Princeton University Astroplasmas Seminar

Abstract: The self-confinement picture of cosmic-ray transport often hinges on the linear theory of growth and damping of magnetic perturbations. Especially the balance between the growth of the resonant streaming instability and non-linear Landau damping plays a crucial role in many astrophysical contexts. Yet, different expressions for the damping rate exist, which lead to widely different physical interpretations. Using hybrid-PIC simulations of the resonant streaming instability, I present a comprehensive assessment of non-linear Landau damping. Our results identify the correct damping rate, scaling with the power in magnetic fields on larger scales. Furthermore, we find an inverse cascade that produces fields on large, non-resonant scales. Applying our findings to self-confinement in the Galaxy, we show that pre-existing turbulence of Alfv\'enic nature at large scales severely affects the damping of waves produced by low-energy cosmic rays; depending on its amplitude, cosmic rays in our Galaxy are either self-confined at all energies or not at all.