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Ann. Geophys., 25, 557-568, 2007
www.ann-geophys.net/25/557/2007/
© European Geosciences Union 2007
Beam effect on electromagnetic ion-cyclotron waves with general loss – cone distribution function in an anisotropic plasma-particle aspect analysis
G. Ahirwar, P. Varma, and M. S. Tiwari
Department of Physics & Electronics, Dr. H. S. Gour University, Sagar, (M.P.) 470003, India
Abstract. The effect of upgoing ion beam and temperature anisotropy on the dispersion
relation, growth rate, parallel and perpendicular resonant energies, and
marginal instability of the electromagnetic ion cyclotron (EMIC) waves, with
general loss-cone distribution function, in a low β homogeneous
plasma, is discussed by investigating the trajectories of the charged
particles. The whole plasma is considered to consist of resonant and
non-resonant particles. The resonant particles participate in an energy
exchange with the waves, whereas the non-resonant particles support the
oscillatory motion of the waves. The effects of the steepness of the loss-cone
distribution, ion beam velocity, with thermal anisotropy on resonant energy
transferred, and the growth rate of the EMIC waves are discussed. It is found
that the effect of the upgoing ion beam is to reduce the energy of transversely
heated ions, whereas the thermal anisotropy acts as a source of free energy
for the EMIC waves and enhances the growth rate. It is found that the EMIC
wave emissions occur by extracting energy of perpendicularly heated ions in
the presence of an upflowing ion beam and a steep loss-cone distribution function
in the anisotropic magnetoplasma. The effect of the steepness of the loss-cone is
also to enhance the growth rate of the EMIC waves. The results are interpreted
for EMIC emissions in the auroral acceleration region.
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