Investigation of the dependence of pe, ped on ne, sep in JET H-Mode plasmas using integrated JETTO-MISHKA-FRANTIC simulations. (March 2023) - Simpson, J.
Abstract: Experimentally, it has been observed in high-confinement (H-Mode) plasmas with Edge Localised Modes (ELMs) on JET that the pressure pedestal ( p e, p e d ) is degraded by approximately a factor of two when there is a change in electron separatrix density, n e, s e p, from 1 − 4 × 1 0 19 m − 3 . Previous work using the pedestal stability code EUROPED, has been able to predict the degradation of p e, p e d but only for n e, s e p ≤ 1 . 5 × 1 0 19 m − 3 . In this work, we apply a coupled code JETTO-MISHKA-FRANTIC, to self-consistently predict the transport in the pedestal region and neutral source with varying separatrix conditions. The code feeds back on the transport in the pedestal region to achieve profiles that are marginally stable to ideal MHD modes (continuous ELM model in JETTO). When accounting for the change in electron separatrix temperature ( T e, s e p ), ion separatrix temperature ( T i, s e p ) and the poloidally integrated neutral flux crossing the separatrix ( Γ s e p, n e u t ) as it changes with n e, s e p (according to a scan in n e, s e p in the edge code EDGE2D-EIRENE), no degradation in p e, p e d was observed in JETTO-MISHKA-FRANTIC in contrast to experiment. Instead, an increase in p e, p e d with n e, s e p was observed which is driven by an increasing density pedestal ( n e, p e d ). Within the presented JETTO-MISHKA-FRANTIC simulations, changing the pedestal width by a factor of two and a half in normalised poloidal flux ( ψ n ) resulted in an approximately 40% degradation in p e, p e d for n e, s e p = 1 − 3 × 1 0 19 m − 3 . This change in pedestal width was not supported by experimental data. A scan in the ratio of particle and energy transport in the pedestal ( D / χ ) was found to have a negligible effect on p e, p e d . Qualitative agreement between JETTO-MISHKA-FRANTIC with EUROPED was found when the input density profiles are identical. Highlights: Experimentally the pressure pedestal is negatively correlated with n e, s e p JINTRAC continuous ELM model was used. Self-consistent changes in B.C's were not able to reproduce the experimental result. The model could only reproduce the experiment with an x3 change in pedestal width. This is not supported by the experiment.