Author

Senbei Du

Date of Award

2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Space Science

Committee Chair

Gary P. Zank

Committee Member

Jakobus A. le Roux

Committee Member

Qiang Hu

Committee Member

Fan Guo

Committee Member

Gary M. Webb

Subject(s)

Space plasmas., Particle acceleration., Magnetic reconnection., Entropy., Heliosphere (Astrophysics)

Abstract

The energization and dissipation of plasma are ubiquitous processes in the heliosphere. They are the key to some of the most outstanding questions in heliophysics such as coronal heating and the acceleration of solar energetic particles. In this dissertation, we investigate plasma energization and dissipation based on the collisionless kinetic equation. Plasma energization is discussed using the evolution equations of bulk flow and thermal energy densities. In a two-fluid description, it has been suggested that the pressure-strain interaction converts bulk kinetic energy into thermal energy. In a single-fluid description, we find that the bulk acceleration and heating are due to the work done by the motional and non-ideal electric field, respectively. Again, the pressure-strain interaction contributes to the conversion between bulk kinetic energy and thermal energy. We also study the dissipation process using the concept of entropy for isotropic and anisotropic fluids, both of which can be derived from thermodynamic principles. We show that the increase of fluid entropy can be understood as a consequence of several mechanisms. In addition to the pressure-strain interaction, heat flux also plays an important role in entropy production. The conclusions are verified using kinetic particle-in-cell simulations of multiple interacting magnetic islands. Finally, we discuss the generation of nonthermal particles in magnetic reconnection. The basic acceleration mechanisms include Fermi acceleration by contracting and merging magnetic islands, and direct acceleration due to the reconnection generated electric field. These mechanisms are verified using a particle tracing technique in simulations. A transport equation approach to particle acceleration is discussed.

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