Electrostatic turbulence and electron heating in collisionless shocks

Abstract: Collisionless shocks are one of the most peculiar phenomena in space where non-linear collective phenomena in the plasma dominate the dynamics. They are believed to be one of the most efficient particle accelerators in the universe, and have internal dynamics that are yet to be fully explored. In this project we aim to understand the interplay between the electrostatic turbulence in the shock ramp and the electron dynamics leading to thermalization across the shock. To do so we first use a machine learning technique to compile a database of shocks crossings observed by magnetospheric multiscale (MMS), which will facilitate both case studies and statistical studies of shocks using MMS. The database contains 2803 shock crossings spanning a period from October 2015 to December 2020. For each crossing we provide key parameters necessary for understanding shock dynamics such as Alfv\'{e}nic Mach number and the angle  between the upstream magnetic field and the vector normal to the shock $\theta_{Bn}$. We then study whistler waves upstream of 11 quasiperpendicular supercritical shocks. We first apply four spacecraft timing method to magnetic field data from MMS to properly characterize the observed whistler waves. We determine their frequency in the plasma rest frame to range from 0.3 to 1.2 the lower hybrid frequency,their wavelength to range from 0.7 to 1.7 ion inertial length and $\theta_{kB}$ to range between $20^\circ$ and $42^\circ$. We then use particle data provided by MMS to show that a reflected beam component in the ion velocity distribution function is in resonance with the observed waves indicating that a kinetic cross field streaming instability (KCFSI) is behind the generation of such waves. Finally a kinetic solver is used to model to observed distribution and reinforce the previous conclusion that the KCFSI is behind the generation of the observed whistlers. We end this thesis by discussing the ongoing projects pertaining to the interaction of electrostatic wave mode determination in the shock ramp and the correlation between whistler waves and electrostatic waves around quasi-perpendicular shocks.

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