The kink instability in magnetized jets

Current-driven instabilities of cold cylindrical jets are studied by means of a global linear analysis in an ideal MHD framework. The magnetic pitch, determines the stability behaviour of the kink. For MHD jets which are likely to have dominantly azimuthal fields, the properties of the fastest growing kink instability become nearly independent of the details of the pitch profile and depend essentially on its value on the axis, P0. The most unstable mode grows with an e-folding time and possesses an axial wavelength in the rest frame of the jet. The magnetic structure of jets with dominantly azimuthal fields will be modified by the fast growing kink instability until most of the current is dissipated. An analysis of the eigenfunction shows that the kink is an internal mode which does not cause a significant sidewise displacement of the jet surface. This suggests that this instability does not disrupt the flow.