Stochastic Ion Heating by a Perpendicularly Propagating Electrostatic Wave

The motion of an ion in the presence of a constant magnetic field and a perpendicularly propagating electrostatic wave with frequency several times the ion cyclotron frequency is shown to become stochastic for fields satisfying E / B₀>1 / 4(Ω / ω)^{1 / 3}(ω / k). This stochasticity condition is independent of how close ω is to a cyclotron harmonic. Applications of current interest in supplementary heating of plasmas with rf power near the lower-hybrid frequency are suggested.