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The linear properties of the geodesic acoustic modes (GAM) in tokamaks areinvestigated by means of the comparison of analytical theory and gyrokineticnumerical simulations. The dependence on the value of the safety factor,finite-orbit-width of the ions in relation to the radial mode width,magnetic-flux-surface shaping, and electron/ion mass ratio are considered.Nonuniformities in the plasma profiles (such as density, temperature, or safetyfactor), electro-magnetic effects, collisions and presence of minority speciesare neglected. Also, only linear simulations are considered, focusing on thelocal dynamics. We use three different gyrokinetic codes: the lagrangian(particle-in-cell) code ORB5, the eulerian code GENE and semi-lagrangian codeGYSELA. One of the main aims of this paper is to provide a detailed comparisonof the numerical results and analytical theory, in the regimes where this ispossible. This helps understanding better the behavior of the linear GAMdynamics in these different regimes, the behavior of the codes, which iscrucial in the view of a future work where more physics is present, and theregimes of validity of each specific analytical dispersion relation.

Cross-code gyrokinetic verification and benchmark on the linear collisionless dynamics of the geodesic acoustic mode