RADIATIVE DAMPING OF TOROIDAL ALFVÉN EIGENMODE IN LOW-SHEAR PLASMAS
Instabilities of Alfvén eigenmodes (AEs) are of significant concern because they can enhance the cross-field transport of alpha particles beyond the neoclassical level in magnetic fusion plasmas. The threshold value of alpha-particle pressure for exciting AEs depends critically on the damping rate of AEs. The damping mechanisms include kinetic damping due to interactions with thermal particles, continuum damping due to Alfvén continuum crossing, and radiative damping due to emitting kinetic Alfvén waves (KAWs). The radiative damping is substantial and can even prevail in high-temperature burning plasmas [1]. We revisit the radiative damping analytic theory for TAE in low-shear plasmas, when TAE has its eigenfrequency at the bottom of TAE-gap and has both poloidal harmonics of the same sign (even TAE). In contrast to earlier papers, we provide the damping calculations in real space rather than Fourier space. This approach is straightforward technically and more enlightening from a physics standpoint thus allowing an easier benchmark of the numerical tools computing the radiative damping.