MHD GAMs and kinetic GAMs driven by energetic particles
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In this dissertation, we investigate the n=0 Geodesic Acoustic Modes (GAM) in the framework of both magneto-hydrodynamics and kinetics. In MHD, the purpose is to understand the numerical results out of the CASTOR code (1). Effects of energetic particle are ignored. The leading perturbation is the density perturbation, which leads to a local GAM. The coupling of density perturbation to the magnetic perturbation, which is treated to be smaller, leads to global a GAM. We recover the numerical results from the CASTOR code and obtain and analytical solution to the radial eigen-mode equation though asymptotic matching. To understand recent experimental results on DIII-D (2) a kinetic theory is constructed in which magnetic perturbations are neglected and energetic ions are treated on the same footing as the thermal species based on drift kinetics. Not only do the energetic particles destabilize the local GAM induced by thermal species, but they are also crucial to establish the global GAM due to their large orbit shifts. Polarization of thermal ions is included. A mechanism for fast GAM excitation through NBI is proposed, based on our local kinetic GAM theory when there exists a loss boundary in pitch angle.