Nuclear fusion

Every atom's nucleus is positively charged, meaning they naturally repel one another like the matching poles of magnets. To trigger fusion, these nuclei must be forced so close together that the "strong nuclear force"—which only acts over microscopic distances—can take over and glue them into a single, heavier nucleus. This process releases a staggering amount of energy because the resulting nucleus weighs slightly less than the sum of its parts; that "missing" mass is converted directly into energy according to Einstein’s $E=mc^2$.

In nature, this happens in the cores of stars, where the sheer weight of gravity provides the necessary pressure. On Earth, we lack that gravitational mass, so we must compensate by heating hydrogen isotopes to temperatures exceeding 100 million degrees Celsius—far hotter than the center of the sun. At these temperatures, matter becomes plasma, a chaotic soup of electrons and nuclei that is notoriously difficult to handle.

Engineers primarily use two methods to contain the 100-million-degree plasma required for fusion. The first, Magnetic Confinement, uses a donut-shaped machine called a Tokamak. Powerful superconducting magnets suspend the plasma in mid-air, preventing it from touching and melting the reactor walls. The goal is to keep the plasma stable long enough for the nuclei to collide and fuse continuously.

The second method, Inertial Confinement, takes a "micro-explosion" approach. Researchers use some of the world's most powerful lasers to blast a tiny fuel pellet for a fraction of a second. This causes the pellet to implode with such intensity that it reaches the density and temperature required for fusion. While magnetic fusion aims for a steady burn, inertial fusion is more like an internal combustion engine, relying on rapid, discrete pulses of energy.

The most "attainable" fusion reaction on Earth uses two isotopes of hydrogen: deuterium and tritium. Deuterium is plentiful and easily extracted from ordinary seawater, making it an almost inexhaustible resource. However, tritium is radioactive and extremely rare in nature. To make fusion commercially viable, reactors must "breed" their own tritium by lining the reactor walls with lithium, which transforms into tritium when struck by neutrons from the fusion reaction.

The ultimate goal is "Aneutronic fusion," using fuels like Boron-11. These reactions produce no neutrons, meaning the reactor wouldn't become radioactive over time and energy could be captured directly as electricity without needing to boil water to turn a turbine. However, these reactions require temperatures ten times higher than the deuterium-tritium mix, keeping them firmly in the realm of future tech.

Unlike nuclear fission—which splits heavy atoms like Uranium—fusion cannot trigger a chain reaction or a "meltdown." If a fusion reactor is damaged or the plasma is disturbed, the reaction simply cools and stops within seconds. There is no risk of a runaway explosion. Furthermore, the primary byproduct of the reaction is helium, an inert gas that poses no environmental threat and is actually a valuable industrial resource.

While the reactor components themselves become radioactive over their 30-year lifespan due to neutron bombardment, this waste is much "cleaner" than fission waste. It loses most of its radioactivity within 50 to 100 years, rather than the thousands of years required for spent nuclear fuel. This makes fusion the "Holy Grail" of energy: high-density, carbon-free, and inherently safe.