Horn-Shaped Structure Attached to the Ring-Shaped Ion Velocity Distribution during Magnetic Reconnection with a Guide Field

Usami, Shunsuke; Horiuchi, Ritoku; Ohtani, Hiroaki

doi:10.1585/pfr.14.3401137

Plasma and Fusion Research

2019

DOI: 10.1585/pfr.14.3401137

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Horn-Shaped Structure Attached to the Ring-Shaped Ion Velocity Distribution during Magnetic Reconnection with a Guide Field

Shunsuke Usami

Ritoku Horiuchi

Hiroaki Ohtani

Abstract: The characteristic feature of a "horn-shaped velocity distribution" in magnetic reconnection in the presence of a guide field is investigated by means of simulation and theory. Particle simulations show that a horn-shaped velocity structure is formed in the downstream, concomitant with a ring-shaped velocity distribution studied in the preceding works. The theory which explains the motion of ions responsible for the horn-shaped structure is constructed as an extension of the basic theory for the ring-shaped st… Show more

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Cited by 2 publications

References 22 publications

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Three-dimensional crescent-shaped ion velocity distributions created by magnetic reconnection in the presence of a guide field

Usami,

Zenitani

2024

Physics of Plasmas

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By means of theory and particle simulations, crescent-shaped ion velocity distributions in the outflow region of symmetric magnetic reconnection in the presence of a guide magnetic field are investigated. Assuming a spatial one-dimensional electromagnetic field, a theoretical model accounting for the shape of crescents is derived. First, following the earlier theoretical models suggested by Bessho et al. [Geophys. Res. Lett. 43, 1828–1836 (2016)] and Zenitani et al. [J. Geophys. Res.: Space Phys. 122, 7396–7413 (2017)], we derive a theoretical model for 2D velocity distributions based on the conservation of the canonical momentum and the energy. The 2D theoretical model exhibits a two-dimensional structure of crescent-shaped velocity distributions and further demonstrates that no magnetic field reversal is required in the formation of crescents, although many researchers have considered that magnetic field reversal plays an essential role. Next, we construct a theoretical model for 3D velocity distributions based not only on the conservation of the canonical momentum in two directions and the energy but also on the conservation of the magnetic moment and the kinetic energy in the moving frame with the reconnection outflow speed, which are applied when the guide field ratio is high. The 3D theoretical model derives a three-dimensional structure of crescents by combination of an antiparallel magnetic field and a guide magnetic field comparable to or greater than the reconnection field. Both of the 2D and 3D theoretical models are consistent with ion velocity distributions found in our particle simulations.

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Three-dimensional crescent-shaped ion velocity distributions created by magnetic reconnection in the presence of a guide field

Usami,

Zenitani

2024

Physics of Plasmas

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Pseudo-Maxwellian Velocity Distribution Formed by the Pickup-like Process in Magnetic Reconnection

Usami

Horiuchi

2022

Front. Astron. Space Sci.

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Focusing on ring-shaped ion velocity distributions with a finite width formed in magnetic reconnection in the presence of a guide magnetic field, intriguing properties such as the formation mechanism, a significant change in the shape, and necessary conditions for the change are investigated by means of theory and simulations. The width of a ring velocity distribution predominantly originates from velocity variations of seed particles for the pickup-like process. A function exactly representing a ring with a width is analytically formulated, assuming a steady supply of seed particles satisfying a Maxwellian velocity distribution and a mixing of gyration phases. The formulated function indicates that when the ring width is larger than a criterion, the local minimum of the ring’s center is changed into the maximum, and the shape is transformed into a mountain shape. Such a mountain-like distribution is defined as “a pseudo-Maxwellian distribution,” because it is almost indistinguishable in shape from a genuine Maxwellian distribution. Actually, particle simulations demonstrate that mountain-shaped ion velocity distributions are formed during magnetic reconnection with a guide magnetic field, and it is nearly concluded that they are pseudo-Maxwellian distributions. Moreover, two types of evidence for pseudo-Maxwellian distributions are shown by simulations. One is to analyze the dependence of the distribution shape on the guide magnetic field, which is explored by the particle simulation. In cases of slightly different values of the guide field, vague shapes of rings with a width are observed as ion velocity distributions. The other is to observe velocity distributions under a hypothetical condition of an artificial zero temperature in the upstream by utilizing a test particle simulation. In the test particle simulation, ring-shaped distributions with a width are clearly seen, because the velocity variations in the upstream are reduced. From the two types of evidence, it is definitely confirmed that the mountain-shaped distributions found in the particle simulations are pseudo-Maxwellian distribution. These results imply that pseudo-Maxwellian distributions would be created for various cases of guide field magnetic reconnection.

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Horn-Shaped Structure Attached to the Ring-Shaped Ion Velocity Distribution during Magnetic Reconnection with a Guide Field

Cited by 2 publications

References 22 publications

Three-dimensional crescent-shaped ion velocity distributions created by magnetic reconnection in the presence of a guide field

Three-dimensional crescent-shaped ion velocity distributions created by magnetic reconnection in the presence of a guide field

Pseudo-Maxwellian Velocity Distribution Formed by the Pickup-like Process in Magnetic Reconnection

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