In Situ Thermal Characterization of the Accelerator Grid of an Ion Thruster

The application of an electric propulsion diagnostic system for in situ thermal characterization of electric thrusters is studied, as described previously. Exemplarily, the surface temperature profile of the accelerator grid of a gridded ion thruster RIT-22 is obtained and characterized. In situ pyrometer line scans in combination with precise measurements of geometrical grid parameters are demonstrated. The accelerator grid surface temperature of the firing thruster is obtained by a model calculation that requires the knowledge of geometrical grid parameters, such as hole diameter, distance between holes, or grid shape. These parameters are also measured in situ with a telemicroscope for high-resolution optical imaging and a triangular laser head for surface profile scanning. The distance between grid surface and pyrometer optics are precisely monitored with the support of the triangular laser head, for which the position is fixed with respect to the pyrometer. The distance measurement allows for correcting the measurement spot size of the pyrometer. The temperature profiles at three different beam power levels (1250, 2250, and 4000 W), and warm-up and cool-down phases demonstrate the capabilities of the complex equipment. It is found that thermal steady state is reached after 4 h of thruster firing. Furthermore, it is shown that the accelerator grid surface temperature increases almost linearly with increasing beam current. [PUBLISHER ABSTRACT]