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Using a polarization-sensitive optical time domain reflectometer (OTDR), plasma current in the International Thermonuclear Experimental Reactor (ITER) can be measured by investigating the Faraday effect-induced polarization rotation in a spun fiber placed around the Vacuum Vessel. However, intrinsic birefringence and external effects like fiber bending and twisting generate unwanted polarization changes and decrease the measurement accuracy. In this paper, a simulation-based approach is developed, considering bending and twisting effects to assess the performance of the reflectometer in measuring plasma current at ITER. The results demonstrate that, for a proper choice of spun sensing fiber parameters (intrinsic beat length and spun period), the performance of the sensor satisfies ITER accuracy.

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In this Letter, a novel, to the best of our knowledge, nondestructive method for measuring the spun fiber parameters (precursor beat length and spun period) is presented both theoretically and experimentally. The proposed technique is based on analyzing the polarization optical frequency domain reflectometer traces. Experimental results are in agreement with the theoretical predictions.

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