Thermal-expansion-induced geometric errors and their impact on electron optics in a Schottky electron source

In a Schottky electron source, thermal expansion of the source assembly under high-temperature operating conditions can alter the electrode geometry, thereby affecting the stability of cathode emission. In this study, coupled thermal-structural simulations were conducted using COMSOL, and electron optical performance was analyzed with Munro's Electron Beam Software. We systematically investigated the transient and steady-state thermal-structural changes in the source assembly and their impact on cathode emission characteristics. The transient results show that the cathode tip reaches 1800 K within 17 s, while the suppressor and extractor require 80 min to reach thermal equilibrium, causing substantial dynamic variations in interelectrode spacing during startup. The steady-state results reveal that all electrodes undergo axial expansion, lateral misalignment, and aperture ellipticity. Under actual operating conditions with an image-plane acceptance angle of 20 mrad, however, the combined image-plane aberration from all electrodes is only 0.05 nm and thus negligible, whereas the image-plane shifts and slopes remain substantial and cannot be overlooked. In addition, axial thermal contraction (suppressor −6.2 μm, cathode −28.0 μm relative to extractor) reduces electrode gaps, increasing brightness by ∼32% and total emission current by ∼39%. This study elucidates how thermally induced structural deformation influences the electron beam emission characteristics, providing a reference for structural optimization and thermal stability design of Schottky electron guns.