Complex eikonal methods applied to geodesic acoustic mode dynamics

Techniques developed in the domain of optical theory are applied to investigate the behavior of Geodesic Acoustic Modes (GAMs). In this context, we show that this approach represents a powerful basis for the description of many characteristics of radial propagation and spreading of GAMs. The most attractive feature of these techniques is represented by their universality and intuitive applicability. We present and apply two different complex-eikonal methods able to describe the spreading of GAMs in terms of local plane waves. The methods are “inhomogeneous wave tracking” and “paraxial WKB” theory. We demonstrate their applicability and efficacy to the GAM dynamics problem by means of a comparison with gyrokinetic simulations.Techniques developed in the domain of optical theory are applied to investigate the behavior of Geodesic Acoustic Modes (GAMs). In this context, we show that this approach represents a powerful basis for the description of many characteristics of radial propagation and spreading of GAMs. The most attractive feature of these techniques is represented by their universality and intuitive applicability. We present and apply two different complex-eikonal methods able to describe the spreading of GAMs in terms of local plane waves. The methods are “inhomogeneous wave tracking” and “paraxial WKB” theory. We demonstrate their applicability and efficacy to the GAM dynamics problem by means of a comparison with gyrokinetic simulations.