Investigation on discharge process and switching characteristics of a pseudospark switch in series with a magnetic switch.

To reduce the commutation loss of the pseudospark switch, we connect a magnetic switch in series to the anode of the pseudospark switch. Herein, the typical discharge process and switching characteristics of a pseudospark switch in series with a magnetic switch are experimentally investigated at a different number of magnetic cores, gas pressures, and applied voltages. The results show that the addition of the magnetic switch extends the duration of the hollow cathode discharge of the pseudospark. Moreover, the rapid increase of the loop current and the fast decrease of the discharge voltage are separated, which is beneficial for reducing the commutation loss. With an increasing number of magnetic cores, the magnetic delay time increases and the commutation loss significantly decreases. However, the trigger delay time hardly changes since the magnetic switch does not affect the development of the pre-breakdown phase. At a fixed applied voltage, the trigger delay, magnetic delay time, and commutation loss decrease with increasing gas pressure. Furthermore, at a fixed gas pressure, the trigger delay of the pseudospark switch in series with a magnetic switch first decreases and then remains unchanged with increasing applied voltage, which is similar to that of a pseudospark switch without a magnetic switch because of the strong enough trigger injection. The magnetic delay time decreases and the commutation loss almost linearly increases with increasing applied voltage.

All-solid-state bipolar pulsed generator based on linear transformer driver and push-pull circuit.

All-solid-state linear transformer drivers (LTDs) are widely used in high-voltage repetitive nanosecond-pulsed generators, and only a few LTD generators can output bipolar rectangular waves currently. Furthermore, owing to the large reverse overshoot when the output pulse width is long, fewer LTD generators can achieve a rectangular wave output with a microsecond pulse width. In this study, a bipolar LTD circuit topology based on a push-pull circuit is proposed for irreversible electroporation. In this topology, a single-stage LTD module has four push-pull branches in its primary winding to achieve a bipolar output and a short-circuited winding with two resistor-capacitor-diode snubbers to suppress forward/reverse overshoot. A single-stage LTD module and a 12-stage LTD have been tested, and the results show that they can output bipolar rectangular pulses with variable parameters. When the output pulse width is 100 ns to 1 µs, the maximum output voltage amplitude is 5.74 kV, the rise time is 29.1 ns, and the reverse overshoot at 1 µs is 2.9%. When the output pulse width is 1-8 µs, the maximum output voltage amplitude is 2.93 kV, the rise time is 24.3 ns, and the reverse overshoot at 8 µs is 11.3%.

High voltage nanosecond pulse generator based on avalanche transistor Marx bank circuit and linear transformer driver.

Avalanche transistor Marx bank circuits (MBCs) are widely used in high voltage repetitive nanosecond pulse generators, but problems exist with respect to increasing the output voltage due to the limited pulsed current. Accordingly, a novel topology based on an avalanche transistor MBC combined with a linear transformer driver is proposed, the latter of which exhibits advantageous stress distribution and modular structure. A four-module prototype with four units in each module is developed in the laboratory. The output characteristics are investigated by varying important parameters such as the main capacitance, the number of conducting units, the number of cascaded modules, and the trigger signal time delay. The test results verify the validity of the proposed topology. For a 50 Ω resistive load, the prototype can generate pulses with an amplitude of 10.9 kV, a rise time of 3.3 ns, and a voltage superposition efficiency of 89%. The topology proposed in this paper may help to provide a method to further improve the output performance of avalanche transistor MBCs.

A novel trigger for pseudospark switch with high repetition rate, low jitter, and compact structure.

This paper presents the design and development of a trigger with a high repetition rate, low jitter, and compact structure for the pseudospark switch (PSS), which includes an improved Marx generator based on avalanche transistors and a corona-plasma trigger unit. The generator adopted a novel 3 × 12-stage Marx circuit based on avalanche transistors in which the failure rate of transistors in the first and second stages was significantly reduced by connecting the parallel capacitors compared to the previous similar generator. The reason for the improved performance was also discussed. The main parameters of output pulses were an amplitude of -7 kV, rise time of 6 ns, jitter of 0.2 ns, and repetition rate of 2 kHz. The corona-plasma trigger unit adopted BaTiO3 ceramics with high εr as the dielectric and was arranged in the hollow cathode of the PSS. The experiments of triggering a PSS prototype were conducted. The influence of anode voltage and pressure on the trigger delay and jitter was studied, and the minimum trigger jitter achieved <1 ns. This trigger worked for 107 shots at the repetition rate of 2 kHz continuously without obvious performance degradation and any failure of the generator. The main advantage of this trigger is the simultaneous combination of the high repetition rate, low jitter, long lifetime, and great simplicity in a compact structure.