Field-aligned potential drops in nonthermal plasmas: Application to plasma sheet boundary layer

Abstract

Kinetic Alfvén waves are observed in the plasma sheet boundary layer (PSBL) as indicated by the Polar satellite. Moreover, the THEMIS and the Polar spacecraft also detected parallel electric fields associated with double layers (DLs) in the PSBL region. Apart from this, the Magnetospheric Multiscale Mission recently reported counterstreaming ion beams in the aforesaid region of the Earth's magnetosphere. Being motivated by these observations, we have investigated kinetic Alfvénic DLs (KADLs) in a two-component low-β Cairns distributed plasma in the plasma sheet boundary layer at altitude 4−6RE. In order to explore KADL structures, the Sagdeev potential technique is employed to construct a nonlinear extended Korteweg–de Vries equation. It is found that our investigation admits only rarefactive KADL structures. Furthermore, the effects of nonthermality and Alfvénic Mach number on KADLs and their corresponding parallel electric field are explored in detail. It is noted that the propagation characteristics of KADL and the electric field profiles are significantly affected by nonthermality. Moreover, the implications of our results to PSBL related to charged particle acceleration are briefly mentioned. The present theoretical results are consistent with the Polar spacecraft observations.