Radial localization of toroidicity-induced Alfvén eigenmodes.

Linear gyrokinetic simulation of fusion plasmas finds a radial localization of the toroidal Alfvén eigenmodes (TAEs) due to the nonperturbative energetic particle (EP) contribution. The EP-driven TAE has a radial mode width much smaller than that predicted by the magnetohydrodynamic theory. The TAE radial position stays around the strongest EP pressure gradients when the EP profile evolves. The nonperturbative EP contribution is also the main cause for the breaking of the radial symmetry of the ballooning mode structure and for the dependence of the TAE frequency on the toroidal mode number. These phenomena are beyond the picture of the conventional magnetohydrodynamic theory.