Kinetic theory of acoustic wave in pair-ion plasmas

A theoretical analysis of the ion acoustic wave in pair-ion plasmas is presented using a kinetic model. It is shown that a small concentration of electrons in pair-ion plasmas can break down the quasineutrality in perturbed systems because the electron Debye length can become very large. In the limit 1⪡λDe2k2 (where λDe is the electron Debye length), the damping is reduced and hence the acoustic wave can be easily excited. The real frequency of acoustic wave can be larger than the ion plasma oscillation frequency in this case. But the decreasing number density of electrons can increase the Landau damping significantly in the limit λDe2k2⪡1. The results are discussed in comparison with the recent experimental and theoretical findings. It is pointed out that this investigation can be very useful for further research on pair-ion plasmas.