Achieving High-Temperature Measurement Using Thermionic Emission from a W–La2O3 Cathode in Low-Pressure Argon Glow Discharge

This study investigates the feasibility of obtaining high-temperature (2000–2200 °C) measurements using thermionic emission from a W–La2O3 cathode in a low-pressure argon glow discharge environment. Compared to a vacuum environment, the cathode emission characteristics and temperature variation patterns in a plasma environment exhibit significant differences. These differences arise primarily from the competitive interplay between the thermionic emission cooling (TEC) effect and the ion bombardment heating (IBH) effect. Among the discharge parameters (temperature, applied bias voltage, and background pressure), the applied bias voltage is the key factor influencing this competitive interplay. Consequently, the cathode surface temperature exhibits three distinct regions as a function of bias voltage: the TEC-dominated region (10–20 V), the transition region (20–40 V), where TEC and IBH are nearly in equilibrium, and the IBH-dominated region (40–60 V). The results indicate that by adjusting the discharge parameters to place thermionic emission in the transition region, the TEC and IBH effects can be mutually offset. Under these conditions, the cathode temperature can be unambiguously determined from the measured emission current using the modified Schottky equation. This approach simplifies the functional relationship between emission current and temperature (J–T), thereby enabling high-temperature measurements to be obtained.