Abstract
The nonlinear interaction of a single particle with an electromagnetic wave at a cyclotron harmonic is studied. Emphasis is on the large wavelength limit (fast wave). The cases of a coherent wave particle interaction and of an incoherent interaction are treated. In both cases explicit expressions for the temporal evolution of the particle perpendicular energy distribution function are presented. The heating is efficient at the first two harmonics. The formation of a suprathermic tail is predicted at the second and higher harmonics.