Intense Electric Currents and Energy Conversion Observed at Electron Scales in the Plasma Sheet During Propagation of High‐Speed Ion Bulk Flows

Abstract

AbstractThe intense electron‐scale current structures (ECSs) with the current density J ≥ 30 nA/m2 are often observed in the Plasma Sheet (PS) during high‐speed bulk flows. Using MMS observations we have analyzed 41 earthward and 37 tailward flow intervals and found 452 and 754 ECSs distributed over the PS region, respectively. Almost all ECSs are generated by high‐speed electron beams. The duration of ECSs is ≤1 s, and many of them have a half‐thickness L ≤ a few ρe (ρe is the gyroradius of thermal electrons). In such thin ECSs electrons become demagnetized and experience the dynamics like that observed in the electron diffusion region. Strong nonideal electric fields (E’) associated with violation of frozen‐in condition for electrons are observed in the ECSs. This results in the intense energy conversion with J·E’ up to hundreds pW/m3. The major part of the dissipating energy is transferred to electron heating and acceleration. We suggest that the ECSs are manifestations of kinetic‐scale turbulence driven by the high‐speed ion bulk flows. The inductive electric fields generated by the growing magnetic fluctuations accelerate electron beams which, in turn, generate the ECSs. The ECSs thinning during their evolution, probably, stops for L ≤ a few ρe. Further thinning leads to development of kinetic instability causing the current disruption and strong electric field generation. The last accelerates new electron beams which generate new ECSs in other locations. Thus, the life cycles of the ECSs contribute to energy cascade in turbulent plasma at electron kinetic scales.