Magnetogenesis via the canonical battery effect

We show by analyzing the time evolution of canonical vorticity that spontaneous generation of magnetic fields within an initially unmagnetized, vorticity-free plasma must be achieved through the canonical battery effect. This effect generalizes well-known magnetogenesis mechanisms across different regimes such as the Biermann battery in the isotropic regime and the Weibel instability in the kinetic regime, the latter of which is further verified by particle-in-cell simulations. Using the canonical battery term, a general prediction of any configuration of the pressure tensor that allows for magnetogenesis can be established. One such configuration—a two-dimensionally localized pressure anisotropy—that does not correspond to either of the mechanisms is derived and numerically verified. The advantage of using this term in magnetogenesis analyses is discussed.