R.J. Cliffe

High-voltage and high-current automatic crowbar

In one common type of single-shot high-current crowbar, a short-circuit path is created by the deliberate failure of the solid insulation separating two conductors, by either the explosive fusing of a conductor carrying the circuit current or the controlled firing of a detonator circuit. Unfortunately, in neither technique does the voltage between the conductors directly initiate the explosion, nor is the crowbar necessarily closed within a set range of the circuit voltage. This paper describes a novel switch that overcomes this difficulty. Semiconductor devices are connected such that they explode and break through the insulation shortly after the voltage between the conductors moves outside a set range.

An ultra-fast electro-optic probe for 500 kV pulsed voltage measurements

This paper describes the use of an assembly of electro-optic components and a high-performance capacitive voltage divider in a novel voltage-measurement probe for use in short-duration 500 kV pulsed-power situations, where conventional probes are unsuitable. Complete electrical isolation is provided between the high-voltage circuit and the recording oscilloscope. Experimental results confirm a predicted rise-time of less than about 3 ns, which is significantly better than that of high-quality 90 MHz bandwidth commercially available probes for the same level of voltage.

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.

A novel carbon gun for use with plasma opening switches

The carbon gun is probably the most common plasma source used in plasma opening switches. Nevertheless, it either produces a contaminated plasma, as the flashover surface erodes, or requires regular treatment with graphite paint. The novel form of the plasma gun described in this paper overcomes the disadvantages of existing designs and produces a cleaner plasma. Experimental results illustrate the performance of a prototype system.

Interfacing transformer for a pulsed load current exceeding 1 MA

In much pulsed power experimentation a capacitor bank is discharged into an inductive load, but although sufficient energy may be available in the capacitors their voltage rating may considerably exceed that necessary for the load and the current delivered during the experiment may accordingly be too low. This paper describes a novel design of air-cored transformer that has been used as an interfacing or matching device in such a situation, where peak load currents between 1 and 2 MA were required. Design considerations led to the use of an air-cored autotransformer connection wound with copper sheet conductors. Although thick wide conductors and clamping are needed to prevent deformation due to high magnetic pressure, the transformer is nevertheless relatively simple, easy to make, lightweight and inexpensive. This paper describes the design and the winding arrangement of the transformer that was constructed, and presents typical experimental results.

An ultrafast probe for high-voltage pulsed measurements

This paper presents the latest stage in the development of a high-voltage electro-optic voltage probe, intended for use in a wide range of fast pulsed-power applications for which more conventional probes are unsuitable. The 500 kV voltage to be measured is attenuated by a special purpose capacitive voltage divider, before being fed to a Pockels cell. The cell also receives light from a laser, and this is modulated by the output of the voltage divider before the emerging signal is converted into electrical form and recorded on a digital storage oscilloscope. Experimental results shown in the paper confirm the fast response and high-voltage capabilities of the probe.

Pulsed-power research at Loughborough University

This is a companion paper to the other papers at the Conference that emanate from Loughborough University, UK. It introduces a few of the other interesting activities that are underway as part of the overall pulsed power research activity.

A ring carbon plasma gun for the plasma opening switch

The carbon plasma gun is commonly used as a source of dense plasma for plasma opening switches. The plasma is produced by the surface flashover of an insulator, although an even distribution is difficult to achieve when overall space restrictions limit the number of guns that can be employed. This paper describes a novel ring gun that, in addition to overcoming this problem, also enhances the switch performance by producing a surface flashover of the insulation that travels along a circular path. A study is presented of an experimental gun, using measured data provided by electrical probes and optical techniques. Supporting theoretical explanations are given.