2D tomography of SXR data from toroidally separated cameras for studies of fast instabilities and impurity inje ction on JET

The spatial distribution of the Soft X-ray (SXR) em issivities in JET plasmas may significantly contribute to the interpretation of experiments wit h the new ITER-like wall, in particular in studies of radiation of impurities. In this perspec tive, two radiation damaged SXR detector arrays were replaced in the recent JET shutdown and a new fast data acquisition system was connected to the SXR diagnostics. To investigate th e relevance of the diagnostic for the 2D tomography, a robust algorithm based on the Minimum Fisher Regularisation (MFR) [1] is being applied to the existing SXR data. The main ch allenge in this respect is due to the different toroidal location of the SXR pinhole came ras at JET. In the present contribution, evolution of the reconstructed SXR emissivity after Ar and Ni injection is studied with particular attention to the role of preferential sm oothing along magnetic flux surfaces. It is demonstrated that the SXR perturbations due to impurities can be spatially analysed with sufficiently low, quantifiable errors. As expected, appreciable distortion of the tomographic reconstructions due to the diagnostic setup is caus ed only by rapid phenomena. In this case, phase shift in data from different cameras may be i ntroduced to adjust data projections to a singular toroidal position. The required phase shi ft can be determined either from the magnetic diagnostic, or from cross-correlation of t he SXR data. With this technique, the m=1 modes and partly the m=2 modes have been clearly localised and reconstructed. Capability of the technique to resolve higer modes numbers via th e rigid body assumption is under investigation.