The fishbone instability in ASDEX Upgrade

In ASDEX Upgrade the excitation of the fishbone instability has been experimentally investigated. The initial frequency of the fishbone oscillation scales with the toroidal precession frequency of the fast trapped ions. A new feature, the coupling of the fishbone mode with the edge localized mode (ELM) instability during high-β discharges, is found. Fishbones occur in ASDEX Upgrade only for βfast = βtor/(1+τE /τsd) above a certain threshold. It is thus possible to calculate their destabilization regime in terms of global plasma parameters, such as plasma current, plasma density, toroidal magnetic field and central electron temperature.