Hybrid simulations of collapse of Alfvenic wave packets

Nonlinear dynamics, of large-amplitude circularly polarized Alfvenic wave p ackets, is investigated using a one-dimensional hybrid model. Kinetic effec ts such as finite-Larmor radius and nonlinear Landau damping, which become significant for plasmas with beta similar to 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 b ecause of the decreasing dispersive effects. However, singularities are arr ested by the wave-particle interactions. At some critical time t(c), which depends on the plasma beta and the initial amplitude of the wave packet, we observe a turning point. At this turning point, the polarization changes f rom LHP to RHP (right-hand polarized). The wave packet then starts broadeni ng due to increasing dispersion associated with the RHP. Implications of co llapse of the magnetic structures are briefly discussed. (C) 2000 American Institute of Physics. [S1070-664X(00)02810-X].