PLASMA SHEATHS

• Lack of electrons close to anode (almost all electrons are swollen very fast by the positive anode)
• Lack of energetic electrons close to cathode (electrons are rejected/slowed down by the negative cathode)

Consequently, there are less ionization/excitation processes close to the cathode and anode. Therefore, due to the lack of photons, dark sheaths will be present close to the anode and cathode in a DC plasma (constant voltage applied on anode).