STATIONARY MHD STRUCTURES

The method of stationary phase and Lighthill's construction are used to develop the generalized Mach cones associated with MHD disturbances generated by a source moving uniformly through a magnetized plasma. In the frame of the source, the wave-number surface is obtained by Doppler shifting its counterpart in the plasma frame. This enables us to directly apply stationary phase methods to deduce the stationary MHD structures generated in the source frame. In the case of sub-fast flow across the magnetic field, these consist of two Alfven lines and two closed hollow wings associated with the slow mode whose group velocity surface reflects the complicated cross-sectional shape of these hollow wings. In super-fast flow these Alfven and slow-mode disturbances lie inside the fast-mode Mach cone. Particular attention is given to the fine structure of the slow mode. The results are relevant to the MHD disturbances created by the motion of a conducting body through a magnetized plasma, such as occurs in tethered satellite systems and the lo Jupiter interaction.