L. Pecastaing

Very Fast Rise-Time Short-Pulse High-Voltage Generator

This paper relates to the development of an ultrafast compact system readily applicable to the field of ultrawideband microwave applications such as transient radar or laser drivers. The design, production, and experimental results of a short-pulse generation system are presented in this paper. The coaxial generator technology based on the principle of a line discharge by means of a high-pressure gas switch in a simple transmission line arrangement is described. In the first stage of the process, the coaxial generator was charged by a high-voltage direct current source. Interesting results were obtained, but due to the jitter of the discharge formative time, the reproducibility of the output pulses was not sufficient. To improve the performance, a pulsed source was developed in order to apply an overvoltage to the gap switch and thus reduce the jitter of the discharge formative time. The characteristics of the pulsed source are defined. A thyristor Marx generator and a pulse transformer using magnetic properties of ferrite cores were combined in order to produce this pulsed source. The main performances of this source are a pulse amplitude of 60 kV, a rise time of 250 ns, and a maximum frequency of 900 Hz from a 1-kV dc supply. Finally, the complete generation system is able to generate pulses with 25-kV amplitude and 70-ps rise time through a 50-Omega impedance from the single shot mode up to 900 Hz. The output pulses reproducibility obtained is better than plusmn5%

High Pulsed Power Sources for Broadband Radiation

This paper explains the design and production of two autonomous ultrawideband (UWB) radiation sources. These sources consist of a high-gain broadband antenna that is driven by one of two subnanosecond pulsed power sources. Each source is made up of a Marx generator and a pulse-forming device based on the use of a gaseous spark gap. The first source combines a four-stage 200-kV/34-J Marx generator with a coaxial pulse-forming line. Its main characteristics are an output voltage of 100 kV, a 250-ps rise time, a subnanosecond pulse duration, and a repetition rate of about 40 Hz. The second pulsed source is a ten-stage subnanosecond Marx generator that delivers pulses in the 250-kV/1.5-J range, with a 300-ps rise time and a subnanosecond pulse duration at a pulse repetition rate of 350 Hz. Probes were produced based on capacitive line dividers to measure both the temporal characteristics and the high-voltage (HV) amplitude of the pulses delivered by the pulsed power sources. The antenna, combined with these two pulsed sources, is a traveling-wave antenna called the Valentine antenna. Some mechanical modifications were made to the antenna to improve its dielectric strength. First, a 3-D model of the antenna was created on time-domain electromagnetic software to study the influence of these modifications on its main radiating characteristics. Its high gain and its capability to radiate short pulses without dispersion allow us to achieve a high measured figure of merit (the maximum value of far-field peak-to-peak electric field strength multiplied by the distance). A new method called the Instantaneous Electromagnetic Field Measurement by Signature of a Neutral Object (MICHELSON) method is used to measure the very intense electromagnetic fields that are radiated. The incident field is diffracted by a special small-dimension target. The diffracted field is measured by a conventional low-power UWB antenna. The target that is used has small dimensions, and no cables are used in the field region; thus, the electromagnetic interference that is generated and undergone by the measurement device is considerably limited. The figure of merit that is measured is 436 kV.

UWB SAR system PULSAR: new generator and antenna developments

PULSAR is an Ultra Wide-Band short pulse Radar developed by the CELAR (French Technical Centre for Armament Electronics) and the IRCOM (Research Institute of Microwave and Optical Communications) in order to detect foliage and ground concealed targets. One of the most promising mission of such potential radar is the detection of buried and surface land mine fields. An instrumentation measurement system has been designed and implemented. This paper deals with the recent development efforts on this system, specially on a new pulse generator and a new UWB antenna. Recently, the LGE (Laboratoire de Génie Electrique) has developed a high voltage pulse coaxial generator. These recent developments allowed to increase the pulse output voltage and the pulse rise time. The new UWB antenna is able to support a very high voltage; the bandwidth and the gain are greater than the ones of the previous antenna.

Self-Contained, Hand-Portable, and Repetitive Ultrawideband Radiation Source

This paper presents the design and experimental results of a hand-portable, self-contained, and repetitive radiation source of high-power ultrawideband (UWB) pulses. This source consists of a deployed UWB antenna driven by a high-pulsed power (HPP) generator and powered by a self-contained 50-kV rapid charger at repetition rates up to 100 Hz. By changing the HPP generator, two different electric wave shapes with two different frequency spectra can be generated. Each HPP generator is based on the use of a repetitive Marx generator. On the one hand, a 200-kV/1.4-J Marx generator is associated with a coaxial pulse-forming stage consisting of two highly pressurized spark gap switches and a Blumlein line, which produces bipolar pulses. Its main characteristics are an output voltage of +100 kV/-100 kV and a pulsewidth of 1.5 ns. On the other hand, we have developed a second eight-stage Marx generator, where the pulse-forming stage is the last stage of the structure. It delivers pulses in the 150-kV/1-J range, with a fall time of 300 ps and an 850-ps pulse duration. Electrical signals are radiated by a deployed Valentine antenna. It is a new traveling wave antenna that is designed to radiate high-voltage repetitive pulses with the challenge of high gain and low dispersion in an extremely restricted volume. The design of a rapid charging power supply is also presented, meeting stringent package constraints while still enabling high repetition rates. It has already demonstrated its capability of charging, from a dc power battery, a 5-nF capacitance up to 50 kV in 5 ms at a 100-Hz repetition rate for some bursts of thousand pulses. The autonomy is more than 35 000 shots (depending on the number of battery packs inside). Electric field measurements were performed on the whole package to determine the figure of merit (the maximum value of far-field peak electric field strength multiplied by the distance) of the UWB source in each configuration (bipolar and monopolar sets). The figure of merit measured is 200 kV for both.

