Electron–ion hybrid mode due to transverse velocity shear

G. Ganguli, Y. C. Lee, P. J. Palmadesso
1988 The Physics of Fluids  
Magnetotail DF contains a substantial velocity shear in the tangential electron drift. 10 • The sheared flow is susceptible to the EIH instability and can broaden the DF by 11 emitting broadband LH waves. 12 • The EIH emissions become more electromagnetic as plasma beta increases. Abstract 14 The stability of a quasi-static near-Earth dipolarization front (DF) is investigated with a 15 two-dimensional electromagnetic particle-in-cell (EMPIC) model. Strongly localized am-16 bipolar electric
more » ... polar electric fields self-consistently generates a highly sheared dawnward ì E × ì B electron 17 drift on the kinetic scale in the DF. EMPIC simulations based on the observed DF thick-18 ness and gradients of plasma/magnetic field parameters reveal that the DF is susceptible to 19 the kinetic electron-ion hybrid (EIH) instability driven by the strong velocity inhomogene-20 ity. The excited waves show a broadband spectrum in the lower hybrid (LH) frequency 21 range, which has been often observed at DFs. The wavelength is comparable to the shear 22 scale length and the growth rate is also in the LH frequency range, which are consistent 23 with the EIH theory. As a result of the LH wave emissions, the velocity shear is relaxed 24 and the DF is broadened. When the plasma beta increases, the wave mode shifts to longer 25 wavelengths with reduced growth rates and enhanced magnetic fluctuations although the 26 wave power is mostly in the electrostatic regime. This study highlights the role of velocity 27 inhomogeneity in the dynamics of DF which has been long neglected. The EIH instability 28 is suggested to be an important mechanism for the wave emissions and steady-state struc-29 ture at the DF. 30
doi:10.1063/1.866982 fatcat:svl3jq5tvjg3rhunvax4llbk7i