Test of fiber optic based current sensors on the Tore Supra tokamak

Fiber optic current sensors have been recently considered for current measurements in ITER. These sensors exploit Ampereʹs law by measuring the change of light polarization along an optical fiber subjected to a magnetic field aligned along the fiber axis. Through collaboration between CEA and SCK·CEN, such fiber optic current sensors have been installed on Tore Supra tokamak as a first demonstration for possible future applications in ITER. This paper aims at reporting the results obtained on Tore Supra. It discusses the technique used to separate the effects of the intrinsic linear birefringence and the magneto-induced circular birefringence, the latter enabling the determination of the current flowing through the area defined by the optic fiber loop. Three optical fibers have been installed on Tore Supra for assessment of their linearity response on a wide range of plasma current from 0.3 to 1.4 MA as well as their long term stability. The extrapolation of the results and the issues related to a future application on ITER are finally discussed.