Neutron field in the Wendelstein-7-X hall

The (d,d)-reactions between the deuterons will produce neutrons with an average energy of 2.46 MeV which are shielded by the concrete wall of 180 cm thickness in case of the Wendelstein 7-X experimental device. The knowledge of the neutron field inside the hall is of special interest for the various diagnostic facilities including neutron diagnostics. The dependence of the neutron flux on the boron concentration as used for the concrete wall and on the thickness of the concrete wall was analyzed. In the interior region of the torus, the flux of fast neutrons (number of neutrons per MeV cm2) is two orders of magnitude higher than in the region close to the concrete wall. By doping the concrete walls with 700 ppm of boron the almost homogeneous flux of thermal neutrons is reduced by a factor of about 30 compared to the case of no boron-admixture.