The fast ␣-particle kinetic effects in fusion plasmas of deuterium and tritium are studied in the perspective that they can give rise to minority populations of fast fuel ions. The resulting modification of the neutron emission spectrum is computed for a plasma in the state of steady thermonuclear burn of conditions similar to those envisaged for the planned ITER tokamak. The nuclear interaction in these scattering ␣-particle knock-on processes is taken into account explicitly and the dependence on plasma parameters is investigated. The findings provide evidence that neutron spectrometry is a potential diagnostic of the fast ␣-particle population in burning fusion plasmas. ͓S1063-651X͑97͒06602-6͔

Suprathermal fuel ions from alpha-particle knock-on collisions in fusion DT plasmas are predicted to cause a weak feature in the neutron spectrum of d+t-->alpha+n. The knock-on feature has been searched for in the neutron emission of high ( >1 MW) fusion-power plasmas produced at JET and was found using a magnetic proton recoil type neutron spectrometer of high performance. Measurement and predictions agree both in absolute amplitude and in plasma-parameter dependence, supporting the interpretation and model. Moreover, the results provide input to projecting alpha-particle diagnostics for future self-heated fusion plasmas.

The first three moments of the energy distributions of products from fusion reactions in thermonuclear plasmas with Maxwellian ion velocity distributions are determined analytically. Relativistic kinematics is used allowing the desired accuracy to be reached, which is 2 to 3 orders of magnitude better than previous analytical results. In particular, neutron spectra of the reactions D(d,n)3He and D(t,n)α for plasma ion temperatures 0 < Ti < 100 keV are studied for which the results are also given in tabulated form with interpolation formulas for the purpose of practical use. The neutron energy distributions are also calculated with numerical methods, in order to assess the analytical results. High accuracy calculations are motivated by the crucial role that neutron measurements are envisaged to play in the next step fusion experiments on burning plasmas, which are also discussed.

Measurement and analysis of the energy distribution of the neutron emission from the nuclear burnup of tritons produced at 1 MeV in d + d → t + p reactions are reported. The results refer to deuterium plasmas with a strongly pulsed neutron production attained with neutral beam heating in the JET tokamak representing both quasi-steady and transient plasma conditions. The measured triton produced neutron spectrum is described with reference to the triton slowing down behaviour in the plasma and pertinent parameter dependences as predicted with a time dependent model. The first study of the triton burnup neutron spectrum for both transient and quasi-steady-state plasma conditions is presented and a description based on classical confinement and slowing down of fast tritons is largely supported.

The energy spectrum of the neutron emission from beam-target reactions in fusion plasmas at the Joint European Torus (JET) has been investigated. Different beam energies as well as injection angles were used. Both measurements and simulations of the energy spectrum were done. The measurements were made with the time-of-flight spectrometer TOFOR. Simulations of the neutron spectrum were based on first principle calculations of neutral beam deposition profiles and the fast ion slowing down in the plasma using the code NUBEAM, which is a module of the TRANSP package. The shape of the neutron energy spectrum was seen to vary significantly depending on the energy of the beams as well as the injection angle and the deposition profile in the plasma. Cross validations of the measured and modeled neutron energy spectra where made, showing a good agreement for all investigated scenarios.