Introduction

Abstract

We have all learned that matter appears in three states: solid, liquid, and gaseous. But in recent years more and more attention has been directed to the properties of matter in a fourth and unique state, which we call plasma. The higher the temperature, the more freedom the constituent particles of the material experience. In solid bodies the atoms and molecules are subject to strict discipline and are constrained to rigid order. In a liquid they can move, but their freedom is limited. In a gas, molecules or atoms move freely; inside the atoms the electrons perform a harmonic dance over their orbits, according to the laws of quantum mechanics. In a plasma, however, the electrons are liberated from the atoms and acquire complete freedom of motion. With the loss of some of their electrons, atoms and molecules acquire a positive electric charge; they are then called ions. Thus, a plasma is a gas consisting of positively and negatively charged particles in such proportions that the total charge is equal to zero. Freely moving electrons can transport electric current; in other words, a plasma is a conducting gas.