Magnetic field evolution in counter streaming electron-positron plasma beams having different drift velocities

The beam instability or filamentation instability compelled by two homogeneous and counter approaching beams composed of an equal number of electrons and positrons is simulated by the particle-in-cell (PIC) method. Both the beams have the same temperature, with a number of cases with different drift velocities. The simulation box is orthogonal to the beam approaching direction. The magnetic field spontaneously increases and reorganizes the charged particles in the domain, resulting in the distributions of particles such that the positrons in one beam and electrons in the other beam have the same distributions. The magnetically trapped particles cause oscillations in the magnetic field, which lead to fluctuating magnetic pressure gradient force (MPGF). The simulation results show that there is no electric field produced by the magnetic field pressure gradient till the sufficient strength of the magnetic field is generated. The filaments, due to filamentation instability, are confined in an elongated shape instead of a circular shape because of the one-dimensional approach. Later, the particle density statistical variations are found to cause a charge separation. During the initial phase of quasi-linear growth of filamentation instability, there is no adequate signature of the electric fields.