Avalanche transistor (AT)-based repetitive nanosecond pulse generators with high amplitude, fast rise time, narrow pulse width, and low jitter have been widely developed and applied in numerous fields. However, relatively little research has been carried out on the positive nanosecond pulse generation with high flexibility in a wide range of output voltage amplitude. In this article, a novel AT-based Marx circuit (MC) topology adopting base-triggering method is proposed to avoid the formation of current filamentation inside the transistors and resolve the contradiction between high-voltage output and high repetition rate operation. A 6×10-stage MC prototype is implemented with optimized parameters to validate the feasibility of the proposed topology. The conduction processes of transistors show that, with the injection of additional base current, the switched-ON modes are transformed, which contributes to reliable conduction of transistors even without sufficient overvoltage ramp. With the adoption of inner triggering loops, the minimum working voltage of the prototype is extended to 1150 V. The operation characteristics of the generator in the whole operation range are investigated in depth. Experimental results illustrate that, at the 75- Ω match-ended coaxial cable, the prototype is capable of generating positive pulses with an adjustable voltage amplitude in the range of 6.50 to 12.39 kV, a basically consistent rise time of 3.6 ns and pulse width of 19.5 ns. Over 10 ⁷ successive pulses are generated at a maximum repetition rate of 1 kHz without any device failure.

The characteristics, breakdown probability, and statistical distribution of breakdown time delay under different du/dt in hundreds of nanoseconds pulse for millimeter gaps have been investigated by employing the statistical experimental method in this paper. The experimental results indicate that both the breakdown time delay and jitter are essentially decreased as the slope of the pulse voltage- du/dt is increased for 1-, 2-, and 4-mm gaps; in particular, increasing the value of du/dt is useful to obtain the smaller relative deviation of breakdown time delay under the same breakdown electric field. The breakdown probabilities for different gaps have been analyzed and a method of utilizing the Gaussian distribution function has been proposed which can be used for evaluating the statistical distribution of breakdown time delay. When the experimental condition is 100% breakdown probability, the breakdown time delay follows a Gaussian distribution. However, it is unsuitable for the fitting of breakdown time delay utilizing a Gaussian function for 2- and 4-mm gaps from the cumulative probability distributions of breakdown time delay because of the lower du/dt values and breakdown probabilities.

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.

The flashover failure and damage of polypropylene (PP) and polyester (PET) films under nanosecond current pulses were experimentally investigated. A nanosecond pulse current test platform was established to study the flashover characteristics, performance degradation, and structural damage of dielectric films under repeated nanosecond current pulses. The accumulation and emission of surface charge influenced by field distortion and trap distribution were analyzed to clarify the mechanism by which the flashover voltage increases linearly with gas pressure at low pressure and saturates at high pressure. The significant effects of pulse energy, gas pressure, and discharge gap on film damage behavior were investigated. The damage pattern of PP and PET films includes surface deformation, reduced flash-voltage tolerance, molecular chain breakage, and group shedding. The damage of PP films is manifested as fine furrows, while PET corresponds to mountainous bumps. With the increasing number of discharges, the breakdown voltage of PP films decreased significantly, while the flash tolerance performance of PET films was more stable. Under the conditions of high pulse current amplitude, small discharge gap, and low air pressure, the damage degree of the film intensifies, which is characterized by severe destruction to the molecular structure and a significant decrease in flashover withstand voltage. Polymer films, flashover, nanosecond current pulses; performance degradation; microstructural damage.

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.

Stable capacitance in the transfer capacitor is crucial for ensuring a reliable output waveform from the high-altitude electromagnetic pulse simulator. Different types of environmental stress pose significant challenges for the performance and reliability of the outdoor simulator and its transfer capacitors. This paper presents a preliminary investigation on the effects of temperature and mechanical stress on both the capacitance of the transfer capacitor fabricated with the polypropylene film and the simulator’s output waveform. Experiments reveal that the capacitance exhibits an approximately linear increase with temperature, reaching a maximum variation of 6.3% at 60 °C. It increases with the heating time and stabilizes after ∼1 h, and the capacitance change under thermal stress is reversible. The capacitance variation remains within 0.22% under the steady-state vibrational stress, whereas it decreases by ∼2.04% with an increasing number of hammer strikes. It is demonstrated that the fluctuation of capacitance caused by the thermal or mechanical stress would result in a deviation of the waveform for the simulator under the parameters in this study. These findings will enhance the understanding of the characteristics of the transfer capacitor under mechanical or thermal stress, thereby facilitating future optimization and rational maintenance of the capacitor with this structure.