Saturation level of ion Weibel instability and isotropization length-scale in electron–ion Weibel-mediated shocks

Abstract

ABSTRACT Ion Weibel instability is considered to be the dominant physics for the dissipation in high-Mach number astrophysical shocks such as supernova remnant shocks and gamma-ray burst shocks. We study the instability dependence on various parameters using theory and particle-in-cell simulations. We demonstrate that electron physics determines the saturation level of the Weibel-generated magnetic field, even though the instability is driven by the ions. We discuss the application to astrophysical and laboratory laser experiment environments to clarify the roles of the ion Weibel instability. We develop a model for the isotropization length-scale in Weibel-mediated shocks and compare its value to other characteristic length-scales of each system. We find that electron heating to near equipartition is crucial for the formation of ultrarelativistic Weibel-mediated shocks. On the other hand, our results imply that non-relativistic shocks in the typical interstellar medium are not purely mediated by the Weibel instability.