Perpendicular nonlinear waves in an electron–positron–ion plasma

Waves propagating perpendicular to a magnetic field in a plasma consisting of electrons, positrons, and ions are studied theoretically and numerically. In a three component plasma, there appears a frequency domain in which the magnetosonic waves cannot propagate; thus, we have two separate modes below the electron cyclotron frequency. Their dispersion relations are discussed. Then, Korteweg–de Vries equations are derived for these modes. A solitary wave of the low-frequency mode has a soliton width 1–103 times as large as the electron skin depth and has an electric potential 1–102 times as large as that in an electron–ion plasma; both of them increase with decreasing ion density. A solitary wave of the high-frequency mode has a soliton width of the order of the electron skin depth and has negligibly small electric potential. Three-fluid simulations show that the low-frequency mode solitary pulse can emit high-frequency mode solitons, if the amplitude of the original pulse is large and the ion density is low.