TY - JOUR
T1 - Energetics of turbulence generated by chiral MHD dynamos
AU - Schober, J.
AU - Brandenburg, A.
AU - Rogachevskii, I.
AU - Kleeorin, N.
N1 - Funding Information:
This project has received funding from the European Union’s Horizon 2020 research and innovation programme as ‘EPFL Fellow’ co-funded by the Marie Skłodowska-Curie Action [grant number 665667]. Support through the National Science Foundation Astrophysics and Astronomy Grant Program [grant number1615100], the Research Council of Norway [FRINATEK grant 231444], and the European Research Council [grant number 694896] are gratefully acknowledged.
Funding Information:
J.S. thanks the organisers of the “2nd Conference on Natural Dynamos” for the interesting and fruitful conference held in Valtice. We are grateful to the three anonymous referees who helped improving this work with their suggestions. I.R. acknowledges the hospitality of NORDITA, the University of Colorado, the Kavli Institute for Theoretical Physics in Santa Barbara and the École Polytechnique Fédérale de Lausanne. We thank for support by the École polytechnique fédérale de Lausanne, Nordita, and the University of Colorado through the George Ellery Hale visiting faculty appointment. Simulations presented in this work have been performed with computing resources provided by the Swedish National Allocations Committee at the Center for Parallel Computers at the Royal Institute of Technology in Stockholm.
Funding Information:
This project has received funding from the European Union's Horizon 2020 research and innovation programme as ?EPFL Fellow? co-funded by the Marie Sk?odowska-Curie Action [grant number 665667]. Support through the National Science Foundation Astrophysics and Astronomy Grant Program [grant number1615100], the Research Council of Norway [FRINATEK grant 231444], and the European Research Council [grant number 694896] are gratefully acknowledged. J.S. thanks the organisers of the ?2nd Conference on Natural Dynamos? for the interesting and fruitful conference held in Valtice. We are grateful to the three anonymous referees who helped improving this work with their suggestions. I.R. acknowledges the hospitality of NORDITA, the University of Colorado, the Kavli Institute for Theoretical Physics in Santa Barbara and the ?cole Polytechnique F?d?rale de Lausanne. We thank for support by the ?cole polytechnique f?d?rale de Lausanne, Nordita, and the University of Colorado through the George Ellery Hale visiting faculty appointment. Simulations presented in this work have been performed with computing resources provided by the Swedish National Allocations Committee at the Center for Parallel Computers at the Royal Institute of Technology in Stockholm.
Publisher Copyright:
© 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group.
PY - 2019/3/4
Y1 - 2019/3/4
N2 - An asymmetry in the number density of left- and right-handed fermions is known to give rise to a new term in the induction equation that can result in a dynamo instability. At high temperatures, when a chiral asymmetry can survive for long enough, this chiral dynamo instability can amplify magnetic fields efficiently, which in turn drive turbulence via the Lorentz force. While it has been demonstrated in numerical simulations that this chiral magnetically driven turbulence exists and strongly affects the dynamics of the magnetic field, the details of this process remain unclear. The goal of this paper is to analyse the energetics of chiral magnetically driven turbulence and its effect on the generation and dynamics of the magnetic field using direct numerical simulations. We study these effects for different initial conditions, including a variation of the initial chiral chemical potential and the magnetic Prandtl number, PrM. In particular, we determine the ratio of kinetic to magnetic energy, Υ, in chiral magnetically driven turbulence. Within the parameter space explored in this study, Υ reaches a value of approximately 0.064–0.074–independently of the initial chiral asymmetry and for PrM = 1. Our simulations suggest, that Υ decreases as a power law when increasing PrM by decreasing the viscosity. While the exact scaling depends on the details of the fitting criteria and the Reynolds number regime, an approximate result of Υ(PrM)=0.1 Pr-0.4M is reported. Using the findings from our numerical simulations, we analyse the energetics of chiral magnetically driven turbulence in the early Universe.
AB - An asymmetry in the number density of left- and right-handed fermions is known to give rise to a new term in the induction equation that can result in a dynamo instability. At high temperatures, when a chiral asymmetry can survive for long enough, this chiral dynamo instability can amplify magnetic fields efficiently, which in turn drive turbulence via the Lorentz force. While it has been demonstrated in numerical simulations that this chiral magnetically driven turbulence exists and strongly affects the dynamics of the magnetic field, the details of this process remain unclear. The goal of this paper is to analyse the energetics of chiral magnetically driven turbulence and its effect on the generation and dynamics of the magnetic field using direct numerical simulations. We study these effects for different initial conditions, including a variation of the initial chiral chemical potential and the magnetic Prandtl number, PrM. In particular, we determine the ratio of kinetic to magnetic energy, Υ, in chiral magnetically driven turbulence. Within the parameter space explored in this study, Υ reaches a value of approximately 0.064–0.074–independently of the initial chiral asymmetry and for PrM = 1. Our simulations suggest, that Υ decreases as a power law when increasing PrM by decreasing the viscosity. While the exact scaling depends on the details of the fitting criteria and the Reynolds number regime, an approximate result of Υ(PrM)=0.1 Pr-0.4M is reported. Using the findings from our numerical simulations, we analyse the energetics of chiral magnetically driven turbulence in the early Universe.
KW - Relativistic magnetohydrodynamics (MHD)
KW - chiral MHD dynamos
KW - early universe
KW - turbulence
UR - http://www.scopus.com/inward/record.url?scp=85053381281&partnerID=8YFLogxK
U2 - 10.1080/03091929.2018.1515313
DO - 10.1080/03091929.2018.1515313
M3 - Article
AN - SCOPUS:85053381281
SN - 0309-1929
VL - 113
SP - 107
EP - 130
JO - Geophysical and Astrophysical Fluid Dynamics
JF - Geophysical and Astrophysical Fluid Dynamics
IS - 1-2
ER -