A study of toroidicity and ellipticity inducedAlfvén eigenmodes (TAEs and EAEs) that are excited before and after sawtoothcrashes during ion cyclotron range of frequency (ICRF) heating in JT-60U is presented.From the TAEs that are observed before sawteeth and that reside inside the q = 1surface an upper limit has been set for q in the plasma centre at the timeof the crash. After the sawtooth crash, EAEs that reside at the q = 1 surfaceare often observed. In a number of discharges the start of the EAE activityis delayed to up to 150 ms after the crash. In some cases TAE activity wasobserved between the sawtooth crash and the onset of the EAE activity. TheseTAEs could be modelled successfully only when it was assumed that the centralsafety factor (q0) rises above unity after the giant sawtooth crash.The appearance of the TAE activity immediately after the giant sawtooth crashis a strong indication that the fast particle drive remains in the plasmacentre. This is consistent with theoretical estimates for the confinement ofdeeply trapped ICRF ions. The delayed appearance of the EAEs is also consistent with thedisappearance of the q = 1 surface from the plasma at the giant sawtoothcrash. The only way to obtain agreement between the experimentally measured EAEfrequencies and the NOVA-K simulations is to assume that the q = 1 surfacereappears in the plasma at the start of the EAE activity. The delayedappearance of the EAE activity seems to be correlated with the electrontemperature just before the crash.
Sawtooth control using electron cyclotron current drive in the presence of energetic particles in high performance ASDEX Upgrade plasmas