A Method to Determine the Weights of Internal Magnetic Measurements for Optimised Equilibrium Reconstructions

In a Tokamak the configuration of the magnetic fields remains the key ingredient to improve performance. A method to choose the weights, to be given to internal measurements of the magnetic fields for improved equilibrium reconstructions, is presented. The approach is based on various statistical indicators applied to the residuals, the difference between the actual measurements and their estimates from the reconstructed equilibrium. In addition to the traditional analysis of the global distributions of the residuals, more sophisticated correlation tests have been performed. The potential of the method is exemplified using the measurements of the Faraday rotation derived from JET polarimeter. The magnetic reconstructions have been obtained with the code EFIT. The results indicate quite clearly that the weights have to be chosen carefully to strike the right balance between the quality of the reconstructions at the edge and in the core. The values of the weights have been shown to depend on the number of available measurements and their error bars. An inappropriate choice of the weights can have significant repercussions on the quality of the magnetic reconstruction both in the edge and in the core.
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EFDP11058 1.90 Mb