Alpha heating and isotopic mass effects in JET plasmas with sawteeth

The alpha heating experiment in the Joint European Torus (JET) 1997 DTE1 campaign is re-examined. Several effects correlated with tritium content and thermal hydrogenic isotopic mass  <  A  >  weaken the conclusion that alpha heating was clearly observed. These effects delayed the occurrence of significant sawtooth crashes allowing the electron and ion temperatures Te and Ti to achieve higher values. Under otherwise equal circumstances Te and Ti were typically higher for discharges with higher  <  A  >, and significant scaling of Ti, Te, and total stored energy with  <  A  >  were observed. The higher Ti led to increased ion–electron heating rates with magnitudes comparable to those computed for alpha electron heating. Rates of other heating/loss processes also had comparable magnitudes. Simulations of Te assuming the observed scaling of Ti are qualitatively consistent with the measured profiles, without invoking alpha heating