Spontaneous magnetization of collisionless plasma through the action of a shear flow
Abstract
We study in a fully kinetic framework the generation of seed magnetic fields through the Weibel instability driven in an initially unmagnetized plasma by a largescale shear force. We develop an analytical model that describes the development of thermal pressure anisotropy via phase mixing, the ensuing exponential growth of magnetic fields in the linear Weibel stage, and its saturation when the seed magnetic fields become strong enough to instigate gyromotion of particles and thereby inhibit their freestreaming. The predicted scaling dependencies of the saturated seed fields on key parameters (e.g., ratio of system scale to electron skin depth, the forcing amplitude) are confirmed by 3D and 2D particleincell simulations using an electronpositron plasma. This work demonstrates the spontaneous magnetization of a collisionless plasma through largescale motions as simple as a shear flow, and therefore has important implications for magnetogenesis in dilute astrophysical systems.
 Publication:

arXiv eprints
 Pub Date:
 October 2021
 arXiv:
 arXiv:2110.01134
 Bibcode:
 2021arXiv211001134Z
 Keywords:

 Physics  Plasma Physics;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 20 pages, 16 figures