Planar electron-acoustic solitary waves and double layers in a two-electron-temperature plasma with nonthermal ions

A rigorous theoretical investigation of nonlinear electron-acoustic (EA) waves in a plasma system (containing cold electrons, hot electrons obeying a Boltzmann distribution, and hot ions obeying a nonthermal distribution) is studied by the reductive perturbation method. The modified Gardner (MG) equation is derived and numerically solved. It has been found that the basic characteristics of the EA Gardner solitons (GSs), which are shown to exist for alpha around its critical value alpha (c) [where alpha is the nonthermal parameter, alpha (c) is the value of alpha corresponding to the vanishing of the nonlinear coefficient of the Korteweg-de Vries (K-dV) equation, e.g. alpha (c) a parts per thousand integral 0.31 for mu=n (h0)/n (i0)=0.5, sigma=T (h) /T (i) =10, n (h0), n (i0) are, respectively, hot electron and nonthermal ion number densities at equilibrium, T (h) (T (i) ) is the hot electron (ion) temperature], are different from those of the K-dV solitons, which do not exist for alpha around alpha (c) , and mixed K-dV solitons, which are valid around alpha similar to alpha (c) , but do not have any corresponding double layers (DLs) solution. The parametric regimes for the existence of the DLs, which are found to be associated with positive potential, are obtained. The present investigations can be observed in various space plasma environments (viz. the geomagnetic tail, the auroral regions, the cusp of the terrestrial magnetosphere, etc.).