A series of hot-electron plasmas were produced at JET with the aim of
clarifying the dependence of the energy confinement time on the electron to ion
temperature ratio, Te/Ti. Although these plasmas showed a clear increase in the
ion heat diffusivity with higher Te/Ti, their energy confinement time remained
constant. In this paper we propose that these observations are consistent
with the predictions of the Weiland model of energy transport. A feedback
loop amplifying the ion diffusivity simultaneously flattens the ion temperature
profile, and keeps the ion heat flux constant. The electron transport shows
no dependence on Te/Ti, and hence there is no scaling of the confinement
time with the temperature ratio. To support these claims we show a series of
numerical simulations using the Weiland model. For scaling law purposes it
is also interesting to note that the energy confinement time does not show any
dependence on the effective input power ratio, Pe/Pi, either. |