The Inability of Ambipolar Diffusion to Set the Inner Scale of Density and Energy in Molecular Clouds


Ambipolar diffusion (AD), or ion-neutral drift, occurs in lightly ionized plasmas where ions are strongly coupled to magnetic fields while neutrals are only weakly collisionally coupled to the ions. Understanding turbulent AD is essential to several areas of star formation, as molecular clouds and protoplanetary disks are both turbulent and partially ionized. We present first results gleaned from 3-D numerical studies of driven turbulence using a version of ZEUS-MP modified to include a semi-implicit, two-fluid treatment of AD. Previous studies of turbulent ambipolar diffusion have been limited to analytic or 2-D numerical studies. Our simulations suggest that AD does not truncate the turbulent cascade of magnetic energy: it does not act as a classical diffusion. Furthermore, it does not appear to set an internal scale for density perturbations, making it an unlikely candidate for creating a characteristic scale for the mass spectrum.

American Astronomical Society Meeting Abstracts