Metal-wire-embedded alumina insulating material using micro and nanoscale 3D printing for surface flashover mitigation in vacuum

Micro and nanoscale 3D printing technic is applied to fabricate functional insulating material which mitigates surface discharge in vacuum based on the microscopic electron multipactor suppression. The proposed alumina ceramic insulator design consists surface-embedded thin metal wires which introduce a local gradient of secondary electron emission yield, such that the trajectories of multipactor electrons are distorted by accumulated negative surface charges and the secondary electron emission avalanche across the insulator surface is intermitted. Considerable increases of surface flashover threshold and surface charging reduction are verified by experiment. Also, additional efforts are made to determine the optimal size and spatial distribution of the metal wire. A convex-shape flashover voltage trace is observed when increasing the wire width, suggesting a trade-off between the multipactor mitigation and the insulator strength. Wire position between the adjacency of cathode triple junction and middle of the insulator is proved to be favorable for flashover mitigation. The physical details of surface flashover mitigation by the proposed insulator design are revealed by an ab initio particle-in-cell (PIC) simulation code, corroborating the experiment from microscopic aspect.

Surface modification of silicone rubber by CF4 radio frequency capacitively coupled plasma for improvement of flashover

The flashover performance of insulating materials plays an important role in the development of high-voltage insulation systems. In this paper, silicone rubber(SIR) is modified by CF4 radio frequency capacitively coupled plasma(CCP) for the improvement of surface insulation performance. The discharge mode and active particles of CCP are diagnosed by the digital single lens reflex and spectrometer. Scanning electron microscopy and X-ray photoelectron spectroscopy is used for the surface physicochemical properties of samples, while the surface charge dissipation, charge accumulation measurement and flashover test are applied for the surface electrical characteristics. Experimental results show that the fluorocarbon groups can be grafted and the surface roughness increase after plasma treatment. Besides, the surface charge dissipation is decelerated and the positive charge accumulation is obviously inhibited for the treated samples. Furthermore, the surface flashover voltage can be increased by 26.67% after 10-minute treatment. It is considered that strong electron affinity of C-F and increased surface roughness can contribute to deepen surface traps, which not only inhibits the development of secondary electron emission avalanche, but also alleviates the surface charge accumulation and finally improve the surface flashover voltage of SIR.