Nonlinear evolution of plasma instabilities in a plasma with counterstreaming ion beams

Summary form only given, as follows. Linear instabilities of counterstreaming ion beams are well known. We have studied here the nonlinear evolution of such instabilities using a 2.5-D particle-in-cell code. The instabilities lead to the generation of non-resonant zero-frequency and a resonant ion cyclotron modes. For sufficiently large counterstreaming velocities, the non-resonant mode dominates. The anomalous cyclotron resonance of this mode with the beam ions causes a strong pitch angle scattering, generating hat-shaped velocity distribution functions in the phase space perpendicular to the ambient magnetic field. The scattering can be effective in trapping the ions in a magnetic mirror.