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This paper describes the successful development of a 1-MV magnetically insulated Tesla transformer. Full details of the construction are provided, together with the basis of the design procedure. Preliminary results for the prototype transformer are presented and discussed, and future paper is outlined. Index Terms--High-voltage techniques, magnetic insulation, pulsed-power systems, transformers.

Electromagnetic flux compression requires high-quality liners, with copper being a much more effective material than the aluminum used in previous experiments at Loughborough for producing fields of 300 T. Unfortunately, similar small-size copper liners cannot be economically manufactured with sufficiently precise tolerances to prevent the development of liner instabilities during an implosion, leading to a much lower magnetic flux density than anticipated. The paper describes how the performance can however be dramatically improved by the use of an aluminum powder cascade, and presents results showing that the use of this technique has enabled flux densities up to 350 T to be generated using only a 70-kJ capacitor bank. Index Terms--Instabilities, liner implosions, phase transitions, ultrahigh magnetic fields.

A research activity involving the detailed consideration of novel high-voltage transformers for pulsed-power applications has recently begun at Loughborough University. Although the main goal is the demonstration of a compact and lightweight unit employing magnetic insulation under vacuum conditions, the initial stage of the work is directed toward the development of a conventional air-cored transformer as a main component in a compact power supply for high power microwave sources. In cooperation with the Swedish Defence Research Agency (FOI), the power supply has been tested with a microwave source of the vircator type. The power generator for the system uses a 70-kJ/25-kV capacitor bank and an exploding wire array to generate a 150-kV voltage pulse in the primary circuit of a transformer. A pressurized S[F.sub.6] spark gap in the secondary circuit sharpens the high-voltage output so that pulses approaching 500 kV and with a rise time well below 100 ns are generated on a 20-[ohm] high-power resistor, with the peak power in excess of 10 GW. Experimental results are presented from final testing of the system, where a reflex triode vircator replaces the 20-[ohm] resistor. Measurements of the microwave emission using free-field sensors are presented, and comments are made with the microwave emission from the same vircator when powered by a Marx generator at FOI. Index Terms--Compact pulsed-power systems, high-power microwaves (HPMs), high-voltage transformers (HVTs), opening switches (OSs).

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. Index Terms--Electromagnetic pulse (EMP) generation, pulse forming line (PFL), spark gap switch, Tesla transformer.

During an initial phase of an ongoing research program at Loughborough University, ultrahigh magnetic fields of up to 300 T (3 MG) have been generated. These have been produced using only 63 kJ from a fast capacitor bank to implode an Aluminum liner in a [theta]-pinch geometry, and 14.7 kJ from a slow capacitor bank to provide an initial magnetic field. The paper analyzes various ways of improving both the [theta]-pinch magnetic flux-compression efficiency and its reproducibility. As a practical illustration, experimental evidence is presented to demonstrate the benefits obtained from the use of an insulator-metallic phase transition cascade made from powder aluminum. Index Terms--Electromagnetic implosions, magnetic flux-compression, phase-transition, shock waves.

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 b 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. Index Terms--Electromagnetic implosions, magnetic flux-compression, numerical analysis.

This paper describes a novel technique for producing an electromagnetic force to accelerate a conducting projectile situated on the remote side of a metallic shield, for use in novel electromagnetic fasteners. The theoretical background for the technique is explained and is supported by measurements of the velocity achieved by the projectile in a prototype unit. The effect of the initial separation between the drive coil and the projectile is investigated, and it is shown that the shield material has little influence on the projectile dynamics. Index Terms--Aircraft maintenance, diffusion processes, electromagnetic induction, magnetic shielding.

This paper describes the development of a prototype high-energy supply system for producing high-intensity electric and magnetic field impulses for use in medical applications. After presenting the technical requirements and the main design features, the paper focuses on the numerical modeling of the double-coil arrangement that produces the impulses. Predicted time variations of both the circuit currents and the spatial and temporal variations of the electric and magnetic field distributions are compared with full-scale experimental results from the prototype system. Methods of increasing the field intensities are also suggested and results from an optimized design are presented. These indicate an ability to stimulate physical structures such as the renal pacemaker, resulting in a ureteric peristalsis wave. Recent experimental findings are presented from what is probably the most powerful magnetic stimulator so far built, and the practical applications of the work are discussed. Index Terms--Electric field effects, magnetic field effects, medical treatment, pulse power systems.

