Nonlinear electron-cyclotron power absorption

The process of nonlinear power absorption of a localized electron-cyclotron wave is investigated on the basis of the analysis of the electron motion in the wave field, by means of a relativistic Hamiltonian formalism under adiabatic conditions, for a wave frequency close to a cyclotron harmonic, and in perpendicular propagation. The computation of the absorbed power density relies on the investigation of the electron energy transitions due to a single crossing of the radiation beam. The absorbed power profiles are explicitly given for the ordinary mode at the first cyclotron harmonic and the extraordinary mode at the second cyclotron harmonic, and are shown to be in good agreement with those obtained by numerical simulation codes. The behavior of the absorbed power versus the frequency and the amplitude of the wave is interpreted by means of the main features of the nonlinear interaction process in momentum space.