JETTO simulations of Te/Ti effects on plasma confinement

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, T-e/T-i. Although these plasmas showed a clear increase in the ion heat diffusivity with higher T-e/T-i, 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 T-e/T-i, 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, P-e/P-i, either.