A total neutron yield constraint implemented to the RNC emissivity reconstruction on ITER tokamak

Abstract

The purpose of the ITER Radial Neutron Camera (RNC) is the measurement of the plasma neutron emissivity profile [neutrons∙s−1 m-3] for burn control purposes. The present RNC design consists of 22 collimated detector systems providing a set of line-integrated neutron measurements [neutrons∙s−1 m-2] with full coverage of the plasma poloidal cross-section; the neutron emissivity can be recovered from the line-integrated measurements by means of dedicated reconstruction techniques (1D spatial inversion, 2D tomography). The present paper focuses on the evaluation of the improvement in the RNC 2D reconstruction of the neutron emissivity obtained by using the total neutron yield value provided by an independent diagnostic as additional constraint in the tomography procedure. The analysis was performed using a tomography code based on the Minimum Fisher Regularization (MFR). A clear improvement of the neutron emissivity reconstruction has been observed when the total neutron yield constraint is considered. The improvement is seen in: extension of the spatial region in which the accuracy of the reconstruction is better than 10 %; better reconstruction of peaked emissivity profiles; and robustness against measurements noise and line of sight data loss.