Electron Acceleration by Plasma Waves in the Io Flux Tube

Details Electron Acceleration by Plasma Waves in the Io Flux Tube Electron Acceleration by Plasma Waves in the Io Flux Tube

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p12a0493c&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #P12A-0493

Physics

0654 Plasmas, 2451 Particle Acceleration, 2704 Auroral Phenomena (2407), 2716 Energetic Particles, Precipitating, 2772 Plasma Waves And Instabilities

Scientific paper

Io's interaction with the jovian magnetosphere generates auroral and radio emissions. The underlying electron acceleration process is not well understood and only few observations exist to constrain the theoretical models. The Galileo spacecraft made a number of low altitudes passes near Io and the plasma wave/particle instruments have collected new information. The source of energy for the electron acceleration is in all likelihood supplied from the Alfvén wings that stretch out from both poles of Io into the two Jovian hemispheres. Here we will present observations that help understand how the electromagnetic energy in the Alfvén wings is transformed into particle acceleration. In particular, intense electromagnetic waves at frequencies up to several times the local proton gyrofrequency have been observed while Galileo was passing over the south and north poles of Io (flybys I25 and I31, respectively). Hot and warm parallel electron beams have been observed during the I0 and I27 flybys, respectively. For some technical reason no particles instrument was on during I25. At the time that this abstract is written data are not yet available from the I32 south polar pass but observations similar to those obtained during the I25 and I31 flybys are expected. We suggest the following three-steps acceleration process: (1) Due to the strongly inhomogeneous conductivity of Io's ionosphere, the currents flowing along the Alfvén wings are distributed inside the whole Alfvén tube and not only on its surface. (2) As the plasma density of the Io torus decreases with increasing latitude, the currents of the Alfvén wings become strongly unstable for "high-frequency/small scale" electromagnetic waves. (3) The current driven "high-frequency/small-scale" waves generated in the direction of Jupiter which are not reflected at the boundary of the Io torus, are able to accelerate efficiently magnetospheric electrons by Landau resonance, up to the required energies and flux. The observation of electron beams during the flyby I31 (and I32) would provide a critical test for this interpretation.

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