Principle of charge-mass invariance of motion and possibility of steady-state solitary electrostatic waves in a nearly symmetric plasma

A quasi-neutral nearly symmetric plasma (i.e., a plasma in which particles with opposite charge polarity have identical charge-to-mass ratios but different masses) is considered. The possibility of the existence of steady-state solitary electrostatic waves in such a plasma is proved rigorously. This is associated with violation of the charge-mass invariance principle for a particle moving in a nearly symmetric plasma, which is in turn due to forces (1/n(+/-))partial derivative P+/-/partial derivative x of a nonelectromagnetic origin.