TRANSIENT HEAT-TRANSPORT STUDIES USING LASER-ABLATED IMPURITY INJECTION IN JET

Following impurity injection by laser ablation (LA) in JET plasmas, th e electron temperature, T-e, is observed to drop at a rate that cannot be accounted for by changes in radiated power, Delta P-rad. T-e start s to drop promptly over a large fraction of the plasma volume, which c an be explained by a non-local change in electron heat diffusivity. Th e change in diffusivity, Delta chi(e), is generally short lived, lasti ng a few milliseconds, even if Delta P(ra)d can persist for longer tim es. No clear relation between Delta P-rad and the strength of the prom pt plasma response to LA can be observed, but only those events with D elta P-rad/P-rad > 0.5 give rise to detectable T-e perturbations. In h ot ion H mode plasmas, Delta chi(e) is found to be spatially non-unifo rm and increasing exponentially with the time delay of the LA relative to the onset of the H mode. Examples of non-monotonic Delta chi(e) pr ofiles are found in plasmas of lower heating power. Energy transport m odels combining local and non-local (or strongly non-linear) features are possible candidates for an explanation of these observations.