Quasi-Stationary Electron-Scale Current Sheet With Very Strong Electrostatic Field: Self-Consistent Structure and Electron Acceleration

Abstract

We study a self-consistent configuration of the intense Electron-Scale Current Sheets (ECSs) under the presence of strong guide field $\left(B_M\right)$. The ECSs were observed within the tailward Bursty Bulk Flow in the extremely hot PS. The purpose of our paper is twofold. First, we would like to determine mechanisms supporting the quasi-stationary ECS configuration, and, second, to investigate the possibility of additional electron acceleration by a strong ambipolar electric field, self-consistently arising in the quasi-stationary ECSs. We demonstrated that the intense ECSs ($\sim 100$ nA/$m^2$) have 1D planar configuration self-consistently balanced by the central field-aligned current and perpendicular currents in its southern and northern edges. The field-aligned current is carried by the suprathermal high-speed electron beam, while the perpendicular currents are supported by electron diamagnetic and $E\times B$ drifts due to the presence of the strong ambipolar electric field ($\sim 50$ mV/m). Electron anisotropy currents are negligible in this configuration. We found that the vertical pressure balance in the ECSs is mainly contributed not by the increase in guide magnetic field, but by the electron pressure enhancement. The strong ambipolar electric field related to the ECSs can accelerate field-aligned electron beams providing the energy gain up to $\sim 8$ keV. This may lead to new ECSs formation in other PS locations contributing to the cascade generation of ECSs in the PS. Our study shed a new light on the mechanisms of the intense ECSs formation in hot collisionless plasma.