Enhancing the Surface Flashover Strength of Polystyrene in Vacuum by Secondary Electron Emission Suppression through Cross-Linking

Abstract

Insulation materials with excellent dielectrics−vacuum interface breakdown strength are irreplaceable in equipment such as particle accelerators, fusion ignition, and related aerospace devices. In this article, the segment structure of a typical insulation polymer, polystyrene, has been modified by introducing divinylbenzene to form cross-linking junctures and adjust the cross-linking density. The influence of cross-linking on its electron absorb-emit feature and further on the vacuum pulsed flashover characteristics has been systematically studied. A series of broadband dielectric spectroscopy (BDS) and thermally stimulated current (TSC) experiments indicate that this cross-linking network inhibits the movement of the polar segments, leading to a drastic change in the charge-trapping behavior of dielectric surface layer materials. The trapping charge density is increased, and the trapping energy is transferred to deeper-level regions. These lead to the observed suppression of secondary electron emission (SEE) of highly cross-linked polystyrenes exposed in vacuum. And, quite sensibly, the nanosecond pulsed vacuum flashover tests show that the polystyrenes with higher crosslinking density have enhanced flashover strength. Moreover, to further investigate the relationship between the dielectric SEE behavior and its vacuum flashover process, a 2-D model is established and analyzed on the basis of the particle in the cell with the Monte Carlo collision (PIC-MCC) method.

Design and 3D printing of porous cavity insulation structure for ultra‐high electrical withstanding capability

“…It is worth noting that the voltage waveforms and electrode types used in flashover voltage testing in representative literatures selected for comparison are the same or similar to those in this study. Clearly, the cavity insulation structures exhibit ultra‐high surface insulation improvement ratio in both the cases of DC [26, 27, 46, 50–54] and impulse [24, 28, 35–38, 46, 55–59] flashover, which far outperform the other flashover mitigation strategies.…”

Largely Enhanced Surface Flashover Voltage of Poly(ether Imide) by Scalable and Durable ZnO Coating: A Gift from In Situ Growth

“…The occurrence of flashover mainly depends on the surface state of the dielectric, such as surface morphology, surface trap, surface charge migration, outgassing from surface, and accompanying gas ionization. − Researchers have put forward various methods to modify the properties of the interface to improve the flashover voltage. Typical methods include − introducing micro-nanostructures on the dielectric surface for morphology modification by 3D printing; modulating the interfacial charge migration behavior by cross-linking or fluorination; changing the surface traps by graphene, Cr 2 O 3 , and other nanoparticles; and regulating the outgassing rate and gas ionization by polythiourea-assisted coating. Although different modification strategies focus on modifying the interface properties from different perspectives, the ultimate goal is to improve the flashover voltage by suppressing surface charge accumulation and mitigate electric field distortion, which can suppress electron multiplication. , …”

Improvement of surface insulating performance for polytetrafluoroethylene film by atmospheric pressure plasma deposition

“…The surface flashover is the discharge throughout the interface of vacuum and insulator, and the flashover voltage is usually lower than the breakdown voltage of vacuum gap and insulator in the same dimension. So the vacuum-insulator interface is the most vulnerable area for insulating performance in vacuum equipment [3][4][5]. The enhancement of surface flashover field strength is an important way to improve the synthetic capability of vacuum devices and ensure the safe operation of key equipment [6,7].…”