Researchers working on China’s “artificial sun” project have discovered a never-before-seen mode of plasma operation that could lead to more stable and effective generation of nuclear fusion energy. The breakthrough could help future fusion experiments create a safe, clean and near-limitless energy source for humanity, the researchers said. The “super I-mode” was first discovered at the Hefei-based Experimental Advanced Superconducting Tokamak (EAST) reactor during a record-breaking 17-minute operation in December 2021. The results, after being thoroughly vetted by peers, were reported on Saturday in the international journal Science Advances. The milestone run – which used magnetic fields to heat up plasma-charged gas made of free-moving electrons and hydrogen ions to 70 million degrees Celsius – achieved high energy confinement both deeper in the plasma and at the plasma edge, wrote the team from the Institute of Plasma Physics, Chinese Academy of Sciences, and their collaborators from the US, Europe and Japan, among others. Further experiments showed that the new mode “exhibits great potential” for application in the International Thermonuclear Experimental Reactor (ITER), the world’s largest fusion reactor now under construction in France, they wrote. “This is an important result for ITER and for fusion,” said physicist Richard Pitts, who leads experiments and plasma operations at ITER. “The significance of the EAST experiments is that they have demonstrated, for the first time, that tokamak plasmas … can be sustained and controlled for very long pulses – more than 1,000 seconds, which is similar to the long pulses ITER aims for in the long term,” Pitts added. “There are all kinds of issues associated with very long pulse operation, and it’s very comforting for us at ITER to see that this has been achieved, even if it is on a much smaller device. A major advantage of the super I-mode was its ability to reduce energy leakage at the plasma edge where the superhot gas directly faced the tokamak’s heat shield, the study’s co-author Song Yuntao said. Chinese scientists hail ‘important step’ towards nuclear fusion “If we compare nuclear fusion reactions to lightning bolts, our goal is to collect as many bolts as possible in a magnetic cage and export the energy for human use in a stable and sustaining way,” Song told China’s state news agency Xinhua on Saturday. “The new operating mode discovered on EAST enables us to collect more lightning bolts without damaging the magnetic cage, while maintaining steady-state operation for a long time,” Song said. Tokamaks like EAST and ITER represent one of the most promising paths towards controlled nuclear fusion. However, how to create high-performing plasma and confine it long enough for the hydrogens to combine to produce net power – the same way our sun gives off light and heat – remains a challenge. In reality, fusion scientists use operating parameters such as temperature and energy – known as “modes” – to control the state of plasma, said Liu Zhihong from the Institute of Plasma Physics in Hefei. Most of today’s tokamaks, EAST included, operate in H-mode, or high-confinement mode. First discovered on a tokamak in Germany in 1982, H-mode was at least 100 times more efficient in confining plasma than the previous low-confinement mode, and made large reactors such as ITER possible. However, a major disadvantage of H-mode operation is the possibility of leading to a rapid release of energy at the plasma edge and damaging surrounding materials. In recent years, scientists have investigated I-mode – or improved confinement mode – in which the fusion energy is released through a more continuous process to prevent damaging the surfaces. The EAST team was surprised to find out that compared with I-mode, their new mode dramatically improved the energy confinement at both the plasma core and the edge, so they called it super I-mode, Liu said. It is not clear if ITER could operate in super I-mode, as the mode was only seen on EAST, Pitts noted. However, ITER planned to operate in “advanced scenarios” similar to the EAST experiments, he said. “These advanced scenarios allow you to run very long plasma durations – up to 3,000 seconds on ITER. In the H-mode, ITER can only go up to about 500-second plasma duration,” Pitts said. EAST is the world’s first fully superconducting tokamak and the first of its kind to operate with a pulse length at the 1,000-second scale. Since it became operational in 2006, the reactor has hosted thousands of experiments conducted either in-house or with the international fusion community. ‘Artificial sun’ tipped to provide electricity in decade if Beijing backs it The EAST team has more than 400 members, with dozens of visiting scientists from all over the world every year. “EAST has become one of the most important platforms for Chinese and foreign scientists to exchange and work together on plasma physics, fusion and other related topics,” Liu said. The US Department of Energy identified EAST as their top partner facility in the field of magnetic confinement fusion, he said. EAST opens up calls for scientific proposals from around the world every year, and international proposals accounted for about half of all applications, Liu said.