Ionization Process of a Plasma

The ionization due to thermal electrons is discussed. Earlier theories on the voltage characteristics of a partially ionized homopolar cell are reconsidered. It is found that the results obtained from the theory on thermal ionization do not agree with experiments within the range of neutral gas densities studied so far, but a better agreement is expected at higher densities. In several cases the ionization rates estimated from experiments suggest that there exists a more powerful ionization mechanism than that provided by thermal electrons. Such a mechanism is probably associated with a highly nonthermal distribution of electron velocities within considerable parts of the plasma volume.