2-D numerical simulation of the ambipolar filamentation of turbulent magnetic fields

Abstract

Magnetic fields play an important role in astrophysics and they often dominate the behavior of magnetized media. We simulate the mechanism (Tagger et al., 1995) by which turbulence in a weakly ionized plasma, as it cascades to the ambipolar scale (where the neutrals are imperfectly coupled to the ions) leads to a filamentation of the magnetic flux tubes: the turbulent velocity of the neutrals is higher in the more ionized regions, because they are better coupled to the ions. This results in a non-linear ponderomotive (< v.del v >) force driving them out of the ionized regions, so that the initial ionization inhomogeneities are strongly amplified. This effect causes the ions and magnetic field to condense and separate from the neutrals, resulting in a filamentary structure. We present the first results of a 2-D, 2-fluid (ions and neutrals) simulation, where a magnetized, weakly ionized plasma is submitted to turbulence in the ambipolar frequency range. We discuss the efficiency of this mechanism, the filamentary structure it should produce, and its relevance to the astrophysical context.