Sustained ‘Artificial Sun’ Promised by 2026 in Fusion Energy Upgrade

Sustained nuclear fusion could be one step closer to reality after Korea’s “artificial sun” received an exciting upgrade to withstand temperatures six times hotter than the center of the sun.

The upgrade will contribute to the development of the world’s largest fusion project, ITER, involving 35 countries including the United States.

Nuclear fusion creates energy in the same way as our sun. The process involves smashing together two atoms with such force that they combine into a single, larger atom, releasing huge amounts of energy along the way.

Unlike nuclear fission—the nuclear reaction that is currently used in the energy sector—fusion does not create radioactive waste. It produces three to four times more energy than fission and does not release carbon dioxide into the atmosphere, unlike burning fossil fuels. Fusion is also a very fragile process that will shut down in a fraction of a second if the correct conditions are not maintained, so there is no risk of nuclear meltdown.

Research into nuclear fusion can be split into two branches: lasers and magnetic confinement. In both cases, the atoms involved are heated to super-high temperatures and confined in a small area, which forces them to fuse.

Korea’s artificial sun, known as KSTAR, is one of the many fusion devices that relies on magnetic confinement using a donut-shaped device called a tokamak. The contraption uses a series of powerful magnets to contain a circular flow of super-hot plasma—a fourth state of matter that is created when atoms are heated to such high temperatures that they are torn apart, resulting in a soup of negatively charged electrons and positively charged ions.

These positively charged ions will usually repel each other, but in the sun, high pressure is created by its intense gravitational forces that thrust the ions together and overcome this repulsion. However, on Earth, it is nearly impossible to replicate this, so the plasma must be heated even more to temperatures roughly six times hotter than the center of the sun or more.

Creating these temperatures requires a lot of energy, which is why scientists have not yet managed to get significantly more energy out of a fusion reaction than they put in.

As well as these vast energy requirements, the materials used inside fusion reactors have to be able to withstand scorchingly hot temperatures. The main part of the reactor that comes into direct contact with the plasma is called the divertor, which acts like an exhaust system for the reaction chamber. As a result, this component must be most resistant to the high temperatures of the fusion plasma.

Initially, KSTAR was fitted with a carbon divertor because of its high melting point. However, when plasma particles smash into the relatively small carbon atoms in the divertor’s walls, they become temporarily stuck to the surface, losing most of their energy and thus limiting how long the overall reaction can be sustained.

Therefore, scientists have suggested using tungsten, a metal with a melting point almost equal to carbon but with a much larger atomic mass. These larger tungsten atoms are more likely to reflect the plasma particles from their surface, allowing most of their energy to be recycled back into the plasma and sustaining the reaction over much longer periods.

To facilitate these extended reactions, KSTAR has been newly fitted with a tungsten divertor. In the past, KSTAR has been able to operate for up to 30 seconds at temperatures of 100 million degrees Celsius (which is actually quite a long time by fusion standards.) But with this new upgrade, the new goal is to achieve 300 seconds by the end of 2026.

While this goal is impressive, it is not the first time such an extended reaction target has been reached. In 2023, China’s Experimental Advanced Superconducting Tokamak (EAST) was able to generate, sustain and confine plasma for 403 seconds in high confinement mode—a state that supports high temperature and particle densities and lays the foundation for more efficient power generation.

Even so, the South Korean team hopes that their upgrade will enable KSTAR to contribute more accurate data to the development and optimization of ITER, the world’s largest tokamak machine, which is currently under construction in France. ITER is expected to produce its first plasma at the end of 2025, with full-scale operations beginning in 2035.

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