Transient heat transport studies using laser ablated impurity injection in JET

Abstract

Following impurity injection by laser ablation (LA) in JET plasmas, the electron temperature, Te, is observed to drop at a rate that cannot be accounted for by changes in radiated power, ΔPrad. Te starts to drop promptly over a large fraction of the plasma volume, which can be explained by a non-local change in electron heat diffusivity. The change in diffusivity, Δχe, is generally short lived, lasting a few milliseconds, even if ΔPrad can persist for longer times. No clear relation between ΔPrad and the strength of the prompt plasma response to LA can be observed, but only those events with ΔPrad/Prad > 0.5 give rise to detectable Te perturbations. In hot ion H mode plasmas, Δχe is found to be spatially non-uniform and increasing exponentially with the time delay of the LA relative to the onset of the H mode. Examples of non-monotonic Δχe profiles are found in plasmas of lower heating power. Energy transport models combining local and non-local (or strongly non-linear) features are possible candidates for an explanation of these observations.