Turbulent dynamo in a weakly ionized medium. (arXiv:1901.02893v1 [astro-ph.GA])

Turbulent dynamo in a weakly ionized medium. (arXiv:1901.02893v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Xu_S/0/1/0/all/0/1">Siyao Xu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Garain_S/0/1/0/all/0/1">Sudip K. Garain</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Balsara_D/0/1/0/all/0/1">Dinshaw S. Balsara</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lazarian_A/0/1/0/all/0/1">A. Lazarian</a>

The small-scale turbulent dynamo is an important process contributing to the
cosmic magnetization. In partially ionized astrophysical plasmas, the dynamo
growth of magnetic energy strongly depends on the coupling state between ions
and neutrals and the ion-neutral collisional damping effect. A new damping
stage of turbulent dynamo in a weakly ionized medium was theoretically
predicted by Xu & Lazarian (2016). By carrying out a 3D two-fluid dynamo
simulation, here we for the first time numerically confirmed the physical
conditions and the linear-in-time growth of magnetic field strength of the
damping stage of dynamo. The dynamo-amplified magnetic field has a
characteristic length as the damping scale, which increases with time and can
reach the injection scale of turbulence after around eight largest
eddy-turnover times given sufficiently low ionization fraction and weak initial
magnetic field. Due to the weak coupling between ions and neutrals, most
turbulent energy carried by neutrals cannot be converted to the magnetic
energy, resulting in a relatively weak magnetic field at the end of dynamo.
This result has important implications for the growth of magnetic fields in the
partially ionized interstellar medium and shock acceleration of Galactic cosmic
rays.

The small-scale turbulent dynamo is an important process contributing to the
cosmic magnetization. In partially ionized astrophysical plasmas, the dynamo
growth of magnetic energy strongly depends on the coupling state between ions
and neutrals and the ion-neutral collisional damping effect. A new damping
stage of turbulent dynamo in a weakly ionized medium was theoretically
predicted by Xu & Lazarian (2016). By carrying out a 3D two-fluid dynamo
simulation, here we for the first time numerically confirmed the physical
conditions and the linear-in-time growth of magnetic field strength of the
damping stage of dynamo. The dynamo-amplified magnetic field has a
characteristic length as the damping scale, which increases with time and can
reach the injection scale of turbulence after around eight largest
eddy-turnover times given sufficiently low ionization fraction and weak initial
magnetic field. Due to the weak coupling between ions and neutrals, most
turbulent energy carried by neutrals cannot be converted to the magnetic
energy, resulting in a relatively weak magnetic field at the end of dynamo.
This result has important implications for the growth of magnetic fields in the
partially ionized interstellar medium and shock acceleration of Galactic cosmic
rays.

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