Equilibrium based iterative tomography technique for soft-x-ray in W7A stellarator

Several algorithms have been developed for x-ray tomography in plasma and applied to the determination of local emissivity distribution at times of particular interest in the discharge (sawteeth, MHD perturbations, disruptions, etc.). Some of these techniques are based on numerical iterative techniques in order to avoid assumptions on emissivity spatial modal structure. They are able to determine any type of structures even those with very localized perturbation, that would require a great number of harmonics, and subsequently a larger amount of detector arrays, in any modal analysis. Iterative numerical techniques have two main drawbacks: high computer time comsumption and possibility of non-real solutions. Trying to avoid them, an iterative method, that uses as initial weights magnetic flux values derived from equilibrium calculations, has been developed. This technique can be applied to any plasma shape and even be used as a 'modified Abel Inversion' when analyzing single array signals. Application using signals from a 30 detector array, have been made for NBI discharges in W7A stellarator, and the obtained reconstructions of local Soft-X-Ray emissivity are compared with theoretical estimations. (author) 2 refs., 4 figs