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P: Fachverband Plasmaphysik

P 7: Theorie/Modellierung I

P 7.9: Talk

Tuesday, March 31, 2009, 15:15–15:30, HS Biochemie (groß)

Radial propagation of geodesic acoustic modes — •Robert Hager and Klaus Hallatschek — Max-Planck-Institut für Plasmaphysik, Garching, Deutschland

The GAM group velocity is estimated from the radial free energy flux and the total free energy applying gyrokinetic and two-fluid theory. This method is much more robust than analytical approaches and can be generalized to include additional physics, e.g. magnetic geometry. The results have been verified with the gyrokinetic code GYRO, the two-fluid code NLET, and analytical calculations. GAMs travel either radially inward or outward depending on the ratio of ion to electron temperature and their gradients. Generally, GAMs propagate much slower than the turbulent motion. Thus, it is unlikely that GAMs are triggered far from the point of their detection, which is crucial to bear in mind concerning the windows of GAM activity observed experimentally and the difference between linear and experimental GAM frequencies. Resonances with the drift velocity restrict GAMs to low radial wave numbers k ∼ ρ_i, which causes Landau damping and the mentioned low propagation velocity. Fast GAMs could arise in the absence of resonances or if the GAM energy is nonlinearly advected by turbulence.