Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsm31b0326m&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SM31B-0326
Physics
2704 Auroral Phenomena (2407), 2753 Numerical Modeling, 7829 Kinetic Waves And Instabilities, 7845 Particle Acceleration, 7867 Wave/Particle Interactions (2483, 6984)
Scientific paper
Ion beams drifting upwards along magnetic field lines are frequently observed in the auroral acceleration cavity. They mainly consist of H+ and O+ originating from the ionosphere and are believed to have been accelerated upwards by the same potential. Due to the mass difference, H+ and O+ form two distinct beams drifting at different speeds, typically in the hundreds of km/s, whereby two-stream instabilities might develop. We present 1D and 2D PIC simulations of the interaction between the H+ and O+ beams. Our simulation model describes an open system where protons and oxygen ions are constantly injected at the boundary, emulating thus the particle influx from the bottom of the cavity. In addition, the model includes a population of plasma sheet protons and strongly magnetized electrons. There are two regimes according to the magnitude of the relative drift between H+ and O+. For small relative drifts, the unstable waves are of the acoustic type and propagate parallel to the magnetic field. They can trap H+ and O+, leading to phase-space vortices. For large relative drifts, the parallel acoustic waves remain stable. Instead, oblique oxygen cyclotron waves grow unstable leading to the formation of conics in the O+ distribution. The border speed between the two regimes depends upon the electron temperature and the ion composition. In both cases, energy is transferred from the protons to the oxygens. We discuss these transfers in connection with the FAST measurements of species dependent energy in the ion beams [Moebius et al., 1998].
Muschietti L.
Roth Ilan
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