Secondary electron emission suppression on alumina surface and its application in multipactor suppression

Abstract

For the high-power microwave (HPM) components applied to the space environment, the seed electrons in the components may resonate with the radio-frequency electrical field and may further lead the secondary electron multiplication to occur, triggering off the phenomenon of multipactor. Multipactor deteriorates the performance of the components, and in severe circumstances, it is even possible to result in the failure of the components or the spacecraft. Alumina ceramic possesses good dielectricity, high hardness, good thermal isolation, low dielectric loss, etc., so it is widely used in HPM systems including dielectric windows, and many other microwave components. However, alumina ceramic possesses a relatively high level of secondary electron yield (SEY or <i>δ</i>), indicating that the devastating effect of multipactor discharge is likely to be triggered off inside the alumina-filled HPM components in the space environment. In this work, the model of alumina loaded coaxil low pass fillter is simulated to verify that reducing the SEY of the alumina surface is effective and necessary to improve the multipactor threshold. After that, we use several technologies to achieve an ultralow SEY on the alumina surface. Firstly, a series of microstructures with different porosities and aspect ratios is fabricated. The results indicate that the microstructure with 67.24% porosity and 1.57 aspect ratio shows an excellent low-SEY property, which is able to suppress the SEY peak value (<i>δ</i><sub>m</sub>) of alumina from 2.46 to 1.10. Then, various process parameters are used to fabricate TiN films on silicon sheets. Experimental results indicate that the TiN film achieves the lowest <i>δ</i><sub>m</sub> of 1.19 when the gas flow ratio of N<sub>2</sub>∶Ar is 7.5∶15. Thereafter, we deposit TiN ceramic coating onto the laser-etched microstructure samples, and an ultralow <i>δ</i><sub>m</sub> of 0.79 is finally achieved on alumina surface. Then we implement a qualitative analysis to explore the influence of surface charge on the secondary electron emission and multipactor for the microstructured alumina surface, discuss the mechanism of low-SEY surfaces mitigating unilateral and bilateral multipactor. For verifying the actual effect of low-SEY technologies on the suppression of multipactor, we use the technologies of constructing microstructure and depositing TiN films on the alumina surface which is filled in the designed coaxial low pass filter. Finally, we obtain a significant improvement in the multipactor threshold for the filter, which increases from 125 W to 650 W, and the improvement is 7.16 dB. This work develops an effective method to reduce SEY for alumina, which is of great scientific significance in revealing the mechanism of multipactor for the dielectric-filled microwave components and also is of engineering application significance in improving the reliability of HPM components.