Scattering efficiency in the non-saturated non-resonant streaming instability

Determine whether the non-saturated non-resonant (Bell) streaming instability provides cosmic-ray scattering efficiency comparable to the saturated regime in supernova remnant shock precursors, and quantify the consequences for diffusion coefficients and maximum particle energies under the shock conditions considered.

Background

The paper discusses that many studies assume steady-state or saturation of the non-resonant streaming instability to justify Bohm-like diffusion, but time-dependent calculations indicate the instability may not reach saturation in young supernova remnants. If the instability does not saturate, the efficiency of particle scattering—and thus acceleration to PeV energies—could differ substantially from saturated expectations.

Numerical and theoretical work has shown Bohm-like diffusion in saturated regimes for certain setups, but the authors point out that the scattering effectiveness prior to saturation has not been established. This uncertainty impacts predictions of the maximum achievable energies and the timing of turbulence growth cycles in the shock precursor.