Interpretation of electromagnetic modes in the sub-TAE frequency range in JET plasmas with elevated monotonic q-profiles

Recent JET deuterium experiments with an advanced tokamak scenario using internal transport barrier (ITB) have been performed to clearly observe destabilized toroidicity-induced Alfvén eigenmodes (TAEs) by fast ions; interestingly, these also exhibit unstable electromagnetic (EM) perturbations in the sub-TAE frequency range. We identify such EM be beta-induced ion temperature gradient (BTG) and not nor acoustic eigenmodes, which are often high-beta plasmas high-power neutral beam injection (NBI). The BTG modes most due high thermal related ITB, compared electron (high Ti/Te), a beta regime. mode experimental characteristics match analytical theory, i.e., location vicinity of rational magnetic surface low shear, scaling diamagnetic ( ωi*), coupling among drift waves. perform linear gyrokinetic simulations validated plasma profiles equilibrium, find kinetically driven ions similar as modes.