Measurements of the Potential Profiles of Glow Discharges Using an Emissive Probe

Glow discharges are produced in air in a ~1-m-long glass vacuum tube under the pressure of 12-113 mtorr. We present the full potential profiles throughout the glow discharge regions characterized using a cold emissive probe with the current-bias method. Secondary electron emission from the probe likely determines the local plasma potential, which replaces the role of thermionic emission that fails in relatively high-pressure plasmas. The measured potential profiles show good agreement with the theoretical expectations. A large potential drop is measured in the cathode dark space followed by a potential plateau through the negative glow and Faraday dark space regions. Striations in the positive column are shown as stair-step-like multiple potential double layers with a potential step close to the ionization energy. This cold emissive probe method can be used for characterizing potentials in even higher pressure (>1 torr) glow discharges that are not yet well understood.