Observation of the Alpha Particle “Knock-On” Neutron Emission from Magnetically Confined DT Fusion Plasmas

Suprathermal fuel ions from α-particle knock-on collisions in fusion DT plasmas are predicted to cause a weak feature in the neutron spectrum of d+t→α+n. The knock-on feature has been searched for in the neutron emission of high ( >10ex0exMW) 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 α-particle diagnostics for future self-heated fusion plasmas.