Abstract
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.
Highlights
Electromagnetic ion-cyclotron (EMIC) waves and the ion beam interactions take place in several space environments, as well as in laboratory plasma
The effects of the ion beam velocity (VD), thermal anisotropy defined by with different distribution indices J on the waves’ growth rate and resonant energies are shown by Figs. 1 to 6
It is observed that the effect of increasing the ion beam velocity is to enhance the growth rate that may be due to the shifting of the resonance condition
Summary
The importance of ion cyclotron waves in auroral physics lies in their ability to heat and accelerate ions, and perhaps to provide anomalous resistivity, allowing the creation of a parallel potential drop. The main feature of our study is to show the effect of an upgoing ion beam and thermal anisotropy on EMIC waves with a general loss-cone distribution function in a low β homogeneous plasma and discuss this effect by investigating the trajectories of the charged particles. The EMIC waves generated in the equatorial magnetosphere travel towards the auroral ionosphere in the converging magnetic field; it is assumed that the distribution may depart from ideally Maxwellian and allow for a general loss-cone distribution function (Duan et al, 2005; Mishra and Tiwari, 2006; Ahirwar et al, 2006). Since the steep loss-cone distribution in the presence of EMIC waves and the ion beam enhances the growth rate, the anomalous resistivity and transport resulting from this instability are likely to play a crucial role in the auroral acceleration region. Both the ion and electrons are assumed to follow the general loss-cone distribution function
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