Promising High-Confinement Regime for Steady-State Fusion

A reproducible stationary high-confinement regime with small “edge-localized modes” (ELMs) has beenachieved recently in the Experimental Advanced Superconducting Tokamak, which has a metal wall and lowplasma rotation as projected for a fusion reactor. We have uncovered that this small ELM regime is enabled bya wide edge transport barrier (pedestal) with a low density gradient and a high density ratio between thepedestal foot and top. Nonlinear simulations reveal, for the first time, that the underlying mechanism for theobserved small ELM crashes is the upper movement of the peeling boundary induced by an initial radiallylocalized collapse in the pedestal, which stops the growth of instabilities and further collapse of the pedestal,thus providing a physics basis for mitigating ELMs in future steady-state fusion reactors.