title: Evaluation of reconstruction errors and identification of artefacts for JET gamma and neutron tomography.
abstract: The Joint European Torus (JET) neutron profile monitor ensures 2D coverage of the gamma and neutron emissive region that enables tomographic reconstruction. Due to the availability of only two projection angles and to the coarse sampling, tomographic inversion is a limited data set problem. Several techniques have been developed for tomographic reconstruction of the 2-D gamma and neutron emissivity on JET, but the problem of evaluating the errors associated with the reconstructed emissivity profile is still open. The reconstruction technique based on the maximum likelihood principle, that proved already to be a powerful tool for JET tomography, has been used to develop a method for the numerical evaluation of the statistical properties of the uncertainties in gamma and neutron emissivity reconstructions. The image covariance calculation takes into account the additional techniques introduced in the reconstruction process for tackling with the limited data set (projection resampling, smoothness regularization depending on magnetic field). The method has been validated by numerically simulations and applied to JET data. Different sources of artefacts that may significantly influence the quality of reconstructions and the accuracy of variance calculation have been identified.
authors.affiliation: National Institute for Laser, Plasma and Radiation Physics, Magurele-Bucharest, Romania.
authors.forename: Teddy
authors.initials: T
authors.lastname: Craciunescu
authors.affiliation: Consorzio RFX, Padova, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Murari
authors.affiliation: CCFE Culham Science Centre, Abingdon, Oxon OX14 3DB, United Kingdom.
authors.forename: Vasily
authors.initials: V
authors.lastname: Kiptily
authors.affiliation: CCFE Culham Science Centre, Abingdon, Oxon OX14 3DB, United Kingdom.
authors.forename: Ivan
authors.initials: I
authors.lastname: Lupelli
authors.affiliation: Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal.
authors.forename: Ana
authors.initials: A
authors.lastname: Fernandes
authors.affiliation: CCFE Culham Science Centre, Abingdon, Oxon OX14 3DB, United Kingdom.
authors.forename: Sergei
authors.initials: S
authors.lastname: Sharapov
authors.affiliation: National Institute for Laser, Plasma and Radiation Physics, Magurele-Bucharest, Romania.
authors.forename: Ion
authors.initials: I
authors.lastname: Tiseanu
authors.affiliation: National Institute for Laser, Plasma and Radiation Physics, Magurele-Bucharest, Romania.
authors.forename: Vasile
authors.initials: V
authors.lastname: Zoita