Arbitrary amplitude ion-acoustic solitary excitations in the presence of excess superthermal electrons

• Published in: Physics of plasmas 2009-06, Vol.16 (6)
• Main Authors: Saini, N. S., Kourakis, I., Hellberg, M. A.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; DISTRIBUTION FUNCTIONS; ELECTRONS; EXCITATION; ION ACOUSTIC WAVES; IONS; MACH NUMBER; PLASMA; SOLITONS
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/1.3143036

Velocity distribution functions with an excess of superthermal particles are commonly observed in space plasmas, and are effectively modeled by a kappa distribution. They are also found in some laboratory experiments. In this paper we obtain existence conditions for and some characteristics of ion-acoustic solitary waves in a plasma composed of cold ions and κ -distributed electrons, where κ > 3 / 2 represents the spectral index. As is the case for the usual Maxwell–Boltzmann electrons, only positive potential solitons are found, and, as expected, in the limit of large κ one recovers the usual range of possible soliton Mach numbers, viz., 1 < M < 1.58 . For lower values of κ , modeling the presence of a greater superthermal component, the range of accessible Mach numbers is reduced. It is found that the amplitude of the largest possible solitons that may be generated in a given plasma (corresponding to the highest allowed Mach number for the given plasma composition) falls off with decreasing κ , i.e., an increasing superthermal component. On the other hand, at fixed Mach number, both soliton amplitude and profile steepness increase as κ is decreased. These changes are seen to be important particularly for κ < 4 , i.e., when the electrons have a “hard” spectrum.