Experiments on accelerating NBI-produced deuterium (D) beam ions from their injection energy of ~110keV up to the MeV energy range with 3rd harmonic ICRH were performed on the Joint European Torus. A renewed set of nuclear diagnostics was used for analysing fast D ions during sawtooth stabilization, monster sawtooth crashes, and during excitation of Alfvén eigenmodes (AEs) residing inside the q = 1 radius. The measurements and modeling of the fast ions with the nonlinear HAGIS code show that monster sawtooth crashes are strongly facilitated by the AE-induced re-distribution of the fast D ions from inside the q = 1 radius to the plasma edge.