dynamic interactions in the diffusion layer. When the numerical resolution is not adequate, the solution does appear to approach a Petschek configuration. The resolved solution contains reverse flow vortices and current sheets, terminated with a current reversal, similar to those obtained by Syrovatsky (JEPT, 33, 933, 1971).
NASA Astrophysics Data System (ADS)
Chai, Kil-Byoung; Zhai, Xiang; Bellan, Paul
2015-11-01
The Caltech astrophysical jet experiment provides a highly resolved demonstration of the interaction between single fluid and 2-fluid scales and possibly kinetic scales as well. The jet evolves through the following sequence: (i) a current-carrying MHD-driven plasma jet self-forms, (ii) the jet undergoes a kink instability, (iii) the kink provides the environment for a secondary, Rayleigh-Taylor (RT) instability, (iv) the RT instability erodes the current channel radius to a scale smaller than ion skin depth to cause fast magnetic reconnection, (v) the reconnection emits broadband obliquely-propagating, right-hand circularly polarized whistler waves, and (vi) the reconnection energizes electrons and ions. The observation of the whistler waves confirms that the reconnection is in the Hall MHD regime (i.e., 2-fluid). An energetic extreme ultraviolet burst is observed at the location of reconnection indicating strong, localized electron heating. Spectroscopic measurement shows simultaneous fast ion heating. The analysis shows that electrons are plausibly heated by Ohmic dissipation, and that ions are plausibly heated stochastically, i.e., the guiding center approximation fails, a kinetic effect.
Magnetic reconnection in the presence of externally driven and self-generated turbulence
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
Explosive turbulent magnetic reconnection.
Higashimori, K; Yokoi, N; Hoshino, M
2013-06-21
We report simulation results for turbulent magnetic reconnection obtained using a newly developed Reynolds-averaged magnetohydrodynamics model. We find that the initial Harris current sheet develops in three ways, depending on the strength of turbulence: laminar reconnection, turbulent reconnection, and turbulent diffusion. The turbulent reconnection explosively converts the magnetic field energy into both kinetic and thermal energy of plasmas, and generates open fast reconnection jets. This fast turbulent reconnection is achieved by the localization of turbulent diffusion. Additionally, localized structure forms through the interaction of the mean field and turbulence. PMID:23829741
NASA Astrophysics Data System (ADS)
Graf von der Pahlen, J.; Tsiklauri, D.
2015-12-01
Magnetic X-point collapse is investigated using a 2.5D fully relativistic particle-in-cell simulation, with varying strengths of guide-field as well as open and closed boundary conditions. In the zero guide-field case we discover a new signature of Hall-reconnection in the out-of-plane magnetic field, namely an octupolar pattern, as opposed to the well-studied quadrupolar out-of-plane field of reconnection. The emergence of the octupolar components was found to be caused by ion currents and is a general feature of X-point collapse. In a comparative study of tearing-mode reconnection, signatures of octupolar components are found only in the out-flow region. It is argued that space-craft observations of magnetic fields at reconnection sites may be used accordingly to identify the type of reconnection [1][2]. Further, initial oscillatory reconnection is observed, prior to reconnection onset, generating electro-magnetic waves at the upper-hybrid frequency, matching solar flare progenitor emission. When applying a guide-field, in both open and closed boundary conditions, thinner dissipation regions are obtained and the onset of reconnection is increasingly delayed. Investigations with open boundary conditions show that, for guide-fields close to the strength of the in-plane field, shear flows emerge, leading to the formation of electron flow vortices and magnetic islands [3]. Asymmetries in the components of the generalised Ohm's law across the dissipation region are observed. Extended in 3D geometry, it is shown that locations of magnetic islands and vortices are not constant along the height of the current-sheet. Vortices formed on opposite sites of the current-sheet travel in opposite directions along it, leading to a criss-cross vortex pattern. Possible instabilities resulting from this specific structure formation are to be investigated [4].[1] J. Graf von der Pahlen and D. Tsiklauri, Phys. Plasmas 21, 060705 (2014), [2] J. Graf von der Pahlen and D. Tsiklauri
NASA Astrophysics Data System (ADS)
Cheng, Chio Z.; Ono, Yasushi; Yang, Ya-Hui; Choe, Gwangson
2012-10-01
Impulsively fast magnetic reconnection has been shown to be the major mechanism responsible for explosive flare non-thermal energy release and acceleration of coronal mass ejection (CME) motion. It has been observed that for most large solar flares non-thermal emissions in hard X-rays (HXR) and millimeter/submillimeter waves impulsively rise and decade during the soft X-ray (SXR) emission rise phase. Moreover, the filament/CME upward motion is accelerated temporally in correlation with the impulsive enhancement of flare non-thermal emission and reconnection electric field in the current sheet in both simulations and observations. The peak reconnection electric field during flare impulsive phase is on the order of a few kV/m for X-class flares. Here, we demonstrated for the first time in laboratory plasma merging experiments the correlation of the magnetic reconnection rate with the acceleration of plasmoid ejected from the current sheet using the TS-4 device of the Tokyo University. Moreover, we have also found that the electron heating occurs in the current sheet and the ion heating occurs in the down-stream outflow region. Thus, we conclude that the plasmoid/CME acceleration is a key mechanism for the impulsive enhancement of magnetic reconnection rate (electric field).
NASA Astrophysics Data System (ADS)
Pucci, Fulvia; Del Sarto, Daniele; Tenerani, Anna; Velli, Marco
2015-04-01
By examining sheets with thicknesses scaling as different powers of the Lundquist number S, we previously showed (Pucci and Velli, 2014) that the growth rate of the tearing mode increases as current sheets thin and, once the inverse aspect ratio reaches a scaling a/L = S-1/3, the time-scale for the instability to develop becomes of the order of the Alfvén time. That means that a fast instability sets in well before Sweet-Parker type current sheets can form. In addition, such an instability produces many islands in the sheet, leading to fast nonlinear evolution and most probably a turbulent disruption of the sheet itself. This has fundamental implications for magnetically driven reconnection throughout the corona, and in particular for coronal heating and the triggering of coronal mass ejections. Here we extend the study of reconnection instabilities to magnetic fields of grater complexity, displaying different current structures such as, for example, multiple or asymmetric current layers. We also consider the possibility of a Δ' dependence on wave-number k-p for different values of p, studying analogies and variations of the trigger scaling relation a/L ~ S-1/3 with respect to the Harris current sheet equilibrium. At large Lundquist numbers in typical Heliospheric plasmas kinetic effects become more important in Ohm's law: we consider the effects of electron skin depth reconnection, showing that we can define a trigger relation similar to the resistive case. The results are important to the transition to fast reconnection in the solar corona, solar wind, magnetosphere as well as laboratory plasmas. F. Pucci and M. Velli, "Reconnection of quasi-singular current sheets: the 'ideal" tearing mode" ApJ 780:L19, 2014.
Jan Egedal-Pedersen
2010-01-29
The study of the collisionless magnetic reconnection constituted the primary work carried out under this grant. The investigations utilized two magnetic configurations with distinct boundary conditions. Both configurations were based upon the Versatile Toroidal Facility (VTF). The first configuration is characterized by open boundary conditions where the magnetic field lines interface directly with the vacuum vessel walls. The reconnection dynamics for this configuration has been methodically characterized and it has been shown that kinetic effects related to trapped electron trajectories are responsible for the high rates of reconnection observed. This type of reconnection has not been investigated before. Nevertheless, the results are directly relevant to observations by the Wind spacecraft of fast reconnection deep in the Earth magnetotail. The second configuration was developed to be specifically relevant to numerical simulations of magnetic reconnection, allowing the magnetic field-lines to be contained inside the device. The configuration is compatible with the presence of large current sheets in the reconnection region and reconnection is observed in fast powerful bursts. These reconnection events facilitate the first experimental investigations of the physics governing the spontaneous onset of fast reconnection. In this Report we review the general motivation of this work, the experimental set-up, and the main physics results.
Multi-Scale Modeling of Magnetospheric Reconnection
NASA Technical Reports Server (NTRS)
Kuznetsova, M. M.; Hesse, M.; Rastatter, L.; Toth, G.; Dezeeuw, D.; Gomobosi, T.
2007-01-01
One of the major challenges in modeling the magnetospheric magnetic reconnection is to quantify the interaction between large-scale global magnetospheric dynamics and microphysical processes in diffusion regions near reconnection sites. There is still considerable debate as to what degree microphysical processes on kinetic scales affect the global evolution and how important it is to substitute numerical dissipation and/or ad hoc anomalous resistivity by a physically motivated model of dissipation. Comparative studies of magnetic reconnection in small scale geometries demonstrated that MHD simulations that included non-ideal processes in terms of a resistive term $\\eta J$ did not produce the fast reconnection rates observed in kinetic simulations. For a broad range of physical parameters 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. We utilize the global MHD code BATSRUS and incorporate nongyrotropic effects in diffusion regions in terms of corrections to the induction equation. 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 selfconsistently using MHD plasma and field parameters in the vicinity of the reconnection site. The location of the reconnection sites is updated during the simulations. To clarify the role of nongyrotropic effects in diffusion region on the global magnetospheric dynamic we perform simulations with steady southward IMF driving of the magnetosphere. Ideal MHD simulations with magnetic reconnection supported by numerical resistivity produce steady configuration with almost stationary near-earth neutral
Final Report: Laboratory Studies of Spontaneous Reconnection and Intermittent Plasma Objects
Egedal-Pedersen, Jan; Porkolab, Miklos
2011-05-31
The study of the collisionless magnetic reconnection constituted the primary work carried out under this grant. The investigations utilized two magnetic configurations with distinct boundary conditions. Both configurations were based upon the Versatile Toroidal Facility (VTF) at the MIT Plasma Science and Fusion Center and the MIT Physics Department. The NSF/DOE award No. 0613734, supported two graduate students (now Drs. W. Fox and N. Katz) and material expenses. The grant enabled these students to operate the VTF basic plasma physics experiment on magnetic reconnection. The first configuration was characterized by open boundary conditions where the magnetic field lines interface directly with the vacuum vessel walls. The reconnection dynamics for this configuration has been methodically characterized and it has been shown that kinetic effects related to trapped electron trajectories are responsible for the high rates of reconnection observed. This type of reconnection has not been investigated before. Nevertheless, the results are directly relevant to observations by the Wind spacecraft of fast reconnection deep in the Earth magnetotail. The second configuration was developed to be relevant to specifically to numerical simulations of magnetic reconnection, allowing the magnetic field-lines to be contained inside the device. The configuration is compatible with the presence of large current sheets in the reconnection region and reconnection is observed in fast powerful bursts. These reconnection events facilitate the first experimental investigations of the physics governing the spontaneous onset of fast reconnection. In the Report we review the general motivation of this work and provide an overview of our experimental and theoretical results enabled by the support through the awards.
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.
NASA Astrophysics Data System (ADS)
Kichigin, G. N.
2016-01-01
Solutions describing solitary fast magnetosonic (FMS) waves (FMS solitons) in cold magnetized plasma are obtained by numerically solving two-fluid hydrodynamic equations. The parameter domain within which steady-state solitary waves can propagate is determined. It is established that the Mach number for rarefaction FMS solitons is always less than unity. The restriction on the propagation velocity leads to the limitation on the amplitudes of the magnetic field components of rarefaction solitons. It is shown that, as the soliton propagates in plasma, the transverse component of its magnetic field rotates and makes a complete turn around the axis along which the soliton propagates.
Frontiers for Laboratory Research of Magnetic Reconnection
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.
Magnetic reconnection physics in the solar wind with Voyager 2
NASA Astrophysics Data System (ADS)
Stevens, Michael L.
2009-08-01
Magnetic reconnection is the process by which the magnetic topology evolves in collisionless plasmas. This phenomenon is fundamental to a broad range of astrophysical processes such as stellar flares, magnetospheric substorms, and plasma accretion, yet it is poorly understood and difficult to observe in situ . In this thesis, the solar wind plasma permeating interplanetary space is treated as a laboratory for reconnection physics. I present an exhaustive statistical approach to the identification of reconnection outflow jets in turbulent plasma and magnetic field time series data. This approach has been automated and characterized so that the resulting reconnection survey can be put in context with other related studies. The algorithm is shown to perform similarly to ad hoc studies in the inner heliosphere. Based on this technique, I present a survey of 138 outflow jets for the Voyager 2 spacecraft mission, including the most distant in situ evidence of reconnection discovered to date. Reconnection in the solar wind is shown to be strongly correlated with stream interactions and with solar activity. The solar wind magnetic field is found to be reconnecting via large, quasi-steady slow- mode magnetohydrodynamic structures as far out as the orbit of Neptune. The role of slow-mode shocks is explored and, in one instance, a well-developed reconnection structure is shown to be in good agreement with the Petschek theory for fast reconnection. This is the first reported example of a reconnection exhaust that satisfies the full jump conditions for a stationary slow-mode shock pair. A complete investigation into corotating stream interactions over the Voyager 2 mission has revealed that detectable reconnection structure occurs in about 23% of forced, global-scale current sheets. Contrary to previous studies, I find that signatures of this kind are most likely to be observed for current sheets where the magnetic field shear and the plasma-b are high. Evidence has been found
NASA Astrophysics Data System (ADS)
Rosenberg, M. J.; Li, C. K.; Fox, W.; Zylstra, A. B.; Stoeckl, C.; Séguin, F. H.; Frenje, J. A.; Petrasso, R. D.
2015-05-01
An evolution of magnetic reconnection behavior, from fast jets to the slowing of reconnection and the establishment of a stable current sheet, has been observed in strongly driven, β ≲20 laser-produced plasma experiments. This process has been inferred to occur alongside a slowing of plasma inflows carrying the oppositely directed magnetic fields as well as the evolution of plasma conditions from collisionless to collisional. High-resolution proton radiography has revealed unprecedented detail of the forced interaction of magnetic fields and super-Alfvénic electron jets (Vjet˜20 VA ) ejected from the reconnection region, indicating that two-fluid or collisionless magnetic reconnection occurs early in time. The absence of jets and the persistence of strong, stable magnetic fields at late times indicates that the reconnection process slows down, while plasma flows stagnate and plasma conditions evolve to a cooler, denser, more collisional state. These results demonstrate that powerful initial plasma flows are not sufficient to force a complete reconnection of magnetic fields, even in the strongly driven regime.
Rosenberg, M. J.; Li, C. K.; Fox, W.; Zylstra, A. B.; Stoeckl, C.; Séguin, F. H.; Frenje, J. A.; Petrasso, R. D.
2015-05-20
An evolution of magnetic reconnection behavior, from fast jets to the slowing of reconnection and the establishment of a stable current sheet, has been observed in strongly-driven, β ≲ 20 laser-produced plasma experiments. This process has been inferred to occur alongside a slowing of plasma inflows carrying the oppositely-directed magnetic fields as well as the evolution of plasma conditions from collisionless to collisional. High-resolution proton radiography has revealed unprecedented detail of the forced interaction of magnetic fields and super-Alfvénic electron jets (Vjet~ 20VA) ejected from the reconnection region, indicating that two-fluid or collisionless magnetic reconnection occurs early in time. Themore » absence of jets and the persistence of strong, stable magnetic fields at late times indicates that the reconnection process slows down, while plasma flows stagnate and plasma conditions evolve to a cooler, denser, more collisional state. These results demonstrate that powerful initial plasma flows are not sufficient to force a complete reconnection of magnetic fields, even in the strongly-driven regime.« less
Rosenberg, M. J.; Li, C. K.; Fox, W.; Zylstra, A. B.; Stoeckl, C.; Séguin, F. H.; Frenje, J. A.; Petrasso, R. D.
2015-05-20
An evolution of magnetic reconnection behavior, from fast jets to the slowing of reconnection and the establishment of a stable current sheet, has been observed in strongly-driven, β ≲ 20 laser-produced plasma experiments. This process has been inferred to occur alongside a slowing of plasma inflows carrying the oppositely-directed magnetic fields as well as the evolution of plasma conditions from collisionless to collisional. High-resolution proton radiography has revealed unprecedented detail of the forced interaction of magnetic fields and super-Alfvénic electron jets (V_{jet}~ 20V_{A}) ejected from the reconnection region, indicating that two-fluid or collisionless magnetic reconnection occurs early in time. The absence of jets and the persistence of strong, stable magnetic fields at late times indicates that the reconnection process slows down, while plasma flows stagnate and plasma conditions evolve to a cooler, denser, more collisional state. These results demonstrate that powerful initial plasma flows are not sufficient to force a complete reconnection of magnetic fields, even in the strongly-driven regime.
Rosenberg, M J; Li, C K; Fox, W; Zylstra, A B; Stoeckl, C; Séguin, F H; Frenje, J A; Petrasso, R D
2015-05-22
An evolution of magnetic reconnection behavior, from fast jets to the slowing of reconnection and the establishment of a stable current sheet, has been observed in strongly driven, β≲20 laser-produced plasma experiments. This process has been inferred to occur alongside a slowing of plasma inflows carrying the oppositely directed magnetic fields as well as the evolution of plasma conditions from collisionless to collisional. High-resolution proton radiography has revealed unprecedented detail of the forced interaction of magnetic fields and super-Alfvénic electron jets (V_{jet}∼20V_{A}) ejected from the reconnection region, indicating that two-fluid or collisionless magnetic reconnection occurs early in time. The absence of jets and the persistence of strong, stable magnetic fields at late times indicates that the reconnection process slows down, while plasma flows stagnate and plasma conditions evolve to a cooler, denser, more collisional state. These results demonstrate that powerful initial plasma flows are not sufficient to force a complete reconnection of magnetic fields, even in the strongly driven regime. PMID:26047236
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
Magnetic reconnection in space
Boozer, Allen H.
2012-09-15
Models of magnetic reconnection in space plasmas generally consider only a segment of the magnetic field lines. The consideration of only a segment of the lines is shown to lead to paradoxical results in which reconnection can be impossible even in a magnetic field constrained to be curl free or can be at an Alfven rate even when the plasma is a perfect conductor. A model of reconnecting magnetic fields is developed which shows the smallness of the interdiffusion distance {delta}{sub d} of magnetic field lines does not limit the speed of reconnection but does provide a reconnection trigger. When the reconnection region has a natural length L{sub r}, the spatial scale of the gradient of magnetic field across the magnetic field lines must reach L{sub g} Almost-Equal-To 0.3L{sub r}/ln(L{sub r}/{delta}{sub d}) for fast reconnection to be triggered, which implies a current density j Almost-Equal-To B/{mu}{sub 0}L{sub g} that is far lower than that usually thought required for fast reconnection. The relation between magnetic reconnection in space and in toroidal laboratory plasmas is also discussed.
Gu, Y J; Klimo, O; Kumar, D; Liu, Y; Singh, S K; Esirkepov, T Zh; Bulanov, S V; Weber, S; Korn, G
2016-01-01
The magnetic quadrupole structure formation during the interaction of two ultrashort high power laser pulses with a collisionless plasma is demonstrated with 2.5-dimensional particle-in-cell simulations. The subsequent expansion of the quadrupole is accompanied by magnetic-field annihilation in the ultrarelativistic regime, when the magnetic field cannot be sustained by the plasma current. This results in a dominant contribution of the displacement current exciting a strong large scale electric field. This field leads to the conversion of magnetic energy into kinetic energy of accelerated electrons inside the thin current sheet. PMID:26871179
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
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
NASA Astrophysics Data System (ADS)
McLaughlin, J. A.; De Moortel, I.; Hood, A. W.; Brady, C. S.
2009-01-01
Context: This paper extends the models of Craig & McClymont (1991, ApJ, 371, L41) and McLaughlin & Hood (2004, A&A, 420, 1129) to include finite β and nonlinear effects. Aims: We investigate the nature of nonlinear fast magnetoacoustic waves about a 2D magnetic X-point. Methods: We solve the compressible and resistive MHD equations using a Lagrangian remap, shock capturing code (Arber et al. 2001, J. Comp. Phys., 171, 151) and consider an initial condition in {v}×{B} \\cdot {hat{z}} (a natural variable of the system). Results: We observe the formation of both fast and slow oblique magnetic shocks. The nonlinear wave deforms the X-point into a “cusp-like” point which in turn collapses to a current sheet. The system then evolves through a series of horizontal and vertical current sheets, with associated changes in connectivity, i.e. the system exhibits oscillatory reconnection. Our final state is non-potential (but in force balance) due to asymmetric heating from the shocks. Larger amplitudes in our initial condition correspond to larger values of the final current density left in the system. Conclusions: The inclusion of nonlinear terms introduces several new features to the system that were absent from the linear regime. A movie is available in electronic form at http://www.aanda.org
Radiative tearing - Magnetic reconnection on a fast thermal-instability time scale
NASA Technical Reports Server (NTRS)
Steinolfson, R. S.; Van Hoven, G.
1984-01-01
Two energy modification mechanisms which are known to occur in sheared magnetic fields are the tearing and thermal instabilities. These processes can be studied separately with formalisms incorporating just the effective driving mechanism of interest (finite resistivity for the tearing mode and unstable radiation for the thermal mode). A model which includes both effects, and a temperature-dependent resistivity, indicates that modified forms of these two instabilities may coexist for identical physical conditions. When they are isolated computationally, one can show that their limiting growth rates are approximately those of the uncoupled instabilities. The spatial structure and energy content of these two new hybrid processes are then individually examined and are found to differ considerably from those obtained from separate treatments of the driving mechanisms. The faster radiative instability, which has a hydromagnetically scaled growth rate like the condensation mode of the thermal instability, is shown to involve a substantial amount of magnetic field reconnection. This can be partially explained by a large temperature drop (or resistivity rise) at the X-point. The island width of the Coulomb-coupled radiative mode is 30 percent of that produced by a comparable level of the slower tearing instability. In addition, the perturbed magnetic energy in the radiative instability is 5 times that of the perturbed thermal energy, indicating an appreciable modification of the initial magnetic structure.
Collisional Behaviors of Astrophysical Collisionless Plasmas
NASA Astrophysics Data System (ADS)
Bret, A.
2015-12-01
In collisional fluids, a number of key processes rely on the frequency of binary collisions. Collisions seem necessary to generate a shock wave when two fluids collide fast enough, to fulfill the Rankine-Hugoniot (RH) relations, to establish an equation of state or a Maxwellian distribution. Yet, these seemingly collisional features are routinely either observed or assumed, in relation with collisionless astrophysical plasmas. This article will review our current answers to the following questions: How do colliding collisionless plasmas end-up generating a shock as if they were fluids? To which extent are the RH relations fulfilled in this case? Do collisionless shocks propagate like fluid ones? Can we use an equation of state to describe collisionless plasmas, like MHD codes for astrophysics do? Why are Maxwellian distributions ubiquitous in particle-in-cell simulations of collisionless shocks? Time and length scales defining the border between the collisional and the collisionless behavior will be given when relevant. In general, when the time and length scales involved in the collisionless processes responsible for the fluid-like behavior may be neglected, the system may be treated like a fluid.
NASA Astrophysics Data System (ADS)
Eastwood, J. P.; Goldman, M. V.; Zhang, X.; Hietala, H.; Krupar, V.; Newman, D. L.; Angelopoulos, V.; Lapenta, G.
2015-12-01
Whistler waves are a ubiquitous plasma phenomenon, observed in a variety of space and laboratory plasma environments. They play a key role in many important and diverse processes, such as particle acceleration in the radiation belts and auroral acceleration region, the dissipation of plasma turbulence at small scales below the inertial range, collisionless shock physics, and magnetic reconnection. In reconnection they may modify the reconnection rate and also whistler physics is crucial to enabling fast reconnection in the Hall reconnection model. Consequently, understanding how whistler waves are generated and how they subsequently interact with the plasma is a problem of wide importance and application. It is well known that whistlers can arise as a result of kinetic instabilities, which grow exponentially from noise as a consequence of unstable electron distributions, for example temperature anisotropy. This is used ubiquitously to predict where and when whistler waves are likely to exist and therefore be of importance in many plasma phenomena. Recently it has been demonstrated theoretically and via computer simulations that whistler waves may also arise via Cerenkov emission from electron hole quasi-particles [Goldman et al., PRL, 2014]. Such wave emission can arise even when the temperature anisotropy leads to damping; in this case the system is analogous to a damped forced oscillator. Here we present novel experimental analysis from THEMIS showing for the first time evidence consistent with the generation of whistlers via Cerenkov emission during magnetotail reconnection. By considering the electromagnetic properties of the electron holes, the amplitude, phase speed and frequency of the associated whistlers, and also the available sub-spin observations of the electron distribution function, we find that the data are best explained by the Cerenkov emission theory rather than by kinetic instabilities due to the electron temperature anisotropy. Whilst the
SELF-ORGANIZATION OF RECONNECTING PLASMAS TO MARGINAL COLLISIONALITY IN THE SOLAR CORONA
Imada, S.; Zweibel, E. G.
2012-08-20
We explore the suggestions by Uzdensky and Cassak et al. that coronal loops heated by magnetic reconnection should self-organize to a state of marginal collisionality. We discuss their model of coronal loop dynamics with a one-dimensional hydrodynamic calculation. We assume that many current sheets are present, with a distribution of thicknesses, but that only current sheets thinner than the ion skin depth can rapidly reconnect. This assumption naturally causes a density-dependent heating rate which is actively regulated by the plasma. We report nine numerical simulation results of coronal loop hydrodynamics in which the absolute values of the heating rates are different but their density dependences are the same. We find two regimes of behavior, depending on the amplitude of the heating rate. In the case that the amplitude of heating is below a threshold value, the loop is in stable equilibrium. Typically, the upper and less dense part of a coronal loop is collisionlessly heated and conductively cooled. When the amplitude of heating is above the threshold, the conductive flux to the lower atmosphere required to balance collisionless heating drives an evaporative flow which quenches fast reconnection, ultimately cooling and draining the loop until the cycle begins again. The key elements of this cycle are gravity and the density dependence of the heating function. Some additional factors are present, including pressure-driven flows from the loop top, which carry a large enthalpy flux and play an important role in reducing the density. We find that on average the density of the system is close to the marginally collisionless value.
Study of the effects of guide field on Hall reconnection
Tharp, T. D.; Yamada, M.; Ji, H.; Lawrence, E.; Dorfman, S.; Myers, C.; Yoo, J.; Huang, Y.-M.; Bhattacharjee, A.
2013-05-15
The results from guide field studies on the Magnetic Reconnection Experiment (MRX) are compared with results from Hall magnetohydrodynamic (HMHD) reconnection simulation with guide field. The quadrupole field, a signature of two-fluid reconnection at zero guide field, is modified by the presence of a finite guide field in a manner consistent with HMHD simulation. The modified Hall current profile contains reduced electron flows in the reconnection plane, which quantitatively explains the observed reduction of the reconnection rate. The present results are consistent with the hypothesis that the local reconnection dynamics is dominated by Hall effects in the collisionless regime of the MRX plasmas. While very good agreement is seen between experiment and simulations, we note that an important global feature of the experiments, a compression of the guide field by the reconnecting plasma, is not represented in the simulations.
BEAMING AND RAPID VARIABILITY OF HIGH-ENERGY RADIATION FROM RELATIVISTIC PAIR PLASMA RECONNECTION
Cerutti, B.; Werner, G. R.; Uzdensky, D. A.; Begelman, M. C. E-mail: greg.werner@colorado.edu E-mail: mitch@jila.colorado.edu
2012-08-01
We report on the first study of the angular distribution of energetic particles and radiation generated in relativistic collisionless electron-positron pair plasma reconnection using two-dimensional particle-in-cell simulations. We discover a strong anisotropy of the particles accelerated by reconnection and the associated strong beaming of their radiation. The focusing of particles and radiation increases with their energy; in this sense, this 'kinetic beaming' effect differs fundamentally from the relativistic Doppler beaming usually invoked in high-energy astrophysics, in which all photons are focused and boosted achromatically. We also present, for the first time, the modeling of the synchrotron emission as seen by an external observer during the reconnection process. The expected light curves comprise several bright symmetric sub-flares emitted by the energetic beam of particles sweeping across the line of sight intermittently, and exhibit super-fast time variability as short as about one-tenth of the system light-crossing time. The concentration of the energetic particles into compact regions inside magnetic islands and particle anisotropy explain the rapid variability. This radiative signature of reconnection can account for the brightness and variability of the gamma-ray flares in the Crab Nebula and in blazars.
Application of PDSLin to the magnetic reconnection problem
NASA Astrophysics Data System (ADS)
Yuan, Xuefei; Li, Xiaoye S.; Yamazaki, Ichitaro; Jardin, Stephen C.; Koniges, Alice E.; Keyes, David E.
2013-01-01
Magnetic reconnection is a fundamental process in a magnetized plasma at both low and high magnetic Lundquist numbers (the ratio of the resistive diffusion time to the Alfvén wave transit time), which occurs in a wide variety of laboratory and space plasmas, e.g. magnetic fusion experiments, the solar corona and the Earth's magnetotail. An implicit time advance for the two-fluid magnetic reconnection problem is known to be difficult because of the large condition number of the associated matrix. This is especially troublesome when the collisionless ion skin depth is large so that the Whistler waves, which cause the fast reconnection, dominate the physics (Yuan et al 2012 J. Comput. Phys. 231 5822-53). For small system sizes, a direct solver such as SuperLU can be employed to obtain an accurate solution as long as the condition number is bounded by the reciprocal of the floating-point machine precision. However, SuperLU scales effectively only to hundreds of processors or less. For larger system sizes, it has been shown that physics-based (Chacón and Knoll 2003 J. Comput. Phys. 188 573-92) or other preconditioners can be applied to provide adequate solver performance. In recent years, we have been developing a new algebraic hybrid linear solver, PDSLin (Parallel Domain decomposition Schur complement-based Linear solver) (Yamazaki and Li 2010 Proc. VECPAR pp 421-34 and Yamazaki et al 2011 Technical Report). In this work, we compare numerical results from a direct solver and the proposed hybrid solver for the magnetic reconnection problem and demonstrate that the new hybrid solver is scalable to thousands of processors while maintaining the same robustness as a direct solver.
Magnetohydrodynamic simulations of turbulent magnetic reconnection
Fan Quanlin; Feng Xueshang; Xiang Changqing
2004-12-01
Turbulent reconnection process in a one-dimensional current sheet is investigated by means of a two-dimensional compressible one-fluid magnetohydrodynamic simulation with spatially uniform, fixed resistivity. Turbulence is set up by adding to the sheet pinch small but finite level of broadband random-phased magnetic field components. To clarify the nonlinear spatial-temporal nature of the turbulent reconnection process the reconnection system is treated as an unforced initial value problem without any anomalous resistivity model adopted. Numerical results demonstrate the duality of turbulent reconnection, i.e., a transition from Sweet-Parker-like slow reconnection to Petschek-like fast reconnection in its nonlinear evolutionary process. The initial slow reconnection phase is characterized by many independent microreconnection events confined within the sheet region and a global reconnection rate mainly dependent on the initially added turbulence and insensitive to variations of the plasma {beta} and resistivity. The formation and amplification of the major plasmoid leads the following reconnection process to a rapid reconnection stage with a fast reconnection rate of the order of 0.1 or even larger, drastically changing the topology of the global magnetic field. That is, the presence of magnetohydrodynamic turbulence in large-scale current sheets can raise the reconnection rate from small values on the order of the Sweet-Parker rate to high values on the order of the Petscheck rate through triggering an evolution toward fast magnetic reconnection. Meanwhile, the backward coupling between the small- and large-scale magnetic field dynamics has been properly represented through the present high resolution simulation. The undriven turbulent reconnection model established here expresses a solid numerical basis for the previous schematic two-step magnetic reconnection models and a possible explanation of two-stage energy release process of solar explosives.
A Reconnection Switch to Trigger gamma-Ray Burst Jet Dissipation
McKinney, Jonathan C.; Uzdensky, Dmitri A.
2012-03-14
Prompt gamma-ray burst (GRB) emission requires some mechanism to dissipate an ultrarelativistic jet. Internal shocks or some form of electromagnetic dissipation are candidate mechanisms. Any mechanism needs to answer basic questions, such as what is the origin of variability, what radius does dissipation occur at, and how does efficient prompt emission occur. These mechanisms also need to be consistent with how ultrarelativistic jets form and stay baryon pure despite turbulence and electromagnetic reconnection near the compact object and despite stellar entrainment within the collapsar model. We use the latest magnetohydrodynamical models of ultrarelativistic jets to explore some of these questions in the context of electromagnetic dissipation due to the slow collisional and fast collisionless reconnection mechanisms, as often associated with Sweet-Parker and Petschek reconnection, respectively. For a highly magnetized ultrarelativistic jet and typical collapsar parameters, we find that significant electromagnetic dissipation may be avoided until it proceeds catastrophically near the jet photosphere at large radii (r {approx} 10{sup 13}-10{sup 14}cm), by which the jet obtains a high Lorentz factor ({gamma} {approx} 100-1000), has a luminosity of L{sub j} {approx} 10{sup 50}-10{sup 51} erg s{sup -1}, has observer variability timescales of order 1s (ranging from 0.001-10s), achieves {gamma}{theta}{sub j} {approx} 10-20 (for opening half-angle {theta}{sub j}) and so is able to produce jet breaks, and has comparable energy available for both prompt and afterglow emission. A range of model parameters are investigated and simplified scaling laws are derived. This reconnection switch mechanism allows for highly efficient conversion of electromagnetic energy into prompt emission and associates the observed prompt GRB pulse temporal structure with dissipation timescales of some number of reconnecting current sheets embedded in the jet. We hope this work helps motivate the
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.
Goldman, M V; Newman, D L; Lapenta, G; Andersson, L; Gosling, J T; Eriksson, S; Markidis, S; Eastwood, J P; Ergun, R
2014-04-11
Kinetic simulations of magnetotail reconnection have revealed electromagnetic whistlers originating near the exhaust boundary and propagating into the inflow region. The whistler production mechanism is not a linear instability, but rather is Čerenkov emission of almost parallel whistlers from localized moving clumps of charge (finite-size quasiparticles) associated with nonlinear coherent electron phase space holes. Whistlers are strongly excited by holes without ever growing exponentially. In the simulation the whistlers are emitted in the source region from holes that accelerate down the magnetic separatrix towards the x line. The phase velocity of the whistlers vφ in the source region is everywhere well matched to the hole velocity vH as required by the Čerenkov condition. The simulation shows emission is most efficient near the theoretical maximum vφ=half the electron Alfven speed, consistent with the new theoretical prediction that faster holes radiate more efficiently. While transferring energy to whistlers the holes lose coherence and dissipate over a few local ion inertial lengths. The whistlers, however, propagate to the x line and out over many 10's of ion inertial lengths into the inflow region of reconnection. As the whistlers pass near the x line they modulate the rate at which magnetic field lines reconnect. PMID:24765977
Magnetic reconnection under anisotropic magnetohydrodynamic approximation
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.
Dynamical plasma response during driven magnetic reconnection.
Egedal, J; Fasoli, A; Nazemi, J
2003-04-01
Direct measurements of a collisionless current channel during driven magnetic reconnection are obtained for the first time on the Versatile Toroidal Facility. The size of the diffusion region is found to scale with the electron drift orbit width, independent of the ion mass and plasma density. Based on experimental observations, analytic expressions governing the dynamical evolution of the current profile and the formation of the electrostatic potential that develops in response to the externally imposed reconnection drive are established. This time response is closely linked to the presence of ion polarization currents. PMID:12689297
Kinetic theory of collisionless tearing at the magnetopause
NASA Astrophysics Data System (ADS)
Daughton, William; Karimabadi, H.
2005-03-01
electron gyroscale in the guide field. During the onset phase, these structures represent a distinct signature of the collisionless tearing mode that is significantly different than the typical ion-scale quadrupole pattern from fast reconnection. Finally, we note that the tearing mode maintains a significant growth rate over a large range of guide field so that component merging cannot be ruled out based on linear theory.
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...
Evolutions of nonsteady state magnetic reconnection
Wan, Weigang; Lapenta, Giovanni
2008-01-01
The full evolutions of collisionless non-steady-state magnetic reconnection are studied with full kinetic particle-in-cell simulations. There are different stages of reconnection: the onset or early growing stage when the out-of-plane electric field (Ey) structure is a monopole at the X-point, the bipolar stage when the Ey structure is bipolar and the outer electron diffusion region (EDR) is being elongated over time, and the possible final steady-state stage when E{sub y} is uniform in the reconnection plane. We find the change of reconnection rate is not empowered or dependent on the length of the EDR. During the early growing stage, the EDR is elongated while the reconnection rate is growing. During the later stage, the reconnection rate may significantly decrease but the length of the inner EDR is largely stable. The results indicate that reconnection is not controlled by the downstream physics, but rather by the availability of plasma inflows from upstream. The physical mechanism of the EDR elongation is studied. The Hall current induced by the quadrupole magnetic field (B{sub y}) is discovered to play an important role in this process. The condition of forming an extended electron super-Alfvenic outflow jet structure in nature is discussed. The jet structure could be elongated during the bipolar stage, and remains stable during steady state. The sufficiency of the electron inflow is crucial for the elongation. Open boundary conditions are applied in the outflow direction.
Zenitani, Seiji
2015-03-15
The shock structure of a plasmoid in magnetic reconnection in low-beta plasmas is investigated by two-dimensional magnetohydrodynamic simulations. Using a high-accuracy code with unprecedented resolution, shocks, discontinuities, and their intersections are resolved and clarified. Contact discontinuities emanate from triple-shock intersection points, separating fluids of different origins. Shock-diamonds inside the plasmoid appear to decelerate a supersonic flow. New shock-diamonds and a slow expansion fan are found inside the Petschek outflow. A sufficient condition for the new shock-diamonds and the relevance to astrophysical jets are discussed.
Chromospheric anemone jets and magnetic reconnection in partially ionized solar atmosphere
NASA Astrophysics Data System (ADS)
Singh, K. A. P.; Shibata, K.; Nishizuka, N.; Isobe, H.
2011-11-01
The solar optical telescope onboard Hinode with temporal resolution of less than 5 s and spatial resolution of 150 km has observed the lower solar atmosphere with an unprecedented detail. This has led to many important findings, one of them is the discovery of chromospheric anemone jets in the solar chromosphere. The chromospheric anemone jets are ubiquitous in solar chromosphere and statistical studies show that the typical length, life time and energy of the chromospheric anemone jets are much smaller than the coronal events (e.g., jets/flares/CMEs). Among various observational parameters, the apparent length and maximum velocity shows good correlation. The velocity of chromospheric anemone jets is comparable to the local Alfvén speed in the lower solar chromosphere. Since the discovery of chromospheric anemone jets by Hinode, several evidences of magnetic reconnection in chromospheric anemone jets have been found and these observations are summarized in this paper. These observations clearly suggest that reconnection occurs quite rapidly as well as intermittently in the solar chromosphere. In the solar corona (λi > δSP), anomalous resistivity arises due to various collisionless processes. Previous MHD simulations show that reconnection becomes fast as well as strongly time-dependent due to anomalous resistivity. Such processes would not arise in the solar chromosphere which is fully collisional and partially-ionized. So, it is unclear how the rapid and strongly time-dependent reconnection would occur in the solar chromosphere. It is quite likely that the Hall and ambipolar diffusion are present in the solar chromosphere and they could play an important role in driving such rapid, strongly time-dependent reconnection in the solar chromosphere.
Chromospheric anemone jets and magnetic reconnection in partially ionized solar atmosphere
Singh, K. A. P.; Shibata, K.; Nishizuka, N.; Isobe, H.
