Generation of Near-Equipartition Magnetic Fields in Turbulent Collisionless Plasmas

The mechanisms that generate seed magnetic fields in our Universe and that amplify them throughout cosmic time remain poorly understood. By means of fully kinetic particle-in-cell simulations of turbulent, initially unmagnetized plasmas, we study the genesis of magnetic fields via the Weibel instability and follow their dynamo growth up to near-equipartition levels. In the kinematic stage of the dynamo, we find that the rms magnetic field strength grows exponentially with rate & gamma;B <^>✓ 0.4urms=L, where L=2 & pi; is the driving scale and urms is the rms turbulent velocity. In the saturated stage, the magnetic field energy reaches about half of the turbulent kinetic energy. Here, magnetic field growth is balanced by dissipation via reconnection, as revealed by the appearance of plasmoid chains. At saturation, the integral-scale wave number of the magnetic spectrum approaches kint <^>✓ 12 & pi;=L. Our results show that turbulence-induced by, e.g., the gravitational buildup of galaxies and galaxy clusters-can magnetize collisionless plasmas with large-scale near-equipartition fields.

Automated summary

We investigate the generation and amplification of magnetic fields through the Weibel instability in turbulent plasmas using kinetic particle-in-cell simulations. We find a relationship between the magnetic field strength and the turbulent velocity, as well as the relationship between the magnetic field energy and the turbulent kinetic energy. Our results suggest that turbulence can magnetize collisionless plasmas and create large-scale near-equipartition magnetic fields in the Universe.