On Electron Adiabaticity in Collisionless Shocks

Comişel, H.

doi:10.3389/fphy.2016.00029

Cited by 1 publication

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“…However, the efficiency of those acceleration processes in realistic collisionless shocks, where typical background plasma parameters are hardly achievable in modern numerical simulations, remains poorly understood. Among the critical background plasma parameters is ω pe /ω ce , the ratio of the electron plasma frequency to the electron cyclotron frequency [8], which is typically large in space and astrophysical plasmas [14] but much smaller in numerical simulations of collisionless shocks [3,15]. The analysis of spacecraft measurements in the Earth's bow shock characterized by ω pe /ω ce ∼ 100 should advance our understanding of the origin and consequences of electrostatic fluctuations in collisionless shocks under realistic background plasma parameters.…”

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confidence: 99%

On the Nature and Origin of Bipolar Electrostatic Structures in the Earth's Bow Shock

et al. 2020

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We present a statistical analysis of large-amplitude bipolar electrostatic structures measured by Magnetospheric Multiscale spacecraft in the Earth's bow shock. The analysis is based on 371 large-amplitude bipolar structures collected in nine supercritical quasi-perpendicular Earth's bow shock crossings. We find that 361 of the bipolar structures have negative electrostatic potentials, and only 10 structures (< 3%) have positive potentials. The bipolar structures with negative potentials are interpreted in terms of ion phase space holes produced by ion streaming instabilities, particularly the two-stream instability between incoming and reflected ions. We obtain an upper estimate for the amplitudes of the ion phase space holes that is in agreement with the measurements. The bipolar structures with positive potentials could be electron phase space holes produced by electron two-stream instabilities. We argue that the negligible number of electron phase space holes among large-amplitude bipolar structures is due to the electron hole transverse instability, the criterion for which is highly restrictive at ω pe /ω ce ≫ 1, a parameter range typical of collisionless shocks in the heliosphere and various astrophysical environments. Our analysis indicates that the original mechanism of electron surfing acceleration involving electron phase space holes is not likely to be efficient in realistic collisionless shocks.

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