On the existence of ion-acoustic double layers in two-electron temperature plasmas
- Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281, B-9000 Gent, Belgium and School of Physics, University of KwaZulu-Natal, Private Bag X54001, Durban 4000 (South Africa)
Earlier Sagdeev pseudopotential treatments of ion-acoustic double layers in plasmas with two electron populations were based on a model in which both electron densities were described by isothermal Boltzmann distributions. Using a more recent fluid-dynamical approach, with polytropic equations of state indices {gamma}{sub j}, one finds analytically that no double layers can be formed for {gamma}{sub j}{>=}3/2, due to total rarefaction of the cooler electrons or infinite compression of the ions. For {gamma}{sub j}<3/2, rarefactive double layers occur, but, just below 3/2, at unrealistically small cool electron densities or large Mach numbers. As {gamma}{sub j} decreases towards 1, these constraints become less restrictive and go over smoothly to those known from Boltzmann studies. Contrary to what appears in the literature, very weak compressive double layers can also be found for Boltzmann electrons, but only for soliton conditions barely above the existence threshold; i.e., marginally super-ion-acoustic. Any slight increase in the critical Mach number destroys the possibility of having positive double layers, and, within the limits of numerical accuracy, no window could be found for {gamma}{sub j}{ne}1, where compressive double layers exist.
- OSTI ID:
- 20782729
- Journal Information:
- Physics of Plasmas, Vol. 13, Issue 4; Other Information: DOI: 10.1063/1.2187448; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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