A new plasma operation scenario Super I Mode has been discovered and demonstrated on the Experimental Advanced Superconducting Tokamak (EAST)

The new high-confinement and self-organising mechanism represents the reliability and advancement of the machine itself but also offers insights into how to better maintain the plasma operating stably and for long duration.

The team from the Institute of Plasma Physics, Hefei Institutes of Physical Science, CAS made the exciting discovery during last year’s EAST campaign in which a stationary plasma with a world-record pulse length of 1,056s was realised.

Scientists were surprised to find that, compared with the I mode initially observed on other fusion devices, this new mode had dramatically improved energy confinement, so it was called ‘Super I mode’.

The new-found mode attracted scientists’ attention with its exciting features. It demonstrated energy confinement much higher than I-mode and comparable to H-mode. Also, during high plasma performance in a long-term test, the heat load on components exposed to high-temperature plasma was moderate due to the absence of large edge-localised-modes.

After data analysis, the scientists identified reasons for the significantly enhanced energy confinement.

Dr Zhang Bin, a young operator in the EAST team, said: “We have maintained the electron internal transport barrier at the plasma centre, which worked together with I-mode at the edge, then energy was greatly confined.”

See also: Waves carrying plasma heat observed for first time

an advanced and open experimental platform

In addition to improved energy confinement, the Super I mode also has advantages over other scenarios such as no metallic impurity accumulation at the core, the particle flux on the diverter remained extremely stable, and sustained quiet stationary plasma-wall interactions.

Overall, it could be expected as the basic operation scenario of ITER, the world’s largest tokamak, funded by 35 nations.

Fusion is the process of two atoms of hydrogen fusing together to form an atom of helium while releasing a large amount of energy, through which the sun and stars are powered.

For fusion scientists who are trying ambitiously to replicate the sun’s power on Earth, they want the fusion reaction to take place in a controlled manner, so that the whole of society could be powered in a totally new but much more efficient and green way.

Highly motivated by this shared goal for all humans, fusion scientists across the world have for decades been exploring in different ways. Dozens of fusion research machines have been designed, constructed and operated as result.

experimental advanced superconducting tokamak

EAST is one of those experimental platforms which was built with a target to address key technological and physics issues of long-pulse operation. It takes tokamak as its technological route and applies magnetic configuration like ITER.

Since its first discharge in 2006, EAST has two rounds of campaign each year. Thousands of experiments were conducted independently by its in-house group or collectively with the international fusion community.

Last year, the machine achieved a plasma temperature of 120 million degrees Celsius for 101 seconds in May. Shortly after it embraced its one hundred thousandth shot followed by a record 1,056 seconds for high-temperature tokamak plasma at the end of the same year.

Scientists immediately looked into data analysis. They wanted more from the ‘story behind the record.’

Professor Qian Jinping, deputy head of the Tokamak Experiment Division, said: “We were all excited about the record. That was for sure a milestone of our machine. But I think how the experiment inspires us was more worth the expectation.

“The machine enables possibility that we testify ideas, observe physical phenomenon then we analyse the data to know why.”

An experimental platform can also be the ground for international scientific collaboration. Each year, EAST opens scientific proposal applications to the world. International participation is seen in the experiment conducting and data sharing.

The research is published in Science Advances.

Image: © HFIPS