Nonlocal interaction of fast magnetosonic waves with alpha-particles in tokamaks

Effects of nonlocal coupling between the fusion alpha particle current density and the fast magnetosonic wave electric field on cyclotron absorption of these waves by alphas are investigated. Such a nonlocality being due to the alpha particle motion along magnetic field lines is very strong because the alpha particle collisions with electrons and bulk ions are very rare and the collisional decorrelation of the wave-particle phase is weak. An alpha particle performs dozens of revolutions around the torus before the dephasing occurs. The expressions for the alpha particle current density and RF power absorbed by alphas in a tokamak are obtained and analysed. They account for the collisional decorrelation, finite Larmor radius and the magnetic drift of a phase.