Abstract

In vacuum physics, the major concerns are substances in gas phase and their behavior at vacuum conditions. Vacuum is the state of gases and vapors whose values are below atmospheric pressure, as discussed and defined later. In vacuum physics, however, we have to study not only gaseous states, but also other forms of matter because they affect the residual vacuum atmosphere. In addition, the mutual interactions between different forms of matter do not allow the absolute abstraction of the gaseous substances. Therefore, prior to the deeper analysis of gases under vacuum condition, all forms of matter are briefly described.