Modulational instability of ion acoustic waves in a magnetised plasma

The modulational instability of ion acoustic waves is studied in the presence of d.c. magnetic field. It is found that while the instability sets in for wave numbers exceeding 1.47 ksub(D) in the absence of the magnetic field, the switching-on of the magnetic field can generate instability earlier. In general, two regions emerge where the waves can become modulationally unstable. The relative sizes of these regions change as the magnetic field and the angle of propagation are varied. (author)