Modeling of chirping toroidal Alfvén eigenmodes in NSTX

Modulation of modeamplitude and frequency of TAE modes, observed experimentally and referred to as chirping, is investigated using a guiding centercode and a δf formalism. Chirpingis observed as the development in time of Fourier sidebandsthat move above and below the nominal modefrequency. Subsequent doubling of the sidebandsis also sometimes observed. Equilibria with conventional positive magnetic shear are used, as well as NSTX reversed shear cases. The onset of chirpingcan be triggered by a sudden increase in modedamping, as can occur by the modecontacting the continuum.Modulation of modeamplitude and frequency of TAE modes, observed experimentally and referred to as chirping, is investigated using a guiding centercode and a δf formalism. Chirpingis observed as the development in time of Fourier sidebandsthat move above and below the nominal modefrequency. Subsequent doubling of the sidebandsis also sometimes observed. Equilibria with conventional positive magnetic shear are used, as well as NSTX reversed shear cases. The onset of chirpingcan be triggered by a sudden increase in modedamping, as can occur by the modecontacting the continuum.