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
The problem of the propagation of a harmonic temperature perturbation in a plasma with both diffusive and nondiffusive energy transport is addressed. The energy flux is modeled by two (radially varying) effective coefficients for the diffusive and nondiffusive transport, and the effects of perturbed energy sinks and of cylindrical geometry are taken into account. A simple, local relationship is found between the two transport coefficients and the gradients of the phase and amplitude of the temperature perturbation. This relationship can be used for the interpretation of heating modulation experiments, provided data at different modulation frequencies are available. Since a harmonic density perturbation in a plasma follows a similar linearized transport equation, a similar model can be applied also to density modulation experiments.
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.
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