Confined Alpha Distribution Measurements in a Deuterium-Tritium Tokamak Plasma

Fusion-produced alpha particles with energy $\ensuremath{\le}$0.7 MeV have been spectroscopically observed in the core of a deuterium-tritium plasma in the TFTR tokamak at alpha densities of $3\ifmmode\times\else\texttimes\fi{}{10}^{16}{\mathrm{m}}^{\ensuremath{-}3}$. During a sawtooth-free discharge, the measured energy spectra at $r/a\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.3$ are in good agreement with those predicted on the basis of collisional transport. Time-resolved measurements during the alpha thermalization after alpha source turn-off show decay of the distribution function to lower energies consistent with the classical slowing-down time of 0.5 s.