Density pedestal prediction model for tokamak plasmas

Abstract

A model for the pedestal density prediction based on neutral penetration combined with pedestal transport is presented. The model is tested against a pedestal database of JET-ILW Type I ELMy H-modes showing good agreement over a wide range of parameters both in standalone modelling (using the experimental temperature profile) and in full Europed modelling that predicts both density and temperature pedestals simultaneously. The model is further tested for ASDEX Upgrade and MAST-U Type I ELMy H-modes and both are found to agree with the same model parameters as for JET-ILW. The JET-ILW experiment where the isotope of the main ion is varied in a D/T scan at constant gas rate and constant βN is successfully modelled as long as the separatrix density ( ne,sep) and pedestal transport coefficient ratio ( D/χ) are varied in accordance with the experimentally observed variation of ne,sep and the isotope dependence of D/χ found in gyrokinetic simulations. The predictions are found to be sensitive to ne,sep which is why the model is combined with an ne,sep model to predict the pedestal for the STEP fusion reactor.