Measurement of DT and DD neutrons with a TOF spectrometer for determination of fuel ion density ratio in ITER

Measurement of the fuel ion density ratio, nD/nT, is required for burning control in ITER. The measured nD/nT ratio must be fed back in real time. A neutron measurement system to measure nD/nT should be operable at high counting rate. The estimated number of emitted DT neutrons is 200 times higher than that of DD neutrons under the ITER standard operation conditions. A neutron measurement system was developed using an intense Cockcroft-Walton type DT neutron generator, where DT neutrons are dominant with slight DD neutron contamination in the neutron beam. The measurement instrument was a TOF spectrometer. Signals originating from each neutron must be distinguished to measure the fuel ratio. We have developed a circuit system with discrimination windows to distinguish each signal pulse, and this system was used to measured DT and DD neutrons separately and simultaneously. The experimental results suggested that this system is suitable for measurement of fuel ion density ratio in ITER.