Occurrence of Flat-top Electron Velocity Distributions in Magnetotail Plasma Jets

TL;DR

This study statistically analyzes flat-top electron velocity distributions in Earth's magnetotail plasma jets, revealing their localized occurrence near reconnection regions and their significance in collisionless plasma dynamics.

Contribution

Introduces a new classification method for eVDFs and demonstrates that flat-top distributions are characteristic of magnetotail plasma jets, especially near reconnection sites.

Findings

Only about 7% of eVDFs in jets are flat-tops.

Most jets exhibit flat-top eVDFs, indicating a common feature.

Flat-top eVDFs are localized near the edges of the current sheet.

Abstract

Non-Maxwellian electron velocity distributions (eVDFs) are ubiquitous in collisionless plasmas. For example, various types of non-Maxwellian eVDFs exist in magnetic reconnection jets in the Earth's magnetotail. At thermal energies, eVDF can be flat-topped due to electron trapping associated with magnetic reconnection. However, the occurrence of such eVDFs in magnetotail reconnection remains largely unconstrained. Here, we statistically investigate flat-top eVDFs in fast plasma jets in the magnetotail using a new method for classifying eVDFs. We show that only $\sim 7\%$ of the eVDFs in the jets are flat-tops. Nevertheless, we find that most jets exhibit flat-top eVDFs, indicating that this signature of parallel acceleration and electron streaming is characteristic of the jets. We find that these flat-top eVDFs are localized within an ion-inertial-length-scale region near the edges of the current sheet and close to the reconnection region. Our results highlight the importance of flat-top eVDFs in non-local thermodynamic equilibrium collisionless plasmas.