Plasma diagnosis for the ITER fusion reactor using a polarimetric fibre sensor

For plasma current sensing in next-generation Tokamak thermonuclear fusion reactors like ITER, optical fibre-based polarimetric sensors (also called FOCS for Fibre-Optics Current Sensor) are being considered as an alternative to conventional technologies thanks to their direct measurement of the plasma current by sensing the magnetic field-induced polarization rotation of the light. While the principle of FOCS is well known its application to ITER must be carefully addressed. The use of FOCS in ITER will indeed be subject to detrimental effects such as vibrations, temperature fluctuations and presence of a fibre bundle between the interrogator and the sensing fibre. This talk summarises our latest results in investigating the application of FOCS to ITER. Results showed that in the presence of vibrations, lo-bi spun fibres are preferred over hi-bi spun fibres to meet the ITER requirement. Additionally, we show that the temperature variation around the ITER vacuum vessel does not significantly affect the measurement error. Finally, a compensation method is proposed for any unwanted polarization changes due to the fibre bundle.