Investigating Micro-Tearing Mode and Drift-Alfven Instability in Pedestal Turbulence

The micro-tearing mode (MTM) has been suggested as one of the potential driving mechanisms for pedestal electron temperature heat turbulence transport. In our study, we derive the dispersion relations of MTM under various limiting cases and compare them with various MTM models. Additionally, we investigate the instability of the drift Alfven wave (DAW) by incorporating the impact of time-dependent thermal forces using Hassam's collisional fluid model. Our finding indicates distinct instability characteristics of MTM and DAW at different rational surface locations. Specifically, MTM exhibits instability near the rational surface, whereas DAW instability occurs away from the rational surface. To simulate the micro-tearing mode, we implement the Hassam's model into BOUT++ framework. Employing a shifted-circle tokamak geometry, our linear global simulations reveal that the growth rate of the linear MTM decreases as collisionality increases, aligning with theoretical expectations. Furthermore, our nonlinear global simulation demonstrates that MTM generates chains of magnetic islands. In the late nonlinear stage, these magnetic islands overlap, leading to the emergence of chaotic magnetic fields. Notably, in the absence of energy source, the initial value simulation shows that MTMs can also trigger crashes in the electron temperature profile due to stochastic and magnetic transport, similar to the effects of ELMs.