On the generation of an electron beam by Io

The interaction between Io and the Jovian magnetosphere generates an Alfvénic disturbance which propagates away from Io. The effect of finite electron inertia on this Alfvén wave, which was not considered in previous models, is shown to produce a parallel electric field but to have no other, significant effects on the Io‐generated waves. The propagation of this disturbance is described analytically, treating it as the result of an impulsive disturbance rather than a continuous wave, and the solution does not require magnetic field strength to remain constant, as previous, similar models did. The wave is reflected by changing density and magnetic field strength as it propagates out of the Io plasma torus. Essentially none of power from the Io interaction reaches Jupiter as an Alfvén wave. However, the wave's parallel electric fields produce an electron beam, through a process of repeated Fermi acceleration. This beam has an estimated power of 0.5 to 1.5×1011 W and the average particle energy is of order 75 keV. This beam is consistent with many observations of Io‐related phenomena at high latitudes.