• instabilities;
  • MHD;
  • ISM: clouds;
  • ISM: kinematics and dynamics


The Kelvin–Helmholtz instability is well known to be capable of converting well-ordered flows into more disordered, even turbulent, flows. As such it could represent a path by which the energy in, for example, bow shocks from stellar jets could be converted into turbulent energy thereby driving molecular cloud turbulence. We present the results of a suite of fully multifluid magnetohydrodynamic simulations of this instability using the hydra code. We investigate the behaviour of the instability in a Hall-dominated and an ambipolar diffusion dominated plasma as might be expected in certain regions of accretion discs and molecular clouds, respectively.

We find that, while the linear growth rates of the instability are unaffected by multifluid effects, the non-linear behaviour is remarkably different with ambipolar diffusion removing large quantities of magnetic energy while the Hall effect, if strong enough, introduces a dynamo effect which leads to continuing strong growth of the magnetic field well into the non-linear regime and a lack of true saturation of the instability.