What makes stars shine
All nuclei carry positive charge and repel one another, but at extreme temperature and pressure they can get close enough for the strong nuclear force to bind them. The resulting nucleus weighs slightly less than the two that formed it, and that missing mass becomes energy according to Einstein's E=mc². Arthur Eddington proposed hydrogen fusion as the Sun's power source in 1920, and Hans Bethe worked out the stellar fusion cycles in 1939, later winning a Nobel Prize. The Sun's core is about 15 million °C, but its immense gravitational pressure makes fusion possible. Elements heavier than iron are forged mainly in supernovae and neutron star mergers.
Building a star on Earth
Without the Sun's gravity, reactors must heat fuel above 100 million °C, and there are two main ways to confine that plasma. The doughnut-shaped tokamak, developed in the Soviet Union in the 1950s, holds it with powerful magnetic fields, while the US National Ignition Facility uses 192 lasers to crush a fuel pellet in an instant (inertial confinement). In December 2022 NIF produced 3.15 MJ from 2.05 MJ of laser energy, the first fusion ignition. South Korea's superconducting tokamak KSTAR, nicknamed the Korean artificial sun, held 100-million-degree plasma for 48 seconds in 2024.
Challenges for fusion power
Deuterium can be extracted from seawater, fusion emits no carbon dioxide, and unlike fission it has no runaway chain reaction and far less long-lived waste, which is why it is pitched as a dream energy source for net zero. But NIF's ignition still fell far short of the electricity the whole laser system consumed, and materials that survive neutron bombardment and breeding scarce tritium remain unsolved. ITER, built in France by seven members including the EU, US, China and Korea, reset its schedule in 2024 to start operation in 2034 and full deuterium-tritium experiments in 2039, while private startups promise pilot plants in the 2030s.
FAQ
- How is fusion different from fission (nuclear power)?
- Fission splits heavy nuclei like uranium, while fusion joins light nuclei. Fusion cannot run away in a chain reaction and produces far less long-lived radioactive waste.
- When will fusion power reach the grid?
- Forecasts vary, but public roadmaps generally aim for grid electricity around 2050. Some private companies claim the 2030s, which still needs to be demonstrated.
Sources reviewed: 2026-10-26
References
- Bethe, H. A. (1939). Energy production in stars. Physical Review, 55(5), 434–456.
- Abu-Shawareb, H., et al. (Indirect Drive ICF Collaboration) (2024). Achievement of target gain larger than unity in an inertial fusion experiment. Physical Review Letters, 132, 065102.
- ITER Organization (2024). ITER Research Plan and baseline update. iter.org.