Making Plasmas

We learnt, in chapter one, how the universe originated from a soup consisting of electrons, positrons, and radiation and how the matter came into being and became almost electric charge neutral as the universe cooled. The reionization of matter commenced with the formation of stars spewing out ultraviolet radiation. Ionization of matter by radiation is the most common process in nature. The stars in galaxies gave rise to the highly ionized state of the interstellar medium. The ultraviolet radiation of the sun created the ionosphere of the Earth. Matter can also be ionized, in addition, by heating, compression, and passing an electric current through it. Let us learn about these mechanisms in the following sections.

Plasma Formation by Photoionization

A gas can be ionized by illuminating it with electromagnetic radiation of the appropriate frequency ν. This process is known as photoionization. It is also called the photoelectric effect generally in the context of emission of electrons from metal surfaces that are subjected to radiation of the right frequency. It is essentially a quantum mechanical effect that confirmed the quantum nature of the electromagnetic radiation and for which Albert Einstein was awarded the Nobel prize in 1921. The ionization process can be described as the release of electrons from the atoms of a gas. The molecules of a gas dissociate into atoms much before the ionization process occurs. A singly charged ion results when a single electron is emitted from a neutral atom.