Ion cyclotron instability due to the thermal anisotropy of drifting ion species

Details Ion cyclotron instability due to the thermal anisotropy of drifting ion species Ion cyclotron instability due to the thermal anisotropy of drifting ion species

Jan 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003jgra..108.1050g&link_type=abstract

Journal of Geophysical Research (Space Physics), Volume 108, Issue A1, pp. SSH 14-1, CiteID 1050, DOI 10.1029/2002JA009576

Physics

Plasma Physics

3

Solar Physics, Astrophysics, And Astronomy: Chromosphere, Space Plasma Physics: Charged Particle Motion And Acceleration, Interplanetary Physics: Solar Wind Plasma, And Astronomy: Coronal Holes

Scientific paper

In a recent study of ion cyclotron waves generated by the thermal anisotropy of oxygen ions, it was shown that the heavy ion drift velocity and a large thermal anisotropy of the heavy ions can destabilize proton-cyclotron waves [Gomberoff and Valdivia, 2003]. Here this study is extended to alpha particles in order to show that a much smaller thermal anisotropy is required to trigger strong proton-cyclotron waves. It is also shown that under some conditions, the alpha particle branch of the dispersion relation becomes unstable for frequency values beyond the proton gyrofrequency. This instability occurs for very large alpha particle thermal anisotropy and very low β∥α = vth2/vA2, where vth and vA are the thermal and Alfvén velocity, respectively. The maximum growth rate of this branch of the dispersion relation occurs for drift velocities of the alpha particles larger than those that drive the maximum growth rate of the proton-cyclotron instability. Finally, it is demonstrated that the combined effect of oxygen ions and alpha particles lead to a complex unstable spectrum, and to an enhancement of the proton-cyclotron instability. This mechanism is like a cascade effect in which low-frequency ion cyclotron waves can drive unstable high-frequency ion cyclotron waves through anisotropic heating and acceleration of heavy ions. These results may be relevant to the understanding of the heating process of the fast solar wind in coronal holes.

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