Abstract
Galileo magnetic field data show the existence of ion cyclotron waves in the near-Io torus. These waves are generated by anisotropies in the pickup ion distributions present in the region. To zeroth order the waves grow at the sulfur dioxide gyrofrequency, are left-hand polarized and propagate along the magnetic field. A more detailed study reveals that in some regions the waves grow over a finite bandwidth, propagate at an angle to the field and are elliptically polarized. In this work we perform a kinetic dispersion analysis for parameters consistent with the Io torus and show that while the parallel propagating SO2+ cyclotron mode has the largest growth, oblique cyclotron waves can also grow with a significant rate in the multicomponent plasma near Io. We find that decreasing the sulfur dioxide pickup ion density can lead to the observed bandwidth of frequencies.