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A major breakthrough in nuclear fusion research has once again placed South Korea’s KSTAR reactor—often referred to as an “artificial sun”—in the global spotlight, strengthening hopes for a future powered by clean and virtually limitless energy.

According to the Korea Institute of Fusion Energy (KFE), KSTAR successfully sustained ultra-hot plasma inside its tokamak reactor for record durations, including 102 seconds in the high-confinement operating mode known as H-mode. The reactor also maintained ion temperatures of 100 million degrees Celsius for 48 seconds, marking another important milestone in fusion energy development.

Understanding the 102-Second Achievement

While headlines have widely reported that the “artificial sun” operated at 100 million degrees Celsius for 102 seconds, the scientific details are more nuanced.

The 102-second figure refers to the duration of H-mode operation, a critical plasma confinement regime required for efficient fusion performance. The plasma itself remained at 100 million degrees Celsius for 48 seconds.

The distinction is significant because the challenge of fusion is not only generating extremely high temperatures but also maintaining stable magnetic confinement for extended periods.

KSTAR had previously sustained plasma at 100 million degrees Celsius for 30 seconds in 2021, making the latest achievement a substantial improvement.

Why 100 Million Degrees Celsius?

Nuclear fusion is the same process that powers the Sun and stars, where light atomic nuclei combine to form heavier elements while releasing vast amounts of energy.

Unlike the Sun, however, fusion reactors on Earth lack the immense gravitational forces found in stellar cores. As a result, scientists must heat fusion fuel to temperatures exceeding 100 million degrees Celsius to create the conditions necessary for atomic nuclei to collide and fuse.

In tokamak reactors such as KSTAR, powerful magnetic fields confine the plasma inside a vacuum chamber, preventing it from touching the reactor walls.

Tungsten Plays a Key Role

A major factor behind KSTAR’s recent success has been the replacement of carbon-based reactor components with tungsten, particularly in the divertor region, which acts as an exhaust system for heat, impurities, and particles escaping from the plasma edge.

According to KFE, the new tungsten divertor experienced surface temperature increases of only about 25% under comparable heat loads, significantly improving durability and enabling longer plasma operations at higher power levels.

This advancement is considered essential for moving from short experimental runs toward the continuous operation required for future commercial fusion power plants.

How Scientists Use KSTAR

KSTAR is not designed to generate commercial electricity. Instead, it serves as a highly advanced research platform for studying plasma behavior and developing technologies needed for future fusion reactors.

Researchers use the facility to:

• Test the ability of materials such as tungsten to withstand extreme heat.

• Study methods for preventing impurities from destabilizing plasma.

• Develop AI-powered real-time plasma control systems.

• Improve plasma heating, fuel injection, and current-control technologies.

• Support international projects such as the fusion reactor under construction in ITER and future DEMO power plant concepts.

Growing International Importance

KSTAR has become increasingly important to the global fusion community.

According to ITER, its plasma control system was successfully tested on KSTAR during the 2026 experimental campaign, achieving first plasma on March 10 and exceeding initial performance targets. This positions KSTAR as a valuable testbed for technologies that will eventually be deployed in the world's largest fusion experiment.

South Korea and France also launched a joint research program between KSTAR and the WEST facility in 2025 to study long-duration plasma operations using tungsten-based reactor environments similar to those required in future power plants.

What Does This Mean for the Future of Energy?

Scientists caution that the latest achievement does not mean fusion-generated electricity is ready for commercial deployment.

However, it represents significant progress toward solving one of fusion energy's greatest challenges: sustaining ultra-hot, stable plasma long enough to produce continuous power.

Fusion energy has the potential to generate enormous amounts of electricity without direct carbon emissions, using abundant fuels such as deuterium and lithium while avoiding the meltdown risks associated with conventional nuclear reactors.

Major challenges remain, including achieving energy-positive operation, maintaining plasma stability for thousands of seconds, and developing materials capable of enduring years of neutron bombardment and extreme heat.

A Global Race Intensifies

South Korea is not alone in the race toward fusion power.

In January 2025, China's EAST reactor—also known as an artificial sun—set a world record by sustaining high-confinement plasma for 1,066 seconds.

The achievement highlights how the focus of fusion research has shifted from merely reaching extreme temperatures to maintaining long-term plasma stability and control.

The Next Goal: 300 Seconds

KSTAR researchers are now aiming to sustain plasma at 100 million degrees Celsius for 300 seconds, or five full minutes.

To reach that milestone, scientists are continuing to improve heating systems, current-control technologies, tungsten components, and AI-assisted plasma management systems.

While commercial fusion power remains years away, every additional second of stable plasma operation provides valuable data, better materials, smarter control systems, and another step toward making the power of the stars a practical source of clean energy on Earth.