2011-11-15
The solar optical telescope onboard Hinode with temporal resolution of less than 5 s and spatial resolution of 150 km has observed the lower solar atmosphere with an unprecedented detail. This has led to many important findings, one of them is the discovery of chromospheric anemone jets in the solar chromosphere. The chromospheric anemone jets are ubiquitous in solar chromosphere and statistical studies show that the typical length, life time and energy of the chromospheric anemone jets are much smaller than the coronal events (e.g., jets/flares/CMEs). Among various observational parameters, the apparent length and maximum velocity shows good correlation. The velocity of chromospheric anemone jets is comparable to the local Alfven speed in the lower solar chromosphere. Since the discovery of chromospheric anemone jets by Hinode, several evidences of magnetic reconnection in chromospheric anemone jets have been found and these observations are summarized in this paper. These observations clearly suggest that reconnection occurs quite rapidly as well as intermittently in the solar chromosphere. In the solar corona ({lambda}{sub i} > {delta}{sub SP}), anomalous resistivity arises due to various collisionless processes. Previous MHD simulations show that reconnection becomes fast as well as strongly time-dependent due to anomalous resistivity. Such processes would not arise in the solar chromosphere which is fully collisional and partially-ionized. So, it is unclear how the rapid and strongly time-dependent reconnection would occur in the solar chromosphere. It is quite likely that the Hall and ambipolar diffusion are present in the solar chromosphere and they could play an important role in driving such rapid, strongly time-dependent reconnection in the solar chromosphere.
Intuitive approach to magnetic reconnection
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.
NASA Astrophysics Data System (ADS)
Sitnov, M. I.; Runov, A. V.; Ohtani, S.
2007-12-01
The physics of fast earthward flows or BBFs, a major mechanism of bursty transfer of the plasma and magnetic flux in the terrestrial magnetotail, remains uncertain and controversial. A part of observations can be explained as signatures of earthward moving flux ropes or secondary plasmoids dragged by the earthward part a larger-scale reconnection region [Slavin et al., 2003]. The statistics of variations of the z-component of the magnetospheric magnetic field in the central plasma sheet [Ohtani et al., 2004] suggest no changes of the magnetic field topology for another group of BBFs. These observations can be explained as signatures of either unsteady reconnection, which remains located tailward of the spacecraft, or other phenomena that are connected but not identical to reconnection in its active phase. These are the plasma bubbles, flux tubes with the reduced specific entropy that may move earthward faster than the neighboring flux tubes due to the buoyancy force. However, the original model of bubbles arising from local reductions of the plasma pressure [Pontius and Wolf, 1990] also explains only a part of observations. Another part [Angelopoulos et al., 1992] reveals no reduction of the plasma pressure in BBFs. One more model, which explains both missing magnetic topology changes and no reduction of the plasma pressure [Sitnov et al., 2005] describes the bubble as a seam in the body of the tail plasma, which appears after the formation and tailward retreat of a small plasmoid, and which is composed of atypical, embedded and bifurcated thin current sheets. Signatures of such atypical current sheets have been convincingly demonstrated recently in CLUSTER observations [Runov et al., 2003]. In this presentation we elaborate the BBF models and compare them with 2001 and 2002 tail CLUSTER observations in the central plasma sheet. These include full-particle simulations of the secondary plasmoid formation in tail-like systems, two- and three- dimensional features and
Drift Wave Turbulence and Magnetic Reconnection
NASA Astrophysics Data System (ADS)
Price, L.; Drake, J. F.; Swisdak, M.
2015-12-01
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 and the magnetotail) 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. We specifically consider stabilization of the lower hybrid drift instability (LHDI) and the development of this instability in the presence of a sheared magnetic field. Further investigations of the relative importance of drift wave turbulence in the development of reconnection will also be considered.
The Time-Dependent Structure of the Electron Reconnection Layer
NASA Technical Reports Server (NTRS)
Hesse, Michael; Zenitani, Seiji; Kuznetsova, Masha; Klimas, Alex
2009-01-01
Collisionless magnetic reconnection is often associated with time-dependent behavior. Specifically, current layers in the diffusion region can become unstable to tearing-type instabilities on one hand, or to instabilities with current-aligned wave vectors on the other. In the former case, the growth of tearing instabilities typically leads to the production of magnetic islands, which potentially provide feedback on the reconnection process itself, as well as on the rate of reconnection. The second class of instabilities tend to modulate the current layer along the direction of the current flow, for instance generating kink-type perturbations, or smaller-scale turbulence with the potential to broaden the current layer. All of these processes contribute to rendering magnetic reconnection time-dependent. In this presentation, we will provide a summary of these effects, and a discussion of how much they contribute to the overall magnetic reconnection rate.
Force balance near an X line in a collisionless plasma
NASA Technical Reports Server (NTRS)
Lyons, L. R.; Pridmore-Brown, D. C.
1990-01-01
The suggestion by Dungey (1988) that the gyroviscosity associated with gradients of the off-diagonal elements of the electron pressure tensor can balance a reconnection electric field along a magnetic X line in a collisionless plasma is investigated. The detailed balance of forces in the vicinity of an X line is evaluated using a two-dimensional magnetic field model and a simple model for particle motion. The results show that the gyroviscosity can indeed provide the force required to balance a reconnection electric field in that region, so that neither collisions nor wave turbulence are necessary for reconnection. The results also show that there should not be a significant increase in current from electron acceleration very near an X line. Reasonable numerical estimates are obtained for conditions expected in the vicinity of the distant X line in the geomagnetic tail.
Slipping magnetic reconnection in coronal loops.
Aulanier, Guillaume; Golub, Leon; Deluca, Edward E; Cirtain, Jonathan W; Kano, Ryouhei; Lundquist, Loraine L; Narukage, Noriyuki; Sakao, Taro; Weber, Mark A
2007-12-01
Magnetic reconnection of solar coronal loops is the main process that causes solar flares and possibly coronal heating. In the standard model, magnetic field lines break and reconnect instantaneously at places where the field mapping is discontinuous. However, another mode may operate where the magnetic field mapping is continuous but shows steep gradients: The field lines may slip across each other. Soft x-ray observations of fast bidirectional motions of coronal loops, observed by the Hinode spacecraft, support the existence of this slipping magnetic reconnection regime in the Sun's corona. This basic process should be considered when interpreting reconnection, both on the Sun and in laboratory-based plasma experiments. PMID:18063789
Global scale-invariant dissipation in collisionless plasma turbulence.
Kiyani, K H; Chapman, S C; Khotyaintsev, Yu V; Dunlop, M W; Sahraoui, F
2009-08-14
A higher-order multiscale analysis of the dissipation range of collisionless plasma turbulence is presented using in situ high-frequency magnetic field measurements from the Cluster spacecraft in a stationary interval of fast ambient solar wind. The observations, spanning five decades in temporal scales, show a crossover from multifractal intermittent turbulence in the inertial range to non-Gaussian monoscaling in the dissipation range. This presents a strong observational constraint on theories of dissipation mechanisms in turbulent collisionless plasmas. PMID:19792654
Laboratory Reconnection Experiments - heating and particle acceleration
NASA Astrophysics Data System (ADS)
Ono, Yasushi
Recent laboratory merging/ reconnection experiments have solved a number of key physics of magnetic reconnection: 1) reconnection heating/ acceleration, 2) fast reconnection mechanisms, 3) plasmoid reconnection, 4) non-steady reconnection and 5) non-thermal particle acceleration using new kinetic interpretations. Especially, significant ion temperatures 1.2keV were documented in the world-largest tokamak merging experiment: MAST after detailed 2D elucidation of ion and electron heating characteristics in TS-3 and 4 merging experiments. The measured 2D contours of ion and electron temperatures in TS-3, 4 and MAST reveal ion heating in the downstream by reconnection outflow and electron heating around the X-point by ohmic heating of current sheet. Their detailed heating mechanisms were further investigated by comparing those results with particle simulations developed by NIFS. The ion acceleration mechanism is mostly parallel acceleration by reconnection electric field and partly perpendicular acceleration by electrostatic potential. The fast shock and ion viscosity are the major dumping (heating) mechanisms for the accelerated ions. We successfully applied the reconnection heating - typically 10-50MW to the high-beta spherical tokamak formation and heating. This paper will review major progresses in those international and interdisciplinary merging tokamak experiments.
Indeterminacy and instability in Petschek reconnection
Forbes, Terry G.; Priest, Eric R.; Seaton, Daniel B.; Litvinenko, Yuri E.
2013-05-15
We explain two puzzling aspects of Petschek's model for fast reconnection. One is its failure to occur in plasma simulations with uniform resistivity. The other is its inability to provide anything more than an upper limit for the reconnection rate. We have found that previously published analytical solutions based on Petschek's model are structurally unstable if the electrical resistivity is uniform. The structural instability is associated with the presence of an essential singularity at the X-line that is unphysical. By requiring that such a singularity does not exist, we obtain a formula that predicts a specific rate of reconnection. For uniform resistivity, reconnection can only occur at the slow, Sweet-Parker rate. For nonuniform resistivity, reconnection can occur at a much faster rate provided that the resistivity profile is not too flat near the X-line. If this condition is satisfied, then the scale length of the nonuniformity determines the reconnection rate.
Multiscale modeling of magnetospheric reconnection
NASA Astrophysics Data System (ADS)
Kuznetsova, M. M.; Hesse, M.; RastäTter, L.; Taktakishvili, A.; Toth, G.; de Zeeuw, D. L.; Ridley, A.; Gombosi, T. I.
2007-10-01
In our efforts to bridge the gap between small-scale kinetic modeling and global simulations, we introduced an approach that allows to quantify the interaction between large-scale global magnetospheric dynamics and microphysical processes in diffusion regions near reconnection sites. We use the global MHD code BATS-R-US and replace an ad hoc anomalous resistivity often employed by global MHD models with a physically motivated dissipation model. The primary kinetic mechanism controlling the dissipation in the diffusion region in the vicinity of the reconnection site is incorporated into the MHD description in terms of nongyrotropic corrections to the induction equation. We developed an algorithm to search for reconnection sites in north-south symmetric magnetotail. Spatial scales of the diffusion region and magnitude of the reconnection electric field are calculated consistently using local MHD plasma and field parameters. The locations of the reconnection sites are constantly updated during the simulations. To clarify the role of nongyrotropic effects in the diffusion region on the global magnetospheric dynamics, we perform simulations with steady southward interplanetary magnetic field driving of the magnetosphere. Ideal MHD simulations with magnetic reconnection supported by numerical resistivity often produce quasi-steady configuration with almost stationary near-Earth neutral line (NENL). Simulations with nongyrotropic corrections demonstrate dynamic quasi-periodic response to the steady driving conditions. Fast magnetotail reconnection supported by nongyrotropic effects results in tailward retreat of the reconnection site with average speed of the order of 100 km/s followed by a formation of a new NENL in the near-Earth thin current sheet. This approach allowed to model for the first time loading/unloading cycle frequently observed during extended periods of steady low-mach-number solar wind with southward interplanetary magnetic field.
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.
Global Simulations of Magnetotail Reconnection
NASA Technical Reports Server (NTRS)
Kuznetsova, M. M.; Hesse, M.; Rastatter, L.; Toth, G.; Gombosi, T.
2007-01-01
There is a growing number of observational evidences of dynamic quasi-periodical magnetosphere response to continuously southward interplan etary magnetic field (IMF). However, traditional global MHD simulatio ns with magnetic reconnection supported by numerical dissipation and ad hoc anomalous resistivity driven by steady southward IMF often prod uce only quasi-steady configurations with almost stationary near-eart h neutral line. This discrepancy can be explained by the assumption that global MHD simulations significantly underestimate the reconnectio n rate in the magnetotail during substorm expansion phase. Indeed, co mparative studies of magnetic reconnection in small scale geometries demonstrated that traditional resistive MHD did not produce the fast r econnection rates observed in kinetic simulations. The major approxim ation of the traditional MHD approach is an isotropic fluid assumption) with zero off-diagonal pressure tensor components. The approximatio n, however, becomes invalid in the diffusion region around the reconn ection site where ions become unmagnetized and experience nongyrotropic behaviour. Deviation from gyrotropy in particle distribution functi on caused by kinetic effects manifests itself in nongyrotropic pressu re tensor with nonzero off-diagonal components. We use the global MHD code BATS-R-US and replace ad hoc parameters such as "critical curren t density" and "anomalous resistivity" with a physically motivated di ssipation model. The key element of the approach is to identify diffusion regions where the isotropic fluid MHD approximation is not applic able. We developed an algorithm that searches for locations of magnet otail reconnection sites. The algorithm takes advantage of block-based domain-decomposition technique employed by the BATS-R-US. Boundaries of the diffusion region around each reconnection site are estimated from the gyrotropic orbit threshold condition, where the ion gyroradius is equal to the distance to the
Turbulent Reconnection Rates from Cluster Observations in the Magneto sheath
NASA Technical Reports Server (NTRS)
Wendel, Deirdre
2011-01-01
The role of turbulence in producing fast reconnection rates is an important unresolved question. Scant in situ analyses exist. We apply multiple spacecraft techniques to a case of nonlinear turbulent reconnection in the magnetosheath to test various theoretical results for turbulent reconnection rates. To date, in situ estimates of the contribution of turbulence to reconnection rates have been calculated from an effective electric field derived through linear wave theory. However, estimates of reconnection rates based on fully nonlinear turbulence theories and simulations exist that are amenable to multiple spacecraft analyses. Here we present the linear and nonlinear theories and apply some of the nonlinear rates to Cluster observations of reconnecting, turbulent current sheets in the magnetos heath. We compare the results to the net reconnection rate found from the inflow speed. Ultimately, we intend to test and compare linear and nonlinear estimates of the turbulent contribution to reconnection rates and to measure the relative contributions of turbulence and the Hall effect.
Turbulent Reconnection Rates from Cluster Observations in the Magnetosheath
NASA Technical Reports Server (NTRS)
Wendel, Deirdre
2011-01-01
The role of turbulence in producing fast reconnection rates is an important unresolved question. Scant in situ analyses exist. We apply multiple spacecraft techniques to a case of nonlinear turbulent reconnection in the magnetosheath to test various theoretical results for turbulent reconnection rates. To date, in situ estimates of the contribution of turbulence to reconnection rates have been calculated from an effective electric field derived through linear wave theory. However, estimates of reconnection rates based on fully nonlinear turbulence theories and simulations exist that are amenable to multiple spacecraft analyses. Here we present the linear and nonlinear theories and apply some of the nonlinear rates to Cluster observations of reconnecting, turbulent current sheets in the magnetosheath. We compare the results to the net reconnection rate found from the inflow speed. Ultimately, we intend to test and compare linear and nonlinear estimates of the turbulent contribution to reconnection rates and to measure the relative contributions of turbulence and the Hall effect.
Supermagnetosonic Jets behind a Collisionless Quasiparallel Shock
Hietala, H.; Vainio, R.; Laitinen, T. V.; Vaivads, A.; Andreeova, K.; Palmroth, M.; Pulkkinen, T. I.; Koskinen, H. E. J.; Lucek, E. A.; Reme, H.
2009-12-11
The downstream region of a collisionless quasiparallel shock is structured containing bulk flows with high kinetic energy density from a previously unidentified source. We present Cluster multispacecraft measurements of this type of supermagnetosonic jet as well as of a weak secondary shock front within the sheath, that allow us to propose the following generation mechanism for the jets: The local curvature variations inherent to quasiparallel shocks can create fast, deflected jets accompanied by density variations in the downstream region. If the speed of the jet is super(magneto)sonic in the reference frame of the obstacle, a second shock front forms in the sheath closer to the obstacle. Our results can be applied to collisionless quasiparallel shocks in many plasma environments.
Matsumoto, Y; Amano, T; Kato, T N; Hoshino, M
2015-02-27
Explosive phenomena such as supernova remnant shocks and solar flares have demonstrated evidence for the production of relativistic particles. Interest has therefore been renewed in collisionless shock waves and magnetic reconnection as a means to achieve such energies. Although ions can be energized during such phenomena, the relativistic energy of the electrons remains a puzzle for theory. We present supercomputer simulations showing that efficient electron energization can occur during turbulent magnetic reconnection arising from a strong collisionless shock. Upstream electrons undergo first-order Fermi acceleration by colliding with reconnection jets and magnetic islands, giving rise to a nonthermal relativistic population downstream. These results shed new light on magnetic reconnection as an agent of energy dissipation and particle acceleration in strong shock waves. PMID:25722406
Stochastic electron acceleration during turbulent reconnection in strong shock waves
NASA Astrophysics Data System (ADS)
Matsumoto, Yosuke
2016-04-01
Acceleration of charged particles is a fundamental topic in astrophysical, space and laboratory plasmas. Very high energy particles are commonly found in the astrophysical and planetary shocks, and in the energy releases of solar flares and terrestrial substorms. Evidence for relativistic particle production during such phenomena has attracted much attention concerning collisionless shock waves and magnetic reconnection, respectively, as ultimate plasma energization mechanisms. While the energy conversion proceeds macroscopically, and therefore the energy mostly flows to ions, plasma kinetic instabilities excited in a localized region have been considered to be the main electron heating and acceleration mechanisms. We present that efficient electron energization can occur in a much larger area during turbulent magnetic reconnection from the intrinsic nature of a strong collisionless shock wave. Supercomputer simulations have revealed a multiscale shock structure comprising current sheets created via an ion-scale Weibel instability and resulting energy dissipation through magnetic reconnection. A part of the upstream electrons undergoes first-order Fermi acceleration by colliding with reconnection jets and magnetic islands, giving rise to a nonthermal relativistic population downstream. The dynamics has shed new light on magnetic reconnection as an agent of energy dissipation and particle acceleration in strong shock waves.
Reconnection in thin current sheets
NASA Astrophysics Data System (ADS)
Tenerani, Anna; Velli, Marco; Pucci, Fulvia; Rappazzo, A. F.
2016-05-01
It has been widely believed that reconnection is the underlying mechanism of many explosive processes observed both in nature and laboratory, but the question of reconnection speed and initial trigger have remained mysterious. How is fast magnetic energy release triggered in high Lundquist (S) and Reynolds (R) number plasmas?It has been shown that a tearing mode instability can grow on an ideal timescale, i.e., independent from the the Lundquist number, once the current sheet thickness becomes thin enough, or rather the inverse aspect ratio a/L reaches a scale a/L~S-1/3. As such, the latter provides a natural, critical threshold for current sheets that can be formed in nature before they disrupt in a few Alfvén time units. Here we discuss the transition to fast reconnection extended to simple viscous and kinetic models and we propose a possible scenario for the transition to explosive reconnection in high-Lundquist number plasmas, that we support with fully nonlinear numerical MHD simulations of a collapsing current sheet.
Gyro-induced acceleration of magnetic reconnection
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.
VINETA II: a linear magnetic reconnection experiment.
Bohlin, H; Von Stechow, A; Rahbarnia, K; Grulke, O; Klinger, T
2014-02-01
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. PMID:24593355
VINETA II: A linear magnetic reconnection experiment
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.
Transition from antiparallel to component magnetic reconnection
NASA Astrophysics Data System (ADS)
Swisdak, M.; Drake, J. F.; Shay, M. A.; McIlhargey, J. G.
2005-05-01
We study the transition between antiparallel and component collisionless magnetic reconnection with two-dimensional particle-in-cell simulations. The primary finding is that a guide field ≈0.1 times as strong as the asymptotic reconnecting field (roughly the field strength at which the electron Larmor radius is comparable to the width of the electron current layer) is sufficient to magnetize the electrons in the vicinity of the X line, thus causing significant changes to the structure of the electron dissipation region. This implies that great care should be exercised before concluding that magnetospheric reconnection is antiparallel. We also find that even for such weak guide fields, strong inward flowing electron beams form in the vicinity of the magnetic separatrices and Buneman unstable distribution functions arise at the X line itself. As in the calculations of Hesse et al. (2002) and Yin and Winske (2003) the nongyrotropic elements of the electron pressure tensor play the dominant role in decoupling the electrons from the magnetic field at the X line, regardless of the magnitude of the guide field and the associated strong variations in the pressure tensor's spatial structure. Despite these changes, and consistent with previous work, the reconnection rate does not vary appreciably with the strength of the guide field as it changes between 0 and a value equal to the asymptotic reversed field.
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.
A Parallel Two-fluid Code for Global Magnetic Reconnection Studies
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.
Studies of Magnetic Reconnection in Colliding Laser-Produced Plasmas
NASA Astrophysics Data System (ADS)
Rosenberg, Michael
2013-10-01
Novel images of magnetic fields and measurements of electron and ion temperatures have been obtained in the magnetic reconnection region of high- β, laser-produced plasmas. Experiments using laser-irradiated foils produce expanding, hemispherical plasma plumes carrying MG Biermann-battery magnetic fields, which can be driven to interact and reconnect. Thomson-scattering measurements of electron and ion temperatures in the interaction region of two colliding, magnetized plasmas show no thermal enhancement due to reconnection, as expected for β ~ 8 plasmas. Two different proton radiography techniques used to image the magnetic field structures show deformation, pileup, and annihilation of magnetic flux. High-resolution images reveal unambiguously reconnection-induced jets emerging from the interaction region and show instabilities in the expanding plasma plumes and supersonic, hydrodynamic jets due to the plasma collision. Quantitative magnetic flux data show that reconnection in experiments with asymmetry in the scale size, density, temperature, and plasma flow across the reconnection region occurs less efficiently than in similar, symmetric experiments. This result is attributed to disruption of the Hall mechanism mediating collisionless reconnection. The collision of plasmas carrying parallel magnetic fields has also been probed, illustrating the deformation of magnetic field structures in high-energy-density plasmas in the absence of reconnection. These experiments are particularly relevant to high- β reconnection environments, such as the magnetopause. This work was performed in collaboration with C. Li, F. Séguin, A. Zylstra, H. Rinderknecht, H. Sio, J. Frenje, and R. Petrasso (MIT), I. Igumenshchev, V. Glebov, C. Stoeckl, and D. Froula (LLE), J. Ross and R. Town (LLNL), W. Fox (UNH), and A. Nikroo (GA), and was supported in part by the NLUF, FSC/UR, U.S. DOE, LLNL, and LLE.
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.
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.
Magnetopause reconnection diffusion regions resolved by the NASA Magnetospheric Multiscale mission
NASA Astrophysics Data System (ADS)
Chen, Li-Jen
2016-07-01
Our understanding of how magnetic reconnection occurs in collisionless plasmas depends highly on our ability to resolve structures of the diffusion region. Unraveling the physical processes in the diffusion region is the primary goal of the NASA mission Magnetospheric Multiscale (MMS). With its first science phase began in September, 2015, the four MMS satellites have encountered both ion and electron diffusion regions during magnetopause reconnection. We will discuss a few diffusion region events including cases with negligible and finite guide fields, and compare the results with particle-in-cell (PIC) simulations. In particular, a close comparison between particle distribution functions observed by MMS and those predicted by PIC will be made to highlight how the unprecedented high-resolution MMS measurements advance the current state-of-knowledge on collisionless reconnection.
Debye scale turbulence within the electron diffusion layer during magnetic reconnection
Jara-Almonte, J.; Ji, H.
2014-03-15
During collisionless, anti-parallel magnetic reconnection, the electron diffusion layer is the region of both fieldline breaking and plasma mixing. Due to the in-plane electrostatic fields associated with collisionless reconnection, the inflowing plasmas are accelerated towards the X-line and form counter-streaming beams within the unmagnetized diffusion layer. This configuration is inherently unstable to in-plane electrostatic streaming instabilities provided that there is sufficient scale separation between the Debye length λ{sub D} and the electron skin depth c/ω{sub pe}. This scale separation has hitherto not been well resolved in kinetic simulations. Using both 2D fully kinetic simulations and a simple linear model, we demonstrate that these in-plane streaming instabilities generate Debye scale turbulence within the electron diffusion layer at electron temperatures relevant to magnetic reconnection both in the magnetosphere and in laboratory experiments.
Intimate connection of turbulence and reconnection: theory, testing and consequences
NASA Astrophysics Data System (ADS)
Lazarian, Alex
2016-07-01
I shall show that magnetic reconnection and turbulence are intrinsically connected: in the presence of turbulence magnetic reconnection gets fast while magnetic turbulence depends on reconnection for its cascading. I shall present the basics of the theory of turbulent magnetic reconnection in non-relativistic and relativistic plasmas, discuss numerical and observational tests of the theory and outline the consequences of the theory from diffusion of magnetic fields in Parker spiral and in the process of star formation to violent flares accelerating energetic particles in solar flares and gamma ray bursts.
Experimental study of ion heating and acceleration during magnetic reconnection
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
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.
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.
Reconnection in Planetary Magnetospheres
NASA Technical Reports Server (NTRS)
Russell, C. T.
2000-01-01
Current sheets in planetary magnetospheres that lie between regions of "oppositely-directed" magnetic field are either magnetopause-like, separating plasmas with different properties, or tail-like, separating plasmas of rather similar properties. The magnetopause current sheets generally have a nearly limitless supply of magnetized plasma that can reconnect, possibly setting up steady-state reconnection. In contrast, the plasma on either side of a tail current sheet is stratified so that, as reconnection occurs, the plasma properties, in particular the Alfven velocity, change. If the density drops and the magnetic field increases markedly perpendicular to the sheet, explosive reconnection can occur. Even though steady state reconnection can take place at magnetopause current sheets, the process often appears to be periodic as if a certain low average rate was demanded by the conditions but only a rapid rate was available. Reconnection of sheared fields has been postulated to create magnetic ropes in the solar corona, at the Earth's magnetopause, and in the magnetotail. However, this is not the only way to produce magnetic ropes as the Venus ionosphere shows. The geometry of the reconnecting regions and the plasma conditions both can affect the rate of reconnection. Sorting out the various controlling factors can be assisted through the examination of reconnection in planetary settings. In particular we observe similar small-scale tearing in the magnetopause current layers of the Earth, Saturn. Uranus and Neptune and the magnetodisk current sheet at Jupiter. These sites may be seeds for rapid reconnection if the reconnection site reaches a high Alfven velocity region. In the Jupiter magnetosphere this appears to be achieved with resultant substorm activity. Similar seeds may be present in the Earth's magnetotail with the first one to reach explosive growth dominating the dynamics of the tail.
Notes on Magnetohydrodynamics of Magnetic Reconnection in Turbulent Media
NASA Astrophysics Data System (ADS)
Browning, Philippa; Lazarian, Alex
2013-10-01
Astrophysical fluids have very large Reynolds numbers and therefore turbulence is their natural state. Magnetic reconnection is an important process in many astrophysical plasmas, which allows restructuring of magnetic fields and conversion of stored magnetic energy into heat and kinetic energy. Turbulence is known to dramatically change different transport processes and therefore it is not unexpected that turbulence can alter the dynamics of magnetic field lines within the reconnection process. We shall review the interaction between turbulence and reconnection at different scales, showing how a state of turbulent reconnection is natural in astrophysical plasmas, with implications for a range of phenomena across astrophysics. We consider the process of magnetic reconnection that is fast in magnetohydrodynamic (MHD) limit and discuss how turbulence—both externally driven and generated in the reconnecting system—can make reconnection independent on the microphysical properties of plasmas. We will also show how relaxation theory can be used to calculate the energy dissipated in turbulent reconnecting fields. As well as heating the plasma, the energy dissipated by turbulent reconnection may cause acceleration of non-thermal particles, which is briefly discussed here.
Notes on Magnetohydrodynamics of Magnetic Reconnection in Turbulent Media
NASA Astrophysics Data System (ADS)
Browning, Philippa; Lazarian, Alex
Astrophysical fluids have very large Reynolds numbers and therefore turbulence is their natural state. Magnetic reconnection is an important process in many astrophysical plasmas, which allows restructuring of magnetic fields and conversion of stored magnetic energy into heat and kinetic energy. Turbulence is known to dramatically change different transport processes and therefore it is not unexpected that turbulence can alter the dynamics of magnetic field lines within the reconnection process. We shall review the interaction between turbulence and reconnection at different scales, showing how a state of turbulent reconnection is natural in astrophysical plasmas, with implications for a range of phenomena across astrophysics. We consider the process of magnetic reconnection that is fast in magnetohydrodynamic (MHD) limit and discuss how turbulence—both externally driven and generated in the reconnecting system—can make reconnection independent on the microphysical properties of plasmas. We will also show how relaxation theory can be used to calculate the energy dissipated in turbulent reconnecting fields. As well as heating the plasma, the energy dissipated by turbulent reconnection may cause acceleration of non-thermal particles, which is briefly discussed here.
The microphysics of collisionless shocks
NASA Astrophysics Data System (ADS)
Wilson, Lynn Bruce, III
2010-11-01
Shock waves in interplanetary (IP) space are of considerable interest due to their potential to damage ground based electronic systems and their ability to energize charged particles. The energization of charged particles at IP shocks has the obvious extrapolation to supernova shock waves, which are thought to be a candidate for generating the most energetic particles in the universe. The observations and theory behind collisionless shock wave evolution suggest that IP shocks should, for the most part, be stable structures which require energy dissipation. In a regular fluid, like our atmosphere, energy dissipation is accomplished through binary particle collisions transferring the loss of bulk flow kinetic energy to heat. Plasmas are mostly collisionless fluids, thus requiring other means by which to dissipate energy. The studies herein were performed using wave and particle data primarily from the Wind spacecraft to investigate the microphysics of IP shock energy dissipation mechanisms. Due to their lower Mach numbers, more simplified geometry, and quasi-perpendicular nature, IP shock waves are an excellent laboratory to study wave-particle related dissipation mechanisms. Utilization of multiple data sets from multiple high time resolution instruments on board the Wind spacecraft, we have performed studies on the transition region microphysics of IP shocks. The work began with a statistical study of high frequency (≥ 1 kHz) waveform capture data during 67 IP shocks with Mach numbers ranging from ∼1-6 found ion-acoustic wave amplitudes correlated with the fast mode Mach number and shock strength. The ion-acoustic waves (IAWs) were estimated to produce anomalous resistivities roughly seven orders of magnitude above classical estimates. Another study was an examination of low frequency waves (0.25 Hz < f < 10 Hz) at five quasi-perpendicular IP shocks found the wave modes to be consistent with oblique precusor whistler waves at four of the events. The strongest
High power heating of magnetic reconnection in merging tokamak experimentsa)
NASA Astrophysics Data System (ADS)
Ono, Y.; Tanabe, H.; Yamada, T.; Gi, K.; Watanabe, T.; , T., Ii; Gryaznevich, M.; Scannell, R.; Conway, N.; Crowley, B.; Michael, C.
2015-05-01
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˜105. 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 Brec2 ˜ Bp2. The guide toroidal field Bt 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 Bt, 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 Bp > 0.4 T will enables us to heat the plasma to the alpha heating regime: Ti > 5 keV without using any additional heating facility.
Asymmetric Reconnection in the Terrestrial Reconnection EXperiment
NASA Astrophysics Data System (ADS)
Olson, Joseph; Egedal, Jan; Forest, Cary; Wallace, John; TREX Team; MPDX Team
2014-10-01
The Terrestrial Reconnection EXperiment (TREX) is a new and versatile addition to the Wisconsin Plasma Astrophysics Laboratory (WiPAL) at the University of Wisconsin-Madison. TREX is optimized for the study of kinetic reconnection in various regimes and to provide the first laboratory evidence in support of a new model describing the dynamics of trapped electrons and correlating pressure anisotropy. The initial configuration implemented in TREX is specially designed to study asymmetric reconnection scenarios. These are particularly relevant to the dayside magnetopause in which the plasma beta of the solar wind and of the magnetosphere can differ by factors of 100-1000. The configuration utilizes the Helmholtz coils to produce a static, uniform magnetic field up to 275 G through the 3 m spherical vacuum vessel. Plasma is produced on a 10 s rep rate while two internal coils are pulsed, creating an opposing magnetic field to induce reconnection with asymmetric high and low beta inflows. A Langmuir and Bdot probe array is swept in between pulses to build up the magnetic profiles in the reconnection region. Preliminary data from these initial runs will be presented.
Spontaneous three-dimensional magnetic reconnection in merging toroidal plasma experiment
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.
Spontaneous three-dimensional magnetic reconnection in merging toroidal plasma experiment
NASA Astrophysics Data System (ADS)
Ii, Toru; Ono, Yasushi
2013-01-01
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.
What Can We Learn about Magnetotail Reconnection from 2D PIC Harris-Sheet Simulations?
NASA Astrophysics Data System (ADS)
Goldman, M. V.; Newman, D. L.; Lapenta, G.
2016-03-01
The Magnetosphere Multiscale Mission (MMS) will provide the first opportunity to probe electron-scale physics during magnetic reconnection in Earth's magnetopause and magnetotail. This article will address only tail reconnection—as a non-steady-state process in which the first reconnected field lines advance away from the x-point in flux pile-up fronts directed Earthward and anti-Earthward. An up-to-date microscopic physical picture of electron and ion-scale collisionless tail reconnection processes is presented based on 2-D Particle-In-Cell (PIC) simulations initiated from a Harris current sheet and on Cluster and Themis measurements of tail reconnection. The successes and limitations of simulations when compared to measured reconnection are addressed in detail. The main focus is on particle and field diffusion region signatures in the tail reconnection geometry. The interpretation of these signatures is vital to enable spacecraft to identify physically significant reconnection events, to trigger meaningful data transfer from MMS to Earth and to construct a useful overall physical picture of tail reconnection. New simulation results and theoretical interpretations are presented for energy transport of particles and fields, for the size and shape of electron and ion diffusion regions, for processes occurring near the fronts and for the j × B (Hall) electric field.
NASA Astrophysics Data System (ADS)
Cassak, P.; Doss, C.; Palmroth, M.; Hoilijoki, S.; Pfau-Kempf, Y.; Ganse, U.; Dorelli, J.
2015-12-01
Flux ropes caused by magnetic reconnection commonly form at the dayside magnetopauses of Earth and other planets, such as Mercury and Jupiter. They are convected tailward due to their interaction with the solar wind and as the result of reconnection. The leading model for their tailward propagation speed at Earth's magnetopause has been described using boundary layer physics (Cowley and Owen, Planet. Space Sci., 37, 1461, 1989). We revisit this topic, noting that during times when the reconnection at both X-lines bracketing the flux ropes remain active, there should be consistency with the scaling laws of asymmetric magnetic reconnection with a flow shear. The convection speed of an isolated reconnecting X-line as a function of arbitrary upstream plasma parameters, including the reconnecting magnetic fields, densities, and upstream flow in the plane of the fields, was recently calculated analytically and tested with two-fluid simulations (Doss et al., J. Geophys. Res., submitted). Here, we present fully electromagnetic kinetic particle-in-cell simulations of local asymmetric reconnection with a flow shear that confirm the prediction in collisionless plasmas relevant to planetary magnetospheres. It is notable that the X-line convects even for sub-Alfvenic flow shear and can reconnect even for flow speeds exceeding twice the magnetosheath Alfven speed, which counters previous models. The application of these results for flux rope motion in global magnetospheric simulations of Earth is discussed, as are applications to the magnetospheres of other planets.
Weak collisionless shocks in laser-plasmas
NASA Astrophysics Data System (ADS)
Cairns, R. A.; Bingham, R.; Trines, R. G. M.; Norreys, P.
2015-04-01
We obtain a theory describing laminar shock-like structures in a collisionless plasma and examine the parameter limits, in terms of the ion sound Mach number and the electron/ion temperature ratio, within which these structures exist. The essential feature is the inclusion of finite ion temperature with the result that some ions are reflected from a potential ramp. This destroys the symmetry between upstream and downstream regions that would otherwise give the well-known ion solitary wave solution. We have shown earlier (Cairns et al 2014 Phys. Plasmas 21 022112) that such structures may be relevant to problems such as the existence of strong, localized electric fields observed in laser compressed pellets and laser acceleration of ions. Here we present results on the way in which these structures may produce species separation in fusion targets and suggest that it may be possible to use shock ion acceleration for fast ignition.
Electron scale structures and magnetic reconnection signatures in the turbulent magnetosheath
NASA Astrophysics Data System (ADS)
Yordanova, E.; Vörös, Z.; Varsani, A.; Graham, D. B.; Norgren, C.; Khotyaintsev, Yu. V.; Vaivads, A.; Eriksson, E.; Nakamura, R.; Lindqvist, P.-A.; Marklund, G.; Ergun, R. E.; Magnes, W.; Baumjohann, W.; Fischer, D.; Plaschke, F.; Narita, Y.; Russell, C. T.; Strangeway, R. J.; Le Contel, O.; Pollock, C.; Torbert, R. B.; Giles, B. J.; Burch, J. L.; Avanov, L. A.; Dorelli, J. C.; Gershman, D. J.; Paterson, W. R.; Lavraud, B.; Saito, Y.
2016-06-01
Collisionless space plasma turbulence can generate reconnecting thin current sheets as suggested by recent results of numerical magnetohydrodynamic simulations. The Magnetospheric Multiscale (MMS) mission provides the first serious opportunity to verify whether small ion-electron-scale reconnection, generated by turbulence, resembles the reconnection events frequently observed in the magnetotail or at the magnetopause. Here we investigate field and particle observations obtained by the MMS fleet in the turbulent terrestrial magnetosheath behind quasi-parallel bow shock geometry. We observe multiple small-scale current sheets during the event and present a detailed look of one of the detected structures. The emergence of thin current sheets can lead to electron scale structures. Within these structures, we see signatures of ion demagnetization, electron jets, electron heating, and agyrotropy suggesting that MMS spacecraft observe reconnection at these scales.
Observed Aspects of Reconnection in Solar Eruptions
NASA Technical Reports Server (NTRS)
Moore, Ronald L.
2010-01-01
Signatures of reconnection in major CME (coronal mass ejection)/flare eruptions and in coronal X-ray jets are illustrated and interpreted. The signatures are magnetic field lines and their feet that brighten in flare emission. CME/flare eruptions are magnetic explosions in which: 1. The field that erupts is initially a closed arcade. 2. At eruption onset, most of the free magnetic energy to be released is not stored in field bracketing a current sheet, but in sheared field in the core of the arcade. 3. The sheared core field erupts by a process that from its start or soon after involves fast tether-cutting reconnection at an initially small current sheet low in the sheared core field. If the arcade has oppositely-directed field over it, the eruption process from its start or soon after also involves fast breakout reconnection at an initially small current sheet between the arcade and the overarching field. These aspects are shown by the small area of the bright field lines and foot-point flare ribbons in the onset of the eruption. 4. At either small current sheet, the fast reconnection progressively unleashes the erupting core field to erupt with progressively greater force. In turn, the erupting core field drives the current sheet to become progressively larger and to undergo progressively greater fast reconnection in the explosive phase of the eruption, and the flare arcade and ribbons grow to become comparable to the pre-eruption arcade in lateral extent. In coronal X-ray jets: 1. The magnetic energy released in the jet is built up by the emergence of a magnetic arcade into surrounding unipolar "open" field. 2. A simple jet is produced when a burst of reconnection occurs at the current sheet between the arcade and the open field. This produces a bright reconnection jet and a bright reconnection arcade that are both much smaller in diameter that the driving arcade. 3. A more complex jet is produced when the arcade has a sheared core field and undergoes an
Formation of Plasmoid Chains in Magnetic Reconnection
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.
Nonlinear regimes of forced magnetic reconnection
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.
Boosting magnetic reconnection by viscosity and thermal conduction
NASA Astrophysics Data System (ADS)
Minoshima, Takashi; Miyoshi, Takahiro; Imada, Shinsuke
2016-07-01
Nonlinear evolution of magnetic reconnection is investigated by means of magnetohydrodynamic simulations including uniform resistivity, uniform viscosity, and anisotropic thermal conduction. When viscosity exceeds resistivity (the magnetic Prandtl number P r m > 1 ), the viscous dissipation dominates outflow dynamics and leads to the decrease in the plasma density inside a current sheet. The low-density current sheet supports the excitation of the vortex. The thickness of the vortex is broader than that of the current for P r m > 1 . The broader vortex flow more efficiently carries the upstream magnetic flux toward the reconnection region, and consequently, boosts the reconnection. The reconnection rate increases with viscosity provided that thermal conduction is fast enough to take away the thermal energy increased by the viscous dissipation (the fluid Prandtl number Pr < 1). The result suggests the need to control the Prandtl numbers for the reconnection against the conventional resistive model.
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.
Aspiration-induced reconnection in spatial public-goods game
NASA Astrophysics Data System (ADS)
Zhang, Hai-Feng; Liu, Run-Ran; Wang, Zhen; Yang, Han-Xin; Wang, Bing-Hong
2011-04-01
In this letter, we introduce an aspiration-induced reconnection mechanism into the spatial public-goods game. A player will reconnect to a randomly chosen player if its payoff acquired from the group centered on the neighbor does not exceed the aspiration level. We find that an intermediate aspiration level can promote cooperation best. This optimal phenomenon can be explained by a negative feedback effect, namely, intermediate aspiration level is able to result in a weak peak of reconnection, which will effectively change the downfall of cooperators and facilitate the fast spreading of cooperation. While insufficient reconnection and excessive reconnection induced by low and high aspiration levels are not conductive to such an effect. Moreover, we find that the intermediate aspiration level can lead to the heterogeneous distribution of degree, which will be beneficial to the evolution of cooperation.
