Oleh

Collisionless shocks of supernova remnants (SNR) are thought to be the acceleration sites of high-energy cosmic rays (CRs). Efficient particle production in the diffusive shock acceleration process requires turbulent amplified magnetic fields in the shock’s precursor. Here we report results of new particle-in-cell (PIC) simulation studies of the nonresonant cosmic-ray-current-driven instability that operates upstream of young SNR shocks and may be responsible for magnetic-field amplification, plasma heating, and hydrodynamical turbulence. Earlier PIC simulations of this instability used computational boxes with periodic boundary conditions. Our current study for the first time applies a realistic setup with open boundaries in the CR drift direction, which accounts for mass conservation in decelerating flows. In this way both the temporal and the spatial development of the instability can be investigated. The results of our large-scale high-resolution PIC experiments demonstrate magnetic-field amplification as expected on the grounds of our earlier studies with periodic simulation boxes. The effects of backreaction on CRs that slow down the initial ambient plasma-CR relative drift velocity, limit further growth of the turbulence and lead to its saturation are also re-confirmed. We discuss a detailed spatio-temporal structure of the shock precursor, the evolution of CR distribution, and the microphysics of the saturation processes.