Higher-order nonequilibrium term (HORNET): An effective power density quantifying evolution towards or away from local thermodynamic equilibrium
Speaker Name: M. Hasan Barbhuiya, West Virginia University
Abstract : When studying energy conversion in plasma systems, such as space plasma, it is common to compare the power densities of different energy conversion mechanisms. A prominent research area focuses on quantifying energy conversion for such weakly collisional plasmas that are routinely not in local thermodynamic equilibrium (LTE), meaning their local phase space densities can be arbitrarily far from a Maxwellian. We introduce the "higher-order nonequilibrium term"; (HORNET) effective power density, which measures the time rate of change of the departure of local phase space densities from LTE. With dimensions of power density, HORNET enables quantitative comparisons with standard power densities, such as the pressure-strain interaction. We compute HORNET using high-resolution particle-in-cell simulations of two plasma phenomena that inherently exhibit non-LTE effects, namely magnetic reconnection and decaying kinetic turbulence in collisionless magnetized plasmas. Comparing HORNET with pressure dilatation, Pi-D, and the divergence of the vector heat flux density (that describe changes to internal energy) reveals that HORNET can be a significant fraction of these other power densities in reconnection and in turbulence, underscoring the importance of capturing the non-LTE evolution in collisionless plasma systems
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