An analysis of the experimental conditions under which low-frequency (70–150 kHz) Alfvén eigenmodes (AE) are excited during the monster sawtooth in Joint European Torus [F. Romanelli et al., Proceedings of the 22nd IAEA Fusion Energy Conference, Geneva, Switzerland, 2008] is presented for the specific case of a discharge with ion cyclotron heating (5 MW). Using a simplified AE model for modes excited at the Alfvén wave continuum maximum with geodesic corrections taken into account, the temporal evolution of the value of the safety factor q0 at the magnetic axis is determined. We describe a new scheme to determine the time variation of q0 that works under conditions in which other standard diagnostics, such as the motional Stark effect do not give reliable results such as during a monster sawtooth.
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Elfimov et al. (2010) studied this question.