Ultralow electron emission yield achieved on alumina ceramic surfaces and its application in multipactor suppression

Abstract

Alumina ceramics used in microwave systems are susceptible to the multiplication of secondary electron emission on the surface due to the influence of resonation between electrons and RF electrical field, and the detrimental effect of multipactor may be therefore triggered. For the alumina-loaded microwave components, low secondary electron yield (SEY) is urgent to be achieved on the inserted alumina surfaces for mitigating multipactor. In this work, for achieving an ultralow SEY surface of alumina, two recognized low-SEY treatments are combined. For the primary SEY suppression, a series of microstructures were fabricated on the alumina surfaces with various porosity and aspect ratio at hundred-micron scales by infrared laser etching. The microstructure with 52.14% porosity and 1.78 aspect ratio showed an excellent low-SEY property, which could suppress the SEY peak value (δm) of alumina from 2.46 to 1.00. For the secondary SEY suppression, the SEY dependence of TiN coating on sputtering parameters was studied, and the lowest δm of 1.19 was achieved when the gas flow ratio of Ar:N2 was 15:7.5. Whereafter, by depositing TiN ceramic coating onto the laser-etched porous samples, an ultralow SEY, δm equaled 0.69, was achieved on the alumina surfaces. The simulation work revealed the impact of dielectric surface charge on electron multiplication and uncovered the mechanism of using low SEY surfaces to inhibit multipactor. Some coaxial filters with alumina filled were fabricated for verification, the results revealed that the multipactor threshold increased from 125 W to 425 W after applying the TiN-coated porous alumina, and to 650 W after treating another multipactor sensitive area with the same low-SEY process. This work developed an advisable method to sharply reduce SEY, which is of great significance for the multipactor mitigation of the alumina-loaded microwave components.

Secondary roughness effect of surface microstructures on secondary electron emission and multipactor threshold for PTFE-filled and PI-filled single ridge waveguides

“…In other words, the high-power RF electric field 'extracts' the lowenergy SEs that were originally trapped in the groove, weakening the SEY suppression effect of the groove structure. The above analysis can also be used to explain why multipactor can still occur in microstructure materials with a δ m of only 0.98, as reported in the literature [35]. These experimental results indicate the limitations of groove structure in suppressing multipactor in microwave components, which could potentially result in an overestimation of the enhancement in the multipactor threshold.…”

“…After modeling the SRW and simulating its electric field distribution, we identified the specific region inside the component that is more susceptible to multipactor effect. For further exploration of multipactor suppression by constructing surface microstructures, we referred to the parameters of microstructures prepared by Wang and Mao on the alumina surface [35].…”

“…Measurement results showed that the SEY peak values (δ m ) of the treated silver and ferrite decreased by 1.1 and 1 respectively, and E 1 (the first energy crossing point) decreased by 25 eV and 150 eV. Compared to the original component with a discharge threshold of 340 W, the circulator with treatment implemented on the ferrite achieved a multipactor threshold of 800 W. Furthermore, the circulator treated on both the ferrite and silver surfaces realized a substantial increase in the multipactor threshold to 3400 W. In 2022, Wang and Mao reported a case of multipactor threshold improvement, which involves a square coaxial filter working in L-band with a bilateral dielectric discharge gap [35]. By constructing micro holes on the alumina surface and coating TiN film, an alumina sheet with an ultralow SEY was successfully achieved, resulting in a reduction of δ m to 0.98.…”

Secondary electron emission reduction from boron nitride composite ceramic surfaces by the artificial microstructures and functional coating

“…Additionally, the real porosity P is slightly larger than the theoretical porosity since the actual side length of the holes is larger than the set side length. This phenomenon is primarily limited by the precision of laser etching and the lateral diffusion effect during the etching process [51]. figure 4(a) shows the 3D morphology of sample #1, and figure 4(b) displays the linear roughness of the cross-section image (white line in figure 4(a)).…”

Effect of atmospheric environment on the stability of secondary electron emission from magnesium oxide and alumina surfaces

“…Secondary electron emission (SEE) is a phenomenon that involves electrons or ions bombarding the surface of a material, triggering the escape of electrons from the surface. SEE may occur in space high-power microwave systems, particle accelerators, and space thrusters [1][2][3][4], which may lead to the phenomenon of multipactor discharge in these systems [5][6][7][8][9][10][11][12]. Apart from these typical occurrence occasions, SEE plays a vital role in high-precision measurement instruments such as scanning electron microscope (SEM), x-ray photoelectron spectroscopy (XPS), and Auger electron spectrometer [13][14][15][16].…”