This paper describes a voltage probe in which the electrooptic Pockels effect is used in the measurement of ultrafast 500-kV pulses. Electrical isolation is provided between the high-voltage and the measurement circuits, and the probe is suitable for use in many applications where more conventional techniques are inapplicable. A special-purpose capacitive voltage divider attenuates the 500 kV to a level acceptable by the crystal of a Pockels Cell. The attenuated voltage then modulates light from a laser system passing through the crystal, with the emerging signal being converted into electrical form and fed to a digital storage oscilloscope to provide a very accurate recording proportional to the divider input voltage. Experimental results confirm both the very fast response of the probe and its high-voltage capability. Index Terms--Optoelectronics, Pockels effect, pulsed high-voltage measurements.

A number of single-pitch minihelical flux-compression generators have been designed, manufactured and tested by Texas Tech University and the University of Missouri-Rolla, as part of a Multidisciplinary University Research Initiative (MURI). Several other Institutions have collaborated in the program, by providing theoretical predictions of the output performance of a generator without having access to the experimental data or making any consequent parameter changes in their numerical codes. As part of this activity, the Plasma and Pulsed Power Group at Loughborough University, Leicestershire, U.K., has used its extensively documented and well-proven two-dimensional (2-D) filamentary modeling approach in conducting detailed theoretical considerations of the behavior of one of the generators. A number of fundamental features of the simulation are described in the paper, such as the inclusion of phase transition in the conductors and the effect of the very high electric field intensity in the contact point region. The ability of the code to provide accurate predictions of the actual generator performance for very-high-input currents is provided by the good agreement achieved with experimental results presented by TTU. Index Terms--Explosive generators, magnetic flux-compression, numerical analysis.

This paper describes a frequency-domain model for the accurate and efficient prediction of harmonic torque pulsations in 3-phase VSI/induction motor drives, which enables rapid considerations to be given to their potentially harmful effects in producing uneven shaft rotation. A detailed analysis is presented for both quasi-square wave (QSW) and optimal PWM modes of switching operation, with the latter technique designed to improve the low-speed drive performance by eliminating low-order harmonic components. A comparison is made with practical results obtained from an experimental 0.56 kW drive and from a comprehensive time-domain model using a numerical solution of the machine equations.

The electrode erosion and lifetime performance of a compact and repetitively triggered field distortion spark gap switch were studied at a repetitive frequency rate of 30 Hz, a peak current of 8.5 kA, and a working voltage of ±35 kV when the switch was filled with a gas mixture of 30% SF6 and 70% N2 at a pressure of 0.3 MPa. The variations of the time-delay jitter and the self-breakdown voltage were both studied for the whole service lifetime of the spark gap switch. The morphology of both the electrodes and the plate insulator, before and after the service lifetime tests, is also analyzed. The results show that during these tests, the time-delay jitter is basically synchronized with the self-breakdown voltage jitter, and both undergo firstly a process of rapidly decreasing their values, then remaining stable, and finally and gradually increasing after 70 000 pulses. The change in the electrode surface roughness (i.e., surface profile) is caused by erosion and chemical deposits in the switch cavity, which are mainly the two factors that affect the time-delay jitter of the switch. Tip protrusions on the electrode surface, due to electrode erosion, contribute to reducing the time-delay jitter. However, due to chemical reactions, fluorides and sulfides are deposited on the switch components, as well as metal particles caused by electrode erosion sputtering. Slowly, after a large number of shots, all these phenomena affect the self-breakdown performance resulting in an increased self-breakdown voltage jitter, which also causes the time-delay jitter to increase. Although there are a number of reasons that contribute to the deterioration of the performance of the switch, it is fortunate that if a switch suffering a degraded performance is reassembled, with the electrodes mechanically polished and all the components cleaned, the optimal performance of the switch can be restored. If maintenance work is carried out regularly to preserve the condition of the switch’s inner components, the service lifetime of the switch can be prolonged. [ABSTRACT FROM AUTHOR]

