Conceptual design of a BackTOF neutron spectrometer for fuel ion ratio measurements at ITER

[摘要] In this paper we present a conceptual design of a back scattering neutron time of flight spectrometer (BackTOF) for use at ITER. The proposed BackTOF design aims at fulfilling the requirements set on a neutron spectrometer system to be used for inferring the core fuel ion ratio in a DT plasma. Specifically we have investigated the requirements on the size, energy resolution, count rate capability, efficiency and signal to background ratio. These requirements are a compact size that fits in roughly 1 m³, an energy resolution of 4% or better, a count rate capability of at least 100 kHz, an efficiency of at least 10⁻⁵ and a signal to background ratio of 1000 or better.Using a Monte Carlo model of the BackTOF spectrometer we find that the proposed BackTOF design is compact enough to be installed at ITER while being capable of achieving a resolution of about 4% FWHM with a count rate capability of 300 kHz and an efficiency at 1.25 · 10⁻³. This is sufficient for achieving the requirements on the fuel ion ratio at ITER. We also demonstrate how data acquisition systems capable of providing both timing and energy information can be used to effectively discriminate random background at high count rates.

[关键词] neutron spectroscopy;time of flight;burning plasma;fuel ion ratio