Equivalent Model of Photoswitch: Application to the UWB Antenna Design Integrating Impulse Feeding

Optoelectronic devices triggered by a laser ∞ash and operating in linear switching regime allow the generation of short pulses with small time jitters (2ps typically). An Ultra Wide Band antenna array combining as many of this photoswitches as antennas has the advantage to increase the radiation power on one hand and to ofier the agility of the radiation beam on the other hand obtained by time delay of laser illumination. During the step of antenna design, it becomes important to take into account the photoswitch integration in order to increase the peak power and the frequency band of the generated output signal. This paper presents an equivalent model of photoswitch obtained with the transient solver of CST Microwave Studio coupled within CST Design Studio. The second part of this article is dedicated to the integration of a photoswitch even within the antenna.

Simple and compact capacitive voltage probe for measuring voltage impulses up to 0.5 MV

The paper describes a simple and compact 0.5 MV high-voltage capacitive probe developed in common by Université de Pau (France) and Loughborough University (UK). Design details are provided, together with a simple and straightforward methodology developed to assess the characteristics of high-voltage probes. The technique uses a 4 kV pulsed arrangement combined with results from a 2D electric field solver and a thorough PSpice circuit analysis. Finally, a practical example of high-voltage measurement performed using such a probe during the development phase of a high power microwave generator is provided.

Ultra Wideband Antennas for High Pulsed Power Applications

1.1 UWB antennas in the field of high pulsed power For the last few years, the generation of high-power electromagnetic waves has been one of the major applications of high pulsed power (HPP). It has aroused great interest in the scientific community since it is at the origin of several technological advances. Several kinds of high power radiation sources have been created. There currently appears to be a strong inclination towards compact and autonomous sources of high power microwaves (HPM) (Cadilhon et al., 2010; Pecastaing et al., 2009). The systems discussed here always consist of an electrical high pulsed power generator combined with an antenna. The HPP generator consists of a primary energy source, a power-amplification system and a pulse forming stage. It sends the energy to a suitable antenna. When this radiating element has good electromagnetic characteristics over a wide band of frequency and high dielectric strength, it is possible to generate high power electromagnetic waves in the form of pulses. The frequency band of the wave that is radiated can cover a very broad spectrum of over one decade in frequency. In this case, the technique is of undoubted interest for a wide variety of civil and military applications. Such applications can include, for example, ultra-wideband (UWB) pulse radars to detect buried mines or to rescue buried people, the production of nuclear electromagnetic pulse (NEMP) simulators for electromagnetic compatibility and vulnerability tests on electronic and IT equipment, and UWB communications systems and electromagnetic jamming, the principle of which consists of focusing high-power electromagnetic waves on an identified target to compromise the target’s mission by disrupting or destroying its electronic components. Over the years, the evolution of the R&D program for the development of HPM sources has evidenced the technological difficulties intrinsic to each elementary unit and to each of the physical parameters considered. Depending on the wave form chosen, there is in fact a very wide range of possibilities for the generation of microwave power. The only real question is

Optimizing the operation of an electrostatic precipitator by developing a multipoint electrode supplied by a hybrid generator

The authors investigated and improved the filtration efficiency of an electrostatic precipitator (ESP). A laboratory-scale pilot unit was developed to allow experimentation under conditions approaching those of the industrial ESPs used by the CEA at Marcoule (France). After elucidating the electrical phenomena and optically analysing the physical processes occurring inside the precipitator, a specific electrode was developed for use with a hybrid power supply. The experiments were based on analysing the variation over time of the electric charge injected into the particle separator, the particle mass collected at the ground electrode and the charges quantity measured on a grid in the airstream after the electrode unit. Photos were also taken under different electrical discharge conditions. The results show that combining a multipoint electrode and a hybrid generator (30 kV dc and 30 kV, 1 kHz) improves the process efficiency and significantly extends the time frame (more than 10 h) during which the process operates at optimum efficiency.

Demonstration of a Novel Pulsed Electric Field Technique Generating Neither Conduction Currents Nor Joule Effects

This paper is devoted to a detailed presentation of all aspects involved in a demonstration of a novel pulsed electric field (PEF) technique that does not generate neither conduction currents nor Joule effects. Details are given of both the experimental arrangement and the electro-optic Kerr-effect-based diagnostic used in the measurement of the intense PEFs in water. The results show unequivocally that the novel technique is effective in significantly reducing the initial concentration of Escherichia coli bacteria. Finally, a brief comment on the way ahead is provided.

MOUNA: An Autonomous, Compact, High-Power, and Wideband Electromagnetic Source Based on a Novel Resonant Pulsed Transformer

Nowadays, a broad range of modern defense applications requires compact pulsed power generators to produce high-power electromagnetic waves. In a conventional design, such generators consist of a primary energy source and an antenna, separated by a power-amplification system, such as a Marx generator or a Tesla transformer, which forwards the energy from the source to the antenna. The present system, however, uses a novel and very compact high-voltage resonant pulsed transformer to drive a dipole antenna. The complete pulsed power source, termed MOUNA (French acronym for “Module Oscillant Utilisant une Nouvelle Architecture”), is composed of a set of batteries, a dc/dc converter for charging four capacitors, four synchronized spark gap switches, a resonant pulsed transformer that can generate 555 kV/265 ns pulses, an oil peaking switch and, during preliminary testing, a dipole antenna. The paper not only provides design details for each system component, but also presents the mechanical arrangement of the complete pulsed power system and the electrical diagnostics, particularly those related to measurement of the resonant transformer output waveform, the line oscillations, and the radiated electric field.