Entropy conservation in simulations of magnetic reconnection
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.
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.
NASA Technical Reports Server (NTRS)
Forbes, T. G.
1988-01-01
Shock waves produced by impulsively driven reconnection are investigated by carrying out numerical experiments using two-dimensional magnetohydrodynamics. The results of the numerical experiments imply that there are three different categories of shocks associated with impulsively driven reconnection: (1) fast-mode, blast waves which rapidly propagate away from the reconnection site; (2) slow-mode, Petschek shocks which are attached to the reconnection site; and (3) fast-mode, termination shocks which terminate the plasma jets flowing out from the reconnection site.
A visualization of Earth's magnetosphere on July 15-16, 2012, shows how constant magnetic reconnection caused by an arriving coronal mass ejection, or CME, from the sun disrupted the magnetosphere,...
THEMIS Sees Magnetic Reconnection
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...
Malyshkin, Leonid M
2008-11-28
The rate of quasistationary, two-dimensional magnetic reconnection is calculated in the framework of incompressible Hall magnetohydrodynamics, which includes the Hall and electron pressure terms in Ohm's law. The Hall-magnetohydrodynamics equations are solved in a local region across the reconnection electron layer, including only the upstream region and the layer center. In the case when the ion inertial length di is larger than the Sweet-Parker reconnection layer thickness, the dimensionless reconnection rate is found to be independent of the electrical resistivity and equal to di/L, where L is the scale length of the external magnetic field in the upstream region outside the electron layer and the ion layer thickness is found to be di. PMID:19113486
Malyshkin, Leonid M.
2008-11-28
The rate of quasistationary, two-dimensional magnetic reconnection is calculated in the framework of incompressible Hall magnetohydrodynamics, which includes the Hall and electron pressure terms in Ohm's law. The Hall-magnetohydrodynamics equations are solved in a local region across the reconnection electron layer, including only the upstream region and the layer center. In the case when the ion inertial length d{sub i} is larger than the Sweet-Parker reconnection layer thickness, the dimensionless reconnection rate is found to be independent of the electrical resistivity and equal to d{sub i}/L, where L is the scale length of the external magnetic field in the upstream region outside the electron layer and the ion layer thickness is found to be d{sub i}.
The onset of magnetic reconnection in three dimensions
Pritchett, P. L.
2013-08-15
The onset of collisionless magnetic reconnection in current sheets containing a localized enhancement of the initial normal magnetic field component is examined using 2D and 3D particle-in-cell simulations that treat a closed system. In the 2D case, the current sheet is found to remain stable for at least several hundred inverse ion cyclotron times. In 3D, however, the system is found to be unstable to a ballooning/interchange type of mode with wavenumber k{sub y}ρ{sub in}∼1 (where ρ{sub in} is the ion gyroradius in the normal field B{sub z}). These modes evolve to form intense “heads” of strongly enhanced B{sub z}; in the wake of the heads are regions of strongly reduced or reversed B{sub z}. These local field reversals lead to the onset of reconnection with reconnection electric fields several times more intense than typical values seen for 2D reconnection.
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.
Magnetic reconnection, buoyancy, and flapping motions in magnetotail explosions
NASA Astrophysics Data System (ADS)
Sitnov, M. I.; Merkin, V. G.; Swisdak, M.; Motoba, T.; Buzulukova, N.; Moore, T. E.; Mauk, B. H.; Ohtani, S.
2014-09-01
A key process in the interaction of magnetospheres with the solar wind is the explosive release of energy stored in the magnetotail. Based on observational evidence, magnetic reconnection is widely believed to be responsible. However, the very possibility of spontaneous reconnection in collisionless magnetotail plasmas has been questioned in kinetic theory for more than three decades. In addition, in situ observations by multispacecraft missions (e.g., THEMIS) reveal the development of buoyancy and flapping motions coexisting with reconnection. Never before have kinetic simulations reproduced all three primary modes in realistic 2-D configurations with a finite normal magnetic field. Moreover, 3-D simulations with closed boundaries suggest that the tail activity is dominated by buoyancy-driven instabilities, whereas reconnection is a secondary effect strongly localized in the dawn-dusk direction. In this paper, we use massively parallel 3-D fully kinetic simulations with open boundaries to show that sufficiently far from the planet explosive processes in the tail are dominated by reconnection motions. These motions occur in the form of spontaneously generated dipolarization fronts accompanied by changes in magnetic topology which extend in the dawn-dusk direction over the size of the simulation box, suggesting that reconnection onset causes a macroscale reconfiguration of the real magnetotail. In our simulations, buoyancy and flapping motions significantly disturb the primary dipolarization front but neither destroy it nor change the near 2-D picture of the front evolution critically. Consistent with recent multiprobe observations, dipolarization fronts are also found to be the main regions of energy conversion in the magnetotail.
Numerical simulations of multiple X-line reconnection in the dayside magnetopause
NASA Astrophysics Data System (ADS)
Kondoh, K.
2015-12-01
We study about the magnetic reconnection evolutions in the dayside geomagnetopause using the MHD numerical simulations on the basis of the spontaneous fast magnetic reconnection model. In this spontaneous reconnection model, the diffusion region is localized and the magnetic reconnection drastically evolves by the positive feedback between the growths of the macroscopic plasma flow and the microscopic resistivity. The localized diffusion region eventually becomes longer in the directions of the reconnection outflow. Then, the secondary reconnection occurs to divide into the two diffusion regions before forming the Sweet-Parker type diffusion region. In this term, background sheath flow helps stretching of the diffusion region and causes the difference of the strength of the reconnection rate at the each x-line.
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.
The Magnetospheric Multiscale Mission: New Data on Magnetic Reconnection
NASA Astrophysics Data System (ADS)
Burch, James
2015-11-01
The Magnetospheric Multiscale (MMS) mission was launched on March 12, 2015 into its Phase 1 elliptical orbit with apogee at 12 Earth radii (RE) . The baseline science goal for MMS is to Understand the microphysics of magnetic reconnection by determining the kinetic processes occurring in the electron diffusion region that are responsible for collisionless magnetic reconnection, especially how reconnection is initiated.In priority order, MMS will address three specific objectives: (1) Determine the role played by electron inertial effects and turbulent dissipation in driving magnetic reconnection in the electron diffusion region; (2) Determine the rate of magnetic reconnection and the parameters that control it. (3) Determine the role played by ion inertial effects in the physics of magnetic reconnection. During the six months of commissioning following launch, all of the instruments on the four spacecraft were made fully operational. Beginning on September 1, 2015 the spacecraft began their first scan of the dayside magnetopause in a tetrahedral formation with separations of 160 km. During Phase 1 the separation will be reduced in steps to 10 km and then adjusted to the separation that is judged to be optimum for reconnection studies. A second scan of the dayside magnetopause will be conducted at this optimum separation. Then apogee will be raised to 25 RE for a scan of the magnetotail with separations variable from 30 km to 400 km. Throughout the mission the payload will be operated at its maximum data rate, which is sufficient to investigate reconnection down to approximately the electron diffusion length scale with full 3D plasma electron distributions obtained in 30 ms, ion distributions at 150 ms, and magnetic and electric fields at 1 ms resolution. 3D plasma and energetic ion composition an energetic electron measurements along with plasma waves will also be made. The spacecraft potential is maintained below +4V by an ion emitter. Because of the large amount
Dispersion discontinuities of strong collisionless shocks
NASA Technical Reports Server (NTRS)
Coroniti, F. V.
1970-01-01
Linear fluid equations are used to estimate wave train properties of strong collisionless shocks. Fast shocks exhibit several dispersion changes with increasing Mach number. For perpendicular propagation into a finite-beta plasma, an ion cyclotron radius trailing wave train exists only for (M sub F)2 is smaller than 2. Oblique fast shocks have a leading ion inertia wave train if M sub A is smaller than root of M(+)/M(-) cos theta/2 and a trailing electron inertia train if M sub A is greater than root of M(+)/M(-) cos theta/2. If the downstream sound speed exceeds the flow speed, linear wave theory predicts a trailing ion acoustic structure which probably resides within the magnetic shock. For a turbulent shock model in which an effective electron-ion collision frequency exceeds the lower hybrid frequency, ions decouple from the magnetic field; the shock wave train now trails with electron inertia and electron gyroradius lengths. Comparisons of this turbulent model and observations on the earth's bow shock are made.
Expansion techniques for collisionless stellar dynamical simulations
Meiron, Yohai; Li, Baile; Holley-Bockelmann, Kelly; Spurzem, Rainer
2014-09-10
We present graphics processing unit (GPU) implementations of two fast force calculation methods based on series expansions of the Poisson equation. One method is the self-consistent field (SCF) method, which is a Fourier-like expansion of the density field in some basis set; the other method is the multipole expansion (MEX) method, which is a Taylor-like expansion of the Green's function. MEX, which has been advocated in the past, has not gained as much popularity as SCF. Both are particle-field methods and optimized for collisionless galactic dynamics, but while SCF is a 'pure' expansion, MEX is an expansion in just the angular part; thus, MEX is capable of capturing radial structure easily, while SCF needs a large number of radial terms. We show that despite the expansion bias, these methods are more accurate than direct techniques for the same number of particles. The performance of our GPU code, which we call ETICS, is profiled and compared to a CPU implementation. On the tested GPU hardware, a full force calculation for one million particles took ∼0.1 s (depending on expansion cutoff), making simulations with as many as 10{sup 8} particles fast for a comparatively small number of nodes.
Fluid vs. kinetic magnetic reconnection with strong guide fields
NASA Astrophysics Data System (ADS)
Stanier, A.; Simakov, Andrei N.; Chacón, L.; Daughton, W.
2015-10-01
The fast rates of magnetic reconnection found in both nature and experiments are important to understand theoretically. Recently, it was demonstrated that two-fluid magnetic reconnection remains fast in the strong guide field regime, regardless of the presence of fast-dispersive waves. This conclusion is in agreement with recent results from kinetic simulations, and is in contradiction to the findings in an earlier two-fluid study, where it was suggested that fast-dispersive waves are necessary for fast reconnection. In this paper, we give a more detailed derivation of the analytic model presented in a recent letter and present additional simulation results to support the conclusions that the magnetic reconnection rate in this regime is independent of both collisional dissipation and system-size. In particular, we present a detailed comparison between fluid and kinetic simulations, finding good agreement in both the reconnection rate and overall length of the current layer. Finally, we revisit the earlier two-fluid study, which arrived at different conclusions, and suggest an alternative interpretation for the numerical results presented therein.
Fluid vs. kinetic magnetic reconnection with strong guide fields
Stanier, A. Simakov, Andrei N.; Chacón, L.; Daughton, W.
2015-10-15
The fast rates of magnetic reconnection found in both nature and experiments are important to understand theoretically. Recently, it was demonstrated that two-fluid magnetic reconnection remains fast in the strong guide field regime, regardless of the presence of fast-dispersive waves. This conclusion is in agreement with recent results from kinetic simulations, and is in contradiction to the findings in an earlier two-fluid study, where it was suggested that fast-dispersive waves are necessary for fast reconnection. In this paper, we give a more detailed derivation of the analytic model presented in a recent letter and present additional simulation results to support the conclusions that the magnetic reconnection rate in this regime is independent of both collisional dissipation and system-size. In particular, we present a detailed comparison between fluid and kinetic simulations, finding good agreement in both the reconnection rate and overall length of the current layer. Finally, we revisit the earlier two-fluid study, which arrived at different conclusions, and suggest an alternative interpretation for the numerical results presented therein.
Reconnection at Earth's Dayside Magnetopause
NASA Astrophysics Data System (ADS)
Cassak, P. A.; Fuselier, S. A.
Magnetic reconnection at Earth's dayside magnetopause plays a crucial role in space weather-related phenomena. The response of the magnetosphere to input from interplanetary space differs greatly depending on where reconnection happens and how efficiently it reconnects magnetic flux from interplanetary space. This chapter is a pedagogical treatment of dayside reconnection. Introductory topics include a guide to the magnetosphere for the uninitiated and a brief history of the field. Technical topics include qualitative properties of dayside reconnection, such as where reconnection occurs and what it looks like, and how reconnection quantitatively depends on ambient conditions, including the effect of asymmetries, the diamagnetic drift, and flow shear. Both observational and theoretical aspects are discussed. The chapter is closed with a discussion of open questions and the outlook for the future of dayside reconnection research.
Dielectric and permeability effects in collisionless plasmas. [in collisionless plasmas
NASA Technical Reports Server (NTRS)
Cole, K. D.
1984-01-01
Using the unabridged Maxwell equations (including vectors D, E and H) new effects in collisionless plasmas are uncovered. In a steady state, it is found that spatially varying energy density of the electric field (E perpendicular) orthogonal to B produces electric current leading, under certain conditions, to the relationship P perpendicular + B(2)/8 pi-epsilon E perpendicular(2)/8 pi = constant, where epsilon is the dielectric constant of the plasma for fields orthogonal to B. In steady state quasi-two-dimensional flows in plasmas, a general relationship between the components of electric field parallel and perpendicular to B is found. These effects are significant in geophysical and astrophysical plasmas. The general conditions for a steady state in collisionless plasma are deduced. With time variations in a plasma, slow compared to ion-gyroperiod, there is a general current, (j-asterisk), which includes the well-known polarization current, given by J-asterisk = d/dt (E x M) + (P x B) x B B(-2) where M and P are the magnetization and polarization vectors respectively.
MULTI-FLUID SIMULATIONS OF CHROMOSPHERIC MAGNETIC RECONNECTION IN A WEAKLY IONIZED REACTING PLASMA
Leake, James E.; Lukin, Vyacheslav S.; Linton, Mark G.; Meier, Eric T.
2012-12-01
We present results from the first self-consistent multi-fluid simulations of chromospheric magnetic reconnection in a weakly ionized reacting plasma. We simulate two-dimensional magnetic reconnection in a Harris current sheet with a numerical model which includes ion-neutral scattering collisions, ionization, recombination, optically thin radiative loss, collisional heating, and thermal conduction. In the resulting tearing mode reconnection the neutral and ion fluids become decoupled upstream from the reconnection site, creating an excess of ions in the reconnection region and therefore an ionization imbalance. Ion recombination in the reconnection region, combined with Alfvenic outflows, quickly removes ions from the reconnection site, leading to a fast reconnection rate independent of Lundquist number. In addition to allowing fast reconnection, we find that these non-equilibria partial ionization effects lead to the onset of the nonlinear secondary tearing instability at lower values of the Lundquist number than has been found in fully ionized plasmas. These simulations provide evidence that magnetic reconnection in the chromosphere could be responsible for jet-like transient phenomena such as spicules and chromospheric jets.
Plasmoid Instabilities Mediated Three-Dimensional Magnetohydrodynamic Turbulent Reconnection
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.
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.
Energetics of the magnetic reconnection in laboratory and space plasmas
NASA Astrophysics Data System (ADS)
Yamada, Masaaki
2014-10-01
The essential feature of magnetic reconnection is that it energizes plasma particles by converting magnetic energy to particle energy. This talk addresses this key unresolved question; how is magnetic energy converted to plasma kinetic energy during reconnection? Our recent study on MRX demonstrates that more than half of the incoming magnetic energy is converted to particle energy at a remarkably fast speed (~ 0.2VA) in the reconnection layer. A question arises as to whether the present results should be applied to magnetic reconnection phenomena in the space astrophysical plasmas. In a reconnection region of effectively similar size in the Earth's magnetotail, the energy partition was carefully measured during multiple passages of the Cluster satellites. The half length of the tail reconnection layer (L) was estimated to be 2000-4000 km namely 3-6 di, (ion skin depth); the scale length of this measurement is very similar to the MRX case, L ~ 3di. Reconnection in the magneto-tail is driven by an external force, i.e., the solar wind, and the boundary conditions are very similar to the MRX setup. The observed energy partition is notably similar, namely, more than 50% of the magnetic energy flux is converted to the particle energy flux, which is dominated by the ion enthalpy flux, with smaller contributions from the electron enthalpy and heat flux. A broad implication will be discussed. Supported by DoE, NASA, NSF.
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.
The mechanisms of electron heating and acceleration during magnetic reconnection
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
Generation of collisionless shock in laser-produced plasmas
NASA Astrophysics Data System (ADS)
Fiuza, Frederico
2015-08-01
Collisionless shocks are ubiquitous in astrophysical environments and are tightly connected with magnetic-field amplification and particle acceleration. The fast progress in high-power laser technology is bringing the study of high Mach number shocks into the realm of laboratory plasmas, where in situ measurements can be made helping us understand the fundamental kinetic processes behind shocks. I will discuss the recent progress in laser-driven shock experiments at state-of-the-art facilities like NIF and Omega and how these results, together with ab initio massively parallel simulations, can impact our understanding of magnetic field amplification and particle acceleration in astrophysical plasmas.
Experimental Investigation of the Trigger Problem in Magnetic Reconnection
NASA Astrophysics Data System (ADS)
Egedal, Jan
2012-07-01
Magnetic reconnection releases magnetic energy not only in steady-state, but also in time-dependent and often explosive events requiring a transition from slow reconnection to fast. The question of what causes this transition is known as the ``trigger problem'' and is not well understood. We address the trigger problem using the Versatile Toroidal Facility (VTF) at MIT. We observe spontaneous reconnection events [1] with exponentially growing reconnection rates, and we characterize the 3D dynamics of these events using multiple internal probes. The observed reconnection is asymmetric: it begins at one toroidal location and propagates around in both directions. The spontaneous onset is facilitated by an interaction between the x-line current channel and a global mode in the electrostatic potential. It is this mode which breaks axisymmetry and enables a localized decrease in x-line current. We model the onset using an empirical Ohm's law and current continuity, which is maintained by ion polarization currents associated with the mode. The model reproduces the exponential growth of the reconnection electric field, and the model growth rate agrees well with the experimentally measured growth rate. The onset location is likely determined by small asymmetries in the in-vessel coils. To further investigate this conjecture new coils have been installed, which allow for controlled changes in toroidal asymmetry. The observations are suggestive of solar flare dynamics and are relevant to tokamak research [3]. [1] Egedal, J. et al. Laboratory Observations of Spontaneous Magnetic Reconnection. Phys. Rev. Lett. 98, 015003 (2007). [2] Katz, N. et al. Laboratory Observation of Localized Onset of Magnetic Reconnection. Phys. Rev. Lett. 104, 255004 (2010). [3] Park, H.K. et al. Self-organized Te redistribution during driven reconnection processes in high-temperature plasmas. Phys. Plasmas 13, 055907 (2006).
NASA Astrophysics Data System (ADS)
Gekelman, Walter; van Compernolle, Bart
2012-10-01
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 is detected by satellites close to the earth. Current sheets can tear into filaments and these are nothing other than flux ropes. Ropes are not static, they exert mutual JxB forces causing them to twist about each other and merge. Kink instabilities cause them to violently smash into each other and reconnect at the point of contact. We report on experiments done in the large plasma device (LAPD) at UCLA (L=17m,dia=60cm,0.3<=B0z<=2.5kG,n˜2x10^12cm-3)on three dimensional flux ropes. Two, three or more magnetic flux ropes are generated from initially adjacent pulsed current channels in a background magnetized plasma. The currents and magnetic fields form exotic shapes with no ignorable direction and no magnetic nulls. Volumetric space-time data show multiple reconnection sites with time-dependent locations. The concept of a quasi-separatrix layer (QSL), a tool to understand 3D reconnection without null points. In our experiment the QSL is a narrow ribbon-like region(s) that twists between field lines. Within the QSL(s) field lines that start close to one another rapidly diverge as they pass through one or more reconnection regions. When the field lines are tracked they are observed to slip along the QSL when reconnection occurs. The Heating and other co-existing waves will be presented.
Turbulent General Magnetic Reconnection
NASA Astrophysics Data System (ADS)
Eyink, G. L.
2015-07-01
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.
NASA Astrophysics Data System (ADS)
Kohler, Susanna
2016-05-01
Because the Sun is so close, it makes an excellent laboratory to study processes we cant examinein distant stars. One openquestion is that of how solar magnetic fields rearrange themselves, producing the tremendous releases of energy we observe as solar flares and coronal mass ejections (CMEs).What is Magnetic Reconnection?Magnetic reconnection occurs when a magnetic field rearranges itself to move to a lower-energy state. As field lines of opposite polarity reconnect, magnetic energy is suddenly converted into thermal and kinetic energy.This processis believed to be behind the sudden releases of energy from the solar surface in the form of solar flares and CMEs. But there are many different models for how magnetic reconnection could occur in the magnetic field at the Suns surface, and we arent sure which one of these reconnection types is responsible for the events we see.Recently, however, several studies have been published presenting some of the first observational support of specific reconnection models. Taken together, these observations suggest that there are likely several different types of reconnection happening on the solar surface. Heres a closer look at two of these recent publications:A pre-eruption SDO image of a flaring region (b) looks remarkably similar to a 3D cartoon for typical breakout configuration (a). Click for a closer look! [Adapted from Chen et al. 2016]Study 1:Magnetic BreakoutLed by Yao Chen (Shandong University in China), a team of scientists has presented observations made by the Solar Dynamics Observatory (SDO) of a flare and CME event that appears to have been caused by magnetic breakout.In the magnetic breakout model, a series of loops in the Suns lower corona are confined by a surrounding larger loop structure called an arcade higher in the corona. As the lower loops push upward, reconnection occurs in the upper corona, removing the overlying, confining arcade. Without that extra confinement, the lower coronal loops expand upward
Magneto-thermal reconnection of significance to space and astrophysics
NASA Astrophysics Data System (ADS)
Coppi, B.
2016-05-01
Magnetic reconnection processes that can be excited in collisionless plasma regimes are of interest to space and astrophysics to the extent that the layers in which reconnection takes place are not rendered unrealistically small by their unfavorable dependence on relevant macroscopic distances. The equations describing new modes producing magnetic reconnection over relatively small but significant distances, unlike tearing types of mode, even when dealing with large macroscopic scale lengths, are given. The considered modes are associated with a finite electron temperature gradient and have a phase velocity in the direction of the electron diamagnetic velocity that can reverse to the opposite direction as relevant parameters are varied over a relatively wide range. The electron temperature perturbation has a primary role in the relevant theory. In particular, when referring to regimes in which the longitudinal (to the magnetic field) electron thermal conductivity is relatively large, the electron temperature perturbation becomes singular if the ratio of the transverse to the longitudinal electron thermal conductivity becomes negligible.
Physics of collisionless phase mixing
Tsiklauri, D.; Haruki, T.
2008-11-15
Previous studies of phase mixing of ion cyclotron (IC), Alfvenic, waves in the collisionless regime have established the generation of parallel electric field and hence acceleration of electrons in the regions of transverse density inhomogeneity. However, outstanding issues were left open. Here we use the 2.5 D, relativistic, fully electromagnetic particle-in-cell code and an analytic magnetohydrodynamic (MHD) formulation, to establish the following points: (i) Using the generalized Ohm's law we find that the parallel electric field is supported mostly by the electron pressure tensor, with a smaller contribution from the electron inertia term. (ii) The generated parallel electric field and the fraction of accelerated electrons are independent of the IC wave frequency remaining at a level of six orders of magnitude larger than the Dreicer value and approximately 20%, respectively. The generated parallel electric field and the fraction of accelerated electrons increase with the increase of IC wave amplitude. The generated parallel electric field seems to be independent of plasma beta, while the fraction of accelerated electrons strongly increases with the decrease of plasma beta (for plasma beta of 0.0001 the fraction of accelerated electrons can be as large as 47%). (iii) In the collisionless regime IC wave dissipation length (that is defined as the distance over which the wave damps) variation with the driving frequency shows a deviation from the analytical MHD result, which we attribute to a possible frequency dependence of the effective resistivity. (iv) Effective anomalous resistivity, inferred from our numerical simulations, is at least four orders of magnitude larger than the classical Spitzer value.
High power heating of magnetic reconnection in merging tokamak experiments
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.
Supercritical Collisionless Shocks as a Mechanism for Preferential Heating in Coronal Holes
NASA Astrophysics Data System (ADS)
Zimbardo, G.
2009-12-01
A long standing problem of the solar corona is that heavy ions in coronal holes are preferentially heated, that is, their temperature is larger than the proton temperature in a way that is more than mass proportional, T_i/T_p > m_i/m_p. Supercritical collisionless shocks can be generated in the reconnection outflow region due to the merging of small magnetic dipoles with the unipolar magnetic field of coronal holes. We present a new model which shows that preferential heating of heavy ions can be caused by ion reflection off quasi-perpendicular collisionless shocks. The ion energization is due to the motional electric field in the shock frame, which is perpendicular to the magnetic field by definition: this can explain the observed temperature anisotropy with large perpendicular temperature. In turn, the temperature anisotropy can cause ion cyclotron emission, as observed in proximity of the Earth's bow shock. In this respect, the paradigm of preferential heating by ion cyclotron resonance is turned upside down. Experimental evidence of heavy ion heating at interplanetary shocks by a number of spacecraft is discussed, as well as the possibility to have a sufficient number of collisionless shocks in the polar corona. The cross-disciplinary character of this study is also emphasized.
NASA Astrophysics Data System (ADS)
Kohler, Susanna
2016-05-01
Because the Sun is so close, it makes an excellent laboratory to study processes we cant examinein distant stars. One openquestion is that of how solar magnetic fields rearrange themselves, producing the tremendous releases of energy we observe as solar flares and coronal mass ejections (CMEs).What is Magnetic Reconnection?Magnetic reconnection occurs when a magnetic field rearranges itself to move to a lower-energy state. As field lines of opposite polarity reconnect, magnetic energy is suddenly converted into thermal and kinetic energy.This processis believed to be behind the sudden releases of energy from the solar surface in the form of solar flares and CMEs. But there are many different models for how magnetic reconnection could occur in the magnetic field at the Suns surface, and we arent sure which one of these reconnection types is responsible for the events we see.Recently, however, several studies have been published presenting some of the first observational support of specific reconnection models. Taken together, these observations suggest that there are likely several different types of reconnection happening on the solar surface. Heres a closer look at two of these recent publications:A pre-eruption SDO image of a flaring region (b) looks remarkably similar to a 3D cartoon for typical breakout configuration (a). Click for a closer look! [Adapted from Chen et al. 2016]Study 1:Magnetic BreakoutLed by Yao Chen (Shandong University in China), a team of scientists has presented observations made by the Solar Dynamics Observatory (SDO) of a flare and CME event that appears to have been caused by magnetic breakout.In the magnetic breakout model, a series of loops in the Suns lower corona are confined by a surrounding larger loop structure called an arcade higher in the corona. As the lower loops push upward, reconnection occurs in the upper corona, removing the overlying, confining arcade. Without that extra confinement, the lower coronal loops expand upward
Inhomogeneous turbulence in magnetic reconnection
NASA Astrophysics Data System (ADS)
Yokoi, Nobumitsu
2016-07-01
Turbulence is expected to play an essential role in enhancing magnetic reconnection. Turbulence associated with magnetic reconnection is highly inhomogeneous: it is generated by inhomogeneities of the field configuration such as the velocity shear, temperature gradient, density stratification, magnetic shear, etc. This self-generated turbulence affects the reconnection through the turbulent transport. In this reconnection--turbulence interaction, localization of turbulent transport due to dynamic balance between several turbulence effects plays an essential role. For investigating inhomogeneous turbulence in a strongly nonlinear regime, closure or turbulence modeling approaches provide a powerful tool. A turbulence modeling approach for the magnetic reconnection is introduced. In the model, the mean-field equations with turbulence effects incorporated are solved simultaneously with the equations of turbulent statistical quantities that represent spatiotemporal properties of turbulence under the effect of large-scale field inhomogeneities. Numerical simulations of this Reynolds-averaged turbulence model showed that self-generated turbulence enhances magnetic reconnection. It was pointed out that reconnection states may be divided into three category depending on the turbulence level: (i) laminar reconnection; (ii) turbulent reconnection, and (iii) turbulent diffusion. Recent developments in this direction are also briefly introduced, which includes the magnetic Prandtl number dependence, spectral evolution, and guide-field effects. Also relationship of this fully nonlinear turbulence approach with other important approaches such as plasmoid instability reconnection will be discussed.
Kinetic simulations of secondary reconnection in the reconnection jet
NASA Astrophysics Data System (ADS)
Huang, S. Y.; Zhou, M.; Yuan, Z. G.; Fu, H. S.; He, J. S.; Sahraoui, F.; Aunai, N.; Deng, X. H.; Fu, S.; Pang, Y.; Wang, D. D.
2015-08-01
Magnetic reconnection, as one important energy dissipation process in plasmas, has been extensively studied in the past several decades. Magnetic reconnection occurring in the downstream of a primary X line is referred to as secondary reconnection. In this paper, we used kinetic simulations to investigate the secondary reconnection in detail. We found that secondary reconnection is reversed by the compression caused by the outflowing jet originating from the primary reconnection site, which results in the erosion of the magnetic island between the two X lines within ~3 ωci-1. We show the observational signatures expected in electromagnetic fields and plasma measurements in the Earth's magnetotail, associated with this mechanism. These simulation results could be applied to interpret the signatures associated with the evolution of earthward magnetic islands in the Earth's magnetotail.
Linear collisionless Landau damping in Hilbert space
NASA Astrophysics Data System (ADS)
Zocco, Alessandro
2015-08-01
The equivalence between the Laplace transform (Landau, J. Phys. USSR 10 (1946), 25) and Hermite transform (Zocco and Schekochihin, Phys. Plasmas 18, 102309 (2011)) solutions of the linear collisionless Landau damping problem is proven.
Critical Differences of Asymmetric Magnetic Reconnection from Standard Models
NASA Astrophysics Data System (ADS)
Nitta, S.; Wada, T.; Fuchida, T.; Kondoh, K.
2016-09-01
We have clarified the structure of asymmetric magnetic reconnection in detail as the result of the spontaneous evolutionary process. The asymmetry is imposed as ratio k of the magnetic field strength in both sides of the initial current sheet (CS) in the isothermal equilibrium. The MHD simulation is carried out by the HLLD code for the long-term temporal evolution with very high spatial resolution. The resultant structure is drastically different from the symmetric case (e.g., the Petschek model) even for slight asymmetry k = 2. (1) The velocity distribution in the reconnection jet clearly shows a two-layered structure, i.e., the high-speed sub-layer in which the flow is almost field aligned and the acceleration sub-layer. (2) Higher beta side (HBS) plasma is caught in a lower beta side plasmoid. This suggests a new plasma mixing process in the reconnection events. (3) A new large strong fast shock in front of the plasmoid forms in the HBS. This can be a new particle acceleration site in the reconnection system. These critical properties that have not been reported in previous works suggest that we contribute to a better and more detailed knowledge of the reconnection of the standard model for the symmetric magnetic reconnection system.
Explosive reconnection in magnetars
NASA Astrophysics Data System (ADS)
Lyutikov, Maxim
2003-12-01
The X-ray activity of anomalous X-ray pulsars and soft γ-ray repeaters may result from the heating of their magnetic corona by direct currents dissipated by magnetic reconnection. We investigate the possibility that X-ray flares and bursts observed from anomalous X-ray pulsars and soft γ-ray repeaters result from magnetospheric reconnection events initiated by development of the tearing mode in magnetically dominated relativistic plasma. We formulate equations of resistive force-free electrodynamics, discuss the relation of the latter to ideal electrodynamics, and give examples of both ideal and resistive equilibria. Resistive force-free current layers are unstable towards the development of small-scale current sheets where resistive effects become important. Thin current sheets are found to be unstable due to the development of the resistive force-free tearing mode. The growth rate of the tearing mode is intermediate between the short Alfvén time-scale τA and a long resistive time-scale τR: Γ~ 1/(τRτA)1/2, similar to the case of non-relativistic non-force-free plasma. We propose that growth of the tearing mode is related to the typical rise time of flares, ~10 ms. Finally, we discuss how reconnection may explain other magnetar phenomena and ways to test the model.
Acceleration during magnetic reconnection
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.
Reconnection of colliding vortex rings.
Chatelain, Philippe; Kivotides, Demosthenes; Leonard, Anthony
2003-02-01
We investigate numerically the Navier-Stokes dynamics of reconnecting vortex rings at small Reynolds number for a variety of configurations. We find that reconnections are dissipative due to the smoothing of vorticity gradients at reconnection kinks and to the formation of secondary structures of stretched antiparallel vorticity which transfer kinetic energy to small scales where it is subsequently dissipated efficiently. In addition, the relaxation of the reconnection kinks excites Kelvin waves which due to strong damping are of low wave number and affect directly only large scale properties of the flow. PMID:12633362
Experimental Study of Current-Driven Turbulence During Magnetic Reconnection
Porkolab, Miklos; Egedal-Pedersen, Jan; Fox, William
2010-08-31
nonlinear solitary wave known to evolve from a strong beam-on-tail instability. We established that fast electrons were produced by magnetic reconnection. Overall, these instabilities were found to be a consequence of reconnection, specifically the strong energization of electrons, leading to steep gradients in both coordinate- and velocity-space. Estimates (using quasi-linear theory) of the anomalous resistivity due to these modes did not appear large enough to substantially impact the reconnection process. Relevant publications: W. Fox, M. Porkolab, et al, Phys. Rev. Lett. 101, 255003 (2008). W. Fox, M. Porkolab, et al, Phys. Plasmas 17, 072303, (2010).
Nonlinear Weibel Instability and Turbulence in Strong Collisionless Shocks
Medvedev, Mikhail M.
2008-08-31
This research project was devoted to studies of collisionless shocks, their properties, microphysics and plasma physics of underlying phenomena, such as Weibel instability and generation of small-scale fields at shocks, particle acceleration and transport in the generated random fields, radiation mechanisms from these fields in application to astrophysical phenomena and laboratory experiments (e.g., laser-plasma and beam-plasma interactions, the fast ignition and inertial confinement, etc.). Thus, this study is highly relevant to astrophysical sciences, the inertial confinement program and, in particular, the Fast Ignition concept, etc. It makes valuable contributions to the shock physics, nonlinear plasma theory, as well as to the basic plasma science, in general.
Collisionless Trapped Electron Mode Turbulence
NASA Astrophysics Data System (ADS)
Lang, Jianying; Chen, Yang; Parker, Scott
2006-10-01
Collisionless Trapped Electron Mode (CTEM) turbulence is a likely canidate for explaining anomolous transport in tokamak discharges that have a strong density gradient relative to the ion temperature gradient. Here, CTEM turbulence is investigated using the Gyrokinetic δf GEM code. GEM is electromagnetic, includes full drift-kinetic electrons, generaly axisymmetric equilbria, collisions and minority species. Here, the flux-tube limit is taken and β is so small that the simulations are essentially electrostatic. Linear theory predicts that the instability occurs at √2ɛRLn>1, which agrees very well with the simulation results. With increasing density gradient, it is observed that the most unstable mode transitions from a CTEM to drift wave mode and the short-wavelength modes are most unstable ( 2 > kρi> 1). Nonlinear simulations are underway to address the parametric dependence of particle and energy transport. The importance of zonal flows for CTEM turbulence, is still not well understood and is under investigation. D. R. Ernst et. al., Phys. Plasma 11 (2004) 2637 T. Dannert and F. Jenko, Phys. Plasma 12 (2005) 072309 R. Gatto et. al., Phys. Plasma 13 (2006) 022306 Y. Chen and S. E. Parker, J. Comput. Phys. 189 (2003) 463 Y. Chen ad S.E. Parker, accepted, to appear in J. Comput. Phys. (2006) J. Wesson (1997) Tokamaks, Oxford Science
Collisional versus Collisionless Dark Matter.
Moore; Gelato; Jenkins; Pearce; Quilis
2000-05-20
We compare the structure and substructure of dark matter halos in model universes dominated by collisional, strongly self-interacting dark matter (SIDM) and collisionless, weakly interacting dark matter (CDM). While SIDM virialized halos are more nearly spherical than CDM halos, they can be rotationally flattened by as much as 20% in their inner regions. Substructure halos suffer ram-pressure truncation and drag, which are more rapid and severe than their gravitational counterparts tidal stripping and dynamical friction. Lensing constraints on the size of galactic halos in clusters are a factor of 2 smaller than predicted by gravitational stripping, and the recent detection of tidal streams of stars escaping from the satellite galaxy Carina suggests that its tidal radius is close to its optical radius of a few hundred parsecs-an order of magnitude smaller than predicted by CDM models but consistent with SIDM models. The orbits of SIDM satellites suffer significant velocity bias, sigmaSIDM&solm0;sigmaCDM=0.85, and are more circular than CDM satellites, betaSIDM approximately 0.5, in agreement with the inferred orbits of the Galaxy's satellites. In the limit of a short mean free path, SIDM halos have singular isothermal density profiles; thus, in its simplest incarnation SIDM, is inconsistent with galactic rotation curves. PMID:10828999
Radiative Magnetic Reconnection in Astrophysics
NASA Astrophysics Data System (ADS)
Uzdensky, D. A.
In this chapter we review a new and rapidly growing area of research in high-energy plasma astrophysics—radiative magnetic reconnection, defined here as a regime of reconnection where radiation reaction has an important influence on the reconnection dynamics, energetics, and/or nonthermal particle acceleration. This influence be may be manifested via a variety of radiative effects that are critical in many high-energy astrophysical applications. The most notable radiative effects in astrophysical reconnection include radiation-reaction limits on particle acceleration, radiative cooling, radiative resistivity, braking of reconnection outflows by radiation drag, radiation pressure, viscosity, and even pair creation at highest energy densities. The self-consistent inclusion of these effects into magnetic reconnection theory and modeling sometimes calls for serious modifications to our overall theoretical approach to the problem. In addition, prompt reconnection-powered radiation often represents our only observational diagnostic tool available for studying remote astrophysical systems; this underscores the importance of developing predictive modeling capabilities to connect the underlying physical conditions in a reconnecting system to observable radiative signatures. This chapter presents an overview of our recent theoretical progress in developing basic physical understanding of radiative magnetic reconnection, with a special emphasis on astrophysically most important radiation mechanisms like synchrotron, curvature, and inverse-Compton. The chapter also offers a broad review of key high-energy astrophysical applications of radiative reconnection, illustrated by multiple examples such as: pulsar wind nebulae, pulsar magnetospheres, black-hole accretion-disk coronae and hot accretion flows in X-ray Binaries and Active Galactic Nuclei and their relativistic jets, magnetospheres of magnetars, and Gamma-Ray Bursts. Finally, this chapter discusses the most critical
Kugland, N. L.; Ross, J. S.; Glenzer, S. H.; Huntington, C.; Martinez, D.; Plechaty, C.; Remington, B. A.; Ryutov, D. D.; Park, H.-S.; Chang, P.-Y.; Fiksel, G.; Froula, D. H.; Drake, R. P.; Grosskopf, M.; Kuranz, C.; Gregori, G.; Meinecke, J.; Reville, B.; Koenig, M.; Pelka, A.; and others
2013-05-15
Collisionless shocks are often observed in fast-moving astrophysical plasmas, formed by non-classical viscosity that is believed to originate from collective electromagnetic fields driven by kinetic plasma instabilities. However, the development of small-scale plasma processes into large-scale structures, such as a collisionless shock, is not well understood. It is also unknown to what extent collisionless shocks contain macroscopic fields with a long coherence length. For these reasons, it is valuable to explore collisionless shock formation, including the growth and self-organization of fields, in laboratory plasmas. The experimental results presented here show at a glance with proton imaging how macroscopic fields can emerge from a system of supersonic counter-streaming plasmas produced at the OMEGA EP laser. Interpretation of these results, plans for additional measurements, and the difficulty of achieving truly collisionless conditions are discussed. Future experiments at the National Ignition Facility are expected to create fully formed collisionless shocks in plasmas with no pre-imposed magnetic field.
