Kinetic Alfvén eigenmodes at ASDEX Upgrade

On the way to a comprehensive understanding of the properties of a burning plasma the physics of super-thermal particles due to external heating and fusion reactions plays a key role. In particular, Alfvén and Alfvén-acoustic type instabilities are predicted to strongly interact with the fast particle population and to contribute critically to the radial redistribution of the energetic ions. This paper focuses on the comparison of the kinetic dispersion relation for BAEs/GAMs (Zonca et al 1996 Plasma Phys. Control. Fusion 38 2011 ) with numerical results obtained by the gyrokinetic eigenvalue code LIGKA (Lauber et al 2007 J. Comput. Phys. 226/1 447–65) and experimental findings at ASDEX Upgrade. It is shown that thermal ions with a finite perpendicular energy (circulating and trapped) modify the dispersion relation significantly for low frequencies. The resulting frequency downshift together with shaping and diamagnetic effects is crucial to explain the mode frequency as measured at ASDEX Upgrade stressing the importance of a kinetic description for frequencies comparable to the thermal ion transit frequency. In the second part the BAE-frequency behaviour during a sawtooth cycle is investigated and the possibility of an accurate q -profile determination via kinetic Alfvén spectroscopy is discussed.