G. A. Woolsey*, G. B. Scelsi, V. Everett and R. Irawan

Division of Physics and Electronics Engineering
University of New England, Armidale, NSW 2351, Australia
gwoolsey@metz.une.edu.au

Optical fibre sensors have many attributes that make them attractive for diagnostics in plasmas and electrical discharges. Their insulating nature and their use of photons for interrogation makes them immune to high voltages and electromagnetic noise, and so they have advantages over the more conventional electric and magnetic probes used to measure plasma parameters. The small dimensions of optical fibres are a further advantage, allowing much better spatial resolution than measuring techniques such as optical spectroscopy and light scattering. Furthermore, the facility for remote sensing provided by optical fibres can be particularly useful when working with large-scale systems.

Apart from our work at the University of New England, the application of optical fibre sensors to plasma systems has been limited to some early measurements of fusion plasma current using Faraday rotation. We have applied established optical fibre sensors to the study of plasmas and discharges, and are developing some new sensors specifically for such study. In this paper, optical fibre sensors for the measurement of temperature and chemical decomposition will be described; and results of measurements made in some dc discharges and rf plasmas with these sensors will be presented.

The temperature sensor is essentially the arm of an optical fibre interferometer in which a phase shift results from the change in refractive index and length brought about by a rise in temperature. The sensor used to monitor possible changes in gas composition and deposition of solid by-products that may occur in a plasma or discharge relies on a measurement of the degree of evanescent-wave absorption of the light travelling through an optical fibre.