NASA Astrophysics Data System (ADS)
Kugland, N. L.; Ross, J. S.; Chang, P.-Y.; Drake, R. P.; Fiksel, G.; Froula, D. H.; Glenzer, S. H.; Gregori, G.; Grosskopf, M.; Huntington, C.; Koenig, M.; Kuramitsu, Y.; Kuranz, C.; Levy, M. C.; Liang, E.; Martinez, D.; Meinecke, J.; Miniati, F.; Morita, T.; Pelka, A.; Plechaty, C.; Presura, R.; Ravasio, A.; Remington, B. A.; Reville, B.; Ryutov, D. D.; Sakawa, Y.; Spitkovsky, A.; Takabe, H.; Park, H.-S.
2013-05-01
Collisionless shocks are often observed in fast-moving astrophysical plasmas, formed by non-classical viscosity that is believed to originate from collective electromagnetic fields driven by kinetic plasma instabilities. However, the development of small-scale plasma processes into large-scale structures, such as a collisionless shock, is not well understood. It is also unknown to what extent collisionless shocks contain macroscopic fields with a long coherence length. For these reasons, it is valuable to explore collisionless shock formation, including the growth and self-organization of fields, in laboratory plasmas. The experimental results presented here show at a glance with proton imaging how macroscopic fields can emerge from a system of supersonic counter-streaming plasmas produced at the OMEGA EP laser. Interpretation of these results, plans for additional measurements, and the difficulty of achieving truly collisionless conditions are discussed. Future experiments at the National Ignition Facility are expected to create fully formed collisionless shocks in plasmas with no pre-imposed magnetic field.
Current sheets and pressure anisotropy in the reconnection exhaust
Le, A.; Karimabadi, H.; Roytershteyn, V.; Egedal, J.; Ng, J.; Scudder, J.; Daughton, W.; Liu, Y.-H.
2014-01-15
A particle-in-cell simulation shows that the exhaust during anti-parallel reconnection in the collisionless regime contains a current sheet extending 100 inertial lengths from the X line. The current sheet is supported by electron pressure anisotropy near the X line and ion anisotropy farther downstream. Field-aligned electron currents flowing outside the magnetic separatrices feed the exhaust current sheet and generate the out-of-plane, or Hall, magnetic field. Existing models based on different mechanisms for each particle species provide good estimates for the levels of pressure anisotropy. The ion anisotropy, which is strong enough to reach the firehose instability threshold, is also important for overall force balance. It reduces the outflow speed of the plasma.
Reconnections of Wave Vortex Lines
ERIC Educational Resources Information Center
Berry, M. V.; Dennis, M. R.
2012-01-01
When wave vortices, that is nodal lines of a complex scalar wavefunction in space, approach transversely, their typical crossing and reconnection is a two-stage process incorporating two well-understood elementary events in which locally coplanar hyperbolas switch branches. The explicit description of this reconnection is a pedagogically useful…
Turbulent reconnection and its implications
Lazarian, A.; Eyink, G.; Vishniac, E.; Kowal, G.
2015-01-01
Magnetic reconnection is a process of magnetic field topology change, which is one of the most fundamental processes happening in magnetized plasmas. In most astrophysical environments, the Reynolds numbers corresponding to plasma flows are large and therefore the transition to turbulence is inevitable. This turbulence, which can be pre-existing or driven by magnetic reconnection itself, must be taken into account for any theory of magnetic reconnection that attempts to describe the process in the aforementioned environments. This necessity is obvious as three-dimensional high-resolution numerical simulations show the transition to the turbulence state of initially laminar reconnecting magnetic fields. We discuss ideas of how turbulence can modify reconnection with the focus on the Lazarian & Vishniac (Lazarian & Vishniac 1999 Astrophys. J. 517, 700–718 ()) reconnection model. We present numerical evidence supporting the model and demonstrate that it is closely connected to the experimentally proven concept of Richardson dispersion/diffusion as well as to more recent advances in understanding of the Lagrangian dynamics of magnetized fluids. We point out that the generalized Ohm's law that accounts for turbulent motion predicts the subdominance of the microphysical plasma effects for reconnection for realistically turbulent media. We show that one of the most dramatic consequences of turbulence is the violation of the generally accepted notion of magnetic flux freezing. This notion is a cornerstone of most theories dealing with magnetized plasmas, and therefore its change induces fundamental shifts in accepted paradigms, for instance, turbulent reconnection entails reconnection diffusion process that is essential for understanding star formation. We argue that at sufficiently high Reynolds numbers the process of tearing reconnection should transfer to turbulent reconnection. We discuss flares that are predicted by turbulent reconnection and relate this process to
Turbulent reconnection and its implications.
Lazarian, A; Eyink, G; Vishniac, E; Kowal, G
2015-05-13
Magnetic reconnection is a process of magnetic field topology change, which is one of the most fundamental processes happening in magnetized plasmas. In most astrophysical environments, the Reynolds numbers corresponding to plasma flows are large and therefore the transition to turbulence is inevitable. This turbulence, which can be pre-existing or driven by magnetic reconnection itself, must be taken into account for any theory of magnetic reconnection that attempts to describe the process in the aforementioned environments. This necessity is obvious as three-dimensional high-resolution numerical simulations show the transition to the turbulence state of initially laminar reconnecting magnetic fields. We discuss ideas of how turbulence can modify reconnection with the focus on the Lazarian & Vishniac (Lazarian & Vishniac 1999 Astrophys. J. 517, 700-718 (doi:10.1086/307233)) reconnection model. We present numerical evidence supporting the model and demonstrate that it is closely connected to the experimentally proven concept of Richardson dispersion/diffusion as well as to more recent advances in understanding of the Lagrangian dynamics of magnetized fluids. We point out that the generalized Ohm's law that accounts for turbulent motion predicts the subdominance of the microphysical plasma effects for reconnection for realistically turbulent media. We show that one of the most dramatic consequences of turbulence is the violation of the generally accepted notion of magnetic flux freezing. This notion is a cornerstone of most theories dealing with magnetized plasmas, and therefore its change induces fundamental shifts in accepted paradigms, for instance, turbulent reconnection entails reconnection diffusion process that is essential for understanding star formation. We argue that at sufficiently high Reynolds numbers the process of tearing reconnection should transfer to turbulent reconnection. We discuss flares that are predicted by turbulent reconnection and relate
NASA Astrophysics Data System (ADS)
Yamada, M.; Yoo, J.; Swanson, C.; Jara Almonte, J.; Ji, H.; Myers, C. E.; Chen, L.
2013-12-01
Quantitative study of the energization of plasma particles in the magnetic reconnection layer has been carried out by monitoring the behavior of electrons and ions in MRX (1, 2). The measured profiles of plasma parameters are quantitatively analyzed with symmetric as well as asymmetric upstream conditions in the context of the two-fluid reconnection physics (1) and compared with the recent numerical simulation results. The electron heating is observed to extend beyond the electron diffusion region and considered to be due to energization by magnetic instabilities of incoming electrons trapped in the magnetic mirror. This energization often occurs impulsively. Ions are accelerated by an electrostatic field across the separatrices to the plasma exhaust region of the reconnection layer and become thermalized through re-magnetization by the exiting magnetic fields. In this paper, the acceleration and heating of ions and electrons which extents much wider than the length scale of the ion skin depth, is addressed quantitatively for the first time in a laboratory reconnection layer. A total energy inventory is calculated based on analysis of the Poynting, enthalpy, flow energy, and heat flux in the measured diffusion layer (3). More than half of the incoming magnetic energy is converted to particle energy during collisionless reconnection. The results will bring a new insight into the conversion mechanism of magnetic energy to that of plasma particles during magnetic reconnection. (1) M. Yamada, R. Kulsrud, H. Ji, Rev. Mod. Phys. v.82, 602 (2010) (2) J. Yoo et al, Phys. Rev. Letts. 110, 215007 (2013) (3) J. Eastwood et al., PRL 110, 225001 (2013) Fig. 1. Measured in-plane ion flow vectors along with the measured 2-D profile of the in-plane plasma potential Φp in the half reconnection plane of MRX. The thin black lines are measured contours of poloidal flux ψp. While ions flow across the separatrices, they turn in-plane electric field Ein.
3D Dynamics of Magnetopause Reconnection Using Hall-MHD Global Simulations
NASA Astrophysics Data System (ADS)
Maynard, K.; Germaschewski, K.; Raeder, J.; Bhattacharjee, A.
2011-12-01
Magnetic reconnection at Earth's magnetopause and in the magnetotail is of crucial importance for the dynamics of the global magnetosphere and space weather. Even though the plasma conditions in the magnetosphere are largely in the collisionless regime, most of the existing research using global computational models employ single-fluid magnetohydrodynamics (MHD) with artificial resistivity. Studies of reconnection in simplified, two-dimensional geometries have established that two-fluid and kinetic effects can dramatically alter dynamics and reconnection rates when compared with single-fluid models. These enhanced models also introduce particular signatures, for example a quadrupolar out-of-plane magnetic field component that has already been observed in space by satellite measurements. However, results from simplified geometries cannot be translated directly to the dynamics of three-dimensional magnetospheric reconnection. For instance, magnetic flux originating from the solar wind and arriving at the magnetopause can either reconnect or be advected around the magnetosphere. In this study, we use a new version of the OpenGGCM code that incorporates the Hall term in a Generalized Ohm's Law to study magnetopause reconnection under synthetic solar wind conditions and investigate how reconnection rates and dynamics of flux transfer events depend on the strength of the Hall term. The OpenGGCM, a global model of Earth's magnetosphere, has recently been ported to exploit modern computing architectures like the Cell processor and SIMD capabilities of conventional processors using an automatic code generator. These enhancements provide us with the performance needed to include the computationally expensive Hall physics.
A Model of Solar Flares Based on Arcade Field Reconnection and Merging of Magnetic Islands
G.S. Choe; C.Z. Cheng
2001-12-12
Solar flares are intense, abrupt releases of energy in the solar corona. In the impulsive phase of a flare, the intensity of hard X-ray emission reaches a sharp peak indicating the highest reconnection rate. It is often observed that an X-ray emitting plasma ejecta (plasmoid) is launched before the impulsive phase and accelerated throughout the phase. Thus, the plasmoid ejection may not be an effect of fast magnetic reconnection as conventionally assumed, but a cause of fast reconnection. Based on resistive magnetohydrodynamic simulations, a solar flare model is presented, which can explain these observational characteristics of flares. In the model, merging of a newly generated magnetic island and a pre-existing island results in stretching and thinning of a current sheet, in which fast magnetic reconnection is induced. Recurrence of homologous flares naturally arises in this model. Mechanisms of magnetic island formation are also discussed.
Electron Weibel Instability Mediated Laser Driven Electromagnetic Collisionless Shock
NASA Astrophysics Data System (ADS)
Jia, Qing; Mima, Kunioki; Cai, Hong-Bo; Taguchi, Toshihiro; Nagatomo, Hideo; He, X. T.
2015-11-01
As a fundamental nonlinear structure, collisionless shock is widely studied in astrophysics. Recently, the rapidly-developing laser technology provides a good test-bed to study such shock physics in laboratory. In addition, the laser driven shock ion acceleration is also interested due to its potential applications. We explore the effect of external parallel magnetic field on the collisionless shock formation and resultant particle acceleration by using the 2D3V PIC simulations. We show that unlike the electrostatic shock generated in the unmagnetized plasma, the shock generated in the weakly-magnetized laser-driven plasma is mostly electromagnetic (EM)-like with higher Mach number. The generation mechanism is due to the stronger transverse magnetic field self-generated at the nonlinear stage of the electron Weibel instability which drastically scatters particles and leads to higher energy dissipation. Simulation results also suggest more ions are reflected by this EM shock and results in larger energy transfer rate from the laser to ions, which is of advantage for applications such as neutron production and ion fast ignition.
Gamma-ray bursts and collisionless shocks
NASA Astrophysics Data System (ADS)
Waxman, E.
2006-12-01
Particle acceleration in collisionless shocks is believed to be responsible for the production of cosmic-rays over a wide range of energies, from a few GeV to > 1020 eV, as well as for the non-thermal emission of radiation from a wide variety of high energy astrophysical sources. A theory of collisionless shocks based on first principles does not, however, exist. Observations of γ-ray burst (GRB) 'afterglows' provide a unique opportunity for diagnosing the physics of relativistic collisionless shocks. Most GRBs are believed to be associated with explosions of massive stars. Their 'afterglows', delayed low energy emission following the prompt burst of γ-rays, are well accounted for by a model in which afterglow radiation is due to synchrotron emission of electrons accelerated in relativistic collisionless shock waves driven by the explosion into the surrounding plasma. Within the framework of this model, some striking characteristics of collisionless relativistic shocks are implied. These include the generation of downstream magnetic fields with energy density exceeding that of the upstream field by ~8 orders of magnitude, the survival of this strong field at distances ~1010 skin-depths downstream of the shock and the acceleration of particles to a power-law energy spectrum, d log n/d logɛ ap -2, possibly extending to 1020 eV. I review in this talk the phenomenological considerations, based on which these characteristics are inferred, and the challenges posed to our current models of particle acceleration and magnetic field generation in collisionless shocks. Some recent theoretical results derived based on the assumption of a self-similar shock structure are briefly discussed. Invited review presented at the 33rd annual European Physical Society Conference, Rome, 2006.
Impulsive reconnection: 3D onset and stagnation in turbulent paradigms
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.
Magnetic reconnection launcher
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.
Numerical Studies of Collisionless Current Layers
NASA Technical Reports Server (NTRS)
Quest, Kevin B.
1993-01-01
The purpose of this proposal was to investigate collisionless current layers using a variety of analytic and numerical tools. The first year of the contract was dedicated to analytical studies, to the porting and adaption of codes being used in this study, and to the numerical simulation of collisionless current layers. The second year entailed the development of multi-dimensional hybrid algorithms as well as the re-examination of the problem of integro-differential equations that occur in the linear stage of plasma instabilities.
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
NASA Astrophysics Data System (ADS)
Scudder, J. D.; Karamibadi, H. Y.; Vu, H. X.; Montag, P. K.
2008-12-01
With a general non-dissipative model of two interacting rotational discontinuities (RDs) with opposing phase velocities along B we have reproduced the recently reported suite of signatures interpreted as those of collisionless magnetic reconnection in the solar wind. This model has been derived analytically and also reinforced with novel hybrid simulations of the interaction. Nearly a complete degeneracy is thus illustrated between the experimental evidence used to support the solar wind reconnection interpretation and the highly probable passing of two RDs through one another in the solar wind plasma that is often modeled as a "sea" of Alfvenic turbulence. The recovered morphology includes (i) the characteristic Walen signature with opposing signs, (ii) the Hall signatures, (iii) the ion phase space beams, (iv) the inferred "reconnection" rate from the non-zero tangential electric field and (v) counter-streaming jets. There is already evidence in the solar wind from B-V correlations that Alfvenic power is propagating in both directions relative to the radial and hence magnetic field direction. From this fact it is clear that the likelihood of the reconnection interpretation of the oppositely signed B-V correlations goes like the product of two probabilities P(a)P(b): P(a) for the inference that the shears are opposing RD layers and P(b) that assesses the probability that an unmeasured electron current scale layer enabling collisionless reconnection is attached to the observed MHD patterns. The present paper explains the observation only assuming that P(a) is a high likely in the Alfven turbulence already documented in the interplanetary medium. None of the presented evidence is compelling that P(b) is appreciable. Thus, by Occam's razor the two RD interaction (without attending reconnection) interpretation is the more likely interpretation of the space data, pending further differentiation of these two possibilities.
Reconnection rates of magnetic fields
Park, W.; Monticello, D.A.; White, R.B.
1983-05-01
The Sweet-Parker and Petschek scalings of magnetic reconnection rate are modified to include the effect of the viscosity. The modified scalings show that the viscous effect can be important in high-..beta.. plasmas. The theoretical reconnection scalings are compared with numerical simulation results in a tokamak geometry for three different cases: a forced reconnection driven by external coils, the nonlinear m = 1 resistive internal kink, and the nonlinear m = 2 tearing mode. In the first two cases, the numerical reconnection rate agrees well with the modified Sweet-Parker scaling, when the viscosity is sufficiently large. When the viscosity is negligible, a steady state which was assumed in the derivation of the reconnection scalings is not reached and the current sheet in the reconnection layer either remains stable through sloshing motions of the plasma or breaks up to higher m modes. When the current sheet remains stable, a rough comparison with the Sweet-Parker scaling is obtained. In the nonlinear m = 2 tearing mode case where the instability is purely resistive, the reconnection occurs on the slower dissipation time scale (Psi/sub s/ approx. eta). In addition, experimental data of the nonlinear m = 1 resistive internal kink in tokamak discharges are analyzed and are found to give reasonable agreement with the modified Sweet-Parker scaling.
Electron acceleration in three-dimensional magnetic reconnection with a guide field
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.
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
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.
Colour Reconnection in WW Events
NASA Astrophysics Data System (ADS)
D'Hondt, J.
2003-07-01
Preliminary results are presented for a measurement of the κ parameter used in the JETSET SK-I model of Colour Reconnection in {W}+{W}^- -> qbar {q}'bar {q}q^' events at LEP2. An update on the investigation of Colour Reconnection effects in hadronic decays of W pairs, using the particle flow in DELPHI is presented. A second method is based on the observation that two different mW estimators have different sensitivity to the parametrised Colour Reconnection effect. Hence the difference between them is an observable with information content about κ.
The Inner Workings of Magnetic Reconnection: Diffusion Region in the Balance
NASA Technical Reports Server (NTRS)
Hesse, Michael
2010-01-01
The question of whether the micro scale controls the macroscale or vice-versa remains one of the most challenging problems in plasmas. A particular topic of interest within this context is collisionless magnetic reconnection, where both points of views are espoused by different groups of researchers. This presentation will focus on this topic. We will begin by analyzing the properties of electron diffusion region dynamics both for guide field and anti-parallel reconnection, and how they can be scaled to different inflow conditions. As a next step, we will study typical temporal variations of the microscopic dynamics with the objective of understanding the potential for secular changes to the macroscopic system. The research will be based on a combination of analytical theory and numerical modeling.
Orientation of x-lines in asymmetric magnetic reconnection
NASA Astrophysics Data System (ADS)
Liu, Yi-Hsin; Hesse, Michael; Kuznetsova, Masha
2015-11-01
At Earth's magnetopause, reconnection proceeds asymmetrically between magnetosheath plasmas, namely solar wind plasmas compressed by Earth's bow shock, and magnetospheric plasmas. In an asymmetric configuration, it is unclear if there is a simple principle to determine the orientation of the x-line. Using fully kinetic simulations, we study this issue and a spatially localized perturbation is employed to induce a single x-line, that has sufficient freedom to choose its orientation in three-dimensional systems. The effect of ion to electron mass ratio is investigated, and the x-line appears to bisect the magnetic shear angle across the current sheet in the large mass ratio limit. The deviation from the bisection angle in the lower mass ratio limit can be explained by the physics of tearing instability. The local physics control of the x-line orientation studied in this slab geometry could potentially interplay with global geometrical effects to determine the location of collisionless magnetic reconnection at Earth's magnetopause.
Roles of Magnetic Reconnection and Developments of Modern Theory^*
NASA Astrophysics Data System (ADS)
Coppi, B.
2007-11-01
The role of reconnection was recognized in Solar and Space Physics and auroral substorms were suggested to originate in the night-side of the Earth's magnetosphere as a result collisionless reconnectionootnotetextB. Coppi, Nature 205, 998 (1965). well before the kind of modern theory employed for this became applied to laboratory plasmas. Experiments have reached low collisionality regimes where, like in space plasmas, the features of the electron distribution and in particular of the electron temperature gradient become important and the factors contributing to the electron thermal energy balance equation (transverse thermal and longitudinal diffusivities, or electron Landau dampingootnotetextB. Coppi, J.W.-K. Mark, L. Sugiyama, G. Bertin, Phys. Rev. Letters 42, 1058 (1978) and J. Drake, et al., Phys. Fluids 26, 2509 (1983). play a key role. For this an asymptotic theory of modes producing macroscopic islands has been developed involving 3 regions, the innermost one related to finite resistivity and the intermediate one to the finite ratio of the to thermal conductivitiesootnotetextB. Coppi, C. Crabtree, and V. Roytershteyn contribution to Paper TH/R2-19, I.A.E.A. Conference 2006.,^4. A background of excited micro-reconnecting modes, driven by the electron temperature gradient, is considered to make this ratio significantootnotetextB. Coppi, in``Collective Phenomena in Macroscopic Systems'' Eds. G. Bertin et al. (World Scientific, 2007) MIT-LNS Report 06/11(2006). ^*Supported in part by the US D.O.E.
Transition from Collisionless to Collisional MRI
Prateek Sharma; Gregory W. Hammett; Eliot Quataert
2003-07-24
Recent calculations by Quataert et al. (2002) found that the growth rates of the magnetorotational instability (MRI) in a collisionless plasma can differ significantly from those calculated using MHD. This can be important in hot accretion flows around compact objects. In this paper, we study the transition from the collisionless kinetic regime to the collisional MHD regime, mapping out the dependence of the MRI growth rate on collisionality. A kinetic closure scheme for a magnetized plasma is used that includes the effect of collisions via a BGK operator. The transition to MHD occurs as the mean free path becomes short compared to the parallel wavelength 2*/k(sub)||. In the weak magnetic field regime where the Alfven and MRI frequencies w are small compared to the sound wave frequency k(sub)||c(sub)0, the dynamics are still effectively collisionless even if omega << v, so long as the collision frequency v << k(sub)||c(sub)0; for an accretion flow this requires n less than or approximately equal to *(square root of b). The low collisionality regime not only modifies the MRI growth rate, but also introduces collisionless Landau or Barnes damping of long wavelength modes, which may be important for the nonlinear saturation of the MRI.
High-energy Nd:glass laser facility for collisionless laboratory astrophysics
NASA Astrophysics Data System (ADS)
Niemann, C.; Constantin, C. G.; Schaeffer, D. B.; Tauschwitz, A.; Weiland, T.; Lucky, Z.; Gekelman, W.; Everson, E. T.; Winske, D.
2012-03-01
A kilojoule-class laser (Raptor) has recently been activated at the Phoenix-laser-facility at the University of California Los Angeles (UCLA) for an experimental program on laboratory astrophysics in conjunction with the Large Plasma Device (LAPD). The unique combination of a high-energy laser system and the 18 meter long, highly-magnetized but current-free plasma will support a new class of plasma physics experiments, including the first laboratory simulations of quasi-parallel collisionless shocks, experiments on magnetic reconnection, or advanced laser-based diagnostics of basic plasmas. Here we present the parameter space accessible with this new instrument, results from a laser-driven magnetic piston experiment at reduced power, and a detailed description of the laser system and its performance.
Hydromagnetic waves for a collisionless plasma in strong magnetic fields
NASA Astrophysics Data System (ADS)
Duhau, S.; de La Torre, A.
1985-08-01
A system of hydrodynamic equations is used to model the behavior of small-amplitude hydromagnetic waves in order to quantify the effects of the electron thermodynamic variables. The system of equations yields a dispersion relationship which is solved with a linear approximation when small perturbations are introduced into the steady state. The disturbances are expressed as a superposition of small amplitude, plane harmonic waves, which are traced as they propagate through a collisionless heat-conducting plasma. Only the mirror stability criterion is found to change when the electron pressure is considered in a zero heat flux. The phase speed will be symmetric with respect to arising from the presence of the heat flux will strongly couple the slow and fast magnetosonic modes with wavenumber vectors in the positive flux vector directions. The subsequent overstability will be independent of the ion anisotropy.
Motion of reconnection region in the Earth's magnetotail. Multiple reconnection.
NASA Astrophysics Data System (ADS)
Alexandrova, Alexandra; Nakamura, Rumi; Semenov, Vladimir S.; Nakamura, Takuma K. M.
2016-04-01
During magnetic reconnection in the Earth's magnetotail, the reconnection site (X-line) can move in a specific direction. We present a detailed statistical study of the X-line motion. Using four-spacecraft Cluster observations, we identify the X-line velocity distinguishing between the single and multiple reconnection events. Most of the X-lines move tailward (radial outward) along the current sheet, however the Earthward motion was estimated for a couple of multiple X-lines. The X-lines also propagate outward from the midnight sector in the dawn-dusk direction in the current sheet plane. We found that the X-line radial motion is consistent with the direction of the radial pressure gradient. Besides, we found that the X-line speed in the Earth-tail direction is comparable and proportional to the reconnection inflow speed and approximately 0.1 of the reconnection outflow speed. These results suggest that both the global pressure distribution and the local reconnection physics may affect the X-line motion. We also discuss the interaction among multiple X-lines based on detailed analysis of an event showing counter-streaming jets from two different X-lines.
The physics of magnetic reconnection onset at the subsolar magnetopause: MMS observations
NASA Astrophysics Data System (ADS)
Retinò, Alessandro
2016-04-01
Magnetic reconnection is a fundamental process occurring in thin current sheets where a change in the magnetic field topology leads to fast magnetic energy conversion into charged particles energy. A key yet poorly understood aspect is how reconnection is initiated in the diffusion region by microphysical processes occurring at electron scales, the so-called onset problem. Reconnection onset leads to the energization of particles around reconnection sites, yet the exact energization mechanisms are also not yet fully understood. Simulations have provided some suggestions on the mechanisms responsible for onset and particle energization, however direct observations have been scarce so far. The four-spacecraft Magnetospheric Multiscale Mission (NASA/MMS) has been launched in March 2015 and allows, for the first time, in-situ observations of reconnection diffusion regions with adequate resolution to study electron scales. Here we present MMS observations in diffusion regions at the subsolar magnetopause and we investigate the conditions for reconnection onset. We select a few events with multiple crossings of the magnetopause current sheet for which signatures of absence of reconnection are rapidly followed by signatures of reconnection, and compare the measured electric field with the electric field due to both kinetic effects (electron pressure tensor, electron inertia terms) and to anomalous resistivity associated to different wave modes (e.g. lower hybrid waves, whistler waves, etc.). We also analyze electron distribution functions to study the mechanisms of electron energization in the diffusion region.
Three-Dimensional Localized Magnetic Reconnection in Torus Plasma Merging Device TS-4
NASA Astrophysics Data System (ADS)
Ii, Toru; Hayashi, Yoshinori; Inomoto, Michiaki; Ono, Yasushi
Three-dimensional (3-D) localized magnetic reconnection was studied experimentally using torus plasma merging device TS-4. The direct measurements of 3-D structures of current sheet revealed two unsteady and fast reconnection mechanisms: 3-D deformation of current sheet and mass ejection. When strong compression force IAcc∼60kA was applied to two plasma toroids with low guide field Bt/B¦¦∼1, toroidal modes n=1-3 of current sheet were observed to grow only during their reconnection and to disappear after the reconnection. This 3-D deformation promoted mass ejection from the current sheet, increasing the reconnection rate as well as reconnection (toroidal) electric field and outflow. On the other hand, the reconnection rate was maintained low under the high guide field Bt/B¦¦∼7 and weak compression IAcc∼0kA. These phenomena suggest that local compression of current sheet triggers its strong dissipation as well as plasma mass ejection, which are responsible for the onset of 3-D localized reconnection.
Geomagnetically Induced Currents From Reconnection
This animations shows a coronal mass ejections collide with Earth's magnetic fields and the fields change shape and strength. Reconnection in the magnetotail causes currents to follow the field lin...
Aeroacoustics of viscous vortex reconnection
NASA Astrophysics Data System (ADS)
Paredes, Pedro; Nichols, Joseph W.; Duraisamy, Karthik; Hussain, Fazle
2011-11-01
Reconnection of two anti-parallel vortex tubes is studied by direct numerical simulations and large-eddy simulations of the incompressible Navier-Stokes equations over a wide range (2000-50,000) of the vortex Reynolds number (Re). A detailed investigation of the flow dynamics is performed and at high Re, multiple reconnections are observed as the newly formed ``bridges'' interact by self and mutual induction. To investigate acoustics produced by the recoil action of the vortex threads, Möhring's theory of vortex sound is applied to the flow field and evaluated at varying far-field locations. The acoustic solver is verified against calculations of laminar vortex ring collision. For anti-parallel vortex reconnection, the resulting far-field spectra are shown to be grid converged at low-to-mid frequencies. To assess the relevance to fully turbulent jet noise, the dependence of reconnection upon Reynolds number is investigated.
NASA Astrophysics Data System (ADS)
Ji, Hantao; Yamada, Masaaki; Prager, Stewart; Daughton, William
2012-10-01
A new large plasma experiment, called the Large Reconnection Experiment or LRX, has been proposed to study magnetic reconnection in regimes directly relevant to fusion, space, and astrophysical plasmas. There are at least two possibly coupled mechanisms to explain why reconnection is fast as compared to the MHD predictions: one by physics beyond MHD, and the other by breakdown of the MHD current sheet via plasmoid instabilities into a state of interacting flux ropes. However, the former works only on the ion scales, much smaller than the plasma size, while the latter is only predicted theoretically. Further progress to study these is currently impeded by several severe limitations (1) in realistic simulations (especially in 3D), (2) in space observations due to a small numbers of in-situ measurements, (3) in solar observations due to limited spatial resolution of remote-sensing techniques, (4) in fusion plasmas due to the limited diagnostic accessibility, and (5) in the existing basic laboratory experiments due to limited scale separations. All of these strongly motivate the well-controlled/diagnosed, collaborative LRX project to simultaneously achieve large scale separations and high Lundquist numbers. Major questions and conceptual design for the LRX project will be discussed.
Vortex reconnection in superfluid helium
Koplik, J. ); Levine, H. )
1993-08-30
A useful physical model for superfluid turbulence considers the flow to consist of a dense tangle of vortex lines which evolve and interact. It has been suggested that these vortex lines can dynamically reconnect upon close approach. Here, we consider the nonlinear Schroedinger equation model of superfluid quantum mechanics, and use numerical simulation to study this topology changing core-scale process. Our results support the idea that vortex reconnection will occur whenever filaments come within a few core lengths of one another.
Reconnection of superfluid vortex bundles.
Alamri, Sultan Z; Youd, Anthony J; Barenghi, Carlo F
2008-11-21
Using the vortex filament model and the Gross-Pitaevskii nonlinear Schroedinger equation, we show that bundles of quantized vortex lines in He II are structurally robust and can reconnect with each other maintaining their identity. We discuss vortex stretching in superfluid turbulence and show that, during the bundle reconnection process, kelvin waves of large amplitude are generated, in agreement with the finding that helicity is produced by nearly singular vortex interactions in classical Euler flows. PMID:19113421
Optical Plasma Diagnostics for Magnetic Reconnection Studies in the Versatile Toroidal Facility
NASA Astrophysics Data System (ADS)
Tarkowski, David; Fasoli, Ambrogio; Egedal, Jan
2000-10-01
Magnetic reconnection studies in a collisionless regime are performed on the MIT Versatile Toroidal Facility (VTF) with emphasis on particle dynamics around the magnetic null point. Plasmas are produced in the VTF by electron cyclotron resonance heating and are confined in a magnetic cusp field. Magnetic reconnection is driven by the ExB drift generated by the combination of the cusp field and the toroidal electric field, which is created by electromagnetic induction using an ohmic transformer. The plasmas are composed primarily of singly ionized argon with typical densities and electron temperatures on the order of 10^17 m-3 and 10 eV. The number of available optical lines and the optical thinness of the plasma suggest that optical diagnostics can play a key role on VTF. Passive spectroscopic measurements yield ion temperature and density and electron temperature as a function of time both before and after the reconnection event. The active measurement is a three level laser induced fluorescence (LIF) scheme. A 10 ns pulsed dye laser is used to pump the 611 nm Argon II line. LIF yields the ion distribution function at a single point in time and can be used to study ion evolution during the reconnection event. Measurement techniques and an analysis of first results will be presented.
NASA Astrophysics Data System (ADS)
Le, A.; Daughton, W. S.
2015-12-01
Fully kinetic simulations have shown that the structure of the thin current sheets that form during collisionless reconnection can fall into a variety of regimes depending on the electron pressure anisotropy [1]. Furthermore, recent two-fluid simulations with anisotropic electron equations of state appropriate for reconnection confirm that the electron pressure anisotropy may drive highly elongated current sheets in the reconnection exhaust [2]. While fully kinetic simulations are useful to model small regions of the Earth's magnetosphere, they are still far too expensive for global modeling. Thus, we have implemented the electron equations of state in the hybrid (kinetic ions and fluid electrons) code H3D [3], and initial 2D hybrid simulations of reconnection agree well with fully kinetic simulations. The updated hybrid code is a first step towards including electron anisotropy and full ion kinetics in global simulations of Earth's magnetosphere and laboratory experiments. [1] Le et al., Phys. Rev. Lett. 110, 135004 (2013)[2] Ohia et al., Phys. Rev. Lett. 109, 115004 (2012) [3] Karimabadi et al., Phys. Plasmas 21, 062308 (2014)
Ng, Jonathan; Huang, Yi -Min; Hakim, Ammar; Bhattacharjee, A.; Stanier, Adam; Daughton, William; Wang, Liang; Germaschewski, Kai
2015-11-05
As modeling of collisionless magnetic reconnection in most space plasmas with realistic parameters is beyond the capability of today's simulations, due to the separation between global and kinetic length scales, it is important to establish scaling relations in model problems so as to extrapolate to realistic scales. Furthermore, large scale particle-in-cell simulations of island coalescence have shown that the time averaged reconnection rate decreases with system size, while fluid systems at such large scales in the Hall regime have not been studied. Here, we perform the complementary resistive magnetohydrodynamic (MHD), Hall MHD, and two fluid simulations using a ten-moment modelmore » with the same geometry. In contrast to the standard Harris sheet reconnection problem, Hall MHD is insufficient to capture the physics of the reconnection region. Additionally, motivated by the results of a recent set of hybrid simulations which show the importance of ion kinetics in this geometry, we evaluate the efficacy of the ten-moment model in reproducing such results.« less
Ng, Jonathan; Huang, Yi-Min; Hakim, Ammar; Bhattacharjee, A.; Stanier, Adam; Daughton, William; Wang, Liang; Germaschewski, Kai
2015-11-01
As modeling of collisionless magnetic reconnection in most space plasmas with realistic parameters is beyond the capability of today's simulations, due to the separation between global and kinetic length scales, it is important to establish scaling relations in model problems so as to extrapolate to realistic scales. Recently, large scale particle-in-cell simulations of island coalescence have shown that the time averaged reconnection rate decreases with system size, while fluid systems at such large scales in the Hall regime have not been studied. Here, we perform the complementary resistive magnetohydrodynamic (MHD), Hall MHD, and two fluid simulations using a ten-moment model with the same geometry. In contrast to the standard Harris sheet reconnection problem, Hall MHD is insufficient to capture the physics of the reconnection region. Additionally, motivated by the results of a recent set of hybrid simulations which show the importance of ion kinetics in this geometry, we evaluate the efficacy of the ten-moment model in reproducing such results. (C) 2015 AIP Publishing LLC.
Ng, Jonathan; Huang, Yi -Min; Hakim, Ammar; Bhattacharjee, A.; Stanier, Adam; Daughton, William; Wang, Liang; Germaschewski, Kai
2015-11-05
As modeling of collisionless magnetic reconnection in most space plasmas with realistic parameters is beyond the capability of today's simulations, due to the separation between global and kinetic length scales, it is important to establish scaling relations in model problems so as to extrapolate to realistic scales. Furthermore, large scale particle-in-cell simulations of island coalescence have shown that the time averaged reconnection rate decreases with system size, while fluid systems at such large scales in the Hall regime have not been studied. Here, we perform the complementary resistive magnetohydrodynamic (MHD), Hall MHD, and two fluid simulations using a ten-moment model with the same geometry. In contrast to the standard Harris sheet reconnection problem, Hall MHD is insufficient to capture the physics of the reconnection region. Additionally, motivated by the results of a recent set of hybrid simulations which show the importance of ion kinetics in this geometry, we evaluate the efficacy of the ten-moment model in reproducing such results.
Ng, Jonathan; Huang, Yi-Min; Hakim, Ammar; Bhattacharjee, A.; Stanier, Adam; Daughton, William; Wang, Liang; Germaschewski, Kai
2015-11-15
As modeling of collisionless magnetic reconnection in most space plasmas with realistic parameters is beyond the capability of today's simulations, due to the separation between global and kinetic length scales, it is important to establish scaling relations in model problems so as to extrapolate to realistic scales. Recently, large scale particle-in-cell simulations of island coalescence have shown that the time averaged reconnection rate decreases with system size, while fluid systems at such large scales in the Hall regime have not been studied. Here, we perform the complementary resistive magnetohydrodynamic (MHD), Hall MHD, and two fluid simulations using a ten-moment model with the same geometry. In contrast to the standard Harris sheet reconnection problem, Hall MHD is insufficient to capture the physics of the reconnection region. Additionally, motivated by the results of a recent set of hybrid simulations which show the importance of ion kinetics in this geometry, we evaluate the efficacy of the ten-moment model in reproducing such results.
Yokoi, N.; Higashimori, K.; Hoshino, M.
2013-12-15
Through the enhancement of transport, turbulence is expected to contribute to the fast reconnection. However, the effects of turbulence are not so straightforward. In addition to the enhancement of transport, turbulence under some environment shows effects that suppress the transport. In the presence of turbulent cross helicity, such dynamic balance between the transport enhancement and suppression occurs. As this result of dynamic balance, the region of effective enhanced magnetic diffusivity is confined to a narrow region, leading to the fast reconnection. In order to confirm this idea, a self-consistent turbulence model for the magnetic reconnection is proposed. With the aid of numerical simulations where turbulence effects are incorporated in a consistent manner through the turbulence model, the dynamic balance in the turbulence magnetic reconnection is confirmed.
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.
Exploring Magnetopause Reconnection with MMS
NASA Astrophysics Data System (ADS)
Burch, J. L.; Torbert, R. B.; Moore, T. E.; Pollock, C. J.; Mauk, B.; Fuselier, S. A.; Nakamura, R.; Hesse, M.; Ergun, R.; Giles, B. L.; Phan, T.; Baker, D. N.
2015-12-01
Magnetospheric Multiscale is a NASA Solar-Terrestrial Probes mission that is designed to conduct a definitive experiment on magnetic reconnection in the boundary regions of the Earth's magnetoshere. Previous missions have established that reconnection occurs somewhere on the magnetopause and in the geomagnetic tail on a nearly continuous basis. Most of the predictions that have been made about reconnection on the MHD and ion scales have been confirmed and new questions posed, particularly at smaller scales. MMS is designed to probe reconnection down to the smallest scales possible thereby allowing the assessment of electron-scale pressure gradients and inertial effects as possible important drivers of magnetic reconnection. Multipoint measurements of 3D electric and magnetic fields and plasma distributions at the required spatial resolution are required along with plasma waves, energetic particles and ion composition to open this new window on reconnection and solve its remaining mysteries. With a wide range of new and vastly improved measurements at 4 locations with separations down to 10 km, MMS is fully operational and nearing the dayside magnetopause where its exploration begins. In this paper results obtained from the first three months of magnetopause crossings will be presented.
Laboratory studies of magnetized collisionless flows and shocks using accelerated plasmoids
NASA Astrophysics Data System (ADS)
Weber, T. E.; Smith, R. J.; Hsu, S. C.
2015-11-01
Magnetized collisionless shocks are thought to play a dominant role in the overall partition of energy throughout the universe, but have historically proven difficult to create in the laboratory. The Magnetized Shock Experiment (MSX) at LANL creates conditions similar to those found in both space and astrophysical shocks by accelerating hot (100s of eV during translation) dense (1022 - 1023 m-3) Field Reversed Configuration (FRC) plasmoids to high velocities (100s of km/s); resulting in β ~ 1, collisionless plasma flows with sonic and Alfvén Mach numbers of ~10. The FRC subsequently impacts a static target such as a strong parallel or anti-parallel (reconnection-wise) magnetic mirror, a solid obstacle, or neutral gas cloud to create shocks with characteristic length and time scales that are both large enough to observe yet small enough to fit within the experiment. This enables study of the complex interplay of kinetic and fluid processes that mediate cosmic shocks and can generate non-thermal distributions, produce density and magnetic field enhancements much greater than predicted by fluid theory, and accelerate particles. An overview of the experimental capabilities of MSX will be presented, including diagnostics, selected recent results, and future directions. Supported by the DOE Office of Fusion Energy Sciences under contract DE-AC52-06NA25369.
