Spectroscopic determination of kinetic parameters for frequency sweeping Alfvén eigenmodes

Abstract

A method for analyzing fundamental kinetic plasma parameters, such as linear drive and external damping rate, based on experimental observations of chirping Alfvén eigenmodes, is presented. The method, which relies on new semiempirical laws for nonlinear chirping characteristics, consists of fitting procedures between the so-called Berk–Breizman model and the experiment in a quasiperiodic chirping regime. This approach is applied to the toroidicity induced Alfvén eigenmode (TAE) on JT-60 Upgrade (JT-60U) [N. Oyama et al., Nucl. Fusion 49, 104007 (2009)], which yields an estimation of the kinetic parameters and suggests the existence of TAEs far from marginal stability. Two collision models are considered, and it is shown that dynamical friction and velocity-space diffusion are essential to reproduce nonlinear features observed in experiments. The results are validated by recovering measured growth and decay of perturbation amplitude and by estimating collision frequencies from experimental equilibrium data.