B.M. Novac

A Compact Battery-Powered Half-Megavolt Transformer System for EMP Generation

High-power electromagnetic pulses are of importance in a variety of applications such as transient radar and particle accelerators and when investigating the effect of strong radio-frequency impulses on electronic systems. With all these possibilities in mind, a compact and portable source has been developed by the Plasma and Pulsed Power Group, Loughborough University, U.K., in collaboration with the Defense Science and Technology Laboratory, U.K. The source is based on a pulsed resonant Tesla transformer that produces nanosecond rise-time pulses at voltages exceeding 0.5 MV. In addition to the Tesla transformer, the other major components include a pulse forming line, a high-voltage fast spark gap switch, and a half-wavelength dipole antenna. The pulsed radiated electric field measured at 10 m from the source has a peak amplitude of 12.4 kV/m

Fast and accurate two-dimensional modelling of high-current, high-voltage air-cored transformers

This paper presents a detailed two-dimensional model for high-voltage air-cored pulse transformers of two quite different designs. A filamentary technique takes magnetic diffusion fully into account and enables the resistances and self and mutual inductances that are effective under fast transient conditions to be calculated. Very good agreement between calculated and measured results for typical transformers has been obtained in several cases, and the model is now regularly used in the design of compact high-power sources.

Design, construction and testing of explosive-driven helical generators

This paper describes the development of a very efficient computer model for the design and performance prediction of explosive-driven helical generators. The model is based on simple theoretical considerations. Validation of the model is achieved by comparing the theoretical and measured performances of existing both high- and low-energy generators. It is shown that, although the basic model predicts accurately the load current history of high-energy generators, a somewhat more elaborate model is needed for low-energy devices. The model has been used in the design of a simple 1 MJ generator with an eight-section stator coil, intended for use as a current source in an investigation of high-current conditioning systems. A description is given of the construction and testing of this device. Experimental results are in accordance with predictions from the design code and establish that, when primed with 40 kJ at 50 kA from a capacitor bank and using 15 kg of high explosive, the generator is capable of delivering an output of 1 MJ at 7 MA to a coaxial load.

Fast exploding-foil switch techniques for capacitor bank and flux compressor output conditioning

This paper describes exploding foil opening and closing switch techniques for use in capacitor bank and flux compressor output conditioning circuits. A simple approach was evolved during an extensive experimental programme, aimed at producing a current pulse with a rise time of a few nanoseconds from the output of a flux compressor (or flux compression generator). Capacitor-based experiments provide data for an empirical model for copper foils, used subsequently in a computer program to predict the results of experiments in which exploding foils are used as both opening and closing switches. The switches operate automatically, thus avoiding the problems of triggering between stages of a conditioning circuit. Data from a 1 MJ flux-compressor exploding-foil opening-switch experiment with a run time of 160 mu s are presented and analysed using the theoretical model.

Lethality mechanisms in Escherichia coli induced by intense sub-microsecond electrical pulses

In this letter, the authors present the inactivation kinetics of cells of Escherichia coli and its mutants following treatment with high-intensity electrical pulses of 700 and 32ns durations. Their experimental results suggest that bacterial inactivation by 700ns pulses is consistent with a mechanism of reversible electroporation, whereas inactivation by 32ns pulses may occur as a result of damage to intracellular components. They believe that their results represent a first step towards elucidating the mechanism of lethality of submicrosecond pulses of different durations in prokaryotes.

A fast and compact θ-pinch electromagnetic flux-compression generator

Ultrahigh magnetic fields up to 300 T (3 MG) have been generated by electromagnetic flux compression using only 63 kJ from a fast capacitor bank to implode aluminium liners, with 14.7 kJ from a slow capacitor bank needed to provide an initial magnetic field. With no initial field present, pulses of magnetic flux density having a time rate-of-change exceeding 3 × 108 T s−1 have been produced and measured, opening the way for a range of dynamic transformer applications. The outcome of the work suggests that, when using fast multi-MA banks, flux compression can be viewed as an alternative to the single-turn coil technique that will move the boundary of the magnetic fields well beyond 300 T without the need for significant additional investments.

Simple 2D model for helical flux-compression generators

This paper presents a simple but complete 2D model for helical flux-compression generators that overcomes many of the limitations present in existing zero-dimensional models. The generator circuit is effectively decomposed into separate z and; current carrying circuits, with each of the; circuits (rings) corresponding to a different current. Use is also made of a technique by which these rings are sequentially switched out of circuit. The approach proposed opens the way to a full understanding of the behavior of cascade systems of generators inductively coupled by dynamic transformers using the so-called flux-trapping technique. In addition, the model can also yield an important insight into the phenomena that differentiates the performance of small generators when primed by a capacitor, a battery, or an externally produced magnetic field. Finally, the numerical code developed in the paper can readily be adapted to model high-energy and high-current generators in which the helical coil and the armature are of variable geometry. Valuable design information is provided on the magnetic and the electric field distributions within the generator and on the likely radial and axial movements of the stator turns.

2-D modeling of electromagnetic flux-compression in /spl theta/-pinch geometry

A major research program underway at Loughborough University involves the generation of ultrahigh magnetic fields up to 300 T (3 MG) by means of magnetic flux-compression. A high pulsed current is discharged into a single-turn driving coil surrounding a liner, with various aspects of the associated practical work being presented in a companion paper. This paper explains the two-dimensional filamentary modeling technique that is used to provide detailed prediction of the liner implosion, driving coil dynamics and magnetic field diffusion through all the metallic elements of the arrangement. The main typical results from numerical experiments are presented and experimental data are compared with theoretical predictions.

2D Modeling of Inductively Coupled Helical Flux-compression Generators—FLUXAR Systems

In a number of single-shot applications and experiments at remote locations where flux-compression generators provide the most practicable power source, it may be necessary to use cascaded generators with inductive coupling between them to provide the required power amplification. The complexity of the resulting system appears to have so far inhibited the development of any simple but complete numerical code, and has prevented a full understanding of the complex action of the overall system. The present paper meets these requirements, by extending an existing simple 2D helical generator code, and shows how this can be used to solve problems arising from the design stage of a prototype system.

Experimental and Numerical Studies of Megagauss Magnetic-Field Generation at LANL-NHMFL

The LANL-NHMFL Megagauss Facility has a well-established history of generating ultrahigh magnetic fields beyond 200 T for a broad range of applications. Using the 2-D Loughborough filamentary modeling, a detailed numerical analysis of the single-turn technique was performed. Single-turn calculations for the standard coil (10 × 10 × 3.2 mm) proved to be extremely accurate up to 40-kV capacitor bank charging, corresponding to a field of 185 T, and also revealed important aspects to be observed during experimentation. For pushing the boundaries toward 500 T, a major effort is under way to perform fast electromagnetic flux compression using a pulsed-power system mainly based on the same capacitor bank. Full details of the design for the new arrangement are given, and based on a well-proven 2-D filamentary modeling, the complex phenomena expected during the flux-compression process are highlighted.