# Introduction to Mathematical Physics/N body problem and matter description/Plasmas

A plasma\index{plasma} is a gas of ionized particle. Description of plasmas is generally much more involved than description of classical gases (or fluids). Indeed, the electromagnetic interaction plays here a fundamental role, and in a fluid description of the system (see chapter chapapproxconti), fluid equations will be coupled to the equations of the electromagnetic field (Maxwell equations). In general, also, the nature of the particle can change after collisions. Plasma state represents a large part of the "visible" matter (more than 99% of the Universe)