Ion-acoustic double layers and solitons in multispecies auroral beam-plasmas

Abstract

A general analysis for small amplitude ion-acoustic double layers and solitons is developed, taking into account any number of ion beams and their charges, together with cold and hot electrons. For auroral plasma parameters, the analysis predicts the excitation of fast and slow hydrogen (as well as oxygen) beam-acoustic modes, which can be either rarefactive double layers or rarefactive or compressive solitons. Variations in the temperature and beam speed of the hydrogen (oxygen) beam can lead to the conversion of modes from originally rarefactive double layers to rarefactive solitons and finally to compressive solitons. Fast and slow hydrogen beam-acoustic modes are the first to be excited. The excitation of fast and slow oxygen modes is usually possible for larger values of beam speeds or beam temperatures. The typical width and speed of the nonlinear modes are in good agreement with the observations of double layers and solitons by the S3-3 and Viking satellites.