KUL/CmPA Seminar: Nonequilibrium solar wind particle distributions: Why care?

Seminar by Dr. Lynn B. Wilson III (He/Him)- NASA Goddard Space Flight Center

Title: Nonequilibrium solar wind particle distributions:  Why care?


The solar wind is a supersonic flow of ionized particles, called a plasma, streaming away from the Sun.  These particles are not observed to be in thermal or thermodynamic equilibrium.  This is because nearly all particle dynamics are governed by non-collisional processes and the particles experience long-range forces (i.e., Coulomb potentials of nearby, charged particles).  There are multiple particle species in the solar wind as well, including but not limited to electrons, protons, alpha-particles, and multiple charge states of heavier ions up past uranium.  When we observe the particle velocity distribution functions (VDFs), they exhibit non-Maxwellian features.  In fact, we do not see any VDFs that are consistent with Maxwellian or even bi-Maxwellian distributions.  All particle VDFs observed to date in the solar wind have nonthermal tails and/or multiple phase space density peaks and/or self-similar profiles.  Okay, so why do we care?  The evolution of these particle VDFs as they stream away from the Sun violate numerous approximations we physicists take for granted including the compressibility of phase space, evidence of inelastic collisions, etc.  These signatures are evidence of irreversible processes, which do not obey Vlasov's equation.  Given that the irreversible processes are not due to binary particle collisions, these processes also do not obey the standard Boltzmann equation.  Such nonequilibrium kinetic processes are of fundamental importance and at the heart of some of the deepest mysteries in physics.

Where: The seminar can be followed in person in building 200B, room 01.04 or online at the following link:​


Tuesday, May 9, 2023 - 14:00 to 16:00

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