Effect of Collisionality and Effective Charge on the \mbox{H-mode} Pedestal Structure in DIII-D and JET

After the installation of the ITER-like-wall, the energy confinement of high triangularity D$_2$ fueled JET baseline plasmas was degraded by up to 40\% due to a reduction in pedestal performance. This could be partially recovered by changing the collisionality ($\nu^\ast$) and/or effective charge ($Z_{eff}$) when seeding N$_2$. Pedestal measurements revealed a widening of the pedestal and a variation in gradient. Comparison to EPED pedestal-model predictions highlights the potential importance of a low-Z, carbon-like, impurity at the plasma edge. We report on a dedicated DIII-D experiment that studied the role of $\nu^\ast$ and $Z_{eff}$ on the pedestal structure through means of D$_2$-fueling, N$_2$-seeding and Li-dropping. Initial analysis shows with increasing D$_2$ fueling the pedestal does not widen and the ELM frequency increases in contrast to equivalent JET plasmas.