Hanwen Zhang

High voltage pulse generators are widely applied in high power microwave, plasma generation, material processing, and scientific research. Pulse forming lines are widely applied in high voltage pulse generators due to their high energy density and great ability with square waveform modulation. To get a higher energy transfer efficiency and lower characteristic impedance, a novel racetrack Blumlein type pulse forming line (R-BPFL) that is formed by two inner cylinders, two middle cylinders, and one outer cylinder is proposed in this paper. Moreover, repetitive operation is significant for pulse generators. Therefore, this paper proposes a high repetitive primary energy storage system incorporating an energy recovery circuit precisely controlled by three thyristors. A parameter optimization methodology is developed through theoretical analysis to simultaneously satisfy both high-frequency operation requirements and maximum compactness. Finally, a repetitive high voltage pulse generator based on the designed R-BPFL and primary energy storage system is constructed and tested. The experimental results show that the generator designed in this paper had an output power of 10.5 GW on a 40 Ω load, a pulse width of about 115 ns, a repetition rate of 20 Hz, and supported 640 pulses in one run.

Surface flashover in vacuum is a critical factor restricting the stable operation of the high-power pulsed generators. Cross-linked polystyrene (XLPS) is always used to manufacture typical insulators for power pulsed generators, so it is important to study the surface insulation performance of the XLPS in a vacuum to improve the normal operation performance of the device. Based on the vacuum surface flashover test platform consisting of a solid-state gigawatt-level pulse generator and a test cavity, XLPS samples with a thickness of 13 mm were used to investigate the influence of roughness on the surface flashover characteristics. Samples with roughness of 1.3, 1.7, 2.2, and $2.7~\mu $ m were tested under both single and 10 Hz modes. It is found that the surface insulation performance of samples increases first and then decreases with the increase of roughness under both modes. Scanning electron microscope (SEM) was used to observe the micromorphology of the sample surface before and after the surface flashover events, enabling analysis of the effect of micromorphology on electron motion. Comparative analysis of the experimental results reveals that the first vacuum surface flashover voltage under both modes primarily depends on the surface roughness. Meanwhile, under 10 Hz mode, the first 50% flashover voltage, the conditioned flashover voltage, and the hold-on voltage are higher than those obtained in single mode, which indicates that the loading condition of the repetition rate pulse has a good aging effect on the sample.

Thermal runaway and electrical instability in pulsed thyristors under repetitive pulses critically limit the reliability of solid-state and compact high-power pulse generators. However, the bidirectional electrothermal effects of pulsed thyristors under repetitive pulses have not been studied. In this paper, they were explored based on mixed semiconductor device and circuit simulations and scaling experiments. The results show that within a ten-microsecond pulse, the maximum temperature rise occurs in the P2 region between the amplifying gate and the cathode under diode protection, whereas that occurs in the J1 junction near the anode without diode protection. The global maximum temperature decreases, and the heating region gradually expands with increasing pulse width. As the repetition rate increases, the temperature of the thyristor case is higher within the same testing time. Affected by higher temperature, the voltage drop and peak power dissipation increase and the anode current decreases. The residual temperature in the previous pulse further increases the heat generation in the next pulse. The electrothermal bidirectional coupling relationship under repetitive pulses was established theoretically, which can guide the application of high-power pulse generators in repetition rate mode.

A high voltage pulse power supply based on a Blumlein type pulse forming line (PFL) with a Periodic Slotted Insulation Structure (PSIS) is designed and constructed in this paper. The Blumlein type PFL with PSIS, which inserts PSIS both in the inner line and outer line of the conventional Blumlein type PFL, is able to obtain output waveforms with higher quality and higher energy efficiency compared with the conventional Blumlein type PFL. Meanwhile, the combined insulation structure formed by the media of PSIS and the glycerin filled with the PFL can be used to optimize the electric field strength of the PFL, thereby improving the stability and reliability of the PFL in the repetitive-operation mode. The experimental results show that the high voltage pulse power supply designed in this paper had an output power of about 5 GW at a 50 Ω load, a pulse width longer than 80 ns, a repetition rate of 20 Hz, and supported 100 pulses in one run.

A solid-state high voltage pulse power supply with three synchronous output voltages is designed and constructed in this paper. The pulse power supply consists of a fractional-turn ratio saturable pulse transformer and three six-stage Marx generators. The FRSPT not only works as step-up pulse transformers but also as magnetic switches of the Marx generators. All magnetic switches are developed based on two communal cores to achieve a perfect multiple-pulse synchronization effect. The experimental results show that the three output voltages have an amplitude of about 168 kV and a rising time of about 102.6 ns with a 2 MΩ dummy load. The pulse power supply can operate stably at frequencies of 1, 5, 10, and 15 Hz with the synchronization jitters less than 1.5 ns.

