Phenomenological studies for optimizing subsonic underwater discharges

Powerful subsonic underwater discharges are used as a tool in various industrial applications. The aim of this article is to find the essential design parameters required for a pulsed-power system to efficiently drive such discharges. Using different capacitor banks and electrode geometries, a large number of studies were conducted in an effort to better understand the phenomenology of the discharge. Without developing a numerical model for the underwater plasma discharge, the phenomenological studies clearly demonstrated that the maximum pressure that can be generated depends on the discharge current, the distance between the electrodes, and the characteristic time of the discharge. The results of this work will allow the design of efficient pulsed-power-driven strong pressure impulse systems

Development and test of a 500-kV compact Marx generator operating at 100-Hz PRF

This article presents the electrical and mechanical design of a compact 13-stage 0.5-MV Marx generator operating at a pulse repetition frequency (PRF) of 100 Hz. The fast-switching process of the generator is based on spark gaps, operated under pressurized air and leading to the generation of an output pulsed voltage with a peak of 0.5 MV and a rise time of 15 ns when operated on a 300- $\Omega$ load. Corona-stabilized electrodes are installed near the main gap of the switches to improve their operational stability and increase the PRF. To ensure compactness, the Marx generator is housed in a cylindrical metal vessel with a height of 92 cm and an outer diameter of 34 cm, having a total volume of 74 L. A highly accurate simulation using both PSpice and CST software packages was used to predict the impulse waveform at the output of the generator and to help in optimizing the generator design. The tests show a good agreement between the experimental data and the theoretical predictions

2-kV thyristor triggered in impact-ionization wave mode by a solid-state spiral generator

Impact-ionization wave triggering of a thyristor enables it to switch significantly higher currents with much faster rise times (d I /d t ) than through conventional triggering; indeed tests on commercial components demonstrate that both current and d I /d t can be increased an order of magnitude over their specified datasheet values by utilizing impact ionization. However, creating an impact ionization wave places stringent requirements on the generator used to trigger the thyristor—particularly the trigger pulse must have a voltage rise rate (d V /d t ) of more than 1 kV/ns and an amplitude over twice the thyristors static breakdown voltage. Given the capacitance of a thyristor is relatively large, often hundreds of pF, this is difficult to achieve with many common triggering methods. In this study, we present a bespoke, cost-effective, trigger generator that has been developed based on spiral/vector inversion techniques coupled to an optimized sharpening circuit. Using this generator, both a 2-kV single thyristor and a 4-kV stack of two thyristors in series were triggered in the impact-ionization mode. The thyristors had a wafer diameter of 32 mm and capacitances of 370 pF. With a single thyristor 100 shots were performed with it switching a peak current of 1.25 kA and an associated d I /d t of 12 kA/ μ s. With two thyristors, peak currents of 2.6 kA and with d I /d t of 25 kA/ μ s were achieved. In all experiments no degradation of the semiconductor structure was observed. The work opens the way for developing very powerful, but still compact, solid-state trigger generators and larger pulsers for a wide range of pulsed power applications. </p

Off-the-shelf diodes as high-voltage opening switches

A semiconductor opening switch (SOS) (also known as SOS diode) is a solid-state nanosecond switch of gigawatt power level. Due to its high pulse repetition rate, long lifetime, and maintenance-free capability, the SOS diodes are becoming increasingly attractive for use in solid-state pulsed power generators. However, the lack of SOS diode manufacturers prevents the widespread use of this technology. This work demonstrates the ability of off-the-shelf diodes to operate in the SOS mode. A wide range of off-the-shelf diodes including rectifier, fast recovery, avalanche, and transient-voltage-suppression (TVS) diodes have been tested as high-voltage opening switches. An experimental arrangement based on a saturating pulse transformer (PT) was developed to test off-the-shelf diodes in the SOS mode. The results obtained were compared with the existent top of the range SOS diodes, used as reference. Two versions of the experimental setup with the initially stored energy of 25 mJ and 10 J were used. The following pulse parameters were obtained using off-the-shelf diodes: 1) peak voltage impulse of 3 kV and rise time of 10 ns with a 110 Ω load (for the 25 mJ setup) and 2) peak voltage impulse of 80 kV and rise time of 20 ns with a 1 k Ω load (for the 10 J setup). Based on the parameters obtained, the door is opened for a future use of off-the-shelf diodes as opening switches in a wide range of solid-state-based pulsed power systems. </p