This work was stimulated by the assumption that for a gas-filled spark gap closing switch operating at a high repetition frequency, there is an optimal frequency range in which the time-delay jitter reaches a minimum value. The experiments to test this assumption use an electrically triggered, field-distortion spark gap filled with the SF6/N2 gas mixture. The results show that indeed, the time-delay jitter decreases for a range of frequencies for which the filling gas can substantially restore the interelectrode insulation before increasing at a higher operation frequency. The experimental results demonstrate the correctness of the abovepresented assumption: the time-delay jitter of the field-distortion spark gap has its minimum when the unit operates in the repetition frequency range between 20 and 30 Hz. Since the recovery time depends on the gas species and the gap distance, the optimum operation frequency range should also vary depending on the spark–gap distance and the filling gas properties. [ABSTRACT FROM AUTHOR]

This paper describes the development of a small field-distortion spark gap switch. Comprehensive experimental studies made with the switch revealed its self-breakdown characteristics, voltage operating range, time delay and jitter, repetition frequency, and finally the electrode erosion processes and duration of its service lifetime. A series of design improvements were required to be implemented in the switch design. For example, to reduce the structural inductance of the switch and to improve its working characteristics, the main electrode was designed as a circular track structure. Similarly, to increase the operation stability and reduce the self-breakdown probability, the trigger electrode was designed as a disk-like structure. Moreover, to balance the gas pressure in the discharge region and increase the stability during closure, a circular hole was added at the center of the trigger electrode. The compact switch has a small size of only 150 mm $\times42$ mm, a weight of 1.5 kg, and can be successfully operated at a voltage over 110 kV, at a repetition rate between 1 and 50 Hz and having a jitter of less than 4 ns. It was experimentally demonstrated that during normal operation conditions, the switch lifetime exceeds 100 000 shots. [ABSTRACT FROM AUTHOR]

The use of explosively driven flux compressors as light and compact autonomous single-shot power supplies for high-power microwave applications requires special attention to be paid to the conditioning and matching elements of the overall system, due to the fast-rising high-voltage output step that is needed. This paper addresses various schemes by which this may be achieved and, based on proven techniques, a practical approach using a high-voltage transformer is described in detail. In addition, it is shown that future developments in long conduction plasma opening switches and fast-pulse compressors will open the way to much more compact and higher performance systems, with characteristics that could also match the requirements of high-power lasers and ion-beam generators. Index Terms--Flux compression, pulsed power supply.

Two-dimensional (2-D) modeling techniques using a filamentary-mesh approach are very well established for use in helical flux-compression generator design and provide results that have been verified experimentally. However, none of the published numerical codes appear to describe adequately certain details involved in calculating the resistance of the helical stator coil. In particular, the skin and proximity effects that arise from diffusion of the magnetic field into the conductor are clearly three-dimensional (3-D) phenomena, and their influence is represented approximately by either existing formulae or a one-dimensional (1-D) description. In most published codes, the formulae that are used provide merely a steady-state approximation to the proximity effect. The present paper outlines a new detailed approach that has been developed for use with an existing 2-D model which forms the first element of an overall more detailed modeling code. It is shown that the scale of the proximity effects in a helical coil carrying a pulsed current can be many times greater than those predicted by the conventional formulae. Index Terms--Coil modeling, flux compression.

This paper presents the basic concepts that underlie a fundamental research activity initiated recently at Loughborough University, U.K. A novel technique is described that enables the so-termed shock-wave-driven flux compression process to be performed inside a laboratory, without the need for any high-explosive charge, and results from preliminary proof-of-principle experiments are analyzed. Details of the necessary ancillary equipment, such as fast (T A / s) generators, electric guns, high-voltage helical transformers, and special transducers are presented, together with a study of the dielectric/metallic phase transition in aluminum 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. Index Terms--High voltage transformer, magnetic flux-compression.

