title: Improved equilibrium reconstructions by advanced statistical weighting of the internal magnetic measurements.
abstract: In a Tokamak the configuration of the magnetic fields remains the key element to improve performance and to maximise the scientific exploitation of the device. On the other hand, the quality of the reconstructed fields depends crucially on the measurements available. Traditionally in the least square minimisation phase of the algorithms, used to obtain the magnetic field topology, all the diagnostics are given the same weights, a part from a corrective factor taking into account the error bars. This assumption unduly penalises complex diagnostics, such as polarimetry, which have a limited number of highly significant measurements. A completely new method to choose the weights, to be given to the internal measurements of the magnetic fields for improved equilibrium reconstructions, is presented in this paper. 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. The potential of the method is exemplified using the measurements of the Faraday rotation derived from JET polarimeter. The results indicate quite clearly that the weights have to be determined carefully, since the inappropriate choice can have significant repercussions on the quality of the magnetic reconstruction both in the edge and in the core. These results confirm the limitations of the assumption that all the diagnostics have to be given the same weight, irrespective of the number of measurements they provide and the region of the plasma they probe.
authors.affiliation: Consorzio RFX-Associazione EURATOM ENEA per la Fusione, I-35127 Padova, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Murari
authors.affiliation: Associazione EURATOM-ENEA - University of Rome "Tor Vergata," Roma, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Gelfusa
authors.affiliation: Associazione EURATOM-ENEA - University of Rome "Tor Vergata," Roma, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Peluso
authors.affiliation: Associazione EURATOM-ENEA - University of Rome "Tor Vergata," Roma, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Gaudio
authors.affiliation: Association EURATOM-CEA, CEA Cadarache, 13108 Saint-Paul-lez-Durance, France.
authors.forename: D
authors.initials: D
authors.lastname: Mazon
authors.affiliation: EURATOM/CCFE Fusion Association, Culham Science Centre, Abingdon, Oxon OX14 3DB, United Kingdom.
authors.forename: N
authors.initials: N
authors.lastname: Hawkes
authors.affiliation: Ecole Normale Supérieure de Cacahn- 61 Avenue du Président Wilson, 94230 Cachan, France.
authors.forename: G
authors.initials: G
authors.lastname: Point
authors.affiliation: EURATOM/CCFE Fusion Association, Culham Science Centre, Abingdon, Oxon OX14 3DB, United Kingdom.
authors.forename: B
authors.initials: B
authors.lastname: Alper
authors.affiliation: Max-Planck-Institut für Plasmaphysik, Teilinstitut Greifswald, EURATOM Association, Wendelsteinstr.1, 17491 Greifswald, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Eich