In process temperature monitoring of energy beam processing.

The use of non-thermal and atmospheric plasma has been growing in recent years. Applications in wound sterilisation, food decontamination, cleaning and the more traditional machining and deposition are just some of the areas in which new technology is being developed. With the growing use of cool plasma comes the requirement to test and understand the temperature distribution of the jets. Current methods into temperature measurement revolve around spectroscopy and other non-contact methods. Spectroscopy can pose a challenge as a measurement device as it lacks the ability to measure overall gas temperatures in non-thermal plasmas. Contact measurement thermometers, such as thermocouples and resistance temperature detectors are an alternative which can provide an insight into the temperature of the ions and neutral species. However these sensors pose a challenge in gaining accurate or precise temperature measurements due to their susceptibility of electromagnetic interference. Fibre Bragg grating sensors have the ability of measuring both temperature and strain without electromagnetic interference. They possess the ability of multiplexing, being able to measure multiple temperatures across a single fibre, which can aid in measuring over a long distance. They also have the added benefit of being small, lightweight and have quick thermal response times. Additionally their small heat capacity reduces the effect on the temperature of the measurand, improving their accuracy over other physical probes. In this experiment fibre Bragg grating sensors 600 μm and 1000 μm in length and 10μm in diameter have been used to characterise the temperature distribution of non- thermal microwave plasma and thermal radio frequency plasma jets. Thermocouples have been used to compare results against current technologies. Results show the fibre Bragg grating sensors have been successful in determining plasma temperature changes over time, distance and across a variety of different parameters.