title: dc-Magnetic-field generation in unmagnetized shear flows.
abstract: The generation of dc magnetic fields in unmagnetized electron-ion shear flows is shown to be associated to either initial thermal effects or the onset of electron-scale shear instabilities, in particular the cold Kelvin-Helmholtz instability. This mechanism, intrinsic to shear gradients on the electron scale, is described through a kinetic model that predicts the growth and the saturation of the dc field in both scenarios. The theoretical results are confirmed by multidimensional particle-in-cell simulations, demonstrating the formation of long-lived magnetic fields (t~100's ω(pi)(-1)) along the full longitudinal extent of the shear layer, with a typical transverse width of √[γ(0)]c/ω(pe), reaching magnitudes eB(dc)/m(e)cω(pe)~β(0)√[γ(0)] for an initial sharp shear. The case of an initial smooth shear is also discussed.
authors.affiliation: GoLP/Instituto de Plasmas e Fusão Nuclear-Laboratório Associado, Instituto Superior Técnico, 1049-001 Lisboa, Portugal. thomas.grismayer@ist.utl.pt
authors.forename: T
authors.initials: T
authors.lastname: Grismayer
authors.forename: E P
authors.initials: EP
authors.lastname: Alves
authors.forename: R A
authors.initials: RA
authors.lastname: Fonseca
authors.forename: L O
authors.initials: LO
authors.lastname: Silva