Alfven Eigenmodes Properties and Dynamics in the TJ-II Stellarator

Full text: Energetic ion driven Alfven Eigenmodes (AEs) in the NBI-heated plasma at the TJ-II stellarator were studied by Heavy Ion Beam Probing (HIBP) in the core, and by Langmuir and Mirnov probes (MP) at the edge. HIBP observed the locally (∼ 1 cm) resolved AE at radii -0.8 <ρ< 0.9. The set of AE branches with low poloidal numbers (m< 8) was detected by MP. AEs on the density, electric potential and poloidal magnetic field oscillations were detected by HIBP at frequencies 50 kHz <ω(AE) < 300 kHz with a high resolution (< 5 kHz). The MP and HIBP data have a high coherency for specific branches of AE. When the density rises, AE frequency is decreasing, but the cross-phase between the density and potential oscillations remains permanent. Comparison with computational MHD mode predictions indicates that some of the more prominent frequency branches can be identified with radially extended HAE (helical), GAE (global) and TAE (toroidal) modes. Example of such identification for observed AE with frequency 177 kHz is given. The mode with couplings between m, n = (1, -1) and (3, -5) components was classified as HAE. The turbulent AE driven flux was small in comparison with the broadband turbulent flux for the same frequency domain. (author)