Measurements of fusion neutron energy spectra at JET by means of time-of-flight techniques

High fluxes of neutrons are emitted from the JET tokamak when deuterium plasmas are raised to high temperatures with neutral beam injection and ion cyclotron resonance heating. The energy distribution of these neutrons carries valuable information concerning the velocity distributions of the reacting ions. A double scattering time-of-flight spectrometer is used for measuring the neutron energy distribution. This spectrometer provides an efficiency of 5 × 10−2 cm2, an energy resolution of 4.6% (FWHM) and is cascade of a maximum count-rate of ≈ 2 × 104c/s. An overview of results obtained at the JET tokamak is provided. The methods of analysis used to obtain information on ion temperatures, fractional contributions of the different neutron source reactions, high energy tail formation and on reactions with impurity ions are described. The use of a time-of-flight counter to measure the ratio of neutron fluences from deuterium-tritium and deuterium-deuterium reactions during the first deuterium-tritium experiment is also described.