Formation of current sheets in magnetic reconnection
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.
Rapid Reconnection and Field Line Topology
NASA Astrophysics Data System (ADS)
Parker, E. N.; Rappazzo, A. F.
Rapid reconnection of magnetic fields arises where the magnetic stresses push the plasma and field so as to increase the field gradient without limit. The intent of the present writing is to show the larger topological context in which this commonly occurs. Consider an interlaced field line topology as commonly occurs in the bipolar magnetic regions on the Sun. A simple model is constructed starting with a strong uniform magnetic field B 0 in the z-direction through an infinitely conducting fluid from the end plate z = 0 to z = L with the field lines tied at both end plates. Field line interlacing is introduced by smooth continuous random turbulent mixing of the footpoints at the end plates. This configuration is well suited to be modeled with the reduced magnetohydrodynamic (MHD) equations, with the equilibria given by the solutions of the 2D vorticity equation in this case. The set of continuous solutions to the "vorticity" equation have greatly restricted topologies, so almost all interlaced field topologies do not have continuous solutions. That infinite set represents the "weak" solutions of the vorticity equation, wherein there are surfaces of tangential discontinuity (current sheets) in the field dividing regions of smooth continuous field. It follows then that current sheets are to be found throughout interlaced fields, providing potential sites for rapid reconnection. That is to say, rapid reconnection and nanoflaring are expected throughout the bipolar magnetic fields in the solar corona, providing substantial heating to the ambient gas. Numerical simulations provide a direct illustration of the process, showing that current sheets thin on fast ideal Alfvén timescales down to the smallest numerically resolved scales. The asymmetric structure of the equilibria and the interlacing threshold for the onset of singularities are discussed. Current sheet formation and dynamics are further analyzed with dissipative and ideal numerical simulations.
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
Bulk ion acceleration and particle heating during magnetic reconnection in a laboratory plasma
Yoo, Jongsoo; Yamada, Masaaki; Ji, Hantao; Jara-Almonte, Jonathan; Myers, Clayton E.
2014-05-15
Bulk ion acceleration and particle heating during magnetic reconnection are studied in the collisionless plasma of the Magnetic Reconnection Experiment (MRX). The plasma is in the two-fluid regime, where the motion of the ions is decoupled from that of the electrons within the ion diffusion region. The reconnection process studied here is quasi-symmetric since plasma parameters such as the magnitude of the reconnecting magnetic field, the plasma density, and temperature are compatible on each side of the current sheet. Our experimental data show that the in-plane (Hall) electric field plays a key role in ion heating and acceleration. The electrostatic potential that produces the in-plane electric field is established by electrons that are accelerated near the electron diffusion region. The in-plane profile of this electrostatic potential shows a “well” structure along the direction normal to the reconnection current sheet. This well becomes deeper and wider downstream as its boundary expands along the separatrices where the in-plane electric field is strongest. Since the in-plane electric field is 3–4 times larger than the out-of-plane reconnection electric field, it is the primary source of energy for the unmagnetized ions. With regard to ion acceleration, the Hall electric field causes ions near separatrices to be ballistically accelerated toward the outflow direction. Ion heating occurs as the accelerated ions travel into the high pressure downstream region. This downstream ion heating cannot be explained by classical, unmagnetized transport theory; instead, we conclude that ions are heated by re-magnetization of ions in the reconnection exhaust and collisions. Two-dimensional (2-D) simulations with the global geometry similar to MRX demonstrate downstream ion thermalization by the above mechanisms. Electrons are also significantly heated during reconnection. The electron temperature sharply increases across the separatrices and peaks just outside of the
Extreme ultra-violet movie camera for imaging microsecond time scale magnetic reconnection
Chai, Kil-Byoung; Bellan, Paul M.
2013-12-15
An ultra-fast extreme ultra-violet (EUV) movie camera has been developed for imaging magnetic reconnection in the Caltech spheromak/astrophysical jet experiment. The camera consists of a broadband Mo:Si multilayer mirror, a fast decaying YAG:Ce scintillator, a visible light block, and a high-speed visible light CCD camera. The camera can capture EUV images as fast as 3.3 × 10{sup 6} frames per second with 0.5 cm spatial resolution. The spectral range is from 20 eV to 60 eV. EUV images reveal strong, transient, highly localized bursts of EUV radiation when magnetic reconnection occurs.
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.
Magnetic reconnection: from the Sweet–Parker model to stochastic plasmoid chains
NASA Astrophysics Data System (ADS)
Loureiro, N. F.; Uzdensky, D. A.
2016-01-01
Magnetic reconnection is the topological reconfiguration of the magnetic field in a plasma, accompanied by the violent release of energy and particle acceleration. Reconnection is as ubiquitous as plasmas themselves, with solar flares perhaps the most popular example. Other fascinating processes where reconnection plays a key role include the magnetic dynamo, geomagnetic storms and the sawtooth crash in tokamaks. Over the last few years, the theoretical understanding of magnetic reconnection in large-scale fluid systems has undergone a major paradigm shift. The steady-state model of reconnection described by the famous Sweet–Parker (SP) theory, which dominated the field for ∼50 years, has been replaced with an essentially time-dependent, bursty picture of the reconnection layer, dominated by the continuous formation and ejection of multiple secondary islands (plasmoids). Whereas in the SP model reconnection was predicted to be slow, a major implication of this new paradigm is that reconnection in fluid systems is fast (i.e. independent of the Lundquist number), provided that the system is large enough. This conceptual shift hinges on the realization that SP-like current layers are violently unstable to the plasmoid (tearing) instability—implying, therefore, that such current sheets are super-critically unstable and thus can never form in the first place. This suggests that the formation of a current sheet and the subsequent reconnection process cannot be decoupled, as is commonly assumed. This paper provides an introductory-level overview of the recent developments in reconnection theory and simulations that led to this essentially new framework. We briefly discuss the role played by the plasmoid instability in selected applications, and describe some of the outstanding challenges that remain at the frontier of this subject. Amongst these are the analytical and numerical extension of the plasmoid instability to (i) 3D and (ii) non
Extension of the electron dissipation region in collisionless Hall magnetohydrodynamics reconnection
Sullivan, Brian P.; Bhattacharjee, A.; Huang, Yi-Min
2009-10-15
This paper presents Sweet-Parker type scaling arguments in the context of hyper-resistive Hall magnetohydrodynamics. Numerical experiments suggest that both cusplike and modestly more extended geometries are realizable. However, the length of the electron dissipation region, which is taken as a parameter by several recent studies, is found to depend explicitly on the level of hyper-resistivity. Furthermore, although hyper-resistivity can produce more extended electron dissipation regions, the length of the region remains smaller than one ion skin depth for the largest values of hyper-resistivity considered here, significantly shorter than current sheets seen in many recent kinetic studies. The length of the electron dissipation region is found to depend on electron inertia as well, scaling like (m{sub e}/m{sub i}){sup 3/8}. However, the thickness of the region appears to scale similarly, so that the aspect ratio is at most very weakly dependent on (m{sub e}/m{sub i})
Phenomenology of Internal Reconnections in NSTX
I. Semenov; S. Mirnov; D. Darrow; L. Roquemore; E.D. Fredrickson; J. Menard; D. Stutman; A. Belov
2002-06-06
The behavior of large-scale MHD modes was investigated in the National Spherical Torus Experiment (NSTX) during Reconnection Events (RE) using combined analysis of magnetic probe signals, and soft X-ray (SXR) data. The comparison of mode dynamics during precursor and disruption stages in T-11M (small circular plasma), TFTR (large circular plasma), and NSTX (large spherical plasma) was done. The analysis shows that the sequence of events of minor and major IREs (internal reconnection events) in NSTX is essentially similar to that for disruptions in moderate aspect ratio tokamaks. The main feature of disruption dynamics apparently affected by small aspect ratio in NSTX appears in the relatively slow thermal quench event (5-10 times longer compared to ordinary tokamaks), which precedes the major IRE. The coincidence of the electron and neutron quench times during the major IRE leads us to the conclusion that the fast ions and hot electrons leave the center of a plasma column simultaneously, i.e., convectively.
Fluxon Modeling of Eruptive Events With and Without Reconnection
NASA Astrophysics Data System (ADS)
DeForest, Craig; Rachmeler, L.; Davey, A.; Kankelborg, C.
2007-05-01
Fluxon MHD models represent the coronal magnetic field as a "skeleton" of discretized field lines. This quasi-Lagrangian approach eliminates numerical resistivity and allows 3-D time-dependent plasma simulation in a desktop workstation.Using our fluxon code, FLUX, we have demonstrated that ideal MHD instabilities can drive fast eruptive events even in the complete absence of magnetic reconnection. The mechanism ("herniation") is probably not the main driver of fast CMEs but may be applicable to microjets, macrospicules, or other small scale events where vortical flows are present in the solar atmosphere. In this presentation, we use time-dependent simulations to demonstrate energy release in several idealized plasma systems with and without magnetic reconnection.This work was funded by NASA's LWS and SHP-SR&T programs.
Collisionless tearing instability in magnetotail plasmas
NASA Technical Reports Server (NTRS)
Wang, Xiaogang; Bhattacharjee, A.; Lui, A. T. Y.
1990-01-01
The problem of the linear stability of collisionless tearing modes in the earth's magnetotail is revisited. It is found that the collisionless tearing mode is linearly unstable with wavelengths of the order of 10 R(E). It is shown that an important feature neglected in earlier theories is a nonzero equilibrium B(y)-field. The physics of the instability is elucidated in the context of a simple slab model and a sheared parabolic model which is representative of the magnetotail in which all three components of the magnetic field are nonzero. The dispersion equation for the instability is obtained by a boundary-layer analysis. The implications of the theory for recent observations on current disruption and diversion during substorms is discussed.
Expansion techniques for collisionless stellar dynamical simulations
NASA Astrophysics Data System (ADS)
Meiron, Yohai
2016-02-01
We present ETICS, a collisionless N-body code based on two kinds of series expansions of the Poisson equation, implemented for graphics processing units (GPUs). The code is publicly available and can be used as a standalone program or as a library (an AMUSE plugin is included). One of the two expansion methods available is the self-consistent field (SCF) method, which is a Fourier-like expansion of the density field in some basis set; the other is the multipole expansion (MEX) method, which is a Taylor-like expansion of the Green's function. MEX, which has been advocated in the past, has not gained as much popularity as SCF. Both are particle-field methods and optimized for collisionless galactic dynamics, but while SCF is a ``pure'' expansion, MEX is an expansion in just the angular part; thus, MEX is capable of capturing radial structure easily, while SCF needs a large number of radial terms.
Diffusion of magnetic field via turbulent reconnection
NASA Astrophysics Data System (ADS)
Santos de Lima, Reinaldo; Lazarian, Alexander; de Gouveia Dal Pino, Elisabete M.; Cho, Jungyeon
2010-05-01
The diffusion of astrophysical magnetic fields in conducting fluids in the presence of turbulence depends on whether magnetic fields can change their topology via reconnection in highly conducting media. Recent progress in understanding fast magnetic reconnection in the presence of turbulence is reassuring that the magnetic field behavior in computer simulations and turbulent astrophysical environments is similar, as far as magnetic reconnection is concerned. This makes it meaningful to perform MHD simulations of turbulent flows in order to understand the diffusion of magnetic field in astrophysical environments. Our studies of magnetic field diffusion in turbulent medium reveal interesting new phenomena. First of all, our 3D MHD simulations initiated with anti-correlating magnetic field and gaseous density exhibit at later times a de-correlation of the magnetic field and density, which corresponds well to the observations of the interstellar media. While earlier studies stressed the role of either ambipolar diffusion or time-dependent turbulent fluctuations for de-correlating magnetic field and density, we get the effect of permanent de-correlation with one fluid code, i.e. without invoking ambipolar diffusion. In addition, in the presence of gravity and turbulence, our 3D simulations show the decrease of the magnetic flux-to-mass ratio as the gaseous density at the center of the gravitational potential increases. We observe this effect both in the situations when we start with equilibrium distributions of gas and magnetic field and when we follow the evolution of collapsing dynamically unstable configurations. Thus the process of turbulent magnetic field removal should be applicable both to quasi-static subcritical molecular clouds and cores and violently collapsing supercritical entities. The increase of the gravitational potential as well as the magnetization of the gas increases the segregation of the mass and magnetic flux in the saturated final state of the
Role of Reconnection and Ballooning Modes in the Near-Earth Neutral Line Model
NASA Astrophysics Data System (ADS)
Zhu, P.; Bhattacharjee, A.; Germascheski, K.; Hegna, C.; Sovinec, C.
2007-05-01
Recent developments in the theory of collisionless reconnection and nonlinear ballooning instabilities in the Earth's magnetotail, tested by observations from Wind and Cluster, have brought new insights to bear on the classical Near-Earth Neutral Line model. These developments underscore the importance of collisionless reconnection in producing an X-line at mid-tail distances (~30 Re) and the growth of a thin and intense current sheet that mediates the development of very strong pressure gradients at near-Earth distances (~10 Re). In turn, these pressure gradients excite ballooning instabilities that are manifested as a westward traveling surge, which can be inferred by analyzing the time-delay between earthward and tailward flux enhancements of energetic ions. The eneregtic ion data also suggests a strong pre-onset pressure gradient that is reduced impulsively at onset. New developments in the theory and simulation of nonlinear ballooning modes appear to be consistent with these observations. Furthermore, the theory predicts the generation of finger-like structures and strongly sheared flows as a consequence of the instability, which pose new challenges for observations. However, despite the robust nonlinear growth of ballooning modes at near-Earth distances, it cannot be claimed that ballooning modes, by themselves, can account for all the important signatures of substorm onset. We will discuss open questions, and directions in which theoretical and modeling studies need to be extended in order to obtain a more complete theory of substorm onset.
Mechanics of viscous vortex reconnection
NASA Astrophysics Data System (ADS)
Hussain, Fazle; Duraisamy, Karthik
2011-02-01
This work is motivated by our long-standing claim that reconnection of coherent structures is the dominant mechanism of jet noise generation and plays a key role in both energy cascade and fine-scale mixing in fluid turbulence [F. Hussain, Phys. Fluids 26, 2816 (1983); J. Fluid Mech. 173, 303 (1986)]. To shed further light on the mechanism involved and quantify its features, the reconnection of two antiparallel vortex tubes is studied by direct numerical simulation of the incompressible Navier-Stokes equations over a wide range (250-9000) of the vortex Reynolds number, Re (=circulation/viscosity) at much higher resolutions than have been attempted. Unlike magnetic or superfluid reconnections, viscous reconnection is never complete, leaving behind a part of the initial tubes as threads, which then undergo successive reconnections (our cascade and mixing scenarios) as the newly formed bridges recoil from each other by self-advection. We find that the time tR for orthogonal transfer of circulation scales as tR≈Re-3/4. The shortest distance d between the tube centroids scales as d ≈a[Re(t0-t)]3/4 before reconnection (collision) and as d ≈b[Re(t -t0)]2 after reconnection (repulsion), where t0 is the instant of smallest separation between vortex centroids. We find that b is a constant, thus suggesting self-similarity, but a is dependent on Re. Bridge repulsion is faster than collision and is more autonomous as local induction predominates, and, given the associated acceleration of vorticity, is potentially a source of intense sound generation. At the higher Re studied, the tails of the colliding threads are compressed into a planar jet with multiple vortex pairs. For Re>6000, there is an avalanche of smaller scales during the reconnection, the rate of small scale generation and the spectral content (in vorticity, transfer function and dissipation spectra) being quite consistent with the structures visualized by the λ2 criterion. The maximum rate of vortex
Dipolarization Fronts from Reconnection Onset
NASA Astrophysics Data System (ADS)
Sitnov, M. I.; Swisdak, M. M.; Merkin, V. G.; Buzulukova, N.; Moore, T. E.
2012-12-01
Dipolarization fronts observed in the magnetotail are often viewed as signatures of bursty magnetic reconnection. However, until recently spontaneous reconnection was considered to be fully prohibited in the magnetotail geometry because of the linear stability of the ion tearing mode. Recent theoretical studies showed that spontaneous reconnection could be possible in the magnetotail geometries with the accumulation of magnetic flux at the tailward end of the thin current sheet, a distinctive feature of the magnetotail prior to substorm onset. That result was confirmed by open-boundary full-particle simulations of 2D current sheet equilibria, where two magnetotails were separated by an equilibrium X-line and weak external electric field was imposed to nudge the system toward the instability threshold. To investigate the roles of the equilibrium X-line, driving electric field and other parameters in the reconnection onset process we performed a set of 2D PIC runs with different initial settings. The investigated parameter space includes the critical current sheet thickness, flux tube volume per unit magnetic flux and the north-south component of the magnetic field. Such an investigation is critically important for the implementation of kinetic reconnection onset criteria into global MHD codes. The results are compared with Geotail visualization of the magnetotail during substorms, as well as Cluster and THEMIS observations of dipolarization fronts.
Reconnection rates, small scale structures and simulations
NASA Technical Reports Server (NTRS)
Matthaeus, W. H.
1983-01-01
The study of reconnection in the context of one fluid, two dimensional magnetohydrodynamics (MHD), with spatially uniform constant density, viscosity and resistivity is though to retain most of the physics important in reconnection. Much of the existing reconnection literature makes use of this approach. This discussion focuses on attempts to determine the properties of reconnection solutions to MHD as precisely as possible without regard to the intrinsic limitations of the model.
Electromagnetic Perturbations in the Reconnecting Current Sheet in MRX
Dorfman, Seth; Ji, Hantao; Yamada, MasAki; Ren Yang; Gerhardt, Stefan; Kulsrud, Russell; McGeehan, Brendan; Wang Yansong
2006-11-30
Magnetic reconnection is a fundamental plasma process in which magnetic field lines break and reconnect, converting magnetic field energy into particle kinetic energy. Electromagnetic fluctuations, which may play a role in fast reconnection, are studied from both an experimental and theoretical standpoint. The waves, which are in the lower hybrid range of frequencies, may be produced by a plasma instability known as the oblique lower hybrid drift instability. When the electron drift velocity is large, the theory predicts coupling between whistler and acoustic waves in the ion frame that may lead to an instability in the vicinity of the current sheet. On the experimental side, an antenna placed in the Magnetic Reconnection Experiment (MRX) at the Princeton Plasma Physics Laboratory is used to apply perturbations, and their propagation characteristics are measured. Results from a 2mm diameter antenna indicate that any induced fluctuations are confined to the current sheet and are preferentially excited in the direction of electron flow within the layer. Preliminary data from a 2cm diameter antenna shows a wave propagating in the electron flow direction at the local electron drift velocity. Thus electron drift appears to play a crucial role in the appearance of fluctuations.
The Theory of Magnetic Reconnection: Past, Present, and Future
NASA Astrophysics Data System (ADS)
Cassak, P. A.
2008-05-01
Magnetic reconnection underlies the energy release observed in eruptive events in the solar corona (such as solar flares and coronal mass ejections) and in the Earth's magnetosphere. The theory of magnetic reconnection was originally developed to understand observations by Ron Giovanelli, who discovered that solar flares occur where the coronal magnetic field changes directions. Pioneers in space plasma theory such as James Dungey, Peter Sweet, Eugene Parker, and Harry Petschek first elucidated the underlying physical effects that lead to this massive energy release. Since then, much effort has been made to understand what process or processes cause magnetic reconnection to be fast enough to be consistent with observations, such as anomalous resistivity, secondary instabilities, and the Hall effect. However, a thorough understanding of this important process remains a topic of intense study. In celebration of the 50th anniversary of Parker's paper predicting the high-speed solar wind, this talk will review the history of the theory of magnetic reconnection. The present status of the field will be discussed, and remaining unanswered questions will be summarized.
Solar flares and magnetic reconnection in quasi-separatrix layers
NASA Astrophysics Data System (ADS)
Aulanier, G.; Demoulin, P.; Janvier, M.; Masson, S.; Pariat, E.
2012-10-01
Magnetic reconnection is a fundamental plasma physics process which is believed to be responsible for the bulk of energy release in solar flares. One the one hand, the onset of fast reconnection in high-Reynolds plasmas has long since been regarded as, perhaps, the major issue to understand. On the other hand, little attention has relatively been given to the three-dimensional nature of this phenomenon. Up to very recently, the latter has mostly been addressed by the solar physics community, presumably due to the wealth of space-borne and ground-based observations of three-dimensional solar coronal features during flares. Among other 3D concept, finite-B ``quasi-separatrix layers'' (QSLs) have been introduced in the nineties, as a generalization of the concept of true separatrices emanating from null-points. In this talk, I will show how both solar and experimental physics have revealed that these QSLs physically behave like true separatrices, in terms of current sheet formation and magnetic reconnection, albeit for the continuous slippage of field lines during the process. I will then show how this ``slip-running reconnection'' occurs in the wake of flux-ropes erupting from the solar corona towrds the heliosphere, and how it it eventually forms the observed post-flare loops in the Sun's corona.
Possible two-step solar energy release mechanism due to turbulent magnetic reconnection
Fan Quanlin; Feng Xueshang; Xiang Changqing
2005-05-15
In this paper, a possible two-step solar magnetic energy release process attributed to turbulent magnetic reconnection is investigated by magnetohydrodynamic simulation for the purpose of accounting for the closely associated observational features including canceling magnetic features and different kinds of small-scale activities such as ultraviolet explosive events in the lower solar atmosphere. Numerical results based on realistic transition region physical parameters show that magnetic reconnections in a vertical turbulent current sheet consist of two stages, i.e., a first slow Sweet-Parker-like reconnection and a later rapid Petschek-like reconnection, where the latter fast reconnection phase seems a direct consequence of the initial slow reconnection phase when a critical state is reached. The formation of coherent plasmoid of various sizes and their coalescence play a central role in this complex nonlinear evolution. The 'observed' values of the rate of cancellation flux as well as the approaching velocity of magnetic fragments of inverse polarity in present simulation are well consistent with the corresponding measurements in the latest observations. The difference between our turbulent magnetic reconnection two-step energy release model and other schematic two-step models is discussed and then possible application of present outcome to solar explosives is described.
Particle Heating and Energization During Magnetic Reconnection Events in MST Plasmas
NASA Astrophysics Data System (ADS)
Dubois, Ami M.; Almagri, A. F.; Anderson, J. K.; den Hartog, D. J.; Forest, C.; Nornberg, M.; Sarff, J. S.
2015-11-01
Magnetic reconnection plays an important role in particle transport, energization, and acceleration in space, astrophysical, and laboratory plasmas. In MST reversed field pinch plasmas, discrete magnetic reconnection events release large amounts of energy from the equilibrium magnetic field, resulting in non-collisional ion heating. However, Thomson Scattering measures a decrease in the thermal electron temperature. Recent fast x-ray measurements show an enhancement in the high energy x-ray flux during reconnection, where the coupling between edge and core tearing modes is essential for enhanced flux. A non-Maxwellian energetic electron tail is generated during reconnection, where the power law spectral index (γ) decreases from 4.3 to 1.8 and is dependent on density, plasma current, and the reversal parameter. After the reconnection event, γ increases rapidly to 5.8, consistent with the loss of energetic electrons due to stochastic thermal transport. During the reconnection event, the change in γ is correlated with the change in magnetic energy stored in the equilibrium field, indicating that the released magnetic energy may be an energy source for electron energization. Recent experimental and computational results of energetic electron tail formation during magnetic reconnection events will be presented. This work is supported by the U.S. DOE and the NSF.
Multiple Spacecraft Study of the Impact of Turbulence on Reconnection Rates
NASA Technical Reports Server (NTRS)
Wendel, Deirdre; Goldstein, Melvyn; Figueroa-Vinas, Adolfo; Adrian, Mark; Sahraoui, Fouad
2011-01-01
Magnetic turbulence and secondary island formation have reemerged as possible explanations for fast reconnection. Recent three-dimensional simulations reveal the formation of secondary islands that serve to shorten the current sheet and increase the accelerating electric field, while both simulations and observations witness electron holes whose collapse energizes electrons. However, few data studies have explicitly investigated the effect of turbulence and islands on the reconnection rate. We present a more comprehensive analysis of the effect of turbulence and islands on reconnection rates observed in space. Our approach takes advantage of multiple spacecraft to find the location of the spacecraft relative to the inflow and the outflow, to estimate the reconnection electric field, to indicate the presence and size of islands, and to determine wave vectors indicating turbulence. A superposed epoch analysis provides independent estimates of spatial scales and a reconnection electric field. We apply k-filtering and a new method adopted from seismological analyses to identify the wavevectors. From several case studies of reconnection events, we obtain preliminary estimates of the spectral scaling law, identify wave modes, and present a method for finding the reconnection electric field associated with the wave modes.
Magnetic reconnection launcher
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.
Electron jet of asymmetric reconnection
NASA Astrophysics Data System (ADS)
Khotyaintsev, Yu. V.; Graham, D. B.; Norgren, C.; Eriksson, E.; Li, W.; Johlander, A.; Vaivads, A.; André, M.; Pritchett, P. L.; Retinò, A.; Phan, T. D.; Ergun, R. E.; Goodrich, K.; Lindqvist, P.-A.; Marklund, G. T.; Le Contel, O.; Plaschke, F.; Magnes, W.; Strangeway, R. J.; Russell, C. T.; Vaith, H.; Argall, M. R.; Kletzing, C. A.; Nakamura, R.; Torbert, R. B.; Paterson, W. R.; Gershman, D. J.; Dorelli, J. C.; Avanov, L. A.; Lavraud, B.; Saito, Y.; Giles, B. L.; Pollock, C. J.; Turner, D. L.; Blake, J. D.; Fennell, J. F.; Jaynes, A.; Mauk, B. H.; Burch, J. L.
2016-06-01
We present Magnetospheric Multiscale observations of an electron-scale current sheet and electron outflow jet for asymmetric reconnection with guide field at the subsolar magnetopause. The electron jet observed within the reconnection region has an electron Mach number of 0.35 and is associated with electron agyrotropy. The jet is unstable to an electrostatic instability which generates intense waves with E∥ amplitudes reaching up to 300 mV m-1 and potentials up to 20% of the electron thermal energy. We see evidence of interaction between the waves and the electron beam, leading to quick thermalization of the beam and stabilization of the instability. The wave phase speed is comparable to the ion thermal speed, suggesting that the instability is of Buneman type, and therefore introduces electron-ion drag and leads to braking of the electron flow. Our observations demonstrate that electrostatic turbulence plays an important role in the electron-scale physics of asymmetric reconnection.
Magnetic reconnection models of flares
NASA Technical Reports Server (NTRS)
Forbes, T. G.
1988-01-01
The most feasible energy source for solar and stellar flares is the energy stored in coronal magnetic fields. To convert a significant fraction of this energy into heat and kinetic energy in a short time requires rapid change in the topology of the magnetic fields, and hence, rapid reconnection of field lines. Recent numerical and analytical models of solar flares suggest that the magnetic energy released by reconnection drives chromospheric ablation in the flare ribbons. Simple theoretical arguments based on compressible reconnection theory predict that the temperature of the ablated plasma should be about 1.03 x 10 to the 6th B exp 0.62 K where B is the coronal magnetic field strength in Gauss.
Tail reconnection triggering substorm onset.
Angelopoulos, Vassilis; McFadden, James P; Larson, Davin; Carlson, Charles W; Mende, Stephen B; Frey, Harald; Phan, Tai; Sibeck, David G; Glassmeier, Karl-Heinz; Auster, Uli; Donovan, Eric; Mann, Ian R; Rae, I Jonathan; Russell, Christopher T; Runov, Andrei; Zhou, Xu-Zhi; Kepko, Larry
2008-08-15
Magnetospheric substorms explosively release solar wind energy previously stored in Earth's magnetotail, encompassing the entire magnetosphere and producing spectacular auroral displays. It has been unclear whether a substorm is triggered by a disruption of the electrical current flowing across the near-Earth magnetotail, at approximately 10 R(E) (R(E): Earth radius, or 6374 kilometers), or by the process of magnetic reconnection typically seen farther out in the magnetotail, at approximately 20 to 30 R(E). We report on simultaneous measurements in the magnetotail at multiple distances, at the time of substorm onset. Reconnection was observed at 20 R(E), at least 1.5 minutes before auroral intensification, at least 2 minutes before substorm expansion, and about 3 minutes before near-Earth current disruption. These results demonstrate that substorms are likely initiated by tail reconnection. PMID:18653845
NASA Astrophysics Data System (ADS)
Stawarz, Julia E.
Turbulence is a ubiquitous phenomenon that occurs throughout the universe, in both neutral fluids and plasmas. For collisionless plasmas, kinetic effects, which alter the nonlinear dynamics and result in small-scale dissipation, are still not well understood in the context of turbulence. This work uses direct numerical simulations (DNS) and observations of Earth's magnetosphere to study plasma turbulence. Long-time relaxation in magnetohydrodynamic (MHD) turbulence is examined using DNS with particular focus on the role of magnetic and cross helicity and symmetries of the initial configurations. When strong symmetries are absent or broken through perturbations, flows evolve towards states predicted by statistical mechanics with an energy minimization principle, which features two main regimes; one magnetic helicity dominated and one with quasi-equipartition of kinetic and magnetic energy. The role of the Hall effect, which contributes to the dynamics of collisionless plasmas, is also explored numerically. At scales below the ion inertial length, a transition to a magnetically dominated state, associated with advection becoming subdominant to dissipation, occurs. Real-space current, vorticity, and electric fields are examined. Strong current structures are associated with alignment between the current and magnetic field, which may be important in collisionless plasmas where field-aligned currents can be unstable. Turbulence within bursty bulk flow braking events, thought to be associated with near-Earth magnetotail reconnection, are then studied using the THEMIS spacecraft. It is proposed that strong field-aligned currents associated with turbulent intermittency destabilize into double layers, providing a collisionless dissipation mechanism for the turbulence. Plasma waves may also radiate from the region, removing energy from the turbulence and potentially depositing it in the aurora. Finally, evidence for turbulence in the Kelvin-Helmholtz instability (KHI) on the
A MAGNETIC RECONNECTION MECHANISM FOR THE GENERATION OF ANOMALOUS COSMIC RAYS
Drake, J. F.; Opher, M.; Swisdak, M.; Chamoun, J. N. E-mail: swisdak@umd.ed
2010-02-01
The recent observations of the anomalous cosmic ray (ACR) energy spectrum as Voyager 1 and Voyager 2 crossed the heliospheric termination shock have called into question the conventional shock source of these energetic particles. We suggest that the sectored heliospheric magnetic field, which results from the flapping of the heliospheric current sheet, piles up as it approaches the heliopause, narrowing the current sheets that separate the sectors and triggering the onset of collisionless magnetic reconnection. Particle-in-cell simulations reveal that most of the magnetic energy is released and most of this energy goes into energetic ions with significant but smaller amounts of energy going into electrons. The energy gain of the most energetic ions results from their reflection from the ends of contracting magnetic islands, a first-order Fermi process. The energy gain of the ions in contracting islands increases their parallel (to the magnetic field B) pressure p{sub ||} until the marginal fire-hose condition is reached, causing magnetic reconnection and associated particle acceleration to shut down. Thus, the feedback of the self-consistent development of the energetic ion pressure on reconnection is a crucial element of any reconnection-based, particle-acceleration model. The model calls into question the strong scattering assumption used to derive the Parker transport equation and therefore the absence of first-order Fermi acceleration in incompressible flows. A simple one-dimensional model for particle energy gain and loss is presented in which the feedback of the energetic particles on the reconnection drive is included. The ACR differential energy spectrum takes the form of a power law with a spectral index slightly above 1.5. The model has the potential to explain several key Voyager observations, including the similarities in the spectra of different ion species.
NASA Astrophysics Data System (ADS)
Den, M.; Horiuchi, R.; Fujita, S.; Tanaka, T.
2011-12-01
Magnetic reconnection is considered to play an important role in space phenomena such as substorm in the Earth's magnetosphere. Tanaka and Fujita reproduced substorm evolution process by numerical simulation with the global MHD code [1]. In the MHD framework, the dissipation model is introduced for modeling of the kinetic effects. They found that the normalized reconnection viscosity, one of the dissipation model employed there, gave a large effect for the dipolarization, central phenomenon in the substorm development process, though that viscosity was assumed to be a constant parameter. It is well known that magnetic reconnection is controlled by microscopic kinetic mechanism. Frozen-in condition is broken due to particle kinetic effects and collisionless reconnection is triggered when current sheet is compressed as thin as ion kinetic scales under the influence of external driving flow [2, 3]. Horiuchi and his collaborators showed that reconnection electric field generated by microscopic physics evolves inside ion meandering scale so as to balance the flux inflow rate at the inflow boundary, which is controlled by macroscopic physics [2]. That is, effective resistivity generated through this process can be expressed by balance equation between micro and macro physics. In this paper, we perform substorm simulation by using the global MHD code developed by Tanaka [3] with this effective resistivity instead of the empirical resistivity model. We obtain the AE indices from simulation data, in which substorm onset can be seen clearly, and investigate the relationship between the substorm development and the effective resistivity model. [1] T. Tanaka, A, Nakamizo, A. Yoshikawa, S. Fujita, H. Shinagawa, H. Shimazu, T. Kikuchi, and K. K. Hashimoto, J. Geophys. Res. 115 (2010) A05220,doi:10.1029/2009JA014676. [2] W. Pei, R. Horiuchi, and T. Sato, Physics of Plasmas,Vol. 8 (2001), pp. 3251-3257. [3] A. Ishizawa, and R. Horiuchi, Phys. Rev. Lett., Vol. 95, 045003 (2005). [4
A Magnetic Reconnection Mechanism for the Generation of Anomalous Cosmic Rays
NASA Astrophysics Data System (ADS)
Drake, J. F.; Opher, M.; Swisdak, M.; Chamoun, J. N.
2010-02-01
The recent observations of the anomalous cosmic ray (ACR) energy spectrum as Voyager 1 and Voyager 2 crossed the heliospheric termination shock have called into question the conventional shock source of these energetic particles. We suggest that the sectored heliospheric magnetic field, which results from the flapping of the heliospheric current sheet, piles up as it approaches the heliopause, narrowing the current sheets that separate the sectors and triggering the onset of collisionless magnetic reconnection. Particle-in-cell simulations reveal that most of the magnetic energy is released and most of this energy goes into energetic ions with significant but smaller amounts of energy going into electrons. The energy gain of the most energetic ions results from their reflection from the ends of contracting magnetic islands, a first-order Fermi process. The energy gain of the ions in contracting islands increases their parallel (to the magnetic field B) pressure p par until the marginal fire-hose condition is reached, causing magnetic reconnection and associated particle acceleration to shut down. Thus, the feedback of the self-consistent development of the energetic ion pressure on reconnection is a crucial element of any reconnection-based, particle-acceleration model. The model calls into question the strong scattering assumption used to derive the Parker transport equation and therefore the absence of first-order Fermi acceleration in incompressible flows. A simple one-dimensional model for particle energy gain and loss is presented in which the feedback of the energetic particles on the reconnection drive is included. The ACR differential energy spectrum takes the form of a power law with a spectral index slightly above 1.5. The model has the potential to explain several key Voyager observations, including the similarities in the spectra of different ion species.
Observing the release of twist by magnetic reconnection in a solar filament eruption.
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
Observing the release of twist by magnetic reconnection in a solar filament eruption
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
Observing the release of twist by magnetic reconnection in a solar filament eruption
NASA Astrophysics Data System (ADS)
Xue, Zhike; Yan, Xiaoli; Cheng, Xin; Yang, Liheng; Su, Yingna; Kliem, Bernhard; Zhang, Jun; Liu, Zhong; Bi, Yi; Xiang, Yongyuan; Yang, Kai; Zhao, Li
2016-06-01
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.
Are Solar Wind Reconnection Events Fossil Sites?
NASA Astrophysics Data System (ADS)
Vu, H. X.; Karimabadi, H.; Scudder, J. D.; Roytershteyn, V.; Daughton, W. S.; Gosling, J. T.; Egedal, J.
2010-12-01
Studies of reconnection in the solar wind led by Gosling and collaborators have revealed surprising results that are posing serious challenges to current theoretical understanding of the reconnection process. This include observations of prolonged quasi-steady reconnection, low magnetic shear angles, and no real bulk heating (i.e., full thermalization rather than appearance of heating due to two beams) or substantial particle acceleration. In contrast, the theoretical expectations have been that reconnection leads to significant bulk heating and particle acceleration. Similarly, recent full particle simulations indicate that reconnection is generally time dependent. We have recently re-examined this apparent discrepancy between observations and theory and propose a resolution to these puzzling observations based on the concept of fossil reconnection site. We have performed large scale 2D fully kinetic simulations of reconnection to very long times to gain an understanding of reconnection structure as they would be seen in the observations. We find that reconnection weakens in time and approaches an asymptotic state which we refer to as fossil state. The properties of the fossil reconnection state explain several of the puzzling aspects of the observations. The implications of these findings for studies of solar wind reconnection are discussed.
Collisionless stellar hydrodynamics as an efficient alternative to N-body methods
NASA Astrophysics Data System (ADS)
Mitchell, Nigel L.; Vorobyov, Eduard I.; Hensler, Gerhard
2013-01-01
The dominant constituents of the Universe's matter are believed to be collisionless in nature and thus their modelling in any self-consistent simulation is extremely important. For simulations that deal only with dark matter or stellar systems, the conventional N-body technique is fast, memory efficient and relatively simple to implement. However when extending simulations to include the effects of gas physics, mesh codes are at a distinct disadvantage compared to Smooth Particle Hydrodynamics (SPH) codes. Whereas implementing the N-body approach into SPH codes is fairly trivial, the particle-mesh technique used in mesh codes to couple collisionless stars and dark matter to the gas on the mesh has a series of significant scientific and technical limitations. These include spurious entropy generation resulting from discreteness effects, poor load balancing and increased communication overhead which spoil the excellent scaling in massively parallel grid codes. In this paper we propose the use of the collisionless Boltzmann moment equations as a means to model the collisionless material as a fluid on the mesh, implementing it into the massively parallel FLASH Adaptive Mesh Refinement (AMR) code. This approach which we term `collisionless stellar hydrodynamics' enables us to do away with the particle-mesh approach and since the parallelization scheme is identical to that used for the hydrodynamics, it preserves the excellent scaling of the FLASH code already demonstrated on peta-flop machines. We find that the classic hydrodynamic equations and the Boltzmann moment equations can be reconciled under specific conditions, allowing us to generate analytic solutions for collisionless systems using conventional test problems. We confirm the validity of our approach using a suite of demanding test problems, including the use of a modified Sod shock test. By deriving the relevant eigenvalues and eigenvectors of the Boltzmann moment equations, we are able to use high order
NASA Astrophysics Data System (ADS)
Abreu, P.
2002-03-01
The preliminary results on the search of colour reconnection effects (CR) from the four experiments at LEP, Aleph, Delphi, L3 and Opal, are reviewed. Extreme models are excluded by studies of standard variables, and on going studies of a method first suggested by L3, the particle flow method1, are yet inconclusive.
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.
Thin-shell instability in collisionless plasma
NASA Astrophysics Data System (ADS)
Dieckmann, M. E.; Ahmed, H.; Doria, D.; Sarri, G.; Walder, R.; Folini, D.; Bret, A.; Ynnerman, A.; Borghesi, M.
2015-09-01
Thin-shell instability is one process which can generate entangled structures in astrophysical plasma on collisional (fluid) scales. It is driven by a spatially varying imbalance between the ram pressure of the inflowing upstream plasma and the downstream's thermal pressure at a nonplanar shock. Here we show by means of a particle-in-cell simulation that an analog process can destabilize a thin shell formed by two interpenetrating, unmagnetized, and collisionless plasma clouds. The amplitude of the shell's spatial modulation grows and saturates after about ten inverse proton plasma frequencies, when the shell consists of connected piecewise linear patches.
