Multiple eigenmodes of geodesic acoustic mode in collisionless plasmas

Abstract

We report a series of eigenmodes of the geodesic acoustic mode (GAM), which includes the standard GAM, a branch of low-frequency mode, and a series of ion sound wave-like modes. The case of Ti≫Te is investigated, and eigenfrequencies of these modes are obtained analytically from a linear gyrokinetic model in collisionless plasmas with a rigid constant electrostatic potential around a magnetic surface.