C.C. Wright

Non invasive rail track detection system using microwave sensor

As fuel costs continue to rise, efficient public transport, especially rail will play an increasingly important role in the UK and worldwide. For the safe operation of the rail system, it is necessary that the condition of the rails can be monitored on a continual basis. An important part of this monitoring process is crack detection. Much research effort has been spent in the development of reliable, repeatable crack detection methods for the use on the service rail. In this research a new crack detection method has been investigated which utilizes microwave sensors to inspect the rail surface. Initial data from experiment are presented.

Low cost undulator magnets for industrial free electron masers

At the University of Liverpool we are developing free electron masers <100 kV as a power source for industrial microwave applications. In order to be considered practical, such a device needs to have a cost comparable with conventional sources of microwave power. To achieve this we required an undulator magnet design which was considerably less expensive than the designs normally used in research-based free electron lasers and free electron masers. This paper describes techniques used to successfully construct low cost undulator magnets.

Development of an extrinsic optical fibre temperature sensor for monitoring liquid temperature in harsh industrial environments

A novel phosphor coated glassware based technique for measuring liquid temperature up to 120 °C has been investigated and developed. The active coating consists of a mixture of two phosphor powders which is applied to three different test vessels. One test vessel containing 40 ml of water is heated by a heating coil and its phosphor coating is connected by two optical fibres positioned directly beneath the external base of the beaker, which are used to transmit and receive light. The remaining two test vessels are individually placed in an industrial free electron laser (IFEL), which provides the necessary microwave radiation for heating liquids. Thermal quenching dominates the luminescence characteristics of one phosphor while the second phosphor does not undergo thermal quenching. Ratios of their emission intensities are calculated and analysed. The resulting ratio decreases linearly as temperature increases. The results presented indicate a temporal response of 1 s as well as good repeatability when calibrated against a thermocouple in the laboratory. This paper also describes testing of the coating and its application in monitoring liquid temperature in an IFEL.

The dimensions of the electron beam tunnel in a folded waveguide TWT

If the optimum performance of a folded waveguide travelling wave tube (FWTWT) is to be achieved, then choosing the correct dimensions for the electron beam tunnel is critical. In this abstract, we consider some of the factors that affect this choice, and suggest an optimum tunnel diameter.

The dependence of the oscillation frequency of an FEM on beam voltage

Abstract A waveguide free electron maser oscillator operating in the X-band frequency range has been constructed. It has been observed that the frequencies of oscillation, although close to the longitudinal modes of the cavity, vary slightly with electron beam voltage. It is proposed that this effect is due to the voltage-dependent variation in the phase of the radiation caused by the interaction with the electron beam. An initial comparison has been made between the observed variation of frequency with voltage and simple calculations carried out using the small signal approximation.

Cut-off mode suppression in a waveguide FEM oscillator

We have constructed a waveguide FEM oscillator for use as a power source in research into industrial microwave applications. We report problems encountered when attempting to increase the output coupling of this device and present the results of our attempted solutions.

Free Electron Maser as a Frequency Agile Microwave Source

Most microwave sources have a very limited operating frequency range without the use of mechanical tuning. This is because they tend to be slow wave devices with an internal structure which prevents wide frequency variation. A waveguide free electron maser is a fast wave device which does not suffer from this limitation. Selection from a wide range of operating frequencies can be made by simply adjusting the operating voltage. This paper reports the development of a reasonably low cost free electron maser (FEM) as a source for applications requiring a frequency agile microwave power source.

Compact Tuneable Terahertz Source

It has recently been proposed that a folded waveguide travelling wave tube could be constructed using silicon microfabrication technology. When configured as an oscillator this device could provide a high power (>100mW), highly efficient (>15%), reliable, compact and cheap source for the terahertz gap. This paper presents the current status of Liverpool John Moores University THz source. This includes theoretical and numerical simulations of the electron beam interaction with the electromagnetic waves (EM) and the design and construction of the EM wave interaction cavity. This research project is supported by the UK EMRS/DTC

Tuneable FEM system as a plasma source for biological applications

There is increasing interest in the use of microwave power for industrial applications. A pulsed tuneable microwave source is beneficial as it allows the high electromagnetic field of a high power to be applied to a target without excessive heating. The free electron maser (FEM) is the tuneable source with ability to operate across a wide range of frequencies from 8 to 20 GHz. Using higher frequencies than the common 2.45 magnetron, increases the fields obtained and also beneficial scaling effects on some applications, such as microwave induced plasmas. The paper presents the basic principles of the FEM system as well as the applications of UV.

Theoretical and experimental results of a compact industrial microwave free electron maser system

The role of microwaves within material technologies has so far been a minor one, this is because the availability of the magnetron source, which can only provide distributed heating, with simple amplitude modulation control. However, we have designed a tunable source, industrial free electron maser (IFEM), which provides sufficient pulsed peak power for various applications, in material processing. This requires focused microwave power, similar to a laser beam, to achieve high power density. In this paper, the theoretical results of the interaction region will be explained as well as the principal of operation and IFEM system set-up. The design and construction of the system main components including electron gun, wiggler magnet, cavity resonator and energy recovery section are reported. Results of the effective industrial use of IFEM to enable striking and maintaining low-pressure plasmas and sufficient average power to perform experiments using germicidal UV and ozone generating lamps are described.