Non-linear evolution of the current filamentation instability on ion time scales

The current filamentation instability (CFI) is a plasma microinstability believed to be responsible for magnetic field generation in many astrophysical environments, such as gamma-ray bursts, supernova remnants and active galactic nuclei. The instability is also relevant in laboratory settings, where it is triggered in the presence of counterstreaming plasma flows and produces intense fields of the order of 10⁶ Gauss.

In this work, we investigate the onset and long-term development of the CFI in counterstreaming electron-ion flows. In order to explore the plasma dynamics on large spatial and long temporal scales, we take full advantage of the semi-implicit algorithm implemented in the energy-conserving Particle-In-Cell code ECsim (1). Our numerical results indicate that the magnetic field driven by the instability survives for hundreds of ion plasma periods. The instability produces magnetic field filaments which evolve from sub-electron scales to beyond the ion inertial length at a rate t ^(0.6-1), depending on the flow velocity and the plasma anisotropy. The ion anisotropy, which remains substantial during the whole duration of our simulations, sustains the coalescence process of magnetic filaments.

(1) G. Lapenta et al., J. Plasma Phys. 83, 705830205 (2017).