A theory for the formation of weak double layer

Solitary electrostatic waves with ion acoustic speed were frequently observed by satellites in the auroral acceleration region. In this paper, the nonlinear ion acoustic waves are studied in the plasma which is composed of warm electrons with the Boltzman distribution and cold ions of equal density. The characteristics of solitary-likc structure in the ion acoustic frequency range are derived with the methods of reductive perturbation and phase plane analysis. The results show that nonlinear ion acoustic waves may develop to a symmetric solitary structure which is compressive and no net potential drop when dissipation does not exist, and in the case with dissipation it may evolve to compressive solitary-like structure with asymmetric shape. produce net potential drop and form weak double layer. The above theoretical results are consistent with observations.