Criteria to define a pair-ion plasma and the role of electrons in   nonlinear dynamics
  A criterion to define a pure pair-ion (PI) plasma is presented. It is suggested that the lighter elements (like H and He) are more suitable to produce PI plasmas. The observation of ion acoustic wave (IAW) in recent experiments with fullerene plasmas clearly indicates the presence of electrons in the system. A set of two coupled non-linear differential equations has been obtained for PI plasma dynamics. In moving frame, it can be reduced to a form similar to Hasegawa-Mima equation but it does not contain drift wave. 
Hamid Saleem
physics.plasm-ph