Measurement of total electron emission yield of insulators based on self-terminating charge neutralization

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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.

Section: Characterization Of Morphology Sey and Multipactor Thresholdmentioning

confidence: 99%

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

Wang

Mao

Zhen

et al. 2022

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“…The SEY values of the untreated dielectric and the porous dielectric were measured using the methods described in the literature [54]. The measurement results are shown in figures 6(a) and (b).…”

Section: Surface Treatment and Sey Measurement For The Filled Dielect...mentioning

confidence: 99%

“…Here, first, we discuss the deficiency of the static SEY measurement results for analyzing the process of multipactor. The SEY measurement method in this study can be referenced in [54]. During the measurement, an electron beam with a certain energy collides with the material surface, and SEs are collected by applying a positive bias voltage of 50 V to the collector electrode, as shown in figure 14(a).…”

Section: Limitations Of Hole/groove Structures To Suppress Multipactormentioning

confidence: 99%

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

Meng,

Xu,

Lian

et al. 2024

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Secondary electron yield (SEY) is a dominant factor in determining the multipactor threshold. In this study, we analyzed the secondary roughness effect of surface microstructures for plastic dielectric on SEY reduction and multipactor mitigation. A single ridge waveguide (SRW) operating in Ku-band, filled with PTFE or PI, was designed with a dielectric-metal multipactor gap. By employing a femtosecond laser, periodic microstructures were fabricated on PTFE and PI surfaces to suppress SEY. The SEY peak values of PTFE and PI decreased from 2.05 to 1.40 and 1.37 to 1.07 by the porous surface. The surface morphologies and cross-sectional images of the porous PTFE and PI demonstrated the existence of secondary roughness structures. Via simulation, we obtained multipactor thresholds of 8496 W, 12374 W, and 9397 W for the SRWs filled with untreated PTFE surface, ideal porous surface (without secondary roughness), and real porous surface (with secondary roughness). Similar works were implemented for the PI-filled SRWs, resulting in simulated multipactor thresholds of 7640 W, 11327 W, and 9433 W. The results indicate that the multipactor effect may not be effectively suppressed under the influence of secondary roughness structures such as plastic velvet and foam. Besides, simulation works indicated that the radio frequency electric field could extract secondary electrons from the microstructures, weakening the mitigation effect of microstructures on multipactor. The impact of surface charging on electron motion was also analyzed by considering energy distribution. It was suggested that the surface microstructures of plastic dielectrics lead to a decrease in the surface charge density and the electrostatic field strength, weakening the self-extinguishing effect and lowering the multipactor threshold. This study provides an in-depth analysis of the effect of secondary roughness on SEY and multipactor for organic dielectrics, which makes significant sense for the further investigation of dielectric multipactor.

“…Additionally, the phase structure of the TiN thin film was evaluated using xray diffraction (XRD, D/max 2400, Rigaku Corporation, Cu Kα1, made in Japan), and the surface element composition of the TiN film was characterized by x-ray photoelectron spectroscopy (XPS, Thermo Fisher ESCALAB Xi+, Al Kα, made in the USA). SEY measurements were conducted using a self-developed system equipped with two neutralization guns to eliminate surface charge accumulation [50]. Due to the poor conductivity of dielectric materials, charge accumulation will occur after electron bombardment on the surface, which affects the accurate measurement of SEY.…”

Section: Characterization Of Morphology and Seymentioning

confidence: 99%

“…Figure 3. (a) Schematic diagram of the SEY measurement system, (b) timing diagram of the electron guns operation[50]. Reprinted from[50], with the permission of AIP Publishing.…”

mentioning

confidence: 99%

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

Lian,

Xu,

Meng

et al. 2024

Boron nitride-silicon dioxide (BN-SiO2) composite ceramic is a typical Hall thruster wall material, and its secondary electron emission (SEE) property dominates the sheath characteristics inside the thrusters. Lowering the SEE yield (SEY) of the wall surface can remarkably improve the sheath stability of Hall thrusters. To accomplish the SEY reduction for BN-SiO2, artificial surface microstructure and surface coating technologies are employed. The morphology analysis demonstrated the shape and feature sizes of the microstructure could be largely controlled by adjusting the laser etching parameters. Then we realized an increasingly significant SEY reduction for BN-SiO2 as the average aspect ratio of the microhole increases. The microstructures showed a remarkable SEY reduction when the laser power was 10 W and the scanning cycle was 50. In this case, the SEY peak values (δm) of the two BN-SiO2 samples with mass ratios of 7:3 and 6:4 decrease from 2.62 and 2.38 to 1.55 and 1.46 respectively. For a further SEY reduction, a sputtering process was employed to deposit TiN film on the microstructures. The results showed that the TiN coating of 246 nm thickness reduced the δm values of the two samples from 1.55 and 1.46 to 0.82 and 0.76, which achieved a notable SEY reduction compared to the original surface. Via simulation work, the SEY reduction achieved by microstructures was theoretically interpreted. Besides, by considering the effect of surface charging, the results of SEY converged to 1 with the irradiation pulse increasing presented. The research demonstrated a remarkable SEY reduction for BN-SiO2 ceramic by constructing surface microstructure and depositing TiN coating, which has application sense for low SEY engineering in specific working scenarios.