Stability of solitary kinetic Alfven waves and ion-acoustic waves in a nonthermal plasma

The KdV-ZK (Korteweg-de Vries-Zakharov-Kuznetsov) equations for kinetic Alf ven and ion-acoustic waves in a nonthermal magnetized plasma have been deri ved. The coefficient of the nonlinear term of this equation for an ion-acou stic wave can vanish along a curve in a two-dimensional parameter space. In this case, two coupled equations constituting a modified KdV-ZK equation d escribing nonlinear behavior of an ion-acoustic wave are derived. The solit ary wave solutions of all these equations are obtained and their stabilitie s are investigated by the Rowlands-Infeld method. It is found that the kine tic Alfven solitons are stable. The instability conditions and the maximum growth rate of the instability for ion-acoustic solitons are determined. (C ) 2000 American Institute of Physics. [S1070-664X(00)00408-0].