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

X Mushinzimana,F Nsengiyumva

doi:10.1063/1.5127199

X Mushinzimana, F Nsengiyumva

Open Access

https://doi.org/10.1063/1.5127199

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Journal: AIP Advances	Publication Date: Jun 1, 2020
Citations: 7	License type: cc-by

Affiliation: University of Rwanda, INES-Ruhengeri

Abstract

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.

Highlights

Negative ion plasmas have been observed in numerous physical systems.[1–15] These observations have motivated several studies of solitary waves propagating in a negative ion plasma.[16–27] From these studies, with further knowledge from related studies,[28–42] it is well known that a negative ion plasma with finite temperature of at least one of the two ion species supports the propagation of two wave modes with different phase speeds
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
The results presented in the upper left panel show that compressive solitons occur at low values of the negative-to-positive ion density ratio, whereas rarefactive solitons occur at high values of α

Summary

INTRODUCTION

Negative ion plasmas have been observed in numerous physical systems.[1–15] These observations have motivated several studies of solitary waves propagating in a negative ion plasma.[16–27] From these studies, with further knowledge from related studies,[28–42] it is well known that a negative ion plasma with finite temperature of at least one of the two ion species supports the propagation of two wave modes with different phase speeds. The significant gaps in the work of Kumar and Mishra[27] in conjunction with the open question associated with stopbands in the soliton existence domains, as mentioned above, motivate us to reconsider the study of large amplitude fast and slow mode solitary waves supported by a negative ion plasma with superthermal electrons. Such plasmas are numerous in space environments.[1,2,55–58] While a comprehensive study of the slow mode will be reported elsewhere, here we report on the fast mode.

PLASMA DENSITIES AND SAGDEEV PSEUDOPOTENTIAL

The minimum and maximum Mach numbers

STOPBANDS IN SOLITON EXISTENCE DOMAINS

SUMMARY AND CONCLUSIONS