  A reproducible stationary improved confinement mode (I-mode) has been
achieved recently in the Experimental Advanced Superconducting Tokamak,
featuring good confinement without particle transport barrier, which could be
beneficial to solving the heat flux problem caused by edge localized modes
(ELM) and the helium ash problem for future fusion reactors. The microscopic
mechanism of sustaining stationary I-mode, based on the coupling between
turbulence transition and the edge temperature oscillation, has been discovered
for the first time. A radially localized edge temperature ring oscillation
(ETRO) with azimuthally symmetric structure ($n=0$,$m=0$) has been identified
and it is caused by alternative turbulence transitions between ion temperature
gradient modes (ITG) and trapped electron modes (TEM). The ITG-TEM transition
is controlled by local electron temperature gradient and consistent with the
gyrokinetic simulations. The self-organizing system consisting with ETRO,
turbulence and transport transitions plays the key role in sustaining the
I-mode confinement. These results provide a novel physics basis for accessing,
maintaining and controlling stationary I-mode in the future.
