The composition of ETG turbulence in JET-ILW pedestals
We compare the structure of electron temperature gradient (ETG) driven turbulence in the pedestals of two JET ITER-like-wall (ILW) type I ELMy H-mode discharges operating with similar experimental inputs but at different levels of gas fuelling. By artificially removing the toroidal drifts from our GENE gyrokinetic simulations and subsequently analysing the turbulence using proper-orthogonal-decomposition, we demonstrate that the high gas (HG) pulse has a substantial component from toroidally driven ETG turbulence whilst the low gas (LG) case is completely driven by slab ETG turbulence. This enables us to understand the discrepancy between the HG and LG ETG heat flux scaling presented in previous work; and with this understanding, we are able to explicitly state why increased gas puffing on JET-ILW leads to confinement degradation and lower pedestal top temperatures.