Cascaded proton acceleration by collisionless electrostatic shock
Xu, T. J.; Shen, B. F. E-mail: zhxm@siom.ac.cn; Zhang, X. M. E-mail: zhxm@siom.ac.cn; Yi, L. Q.; Wang, W. P.; Zhang, L. G.; Xu, J. C.; Zhao, X. Y.; Shi, Y.; Liu, C.; Pei, Z. K.
2015-07-15
A new scheme for proton acceleration by cascaded collisionless electrostatic shock (CES) is proposed. By irradiating a foil target with a moderate high-intensity laser beam, a stable CES field can be induced, which is employed as the accelerating field for the booster stage of proton acceleration. The mechanism is studied through simulations and theoretical analysis, showing that a 55 MeV seed proton beam can be further accelerated to 265 MeV while keeping a good energy spread. This scheme offers a feasible approach to produce proton beams with energy of hundreds of MeV by existing available high-intensity laser facilities.
Scattering of radiation in collisionless dusty plasmas
Tolias, P.; Ratynskaia, S.
2013-04-15
Scattering of electromagnetic waves in collisionless dusty plasmas is studied in the framework of a multi-component kinetic model. The investigation focuses on the spectral distribution of the scattered radiation. Pronounced dust signatures are identified in the coherent spectrum due to scattering from the shielding cloud around the dust grains, dust acoustic waves, and dust-ion acoustic waves. The magnitude and shape of the scattered signal near these spectral regions are determined with the aid of analytical expressions and its dependence on the dust parameters is investigated. The use of radiation scattering as a potential diagnostic tool for dust detection is discussed.
Collisionless Relaxation in Non-Neutral Plasmas
Levin, Yan; Pakter, Renato; Teles, Tarcisio N.
2008-02-01
A theoretical framework is presented which allows us to quantitatively predict the final stationary state achieved by a non-neutral plasma during a process of collisionless relaxation. As a specific application, the theory is used to study relaxation of charged-particle beams. It is shown that a fully matched beam relaxes to the Lynden-Bell distribution. However, when a mismatch is present and the beam oscillates, parametric resonances lead to a core-halo phase separation. The approach developed accounts for both the density and the velocity distributions in the final stationary state.
Lower-hybrid instabilities and turbulence associated with reconnection in asymmetric current sheets
NASA Astrophysics Data System (ADS)
Roytershteyn, V.; Daughton, W.; Karimabadi, H.
2011-10-01
The role of microscopic plasma turbulence in enabling magnetic reconnection is a long-standing problem in plasma physics. In this work, we consider reconnection in asymmetric current sheets as encountered for example at the Earth's magnetopause and laboratory experiments, such as MRX. Using 3D PIC simulations with Monte-Carlo treatment of Coulomb collisions, we demonstrate that Lower-Hybrid (LH) turbulence naturally arises in this configuration in both collisionless and weakly collisional plasma. Two sources of LH turbulence are identified. In regimes with moderate ratio of electron-to-ion temperature Te <=Ti and low overall β, electromagnetic LH instability with hybrid wavelength k(ρeρi) 1 / 2 ~ 1 (Daughton, 2003) localized near the X-line can reach large amplitude. This mode produces substantial modifications to the average force balance in the form of fluctuation-induced drag and stress terms and significantly alters the structure of the diffusion region. It persists in weakly collisional regimes typical of MRX. Under parameters typical of the magnetopause, LH turbulence is predominantly localized around the separatrices on the low- β side of the current sheet, where it is driven by short-wavelength instability with kρe ~ 1 (e.g. Davidson, 1977). Under these conditions, the overall structure of the reconnection region is not appreciably modified compared to 2D simulations.
NASA Astrophysics Data System (ADS)
Rossi, C.; Califano, F.; Retinò, A.; Sorriso-Valvo, L.; Henri, P.; Servidio, S.; Valentini, F.; Chasapis, A.; Rezeau, L.
2015-12-01
The turbulence developing inside Kelvin-Helmholtz vortices has been studied using a two-fluid numerical simulation. From an initial large-scale velocity shear, the nonlinear evolution of the instability leads to the formation of a region inside the initial vortex characterized by small-scale fluctuations and structures. The magnetic energy spectrum is compatible with a Kolmogorov-like power-law decay, followed by a steeper power-law below proton scales, in agreement with other studies. The magnetic field increments show non-Gaussian distributions with increasing tails going towards smaller scales, consistent with presence of intermittency. The strong magnetic field fluctuations populating the tails of the distributions have been identified as current sheets by using the Partial Variance of the Increments (PVI) method. The strongest current sheets (largest PVI) appear around proton scales and below. By selecting several of such current sheets, it has been found that most of them are consistent with ongoing magnetic reconnection. The detailed study of one reconnecting current sheet as crossed by a virtual spacecraft is also presented. Inflow and outflow regions have been identified and the reconnection rate has been estimated. The observation of reconnection rates higher than typical fast rate ˜0.1 suggests that reconnection in turbulent plasma can be faster than laminar reconnection. This study indicates that intermittency and reconnecting current sheets are important ingredients of turbulence within Kelvin-Helmholtz vortices and that reconnection can play an important role for energy dissipation therein.
NASA Astrophysics Data System (ADS)
Kuwahata, Akihiro; Inomoto, Michiaki; Yanai, Ryoma; Ono, Yasushi
2015-11-01
Impulsive enhancement of magnetic reconnection is one of the potential candidates to invoke various explosive events observed in nature and laboratory plasmas. In TS-3 laboratory experiment with a guide field of Bguide /Brec = 1-2.5, impulsive growth of the reconnection electric field was observed just behind the onset of large-amplitude electromagnetic fluctuations (f = 1.5-2 fci and the amplitude was 0.1Brec). It was found that both the fluctuation amplitude and the enhanced reconnection electric field during the fluctuation period showed positive correlation with the guide field. The normalized reconnection rate of about 0.03 before the onset of fluctuations was reasonably comparable with the classical reconnection rate of Sweet-Parker model. However, the reconnection rate rose up to 0.11 after the fluctuations onset, suggesting that the transition from slow steady reconnection to fast impulsive reconnection took place. Since the fluctuation amplitude was so large that the nonlinear terms of the induced electric field was not negligible. The electric field enhancement due to the nonlinear contribution from the observed fluctuation was 650 V/m, which showed good agreement with the experimentally observed electric field increment of about 800 V/m.
Nonlinear Gyroviscous Force in a Collisionless Plasma
Belova, E.V.
2001-05-23
Nonlinear gyroviscous forces in a collisionless plasma with temperature variations are calculated from the gyrofluid moments of the gyrokinetic Vlasov equation. The low-frequency gyrokinetic ordering and electrostatic perturbations are assumed, and an additional finite Larmor radius (FLR) expansion is performed. This approach leads naturally to an expression for the gyroviscous force in terms of the gyrocenter distribution function, thus including all resonant effects, and represents a systematic FLR expansion in a general form (no assumption of any closure is made). The expression for the gyroviscous force is also calculated in terms of the particle-fluid moments by making the transformation from the gyrocenter to particle coordinates. The calculated expression represents a modification of the Braginskii gyroviscosity for a collisionless plasma with nonuniform temperature. It is compared with previous calculations based on the traditional fluid approach. As a byproduct of the gyroviscosity calculations, we derive a set of nonlinear reduced gyrofluid (and a corresponding set of particle-fluid) moment equations with FLR corrections, which exhibit a generalized form of the ''gyroviscous cancellation.''
The collisionless magnetoviscous-thermal instability
Islam, Tanim
2014-05-20
It is likely that nearly all central galactic massive and supermassive black holes are nonradiative: their accretion luminosities are orders of magnitude below what can be explained by efficient black hole accretion within their ambient environments. These objects, of which Sagittarius A* is the best-known example, are also dilute (mildly collisional to highly collisionless) and optically thin. In order for accretion to occur, magnetohydrodynamic (MHD) instabilities must develop that not only transport angular momentum, but also gravitational energy generated through matter infall, outward. A class of new magnetohydrodynamical fluid instabilities—the magnetoviscous-thermal instability (MVTI)—was found to transport angular momentum and energy along magnetic field lines through large (fluid) viscosities and thermal conductivities. This paper describes the analog to the MVTI, the collisionless MVTI (CMVTI), that similarly transports energy and angular momentum outward, expected to be important in describing the flow properties of hot, dilute, and radiatively inefficient accretion flows around black holes. We construct a local equilibrium for MHD stability analysis in this differentially rotating disk. We then find and characterize specific instabilities expected to be important in describing their flow properties, and show their qualitative similarities to instabilities derived using the fluid formalism. We conclude with further work needed in modeling this class of accretion flow.
Closure of fluid equations in collisionless magnetoplasmas
Chust, T.; Belmont, G.
2006-01-15
The possibility of using fluid equations in collisionless plasmas is revisited, and the conditions of validity of several possible closure equations are investigated. A new derivation of the well-known 'double-adiabatic' Chew-Goldberger-Low (CGL) laws is first presented. These laws are shown to demand two different kinds of conditions for ensuring (1) particle gyrotropy and (2) adiabaticity. Both kinds of conditions are investigated in detail. The usual slow and large-scales conditions (hereafter 'sls'), which are shown to be necessary for gyrotropy, are provided in a rigorous form. The role of the fundamental symmetries of the system, especially in the directions parallel and perpendicular to the magnetic field, is also emphasized for determining any 'fluid-type' behavior of a collisionless magnetoplasma. More general closure equations are afterwards proposed, relaxing first the conditions for adiabaticity and then, more speculatively, the sls conditions for gyrotropy. The dependence of these new closure equations on the shape of the velocity distribution functions is discussed, the CGL case being singular since it is shown to be fully independent of this shape.
On phase diagrams of magnetic reconnection
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.
A MODEL OF ACCELERATION OF ANOMALOUS COSMIC RAYS BY RECONNECTION IN THE HELIOSHEATH
Lazarian, A.; Opher, M. E-mail: mopher@gmu.ed
2009-09-20
We discuss a model of cosmic ray acceleration that accounts for the observations of anomalous cosmic rays (ACRs) by Voyager 1 and 2. The model appeals to fast magnetic reconnection rather than shocks as the driver of acceleration. The ultimate source of energy is associated with magnetic field reversals that occur in the heliosheath. It is expected that the magnetic field reversals will occur throughout the heliosheath, but especially near the heliopause where the flows slow down and diverge with respect to the interstellar wind and also in the boundary sector in the heliospheric current sheet. While the first-order Fermi acceleration theory within reconnection layers is in its infancy, the predictions do not contradict the available data on ACR spectra measured by the spacecraft. We argue that the Voyager data are one of the first pieces of evidence favoring the acceleration within regions of fast magnetic reconnection, which we believe to be a widely spread astrophysical process.
NASA Technical Reports Server (NTRS)
Collins, William
1989-01-01
The dispersion equation of Barnes (1966) is used to study the dissipation of asymptotic wave packets generated by localized periodic sources. The solutions of the equation are linear waves, damped by Landau and transit-time processes, in a collisionless warm plasma. For the case of an ideal MHD system, most of the waves emitted from a source are shown to cancel asympotically through destructive interference. The modes transporting significant flux to asymptotic distances are found to be Alfven waves and fast waves with theta (the angle between the magnetic field and the characteristics of the far-field waves) of about 0 and about pi/2.
Nemov, V. V.; Kasilov, S. V.; Kernbichler, W.
2014-06-15
An approach for the direct computation of collisionless losses of high energy charged particles is developed for stellarator magnetic fields given in real space coordinates. With this approach, the corresponding computations can be performed for magnetic fields with three-dimensional inhomogeneities in the presence of stochastic regions as well as magnetic islands. A code, which is based on this approach, is applied to various stellarator configurations. It is found that the life time of fast particles obtained in real-space coordinates can be smaller than that obtained in magnetic coordinates.
Laboratory Magnetic Reconnection Experiments with Colliding, Magnetized Laser-Produced Plasma Plumes
NASA Astrophysics Data System (ADS)
Fox, W. R., II; Bhattacharjee, A.; Deng, W.; Moissard, C.; Germaschewski, K.; Fiksel, G.; Barnak, D.; Chang, P. Y.; Hu, S.; Nilson, P.
2014-12-01
We present results from experiments and simulations of magnetic reconnection between colliding plumes of laser-produced plasma. In the experiments, which open up a new experimental regime for reconnection study, bubbles of high-temperature, high-density plasma are created by focusing lasers down to sub-millimeter-scale spots on a plastic or metal foil, ionizing the foil into hemispherical bubbles that expand supersonically off the surface of the foil. If multiple bubbles are created at small separation, the bubbles expand into one another, and the embedded magnetic fields (either self-generated or externally imposed) are squeezed together and reconnect. We will review recent experiments, which have observed magnetic field annihilation, outflow jets, particle energization, and the formation of elongated current sheets. We compare the results against experiments with unmagnetized plumes, which observe the Weibel instability as the two plumes collide and interact. Particle-in-cell simulations of the strongly driven reconnection in these experiments show fast reconnection due to two-fluid effects, flux pile-up, and plasmoid formation, and show particle energization by reconnection.
Numerical experiments of magnetic reconnection in the solar flare and CME current sheet
NASA Astrophysics Data System (ADS)
Mei, Zhixing; Lin, Jun; Shen, Chengcai
2012-07-01
Magnetic reconnection plays a critical role in the energy conversion in the solar eruption. This paper performs a set of MHD experiments for the magnetic reconnection process in a current sheet formed in a disrupting magnetic configuration. The eruption results from the loss of equilibrium in the magnetic configuration that includes a current-carrying flux rope, which is used to model the filament floating in the corona. In order to study the fine structure and micro process inside the current sheet (CS), the mesh refinement technology is used to depress the numerical diffusion. A uniform physical diffusion is applied and results in a Lundquist number S=10^4 in the vicinity of CS. Because of the advantage of the foregoing setting, some features appear with high resolution, including plasmoids due to the tearing mode and the plasmoid instabilities, turbulence regions, and the slow mode shocks. Inside CS, magnetic reconnection goes through the Sweet-Parker and the fractal fashions, and eventually, it displays a time-dependent Petschek pattern. Our results seem to support the concept of fractal reconnection suggested by Shibata et al. (1995) and Shibata & Tanuma (2001). And our results suggest that the CS evolves through a Sweet-Parker reconnection prior to the fast reconnection stage. For the first time, the detailed features and/or fine structures inside the CME/flare CS in the eruption were investigated in this work.
NASA Astrophysics Data System (ADS)
Mei, Z.; Shen, C.; Wu, N.; Lin, J.; Murphy, N. A.; Roussev, I. I.
2012-10-01
Magnetic reconnection plays a critical role in energy conversion during solar eruptions. This paper presents a set of magnetohydrodynamic experiments for the magnetic reconnection process in a current sheet (CS) formed in the wake of the rising flux rope. The eruption results from the loss of equilibrium in a magnetic configuration that includes a current-carrying flux rope, representing a pre-existing filament. In order to study the fine structure and micro processes inside the CS, mesh refinement is used to reduce the numerical diffusion. We start with a uniform, explicitly defined resistivity which results in a Lundquist number S = 104 in the vicinity of CS. The use of mesh refinement allows the simulation to capture high-resolution features such as plasmoids from the tearing mode and plasmoid instability regions of turbulence and slow-mode shocks. Inside the CS, magnetic reconnection goes through the Sweet-Parker and the fractal stages, and eventually displays a time-dependent Petschek pattern. Our results support the concept of fractal reconnection suggested by Shibata et al. and Shibata & Tanuma, and also suggest that the CS evolves through Sweet-Parker reconnection prior to the fast reconnection stage. For the first time, the detailed features and/or fine structures inside the coronal mass ejection/flare CS in the eruption were investigated in this work.
Localized enhancements of energetic particles at oblique collisionless shocks
NASA Astrophysics Data System (ADS)
Fraschetti, F.; Giacalone, J.
2015-04-01
We investigate the spatial distribution of charged particles accelerated by non-relativistic oblique fast collisionless shocks using three-dimensional test-particle simulations. We find that the density of low-energy particles exhibits a localized enhancement at the shock, resembling the `spike' measured at interplanetary shocks. In contrast to previous results based on numerical solutions to the focused transport equation, we find a shock spike for any magnetic obliquity, from quasi-perpendicular to parallel. We compare the pitch-angle distribution with respect to the local magnetic field and the momentum distribution far downstream and very near the shock within the spike; our findings are compatible with predictions from the scatter-free shock drift acceleration limit in these regions. The enhancement of low-energy particles measured by Voyager 1 at solar termination shock is comparable with our profiles. Our simulations allow for predictions of suprathermal protons at interplanetary shocks within 10 solar radii to be tested by Solar Probe mission. They also have implications for the interpretation of ions accelerated at supernova remnant shocks.
Landau, Case, van Kampen and Collisionless Fluid Closures
NASA Astrophysics Data System (ADS)
Joseph, Ilon
2015-11-01
Landau damping represents a fundamental paradox within plasma physics. The equations of motion of classical particles and fields are symmetric under time-reversal; yet, the open system formed by integration over velocity space is not invariant and damping results from phase-mixing. Here, it is shown that the Case-van Kampen theorem can be extended to magnetized plasmas: the linear eigenfunctions provide a complete representation of the particle distribution function and exponentially damped and growing eigenmodes must appear in pairs. The numerical Case-van Kampen transformation can performed efficiently in Fourier velocity space and allows fast timescales in the evolution of the system to be treated using exponential integration. On the other hand, fluid moments require integration over velocity space, and, thus, representation of Landau damping requires explicit introduction of the arrow of time through a collisionless damping operator. This operator captures linear phenomena at the cost of damping nonlinear phenomena such as the plasma echo. Numerical comparisons of these two rather different representations will be presented. LLNL-ABS-674917 prepared by LLNL under Contract DE-AC52-07NA27344.
The Plasmaspheric Plume and Magnetopause Reconnection
NASA Technical Reports Server (NTRS)
Walsh, B. M.; Phan, T. D.; Sibeck, D. G.; Souza, V. M.
2014-01-01
We present near-simultaneous measurements from two THEMIS spacecraft at the dayside magnetopause with a 1.5 h separation in local time. One spacecraft observes a high-density plasmaspheric plume while the other does not. Both spacecraft observe signatures of magnetic reconnection, providing a test for the changes to reconnection in local time along the magnetopause as well as the impact of high densities on the reconnection process. When the plume is present and the magnetospheric density exceeds that in the magnetosheath, the reconnection jet velocity decreases, the density within the jet increases, and the location of the faster jet is primarily on field lines with magnetosheath orientation. Slower jet velocities indicate that reconnection is occurring less efficiently. In the localized region where the plume contacts the magnetopause, the high-density plume may impede the solar wind-magnetosphere coupling by mass loading the reconnection site.
The Driving Magnetic Field and Reconnection in CME/Flare Eruptions and Coronal Jets
NASA Technical Reports Server (NTRS)
Moore, Ronald L.
2010-01-01
Signatures of reconnection in major CME (coronal mass ejection)/flare eruptions and in coronal X-ray jets are illustrated and interpreted. The signatures are magnetic field lines and their feet that brighten in flare emission. CME/flare eruptions are magnetic explosions in which: 1. The field that erupts is initially a closed arcade. 2. At eruption onset, most of the free magnetic energy to be released is not stored in field bracketing a current sheet, but in sheared field in the core of the arcade. 3. The sheared core field erupts by a process that from its start or soon after involves fast "tether-cutting" reconnection at an initially small current sheet low in the sheared core field. If the arcade has oppositely-directed field over it, the eruption process from its start or soon after also involves fast "breakout" reconnection at an initially small current sheet between the arcade and the overarching field. These aspects are shown by the small area of the bright field lines and foot-point flare ribbons in the onset of the eruption. 4. At either small current sheet, the fast reconnection progressively unleashes the erupting core field to erupt with progressively greater force. In turn, the erupting core field drives the current sheet to become progressively larger and to undergo progressively greater fast reconnection in the explosive phase of the eruption, and the flare arcade and ribbons grow to become comparable to the pre-eruption arcade in lateral extent. In coronal X-ray jets: 1. The magnetic energy released in the jet is built up by the emergence of a magnetic arcade into surrounding unipolar "open" field. 2. A simple jet is produced when a burst of reconnection occurs at the current sheet between the arcade and the open field. This produces a bright reconnection jet and a bright reconnection arcade that are both much smaller in diameter that the driving arcade. 3. A more complex jet is produced when the arcade has a sheared core field and undergoes an
Radiation from Accelerated Particles in Shocks and Reconnections
NASA Technical Reports Server (NTRS)
Nishikawa, K. I.; Choi, E. J.; Min, K. W.; Niemiec, J.; Zhang, B.; Hardee, P.; Mizuno, Y.; Medvedev, M.; Nordlund, A.; Frederiksen, J.; Sol, H.; Pohl, M.; Hartmann, D. H.; Fishman, G. J.
2012-01-01
Plasma instabilities are responsible not only for the onset and mediation of collisionless shocks but also for the associated acceleration of particles. We have investigated particle acceleration and shock structure associated with an unmagnetized relativistic electron-positron jet propagating into an unmagnetized electron-positron plasma. Cold jet electrons are thermalized and slowed while the ambient electrons are swept up to create a partially developed hydrodynamic-like shock structure. In the leading shock, electron density increases by a factor of about 3.5 in the simulation frame. Strong electromagnetic fields are generated in the trailing shock and provide an emission site. These magnetic fields contribute to the electrons transverse deflection and, more generally, relativistic acceleration behind the shock. We have calculated, self-consistently, the radiation from electrons accelerated in the turbulent magnetic fields. We found that the synthetic spectra depend on the Lorentz factor of the jet, its thermal temperature and strength of the generated magnetic fields. Our initial results of a jet-ambient interaction with anti-parallelmagnetic fields show pile-up of magnetic fields at the colliding shock, which may lead to reconnection and associated particle acceleration. We will investigate the radiation in a transient stage as a possible generation mechanism of precursors of prompt emission. In our simulations we calculate the radiation from electrons in the shock region. The detailed properties of this radiation are important for understanding the complex time evolution and spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.
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
Vortex reconnection in a swirling flow
NASA Astrophysics Data System (ADS)
Alekseenko, S. V.; Kuibin, P. A.; Shtork, S. I.; Skripkin, S. G.; Tsoy, M. A.
2016-04-01
Processes of vortex reconnection on a helical vortex, which is formed in a swirling flow in a conical diffuser, have been studied experimentally. It has been shown that reconnection can result in the formation of both an isolated vortex ring and a vortex ring linked with the main helical vortex. A number of features of vortex reconnection, including the effects of asymmetry, generation of Kelvin waves, and formation of various bridges, have been described.
Magnetic reconnection in a compressible MHD plasma
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.
Simulating Magnetotail Reconnection in the Presence of a Significant Guide Field
NASA Astrophysics Data System (ADS)
Ashour-Abdalla, Maha; Lapenta, Giovanni; Walker, Raymond; El-Alaoui, Mostafa; Liang, Haoming; Zhou, Meng; Berchem, Jean; Goldstein, Melvyn
2016-04-01
For a large number of solar wind driven substorms a significant guide field is present in the magnetotail. We have developed a new simulation approach for magnetotail reconnection in which we combine results from global magnetohydrodynamic simulations of the solar wind, magnetosphere and ionosphere system with large-scale 3D particle-in-cell simulations of the magnetotail. In this approach we first run a global MHD simulation driven by upstream solar wind observations. Then we use the results from the MHD simulation to set the initial and boundary conditions of a large-scale PIC simulation. We have selected the iPIC3D kinetic code to go along with the UCLA global simulation model. Our approach allows us to investigate indicators of reconnection in a realistic magnetospheric configuration, which is essential to determine the dynamics of the substorm process, in particular the evolution of reconnection and dipolarization fronts. In preparation for the MMS phase in the magnetotail, we have developed an analysis system with multiprobes so we can directly compare the simulation results with MMS observations and have applied our multiscale simulation approach to the solar wind driven substorm observed on March 1, 2008. This substorm was characterized by a significant guide field. In the PIC simulation fast but episodic reconnection is found in the near-Earth tail. The reconnection has a complex 3D structure. When normalized by the Alfvén speed and magnetic field magnitude, the reconnection rate although highly variable oscillates about the expected value of 0.1. The location of reconnection also is highly variable. In the simulation it moves several RE across the tail in less than two minutes. We have evaluated several indicators of reconnection and find that agyrotropy (or non-gyrotropy) is the most reliable indicator.
Dissipation in Relativistic Pair-Plasma Reconnection
NASA Technical Reports Server (NTRS)
Hesse, Michael; Zenitani, Seiji
2007-01-01
We present an investigation of the relativistic dissipation in magnetic reconnection. The investigated system consists of an electron-positron plasma. A relativistic generalization of Ohm's law is derived. We analyze a set of numerical simulations, composed of runs with and without guide magnetic field, and of runs with different species temperatures. The calculations indicate that the thermal inertia-based dissipation process survives in relativistic plasmas. For anti-parallel reconnection, it is found that the pressure tensor divergence remains the sole contributor to the reconnection electric field, whereas relativistic guide field reconnection exhibits a similarly important role of the bulk inertia terms.
Dissipation in relativistic pair-plasma reconnection
Hesse, Michael; Zenitani, Seiji
2007-11-15
An investigation into the relativistic dissipation in magnetic reconnection is presented. The investigated system consists of an electron-positron plasma. A relativistic generalization of Ohm's law is derived. A set of numerical simulations is analyzed, composed of runs with and without guide magnetic field, and of runs with different species temperatures. The calculations indicate that the thermal inertia-based dissipation process survives in relativistic plasmas. For antiparallel reconnection, it is found that the pressure tensor divergence remains the sole contributor to the reconnection electric field, whereas relativistic guide field reconnection exhibits a similarly important role of the bulk inertia terms.
A collisionless plasma thruster plume expansion model
NASA Astrophysics Data System (ADS)
Merino, Mario; Cichocki, Filippo; Ahedo, Eduardo
2015-06-01
A two-fluid model of the unmagnetized, collisionless far region expansion of the plasma plume for gridded ion thrusters and Hall effect thrusters is presented. The model is integrated into two semi-analytical solutions valid in the hypersonic case. These solutions are discussed and compared against the results from the (exact) method of characteristics; the relative errors in density and velocity increase slowly axially and radially and are of the order of 10-2-10-3 in the cases studied. The plasma density, ion flux and ambipolar electric field are investigated. A sensitivity analysis of the problem parameters and initial conditions is carried out in order to characterize the far plume divergence angle in the range of interest for space electric propulsion. A qualitative discussion of the physics of the secondary plasma plume is also provided.
The stability of a collisionless cosmological shell
NASA Technical Reports Server (NTRS)
White, Simon D. M.; Ostriker, J. P.
1990-01-01
The P3 M technique is used here to simulate the evolution of collisionless shells in an Omega = 1 universe. Starting from the spherical similarity solution, a bootstrap technique is used to follow the evolution over very large expansion factors. It is found that the overall structure follows the similarity solution for a long period during which bound clumps grow within the shell. At late times the growth of structure depends on induced velocity perturbations in material outside the shell. If such perturbations are suppressed, structure on the shell becomes self-similar. When induced motions in the background medium are included, the evolution at late times is dominated by large-scale modes as predicted by linear stability analysis. The stable final state appears to consist of one or two massive clumps on the edge of a spherical void. The possible application of these results to the origin of galaxies and large-scale structure is discussed.
Theory and simulation of collisionless parallel shocks
NASA Technical Reports Server (NTRS)
Quest, K. B.
1988-01-01
This paper presents a self-consistent theoretical model for collisionless parallel shock structure, based on the hypothesis that shock dissipation and heating can be provided by electromagnetic ion beam-driven instabilities. It is shown that shock formation and plasma heating can result from parallel propagating electromagnetic ion beam-driven instabilities for a wide range of Mach numbers and upstream plasma conditions. The theoretical predictions are compared with recently published observations of quasi-parallel interplanetary shocks. It was found that low Mach number interplanetary shock observations were consistent with the explanation that group-standing waves are providing the dissipation; two high Mach number observations confirmed the theoretically predicted rapid thermalization across the shock.
The extent of non-thermal particle acceleration in relativistic, electron-positron reconnection
Werner, Greg; Guo, Fan
2015-07-21
Reconnection is studied as an explanation for high-energy flares from the Crab Nebula. The production of synchrotron emission >100 MeV challenges classical models of acceleration. 3D simulation shows that reconnection, converting magnetic energy to kinetic energy, can accelerate beyond γ_{rad}. The power-law index and high-energy cutoff are important for understanding the radiation spectrum dN/dγ = f(γ) ∝ γ^{-α}. α and cutoff were measured vs. L and σ, where L is system (simulation) size and σ is upstream magnetization (σ = B^{2}/4πnmc^{2}). α can affect the high-energy cutoff. In conclusion, for collisionless relativistic reconnection in electron-positron plasma, without guide field, n_{b}/n_{d}=0.1: (1) relativistic magnetic reconnection yields power-law particle spectra, (2) the power law index decreases as σ increases, approaching ≈1.2. (3) the power law is cut off at an energy related to acceleration within a single current layer, which is proportional to the current layer length (for small systems, that length is the system length, yielding γ_{c2} ≈ 0.1 L/ρ_{0}; for large systems, the layer length is limited by secondary tearing instability, yielding γ_{c1} ≈ 4σ; the transition from small to large is around L/ρ_{0} = 40σ.). (4) although the large-system energy cutoff is proportional to the average energy per particle, it is significantly higher than the average energy per particle.
The microphysics of collisionless shock waves.
Marcowith, A; Bret, A; Bykov, A; Dieckman, M E; Drury, L O'C; Lembège, B; Lemoine, M; Morlino, G; Murphy, G; Pelletier, G; Plotnikov, I; Reville, B; Riquelme, M; Sironi, L; Novo, A Stockem
2016-04-01
Collisionless shocks, that is shocks mediated by electromagnetic processes, are customary in space physics and in astrophysics. They are to be found in a great variety of objects and environments: magnetospheric and heliospheric shocks, supernova remnants, pulsar winds and their nebulæ, active galactic nuclei, gamma-ray bursts and clusters of galaxies shock waves. Collisionless shock microphysics enters at different stages of shock formation, shock dynamics and particle energization and/or acceleration. It turns out that the shock phenomenon is a multi-scale non-linear problem in time and space. It is complexified by the impact due to high-energy cosmic rays in astrophysical environments. This review adresses the physics of shock formation, shock dynamics and particle acceleration based on a close examination of available multi-wavelength or in situ observations, analytical and numerical developments. A particular emphasis is made on the different instabilities triggered during the shock formation and in association with particle acceleration processes with regards to the properties of the background upstream medium. It appears that among the most important parameters the background magnetic field through the magnetization and its obliquity is the dominant one. The shock velocity that can reach relativistic speeds has also a strong impact over the development of the micro-instabilities and the fate of particle acceleration. Recent developments of laboratory shock experiments has started to bring some new insights in the physics of space plasma and astrophysical shock waves. A special section is dedicated to new laser plasma experiments probing shock physics. PMID:27007555
The microphysics of collisionless shock waves
NASA Astrophysics Data System (ADS)
Marcowith, A.; Bret, A.; Bykov, A.; Dieckman, M. E.; O'C Drury, L.; Lembège, B.; Lemoine, M.; Morlino, G.; Murphy, G.; Pelletier, G.; Plotnikov, I.; Reville, B.; Riquelme, M.; Sironi, L.; Stockem Novo, A.
2016-04-01
Collisionless shocks, that is shocks mediated by electromagnetic processes, are customary in space physics and in astrophysics. They are to be found in a great variety of objects and environments: magnetospheric and heliospheric shocks, supernova remnants, pulsar winds and their nebulæ, active galactic nuclei, gamma-ray bursts and clusters of galaxies shock waves. Collisionless shock microphysics enters at different stages of shock formation, shock dynamics and particle energization and/or acceleration. It turns out that the shock phenomenon is a multi-scale non-linear problem in time and space. It is complexified by the impact due to high-energy cosmic rays in astrophysical environments. This review adresses the physics of shock formation, shock dynamics and particle acceleration based on a close examination of available multi-wavelength or in situ observations, analytical and numerical developments. A particular emphasis is made on the different instabilities triggered during the shock formation and in association with particle acceleration processes with regards to the properties of the background upstream medium. It appears that among the most important parameters the background magnetic field through the magnetization and its obliquity is the dominant one. The shock velocity that can reach relativistic speeds has also a strong impact over the development of the micro-instabilities and the fate of particle acceleration. Recent developments of laboratory shock experiments has started to bring some new insights in the physics of space plasma and astrophysical shock waves. A special section is dedicated to new laser plasma experiments probing shock physics.
NASA Astrophysics Data System (ADS)
Uzdensky, Dmitri
2015-11-01
Magnetic reconnection is a fundamental plasma process believed to play an important role in energetics of magnetically-dominated coronae of various astrophysical objects including accreting black holes. Building up on recent advances in kinetic simulations of relativistic collisionless reconnection, we investigate nonthermal particle acceleration and its key observational consequences for these systems. We argue that reconnection can efficiently accelerate coronal electrons (as well as ions) up to hundreds of MeV or even GeV energies. In brightest systems, radiation back-reaction due to inverse-Compton (and/or synchrotron) emission becomes important at these energies and limits any further electron acceleration, thereby turning reconnection layers into powerful and efficient radiators of γ-rays. We then evaluate the rate of absorption of the resulting γ-ray photons by the ambient soft (X-ray) photon fields and show that it can be a significant source of pair production, with important implications for the composition of black-hole coronae and jets. Finally, we assess the prospects of laboratory studies of magnetic reconnection in the physical regimes relevant to black-hole accretion flows using modern and future laser-plasma facilities. This work is supported by DOE, NSF, and NASA.
Current Sheet Formation and Reconnection at a Magnetic X Line
NASA Astrophysics Data System (ADS)
DeVore, C. Richard; Antiochos, S. K.
2011-05-01
Phenomena ranging from the quiescent heating of the ambient plasma to the highly explosive release of energy and acceleration of particles in flares are conjectured to result from magnetic reconnection at electric current sheets in the Sun's corona. We are investigating numerically the formation and eventual reconnection of a current sheet in an initially potential 2D magnetic field containing a null. Subjecting this simple configuration to unequal stresses in the four quadrants bounded by the X-line separatrix distorts the potential null into a double-Y-line current sheet. Although the gas pressure is finite in our simulations, so that the plasma beta is infinite at the null, we find that even small distortions of the magnetic field induce the formation of a tangential discontinuity there. This result is well known to occur in the zero-beta, force-free limit; surprisingly, it persists into the high-beta regime where, in principle, a small plasma pressure inhomogeneity could balance all of the magnetic stress. In addition to working to understand the dynamical details of this ideal process, we are examining the effect of resistive dissipation on the development of the current sheet and are seeking to determine the critical condition for fast-reconnection onset in the sheet. Our progress on understanding these issues, and the implications for the dynamic activity associated with current sheets in the solar corona, will be reported at the conference. We gratefully acknowledge NASA sponsorship of our research.
Zocco, Alessandro; Schekochihin, Alexander A.
2011-10-15
A minimal model for magnetic reconnection and, generally, low-frequency dynamics in low-beta plasmas is proposed. The model combines analytical and computational simplicity with physical realizability: it is a rigorous limit of gyrokinetics for plasma beta of order the electron-ion mass ratio. The model contains collisions and can be used both in the collisional and collisionless reconnection regimes. It includes gyrokinetic ions (not assumed cold) and allows for the topological rearrangement of the magnetic field lines by either resistivity or electron inertia, whichever predominates. The two-fluid dynamics are coupled to electron kinetics--electrons are not assumed isothermal and are described by a reduced drift-kinetic equation. The model, therefore allows for irreversibility and conversion of magnetic energy into electron heat via parallel phase mixing in velocity space. An analysis of the exchanges between various forms of free energy and its conversion into electron heat is provided. It is shown how all relevant linear waves and regimes of the tearing instability (collisionless, semicollisional, and fully resistive) are recovered in various limits of our model. An efficient way to simulate our equations numerically is proposed, via the Hermite representation of the velocity space. It is shown that small scales in velocity space will form, giving rise to a shallow Hermite-space spectrum, whence it is inferred that, for steady-state or sufficiently slow dynamics, the electron heating rate will remain finite in the limit of vanishing collisionality.
The reconnection site of temporal cusp structures
NASA Astrophysics Data System (ADS)
Trattner, K. J.; Fuselier, S. A.; Petrinec, S. M.; Yeoman, T. K.; Escoubet, C. P.; Reme, H.
2008-07-01
The strong precipitating particle flux in the cusp regions is the consequence of magnetic reconnection between the interplanetary magnetic field and the geomagnetic field. Magnetic reconnection is thought to be the dominant process for mass, energy, and momentum transfer from the magnetosheath into the magnetosphere. Observations of downward precipitating cusp ions by polar orbiting satellites are instrumental in unlocking many questions about magnetic reconnection, e.g., their spatial and temporal nature and the location of the reconnection site at the magnetopause. In this study we combine cusp observations of structures in the precipitating ion-energy dispersion by the Cluster satellites with Super Dual Auroral Radar Network radar observations to distinguish between the temporal and spatial magnetic reconnection processes at the magnetopause. The location of the cusp structures relative to the convection cells is interpreted as a temporal phenomenon caused by a change in the reconnection rate at the magnetopause. The 3-D plasma observations of the Cluster Ion Spectrometry instruments onboard the Cluster spacecraft also provide the means to estimate the location of the reconnection site. While an earlier study of a spatial cusp structure event revealed bifurcated reconnection locations in different hemispheres as origins for the precipitating ions creating the cusp structures, the same method applied to the temporal cusp structures in this study shows only a single tilted reconnection line close to the subsolar point. Tracing the distance to the reconnection site provides not only the location of the reconnection line but can also be used to distinguish between spatial and temporal cusp structures.
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.
The "Newton Challenge": Properties of Forced Magnetic Reconnection
NASA Astrophysics Data System (ADS)
Pritchett, P. L.
2005-05-01
Inspired by the observations of thin (ion-scale) current sheets at important magnetospheric boundaries, the study of the properties of thin current sheets has become very popular in recent years. Most of these investigations, however, have ignored the question of how the sheets are formed. Instead, usually a simple Harris-type current sheet is postulated at the outset, and the resulting behavior is then determined. Recently, a collaborative effort, dubbed the "Newton Challenge" and involving J. Birn, K. Galsgaard, M. Hesse, M. Hoshino, J. Huba, G. Lapenta, P.~L. Pritchett, K. Schindler, L. Yin, J. Büchner, T. Neukirch, and E.~R. Priest, was begun to investigate the transition from thicker to thin current sheets that can occur as a result of magnetopause deformations imposed by the solar wind. A standard 2-D model problem in which current sheet thinning was forced by imposing a finite deformation of the field above and below the current sheet was studied by a variety of physical models ranging from resistive MHD to fully kinetic particle models. The aim was to determine whether differences would arise between the fluid and kinetic treatments that might affect the onset of magnetic reconnection. The initial results indicate that full-particle, hybrid, and Hall-MHD models lead to fast reconnection and similar final states despite differences in energy transfer and dissipation. Resistive MHD simulations show reduced reconnection rates that depend on the magnitude of the resistivity. These results will be reviewed, and additional features of forced reconnection, including continuous forcing, open boundaries, the presence of a normal field component, and 3-D effects, will be discussed.
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.
Kinetic model for the collisionless sheath of a collisional plasma
NASA Astrophysics Data System (ADS)
Tang, Xian-Zhu; Guo, Zehua
2016-08-01
Collisional plasmas typically have mean-free-path still much greater than the Debye length, so the sheath is mostly collisionless. Once the plasma density, temperature, and flow are specified at the sheath entrance, the profile variation of electron and ion density, temperature, flow speed, and conductive heat fluxes inside the sheath is set by collisionless dynamics, and can be predicted by an analytical kinetic model distribution. These predictions are contrasted here with direct kinetic simulations, showing good agreement.
Borgogno, D.; Califano, F.; Pegoraro, F.; Faganello, M.
