Characteristics of type I ELM energy and particle losses in existing devices and their extrapolation to ITER

TLDR

Type I ELM energy losses in tokamaks are linked to pedestal density, temperature, and magnetic shear, which together determine the plasma volume affected by the ELMs. Across JET and DIII‑D, normalized Type I ELM energy loss decreases with pedestal collisionality, particle losses depend mainly on the ELM‑affected volume, and the divertor power and particle flux timescales are governed by the ion transport time τ||Front, indicating that under certain conditions ITER‑acceptable minimum ELMs can be achieved.

Abstract

Analysis of Type I ELMs from ongoing experiments shows that ELM energy losses are correlated with the density and temperature of the pedestal plasma before the ELM crash. The Type I ELM plasma energy loss normalized to the pedestal energy is found to correlate across experiments with the collisionality of the pedestal plasma (ν*ped), decreasing with increasing ν*ped. Other parameters affect the ELM size, such as the edge magnetic shear, etc, which influence the plasma volume affected by the ELMs. ELM particle losses are influenced by this ELM affected volume and are weakly dependent on other pedestal plasma parameters. In JET and DIII-D, under some conditions, ELMs can be observed (`minimum' Type I ELMs with energy losses acceptable for ITER), that do not affect the plasma temperature. The duration of the divertor ELM power pulse is correlated with the typical ion transport time from the pedestal to the divertor target (τ||Front = 2πRq95/cs,ped) and not with the duration of the ELM-associated MHD activity. Similarly, the timescale of ELM particle fluxes is also determined by τ||Front. The extrapolation of the present experimental results to ITER is summarized.