Absolutely calibrated measurements of the neutron yields which need to cover both D-D and D-T phase of the international thermal-nuclear experimental reactor(ITER)are impor- tant for the evaluation of fusion power and fusion gain Q in D-D and D-T operations.This paper describes the in-situ calibration techniques and methods,the neutron sources including ^(252)Cf and neutron generator for calibration,the preliminary accuracy assessment and the error analyses.In addition,some difficult problems regarding the in situ calibration for the neutron flux monitor (NFM)on ITER are presented and discussed.
Neutron flux monitor (NFM) as an important diagnostic sub-system in ITER (in-ternational thermonuclear experimental reactor) provides a global neutron source intensity,fusionpower and neutron flux in real time.Three types of neutron flux monitor assemblies with differentsensitivities and shielding materials have been designed.Through MCNP (Mante-Carlo neutralparticle transport code) calculations,this extended system of NFM can detect the neutron flux ina range of 10~4 n/(cm^2.s) to 10^(14) n/(cm^2.s).It is capable of providing accurate neutron yield mea-surements for all operational modes encountered in the ITER experiments including the in-situcalibration.Combining both the counting mode and Campbelling (MSV;Mean Square Voltage)mode in the signal processing units,the requirement of the dynamic range (10~7) for these NFMsand time resolution (1 ms) can be met.Based on a uncertainty analysis,the estimated abso-lute measurement accuracies of the total fusion neutron yield can reach the required 10% level inboth the early stage of the DD-phase and the full power DT operation mode.In the advancedDD-phase,the absolute measurement accuracy would be better than 20%.