A prolate spheroidal reflector was designed, manufactured, and attached to a bipolar former at the output of a 10-GW-Tesla-driven Blumlein pulsed power generator. The reflector, operated in water, is capable of producing intense pulsed electric fields of the order of 50 kV/cm. Constructional details are provided, together with experimental results, and a detailed analysis using 3-D software modeling of the reflector that provides results in good agreement with experimental data. [ABSTRACT FROM AUTHOR]

A number of published papers are reporting that electromagnetic radiation is being generated by unexpected sources such as explosives, metal fracturing, or peeling common adhesive tape under vacuum. Here, we report on an unconventional microwave source (UMS) that produces, with a high degree of reproducibility, electromagnetic radiation covering an unusually wide frequency spectrum ranging from hundreds of kilohertz to many tens of gigahertz. The UMS is based on picosecond electric breakdown of a polymer and does not require vacuum technology. [ABSTRACT FROM AUTHOR]

A bipolar Blumlein former has been designed and successfully implemented as an extension to an existing 10-GW-Tesla-driven Blumlein pulsed power generator. The new system is capable of generating a voltage impulse with a peak-to-peak value reaching 650 kV and having a high-frequency limit of the bandwidth well in excess of 1 GHz. Constructional details are provided, together with experimental results and analysis using the 3-D software modeling of the bipolar former that provides the results in good agreement with experimental data. [ABSTRACT FROM AUTHOR]

The temperature dependence of the Kerr constant for water has been determined over the range 19 °C–45 °C at a wavelength of 658 nm. This paper presents the experimental arrangement used for this purpose and the data obtained, for which a polynomial fit is provided. A formula is also suggested to help estimate the variation of the Kerr constant for water with both temperature and wavelength. [ABSTRACT FROM AUTHOR]

A number of high-power applications require a transportable high-energy, high-current GW generator to drive a pulsed power system at the output. A first prototype, based on exploding wire technology and using an H-bridge circuit configuration, was developed at Loughborough University a few years ago and has been previously reported. The present stage of the work has necessitated the development of a more powerful and energetic source, and this is now based on inductive storage technology. A 400 kJ capacitor bank is connected by a high-Coulomb explosively driven closing switch with an air-cored 0.6 MV transformer, an exploding wire array, and a high-power diode based on a polarity-dependent spark-gap completing the arrangement. The GW generator, including the command and control module, is accommodated in two ISO containers. The various components of the generator are described in this paper, together with results obtained from full-scale tests. [ABSTRACT FROM PUBLISHER]

A repetitive 0.6 MV, 10 GW Tesla-driven Blumlein pulsed power generator, with an overall energy efficiency in excess of 90%, has been designed, manufactured and demonstrated by the Pulsed Power Group at Loughborough University. This paper describes the application of various numerical techniques used to design a successful generator, such as filamentary modeling and electrostatic and transient circuit analysis. All the major parameters of both the Tesla transformer and the Blumlein pulse-forming line were determined, enabling accurate modeling of the overall unit to be performed. The wide-bandwidth embedded sensors used to monitor the dynamic characteristics of the overall system are also presented. Experimental results obtained during this major experimental program are compared with theoretical predictions and the way ahead toward generating faster output voltage impulses is considered. [ABSTRACT FROM PUBLISHER]

This paper provides an overview of the response of the tuned secondary circuit of a Tesla transformer, following impulse excitation from the tuned primary circuit. Multiorder oscillatory voltages and currents are energized in the secondary circuit, and research is ongoing to determine the fundamental and higher order modes for various secondary winding configurations, with the aim of developing design techniques that can be used to suppress the generation of the higher order modes. It is anticipated that this will lead to generators which exhibit enhanced spectral purity and which will be better suited to use in electronic warfare applications than conventionally wound Tesla transformers. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper describes the successful development of a 1-MV magnetically insulated Tesla transformer. Full details of the construction are provided, together with the basis of the design procedure. Preliminary results for the prototype transformer are presented and discussed, and future paper is outlined. [ABSTRACT FROM AUTHOR]

During an initial phase of an ongoing research program at Loughborough University, ultrahigh magnetic fields of up to 300 T (3 MG) have been generated. These have been produced using only 63 LI from a fast capacitor bank to implode an aluminum liner in a θ-pinch geometry, and 14.7 kJ from a slow capacitor bank to provide an initial magnetic field. The paper analyzes various ways of improving both the θ-pinch magnetic flux-compression efficiency and its reproducibility. As a practical illustration, experimental evidence is presented to demonstrate the benefits obtained from the use of an insulator-metallic phase transition cascade made from powder aluminum. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]