Basic Concepts of Plasma Generation

Abstract

As described in Part I of this book dealing with fundamental concepts of the plasma state, passing an electric current through a gas gives rise to the formation of plasmas. Since gases at room temperature are excellent insulators, a sufficient number of charge carriers must be generated to make the gas electrically conducting. This process is known as electrical breakdown, and there are a number of ways by which this may be accomplished. The application of a strong electric field between a pair of electrodes can lead to a breakdown of the originally nonconducting gas leading to the establishment of a conducting path. The passage of the electrical current through the gap between the electrodes leads in turn to an array of phenomena known as gaseous discharges. These are the most common, but not the only means for producing a plasma. For certain applications, plasmas are produced by electrode-less radio frequency (RF), capacitive or inductively coupled discharges, microwaves, shock waves, lasers, or high-energy particle beams. Finally, heating gases (vapors) in a high-temperature furnace may also lead to the generation of plasma. Because of inherent temperature limitations, this method is restricted to metal vapors with low ionization potentials.