Magnetic turbulence amplification through nonresonant Bell’s instability in shock precursors of young supernova remnants
O. Kobzar*, J. Niemiec, M. Pohl and A. Bohdan
August 16, 2017
August 03, 2018
In the present work we study the cosmic-ray-current-driven nonresonant Bell's instability operating upstream of a young supernova remnant shocks with use of a very-large scale 2D fully kinetic Particle-In-Cell simulations. In contrast to earlier simulation works that used periodic simulation boxes here for the first time we apply a new realistic setup with open boundaries in the CR drift direction, which accounts for mass conservation in decelerating flows. This setup allows us to investigate both the temporal and the spatial development of the instability. The results demonstrate magnetic-field amplification to nonlinear amplitudes, as expected on the basis of earlier studies with periodic simulation boxes. The effects of backreaction on CRs that slow down the initial ambient plasma-to-CR relative drift velocity, limit further growth of the turbulence and lead to its saturation are also re-confirmed. We discuss new features observed in the flow that provide additional field amplification through plasma compression and filamentation. We show that electromagnetic turbulence inelastically scatters CRs and strongly modifies their distribution. Spatial CR scattering in the precursor is compatible with Bohm diffusion. The turbulence also leads to the strong nonadiabatic heating of the ambient plasma. Ion distributions show supra-thermal tails resulting from stochastic scattering in the turbulent electric fields.
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