One‐dimensional hybrid simulations of planetary ion pickup: Effects of variable plasma and pickup conditions

Abstract

The one‐dimensional hybrid simulation technique using massless fluid electrons and kinetic ions has been shown to successfully reproduce the growth of electromagnetic plasma waves generated by ion populations with a ring velocity distributions (T⊥ > T∥). Such populations are found at Jupiter and Saturn, where newborn ions are picked up into corotating plasma flows that are nearly perpendicular to the background magnetic field. In previous simulation work, which focused on pickup ion generated waves near Io, we considered all the pickup ions to be present in the simulation at the start of the run (initial value). For a more realistic treatment of ion pickup, we now modify the simulation to include continuous ion injection over time. There are several important differences between the initial value and the injection simulations, namely that when ions are injected, the generated waves eventually reach a quasi‐steady level, which is proportional to the injection rate. The results indicate that less than 20% of the pickup ion energy resides in the waves at any given time. Indeed, for certain conditions, the ion cyclotron waves observed at Io may represent only a few percent of the initial pickup ion energy. We carry out simulations varying the plasma and pickup conditions, including the background plasma density and temperature, pickup rate, and multiple pickup ion species to see how the wave amplitudes are affected. We also briefly look at the oblique propagation of the waves to estimate group velocities.