Energy partition in collisionless counter-streaming plasmas

The counter-streaming of plasma outflows drive magnetic field amplification, plasma heating, and high-energy particles acceleration in numerous astrophysical environments, from supernova remnant shocks to active galactic nuclei jets. Understanding how energy is redistributed between the electromagnetic field and the different plasma species in these collisionless systems is a fundamental long-standing problem. In this work we use fully-kinetic 3D simulations to investigate energy partition in weakly magnetized counter-propagating plasmas. The simulations reveal the importance of the non-linear coupling between the ion Weibel and the resonant drift-kink instabilities in mediating the flows thermalization. The 3D kinking of the Weibel current filaments causes a rapid increase of the filaments radius by merging, and generates magnetic amplification via a dynamo-type mechanism. During this process, the electrons can extract a significant fraction of the ion drift kinetic energy by magnetic pumping. The final temperature ratio Te/Ti and energy partition obtained are functions of the mass ratio, with up to a few percent of the ion kinetic energy being converted into magnetic field perturbations and electron heating.