On radiative damping of reversed shear Alfvén eigenmode in tokamak plasmas

We have derived analytically, via variational-WKB analyses, the radiative damping rate of reversed shear Alfvén eigenmode (RSAE) in tokamak plasmas. Here, the radiative damping occurs via “tunnelling” coupling to radially propagating convectively damped kinetic Alfvén waves. Our analytical result is found to be consistent with one expression conjectured based on simulations and, thereby, resolves ambiguities among the various conjectured expressions. Furthermore, it is found that the radiative damping rate of toroidal Alfvén eigenmode (TAE) could, typically, be significantly larger than that of RSAEs, implying, thus, energetic particles should excite RSAEs more readily than TAEs in tokamak fusion plasmas.