Large amplitude ion-acoustic solitary waves in a warm negative ion plasma with superthermal electrons: The fast mode revisited

Large amplitude ion-acoustic fast mode solitary waves in a negative ion plasma with kappa electrons are revisited, using the Sagdeev pseudopotential approach. As is well known, this plasma supports the propagation of both compressive and rarefactive solitons, and there exist a range of parameter values in which the two types of structures coexist. This is confirmed by the present study, which is based on well-established soliton existence domains. After investigating the existence of solitons in terms of the lower and upper Mach number limits for broader regions in the parameter space, we have found that as a result of the ion thermal effects, the range of the allowed Mach numbers is reduced and only small amplitude rarefactive solitons propagate in this plasma, an effect that is enhanced by the superthermal behavior of the electrons. Rearranging our analytical work so as to get a two-positive ion plasma, our results show the presence of stopbands in the soliton existence domains, as reported by Nsengiyumva et al. [Phys. Plasmas 21, 102301 (2014)], despite the use of different normalization and different parameter space. This suggests that the observed stopbands are a real phenomenon, which needs consideration when studying plasma waves.