Analysis of evolution of γ-ray emission induced by MeV ions in JET

The paper investigates the temporal evolution of γ-ray emission induced by nuclear reactions between energetic D-T fusion-born alpha particles with beryllium impurity ions in JET plasmas, 9Be(α, nγ)12C. During and after tritium NBI blips into JET deuterium plasmas there occurs a delay between alpha production and γ-emission. The delay time observed renders possible the assessment of alpha transport, e.g. loss rates of alphas, and hence may be used for fast ion diagnostics if the characteristic confinement time does not exceed ∼20% of the Spitzer slowing-down time. The analysis of the measured relaxation of γ-emission is further demonstrated for examining the energy distributions of ICRH accelerated 4He ions in the MeV energy range.