Weibel Mechanism of Magnetic-Field Generation in the Process of Expansion of a Collisionless-Plasma Bunch with Hot Electrons

Abstract

We perform qualitative physical analysis and particle-in-cell two-dimensional numerical simulation of the Weibel mechanism of magnetic-field generation due to the self-consistent formation of filaments of the hot-electron current with anisotropic velocity distribution, which occurs in the process of decay of a strong discontinuity in a collisionless plasma with a great difference in the number density and temperature of electrons. Anisotropy of the electron distribution is mainly stipulated by their quasiadiabatic expansion and a significant decrease in the thermal velocities in the normal direction to the front of the formed electrostatic shock wave at a weak decrease in the thermal velocities in the transverse directions. A strong magnetic field is formed in a layer with the maximum anisotropy under the front, covers the entire region of the expanding plasma, and, at the nonlinear evolution stage, acquires quasiperiodic modulation along the normal to the front, which correlates with the modulation of the electron anisotropy degree. The considered scenario of development of the Weibel instability is of interest for analysis of experiments with femtosecond laser plasma and interpretation of such phenomena in the case of a decay of strong discontinuities in a nonequilibrium space plasma.