OBSERVATION OF ALPHA-HEATING IN JET DT PLASMAS

An experiment at the Joint European Torus (JET) has demonstrated clear self-heating of a deuterium-tritium plasma by alpha particles produce d in fusion reactions. The alpha heating was identified by scanning th e plasma and neutral beam mixtures together from pure deuterium to nea rly pure tritium in a 10.5 MW hot ion H mode. At an optimum mixture of (60 +/- 20)% T, the fusion gain (= P-fusion/P-absorbed) was 0.65 and the alpha heating showed clearly as a maximum in electron temperature. The change in temperature produced by alpha heating was T-e(0) = 1.3 +/- 0.23 keV in 12.2 keV. The effect of the heating could also be seen in the ion temperature and energy content.