The detection of Alfvén cascades is of great importance for the development of advanced plasma scenarios with reversed magnetic shear on the JET tokamak, since they allow the determination of the minimum of the safety factor and provide valuable information on the modes that may redistribute fast ions via resonant interaction. X-mode reflectometry is particularly powerful for this diagnosis since the time-frequency evolution, the mode amplitude and the radial localization of these Alfvén eigenmodes (AEs) can be simultaneously obtained. This paper reports on the first successful localized measurements of AEs achieved with the recently upgraded X-mode reflectometry diagnostic on JET.
Identifying Alfvén eigenmodes in the early phase of advanced tokamak plasmas