Multi-scale core-edge instabilities and particle acceleration unveiled in EAST ion temperature peak discharge

Controlling fast particles in tokamaks is crucial for both safe device operation and optimal plasma performance. We report the first observation, on EAST with a fully metallic wall, of a central ion temperature peaking (Ti-peak) regime reaching 9 keV, achieved through the synergistic combination of high-power neutral beam injection (NBI) and argon (Ar) injection. Within this Ti-peak regime, we observe multiple instabilities spanning different scales, including fishbone (FB), long-lived mode (LLM), beta-induced Alfvén eigenmode (BAE), and ion-scale turbulence. Notably, the presence of FB and LLM instabilities is associated with a suppression of ion-scale turbulence and a flattening of the core current density profile. Furthermore, edge fast-ion-driven high-frequency magnetic fluctuations are found to be modulated by an n=0 low-frequency mode excited by core sawtooth crashes, revealing a core-edge coupling mechanism. Ar injection also induces the generation of fast electrons (40–100 keV) in the region around ρ ≈ 0.4. These findings have immediate implications for future fusion reactors, as the multiscale physics and core-edge coupling dynamics observed here are directly relevant to the management of alpha particles generated by fusion reactions.