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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]

A polypropylene (PP) film is usually employed as the main insulation of the peaking capacitor, which is important in an electromagnetic pulse simulator to generate high-amplitude nanosecond pulse. The flashover voltage of PP films under nanosecond pulse limits the highest working voltage of a peaking capacitor. Surface fluorination was employed to increase the flashover voltage of PP. The flashover voltages of PP samples with different fluorination times (0, 4, and 6 h) were tested in an oven with nanosecond pulse voltage. The results showed that the flashover voltage of the PP film with 6-h surface fluorination was increased about 15% than the untreated film in the air. To clarify the influential mechanism, the physicochemical properties of PP film samples were tested and characterized. The results of thermally stimulated depolarization current (TSDC) showed that the trap density of the PP film increased obviously after fluorination treatment. With the increase in treatment time, the trap depth and density were increased obviously. The surface conductivity of PP films slightly decreased with the increase in fluorination time. The mechanism of surface fluorination on the influence of the flashover performance of the PP film under nanosecond pulse is discussed. It is concluded that surface fluorination significantly increases the carbon–fluorine (C–F) bond of the PP film, resulting in the increase in the depth and density of the surface trap, and then, a large amount of homocharges trapped in the surface trap reduces the electric field near the electrode. [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]