The ion acoustic instability during collisionless two-ion-species plasma expansion

A hypothesis of the electrostatic field for the expansion of a plasma composed of two ion species into a vacuum is proposed. The solution for expansion is derived analytically and verified by numerical simulations. The expansion region is predicted to exhibit a constant velocity difference between the two ion components, which could result in ion beam instability and, thus, an increase in ion temperature. The instability, which occurs in CH plasma, is also verified theoretically and examined by particle-in-cell simulations.