Count rate performance of spectrometers for fusion neutrons

The count rate capability of high-resolution neutron spectrometers for fusion plasmas is discussed. In particular, the question of the intrinsic rate limitations in neutron time-of-flight (TOF) spectrometers is assessed quantitatively for two design approaches where the proton recoils from n+H scatterings are detected with in-beam and out-of-beam detectors. It is found that the count rate capability limit lies in the range 50–400 kHz for TOF depending on approach. Comparison is made with other types of neutron spectrometers for fusion experiments. It is shown, for the first time, that neutron spectrometers fall into distinct categories depending on the underlying detection methods and that this information can be used for assessing capability limits of neutron spectrometry as a diagnostic for fusion plasmas.