Plasma Fundamentals

Abstract

Plasma physics has a reputation of being very difficult to understand, and this is probably true when compared with fluid dynamics or electromagnetics in dielectric media. The reason is twofold. First, being a charged fluid, a plasma’s particles interact with one another not just by collisions, but by long-range electric and magnetic fields. This is more complicated than treating the charged particles one at a time, such as in an electron beam, because the fields are modified by the plasma itself , and plasma particles can move to shield one another from imposed electric fields. Second, most plasmas are too tenuous and hot to be considered continuous fluids, such as water (≈3 × 10²² cm⁻³) or air (≈3 × 10¹⁹ cm⁻³). With particle densities of 10⁹⁻¹³ cm⁻³ , plasmas do not always behave like continuous fluids. The discrete nature of the ions and electrons makes a difference; this kind of detail is treated in the kinetic theory of plasmas. Fortunately , with a few exceptions, the fluid theory of plasmas is all that is required to understand the behavior of low-temperature industrial plasmas, and the quantum mechanical effects of semiconducting solids also do not come into play.