ABSTRACT
Plasmas make up more than 99% of visible matter in the universe. They consist of positive ions, electrons or negative ions, and neutral particles. Plasma is regarded as the fourth state of matter. When a solid (the first state of matter) is heated, the particles in it get sufficient energy to loosen their structure and thus melt to form a liquid (the second state of matter). After obtaining sufficient energy, the particles in a liquid escape from it and vaporize to gas (the third state of matter). Subsequently, when a significant amount of energy is applied to the gas through mechanisms such as an electric discharge, the electrons that escape from atoms or molecules not only allow ions to move more freely but also produce more electrons and ions via collisions after accelerating rapidly in an electric field. Eventually, the higher number of electrons and ions change the electrical property of the gas, which thus becomes ionized gas or plasma (Figure 1.1).
