Simulações computacionais da influência da não girotropia dos elétrons na propagação de ondas paralelas em plasmas espaciais

Abstract

Intense emission of radio waves are observed in the interplanetary medium, normally as a result of the interaction of charged particles in the solar wind with the interplanetary electric and magnetic fields. Among the possible mechanisms that affect the electrostatic and electromagnetic emission in interplanetary medium are the characteristics of the velocity distribution function. When the particle distribution is symmetrical in the perpendicular plane to the magnetic field lines the distribution is called gyrotropic, whose distribution function depend only on the parallel and perpendicular particle velocities. If the symmetry around the field lines is broken, the distribution function also depend on the gyrophase angle and is called nongyrotropic. Important examples of nongyrotropic distributions are found in many processes in space plasmas, such as in collisionless shock waves and in the interaction of the solar wind with comets. Recent studies suggest that nongyrotropy may be related to the instability generation and growth waves in plasmas. In this work we studied the influence of a nongyrotropic electron beam in a gyrotropic background plasma via particle-in-cell (PIC) simulations, which are performed using the modified code KEMPO 1D. The results shows that the nongyrotropy plays an important role in the emission of electromagnetic waves with parallel propagation. This emission is represented by a plasma mode propagation only observed when the distribution is nongyrotropic, which was called NG mode (NonGyrotropic). It was also observed that the gyrophase angle is related to the emission intensity and the pitch angle is related to the wave speed propagation. Also, we found that the nongyrotropy can, in fact, introduce a free energy into the system, represented by the increase of the magnetic energy when compared to the gyrotropic case.