The 2.5-MeV Neutron Time of Flight Spectrometer for Optimized Count Rate (TOFOR)

Abstract

Neutron emission spectroscopy (NES) diagnostic can give valuable information of both thermal and auxiliary heated tokamak plasmas. The information can be achieved given that the neutron yield rate (Y _n ) is high and that the NES diagnostic can operate at high count rates. This has been demonstrated with the Magnetic Proton Recoil (MPR) neutron spectrometer¹ at the Joint European Torus (JET). The MPR has reached count rates of 0.6 MHz measuring the neutron emission from d + t → α + n reactions in deuterium-tritium (DT) plasmas. To achieve the same NES performance in pure D-plasmas, the efficiency of the instrument must be a factor of 100 higher due to the lower Y _n value of the d + d → ³ He + n reaction so correspondingly higher efficiency is needed. This can be achieved with the time-of-flight technique but it has a problem in the count rate C _n capability so the design must be optimized to approach its intrinsic upper limit. This project is about the time-of-flight optimized for rate (TOFOR), which is a NES diagnostic designed for high count rates to give high quality data for D-plasmas comparable with those obtained with the MPR for DT-plasmas.