Spontaneous Onset of Collisionless Magnetic Reconnection on an Electron Scale

Liu, Dongkuan; Lu, San; Lu, Quanming; Ding, Weixing; Wang, Shui

doi:10.3847/2041-8213/ab72fe

Cited by 13 publications

(15 citation statements)

References 39 publications

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“…The common thread throughout all theories of magnetic reconnection is an initial condition of a thin current sheet (TCS) separating opposing magnetic fields. Various simulations have suggested the maximum current sheet thickness which would support reconnection onset is between several ion inertial lengths (Birn, 1980 ) and two electron inertial lengths (D. Liu et al., 2020 ) depending on the exact instability which instigates reconnection onset. Despite the continuing debate over the precise onset mechanism, it would seem that a central current sheet of thickness in the range of the ion gyroradius or smaller is a necessary precondition for magnetic reconnection in the tail.…”

Section: Introductionmentioning

confidence: 99%

Applying Magnetic Curvature to MMS Data to Identify Thin Current Sheets Relative to Tail Reconnection

et al. 2023

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Thin current sheets (TCSs) have been postulated to be a necessary precondition for reconnection onset. Magnetic reconnection X‐lines in the magnetotail have been observed to be more common duskward of midnight. We take advantage of the MMS tetrahedral formation during the 2017–2020 MMS tail seasons to calculate the thickness of the cross‐tail neutral sheet relative to ion gyroradius. While a similar technique was applied to Cluster data, current sheet thickness over a broader range of radial distances has not been robustly explored before this study. We compare our analysis to recent theories regarding mechanisms of tail current sheet thinning and to recent simulations. We find MMS spent more than twice as long in ion‐scale TCSs in the pre‐midnight sector than post‐midnight, despite nearly even plasma sheet dwell time. The dawn‐dusk asymmetry in the distribution of Ion Diffusion Regions, as previously reported in relation to regions of TCSs, is also analyzed.

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Section: Introductionmentioning

confidence: 99%

Applying Magnetic Curvature to MMS Data to Identify Thin Current Sheets Relative to Tail Reconnection

et al. 2023

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“…As for the effect of the mass ratio, the larger the mass ratio, the larger the difference between the ion frozen-in term dominated by ion dynamics and the Hall term dominated by the electron dynamics, which leads to a larger LEF. Previous simulations have also shown that the halfwidth of the current sheet decreases with the increment of the mass ratio (Guo & Lu 2007;Liu et al 2020).…”

Section: The Effect Of Upstream Parameters On the Lefmentioning

confidence: 74%

“…During the onset phase, the reconnection rate is small, which is insufficient to dissipate the inflowing magnetic flux timely. Therefore, the magnetic flux is piled up in the inflow region, which compresses and narrows down the current sheet (Liu et al 2020). On the other hand, the reconnecting current sheet is elongated in the fast reconnection phase (e.g., Daughton et al 2006); thus, the system would self-consistently increase δ to keep the large aspect ratio so that the fast reconnection is maintained (Liu et al 2020).…”

Section: Why Is the Current Sheet Thinning And Thickening?mentioning

confidence: 99%

“…However, a thin current sheet satisfying ρ i > δ (here δ is the half-width of the current sheet, which is evaluated as the distance between J y,peak and J y,peak /e, where e is Euler's number) in symmetric reconnection may also give rise to the LEF, which is formed to prevent ions from crossing the current sheet to the other side in symmetric reconnection (see the illustration in Figure 1). The magnetotail neutral sheet can be thinner than the ion gyro-radius during the disturbed time and before the reconnection onset (e.g., Sergeev et al 1993;Lee et al 1995;Asano et al 2004;Nakamura et al 2008;Liu et al 2020;Lu et al 2020;Yushkov et al 2021). Here we show that the LEF can be generated upstream of the Hall electric field on both sides of the current sheet in symmetric reconnection if the current sheet is sufficiently thin.…”

Section: Introductionmentioning

confidence: 99%

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Larmor Electric Field in Symmetric Magnetic Reconnection

Zhou

Song

et al. 2023

ApJ

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The Larmor electric field (LEF) was previously suggested as a signature to identify the diffusion region in asymmetry reconnection. Using 2.5D particle-in-cell simulations, we show that the LEF also exists in symmetric reconnection, manifested as a transient structure upstream of the Hall electric field. The LEF emerges during the rapid growth phase of the reconnection rate and has opposite polarity to the Hall field. The half-width of the current sheet spontaneously decreases to the electron scale as the evolution of reconnection, which gives rise to the LEF. The current sheet later thickens to maintain the fast reconnection rate, which causes the disappearance of the LEF. We further find that the magnitude of LEF is sensitive to the initial half-width current sheet, the background plasma temperature and density, the guide-field strength, and the ion–electron mass ratio. Our results provide new insight into the dynamics around the diffusion region. The LEF can help satellites not only locate the diffusion region but also identify the onset phase of reconnection in the magnetotail.

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“…In the inflow region (Figure 4(d)), the PDF of E || acceleration is broader than that of the other two mechanisms, which suggests that the energy exchange between magnetic fields and electrons in the inflow region is primarily through the parallel electric field. The net positive betatron acceleration is probably caused by the flux pileup in the inflow region (Liu et al 2020). Figure 4(e) shows that the betatron acceleration has the broadest distribution in the outflow region.…”

Section: Statistical Resultsmentioning

confidence: 95%

Contrasting the Mechanisms of Reconnection-driven Electron Acceleration with In Situ Observations from MMS in the Terrestrial Magnetotail

Zhou

Zhong

et al. 2022

ApJ

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The question of how magnetic reconnection accelerates particles is a long-standing problem in space physics and astrophysics. Earth’s magnetosphere is an ideal laboratory for investigating this issue via in situ satellite observations. This article presents a statistical study of the electron acceleration produced by different mechanisms in the near-Earth magnetotail using the unique measurement capabilities of the Magnetospheric Multiscale mission. We find that the average acceleration rates and occurrence rates of large acceleration tend to be higher in outflows with greater speeds. Betatron and first-order Fermi accelerations are intensified near the neutral sheet, while the acceleration from E ∣∣ is not only intensified in the neutral sheet but also significant far away from it, likely in the separatrix region. In contrast to previous studies suggesting that the acceleration and energy conversion predominantly occur in the outflow region, we find that the acceleration rate near the X line is comparable to that in the outflow.

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Spontaneous Onset of Collisionless Magnetic Reconnection on an Electron Scale

Cited by 13 publications

References 39 publications

Applying Magnetic Curvature to MMS Data to Identify Thin Current Sheets Relative to Tail Reconnection

Applying Magnetic Curvature to MMS Data to Identify Thin Current Sheets Relative to Tail Reconnection

Larmor Electric Field in Symmetric Magnetic Reconnection

Contrasting the Mechanisms of Reconnection-driven Electron Acceleration with In Situ Observations from MMS in the Terrestrial Magnetotail

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