STABILITY OF ION-ACOUSTIC CNOIDAL AND SOLITARY WAVES IN A MAGNETIZED PLASMA

The Zakharov-Kuznetsov equation describes nonlinear ion-acoustic waves in a strongly magnetized plasma and is used here to investigate the s tability of nonlinear periodic and solitary ion-acoustic waves in a st rong uniform magnetic field with respect to long wavelength plane wave perturbations in an arbitrary direction. A dispersion relation is obt ained in the form of a quadratic equation. From this it is found that there is instability when the angle between the direction of propagati on and the external magnetic field exceeds a critical value. The growt h rate is computed and attains a maximum when the said angle is pi/2. A solitary wave is always found to be unstable unless the perturbation is along the direction of propagation.