H.R. Stewardson

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.

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.

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.

A fast electro-optic high-voltage sensor

This communication describes the construction and testing of a fast electro-optic high-voltage sensor, intended for use in a variety of pulsed-power applications. A 150 kV coaxial high-voltage cable is adapted to form an adjustable voltage divider, with the voltage across the lower section of the divider being measured with the aid of a Pockels cell. As developed, the sensor has been employed to measure 15 kV pulses with a rise time of less than 3 ns, and work is in hand to extend the pulse voltage measurement into the megavolt region.

Fuse conditioning of the output of a capacitor bank to drive a PEOS

The paper details power capacitor bank experiments performed to assess the performance of a pulsed power plasma erosion opening switch (PEOS). A description is given of the PEOS, which was of an inexpensive and expendable design, and was intended for use as the final stage of a flux compressor output conditioning circuit. Techniques using automatically operating exploding foils, as both opening and closing switches, condition the 9 /spl mu/s quarter-wave output pulse from the capacitor bank to a 400 ns pulse to the PEOS. An outline is given of the computer modelling and the experimental procedures used to establish the optimum operating conditions, and results are presented which illustrate the behaviour of the PEOS.

Pulsed-power Technology And Experimentation At Loughborough University Of Technology

The paper introduces the pulsed-power programme of research at Loughborough University of Technology (LUT), which began some 15 years ago with the production and measurement of blast waves from exploding wires. More recently LUT have assembled facilities and techniques, both in the laboratory and on firing ranges, for investigation into methods of conditioning and sharpening the output of a flux compressor (FC) and for participating in a collaborative investigation of propellant and explosively driven magneto-hydrodynamic (MHD) devices. The various facilities and the FC conditioning techniques are described, their contributions to the MHD investigation are outlined and typical results are presented.

A two-stage exploding-foil/plasma erosion opening switch conditioning system

When a load requiring a very fast rising current is fed from a flux-compression generator, it is necessary to introduce a conditioning circuit in order to reduce the rise time of the generator output current substantially. The final stage of this circuit will include a plasma erosion opening switch, which is the fastest known opening switch for use at the current levels involved. This paper presents results obtained during the development of a novel two-stage conditioning circuit and compares the experimental performance of the circuit with results provided by a computer simulation. A time compression of the rise time of the currents from microseconds to less than 100 ns was obtained, representing a 40-fold increase in the corresponding signals.

SHARPENING A FLUX COMPRESSOR OUTPUT USING EXPLODING FOIL & PLASMA SWITCHING TECHNIQUES

The paper describes an on-going research programme into compact explosively-driven energy sources, together with the techniques and conditioning circuits used to produce sharp high-voltage output pulses. Both flux compressor (FC) and magnetohydrodynamic (MHD) sources are considered. An outline is given of FC designs and firing arrangements, and the potential and use of explosively-driven MHD sources with meatgrinder techniques for initial priming are mentioned. A description is given of output conditioning experiments, both in the laboratory and on the firing range, in which exploding and explosively-formed foil and plasma switching techniques are all used.

A novel flux compression/dynamic transformer technique for high-voltage pulse generation

The paper presents the basic concepts that underlie an EPSRC funded research activity initiated at Loughborough University. A novel technique is described that enables the so termed shock wave driven flux compression process to be performed inside a laboratory, without the use of any high-explosive charge, and results from preliminary proof of principle experiments are analysed. Details of the necessary ancillary equipment, such as fast (TA/s) generators, electric guns, high voltage resistors, high voltage vacuum helical transformers and specific transducers are presented, together with a study of the dielectric/metallic phase transition in aluminium powder. The paper concludes by showing how the different concepts can be combined, leading to a high-voltage pulse generator with a fast-rising output.