A research group led by Prof. SUN Youwen from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences, in collaboration Prof. YE Minyou from the University of Science and Technology of China, has achieved a new plasma confinement regime using small 3D magnetic perturbations that simultaneously suppress edge instabilities and enhance core plasma confinement in the Experimental Advanced Superconducting Tokamak (EAST).

These research results were published in PRX Energy.

Sustained high plasma confinement at both the core and the edge without edge crash events due to edge instabilities is critical for efficient fusion energy production in tokamaks. However, achieving stable, high-core confinement with an internal transport barrier (ITB) is extremely challenging, especially in tungsten-wall devices where tungsten impurity accumulation must be controlled. Furthermore, controlling edge instabilities usually results in degraded core plasma confinement.

In this study, the researchers applied small 3D magnetic perturbations localized at the plasma edge. This method achieved the suppression of edge instabilities and control of tungsten impurities. For the first time, it also enabled the induction and sustained confinement of high-core plasma with an ITB. Through in-depth investigation, the researchers uncovered the complex physical mechanisms underlying ITB formation. This process involves multiscale, nonlinear interactions among small magnetic perturbations, tungsten impurities, plasma rotation, and current profiles.

Compared to conventional methods, ITB formation using magnetic perturbations is independent of the initial plasma conditions and features a power threshold reduced by more than half. Further studies have shown that magnetic perturbations can not only sustain ITBs stably and effectively allow for active control of ITB behavior by adjusting perturbation profiles.

Using this method, effective ITB control has been achieved over a broad range of plasma densities and edge safety factors on EAST. This breakthrough demonstrates a method for achieving both stable edges and high-performing cores, which is critical for the efficient operation of future fusion reactors.

This work opens a new direction for studying complex nonlinear plasma dynamics under 3D fields in tokamaks and establishes a novel approach for investigating, controlling, and optimizing internal transport barriers in future fusion reactors.

Demonstration of simultaneously achieved formation of ITB and edge instabilities suppression using small 3D magnetic perturbations in EAST. (Image by SHENG Hui)