1MHD induced Fast-Ion Losses on ASDEX Upgrade

Abstract. A detailed knowledge of the interplay between MHD instabilities and energetic particles has been gained from direct measurements of fast-ion losses (FIL). Time-resolved energy and pitch angle measurements of FIL caused by Neoclassical Tearing Modes (NTMs) and Toroidicity-induced Alfven Eigenmodes (TAEs) have been obtained using a scintillator based FIL-detector. The study of FIL due to TAEs has revealed the existence of a new core localized MHD fluctuation, the Sierpes mode. The Sierpes mode is a non-pure Alfvenic fluctuation which appears in the acoustic branch, dominating the transport of fast-ions in ICRF heated discharges. The internal structure of both, TAEs and Sierpes mode has been reconstructed by means of highly-resolved multichord soft X-ray measurements. A spatial overlapping of their eigenfunctions leads to a FIL coupling, showing the strong influence that a core-localised fast-ion driven MHD instability may have on the fast-ion transport. We have identified the FIL mechanisms due to NTMs as well as due to TAEs. Drift islands formed by fast-ions in particle phase space are responsible for the loss of NBI fast-ions due to NTMs. In ICRF heated plasmas, a resonance condition fulfilled by the characteristic trapped fast-ion orbit frequencies lead to a phase-matching between fast-ion orbit and NTM or TAE magnetic fluctuation. The banana tips of a resonant trapped fast-ion bounce radially due to an E×B-drift in the TAE-case. The NTM radial bounce of the fast-ion banana tips is caused by th