Analysis of the virtual cathode and floating potential of a thermionic emissive probe operating in the space-charge-limited regime

Abstract

This paper analyses by this and characterizes a thermionic emissive probe operating in both the temperature-limited current regime (T-region) and the space-charge-limited current regime (S-region) characterized by the formation of a virtual cathode. For this last case, we obtain the potential profile, the emitted current that overcomes the virtual cathode, as well as the thickness and depth of the potential well in front of the probe for different probe temperatures, plasma electron temperatures and neutral gas pressures. From these results, we obtain the I–V curves and the floating potential. Depending on the probe radius, when the floating potential is reached in the S-region, its value saturates, becoming almost independent of the probe temperature and the electron temperature.