ABSTRACT
The plasma state is often referred to as the fourth state of matter [1]. It is characterized by the presence of free positive (and sometimes also negative) ions and negatively charged electrons in a neutral background gas. The charge carrier concentration can vary from 105 m −3 in a dilute interstellar plasma to 1028 m −3 in a dense stellar plasma. Most matter in the universe is found in the plasma state. Examples include the sun and other stars, interstellar matter and the terrestrial ionosphere. Naturally occurring plasmas on Earth are rare and include lightning and flames. Plasmas generated for technological applications include, among others, welding arcs, plasma torches, high-pressure lamps and the ignition spark in an internal combustion engine. In the efforts to solve the energy problem on Earth, magnetically confined plasmas in nuclear fusion reactors are one of several choices to achieve the extreme conditions under which nuclear fusion might occur [1]. This chapter focuses primarily on gaseous plasmas at pressures ranging from a fraction of an atmosphere to at most atmospheric pressure. Plasmas are generally created by supplying a sufficient amount of energy to a volume containing a neutral gas, so that free electrons and ions are generated from the atoms and molecules in the gas. The energy may be supplied in the form of electrical energy, heat, ultraviolet radiation or particle beams. In technical plasma devices, the input energy is generally supplied as electrical energy that causes the ignition of a gas discharge. Chemical reactions among the different neutral and ionic atomic and molecular species occur in this gaseous atmosphere (volume processes) and also at the surfaces that surround the plasma (surface or wall processes). The study and the technical utilization of these chemical reactions is referred to as plasma chemistry [2-7].
