Nuclear fusion reactor in South Korea runs at 100 million degrees C for a record-breaking 48 seconds

South Korea's "artificial sun" has set a new fusion record after superheating a plasma loop to 180 million degrees Fahrenheit (100 million degrees Celsius) for 48 seconds, scientists have announced. 

The Korea Superconducting Tokamak Advanced Research (KSTAR) reactor broke the previous world record of 31 seconds, which was set by the same reactor in 2021.The breakthrough is a small but impressive step on the long road to a source of near-unlimited clean energy. 

Scientists have been trying to harness the power of nuclear fusion — the process by which stars burn — for more than 70 years. By fusing hydrogen atoms to make helium under extremely high pressures and temperatures, so-called main-sequence stars convert matter into light and heat, generating enormous amounts of energy without producing greenhouse gases or long-lasting radioactive waste. 

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But replicating the conditions found inside the hearts of stars is no simple task. The most common design for fusion reactors — the tokamak — works by superheating plasma (one of the four states of matter, consisting of positive ions and negatively charged free electrons) and trapping it inside a donut-shaped reactor chamber with powerful magnetic fields.

Keeping the turbulent and superheated coils of plasma in place long enough for nuclear fusion to happen, however, has been a painstaking process. Soviet scientist Natan Yavlinsky designed the first tokamak in 1958, but no one has ever managed to create a reactor that is able to put out more energy than it takes in.

One of the main stumbling blocks has been how to handle a plasma that's hot enough to fuse. Fusion reactors require very high temperatures — many times hotter than the sun — because they have to operate at much lower pressures than where fusion naturally takes place inside the cores of stars. The core of the actual sun, for example, reaches temperatures of around 27 million F (15 million C) but has pressures roughly equal to 340 billion times the air pressure at sea level on Earth.

Cooking plasma to these temperatures is the relatively easy part, but finding a way to corral it so that it doesn't burn through the reactor without also ruining the fusion process is technically tricky. This is usually done either with lasers or magnetic fields.

To extend their plasma's burning time from the previous record-breaking run, the scientists tweaked aspects of their reactor's design, including replacing carbon with tungsten to improve the efficiency of the tokamak’s "divertors," which extract heat and ash from the reactor.

"Despite being the first experiment run in the environment of the new tungsten divertors, thorough hardware testing and campaign preparation enabled us to achieve results surpassing those of previous KSTAR records in a short period," Si-Woo Yoon, the director of the KSTAR Research Center, said in a statement.

KSTAR scientists are aiming to push the reactor to sustain temperatures of 180 million F for 300 seconds by 2026.

The record joins others made by competing fusion reactors around the world, including one by the U.S. government-funded National Ignition Facility (NIF), which sparked headlines after the reactor core briefly put out more energy than was put into it.