Mode excitation by an antenna in global gyrokinetic simulations

Abstract

In order to get a better understanding of the linear and non-linear plasma interaction of microinstabilities and associated turbulence with different specific modes, an antenna is implemented in the global gyrokinetic code ORB5. It consists in applying an external perturbation to the plasma to excite various types of modes and study their coupling with the rest of the system. The contributions of the antenna and plasma perturbed fields are considered separately and, optionally, the plasma response can be linearized by neglecting the perturbed plasma field contribution in the particle orbits. As a proof of principle, we apply stationary E B flows and measure their impact on the linear growth rate of ion temperature gradient (ITG) -driven instability. We distinguish zero and finite shearing rate radial profiles. In the latter case, we show that sheared E x B flows can destabilize ITG modes. Future applications include the study of time-dependent zonal structures coupling with electrostatic instabilities, the radial propagation of avalanche-like structures, or the excitation of Alfvén eigenmodes.