Abstract
Flashover plasma characteristics across a large-scale ceramic vacuum interface initiated by explosive electron emission (EEE) are investigated with the experimental and simulation methods. Driven by a negative high voltage pulse (-300 kV, 150 ns), flashover plasma luminescence processes were observed by a high-speed framing camera and the accompanied spectrum characteristics were measured by a spectrograph. Compared with flashover initiated by field electron emission (FEE), a faster light expansion velocity and higher electron temperature of flashover initiated by EEE were obtained which were 200 cm/μs and 4.57 eV, respectively. Radial and angular components characteristics of expansion velocity were analyzed as well and their maximum values were 200 cm/μs and 50 cm/μs. Furthermore, comparisons of flashover initiated by EEE and FEE were conducted by particle-in-cell methods and the results agreed with the experimental observations. From these results it can be concluded that due to higher primary electron energy and stronger secondary electron avalanche and gas ionization, flashover along the ceramic interface initiated by EEE has an easier and faster develop process compared with that initiated by FEE. This work can give a reference for evaluation and design of ceramic vacuum interfaces for high-current applications.
Highlights
Vacuum interfaces are one of the most important parts for the high-current accelerators,[1,2,3,4] pulsed power systems,[5,6,7] and high-power microwave (HPM) devices.[8,9,10] With the practical applications of pulsed power and HPM technologies, there is a trend to make the HPM devices compact and maintaining high vacuum state for a long period.[11,12] Low relative permittivity and eminent machining characteristics make the organic materials be the conventional vacuum interfaces
Vacuum surface flashover phenomenon has been heavily studied in the past several decades[1,2,5,6,7,8] and many theories have been proposed such as secondary electron emission avalanche (SEEA) and electron triggered polarization relaxation (ETPR).[3,4]
Surface flashover plasma characteristics across a 300 mm diameter ceramic vacuum interface initiated by electron emission (EEE) are investigated, basing on a high voltage nanosecond electron modulator platform
Summary
Vacuum interfaces are one of the most important parts for the high-current accelerators,[1,2,3,4] pulsed power systems,[5,6,7] and high-power microwave (HPM) devices.[8,9,10] With the practical applications of pulsed power and HPM technologies, there is a trend to make the HPM devices compact and maintaining high vacuum state for a long period.[11,12] Low relative permittivity and eminent machining characteristics make the organic materials be the conventional vacuum interfaces. Environment have been investigated with the optical and electrical diagnostic methods[6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,22,23,29,30,31,32] and researches have proposed methods to improve the insulation performance.[1,5,11,12,17,24,25,26,27,28] As for ceramic vacuum interfaces, geometry structure optimization[11,12,21] and surface treatment[25,27,28,33,34,35,36] are the common ways to increase their flashover voltages These researches have greatly improved the insulation performances and applications of ceramic vacuum interfaces, there are still some deficiencies for these works.
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