Reversible collisionless magnetic reconnection

Ishizawa, A.; Watanabe, T.‐H.

doi:10.1063/1.4826201

Cited by 12 publications

(11 citation statements)

References 21 publications

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“…t ) = d e (b (u) t − b (d) t ). (21)When the boundary layer is moving at a speed V n in the X direction, the condition(19) is transformed tov (d) t b n − (v n − V n )b (d) t = v (u) t b n − (v n − V n )b (u) t ,(22)in the rest frame, and the condition(21)is unchanged. Since these conditons also yieldρ s (v n − V n ) = −d e b n ,(23)we need to impose at least two matching conditions among(21),(22) and(23).B.…”

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confidence: 99%

Explosive magnetic reconnection caused by an X-shaped current-vortex layer in a collisionless plasma

2015

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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 Xshaped current-vortex layer centered at the reconnection point. A high-resolution simulation of this model for an unprecedentedly small electron skin depth d e and ion-sound gyroradius ρ s , satisfying d e = ρ 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.

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confidence: 99%

Explosive magnetic reconnection caused by an X-shaped current-vortex layer in a collisionless plasma

2015

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“…The former may be expected in the inner diffusion region, and the latter in larger regions around the outflow, leading to the expectation that collisionless magnetic reconnection is indeed irreversible—an expectation consistent with the apparent lack of observations of magnetic reconnection reversing. However, some models indicate that careful reversal of time, particle motion, and magnetic fields can lead to reversible behavior for some system parameters (Ishizawa & Watanabe, ). Determining where entropy is produced, to what degree, and how it can best be measured is both one of the most challenging and rewarding future research topics.…”

Section: Future Research Directions For Magnetic Reconnectionmentioning

confidence: 99%

Magnetic Reconnection in the Space Sciences: Past, Present, and Future

2020

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Magnetic reconnection converts, often explosively, stored magnetic energy to particle energy in space and in the laboratory. Through processes operating on length scales that are tiny, it facilitates energy conversion over dimensions of, in some cases, hundreds of Earth radii. In addition, it is the mechanism behind large current disruptions in fusion machines, and it can explain eruptive behavior in astrophysics. We have known about the importance of magnetic reconnection for quite some time based on space observations. Theory and modeling employed magnetized fluids, a very simplistic description. While successful at modeling the large‐scale consequences of reconnection, it is ill suited to describe the engine itself. This is because, at its heart, magnetic reconnection in space is kinetic, that is, governed by the intricate interaction of charged particles with the electromagnetic fields they create. This complex interaction occurs in very localized regions and involves very short temporal variations. Researching reconnection requires the ability to measure these processes as well as to express them in models vastly more complex than fluid approaches. Until very recently, neither of these capabilities existed. With the advent of NASA's Magnetospheric Multiscale mission and modern modeling advances, this has now changed, and we have now determined its small‐scale structure in exquisite detail. In this paper, we review recent research results to predict what will be achieved in the future. We discuss how reconnection contributes to the evolution of larger‐scale systems, and its societal impacts in the context of threatening space hazards, customarily referred to as “space weather.”

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“…In strongly magnetized plasmas, the collective motions of charged particles can be described using the gyrokinetic equations in a characteristic time scale longer than the gyro period [17]. The gyrokinetic equations are often used for the analysis of turbulent transport in fusion plasmas [18], and they were recently applied to the magnetic reconnection with a strong guide field [19][20][21].…”

Section: Introductionmentioning

confidence: 99%

Structure of the Electron Distribution Function and Induced Beam Instability in Collisionless Magnetic Reconnection with a Strong Guide Field

Shimomura¹,

Watanabe²,

Maeyama³

et al. 2020

Plasma and Fusion Research

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A phase space structure of the electron distribution function is investigated by the gyrokinetic theory and numerical simulations to investigate a possible mechanism of the excitation of the beam instability which induces collisionless magnetic reconnection in a strong guide field. It is shown that the perturbed electron distribution function develops in proportion to the shifted Maxwellian distribution as the reconnection electric field accelerates electrons along the guide field at the X-point, with parity symmetry around the z-axis. The accelerated electrons are expected to excite the kinetic Alfvén waves (KAWs) when the beam velocity exceeds the Alfvén speed. The obtained results suggest a possible scenario for anomalous resistivity generation in the case with the strong guide field where the beam electrons accelerated at the X-point lose their parallel momentum through interactions with the self-excited KAWs.

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Reversible collisionless magnetic reconnection

Cited by 12 publications

References 21 publications

Explosive magnetic reconnection caused by an X-shaped current-vortex layer in a collisionless plasma

Explosive magnetic reconnection caused by an X-shaped current-vortex layer in a collisionless plasma

Magnetic Reconnection in the Space Sciences: Past, Present, and Future

Structure of the Electron Distribution Function and Induced Beam Instability in Collisionless Magnetic Reconnection with a Strong Guide Field

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