Alfven eigenmode stabillty and fast particle transport in JET

摘要

A hybrid magnetohydrodynamic-gyrokinetic model based on a Lagrangian formalism for the particle motion was developed for the stability analysis of global Alfven eigenmodes (AE) in the presence of energetic ions. A weak turbulence description was applied to the evolution of the unstable AE amplitudes and alpha particle redistribution and loss. It is found that finite orbit effects of very energetic ions reduce the instability drive by the alpha particles in JET, where the most unstable AE's have toroidal mode numbers between n = 4 to n = 10. Non-linear simulations show that wave saturation amplitude, proportional to the linear growth rate square, is delta B/B < 10~(-4) for the most un-stable JET scenarios. Therefore, no significant alpha particle redistribution is expected. Detailed simulations of JET DT experiments shows that the most unstable conditions occur in power switich off experiments. In this scenario the strong damping provided by the bulk and beam ions decreases faster than the drive provided by the slowing down alpha particles.