Microscale Dynamics and Non-Maxwellian Equilibria: Decoding Collisionless Processes in the Space Plasmas

Objective

Plasma is the most common state of matter in the Universe. In most plasma environments, such as accretion disks, intracluster medium, and the heliosphere, the interparticle collision frequency is much smaller than the characteristic particle time scale, so the plasma is effectively collisionless. As a result, the velocity distribution function of charged particles, such as electrons, is not bound to the Maxwell-Boltzmann thermodynamic equilibrium. Nevertheless, stable non-Maxwellian equilibria can exist in collisionless plasma. In particular, recent advances using Lynden-Bell statistical mechanics theory and kinetic Vlasov theory of electrostatic turbulence suggest that non-Maxwellian equilibria are universal. This project aims to understand the varieties of such equilibria and their universality in the heliospheric plasma. To this end, we will propose an innovative data-driven approach, combining in situ observations from state-of-the-art spacecraft, theory, and numerical simulations, to characterise the non-Maxwellian equilibria. Using in situ spacecraft observations, we will statistically describe the different non-Maxwellian equilibria in the heliosphere. In addition, we will use kinetic Vlasov theory and numerical simulations to show how microscale turbulence shapes these equilibria through the interaction between electrons and electromagnetic fields. Together, these steps are designed to help us understand and conceptualise the statistical thermodynamics of a collisionless, turbulent plasma at a new level.