Plasma is composed of electrons, ions, atoms and neutral molecules. It is a physical concept. In nature, it is in the atmosphere about 60 ~ 100 kilometers above the ground. Under the radiation of ultraviolet rays in sunlight and other cosmic rays, the molecules in the air are ionized and become electronsIons. These electrons and ions, neutral molecules, atoms are mixed together. Therefore, the atmosphere at this altitude is also called the ionosphere. We know that ordinary gases are composed of molecules, while plasma is composed of a large number of ions, electrons, neutral molecules and atoms; The force between ordinary molecules is a short-range force, and the force between plasma particles is a long-range force, which is a Coulomb force; The most common gas has no obvious interaction between molecules at room temperature, and its motion can be described according to the law of molecular motion, while plasma is different. Although it is the same as ordinary gas and does not show electricity externally, its motion will cause current, which will produce a magnetic field, and the local accumulation of positive and negative charges caused by motion, The accumulated charge will generate an electric field. Due to the action of electric field force and force Lorentz force, the electric field and magnetic field generated by the plasma will affect the movement of charged ions. The Lorentz force can make the plasma constrained by the magnetic field and do the cyclotron movement under the action of Lorentz force. Generally, matter has three states, namely, solid, liquid and gas. According to the different conductivity, solid sub conductors, semiconductors and insulators; The liquid conducts electricity through the positive and negative ions therein; Gas is generally non-conductive. Plasma generally has great conductivity, which is completely different from ordinary gas in electromagnetic properties. Therefore, some people call plasma the fourth state of matter.