Development of a Time of Flight Spectrometer for nd/nt Fuel Ratio Measurement in Burning Plasma

Abstract

A neutron spectrometer system based on TOF (time of flight) measurement has been studied for determination of fuel density ratio in ITER. The effective collimator diameter was examined against both the saturation of the first detector and measurement efficiency as a spectrometer to achieve the sufficient statistics with required time resolution. Relation between collimator diameter and lower limit measurement efficiency was obtained. Measurement efficiency for every design of TOF spectrometer was calculated with MCNP. Those results indicate that two or three collimators of different size are needed to attain statistics errors within 10 %. An experiment to test the TOF spectrometer and to evaluate the system efficiency was conducted using accelerator neutron source. The result shows that both DD and DT neutrons are measured separately and simultaneously with a fast discrimination electronics system. The fast discrimination improves the counting capability by one order of magnitude.