Measurements and simulations of the neutron production at W7-AS

The 2.5 MeV neutron diagnostic system on the W7-AS stellarator comprises a set of BF3 and 3He neutron counters, a NE-213 scintillator and activation foils. The neutron counter set provides a dynamic range of several orders of magnitude while the scintillator provides fast resolution needed for studying transient events. The counters are calibrated in situ using a 238Pu/B neutron source placed at discrete points inside the vacuum vessel. The activation samples have been used to determine the total neutron yields as well as to measure the fluence of fast and thermal neutrons at various positions in the diagnostic hall of W7-AS. Neutron transport calculations have been performed using the Monte Carlo neutron photon transport code in order to determine the neutron fluence and energy distribution at the irradiation positions and to simulate the measured counter signals for the in situ calibration. The accuracy of the neutronics simulations depends on the quality of the geometric model and the material composit...