12-20 July 2017
Asia/Seoul timezone
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BEXCO - Room B(103/104/105)

[CRI008] Magnetic turbulence amplification through nonresonant Bell’s instability in shock precursors of young supernova remnants


  • Oleh KOBZAR

Primary authors

  • Oleh KOBZAR (Institute of Nuclear Physics PAS, Poland)



Young shell-type supernova remnants (SNRs) are believed to be a source of Galactic cosmic rays (CRs) with energies up to a few PeV. These particles are assumed to be energized via diffusive shock acceleration (DSA) in collisionless shock waves. Effective DSA process requires turbulent magnetic fields amplified to levels much higher than typically found in the interstellar medium. Such fields can be generated by CRs themselves through nonresonant Bell’s instability in the shock precursor. We study the Bell’s instability with very-large scale 2D fully kinetic Particle-In-Cell (PIC) simulations. In contrast to earlier simulation works that used periodic simulation boxes here for the first time we use 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.