2015-03-15
In an almost collisionless magnetohydrodynamic plasma in a relatively strong magnetic field, stresses can be conveyed far from the region where they are exerted, e.g., through the propagation of Alfvèn waves. The forced dynamics of line-tied magnetic structures in solar and stellar coronae (see, e.g., A. F. Rappazzo and E. N. Parker, Astrophys. J. 773, L2 (2013) and references therein) is a paradigmatic case. Here, we investigate how this action at a distance develops from the equatorial region of the Kelvin-Helmholtz unstable flanks of the Earth's magnetosphere leading to the onset, at mid latitude in both hemispheres, of correlated double magnetic field line reconnection events that can allow the solar wind plasma to enter the Earth's magnetosphere.
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.
Steady magnetic reconnection in three dimensions
NASA Technical Reports Server (NTRS)
Priest, E. R.; Forbes, T. G.
1989-01-01
The concept of magnetic reconnection, defined to occur when there is an electric field parallel to field lines which are potential reconnection locations and near which the field has an X-type topology in a plane normal to the field line, has been generalized to three-dimensional configurations. A continuum of neighboring potential singular lines is found to exist, one of which supports reconnection, depending upon the imposed flow or electric field. For the case of steady reconnection, the nearby flow and electric field are shown to be severely constrained in the ideal region by the condition that the electric field = 0 there. It is noted that reconnection may occur at singularities of the electric field where this constraint fails and there is singular plasma jetting.
Role of reconnection in AGN jets
NASA Astrophysics Data System (ADS)
Lyutikov, Maxim
2003-10-01
We discuss the possible role of reconnection in electro-magnetically dominated cores of relativistic AGN jets. We suggest that reconnection may proceed in a two-fold fashion: initial explosive collapse on the Alfvén time-scale of a current-carrying jet (which is of the order of the light crossing time) and subsequent slow quasi-steady reconnection. Sites of explosive collapse are associated with bright knots, while steady-state reconnection re-energizes particles in the 'bridges' between the knots. Ohmic dissipation in reconnection layers leads to particle acceleration either by inductive electric fields or by stochastic particle acceleration in the ensuing electro-magnetic turbulence.
Quantifying gyrotropy in magnetic reconnection
NASA Astrophysics Data System (ADS)
Swisdak, M.
2016-01-01
A new scalar measure of the gyrotropy of a pressure tensor is defined. Previously suggested measures are shown to be incomplete by means of examples for which they give unphysical results. To demonstrate its usefulness as an indicator of magnetic topology, the new measure is calculated for electron data taken from numerical simulations of magnetic reconnection, shown to peak at separatrices and X points, and compared to the other measures. The new diagnostic has potential uses in analyzing spacecraft observations, and so a method for calculating it from measurements performed in an arbitrary coordinate system is derived.
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
Collisionless relaxation in beam-plasma systems
Backhaus, Ekaterina Yu.
2001-05-01
This thesis reports the results from the theoretical investigations, both numerical and analytical, of collisionless relaxation phenomena in beam-plasma systems. Many results of this work can also be applied to other lossless systems of plasma physics, beam physics and astrophysics. Different aspects of the physics of collisionless relaxation and its modeling are addressed. A new theoretical framework, named Coupled Moment Equations (CME), is derived and used in numerical and analytical studies of the relaxation of second order moments such as beam size and emittance oscillations. This technique extends the well-known envelope equation formalism, and it can be applied to general systems with nonlinear forces. It is based on a systematic moment expansion of the Vlasov equation. In contrast to the envelope equation, which is derived assuming constant rms beam emittance, the CME model allows the emittance to vary through coupling to higher order moments. The CME model is implemented in slab geometry in the absence of return currents. The CME simulation yields rms beam sizes, velocity spreads and emittances that are in good agreement with particle-in-cell (PIC) simulations for a wide range of system parameters. The mechanism of relaxation is also considered within the framework of the CME system. It is discovered that the rapid relaxation or beam size oscillations can be attributed to a resonant coupling between different modes of the system. A simple analytical estimate of the relaxation time is developed. The final state of the system reached after the relaxation is complete is investigated. New and accurate analytical results for the second order moments in the phase-mixed state are obtained. Unlike previous results, these connect the final values of the second order moments with the initial beam mismatch. These analytical estimates are in good agreement with the CME model and PIC simulations. Predictions for the final density and temperature are developed that show
NASA Astrophysics Data System (ADS)
Radioti, A.; Grodent, D.; Jia, X.; Gérard, J.-C.; Bonfond, B.; Pryor, W.; Gustin, J.; Mitchell, D. G.; Jackman, C. M.
2016-01-01
We present high-resolution Cassini/UVIS (Ultraviolet Imaging Spectrograph) observations of Saturn's aurora during May 2013 (DOY 140-141). The observations reveal an enhanced auroral activity in the midnight-dawn quadrant in an extended local time sector (∼02 to 05 LT), which rotates with an average velocity of ∼45% of rigid corotation. The auroral dawn enhancement reported here, given its observed location and brightness, is most probably due to hot tenuous plasma carried inward in fast moving flux tubes returning from a tail reconnection site to the dayside. These flux tubes could generate intense field-aligned currents that would cause aurora to brighten. However, the origin of tail reconnection (solar wind or internally driven) is uncertain. Based mainly on the flux variations, which do not demonstrate flux closure, we suggest that the most plausible scenario is that of internally driven tail reconnection which operates on closed field lines. The observations also reveal multiple intensifications within the enhanced region suggesting an x-line in the tail, which extends from 02 to 05 LT. The localised enhancements evolve in arc and spot-like small scale features, which resemble vortices mainly in the beginning of the sequence. These auroral features could be related to plasma flows enhanced from reconnection which diverge into multiple narrow channels then spread azimuthally and radially. We suggest that the evolution of tail reconnection at Saturn may be pictured by an ensemble of numerous narrow current wedges or that inward transport initiated in the reconnection region could be explained by multiple localised flow burst events. The formation of vortical-like structures could then be related to field-aligned currents, building up in vortical flows in the tail. An alternative, but less plausible, scenario could be that the small scale auroral structures are related to viscous interactions involving small-scale reconnection.
Laboratory Study of Magnetic Reconnection in 3D Geometry Relevant to Magnetopause and Magnetotail
NASA Astrophysics Data System (ADS)
Ren, Y.; Lu, Q.; Ji, H.; Mao, A.; Wang, X.; E, P.; Wang, Z.; Xiao, Q.; Ding, W.; Zheng, J.
2015-12-01
Laboratory Study of Magnetic Reconnection in 3D Geometry Relevant to Magnetopause and Magnetotail Y. Ren1,2, Quaming Lu3, Hantao Ji1,2, Aohua Mao1, Xiaogang Wang1, Peng E1, Zhibin Wang1, Qingmei Xiao1, Weixing Ding4, Jinxing Zheng51 Harbin Institute of Technology, Harbin, China2 Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 3University of Science and Technology of China, Hefei, China 4University of California at Los Angeles, Los Angeles, CA, 90095 5ASIPP, Hefei, China A new magnetic reconnection experiment, Harbin reconnection eXperiment (HRX), is currently being designed as a key part of Space Plasma Environment Research Facility (SPERF) at Harbin Institute of Technology in Harbin, China. HRX aims to provide a unique experimental platform for studying reconnections in 3D geometry relevant to magnetopause and magnetotail to address: the role of electron and ion-scale dynamics in the current sheet; particle and energy transfer from magnetosheath to magnetosphere; particle energization/heating mechanisms during magnetic reconnection; 3D effects in fast reconnection, e.g. the role of 3D magnetic null point. HRX employs a unique set of coils to generate the required 3D magnetic geometry and provides a wide range of plasma parameters. Here, important motivating scientific problems are reviewed and the physics design of HRX is presented, including plasma parameters determined from Vlasov scaling law, reconnection scenarios explored using vacuum magnetic field calculations and numerical simulations of HRX using hybrid and MHD codes. Plasma diagnostics plan and engineering design of important coils will also be briefly presented.
Intense laser driven collision-less shock and ion acceleration in magnetized plasmas
NASA Astrophysics Data System (ADS)
Mima, K.; Jia, Q.; Cai, H. B.; Taguchi, T.; Nagatomo, H.; Sanz, J. R.; Honrubia, J.
2016-05-01
The generation of strong magnetic field with a laser driven coil has been demonstrated by many experiments. It is applicable to the magnetized fast ignition (MFI), the collision-less shock in the astrophysics and the ion shock acceleration. In this paper, the longitudinal magnetic field effect on the shock wave driven by the radiation pressure of an intense short pulse laser is investigated by theory and simulations. The transition of a laminar shock (electro static shock) to the turbulent shock (electromagnetic shock) occurs, when the external magnetic field is applied in near relativistic cut-off density plasmas. This transition leads to the enhancement of conversion of the laser energy into high energy ions. The enhancement of the conversion efficiency is important for the ion driven fast ignition and the laser driven neutron source. It is found that the total number of ions reflected by the shock increases by six time when the magnetic field is applied.
NASA Astrophysics Data System (ADS)
Petrinec, S. M.; Burch, J. L.; Fuselier, S. A.; Gomez, R. G.; Lewis, W.; Trattner, K. J.; Ergun, R.; Mauk, B.; Pollock, C. J.; Schiff, C.; Strangeway, R. J.; Russell, C. T.; Phan, T.-D.; Young, D.
2016-06-01
Magnetic reconnection at the Earth's magnetopause is the primary process by which solar wind plasma and energy gains access to the magnetosphere. One indication that magnetic reconnection is occurring is the observation of accelerated plasma as a jet tangential to the magnetopause. The direction of ion jets along the magnetopause surface as observed by the Fast Plasma Instrument (FPI) and the Hot Plasma Composition Analyzer (HPCA) instrument on board the recently launched Magnetospheric Multiscale (MMS) set of spacecraft is examined. For those cases where ion jets are clearly discerned, the direction of origin compares well statistically with the predicted location of magnetic reconnection using convected solar wind observations in conjunction with the Maximum Magnetic Shear model.
Yamada, M.; Manickam, J.; Pomphrey, N.; Levinton, F.M.; Nagayama, Y.
1994-01-01
Magnetic reconnection is investigated in high temperature TFTR tokamak plasmas by a set of non-perturbative diagnostics. During the crash phase of sawtooth oscillations in the plasma discharges, the ECE (electron cyclotron emission) diagnostic measures a fast flattening of the 2-D electron temperature profile in a poloidal plane, an observation consistent with the Kadomtsev reconnection theory. On the other hand motional Stark effect(MSE) measurements indicate that central q values do not relax to unity after the crash, but increase only by 5-10%, typically from 0.7 to 0.75. The latter result is in contradiction with the models of Kadomtsev and/or Wesson. A heuristic model for the magnetic reconnection at the sawtooth crash is also presented.
Nonlinear theory of collisionless trapped ion modes
Hahm, T.S.; Tang, W.M.
1996-03-01
A simplified two field nonlinear model for collisionless trapped-ion-mode turbulence has been derived from nonlinear bounce-averaged drift kinetic equations. The renormalized thermal diffusivity obtained from this analysis exhibits a Bohm-like scaling. A new nonlinearity associated with the neoclassical polarization density is found to introduce an isotope-dependent modification to this Bohm-like diffusivity. The asymptotic balance between the equilibrium variation and the finite banana width induced reduction of the fluctuation potential leads to the result that the radial correlation length decreases with increasing plasma current. Other important conclusions from the present analysis include the predictions that (i) the relative density fluctuation level {delta}n/n{sub 0} is lower than the conventional mixing length estimate, {Delta}r/L{sub n} (ii) the ion temperature fluctuation level {delta}T{sub i}/T{sub i} significantly exceeds the density fluctuation level {delta}n/n{sub 0}; and (iii) the parallel ion velocity fluctuation level {delta}v{sub i}{sub {parallel}}/v{sub Ti} is expected to be negligible.
Turbulent dynamo in a collisionless plasma.
Rincon, François; Califano, Francesco; Schekochihin, Alexander A; Valentini, Francesco
2016-04-12
Magnetic fields pervade the entire universe and affect the formation and evolution of astrophysical systems from cosmological to planetary scales. The generation and dynamical amplification of extragalactic magnetic fields through cosmic times (up to microgauss levels reported in nearby galaxy clusters, near equipartition with kinetic energy of plasma motions, and on scales of at least tens of kiloparsecs) are major puzzles largely unconstrained by observations. A dynamo effect converting kinetic flow energy into magnetic energy is often invoked in that context; however, extragalactic plasmas are weakly collisional (as opposed to magnetohydrodynamic fluids), and whether magnetic field growth and sustainment through an efficient turbulent dynamo instability are possible in such plasmas is not established. Fully kinetic numerical simulations of the Vlasov equation in a 6D-phase space necessary to answer this question have, until recently, remained beyond computational capabilities. Here, we show by means of such simulations that magnetic field amplification by dynamo instability does occur in a stochastically driven, nonrelativistic subsonic flow of initially unmagnetized collisionless plasma. We also find that the dynamo self-accelerates and becomes entangled with kinetic instabilities as magnetization increases. The results suggest that such a plasma dynamo may be realizable in laboratory experiments, support the idea that intracluster medium turbulence may have significantly contributed to the amplification of cluster magnetic fields up to near-equipartition levels on a timescale shorter than the Hubble time, and emphasize the crucial role of multiscale kinetic physics in high-energy astrophysical plasmas. PMID:27035981
Turbulent dynamo in a collisionless plasma
NASA Astrophysics Data System (ADS)
Rincon, François; Califano, Francesco; Schekochihin, Alexander A.; Valentini, Francesco
2016-04-01
Magnetic fields pervade the entire universe and affect the formation and evolution of astrophysical systems from cosmological to planetary scales. The generation and dynamical amplification of extragalactic magnetic fields through cosmic times (up to microgauss levels reported in nearby galaxy clusters, near equipartition with kinetic energy of plasma motions, and on scales of at least tens of kiloparsecs) are major puzzles largely unconstrained by observations. A dynamo effect converting kinetic flow energy into magnetic energy is often invoked in that context; however, extragalactic plasmas are weakly collisional (as opposed to magnetohydrodynamic fluids), and whether magnetic field growth and sustainment through an efficient turbulent dynamo instability are possible in such plasmas is not established. Fully kinetic numerical simulations of the Vlasov equation in a 6D-phase space necessary to answer this question have, until recently, remained beyond computational capabilities. Here, we show by means of such simulations that magnetic field amplification by dynamo instability does occur in a stochastically driven, nonrelativistic subsonic flow of initially unmagnetized collisionless plasma. We also find that the dynamo self-accelerates and becomes entangled with kinetic instabilities as magnetization increases. The results suggest that such a plasma dynamo may be realizable in laboratory experiments, support the idea that intracluster medium turbulence may have significantly contributed to the amplification of cluster magnetic fields up to near-equipartition levels on a timescale shorter than the Hubble time, and emphasize the crucial role of multiscale kinetic physics in high-energy astrophysical plasmas.
MHD results from a collisionless fluid model
NASA Astrophysics Data System (ADS)
Ramos, J. J.
2002-11-01
A non-conventional closure ansatz for collisionless MHD has been proposed in Ref.[1]. The truncation of the set of fluid moment equations is suggested by a comparison between the standard non-relativistic set and the non-relativistic limit of the relativistic set derived in Ref.[2]. The resulting model is a closed system of evolution equations in conservation form for the particle, momentum and energy densities, and the energy flux, allowing for pressure anisotropy and parallel heat flux. The static equilibrium condition is the same as in the Chew-Goldberger-Low theory, supplemented by the condition that the parallel energy flux be constant along the magnetic field. We study the linear perturbations about such static equilibria to derive the MHD wave dispersion relations in a homogeneous background and the perturbed potential energy associated with a stability energy principle. [1] J.J. Ramos, 2002 International Sherwood Theory Meeting, Rochester, NY, paper 1D25. [2] R.D. Hazeltine and S.M. Mahajan, Ap. J. 567, 1262 (2002).
Electrostatic Potential Across Supercritical Collisionless Shock
NASA Astrophysics Data System (ADS)
Khotyaintsev, Y. V.; Vaivads, A.; Krasnoselskikh, V.
2013-12-01
Using multi-spacecraft Cluster observations of the Earth's bow shock we estimate the electrostatic potential across a supercritical quasi-perpendicular collisionless shock. We find the potential values of the order of several kV, which correspond roughly to the kinetic energy of the inflowing solar wind. It is expected that the plasma flow in the de Hoffmann-Teller frame is field-aligned, and thus the potential computed in this frame is the parallel potential experienced by both ions and electrons. Contrary to this expectation, we show that most of the potential computed in the de Hoffmann-Teller frame is contributed by sub-proton scale Hall electric field, E~JxB/ne, which exists due to decoupling of electron and ion motions at such small scales (ions are demagnetized, and electrons are still well magnetized), and therefore the electron motion in such field is perpendicular to B. In order to calculate the parallel potential drop experienced by electrons, one needs to go to the 'electron' Hoffmann-Teller frame at small scales, in which the JxB/ne field is zero. In this 'electron' frame we find much smaller values of the potential drop across the shock of the order of 100 eV, which is comparable to the change of electron temperature across the shock, and is in agreement with theoretical estimates.
NASA Astrophysics Data System (ADS)
Li, Shiyou; Chen, Xiaoqian; Guo, Jianming
2016-07-01
The electrostatic solitary waves (ESWs) have been widely observed and studied for many years. In the magnetic reconnection process, ESWs are regarded as one kind of means for the fast energy release by outward propagating electrons along re-connecting magnetic field lines. In this report, we present observation evidences of two kinds of unusual structures of ESWs associated with magnetic reconnection in the near-Earth magnetotail, including the 2-D ESWs and the tri-polar ESWs. First of all, more than 300 of electrostatic solitary waves (ESWs) with large perpendicular component which is bi-polar waveform structure are observed in the boundary layer within magnetic reconnection diffusion region in the near-Earth magnetotail. Such kinds of ESWs are named as 2-D ESWs. Singe-Reconnection-Based-Statistical study of 2-D ESWs is performed. Secondly, more than 200 waveforms with clear tri-polar characteristics are differentiated along the plasma sheet boundary layer near the magnetic reconnection X-line in the near-Earth magnetotail. Within reconnection diffusion region, the tri-polar ESWs are ample and are continuously observed during one burst interval (8.75 seconds) of the Geotail/WFC in the neutral plasma sheet where and thus the tri-polar ESW is suggested to be one kind of steady-going solitary structure. Statistical analysis to the characteristics of tri-polar ESWs will also be carried out. The observation of 2-D ESWs and the tri-polar ESWs presents evidence of complex structure of electron holes within the reconnection diffusion region and is helpful to the understanding of the energy release process of reconnection.
NASA Astrophysics Data System (ADS)
Bhattacharjee, Amitava
2015-11-01
In recent years, new developments in reconnection theory have challenged classical nonlinear reconnection models. One of these developments is the so-called plasmoid instability of thin current sheets that grows at super-Alfvenic growth rates. Within the resistive MHD model, this instability alters qualitatively the predictions of the Sweet-Parker model, leading to a new nonlinear regime of fast reconnection in which the reconnection rate itself becomes independent of S. This regime has also been seen in Hall MHD as well as fully kinetic simulations, and thus appears to be a universal feature of thin current sheet dynamics, including applications to reconnection forced by the solar wind in the heliosphere and spontaneously unstable sawtooth oscillations in tokamaks. Plasmoids, which can grow by coalescence to large sizes, provide a powerful mechanism for coupling between global and kinetic scales as well as an efficient accelerator of particles to high energies. In two dimensions, the plasmoids are characterized by power-law distribution functions followed by exponential tails. In three dimensions, the instability produces self-generated and strongly anisotropic turbulence in which the reconnection rate for the mean-fields remain approximately at the two-dimensional value, but the energy spectra deviate significantly from anisotropic strong MHD turbulence phenomenology. A new phase diagram of fast reconnection has been proposed, guiding the design of future experiments in magnetically confined and high-energy-density plasmas, and have important implications for explorations of the reconnection layer in the recently launched Magnetospheric Multiscale (MMS) mission. This research is supported by DOE, NASA, and NSF.
Evidence for Gradual External Reconnection Before Explosive Eruption of a Solar Filament
NASA Technical Reports Server (NTRS)
Sterling, Alphonse C.; Moore, Ronald L.
2004-01-01
We observe a slowly evolving quiet-region solar eruption of 1999 April 18, using extreme-ultraviolet (EUV) images from the EUV Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO) and soft X-ray images from the Soft X-ray Telescope (SXT) on Yohkoh. Using difference images, in which an early image is subtracted from later images, we examine dimmings and brightenings in the region for evidence of the eruption mechanism. A filament rose slowly at about 1 km/s for 6 hours before being rapidly ejected at about 16 km/s leaving flare brightenings and postflare loops in its wake. Magnetograms from the Michelson Doppler Imager (MDI) on SOHO show that the eruption occurred in a large quadrupolar magnetic region with the filament located on the neutral line of the quadrupole s central inner lobe between the inner two of the four polarity domains. In step with the slow rise, subtle EIT dimmings commence and gradually increase over the two polarity domains on one side of the filament, i.e., in some of the loops of one of the two sidelobes of the quadrupole. Concurrently, soft X-ray brightenings gradually increase in both sidelobes. Both of these effects suggest heating in the sidelobe magnetic arcades. which gradually increase over several hours before the fast eruption. Also, during the slow pre- eruption phase, SXT dimmings gradually increase in the feet and legs of the central lobe, indicating expansion of the central-lobe magnetic arcade enveloping the filament. During the rapid ejection. these dimmings rapidly grow in darkness and in area, especially in the ends of the sigmoid field that erupts with the filament. and flare brightenings begin underneath the fast-moving but still low-altitude filament. We consider two models for explaining the eruption: "breakout. which says that reconnection occurs high above the filament prior to eruption, and tether cutting, which says that the eruption is unleashed by reconnection beneath the filament. The pre
Evidence for Gradual External Reconnection Before Explosive Eruption of a Solar Filament
NASA Technical Reports Server (NTRS)
Sterling, Alphonse C.; Moore, Ronald L.
2003-01-01
We observe a slowly-evolving quiet region solar eruption of 1999 April 18, using EUV images from the EUV Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO), and soft X-ray images from the Soft X-ray Telescope (SXT) on Yohkoh. Using difference images, where an early image is subtracted from later images, we examine dimmings and brightenings in the region for evidence of the eruption mechanism. A filament rose slowly at about 1 kilometer per second for six hours before being rapidly ejected at about 16 kilometers per second, leaving flare brightenings and post-flare loops in its wake. Magnetograms from the Michelson Doppler Imager (MDI) on SOHO show that the eruption occurred in a large quadrupo1ar magnetic region, with the filament located on the neutral line of the quadrupole's central inner lobe, between the inner two of the four polarity domains. In step with the slow rise, subtle EIT dimmings commence and gradually increase over the two polarity domains on one side of the filament, i.e. in some of the loops of one of the two side lobes of the quadrupole. Concurrently, soft X-ray brightenings gradually increase in both side lobes. Both of these effects suggest heating in the side-lobe magnetic arcades, which gradually increase over several hours before the fast eruption. Also during the slow pre-eruption phase, SXT dimmings gradually increase in the feet and legs of the central lobe, indicating expansion of the central-lobe magnetic arcade enveloping the filament. During the rapid ejection, these dimmings rapidly grow in darkness and in area, especially in the ends of the sigmoid field that erupts with the filament, and flare brightenings begin underneath the fast-moving but still low-altitude filament. We consider two models for explaining the eruption: "breakout," which says that reconnection occurs high above the filament prior to eruption, and tether cutting, which says that the eruption is unleashed by reconnection beneath the filament
Investigation of magnetic reconnection during a sawtooth crash in a high-temperature tokamak plasma
NASA Astrophysics Data System (ADS)
Yamada, M.; Levinton, F. M.; Pomphrey, N.; Budny, R.; Manickam, J.; Nagayama, Y.
1994-10-01
In this paper a laboratory investigation is made on magnetic reconnection in high-temperature Tokamak Fusion Test Reactor (TFTR) plasmas [Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 51]. The motional Stark effect (MSE) diagnostic is employed to measure the pitch angle profile of magnetic field lines, and hence the q profile. An analytical expression that relates pitch angle to q profile is presented for a toroidal plasma with circular cross section. During the crash phase of sawtooth oscillations in plasma discharges, the ECE (electron cyclotron emission) diagnostic measures a fast flattening of the two-dimensional (2-D) electron temperature profile in a poloidal plane, an observation consistent with the Kadomtsev reconnection theory. On the other hand, the MSE measurements indicate that central q values do not relax to unity after the crash, but increase only by 5%-15%, typically from 0.7 to 0.8. The latter result is in contradiction with the 2-D models of Kadomtsev and/or Wesson. In the present study this puzzle is addressed by a simultaneous analysis of electron temperature and q profile evolutions. Based on a heuristic model for magnetic reconnection during the sawtooth crash, the small change of q, i.e., partial reconnection, is attributed to the precipitous drop of pressure gradients that drive the instability and the reconnection process, as well as flux conserving plasma dynamics.
Investigation of magnetic reconnection during a sawtooth crash in a high-temperature tokamak plasma
Yamada, M.; Levinton, F.M.; Pomphrey, N.; Budny, R.; Manickam, J.; Nagayama, Y. )
1994-10-01
In this paper a laboratory investigation is made on magnetic reconnection in high-temperature Tokamak Fusion Test Reactor (TFTR) plasmas [[ital Plasma] [ital Physics] [ital and] [ital Controlled] [ital Nuclear] [ital Fusion] [ital Research] 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 51]. The motional Stark effect (MSE) diagnostic is employed to measure the pitch angle profile of magnetic field lines, and hence the [ital q] profile. An analytical expression that relates pitch angle to [ital q] profile is presented for a toroidal plasma with circular cross section. During the crash phase of sawtooth oscillations in plasma discharges, the ECE (electron cyclotron emission) diagnostic measures a fast flattening of the two-dimensional (2-D) electron temperature profile in a poloidal plane, an observation consistent with the Kadomtsev reconnection theory. On the other hand, the MSE measurements indicate that central [ital q] values do not relax to unity after the crash, but increase only by 5%--15%, typically from 0.7 to 0.8. The latter result is in contradiction with the 2-D models of Kadomtsev and/or Wesson. In the present study this puzzle is addressed by a simultaneous analysis of electron temperature and [ital q] profile evolutions. Based on a heuristic model for magnetic reconnection during the sawtooth crash, the small change of [ital q], i.e., partial reconnection, is attributed to the precipitous drop of pressure gradients that drive the instability and the reconnection process, as well as flux conserving plasma dynamics.
Nonthermally dominated electron acceleration during magnetic reconnection in a low-β plasma
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.
Ebrahimi, F.; Bhattacharjee, A.; Raman, R.; Hooper, E. B.; Sovinec, C. R.
2014-05-15
We numerically examine the physics of fast flux closure in transient coaxial helicity injection (CHI) experiments in National Spherical Torus Experiment (NSTX). By performing resistive Magnetohydrodynamics (MHD) simulations with poloidal injector coil currents held constant in time, we find that closed flux surfaces are formed through forced magnetic reconnection. Through a local Sweet-Parker type reconnection with an elongated current sheet in the injector region, closed flux surfaces expand in the NSTX global domain. Simulations demonstrate outflows approaching poloidally Alfvénic flows and reconnection times consistent with the Sweet-Parker model. Critical requirements for magnetic reconnection and flux closure are studied in detail. These primary effects, which are magnetic diffusivity, injector flux, injector flux footprint width, and rate of injector voltage reduction, are simulated for transient CHI experiments. The relevant time scales for effective reconnection are τ{sub V}<τ{sub rec}≈τ{sub A}√(S)(1+Pm){sup 1/4}<τ{sub R}, where τ{sub V} is the time for the injector voltage reduction, τ{sub A} is the poloidal Alfvén transit time, τ{sub R} is the global resistive diffusion time, and Pm and S are Prandtl and Lundquist numbers.
Nonthermally dominated electron acceleration during magnetic reconnection in a low-β plasma
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.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
NASA Astrophysics Data System (ADS)
Ohia, Obioma; Egedal, Jan; Lukin, Vyacheslav S.; Daughton, William; Le, Ari
2015-11-01
Magnetic reconnection in weakly-collisional, a process linked to solar flares, coronal mass ejections, and magnetic substorms, has been widely studied through fluid and kinetic simulations. While two-fluid models often reproduce the fast reconnection rate of kinetic simulations, significant differences are observed in the structure of the reconnection regions. Recently, new equations of state that accurately account for the development of anisotropic electron pressure due to the electric and magnetic trapping of electrons have been developed. Guide-field, fluid simulations using these equations of state have been shown to reproduce the detailed reconnection region observed in kinetic simulations. Implementing this two-fluid simulation using the HiFi framework, we describe a mechanism for regulation of electron pressure anisotropy as well as study force balance of the electron layers in guide-field reconnection. Scaling laws for the heating observed in these layers based on upstream conditions are derived. Formerly of U.S. Naval Research Laboratory. Any opinions, findings, conclusions and/or recommendations are those of author and do not necessarily reflect the views of the National Science Foundation.
Tian, Hui; Reeves, Katharine K.; Raymond, John C.; Chen, Bin; Murphy, Nicholas A.; Li, Gang; Guo, Fan; Liu, Wei
2014-12-20
Magnetic reconnection is believed to be the dominant energy release mechanism in solar flares. The standard flare model predicts both downward and upward outflow plasmas with speeds close to the coronal Alfvén speed. Yet, spectroscopic observations of such outflows, especially the downflows, are extremely rare. With observations of the newly launched Interface Region Imaging Spectrograph (IRIS), we report the detection of a greatly redshifted (∼125 km s{sup –1} along the line of sight) Fe XXI 1354.08 Å emission line with a ∼100 km s{sup –1} nonthermal width at the reconnection site of a flare. The redshifted Fe XXI feature coincides spatially with the loop-top X-ray source observed by RHESSI. We interpret this large redshift as the signature of downward-moving reconnection outflow/hot retracting loops. Imaging observations from both IRIS and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory also reveal the eruption and reconnection processes. Fast downward-propagating blobs along these loops are also found from cool emission lines (e.g., Si IV, O IV, C II, Mg II) and images of AIA and IRIS. Furthermore, the entire Fe XXI line is blueshifted by ∼260 km s{sup –1} at the loop footpoints, where the cool lines mentioned above all exhibit obvious redshift, a result that is consistent with the scenario of chromospheric evaporation induced by downward-propagating nonthermal electrons from the reconnection site.
Investigation of magnetic reconnection during a sawtooth crash in a high temperature tokamak
Yamada, M.; Pomphrey, N.; Budney, R.; Macickam, J.; Levinton, F.; Nagayama, Y.
1994-09-01
This paper reports on a recent laboratory investigation on magnetic reconnection in high temperature tokamak plasmas. The motional stark effect(MSE) diagnostic is employed to measure the pitch angle of magnetic field lines, and hence the q profile. An analytical expression that relates pitch angle to q profile has been developed for a toroidal plasma with circular cross section. During the crash phase of sawtooth oscillations in the plasma discharges, the ECE (electron cyclotron emission) diagnostic measures a fast flattening of the 2-D electron temperature profile in a poloidal plane, an observation consistent with the Kadomtsev reconnection theory. On the other hand motional the MSE measurements indicate that central q values do not relax to unity after the crash, but increase only by 5-10%, typically from 0.7 to 0.75. The latter result is in contradiction with the models of Kadomtsev and/or Wesson. The present study addresses this puzzle by a simultaneous analysis of electron temperature and q profile evolutions. Based on a heuristic model for the magnetic reconnection during the sawtooth crash, the small change of q, i.e. partial reconnection, is attributed to the precipitous drop of pressure gradients which drive the instability and the reconnection process as well as flux conserving plasma dynamics.
An Experiment to Investigate the Role of Neutrals in Magnetic Reconnection
NASA Astrophysics Data System (ADS)
Lawrence, Eric; Yoo, Jongsoo; Yamada, Masaaki; Ji, Hantao; Dorfman, Seth; Tharp, Tim; Myers, Clayton
2010-11-01
Magnetic reconnection in the solar chromosphere has become a topic of recent interest as it may be a source of energy transfer into the corona [1], and observations show evidence of fast reconnection [2]. Unlike the corona, the plasma in the chromosphere is relatively cool (T ˜10^4 K) and is weakly to partially ionized (nn/n ˜10^0-10^4). Furthermore, simulations have shown that the reconnection rate can depend on the ionization fraction and neutral collisionality [3]. Damping due to ion-neutral viscosity may also play a role. In the Magnetic Reconnection Experiment (MRX), we plan to study the effects of neutrals on reconnection in a controlled laboratory setting. A optical probe diagnostic is used to measure neutral density, and we plan to develop a UV diagnostic to facilitate comparisons with solar observations. Initial pressure scans have shown that we can access a parameter space relevant to the chromosphere. [4pt] [1] P. A. Sturrock, ApJ 521, 451 (1999).[0pt] [2] J. Chae, et al., J. Korean Astron. Soc., 36, 13 (2003).[0pt] [3] P. D. Smith, et al., A&A 486, 569 (2008).
Physics of Reconnection and MMS Mission
NASA Technical Reports Server (NTRS)
Kuznetsova, M. M.; Hesse, M.; Gombosi, T.
2009-01-01
Reconnection is the most important process driving the Earth's magnetosphere. Key to the success of the MMS science plan is the coupling of theory and observation. Determining the kinetic processes occurring in the diffusion region and physical parameters that control the rate of magnetic reconnection are among primary objectives of the MMS mission. Analysis of the role played by particle inertial effects in the diffusion region where the plasma is unmagnetized will be presented. The reconnection electric field in he diffusion region is supported primarily by particle non-gyrotropic effects. At the quasi-steady stage the reconnection electric field serves to accelerate and heat the incoming plasma population to maintain the current flow in the diffusion region the pressure balance. The primary mechanism controlling the dissipation in the vicinity of the reconnection site is incorporated into the fluid description in terms of non-gyrotropic corrections to the. induction and energy equations. The results of kinetic and fluid simulations illustrating the physics of magnetic reconnection will be presented. We will dem:tistrate that kinetic nongyrotropic effects can significantly alter the global magnetosphere evolution and location of reconnection sites.
Reconnection in semicollisional, low-{beta} plasmas
Schmidt, S.; Guenter, S.; Lackner, K.
2009-07-15
Reconnection of semicollisional, low-{beta} plasmas is studied numerically for two model problems using a two-field description of the plasma including electron pressure effects (and hence kinetic Alfven-wave dynamics). The tearing unstable Harris sheet, with the global parameters of the Geospace Environment Modeling-challenge case, shows a linear growth of the peak reconnection rate with the drift parameter {rho}{sub s} when this scale is significantly larger than the resistive skin depth, and the island is smaller than the Harris sheet current layer width. As exemplary for a driven, rather than a spontaneous reconnection situation we study as second model system two coalescing islands, starting from a nonequilibrium situation. The peak reconnection rate again increases initially linearly with {rho}{sub s} but saturates and becomes {rho}{sub s} independent for larger values. In this saturated regime, no flux pileup occurs, and the reconnection is limited by the rate of approach of the two coalescing islands. The qualitative differences between spontaneous and driven reconnection cases and their scaling behavior are best understood by considering the reconnection rate as a triple product of outflow Mach number, outflow to inflow channel width ratio, and magnetic energy density at a height {rho}{sub s} above the X point.
Continuous magnetic reconnection at Earth's magnetopause.
Frey, H U; Phan, T D; Fuselier, S A; Mende, S B
2003-12-01
The most important process that allows solar-wind plasma to cross the magnetopause and enter Earth's magnetosphere is the merging between solar-wind and terrestrial magnetic fields of opposite sense-magnetic reconnection. It is at present not known whether reconnection can happen in a continuous fashion or whether it is always intermittent. Solar flares and magnetospheric substorms--two phenomena believed to be initiated by reconnection--are highly burst-like occurrences, raising the possibility that the reconnection process is intrinsically intermittent, storing and releasing magnetic energy in an explosive and uncontrolled manner. Here we show that reconnection at Earth's high-latitude magnetopause is driven directly by the solar wind, and can be continuous and even quasi-steady over an extended period of time. The dayside proton auroral spot in the ionosphere--the remote signature of high-latitude magnetopause reconnection--is present continuously for many hours. We infer that reconnection is not intrinsically intermittent; its steadiness depends on the way that the process is driven. PMID:14654835
Magnetic reconnection and solar flare loops
NASA Technical Reports Server (NTRS)
Forbes, T. G.
1987-01-01
Reconnection models of the main phase of large solar flares are used to explain the energetics and the motions of the large flare loops that occur during this phase. Correct predictions for the density and temperature of the X-ray emitting loops are obtained by coupling magnetic reconnection with chromospheric ablation. In the reconnection models the ablation is driven by the thermal conduction of heat along magnetic field lines connecting the reconnection shocks in the corona with the flare ribbons in the chromosphere. Combining the compressible reconnection theory of Soward and Priest (1982) with the magnetohydrodynamic (MHD) subshock criteria of Coroniti (1970) shows that the Petschek-type slow-mode shocks in the vicinity of the x-line always dissociate into pairs of isothermal slow-mode subshocks and thermal conduction fronts. The rate of expansion of the loops is a function of the reconnection rate, and loops can be evolving self-similarly in time with their height increasing as sq root t and the reconnection rate decreasing as t to the minus 1.
NASA Astrophysics Data System (ADS)
Schaeffer, Derek
2013-10-01
Collisionless shocks occur ubiquitously in space plasmas and have been extensively studied insitu by spacecraft, though they are inherently limited in their flexibility. We present laboratory experiments utilizing a highly flexible laser geometry at UCLA to study the generation of magnetized, perpendicular collisionless shocks by a super-Alfvénic laser-ablated piston. Experiments were carried out on the LArge Plasma Device (LAPD), which can create a highly reproducible 20 m long by Ø1 m H or He magnetized (<= 2 kG) ambient plasma. The 100 J Raptor laser was used to ablate perpendicular to the background magnetic field a carbon target embedded in the LAPD plasma. Emission spectroscopy revealed a significant spread between laser debris charge states, consistent with 2D hybrid simulations that show fast-moving, highly ionized debris slipping through the ambient plasma, while slower, lower charge states drive a diamagnetic cavity. The cavity grew to several ion gyroradii and lasted around one gyroperiod, large and long enough to act like a piston by allowing laminar fields at the cavity edge to transfer energy from the debris to the background plasma. This is confirmed by spectroscopy, which shows a reduction in debris velocities relative to a non-magnetic case, and Thomson scattering, which shows an increase in electron densities and temperatures in the ambient plasma. An increase in the intensity of the ambient plasma seen by gated imaging also indicates an energetic population of electrons coincident with the cavity edge, while Stark-broadened ambient lines may indicate strong local electric fields. Magnetic flux probes reveal that the cavity launches whistler waves parallel to the background field, as well as a super-Alfvénic magnetosonic wave along the blowoff axis that has a magnetic field compression comparable to the Alfvenic Mach number, consistent with simulations that suggest a weak collisionless shock was formed. Supported by DOE and DTRA.
Magnetic reconnection in a weakly ionized plasma
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.
Properties of GRB Lightcurves from Magnetic Reconnection
NASA Astrophysics Data System (ADS)
Beniamini, Paz; Granot, Jonathan
2016-04-01
The energy dissipation mechanism within Gamma-Ray Burst (GRB) outflows, driving their extremely luminous prompt γ-ray emission is still uncertain. The leading candidates are internal shocks and magnetic reconnection. While the emission from internal shocks has been extensively studied, that from reconnection still has few quantitative predictions. We study the expected prompt-GRB emission from magnetic reconnection and compare its temporal and spectral properties to observations. The main difference from internal shocks is that for reconnection one expects relativistic bulk motions with Lorentz factors Γ' ≳ a few in the jet's bulk frame. We consider such motions of the emitting material in two anti-parallel directions (e.g. of the reconnecting magnetic-field lines) within an ultra-relativistic (with Γ ≫ 1) thin spherical reconnection layer. The emission's relativistic beaming in the jet's frame greatly affects the light-curves. For emission at radii R0 < R < R0 + ΔR (with Γ = const) the observed pulse width is ΔT ˜ (R0/2cΓ2) max (1/Γ', ΔR/R0), i.e. up to ˜Γ' times shorter than for isotropic emission in the jet's frame. We consider two possible magnetic reconnection modes: a quasi steady-state with continuous plasma flow into and out of the reconnection layer, and sporadic reconnection in relativistic turbulence that produces relativistic plasmoids. Both of these modes can account for many observed prompt-GRB properties: variability, pulse asymmetry, the very rapid declines at their end and pulse evolutions that are either hard to soft (for Γ' ≲ 2) or intensity tracking (for Γ' > 2). However, only the relativistic turbulence mode can naturally account also for the following correlations: luminosity-variability, peak luminosity - peak frequency and pulse width energy dependence / spectral lags.
