Shu-Wei Tsao, UT-Austin

"Compressional Magnetic Fluctuations in Global Gyrokinetics and Reconnection Heating in the Solar Corona"

Abstract: In the area of gyrokinetic simulations of turbulence in magnetized plasmas such as those in fusion devices, global frameworks are used to address radial profile effects. However, limitations regarding the treatment of parallel magnetic fluctuations in global gyrokinetics persist. In this thesis, we present the derivation of a set of self-consistent field equations, without introducing a large-wavelength approximation, that account for compressional magnetic field fluctuations in global gyrokinetics. Possible numerical implementations are discussed that address the issue of large condition numbers limiting matrix inversions. This provides the bases of more accurate future studies, e.g., of turbulence in the tokamak pedestal.

Reconnection turbulence, a potential solution to the coronal heating problem, is driven by tearing modes arising from current sheets. While kinetic simulations have been reported in the past that study this system, they had to employ simplified physical settings due to the prohibitive expense of simulating at the strong coronal guide field with hydrogen ions. To accurately model this phenomenon under realistic conditions, a gyrokinetic framework is applied instead. Simulations with hydrogen mass ratio and realistic coronal $beta$ in both spatially 2D and 3D linear and nonlinear simulations are presented and investigated in this thesis. The heating rate for the 2D system agrees with existing observations. Linear analyses of the impact of effects such as field-line twist, magnetic trapping, and frozen-in flux conditions are discussed for the 3D case. Preliminary results from nonlinear simulations at realistic parameters and in 3D coronal loop geometry confirm that reconnection turbulence and associated heating may indeed explain the large temperatures in the solar corona.