Stochastic behaviour in presence of an electrostatic wave due to the crossing of multiple cyclotron resonances in an inhomogeneous magnetic field

The criterion for the occurence of stochastic behaviour of particle trajectories in the field of an electrostatic wave is obtained taking into account the longitudinal inhomogeneity of the ambient magnetic field. The origin of the stochasticity is explained. The optimum conditions for particle heating are obtained at a wave amplitude below the threshold of stochasticity in a homogeneous plasma.