New Steady-State Quiescent High-Confinement Plasma in an Experimental Advanced Superconducting Tokamak

A critical challenge facing the basic long-pulse high-confinement operation scenario ($H$ mode) for ITER is to control a magnetohydrodynamic (MHD) instability, known as the edge localized mode (ELM), which leads to cyclical high peak heat and particle fluxes at the plasma facing components. A breakthrough is made in the Experimental Advanced Superconducting Tokamak in achieving a new steady-state $H$ mode without the presence of ELMs for a duration exceeding hundreds of energy confinement times, by using a novel technique of continuous real-time injection of a lithium (Li) aerosol into the edge plasma. The steady-state ELM-free $H$ mode is accompanied by a strong edge coherent MHD mode (ECM) at a frequency of 35–40 kHz with a poloidal wavelength of 10.2 cm in the ion diamagnetic drift direction, providing continuous heat and particle exhaust, thus preventing the transient heat deposition on plasma facing components and impurity accumulation in the confined plasma. It is truly remarkable that Li injection appears to promote the growth of the ECM, owing to the increase in Li concentration and hence collisionality at the edge, as predicted by GYRO simulations. This new steady-state ELM-free $H$-mode regime, enabled by real-time Li injection, may open a new avenue for next-step fusion development.