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.

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

Drilling is a part of our everyday life. The present drilling technologies are reaching their efficiency limits, therefore some novel alternatives are needed. A promising method is plasma channel drilling (PCD), where a rock is fragmented with high voltage pulses. Due to the specifics of the process, PCD operations require an isolating medium, usually water, around the electrodes (drill bit). When a very fast rising high voltage pulse is applied to the rock surface the electrical strength of the rock is lower than that of the surrounding water. Thereafter, the electrical breakdown creates an arc in the rock, which by thermal expansion causes mechanical fragmentation. So far, the main research has been done with large scale Marx generators with drill bit sizes of more than 10 cm. Additionally, only high energy pulses have been applied to the rock. Therefore, in this thesis the focus is on studying the lower limits of PCD, designing suitable compact modulators and experimentally finding optimum energy levels. In order to define specifications for the pulse generator, a literature review was conducted. For water, several scientific sources were

Compact Pulse Modulator for Plasma Channel Drilling

The development of an autonomous, repetitive, pulsed power generator is presented. This work is a coordinate effort between CEA, Pau University and Technix to develop a tightly integrated unit, including a battery pack, an intermediate dc/dc converter, a high voltage dc/dc converter, the control system and a high PRF Marx generator. Pau University has designed the Marx generator. They have built a 170 mm diameter, 330 mm length Marx generator capable of delivering 200 kV pulses into 50 Ω impedance with tens nanosecond rise times and a 100 Hz repetition rate, enabling it to drive a pulse forming line and peaking switches. The French Atomic Energy Commission has worked closely with the French company Technix in developing a rapid charging power supply to meet stringent package constraints and still permit high pulse repetition rates. This system has already demonstrated the ability to charge, from DC battery power, a 5 nF capacitance up to 50 kV in 5 ms in a burst of one thousand pulses with 100 Hz repetition rate, delivering a peak power of 3.2 kW. The autonomy is more than 35000 shots or 35 bursts. This generator is equipped with a microcontroller which is remote at a distance up to 75 m with an optical fiber interface. Details of this repetitive peak power generator are presented in this paper. Results of preliminary tests are also included.

Compact and portable, repetitive high peak power generator for an ultra-wideband source

The paper presents a study on the development of an autonomous, repetitive, pulsed power generator based on a self-loaded Marx generator. Three French entities: CEA, Technix and LGE (Pau University), developed a tightly integrated unit, including a battery pack, an intermediate dc/dc converter, a high-voltage dc/dc converter, a control system, and a high pulse repetition frequency (PRF) Marx generator with its integrated pulse-forming line (PFL). This complete device is able to deliver 150 kV pulses into a 50 Ω impedance with the following principle characteristics: a rise time of about 650 ps, a fall time lower than 300 ps, a pulse width of about 1.6 ns, a repetition rate of 100 Hz and a burst duration of 10 s. The details of this repetitive peak power generator are presented in this paper. The results of preliminary tests are also included.

Compact Self-Loaded Marx Generator with Integrated Pulse-forming Line for an Ultra-Wideband Source

Marx generator connected to peaking capacitor and peaking switch can generate Ultra-Wideband (UWB) radiation. A new peaking switch is designed for converting the existing nanosecond Marx generator to a UWB source. The paper explains the particle in cell (PIC) simulation for this peaking switch, using MAGIC 3D software. This peaking switch electrode is made up of copper tungsten material and is fixed inside the hermitically sealed derlin material. The switch can withstand a gas pressure up to 13.5 kg/cm2. The lower electrode of the switch is connected to the last stage of the Marx generator. Initially Marx generator (without peaking stage) in air; gives the output pulse with peak amplitude of 113.75 kV and pulse rise time of 25 ns. Thus, we design a new peaking switch to improve the rise time of output pulse and to pressurize this peaking switch separately (i.e. Marx and peaking switch is at different pressure). The PIC simulation gives the particle charge density, current density, E counter plot, emitted electron current, and particle energy along the axis of gap between electrodes. The charge injection and electric field dependence on ionic dissociation phenomenon are briefly analyzed using this simulation. The model is simulated with different gases (N2, H2, and Air) under different pressure (2kg/cm2, 5kg/cm2, 10kg/cm2).

Particle in cell simulation of peaking switch for breakdown evaluation

Traditional uses of the Marx generator have been limited to energy storage and delivering systems, such as charging capacitors or pulse forming lines. However, low energy, compact, high peak power Marx generators can be used as repetitive drivers for many applications. This paper presents the design, the realisation and experimental tests of a repetitive auto-triggered Marx generator expected to be the driver of a broadband radiation system. This whole system consists of a pulsed power source, i.e. a pulse forming line charged by a Marx bank and an UWB antenna array. Design of the Marx generator were planned to reach a voltage level of up to 400kV, a 200Hz repetition rate and a good reproducibility. In this way, the generator is supplied with a high voltage pulsed power supply; charging and discharging circuits were made of home-designed inductors. Furthermore, we focus on the first stage of this Marx generator in which a new simple auto-triggered spark-gap was integrated. The Marx is then combined to a forming line and a peaking spark gap to deliver rectangular output pulses with rise-times closed to 250ps.

A. Silvestre de Ferron

Papers

Repetitive auto-triggered Marx generator as the driver of an ultrawideband source