  This study delves into Microtearing Modes (MTMs) in tokamak plasmas,
employing advanced simulations within the BOUT++ framework. The research,
centering on collisional MTMs influenced by the time-dependent thermal force,
enhances our understanding of plasma dynamics. It achieves this through the
simplification and linearization of control equations in detailed linear
simulations. The study meticulously evaluates various conductivity models,
including those proposed by Larakers, Drake, and Hassam, under diverse plasma
conditions and collision regimes. A notable achievement of this research is the
derivation of a unified dispersion relation that encompasses both MTM and
Drift-Alfven Wave (DAW) instabilities. It interestingly reveals that DAW and
MTM exhibit instability at different proximities to the rational surface.
Specifically, MTMs become unstable near the rational surface but stabilize
farther away, whereas the drift-Alfven instability manifests away from the
rational surface. Further, the study re-derives MTM dispersion relations based
on Ohm's law and the vorticity equation, providing a thorough analysis of
electromagnetic and electrostatic interactions in tokamaks. Global simulations
demonstrate an inverse correlation between MTM growth rates and collisionality,
and a direct correlation with temperature gradients. The nonalignment of the
rational surface with the peak of electron local diamagnetic frequency
stabilizes the MTMs. Nonlinear simulations highlight electron temperature
relaxation as the primary saturation mechanism for MTMs, with magnetic flutter
identified as the dominant mode of electron thermal transport.
