Princeton Center for Heliophysics Seminar

A recurring theme in the fundamental plasma physics of heliospheric, planetary, and astrophysical plasmas is the ultimate fate of large scale energy when it reaches small scales. This is certainly topical for magnetic reconnection, turbulence, and shocks which underly many physical processes of importance to these settings. In collisional plasmas, the fate of the energy is relatively straight-forward — it is irreversibly dissipated into heat at small-scale structures. In weakly collisional or collisionless plasmas, it is much less clear. This presentation will discuss our recent efforts to investigate entropy in the kinetic theory description as a possible tool. Recent theoretical developments have included a kinetic entropy-based non-Maxwellianity parameter and its applications. Numerically, we show kinetic entropy measures in fully-kinetic particle-in-cell (PIC) simulations of magnetic reconnection. We also show a comparison of a collection of measures that have been used to investigate kinetic-scale energy conversion in simulations of reconnection and turbulence using a suite of PIC, hybrid-Vlasov, and full Vlasov simulations. Finally, we show results of measuring kinetic entropy using the Magnetospheric Multiscale (MMS) satellites and discuss potential comparisons with laboratory plasma experiments.