Occurrence of Flat‐Top Electron Velocity Distributions in Magnetotail Plasma Jets

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 at least of the eVDFs in the jets are flat‐tops. In addition, 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 the ion diffusion region. Our results highlight the importance of flat‐top eVDFs in non‐local thermodynamic equilibrium collisionless plasmas.