Alpha heating, isotopic mass, and fast ion effects in deuterium-tritium experiments

Alpha heating experiments in the Tokamak Fusion Test Reactor (TFTR) and in the Joint European Torus (JET) 1997 DTE1 campaign are reexamined. In TFTR supershots central electron heating of both deuterium only and deuteriumtritium supershots was dominated by thermal ion-electron heat transfer rate pie. The higher Tein deuterium-tritium supershots was mainly due to higher Tilargely caused by isotopic mass effects of neutral beam-thermal ion heating. The thermal ion-electron heating dominated the electron heating in the center. The ratio of the predicted alpha to total electron heating rates falpis less than 0.30. Thus alpha heating (and possible favorable isotopic mass scaling of the thermal plasma) were too small to be measured reliably. The JET alpha heating Hot-Ion H-mode discharges had lower Ti/Te, and thus had lower pieand the deuterium-tritium DT discharges had higher falpthan in TFTR. There were not enough comparable discharges to verify alpha heating. The high performance phases consisted of rampup to brief flattop durations. At equal times during the rampup phase central Teand Tiwere linearly correlated with the thermal hydrogenic isotopic mass 〈A〉hydwhich co-varied with beam ion pressure, the tritium fraction of neutral beam power, and the time delay to the first significant sawteeth which interrupted the Teincreases. For both devices the expected alpha heating rate and the null hypothesis of no alpha heating are consistent with the measurements within the measurement and modeling uncertainties.