Magnetogenesis via the canonical battery effect
ORAL · Invited
Abstract
Magnetic fields are ubiquitous in the Universe, underpinning the dynamics of stars, planets, galaxies, accretion disks, neutron stars, and the intergalactic medium. These structures, composed of magnetized plasmas capable of supporting convective flows, typically exhibit large-scale magnetic fields attributed to turbulent dynamo effects. However, dynamo processes require an initial seed magnetic field, and the mechanisms generating these weak fields remain poorly understood.
In this talk, we demonstrate that the "canonical battery effect" is responsible for seed magnetogenesis. By taking the curl of the first moment of the Vlasov equation for any species, we derive an equation describing the time evolution of canonical vorticity. This equation reveals that, given an initially zero magnetic field and fluid vorticity, the only term capable of spontaneously generating magnetic fields is the canonical battery term, related to the species' pressure tensor.
We show that the canonical battery term generalizes popular magnetogenesis mechanisms. Firstly, it is shown trivially that the well-known Biermann battery is a specific case of the canonical battery for isotropic, scalar pressure. Secondly, particle-in-cell simulations demonstrate that the canonical battery also underlies the Weibel instability.
The canonical battery term enables the prediction of new pressure tensor configurations that induce spontaneous magnetogenesis. One such configuration, a 2D-localized pressure anisotropy, is shown to generate quadrupole magnetic fields which are important for various processes such as magnetic reconnection and flux rope generation. This mechanism is verified by particle-in-cell simulations. Various potential studies and extensions arising from this framework are discussed.
In this talk, we demonstrate that the "canonical battery effect" is responsible for seed magnetogenesis. By taking the curl of the first moment of the Vlasov equation for any species, we derive an equation describing the time evolution of canonical vorticity. This equation reveals that, given an initially zero magnetic field and fluid vorticity, the only term capable of spontaneously generating magnetic fields is the canonical battery term, related to the species' pressure tensor.
We show that the canonical battery term generalizes popular magnetogenesis mechanisms. Firstly, it is shown trivially that the well-known Biermann battery is a specific case of the canonical battery for isotropic, scalar pressure. Secondly, particle-in-cell simulations demonstrate that the canonical battery also underlies the Weibel instability.
The canonical battery term enables the prediction of new pressure tensor configurations that induce spontaneous magnetogenesis. One such configuration, a 2D-localized pressure anisotropy, is shown to generate quadrupole magnetic fields which are important for various processes such as magnetic reconnection and flux rope generation. This mechanism is verified by particle-in-cell simulations. Various potential studies and extensions arising from this framework are discussed.
*This work was supported by the JRG Program at the APCTP through the Science and Technology Promotion Fund and Lottery Fund of the Korean government, and by the local governments---Gyeongsangbuk-do and Pohang City. This work was also supported by the NRF of Korea under Grant No. NRF-RS-2023-00281272. The computations were conducted on the KAIROS supercomputing cluster at the Korean Institute of Fusion Energy, and on the APCTP computing server.
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Publication: M. Laishram, G. S. Yun, Y. D. Yoon, "Magnetogenesis via the canonical battery effect," under review in Physical Review Letters
Presenters
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Young Dae Yoon
- Asia Pacific Center for Theoretical Physics