Validation of Joint European Torus polarimetric measurements with residual analysis

Recently a complete model of JET polarimeter calibration has been developed. A specific propagation code has also been written to simulate the measurements of both the vertical and horizontal chords during plasma operation. In this paper, these two models have been checked with residual analysis methods valid for nonlinear systems. The differences between the estimates of the codes and the experimental measurements, during both calibration and plasma operation, have been calculated and analysed statistically. The distribution of the residuals confirms the quality of the model developed to interpret the calibration of the diagnostic. On the other hand, during plasma operation, the residuals do not present a Gaussian distribution and there is clear evidence of serial correlation at subsequent times. Correlation analysis with the inputs indicates that problems with the magnetic field topology, provided by an independent equilibrium code, are the source of the inadequacies in the results of the propagation model.