Hybrid simulations of collapse of Alfvénic wave packets

Nonlinear dynamics, of large-amplitude circularly polarized Alfvénic wave packets, is investigated using a one-dimensional hybrid model. Kinetic effects such as finite-Larmor radius and nonlinear Landau damping, which become significant for plasmas with β∼ 1. are appropriately accounted for in these high-resolution hybrid simulations. Spatio-temporal evolution, of the left-hand polarized (LHP) wave packets, shows that they collapse because of the decreasing dispersive effects. However, singularities are arrested by the wave-particle interactions. At some critical time t_e, which depends on the plasma β and the initial amplitude of the wave packet, we observe a turning point. At this turning point, the polarization changes from LHP to RHP (right-hand polarized). The wave packet then starts broadening due to increasing dispersion associated with the RHP. Implications of collapse of the magnetic structures are briefly discussed.