Orifice plate surface temperature measurement of a LaB₆ hollow cathode using a near-infrared two-color radiation thermometer

This study measured the two-dimensional orifice plate surface temperature of a 20-A-class LaB₆ hollow cathode using a near-infrared two-color radiation thermometer. The thermometer technique resolved the orifice plate temperature with an accuracy of approximately 166 ℃. With this technique, the surface temperature of the orifice plate was found nearly uniform, with no observed temperature gradient on the orifice plate. Consequently, the operational characteristics of the hollow cathode are discussed in relation to the average surface temperature. Data analysis revealed that the orifice plate temperature was not sensitive to the mass flow rate; conversely, it was highly sensitive to the discharge current. Moreover, for the same input power, the orifice plate temperature was higher in the high-current, low-voltage mode also known as the spot mode indicating efficient emitter heating. The measurement system developed in this study provides a more precise evaluation of the orifice plate temperature and allows for estimating the internal conditions of a hollow cathode, thus facilitating more appropriate design evaluations under various operating conditions.