The trigger generator made with a spiral generator (SG) has the advantages of light weight, compact structure, and low cost and has promising applications in the pulsed power field. This paper introduces a compact solid-state high-voltage pulse trigger system based on an improved SG, which has improved repetition rate and lowered the demands for semiconductor switches’ maximum current and current rise rate when compared with previous studies. The improvement is achieved by winding outward an additional layer of the passive layer and low-voltage metal strip, which realizes a significant reduction of the peak current and current rise rate of the discharge switch. The final dimension of the trigger is 25 × 10 × 10 cm3, excluding the power supply. An experiment carried out in single shot mode shows that the peak value of the output pulse can reach 50 kV with a leading edge of 57 ns. Repetitive experiments were carried out up to 1 kHz, with the peak voltage of the output pulse being 30.5 kV, the leading edge being 48 ns, and the jitter being 0.84 ns. Finally, the generator is used to trigger a gas switch, and it works stably and reliably.

Pulse forming lines (PFL) are widely applied in high-power pulsed power generators due to their high energy density and great ability with square waveform modulation. However, the three-cylinder coaxial Blumlein line (tPFL), a commonly used PFL structure, has low energy efficiency due to the difference in impedance of the outer and inner lines. In order to increase the outer line impedance and improve the output waveform of the PFL, a racetrack Blumlein pulse forming line (r-B PFL), formed by two inner cylinders, two middle cylinders, and one outer cylinder that resembles a runway shape, is proposed in this paper. The glycerin energy storage technology and the spiral line technology were applied in the PFL. Moreover, the r-B PFL was tested experimentally after its construction, yielding a satisfactory result. The PFL structure in which multiple middle cylinders share the same outer cylinder achieves a higher outer line impedance, leading to a high energy efficiency of the PFL, which contributes to the PFL development trend toward compactness and miniaturization.

Pulsed power generators utilizing magnetic switch technology within the 100 ns scale have become widespread for surface treatment, high power microwave generation, and food processing, in which the dynamic characteristics of the magnetic switch perform an important function. The saturation process, electric field between layers, and energy loss are closely associated with the applied time scale of the magnetic core, which affects the dynamic characteristics of the switch. However, compared with the study within the microsecond scale, the dynamic characteristics of magnetic switches within the 100 ns scale have not been studied in depth. In this paper, the dynamic characteristics of a coaxial magnetic switch modulating pulse forming networks (PFNs) are studied via both field-loop co-simulation and scaled experimental test. It is found that increasing PFN section number (Ns) leads to an acceleration in the saturation process of the core, which helps understand the switch performance of the magnetic core more clearly. With respect to a specific magnetic switch based on a ferromagnetic core, it is quantitatively analyzed that increasing Ns from 1 to 10 leads to a 16.1% reduction in core saturation time (tsat), a 13.4% increase in eddy loss (EET), and a 5.7% rise in maximum interlamination field strength (Emax) under the 100 ns scale; however, tsat is reduced by 19.3%, EET increases by 5.2%, and Emax rises by 2.3% under the microsecond scale. The results could provide a design reference for magnetic switches in pulsed power generators.

The non-uniform current distribution in high-power thyristors leads to a significant rise in local junction temperature (Tlj), potentially threatening the reliability of high-power thyristors. For online monitoring Tlj, a novel temperature-sensitive electrical parameter (TSEP) method was proposed based on peak stray gate current (ipsg). First, simplified turn-off models for high-power thyristors with an amplifying gate were set up to explore the variations of gate-cathode voltage and stray gate current in the turn-off transition. Subsequently, the theoretical relationship between ipsg and Tlj was established. Significantly, the physical meaning of Tlj was illustrated by the theoretical relationship and the temperature distribution simulation. Next, the feasibility of the proposed method was verified by the temperature calibration experiment. Considering self-heating, the temperature sensitivity is 89 mA/℃ at a thyristor voltage of 1.0 kV, which increases with increasing thyristor voltage. Finally, an online monitoring Tlj case was carried out based on a tunnel magnetoresistance current sensor. The proposed method is easy to implement and is capable of measuring local junction temperature concerning major heat generation regions, which is suitable for high-voltage applications.