One‐dimensional hybrid simulations of obliquely propagating ion cyclotron waves: Application to ion pickup at Io

[1] In Jupiter and Saturn's magnetospheres, ionization of neutrals produced by the satellites and rings results in populations of newborn pickup ions with T ⊥ > T, which are unstable to the generation of electromagnetic ion cyclotron waves. Linear dispersion analysis of this anisotropy instability finds maximum growth at parallel propagation, with decreasing growth rates at wave vector angles, θ, oblique to the ambient magnetic field, B 0 . Observed S + and SO + ion cyclotron waves near the Jovian moon, Io, propagate at a variety of angles within 60° of B 0 . Using one-dimensional hybrid simulation, we study the properties of the obliquely propagating waves in the lo plasma torus environment for θ≤ 60°. We find that the maximum growth rate decreases with increasing angle from B 0 , as predicted by linear theory, with the growth rate at θ = 60° equal to ∼70% the growth rate at parallel propagation. At the oblique angles, cyclotron harmonics of S + and SO + are excited and grow larger with θ. At 0 = 60°, the fundamental mode saturation amplitude is roughly four times that of the first harmonic. However, we do not expect to see these harmonics in the lo torus because thermalized O + and S + damps their growth. We also find that SO + cyclotron waves may dominate over S + if n SO +/n SO + 2 > 2.5 - 3.