Pedestal stability comparison and ITER pedestal prediction

TLDR

The pedestal height at the edge transport barrier strongly influences fusion performance, and large ELMs driven by pedestal free energy can limit material lifetimes, making accurate prediction of pedestal height and ELM behavior in ITER essential for performance optimization. The study compares observed and predicted edge stability boundaries across tokamaks for various ELM regimes and introduces the EPED1 model that self‑consistently combines a width model with peeling–ballooning stability calculations. The authors employ high‑resolution pedestal diagnostics and efficient stability codes to compare observations with predicted stability boundaries, test the EPED1 model against experimental data, and apply it to initial ITER pedestal.

Abstract

The pressure at the top of the edge transport barrier (or ‘pedestal height’) strongly impacts fusion performance, while large edge localized modes (ELMs), driven by the free energy in the pedestal region, can constrain material lifetimes. Accurately predicting the pedestal height and ELM behavior in ITER is an essential element of prediction and optimization of fusion performance. Investigation of intermediate wavelength MHD modes (or ‘peeling–ballooning’ modes) has led to an improved understanding of important constraints on the pedestal height and the mechanism for ELMs. The combination of high-resolution pedestal diagnostics, including substantial recent improvements, and a suite of highly efficient stability codes, has made edge stability analysis routine on several major tokamaks, contributing both to understanding, and to experimental planning and performance optimization. Here we present extensive comparisons of observations to predicted edge stability boundaries on several tokamaks, both for the standard (Type I) ELM regime, and for small ELM and ELM-free regimes. We further discuss a new predictive model for the pedestal height and width (EPED1), developed by self-consistently combining a simple width model with peeling–ballooning stability calculations. This model is tested against experimental measurements, and used in initial predictions of the pedestal height for ITER.