Field aligned current and particle acceleration in the near-Io plasma torus

Abstract

A model of the field aligned current system in the Jovian Magnetosphere, particularly near Io-plasma torus, is developed on the basis of two important features: (i) sheared plasma flow around Io, and (ii) mass injection from the atmosphere of Io into this motion. It is shown that the mass-momentum transfer from Io can produce a large enough current along the magnetic field which can generate ion-cyclotron waves. A nonlinear mechanism which generates kinetic “Alfvèn” waves from these waves has been reexamined. It is found that the kinetic “Alfvèn” wave generated by this mechanism can produce a sufficiently large electric field along the magnetic field to accelerate particles to a few tens of keV within a fraction of the “Alfvèn” wave period. Thus, this model is capable of generating both electrostatic and electromagnetic waves associated with energetic electron beams which were observed by the Galileo space craft during its passage near Io.