Perturbative and non-perturbative modes in START and MAST

Neutral beam heated plasmas in spherical tokamaks exhibit a wide variety of Alfven eigenmodes (AEs) and so provide important information on the physics of highly energetic ions and their associated instabilities, which is one of the most important issues for the fusion programme. Measurements of the internal AE mode amplitude provide input for simulations of potential ion and alpha particle losses due to energetic particle driven modes in ITER and other next step devices. New observations and results of the analysis of perturbative and non-perturbative modes on MAST and START spherical tokamaks are presented in the paper together with prospects for diagnostic applications. Comparison of the mode amplitude measured with Mirnov coils with that estimated from the frequency sweep speed of chirping modes shows good correlation for all EP driven modes analysed, both perturbative and non-perturbative.