Relativistic effects in the interaction of electrons with a slow extraordinary wave

The peculiarities of resonant interaction between slow extraordinary (SE) waves and relativistic electrons have been studied. General equations of motion of relativistic electrons in the field of SE wave and a uniform ambient magnetic field are derived. Conditions of applicability of the isolated resonance approximation are elucidated. In this approximation, the equations of motion are reduced to one-dimensional set of equations, similar to that describing resonant wave–particle interaction for Langmuir waves in a homogeneous isotropic plasma. This similarity permits to calculate the linear growth rate of SE wave propagating at an arbitrary angle to the external magnetic field. Calculations performed are apt for all frequencies and wave normal angles of SE waves, except for the case when k∥c/ω=1 that requires special consideration.