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 produced in fusion reactions. The alpha heating was identified by scanning the plasma and neutral beam mixtures together from pure deuterium to nearly pure tritium in a 10.5 MW hot ion H mode. At an optimum mixture of $(60\pm 20)\%\mathrm{T}$, the fusion gain ( ${=P}_{\mathrm{fusion}}/P_{\mathrm{absorbed}}$) was 0.65 and the alpha heating showed clearly as a maximum in electron temperature. The change in temperature produced by alpha heating was $T_e\left(0\right)=1.3\mathrm{}\pm 0.23\mathrm{keV}$ in 12.2 keV. The effect of the heating could also be seen in the ion temperature and energy content.