China’s ‘Artificial Sun’ Reactor Breaks Major Fusion Milestone

China’s Experimental Advanced Superconducting Tokamak (EAST), popularly known as the “artificial sun”, has achieved a groundbreaking advancement in nuclear fusion research. 

• It successfully exceeded the Greenwald Limit, marking a breakthrough in plasma confinement and density.

The Experimental Advanced Superconducting Tokamak (EAST) Reactor

• EAST is a tokamak, a donut-shaped device that uses powerful magnetic fields to confine and control hot plasma.
• Location: Hefei, China
• Achievement: 
  • World leader in experimental fusion reactors and has repeatedly set records for sustained high-temperature plasma operation.
  • In 2025, EAST achieved stable plasma at over 100 million°C for more than 1,000 seconds (a world record at the time).
• Role:  It serves as a key testbed for technologies that will support larger projects like ITER (the international experimental reactor under construction in France).

The Greenwald Limit

• The Greenwald Limit is an empirical rule discovered in 1988 by physicist Martin Greenwald.
  • Empirical means it is based on observations, not a strict fundamental limit like the speed of light.
• It sets a practical upper limit on how dense the plasma can be before it becomes unstable and escapes magnetic confinement, damaging the reactor.
• Importance: 
  • Higher plasma density is desirable because fusion power increases dramatically with density (roughly proportional to the square of density). 
  • Overcoming this limit has been a major goal in fusion research.

Exceeding the Greenwald Limit

• EAST maintained plasma density 1.3–1.65 times the Greenwald Limit.
• Usual operational range: 0.8–1.0.
• Significance:
• • First validation of a density-free regime in a major superconducting tokamak.
  • Brings fusion closer to practical, limitless clean energy.

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What is Nuclear Fusion?

• Nuclear fusion is the process that powers the sun and stars. 
• Nuclear fusion occurs when two light atomic nuclei (usually isotopes of hydrogen) combine under extreme heat and pressure to form a heavier nucleus, releasing enormous energy.  
• Fusion vs Fission: Unlike nuclear fission (used in current power plants), fusion produces minimal radioactive waste and no greenhouse gases, offering a clean, virtually unlimited energy source.
• Challenges: However, achieving controlled fusion on Earth has been challenging for over 70 years. 
  • Reactors must heat plasma (the super-hot, fourth state of matter) to millions of degrees while confining it long enough for fusion to occur.

Advantages of Nuclear Fusion

• Near-limitless Fuel Supply: Deuterium is abundant in seawater; tritium can be bred inside reactors.
• No long-lived Radioactive Waste: Produces mostly short-lived waste and inert helium gas (unlike fission’s long-term high-level waste).
• Safety: No risk of meltdown; no runaway chain reaction. 
• Clean Energy: Zero carbon emissions during operation.
• Energy Density: Millions of times higher per unit mass than fossil fuels.

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