Toroidal Alfven eigenmodes with nonlinear gyrokinetic and fluid hybrid models

Alfven eigenmodes may be important in driving fast particle transport in magnetic confinement fusion devices, with potentially deleterious results. To explain and predict this behaviour, numerical simulations are necessary. In order to predict transport, modes must be simulated through to their nonlinear saturated state. In this work, the first simulations of non-linear wave-particle interaction between an energetic particle population and a Toroidal Alfven Eigenmode are performed in which fluctuations responding self-consistently to modification of the fast particle profile are calculated with gyrokinetic treatment of all plasma species. Results from two such gyrokinetic codes are compared with new results from non-perturbative and perturbative fluidgyrokinetic hybrid codes. There is a power-law relationship between the saturated magnetic perturbation amplitude, delta B/B-0, and the linear mode growth rate, gamma(L). All models show a transition from a higher to a lower exponent regime with increasing gamma(L). Measured values of the higher exponent from different codes fall in a range between 1.45 and 1.79, while the lower exponent falls in a range between 0.47 and 0.79. There is a consistent difference of 1.0 between the higher and lower exponents independent of the model. The absolute level of saturated delta B/B-0 is determined by the damping rate. In the fluid-gyrokinetic hybrid codes, an ad- hoc damping is applied, while in the gyrokinetic case the measured damping is consistent with the estimated rate of physical electron Landau damping.