Magnetophotonic sensor systems for fibre-optic magnetic diagnostics in tokamak fusion reactors

Electrical power generation through controlled nuclear fusion has the potential to make a substantial contribution to the global generation pool within the next century. However, continuous operation of fusion reactors is not yet achieved. As such, a key objective of the next-generation machines is to increase the duration of operational pulses. As fusion reactors progress towards steady-state operation, the use of present inductive transducers as part of critical magnetic diagnostic systems becomes increasingly unfeasible. In this thesis, it is proposed that due to their record of high performance in adverse conditions, optical fibre sensors may be the most appropriate alternative measurement technology. However, in order to reap the benefits associated with fibre sensors - such as minimised wiring, serial multiplexing, and electrical and chemical passivity - a new class of intrinsic point sensors is required that can operate within the extremely harsh nuclear fusion environment. To achieve this, two spectrally-encoding reflection-mode sensors that function on a purely magnetophotonic basis are developed, since it is shown that only this mechanism will succeed in the fusion environment. By exploiting the nonreciprocality of the Faraday effect, it is shown how fibre Bragg gratings incorporating structural defects can yield enhanced, localised measurements. An alternative scheme enables direct measurement of the magnetic circular birefringence using polarisation mode switching. Both techniques provide a true all-fibre point measurement of magnetic field and retain serial multiplexing capabilities. Additionally, a supporting interrogation system is demonstrated that combines high-resolution measurement with high-speed multiplexing. The transducers and associated systems described in this thesis are shown to meet the criteria both for performance and for environmental robustness. As such, their further development as part of a tokamak magnetic diagnostic scheme is recommended.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral-pg

Grantor dc:publisher.institution

University of Strathclyde

Year dc:date.issued

2011

Author dc:creator

• Orr, Philip J. G.

DOI

10.48730/9dm4-g851

Identifier

T12939

OAI identifier oai:identifier

oai:strathclyde:tx31qh71t