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

Abstract

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.

Electron Heating in Magnetosheath Turbulence: Dominant Role of the Parallel Electric Field Within Coherent Structures

“…Here we employ the method that has been used to calculate the acceleration rate in reconnection. This method considers the particle energy gain under guiding center approximation (Dahlin et al, 2014;Ma et al, 2020Ma et al, , 2022Zhong et al, 2020;Zhou et al, 2018). The integrated energy gain of electrons in a unit volume per unit time for betatron acceleration is given by:…”

“…Here we employ the method that has been used to calculate the acceleration rate in reconnection. This method considers the particle energy gain under guiding center approximation (Dahlin et al., 2014; Ma et al., 2020, 2022; Zhong et al., 2020; Zhou et al., 2018). The integrated energy gain of electrons in a unit volume per unit time for betatron acceleration is given by: $$${\mathrm{W}}_{\mathrm{b}}={\mathrm{P}}_{\mathrm{e}\perp }{\boldsymbol{v}}_{\boldsymbol{E}\times \boldsymbol{B}}\cdot \frac{\nabla \mathbf{B}}{\mathrm{B}}+\frac{{\mathrm{P}}_{\mathrm{e}\perp }}{\mathrm{B}}\frac{\partial \mathbf{B}}{\partial \mathrm{t}}$$$ where $${\mathrm{P}}_{\mathrm{e}\perp }$$ is the perpendicular electron pressure, v E×B is the E × B drift speed, $$\nabla \mathbf{B}$$ is the gradient of the total magnetic field.…”

Electron Acceleration via Secondary Reconnection in the Separatrix Region of Magnetopause Reconnection

“…Secondly, the secondary reconnection can accelerate/heat electrons through Fermi reflection. Figure 4i shows the estimated power density of the first-order Fermi acceleration (Dahlin et al, 2014;Zhong et al, 2020b;Ma et al, 2020;2022), which has a significant positive peak of ~ 2,650 eV/s/cm 3 at the current sheet center.…”

Quantitative Analysis of Electron Heating and Acceleration in Coalescing Magnetic Flux Ropes at Earth's Magnetopause

“…In principle, the first-order acceleration of a well-magnetized particle includes Fermi, betatron mechanism, and direct acceleration by parallel electric field (e.g., Northrop, 1963). The power densities of the first-order Fermi, betatron, and E || mechanism can be estimated using the following formulas (Akhavan-Tafti et al, 2019;Dahlin et al, 2014;Ma et al, 2020Ma et al, , 2022Xu et al, 2023;Zhong et al, 2020):…”