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For nanosecond pulsed gas discharge under hundreds of kV/cm in sulfur hexafluoride (SF6), the electric field emission (EFE) effect may be the mechanism of the initial electrons. Electrode surface micro-protrusions (ESMPs) generated after discharging, would affect the discharge process under a high electric field. To investigate the effect of ESMPs on the breakdown time delay and jitter, the breakdown characteristics of different electrode materials and surface roughness are determined in this paper. Three types of electrode materials include stainless 304L, EDM-AF5 graphite, and CuW70 W-Cu alloy. The influences of stainless 304L electrodes with surface roughness coefficients of 1.6 and 0.8 on the breakdown delay and jitter are compared. After 700 discharge shots, the morphology characteristics and distributions of ESMPs are observed by a contourgraph. Based on the statistical results of ESMPs and EFE theory, the relationship between the electric field of EFE and ESMPs can be calculated. In addition, the effective electron rates of negative ion detachment (NID) are estimated. The experimental and calculation results indicate that the initial electrons are mainly produced by the EFE effect. When the pressure is below 0.5 MPa, the NID effect is limited and the breakdown time delay and jitter are dependent on the height to radius ratio and distributions of ESMPs. Once the pressure exceeds 0.5 MPa, the NID effect will be significant and the influence of ESMPs can be neglected. [ABSTRACT FROM AUTHOR]

Coaxial peaking capacitor is a key component in high-altitude electromagnetic pulse (EMP) simulators with fast front pulse output. It poses significant technical and engineering challenges in limiting radiation field amplitude and test space. This paper presents the design and testing of a 180 pF, 3 MV coaxial peaking capacitor with improved insulation performance. In the insulation design, the length of the dielectric film is extended to reduce the background electric field on the flashover path. The electric field threshold obtained from image diagnosis is used as a reference. During capacitor testing, the insulation characteristics are diagnosed using both direct and indirect methods. The voltage measured by a D-dot probe, the output waveform of the Marx generator in the primary source, and the radiation field waveform are analyzed to understand the flashover characteristics of the capacitor and to improve the reliability of the test results. The experimental results demonstrate that the peaking capacitor can operate stably at 3.0 MV. If flashover occurring on the dropping edge of the pulse is permitted, the operating voltage can be greater than 3.7 MV without significantly affecting the radiation field waveform. The analysis on the surface flashover morphology of the peaking capacitor reveals that the flashover mainly occurs at the dropping edge of the capacitor's waveform, indicating that the damage to the film is not serious. This research significantly increases the working voltage of coaxial peaking capacitors and contributes to the development of high-altitude EMP simulation technology. [ABSTRACT FROM AUTHOR]

As one of the key components of an electromagnetic pulse simulator, the peaking capacitor is coaxially constructed with a laminate structure utilizing alternative thin metal rings and polymer film dielectrics, which is designed as a part of the antenna. This paper presents a coaxial film capacitor with a novel structure to improve its flashover performance. First, the relationship between the capacitance and the capacitor's structural parameters are deduced, and a theoretical basis of lengthening the polymer film dielectrics to enhance the flashover performance is discussed. Based on the theoretical analysis, two 150 pF, 3-layer coaxial film capacitors with different extended lengths for the polymer film dielectrics (10 and 60 mm) are designed and developed. For the capacitor with a 60 mm extended film dielectric, the polymethylmethacrylate rings are adhered to the thin metal rings to support the polymer film dielectrics using a soft adhesive. Electric field analyses show that a longer extended length could decrease the surface field at the edge of the polymer film dielectric by as much as 93%. Comparative insulation experiments show that the flashover voltage for the improved capacitor is 89.9% higher than the original one. The influence of the capacitor's polymer extensions (including the polymer supporting rings and the film dielectrics) on the radiating field of a cone antenna is analyzed numerically, and the results show that only slight changes are introduced into the radiating field. Finally, a designed 350 pF, 20-layer coaxial film capacitor with lengthened film dielectrics is presented. [ABSTRACT FROM AUTHOR]