The excitation collisions give rise to excited species, which can decay to lower levels by the emission of light. This process is responsible for the characteristic name of the "glow" discharge. The ionization collisions create ion-electron pairs. The ions are accelerated toward the cathode, where they release secondary electrons. These electrons are accelerated away from the cathode and can give rise to more ionization collisions. In its simplest way, the combination of secondary electron emission at the cathode and ionization in the gas, gives rise to a self-sustained plasma. Most modern plasmas are generated by either a DC current flowing through the gas or a radio frequency (RF) field exposed to the gas. RF plasmas do not require DC current flow, and thus, can be used to process insulating and conducting materials.

In the direct current (DC) glow discharge, a continuous potential difference is applied between cathode and anode, giving rise to a constant current. A schematic representation of a chamber, plasma glow and plot of potential is given in Fig. 3.28. The ionization breakdown of a heavy inert gas such as argon occurs when a spark voltage (V_DC) is applied which is greater than the breakdown voltage (V_br). The number of ions resulting (Ar⁺ plus electrons e^-) will be much lower; typically less than 1% of the atoms in the chamber. Plasma maintains almost perfect charge balance. To maintain a self sustaining plasma, the V_DC has to to much higher compared to V_br. The plasma is highly conductive at low frequencies due to electrons. The conductivity of ions compared to electrons is much lower because ions are heavy and have much lower velocities. However, this set-up gives problems, due to the constant current; the electrodes will be charged up, leading to burn-out of the glow discharge.