http://arxiv.org/abs/2301.06033
Small-scale fluctuating magnetic fields of order $n$G to $\mu$G are observed in supernova shocks and galaxy clusters, where amplifications of the field are likely caused by the Biermann battery mechanism. However, these fields cannot be amplified further without the turbulent dynamo, which generates magnetic energy through the stretch-twist-fold (STF) mechanism. Thus, we present here novel three-dimensional magnetohydrodynamic (MHD) simulations of a laser-driven shock propagating into a stratified, multiphase medium, to investigate the post-shock turbulent magnetic field amplification via the turbulent dynamo. The configuration used here is currently being tested in the shock tunnel at the National Ignition Facility (NIF). In order to probe the statistical properties of the post-shock turbulent region, we use $384 \times 512 \times 384$ tracer trajectories to track its evolution through the Lagrangian framework, thus providing a high-fidelity analysis of the shocked medium. Our simulations indicate that the growth of the magnetic field, which accompanies the near-Saffman power-law kinetic energy decay ($E_{\textrm{kin}} \propto t^{-1.15})$ in the absence of turbulence driving, exhibits slightly different characteristics as compared to periodic box simulations. Seemingly no distinct phases exist in its evolution, because the shock passage and time to observe the magnetic field amplification during the turbulence decay are very short, with only $\sim0.3$ of a turbulent turnover time. Yet, the growth rates are still consistent with those expected for compressive (curl-free) turbulence driving in subsonic, compressible turbulence. Phenomenological understanding of the dynamics of the magnetic and velocity fields are also elucidated via Lagrangian frequency spectra, which are consistent with the expected inertial range scalings via the Eulerian-Lagrangian bridge.
J. Hew and C. Federrath
Wed, 18 Jan 23
107/133
Comments: 14 pages, 19 figures. Submitted to MNRAS. Comments are welcome