A high-confinement, no-ELM regime in JET: the EDA H-mode

This work presents the achievement of the EDA H-mode in the Joint European Torus with the beryllium-tungsten wall (JET-ILW) for the first time, an important milestone in addressing the critical challenge of transient heat loads in fusion reactors. The EDA H-mode is a high-confinement regime without edge localized modes (ELMs) that exhibits several desirable properties for a reactor. Its observation in metallic-walled devices was previously restricted to only Alcator C-Mod [1] and ASDEX Upgrade (AUG) [2], highlighting the relevance of its extension to JET, the world’s largest non-carbon tokamak.

The experiments were performed in deuterium, with a toroidal magnetic field of 2.8 T and a plasma current of 1.5 MA. The EDA regime was accessed and sustained by combining ion cyclotron resonance heating, strong plasma shaping, and sufficient fueling. Compared to AUG plasmas with the same heating method, EDA H-modes at JET feature a significantly higher core temperature at a similar LH-normalized power, P/P_LH ~ 2. Additional noteworthy qualities include no-torque operation at a high Greenwald fraction with no impurity accumulation despite the absence of ELMs. The plasma edge instead exhibits the main EDA signature, a benign quasi-coherent mode that likely regulates pedestal transport.

In addition to characterizing the EDA H-mode in JET, research directions and implications for upcoming devices are discussed. This is particularly relevant to the full-tungsten ITER and SPARC, which predominantly feature wave-based external heating methods. Overall, the EDA H-mode is a promising regime that could become a key no-ELM scenario in future reactors.

[1] Y. Takase et al 1997 Phys. Plasmas 4 1647

[2] L. Gil et al 2020 Nucl. Fusion 60 054003