In a tokamak plasma, toroidicity induced Alfvén eigenmodes (TAEs) are excited by and alter the orbits of resonant fast ions with the character of these modes defined by both thermal and supra-thermal fast ion populations. To explore the stability of TAEs in ASDEX Upgrade, the effects of magnetic shear and density on TAEs, the decay and growth rate of individual TAEs and fast ion drive rates have been studied. In particular, the mode structure of TAEs, the dependence of the ICRF power-density threshold on the toroidal mode number n, the effect of magnetic shear at the plasma edge on low-n TAEs (n ⩽ 2) and a comparison of measured decay rates of TAEs with predictions made by the LIGKA code are discussed. In addition, fast ion pressure profiles generated by the ICRF power deposition codes PION and TORIC and the equilibrium code CLISTE have been examined to see if they lead to a sufficient fast ion drive rate for the observed TAEs, and to benchmark a formula for volume averaged βfast using measurable quantities in ICRH-only plasmas.
Alfvén eigenmode stability and fast ion loss in DIII-D and ITER reversed magnetic shear plasmas