Property of neoclassical GAMs induced by pellet generated plasma perturbations in the gyrokinetic code XGC

A pellet source model has been implemented into the gyrokinetic code XGC and applied to neoclassical geodesic acoustic mode (GAM) study as the first step to investigate potentially rapid kinetic spread of pellet-born particles following their injection into plasma. In this study, GAM oscillations of the radial electric field, as well as of their effect on the radial particle and energy fluxes, are studied and the observed frequencies agree with theoretical expectations. It is verified that (i) GAM oscillations are driven both within the pellet-fuelled region and for locations at a larger radius than this region and not for locations radially inside the pellet-fuelled region, and that, (ii) even though the poloidal spread along the magnetic field lines is fast, the time-averaged radial plasma transport under GAM oscillations is kept to roughly the same level as the neoclassical transport in the absence of plasma turbulence.