Self-similar neutral-plasma isothermal expansion into a vacuum

The self-similar solutions are obtained for isothermal expansions of neutral plasmas into a vacuum. The classic solution given by Mora [ Phys. Fluids 22 , 12 ( 1979 )] corresponds to a special case of our solution. Some special solutions have been pointed out by Gurevich [ Phys. Rev. Lett. 42 , 769 ( 1979 )] and observed by a lot of experiments. The formulation of ion velocity with respect to the acceleration time is proposed for the general solution, and the numerical result can be obtained easily. The electric field and ion velocity at the ion front have been achieved.