Driven reconnection in the earth's magnetotail
NASA Technical Reports Server (NTRS)
Forbes, T. G.
1991-01-01
In the standard reconnection model, a low flow speed leads to steady reconnection at a distant-tail x-line, but a high flow speed leads to the formation of a near-earth x-line and the onset of an auroral substorm. This paper discusses recent work which suggests that a pile-up of magnetic flux in the earth's magnetotail will occur whenever reconnection is strongly driven by the solar wind and that the near-earth x-line might result from a flux pile-up at the distant-tail x-line.
Kinetic Structure of the Reconnection Diffusion Region
NASA Astrophysics Data System (ADS)
Khotyaintsev, Yuri
2016-04-01
We present high-resolution multi-spacecraft observations of electromagnetic fields and particle distributions by Magnetospheric Multiscale (MMS) mission throughout a reconnection layer at the sub-solar magnetopause. We study which terms in the generalized Ohm's law balance the observed electric field throughout the region. We also study waves and particle distribution functions in order to identify kinetic boundaries created due to acceleration and trapping of electrons and ions as well as mixing of electron populations from different sides of the reconnecting layer. We discuss the interplay between particles, waves, and DC electric and magnetic fields, which clearly demonstrates kinetic and multi-scale nature of the reconnection diffusion region.
NASA Astrophysics Data System (ADS)
Hassan, Ehab; Horton, W.; Hatch, D. R.; Agullo, O.; Muraglia, M.; Benkadda, S.; InstituteFusion Studies Collaboration; PIIM/CNRS, AMU, Marseille, France Collaboration
2015-11-01
Fast reconnection in the magnetosphere and the geomagnetic tail involves electron scale dynamics that includes the electron inertial scale length on the inner scale and the ion gyroradius on the outer scale. New forms of the partial differential equations for the electric and magnetic field during the fast interchange dynamics. Typical data is that of the fast reconnection with dominant electron heating reported in the Nakamura et al. from CLUSTER data. New formulas extend to smaller scales the previous simulations of Horton et al. [2007] for this event by including more electron dynamics and heating. 3D-simulations and movies of the dynamics are presented. Supported by US-DoE grant to UT and CNRS grant to AMU.
Shearing Box Simulations of the MRI in a Collisionless Plasma
Sharma, Prateek; Hammett, Gregory, W.; Quataert, Eliot; Stone, James, M.
2005-08-31
We describe local shearing box simulations of turbulence driven by the magnetorotational instability (MRI) in a collisionless plasma. Collisionless effects may be important in radiatively inefficient accretion flows, such as near the black hole in the Galactic Center. The MHD version of ZEUS is modified to evolve an anisotropic pressure tensor. A fluid closure approximation is used to calculate heat conduction along magnetic field lines. The anisotropic pressure tensor provides a qualitatively new mechanism for transporting angular momentum in accretion flows (in addition to the Maxwell and Reynolds stresses). We estimate limits on the pressure anisotropy due to pitch angle scattering by kinetic instabilities. Such instabilities provide an effective ''collision'' rate in a collisionless plasma and lead to more MHD-like dynamics. We find that the MRI leads to efficient growth of the magnetic field in a collisionless plasma, with saturation amplitudes comparable to those in MHD. In the saturated state, the anisotropic stress is comparable to the Maxwell stress, implying that the rate of angular momentum transport may be moderately enhanced in a collisionless plasma.
Vortex-induced magnetic reconnection and single X line reconnection at the magnetopause
Fu, S.Y.; Pu, Z.Y.; Liu, Z.X.
1995-04-01
The authors present the results of two-dimensional MHD simulations of two different models of magnetic reconnection, a vortex-induced magnetic reconnection, and a bursty single X line reconnection. They look at the implications of the magnetic topolgy of the magnetopause for the occurrence of conditions conducive to these two processes. They also discuss the physical implications which could be derived from these two models.
NASA Astrophysics Data System (ADS)
Hoshino, Masahiro
2016-07-01
Understanding of the particle acceleration and plasma heating in a current sheet is an important problem in space and astrophysical plasmas. So far the inertia resistivity associated with tearing instability and the current driven instability such as the lower hybrid drift instability (LHDI) have been discussed as possible candidates for the origin of microscopic process of magnetic energy dissipation. It is known that the inertia resistivity effectively works at the neutral sheet, while the LHDI is mainly excited in the plasma sheet boundary. Then it is commonly understood that the role of the LHDI to the magnetic field dissipation is less important than that of the inertia resistivity. However, the heated electrons together with the activity of lower hybrid drift waves are often observed in the plasma sheet boundary by modern satellite observations, and their impact on the magnetic field dissipation at the neutral sheet might not be necessarily neglected. In addition, the nonlinear coupling between them is not theoretically understood yet. In this talk, we study the coupling of the collisionless reconnection and the LHDI by using a three-dimensional PIC simulation, and discuss that the current driven instabilities dynamically play an important role on magnetic reconnection.
Spontaneous reconnection at a separator current layer: 1. Nature of the reconnection
NASA Astrophysics Data System (ADS)
Stevenson, J. E. H.; Parnell, C. E.
2015-12-01
Magnetic separators, which lie on the boundary between four topologically distinct flux domains, are prime locations in three-dimensional magnetic fields for reconnection, especially in the magnetosphere between the planetary and interplanetary magnetic fields and also in the solar atmosphere. Little is known about the details of separator reconnection, and so the aim of this paper, which is the first of two, is to study the properties of magnetic reconnection at a single separator. Three-dimensional, resistive magnetohydrodynamic numerical experiments are run to study separator reconnection starting from a magnetohydrostatic equilibrium which contains a twisted current layer along a single separator linking a pair of opposite-polarity null points. The resulting reconnection occurs in two phases. The first is short involving rapid reconnection in which the current at the separator is reduced by a factor of around 2.3. Most (75%) of the magnetic energy is converted during this phase, via Ohmic dissipation, directly into internal energy, with just 0.1% going into kinetic energy. During this phase the reconnection occurs along most of the separator away from its ends (the nulls) but in an asymmetric manner which changes both spatially and temporally over time. The second phase is much longer and involves slow impulsive bursty reconnection. Again, Ohmic heating dominates over viscous damping. Here the reconnection occurs in small localized bursts at random anywhere along the separator.
Yamada, Masaaki; Yoo, Jongsoo; Myers, Clayton E.
2016-05-11
Here, magnetic reconnection is a fundamental process at work in laboratory, space, and astrophysical plasmas, in which magnetic field lines change their topology and convert magnetic energy to plasma particles by acceleration and heating. One of the most important problems in reconnection research has been to understand why reconnection occurs so much faster than predicted by magnetohydrodynamics theory. Following the recent pedagogical review of this subject [Yamada et al., Rev. Mod. Phys. 82, 603 (2010)], this paper presents a review of more recent discoveries and findings in the research of fast magnetic reconnection in laboratory, space, and astrophysical plasmas. Inmore » spite of the huge difference in physical scales, we find remarkable commonality between the characteristics of the magnetic reconnection in laboratory and space plasmas. In this paper, we will focus especially on the energy flow, a key feature of the reconnection process. In particular, the experimental results on the energy conversion and partitioning in a laboratory reconnection layer [Yamada et al., Nat. Commun. 5, 4474 (2014)] are discussed and compared with quantitative estimates based on two-fluid analysis. In the Magnetic ReconnectionExperiment, we find that energy deposition to electrons is localized near the X-point and is mostly from the electric field component perpendicular to the magnetic field. The mechanisms of ion acceleration and heating are also identified, and a systematic and quantitative study on the inventory of converted energy within a reconnection layer with a well-defined but variable boundary. The measured energy partition in a reconnection region of similar effective size (L ≈ 3 ion skin depths) of the Earth's magneto-tail [Eastwood et al., Phys. Rev. Lett. 110, 225001 (2013)] is notably consistent with our laboratory results. Finally, to study the global aspects of magnetic reconnection, we have carried out a laboratory experiment on the stability criteria for
NASA Astrophysics Data System (ADS)
Yamada, Masaaki; Yoo, Jongsoo; Myers, Clayton E.
2016-05-01
Magnetic reconnection is a fundamental process at work in laboratory, space, and astrophysical plasmas, in which magnetic field lines change their topology and convert magnetic energy to plasma particles by acceleration and heating. One of the most important problems in reconnection research has been to understand why reconnection occurs so much faster than predicted by magnetohydrodynamics theory. Following the recent pedagogical review of this subject [Yamada et al., Rev. Mod. Phys. 82, 603 (2010)], this paper presents a review of more recent discoveries and findings in the research of fast magnetic reconnection in laboratory, space, and astrophysical plasmas. In spite of the huge difference in physical scales, we find remarkable commonality between the characteristics of the magnetic reconnection in laboratory and space plasmas. In this paper, we will focus especially on the energy flow, a key feature of the reconnection process. In particular, the experimental results on the energy conversion and partitioning in a laboratory reconnection layer [Yamada et al., Nat. Commun. 5, 4474 (2014)] are discussed and compared with quantitative estimates based on two-fluid analysis. In the Magnetic Reconnection Experiment, we find that energy deposition to electrons is localized near the X-point and is mostly from the electric field component perpendicular to the magnetic field. The mechanisms of ion acceleration and heating are also identified, and a systematic and quantitative study on the inventory of converted energy within a reconnection layer with a well-defined but variable boundary. The measured energy partition in a reconnection region of similar effective size (L ≈ 3 ion skin depths) of the Earth's magneto-tail [Eastwood et al., Phys. Rev. Lett. 110, 225001 (2013)] is notably consistent with our laboratory results. Finally, to study the global aspects of magnetic reconnection, we have carried out a laboratory experiment on the stability criteria for solar flare
Collisionless Damping of Laser Wakes in Plasma Channels
Li, X.; Shvets, G.
1998-08-01
Excitation of accelerating modes in transversely inhomogeneous plasma channels is considered as an initial value problem. Discrete eigenmodes are supported by plasma channels with sharp density gradients. These eigenmodes are collisionlessly damped as the gradients are smoothed. Using collisionless Landau damping as the analogy, the existence and damping of these "quasi-modes" is studied by constructing and analytically continuing the causal Green's function of wake excitation into the lower half of the complex frequency plane. Electromagnetic nature of the plasma wakes in the channel makes their excitation nonlocal. This results in the algebraic decay of the fields with time due to phase-mixing of plasma oscillations with spatially-varying fequencies. Characteristic decay rate is given by the mixing time, which corresponds to the dephasing of two plasma fluid elements separated by the collisionless skin depth. For wide channels the exact expressions for the field evolution are derived. Implications for electron acceleration in plasma channels are discussed.
Collisionless Weibel shocks: Full formation mechanism and timing
Bret, A.; Stockem, A.; Narayan, R.; Silva, L. O.
2014-07-15
Collisionless shocks in plasmas play an important role in space physics (Earth's bow shock) and astrophysics (supernova remnants, relativistic jets, gamma-ray bursts, high energy cosmic rays). While the formation of a fluid shock through the steepening of a large amplitude sound wave has been understood for long, there is currently no detailed picture of the mechanism responsible for the formation of a collisionless shock. We unravel the physical mechanism at work and show that an electromagnetic Weibel shock always forms when two relativistic collisionless, initially unmagnetized, plasma shells encounter. The predicted shock formation time is in good agreement with 2D and 3D particle-in-cell simulations of counterstreaming pair plasmas. By predicting the shock formation time, experimental setups aiming at producing such shocks can be optimised to favourable conditions.
Low Frequency Waves at and Upstream of Collisionless Shocks
NASA Astrophysics Data System (ADS)
Wilson, L. B.
2016-02-01
This chapter focuses on the range of low frequency electromagnetic modes observed at and upstream of collisionless shocks in the heliosphere. It discusses a specific class of whistler mode wave observed immediately upstream of collisionless shock ramps, called a whistler precursor. Though these modes have been (and are often) observed upstream of quasi-parallel shocks, the authors limit their discussion to those observed upstream of quasi-perpendicular shocks. The chapter discusses the various ion velocity distributions observed at and upstream of collisionless shocks. It also introduces some terminology and relevant instabilities for ion foreshock waves. The chapter discusses the most common ultra-low frequency (ULF) wave types, their properties, and their free energy sources. It discusses modes that are mostly Alfvénic (i.e., mostly transverse but can be compressive) in nature.
Characterization of reconnecting vortices in superfluid helium.
Bewley, Gregory P; Paoletti, Matthew S; Sreenivasan, Katepalli R; Lathrop, Daniel P
2008-09-16
When two vortices cross, each of them breaks into two parts and exchanges part of itself for part of the other. This process, called vortex reconnection, occurs in classical and superfluids, and in magnetized plasmas and superconductors. We present the first experimental observations of reconnection between quantized vortices in superfluid helium. We do so by imaging micrometer-sized solid hydrogen particles trapped on quantized vortex cores and by inferring the occurrence of reconnection from the motions of groups of recoiling particles. We show that the distance separating particles on the just-reconnected vortex lines grows as a power law in time. The average value of the scaling exponent is approximately 1/2, consistent with the self-similar evolution of the vortices. PMID:18768790
The Dissipation Mechanism of Magnetic Reconnection
NASA Technical Reports Server (NTRS)
Hesse, Michael
2008-01-01
Magnetic reconnection is arguably the most efficient transport and energy conversion mechanism in almost ideal plasmas. Reconnection controls the overall dynamics in space and astrophysics plasmas, as well as in many laboratory plasma systems. Reconnection operates by means of a localized diffusion region, where deviations from the plasma idealness condition generate electric fields and permit plasma transport even far away from the diffusion region itself. Recent advances in analytic theory and computer modeling have begun to shed light on the internal dynamics of the diffusion region. In particular, we begin to understand the delicate nature of the force balance in the inner diffusion region, where particles can become unmagnetized and where electric field forces are important. This presentation will provide a brief introduction of the reconnection process and its applications. This introduction will be followed by a detailed analysis of the current understanding of dissipation region physics, and by an outlook toward future research.
The Inner Workings of Magnetic Reconnection
NASA Technical Reports Server (NTRS)
Hesse, Michael; Zenitani, S.
2007-01-01
Magnetic reconnection is arguably the most efficient transport and energy conversion mechanism in almost ideal plasmas. Reconnection controls the overall dynamics in space and astrophysics plasmas, as well as in many laboratory plasma systems. Reconnection operates by means of a localized diffusion region, where deviations from the plasma idealness condition generate electric fields and permit plasma transport even far away from the diffusion region itself. Recent advances in analytic theory and computer modeling have begun to shed light on the internal dynamics of the diffusion region. In particular, we begin to understand the delicate nature of the force balance in the inner diffusion region, where particles can become unmagnetized and where electric field forces are important. This presentation will provide a brief introduction of the reconnection process and its applications. This introduction will be followed by a detailed analysis of the current understanding of dissipation region physics, and by an outlook toward future research.
Forcing continuous reconnection in hybrid simulations
Laitinen, T. V. Janhunen, P.; Jarvinen, R.; Kallio, E.
2014-07-15
We have performed hybrid simulations of driven continuous reconnection with open boundary conditions. Reconnection is started by a collision of two subsonic plasma fronts with opposite magnetic fields, without any specified magnetic field configuration as initial condition. Due to continued forced plasma inflow, a current sheet co-located with a dense and hot plasma sheet develops. The translational symmetry of the current sheet is broken by applying a spatial gradient in the inflow speed. We compare runs with and without localized resistivity: reconnection is initiated in both cases, but localized resistivity stabilizes it and enhances its efficiency. The outflow speed reaches about half of Alfvén speed. We quantify the conversion of magnetic energy to kinetic energy of protons and to Joule heating and show that with localized resistivity, kinetic energy of protons is increased on average five-fold in the reconnection in our simulation case.
Model of two-fluid reconnection.
Malyshkin, Leonid M
2009-12-01
A theoretical model of quasistationary, two-dimensional magnetic reconnection is presented in the framework of incompressible two-fluid magnetohydrodynamics. The results are compared with recent numerical simulations and experiment. PMID:20366155
Characterization of reconnecting vortices in superfluid helium
Bewley, Gregory P.; Paoletti, Matthew S.; Sreenivasan, Katepalli R.; Lathrop, Daniel P.
2008-01-01
When two vortices cross, each of them breaks into two parts and exchanges part of itself for part of the other. This process, called vortex reconnection, occurs in classical and superfluids, and in magnetized plasmas and superconductors. We present the first experimental observations of reconnection between quantized vortices in superfluid helium. We do so by imaging micrometer-sized solid hydrogen particles trapped on quantized vortex cores and by inferring the occurrence of reconnection from the motions of groups of recoiling particles. We show that the distance separating particles on the just-reconnected vortex lines grows as a power law in time. The average value of the scaling exponent is approximately ½, consistent with the self-similar evolution of the vortices. PMID:18768790
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.
Relating magnetic reconnection to coronal heating
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
Stellar dynamics around a massive black hole - I. Secular collisionless theory
NASA Astrophysics Data System (ADS)
Sridhar, S.; Touma, Jihad R.
2016-06-01
We present a theory in three parts, of the secular dynamics of a (Keplerian) stellar system of mass M orbiting a black hole of mass M• ≫ M. Here we describe the collisionless dynamics; Papers II and III are on the (collisional) theory of resonant relaxation. The mass ratio, ε = M/M• ≪ 1, is a natural small parameter implying a separation of time-scales between the short Kepler orbital periods and the longer orbital precessional periods. The collisionless Boltzmann equation (CBE) for the stellar distribution function (DF) is averaged over the fast Kepler orbital phase using the method of multiple scales. The orbit-averaged system is described by a secular DF, F, in a reduced phase space. F obeys a secular CBE that includes stellar self-gravity, general relativistic corrections up to 1.5 post-Newtonian order, and external sources varying over secular times. Secular dynamics, even with general time dependence, conserves the semimajor axis of every star. This additional integral of motion promotes extra regularity of the stellar orbits, and enables the construction of equilibria, F0, through a secular Jeans theorem. A linearized secular CBE determines the response and stability of F0. Spherical, non-rotating equilibria may support long-lived, warp-like distortions. We also prove that an axisymmetric, zero-thickness, flat disc is secularly stable to all in-plane perturbations, when its DF, F0, is a monotonic function of the angular momentum at fixed energy.
Stellar Dynamics around a Massive Black Hole I: Secular Collisionless Theory
NASA Astrophysics Data System (ADS)
Sridhar, S.; Touma, Jihad R.
2016-03-01
We present a theory in three parts, of the secular dynamics of a (Keplerian) stellar system of mass M orbiting a black hole of mass M• ≫ M. Here we describe the collisionless dynamics; Papers II and III are on the (collisional) theory of Resonant Relaxation. The mass ratio, ε = M/M• ≪ 1, is a natural small parameter implying a separation of time scales between the short Kepler orbital periods and the longer orbital precessional periods. The collisionless Boltzmann equation (CBE) for the stellar distribution function (DF) is averaged over the fast Kepler orbital phase using the method of multiple scales. The orbit-averaged system is described by a secular DF, F, in a reduced phase space. F obeys a secular CBE that includes stellar self-gravity, general relativistic corrections up to 1.5 post-Newtonian order, and external sources varying over secular times. Secular dynamics, even with general time dependence, conserves the semi-major axis of every star. This additional integral of motion promotes extra regularity of the stellar orbits, and enables the construction of equilibria, F0, through a secular Jeans theorem. A linearized secular CBE determines the response and stability of F0. Spherical, non-rotating equilibria may support long-lived, warp-like distortions. We also prove that an axisymmetric, zero-thickness, flat disc is secularly stable to all in-plane perturbations, when its DF, F0, is a monotonic function of the angular momentum at fixed energy.
NASA Astrophysics Data System (ADS)
Nalewajko, Krzysztof; Uzdensky, Dmitri A.; Cerutti, Benoît; Werner, Gregory R.; Begelman, Mitchell C.
2015-12-01
We investigate the distribution of particle acceleration sites, independently of the actual acceleration mechanism, during plasmoid-dominated, relativistic collisionless magnetic reconnection by analyzing the results of a particle-in-cell numerical simulation. The simulation is initiated with Harris-type current layers in pair plasma with no guide magnetic field, negligible radiative losses, no initial perturbation, and using periodic boundary conditions. We find that the plasmoids develop a robust internal structure, with colder dense cores and hotter outer shells, that is recovered after each plasmoid merger on a dynamical timescale. We use spacetime diagrams of the reconnection layers to probe the evolution of plasmoids, and in this context we investigate the individual particle histories for a representative sample of energetic electrons. We distinguish three classes of particle acceleration sites associated with (1) magnetic X-points, (2) regions between merging plasmoids, and (3) the trailing edges of accelerating plasmoids. We evaluate the contribution of each class of acceleration sites to the final energy distribution of energetic electrons: magnetic X-points dominate at moderate energies, and the regions between merging plasmoids dominate at higher energies. We also identify the dominant acceleration scenarios, in order of decreasing importance: (1) single acceleration between merging plasmoids, (2) single acceleration at a magnetic X-point, and (3) acceleration at a magnetic X-point followed by acceleration in a plasmoid. Particle acceleration is absent only in the vicinity of stationary plasmoids. The effect of magnetic mirrors due to plasmoid contraction does not appear to be significant in relativistic reconnection.
Gosling, J. T.; Phan, T. D.
2013-02-01
Using Wind 3 s plasma and magnetic field data, we have identified nine reconnection exhausts within a solar wind disturbance on 1998 October 18-20 driven by a moderately fast interplanetary coronal mass ejection (ICME). Three of the exhausts within the ICME were associated with current sheets having local field shear angles, {theta}, ranging from 4 Degree-Sign to 9 Degree-Sign , the smallest reported values of {theta} yet associated with reconnection exhausts in a space plasma. They were observed in plasma characterized by extremely low (0.02-0.04) plasma {beta}, and very high (281-383 km s{sup -1}) Alfven speed, V{sub A}. Low {beta} allows reconnection to occur at small {theta} and high V{sub A} leads to exhaust jets that are fast enough relative to the surrounding solar wind to be readily identified. Very small-{theta} current sheets are common in the solar wind at 1 AU, but typically are not associated with particularly low plasma {beta} or high V{sub A}. On the other hand, small-{theta} current sheets should be common in the lower solar corona, a plasma regime of extremely low {beta} and extremely high V{sub A}. Our observations lend credence to models that predict that reconnection at small-{theta} current sheets is primarily responsible for coronal heating.
Stepwise tailward retreat of magnetic reconnection: THEMIS observations of an auroral substorm
NASA Astrophysics Data System (ADS)
Ieda, A.; Nishimura, Y.; Miyashita, Y.; Angelopoulos, V.; Runov, A.; Nagai, T.; Frey, H. U.; Fairfield, D. H.; Slavin, J. A.; Vanhamäki, H.; Uchino, H.; Fujii, R.; Miyoshi, Y.; Machida, S.
2016-05-01
Auroral stepwise poleward expansions were clarified by investigating a multiple-onset substorm that occurred on 27 February 2009. Five successive auroral brightenings were identified in all-sky images, occurring at approximately 10 min intervals. The first brightening was a faint precursor. The second brightening had a wide longitude; thus, it represented the Akasofu substorm onset. Other brightenings expanded poleward; thus, they were interpreted to be auroral breakups. These breakups occurred stepwise; that is, later breakups were initiated at higher latitudes. Corresponding reconnection signatures were studied using Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite observations between 8 and 24 RE down the magnetotail. The Akasofu substorm onset was not accompanied by a clear reconnection signature in the tail. In contrast, the three subsequent auroral breakups occurred simultaneously (within a few minutes) with three successive fast flows at 24 RE; thus, these were interpreted to be associated with impulsive reconnection episodes. These three fast flows consisted of a tailward flow and two subsequent earthward flows. The flow reversal at the second breakup indicated that a tailward retreat of the near-Earth reconnection site occurred during the substorm expansion phase. In addition, the earthward flow at the third breakup was consistent with the classic tailward retreat near the end of the expansion phase; therefore, the tailward retreat is likely to have occurred in a stepwise manner. We interpreted the stepwise characteristics of the tailward retreat and poleward expansion to be potentially associated by a stepwise magnetic flux pileup.
Patchy reconnection in the solar corona
NASA Astrophysics Data System (ADS)
Guidoni, Silvina Esther
2011-05-01
Magnetic reconnection in plasmas, a process characterized by a change in connectivity of field lines that are broken and connected to other ones with different topology, owes its usefulness to its ability to unify a wide range of phenomena within a single universal principle. There are newly observed phenomena in the solar corona that cannot be reconciled with two-dimensional or steady-state standard models of magnetic reconnection. Supra-arcade downflows (SADs) and supra-arcade downflowing loops (SADLs) descending from reconnection regions toward solar post-flare arcades seem to be two different observational signatures of retracting, isolated reconnected flux tubes with irreducible three-dimensional geometries. This dissertation describes work in refining and improving a novel model of patchy reconnection, where only a small bundle of field lines is reconnected across a current sheet (magnetic discontinuity) and forms a reconnected thin flux tube. Traditional models have not been able to explain why some of the observed SADs appear to be hot and relatively devoid of plasma. The present work shows that plasma depletion naturally occurs in flux tubes that are reconnected across nonuniform current sheets and slide trough regions of decreasing magnetic field magnitude. Moreover, through a detailed theoretical analysis of generalized thin flux tube equations, we show that the addition to the model of pressure-driven parallel dynamics, as well as temperature-dependent, anisotropic viscosity and thermal conductivity is essential for self-consistently producing gas-dynamic shocks inside reconnected tubes that heat and compress plasma to observed temperatures and densities. The shock thickness can be as long as the entire tube and heat can be conducted along tube's legs, possibly driving chromospheric evaporation. We developed a computer program that solves numerically the thin flux tube equations that govern the retraction of reconnected tubes. Simulations carried out
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
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
Local Diagnosis of Reconnection in 3D
NASA Astrophysics Data System (ADS)
Scudder, J. D.; Karimabadi, H.; Daughton, W. S.; Roytershteyn, V.
2014-12-01
We demonstrate (I,II) an approach to find reconnection sites in 3D where there is no flux function for guidance, and where local observational signatures for the ``violation of frozen flux'' are under developed, if not non-existent. We use 2D and 3D PIC simulations of asymmetric guide field reconnection to test our observational hierarchy of single spacecraft kinetic diagnostics - all possible with present state of the art instrumentation. The proliferation of turbulent, electron inertial scale layers in the realistic 3D case demonstrates that electron demagnetization, while necessary, is not sufficient to identify reconnection sites. An excellent local, observable, single spacecraft proxy is demonstrated for the size of the theoretical frozen flux violation. Since even frozen flux violations need not imply reconnection is at hand, a new calibrated dimensionless method is used to determine the importance of such violations. This measure is available in 2D and 3D to help differentiate reconnection layers from weaker frozen flux violating layers. We discuss the possibility that this technique can be implemented on MMS. A technique to highlight flow geometries conducive to reconnection in 3D simulations is also suggested, that may also be implementable with the MMS flotilla. We use local analysis with multiple necessary, but theoretically independent electron kinetic conditions to help reduce the probability of misidentification of any given layer as a reconnection site. Since these local conditions are all necessary for the site, but none is known to be sufficient, the multiple tests help to greatly reduce false positive identifications. The selectivity of the results of this approach using PIC simulations of 3D asymmetric guide field reconnection will be shown using varying numbers of simultaneous conditions. Scudder, J.D., H. Karimabadi, W. Daughton and V. Roytershteyn I, II, submitted Phys. Plasma., 2014
Magnetic Reconnection in Interplanetary Coronal Mass Ejections
NASA Astrophysics Data System (ADS)
Fermo, R. L.; Opher, M.; Drake, J. F.
2014-12-01
Magnetic reconnection is a ubiquitous phenomenon in many varied space and astrophysical plasmas, and as such plays an important role in the dynamics of interplanetary coronal mass ejections (ICMEs). It is widely regarded that reconnection is instrumental in the formation and ejection of the initial CME flux rope, but reconnection also continues to affect the dynamics as it propagates through the interplanetary medium. For example, reconnection on the leading edge of the ICME, by which it interacts with the interplanetary medium, leads to flux erosion. However, recent in situ observations by Gosling et al. found signatures of reconnection exhausts in the interior. In light of this data, we consider the stability properties of systems with this flux rope geometry with regard to their minimum energy Taylor state. Variations from this state will result in the magnetic field relaxing back towards the minimum energy state, subject to the constraints that the toroidal flux and magnetic helicity remain invariant. In reversed field pinches, this relaxation is mediated by reconnection in the interior of the system, as has been shown theoretically and experimentally. By treating the ICME flux rope in a similar fashion, we show analytically that the the elongation of the flux tube cross section in the latitudinal direction will result in a departure from the Taylor state. The resulting relaxation of the magnetic field causes reconnection to commence in the interior of the ICME, in agreement with the observations of Gosling et al. We present MHD simulations in which reconnection initiates at a number of rational surfaces, and ultimately produces a stochastic magnetic field. If the time scales for this process are shorter than the propagation time to 1 AU, this result explains why many ICME flux ropes no longer exhibit the smooth, helical flux structure characteristic of a magnetic cloud.
Nonlinearly interacting trapped particle solitons in collisionless plasmas
NASA Astrophysics Data System (ADS)
Mandal, Debraj; Sharma, Devendra
2016-02-01
The formulation of collective waves in collisionless plasmas is complicated by the kinetic effects produced by the resonant particles, capable of responding to the smallest of the amplitude disturbance. The dispersive plasma manifests this response by generating coherent nonlinear structures associated with phase-space vortices, or holes, at very small amplitudes. The nonlinear interaction between solitary electron phase-space holes is studied in the electron acoustic regime of a collisionless plasma using Vlasov simulations. Evolution of the analytic trapped particle solitary solutions is examined, observing them propagate stably, preserve their identity across strong mutual interactions in adiabatic processes, and display close correspondence with observable processes in nature.
Multiscale Modeling of Solar Coronal Magnetic Reconnection
NASA Technical Reports Server (NTRS)
Antiochos, Spiro K.; Karpen, Judith T.; DeVore, C. Richard
2010-01-01
Magnetic reconnection is widely believed to be the primary process by which the magnetic field releases energy to plasma in the Sun's corona. For example, in the breakout model for the initiation of coronal mass ejections/eruptive flares, reconnection is responsible for the catastrophic destabilizing of magnetic force balance in the corona, leading to explosive energy release. A critical requirement for the reconnection is that it have a "switch-on' nature in that the reconnection stays off until a large store of magnetic free energy has built up, and then it turn on abruptly and stay on until most of this free energy has been released. We discuss the implications of this requirement for reconnection in the context of the breakout model for CMEs/flares. We argue that it imposes stringent constraints on the properties of the flux breaking mechanism, which is expected to operate in the corona on kinetic scales. We present numerical simulations demonstrating how the reconnection and the eruption depend on the effective resistivity, i.e., the effective Lundquist number, and propose a model for incorporating kinetic flux-breaking mechanisms into MHO calculation of CMEs/flares.
Impulsive Reconnection in the Sun's Atmosphere
NASA Technical Reports Server (NTRS)
Antiochos, Spiro K.
2009-01-01
Recent high-resolution observations from the Hinode mission show dramatically that the Sun's atmosphere is filled with explosive activity ranging from chromospheric explosions that reach heights of Mm, to coronal jets that can extend to solar radii, to giant coronal mass ejections (CME) that reach the edge of the heliosphere. The driver for all this activity is believed to be 3D magnetic reconnection. From the large variation observed in the temporal behavior of solar activity, it is clear that reconnection in the corona must take on a variety of distinct forms. The explosive nature of jets and CMEs requires that the reconnection be impulsive in that it stays off until a substantial store of free energy has been accumulated, but then turns on abruptly and stays on until much of this free energy is released. The key question, therefore, is what determines whether the reconnection is impulsive or not. We present some of the latest observations and numerical models of explosive and non-explosive solar activity. We argue that, in order for the reconnection to be impulsive, it must be driven by a quasi-ideal instability. We discuss the generality of our results for understanding 31) reconnection in other contexts.
Solar Polar Jets Driven by Magnetic Reconnection, Gravity, and Wind
NASA Astrophysics Data System (ADS)
DeVore, C. Richard; Karpen, Judith T.; Antiochos, Spiro K.
2014-06-01
Polar jets are dynamic, narrow, radially extended structures observed in solar EUV emission near the limb. They originate within the open field of coronal holes in “anemone” regions, which are intrusions of opposite magnetic polarity. The key topological feature is a magnetic null point atop a dome-shaped fan surface of field lines. Applied stresses readily distort the null into a current patch, eventually inducing interchange reconnection between the closed and open fields inside and outside the fan surface (Antiochos 1996). Previously, we demonstrated that magnetic free energy stored on twisted closed field lines inside the fan surface is released explosively by the onset of fast reconnection across the current patch (Pariat et al. 2009, 2010). A dense jet comprised of a nonlinear, torsional Alfvén wave is ejected into the outer corona along the newly reconnected open field lines. Now we are extending those exploratory simulations by including the effects of solar gravity, solar wind, and expanding spherical geometry. We find that the model remains robust in the resulting more complex setting, with explosive energy release and dense jet formation occurring in the low corona due to the onset of a kink-like instability, as found in the earlier Cartesian, gravity-free, static-atmosphere cases. The spherical-geometry jet including gravity and wind propagates far more rapidly into the outer corona and inner heliosphere than a comparison jet simulation that excludes those effects. We report detailed analyses of our new results, compare them with previous work, and discuss the implications for understanding remote and in-situ observations of solar polar jets.This work was supported by NASA’s LWS TR&T program.
NASA Astrophysics Data System (ADS)
Wang, S.; Mouikis, C.; Kistler, L. M.; Karimabadi, H.; Liu, Y.; Roytershteyn, V.; Genestreti, K.
2013-12-01
It is still an open question whether and how heavy ions (e.g., O+) are involved in magnetopause reconnection. From the fluid perspective, the O+ increases the ion mass density, slowing the Alfvén speed and therefore slowing the reconnection rate. However, because of the large O+ gyroradius, O+ is often not fully entrained in the flow, and its effect depends on kinetic processes. In this study, we analyze magnetopause reconnection events when Cluster crosses the diffusion region or the outflow region. The velocity distribution functions (VDF) provide evidence that O+ ions are accelerated in the reconnection process. Using the results from a three-species (O+, H+ and e-) symmetric PIC simulation, we first evaluate methods to calculate the reconnection rate to determine how well they work in different regions in the reconnection geometry. We apply these methods to the magnetopause reconnection events and evaluate their usefulness in this region, where the asymmetric structure and the magnetopause motion need to be taken into account, so that the more solid methods can be used in future studies. The goal is to understand the behavior of the heavy ions and determine whether they affect the reconnection rate.
Does Flare Reconnection Occur Before or After Explosive Coronal Mass Ejection Acceleration?
NASA Astrophysics Data System (ADS)
Guidoni, Silvina E.; Karpen, Judith T.; DeVore, C. R.; Qiu, Jiong
2015-04-01
The mechanism for producing fast coronal mass ejections/eruptive flares (CME/EFs) is hotly debated. Most models rely on ideal instability/loss of equilibrium or magnetic reconnection; these two categories of models predict different causal relationships between CMEs and flares. In both cases, flare reconnection disconnects the bulk of the CME from the Sun, but in the former models, flare reconnection onset is a consequence of the fast outward motion of the CME while in the later models reconnection is what causes the CME acceleration. Discriminating between these models requires continuous, high-cadence observations and state-of-the-art numerical simulations that enable the relative timing of key stages in the events to be determined. With the advent of SDO, STEREO, and massively parallel supercomputers, we are well poised to tackle this major challenge to our understanding of solar activity. In recent work (Karpen et al. 2012), we determined the timing and location of triggering mechanisms for the breakout initiation model (Antiochos et al. 1999), using ultra-high-resolution magnetohydrodynamic simulations with adaptive mesh refinement and high-cadence analysis. This approach enabled us to resolve as finely as possible the small scales of magnetic reconnection and island formation in the current sheets, within the global context of a large-scale solar eruption. We found that the explosive acceleration of the fast CME occurs only after the onset of rapid reconnection at the flare current sheet formed in the wake of the rising CME flux rope. In the present work, we compare flare reconnection rates, measured from flare ribbon UV brightenings observed by SDO/AIA and magnetograms from SDO/HMI, with the height evolution of CME fronts and cores, measured from STEREO/SECCHI EUV and coronagraph images. We also calculate these quantities from numerical simulations and compare them to observations, as a new test of the breakout initiation model. This work was supported by
Reconnection Processes in the Chromosphere and Corona
NASA Astrophysics Data System (ADS)
Shibata, Kazunari
2012-07-01
Magnetic reconnection is a fundamental key physical process in magnetized plasmas. Recent space solar observations revealed that magnetic reconnection is ubiquitous in the solar chromospheres and corona. Especially recent Hinode observations has found various types of tiny chromospheric jets, such as chromospheric anemone jets (Shibata et al. 2007), penumbral microjets (Katsukawa et al. 2007), light bridge jets from sunspot umbra (Shimizu et al. 2009), etc. It was also found that the corona is full of tiny X-ray jets (Cirtain et al. 2007). Often they are seen as helical spinning jets (Shimojo et al. 2007, Patsourakos et al. 2008, Pariat et al. 2009, Filippov et al. 2009, Kamio et al. 2010) with Alfvenic waves (Nishizuka et al. 2008, Liu et al. 2009) and there are increasing evidence of magnetic reconnection in these tiny jets. We can now say that as spatial resolution of observations become better and better, smaller and smaller flares and jets have been discovered, which implies that the magnetized solar atmosphere consist of fractal structure and dynamics, i.e., fractal reconnection. Bursty radio and hard X-ray emissions from flares also suggest the fractal reconnection and associated particle acceleration. Since magnetohydrodynamics (MHD) does not contain any characteristic length and time scale, it is natural that MHD structure, dynamics, and reconnection, tend to become fractal in ideal MHD plasmas with large magnetic Reynolds number such as in the solar atmosphere. We would discuss recent observations and theories related to fractal reconnection in the chromospheres and corona, and discuss possible implication to chromospheric and coronal heating.
Chain Reconnections Observed in Sympathetic Eruptions
NASA Astrophysics Data System (ADS)
Joshi, Navin Chandra; Schmieder, Brigitte; Magara, Tetsuya; Guo, Yang; Aulanier, Guillaume
2016-04-01
The nature of various plausible causal links between sympathetic events is still a controversial issue. In this work, we present multiwavelength observations of sympathetic eruptions, associated flares, and coronal mass ejections (CMEs) occurring on 2013 November 17 in two close active regions. Two filaments, i.e., F1 and F2, are observed in between the active regions. Successive magnetic reconnections, caused for different reasons (flux cancellation, shear, and expansion) have been identified during the whole event. The first reconnection occurred during the first eruption via flux cancellation between the sheared arcades overlying filament F2, creating a flux rope and leading to the first double-ribbon solar flare. During this phase, we observed the eruption of overlying arcades and coronal loops, which leads to the first CME. The second reconnection is believed to occur between the expanding flux rope of F2 and the overlying arcades of filament F1. We suggest that this reconnection destabilized the equilibrium of filament F1, which further facilitated its eruption. The third stage of reconnection occurred in the wake of the erupting filament F1 between the legs of the overlying arcades. This may create a flux rope and the second double-ribbon flare and a second CME. The fourth reconnection was between the expanding arcades of the erupting filament F1 and the nearby ambient field, which produced the bi-directional plasma flows both upward and downward. Observations and a nonlinear force-free field extrapolation confirm the possibility of reconnection and the causal link between the magnetic systems.