| OT10 · Effects on Ion Cyclotron Emission of the Orbit Topology Changes from the Wave-Particle Interactions
T. Hellsten, K. Holmström, T. Johnson, T. Bergkvist, and M. Laxåback
Alfvén Laboratory, Association VR-Euratom, Sweden
Abstract: It is known that non-relaxed distribution functions can give rise to excitation of magnetosonic waves by ion cyclotron interactions when the distribution function increases with respect to the perpendicular velocity. We have found that in a toroidal plasma also collisional relaxed distribution functions of central peaked high-energy ions can destabilise magnetosonic eigenmodes by ion cyclotron interactions, due to the change in localisation of the orbits establishing inverted distribution functions with respect to energy along the characteristics describing the cyclotron interactions. This can take place by interactions with barely co-passing and marginally trapped high-energy ions at the plasma boundary. The interactions are enhanced by tangential interactions, which can also prevent the interactions to reach the stable part of the characteristics where they interact with more deeply trapped orbits.
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