Improved in situ calibration technique for ITER ex-vessel neutron yield monitor

The ITER neutron diagnostic system needs to cover both the DD- and DT-phases of ITER experiments. To ensure the required accuracy for diagnosing both phases, it is preferable to calibrate the diagnostic system to both DD and DT neutrons. In this paper, the feasibility of two kinds of calibration measurements has been verified through MCNP simulations for the ITER ex-vessel neutron yield monitor. It is indicated that both calibration procedures using DD and DT neutron generators can be implemented with the required accuracies within a realistic measurement time. In the advanced DD-phase of the ITER experiment with high density D plasma producing high energy tritons, where a number of DT neutrons are produced, the independent calibration to DD or DT neutrons could lead to unacceptable measurement uncertainty. An effective method to reduce the measurement uncertainty for the two-component neutron source is discussed.