Potential hill electron-acoustic solitons and double layers in plasmas with two electron species

Abstract

In the description of (high-frequency) electron-acoustic solitons in a plasma consisting of positive ions, cool electrons, and hot electrons, the dynamics of the ions plays no essential role and can be eliminated from the treatment, the ions merely providing a constant positive background. It is widely believed that in such a plasma only potential dip solitary waves can be generated. In a potential dip the cooler electrons are compressed and the hotter electrons rarefied, both being driven towards their sonic points, the cooler ones from above, the hotter ones from below. This transonic feature gives rise to the solitary wave. However, it is shown that the restriction to potential dip solitons is due to the neglect of the inertia of the hot electrons, implicitly or explicitly assumed by most authors. If hot electron inertia is retained, there exists a parameter range where potential hill solitary waves are formed, with both electron species being driven away from their sonic points. This has important consequences for the reinterpretation of several astrophysical phenomena involving two-electron plasmas.