# A New Theory of Kinetic-Scale Energy Conversion and Dissipation

## Presentation Type

Talk

## Presenter Format

Virtual Meeting Talk

## Topic

Fundamental Processes in Comparative Magnetospheres

## Start Date

13-5-2022 2:30 PM

## Abstract

The Magnetospheric Multiscale (MMS) mission has enabled research into kinetic-scale energy conversion and dissipation in exquisite detail. Studying energy conversion is complicated where collisions are extremely weak, leading to systems far from local thermodynamic equilibrium (LTE). Recently, the crucial role played by non-LTE effects in impacting the evolution of plasma temperature has been emphasized [Y. Yang et al., Phys. Plasmas, 24, 072306 (2017)]. The key non-LTE term is known as Pi-D, which appears in the temperature evolution equation. In this study, we show the temperature evolution equation is incomplete, missing key kinetic physics that can play an important role in energy conversion. We argue that energy conversion can be thought of as a hierarchy of changes to all moments of the phase space density. Work due to compression changes the zeroth moment (density), while Pi-D and heat flux change the second moment (temperature); both are described by the temperature evolution equation. However, the equation is agnostic to changes to any higher order moment. We develop a new paradigm to describe these manifestly non-LTE kinetic effects. Using entropy defined in kinetic theory, we derive an energy evolution equation that supplants the first law of thermodynamics – we dub it “the first law of kinetic theory.” We show this law retains all information described by the temperature evolution equation, in addition to describing energy conversion to all higher order moments. We compare and contrast amplitudes and profiles of terms in the first law of kinetic theory in particle-in-cell simulations of symmetric magnetic reconnection.

A New Theory of Kinetic-Scale Energy Conversion and Dissipation

The Magnetospheric Multiscale (MMS) mission has enabled research into kinetic-scale energy conversion and dissipation in exquisite detail. Studying energy conversion is complicated where collisions are extremely weak, leading to systems far from local thermodynamic equilibrium (LTE). Recently, the crucial role played by non-LTE effects in impacting the evolution of plasma temperature has been emphasized [Y. Yang et al., Phys. Plasmas, 24, 072306 (2017)]. The key non-LTE term is known as Pi-D, which appears in the temperature evolution equation. In this study, we show the temperature evolution equation is incomplete, missing key kinetic physics that can play an important role in energy conversion. We argue that energy conversion can be thought of as a hierarchy of changes to all moments of the phase space density. Work due to compression changes the zeroth moment (density), while Pi-D and heat flux change the second moment (temperature); both are described by the temperature evolution equation. However, the equation is agnostic to changes to any higher order moment. We develop a new paradigm to describe these manifestly non-LTE kinetic effects. Using entropy defined in kinetic theory, we derive an energy evolution equation that supplants the first law of thermodynamics – we dub it “the first law of kinetic theory.” We show this law retains all information described by the temperature evolution equation, in addition to describing energy conversion to all higher order moments. We compare and contrast amplitudes and profiles of terms in the first law of kinetic theory in particle-in-cell simulations of symmetric magnetic reconnection.