Published online by Cambridge University Press: 19 January 2004
The modified Kadomtsev–Petviashvili (KP) (1970) equation, describing the long-time evolution of weakly nonlinear and weakly dispersive ion-acoustic waves in a multispecies plasma consisting of non-isothermal electrons, admits soliton solutions having a sech4 profile. The higher-order stability analysis of this soliton is made using the method developed by Allen and Rowlands [J. Plasma Phys.50, 413 (1993); 53, 63 (1995)]. Though there is stability at the order $k$, there may arise instability at the order $k^{2}$, where $k$ is the wave number of a long-wavelength plane-wave perturbation. This instability occurs when the dimensionless width of the soliton exceeds a critical value.