The generation of high-power microwaves can be used in the field of military (protection of convoys and improvised explosive device neutralization) and civil applications (study of biological phenomena such as electroporation, treatment of waste water, and so on). The implementation of such systems requires the use of a high-voltage pulsed source capable of operating in repetitive mode at 100 Hz for a few seconds or at 1 Hz during several hours. A pulse forming line (PFL) is used to convert the monopolar output signal of the generator into a bipolar pulse, which is more suitable to feed an antenna. It induces significant constraints for the pulse generator, which has to supply a mismatched load. Further constraints such as weight, volume, and energy efficiency have to be considered to facilitate the integration of the system on mobile platforms. It also has to be easily remote-controlled to facilitate its use in an operational context. A parametric study was conducted to design a short-pulse Marx generator dedicated to this kind of application. The best compromise was chosen to generate short-rise time high-voltage pulses with a low quantity of energy. For higher energy levels, other stages with a higher capacity can easily be used, using our modular coaxial structure. The tested 11-stage short-pulse Marx generator, connected to a PFL, reached an output voltage of 420 kV, with a rise time , at a 40-kV charging voltage. Inductive charging circuits allow operation in repetitive mode up to 100 Hz during a few seconds. The generator was operated at 1 Hz during several hours using a remote-controlled charging unit. For mobile applications, the generator can be charged by a battery-powered power supply unit.
The need for repetitive high-power microwave systems, for instance within the scope of convoy protection, requires the availability of compact, repetitive pulsed-power generators.The development and the first experimental results of an upgraded balanced ISL Marx generator for future repetitive operations at pulse repetition frequencies in the order of 100 Hz are introduced.A key objective is to keep the fundamental modular coaxial concept by reason of its scalability and compactness.Simulation models were developed under the PSpice software package in order to investigate the charging and discharging phases of the Marx generator and also to determine the design criteria for repetitive operations.The charging resistors were replaced by ultracompact inductors for rapid charging, being able to withstand pulsed voltages up to 60 kV and pulsed currents up to 1.4 kA during the discharge phase.An improved type of strontium-titanate high-voltage ceramic capacitor was successfully tested experimentally up to 70 kV.Each new elementary stage of the Marx generator consists of eight 1.1 nF sectors of a cylinder capacitors mounted in parallel, two charging inductors of about 17.8 µH and two halves of spherical spark gaps.The pressurized self-triggered gas switches are arranged along the axis for fast consecutive breakdown thanks to the UV radiation emitted during the breakdown in each gap.The stages are installed in individual fibreglass housings.First experimental results of a 4-stage Marx generator in repetitive operation, driven by a 4 kW capacitor charging power supply up to a maximum voltage of 40 kV, are presented.
This paper presents the design and the performances of an ultra compact, general-purpose, and high-power ultrawide band (UWB) source named GIMLI. The system was developed for dual use, from laboratory to battlefield applications. The power supply is a dedicated coaxial Marx generator composed of specifically designed stages. In an 11 stages configuration, the rise time can be less than 15 ns (measured on a 50 Ω load) with an operating voltage reaching values up to 500 kV (with an open circuit configuration). An ultra compact (less than 2 liters) pulse forming stage (PFS) is directly connected to the output of the Marx generator. It is composed of a pulse sharpening assembly made up of a peaking and a multi channel grounding spark gap, running under a high pressure of nitrogen. These switches are followed by a monopulse-to-monocycle converter module, which is based on a Blumlein coaxial line. The bipolar signal at the output of the PFS has a total duration which can be adjusted from 1 to a few ns by the use of different lengths of the Blumlein module. For example, the smallest device generates a signal composed of two Gaussian pulses. A positive one is followed by a negative one and the two are separated by less than 500 ps peak to peak with rise times lower than 250 ps. Measured on a 50 Ω dedicated ultra wideband resistive load, the peak-to-peak output voltage is tunable up to 400 kV. With a right adjustment (in pressure and in distances inside the electrodes chamber) the maximum dV/dt can reach 2.10 15 V/s. If a more important slope is required, it is possible to insert a pre-peaking stage between the Marx generator and the PFS. Using this stage allows to get performances in the order of 5.10 15 V/s (rise times lower than 150 ps). The use of a coaxial 50 Ω output enables to connect the GIMLI source to many different types of antennas, allowing the radiation of WB or UWB electromagnetic signals. For instance, high-power radiation tests were performed with the pulser connected to a specific half TEM ridged horn. The results showed that the electrical field acquired at 10 m was higher than 150 kV/m peak to peak.
Experimental and theoretical investigations on the possibilities of steering a supersonic projectile by using a plasma actuator started in 2001, but they have not been published up to now, for confidentiality reasons. The experimental study shows the possibility of activating plasma discharges at the tip of a supersonic projectile flying in conditions encountered at a low altitude. Plasma discharges were produced by the use of high-voltage generators that were able to supply electric discharges between two electrodes flush with the conical surface of the projectile nose. Visualizations show that the generation of a plasma discharge produces a perturbation between the projectile surface and the shock wave attached to the conical projectile tip. The perturbation is strong enough to distort the shock wave. A numerical simulation was performed for an ideal gas, in which the plasma discharge was modeled as a transverse hot jet. The comparison between the flow visualizations and the numerical results shows the similarity between the visualized and the computed flow structures. The results show that the asymmetry of the flowfield around the projectile produces a lateral force and a pitching moment that favorably combine to steer the projectile.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
