Impact of calibration technique on measurement accuracy for the JET core charge-exchange system

The core charge-exchange diagnostic at the Joint European Torus (JET) provides measurements of the impurity ion temperature T-i, toroidal velocity V-Phi, and impurity ion densities n(imp), across the whole minor radius. A contribution to the uncertainty of the measured quantities is the error resulting from the multi-Gaussian fit and photon statistics, usually quoted for each measured data. Absolute intensity calibration and especially alignment of the viewing directions can introduce an important systematic error. The technique adopted at JET to reduce this systematic contribution to the error is presented in this paper. The error in T-i, V-Phi, and n(imp) is then discussed depending on their use.