Magnetic field growth in weakly ionized astrophysical plasmas

Abstract: The small-scale turbulent dynamo is an important process contributing to the cosmic magnetization. In partially ionized astrophysical plasmas in e.g., the early Universe, cold phases of the interstellar medium, protoplanetary disks, the solar chromosphere, 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, 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. 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 the dynamo. This result has important implications for the generation of magnetic fields in the partially ionized interstellar medium and shock acceleration of Galactic cosmic rays.

Speaker: Siyao Xu, Univ. of Wisconsin at Madison