In order to understand the effects of secondary plasma, it is important to first understand physical plasma. Here is an explanation: By definition, physical plasma is an excited gas that consists of charged atoms, molecular fragments, and excited molecules, as well as radicals. As long as the energy is sufficient, this state is maintained. However, if the energy becomes too low, the species recombine quickly into uncharged, but still reactive molecules. This state is not considered plasma, but rather a gas mixture, which is why it is called secondary plasma.