ANOMALOUS ION MIXING WITHIN A KELVIN-HELMHOLTZ VORTEX IN A COLLISIONLESS PLASMA

Anomalously fast ion mixing is observed in a hybrid code simulation (particle ions and a massless electron fluid) of the Kelvin-Helmholtz instability in a collisionless plasma. While the traditional view predicts that the ion mixing occurs on a time scale longer than the roll-up time T(V) of the Kelvin-Helmholtz vortex by a factor of (velocity shear scale length)/(ion Larmor radius), the simulation results show that the mixing occurs within a time scale comparable to T(V). We show that this fast mixing is due to the scattering of ions by unsteady electromagnetic fields.