Destabilization of Strongly Magnetized Jets

Simulations of strongly magnetized slab jets in uniform expansion in an external atmosphere have been performed and compared to an unmagnetized expanding slab jet. A strongly magnetized super-Alfvénic jet with lower magnetosonic Mach number but with sonic Mach number equal to a purely fluid jet destabilizes in a much shorter distance than the fluid jet. A strongly magnetized sub-Alfvénic jet remains stable until the jet becomes super-Alfvénic. At the Alfvén point the jet is submagnetosonic and destabilizes abruptly. Results from a spatial stability analysis of the magnetized slab jet are compared to the numerical simulations. In general, predictions based on the theory are borne out by the simulations. In particular, the stability properties of a super-Alfvénic jet are confirmed to be a function of the magnetosonic Mach number, and the theoretical prediction of rapid jet destabilization at the Alfvén point transition between sub-Alfvénic and super-Alfvénic flow is confirmed. However, nonlinear effects associated with decreasing the jet density relative to the external density and with increasing the magnetic field strength can increase the destabilization-decollimation length and reduce decollimation, respectively. Some of the implications for three-dimensional jets are considered.