A spatial stability analysis of the Kelvin-Helmholtz instability of a magnetized slab jet is performed and compared to results of numerical simulations. Provided the jet is super-Alfvénic the dispersion relation describing the propagation and growth of Fourier components of some initial perturbation admits the same type of solutions as for a purely fluid jet. A growing fundamental sinusoidal mode at long wavelengths can be identified with an Alfvén wave-like disturbance of the jet. Growing internal reflection modes at shorter wave-lengths can be identified with fast magnetosonic waves reflecting off the jet's boundaries. Supermagnetosonic resonances comparable to the supersonic resonances of a strictly fluid jet exist where resonant wavelengths and growth lengths scale with the magnetosonic Mach number. The resonances disappear when the jet becomes transmagnetosonic but still super-Alfvénic and only the fundamental sinusoidal mode remains. The fundamental mode is stabilized when the jet is sub-Alfvénic, but for jet velocities slightly less than the slow magnetosonic speed reflection modes can grow even on a sub-Alfvénic jet. This behavior is qualitatively similar to the stability properties of a magnetized cylindrical jet. While the simulations reveal significant non-linear effects associated with increasing magnetic tension, the jet is not stabilized by nonlinear effects, and the linear analysis provides a reasonable description of the spatial stability properties of the jet. The results suggest that a jet which is initially sub-Alfvénic and stable to disruption will be doomed to disruption at the Alfvén point if it becomes super-Alfvénic as a result of jet expansion.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science
- Galaxies : jets