A new plasma operation scenario, Super I mode, was discovered and demonstrated on the Experiment Advanced Superconducting Tokamak (EAST). The new high-confinement and self-organizing mechanism represents the reliability and advancement of the machine itself, while also offers insights into how to better maintain the plasma operating stably and for long duration.
The new finding was reported on Science Advances by a research team from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences.
The exciting discovery was made during campaign of EAST last year, in which a stationary plasma with a world-record pulse length of 1,056 seconds was realized.
The researchers were surprised to find that the new mode even dramatically improved the energy confinement compared with the I mode originally observed on other fusion devices, hence it was called Super I mode.
This newly discovered mode has caught the attention of scientists for its exciting features. It exhibits a much higher energy confinement than I-mode and is comparable to H-mode.There are more. During long term high plasma performance, the thermal load of the element exposed to high temperature plasma is moderate because there is no edge-localized-modes.
After analyzing the data, the researchers figured out why the energy confinement had increased significantly.
"We have maintained the internal electron transport barrier at the plasma center," said Dr ZHANG Bin, a young operator in EAST team, "which works together with I-mode at the edge, then the energy is greatly confined."
In addition to improved energy confinement, the Super I mode has other advantages, such as no metallic impurity central accumulation at the core, favorable particle fluxes on the divertor to remain extremely stable, and sustained quiet stationary plasma-wall interactions. Overall, it can serve as the basic operation scenario of the International Thermonuclear Experimental Reactor (ITER), the world's largest tokamak joined by 35 nations.
