Characteristics of the Plasma Generated by Primary Electrons at Lowered Pressure

Plasma characteristics in the gap at lowered pressure in the presence of primary electrons are analyzed for the hydrodynamic model in the cold ion approximation. It is demonstrated that at a certain critical ionization level, the plasma state changes abruptly. The potential drop in the plasma can be not only more, but also less than ln(2)kTe/e, and hence the velocity of ions exiting from the plasma can be more or less than the Bohm velocity. For low ionization intensity and formation of the plasma with a high fraction of primary electrons, the velocity of secondary electron exiting from the plasma becomes equal to their thermal velocity, and their distribution differs significantly from the Boltzmann distribution.