Desai, RT; Cowee, MM; Wei, H; Fu, X; Gary, SP; Volwerk, M; Coates, AJ; (2017) Hybrid simulations of positively and negatively charged pickup ions and cyclotron wave generation at Europa. Journal of Geophysical Research: Space Physics , 122 (10) 10,408-10,420. 10.1002/2017JA024479.

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Abstract

In the vicinity of Europa, Galileo observed bursty Alfvén-cyclotron wave power at thegyrofrequencies of a number of species including K+,O+2,Na+, and Cl+, indicating the localized pickupof these species. Additional evidence for the presence of chlorine was the occurrence of both left-hand(LH) and right-hand (RH) polarized transverse wave power near the Cl+gyrofrequency, thought to bedue to the pickup of both Cl+and the easily formed chlorine anion, Cl−. To test this hypothesis, we useone-dimensional hybrid (kinetic ion, massless fluid electron) simulations for both positive and negativepickup ions and self-consistently reproduce the growth of both LH and RH Alfvén-cyclotron waves inagreement with linear theory. We show how the simultaneous generation of LH and RH waves can result innongyrotropic ion distributions and increased wave amplitudes, and how even trace quantities of negativepickup ions are able to generate an observable RH signal. Through comparing simulated and observed waveamplitudes, we are able to place the first constraints on the densities of Chlorine pickup ions in localizedregions at Europa.

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