On December 5th, 2022, for the first time in nearly a century of controlled fusion research, scientists at the National Ignition Facility (NIF) of the Lawrence Livermore National Laboratory successfully generated a fusion reaction that produced more energy than that required to start the reaction. This process is called fusion ignition. 

The net gain of more than 1.3 megajoules (MJ) of energy produced in the NIF reaction has excited physicists and fusion researchers worldwide, sparking debate to the prospects of virtually limitless and carbon-free power. If further developments are made, and various challenges overcome, it is thought that nuclear fusion technology could potentially diminish, if not end, human dependence on fossil fuels and other non-renewable energy sources. 

Nuclear fusion is a reaction in which the nuclei of two atoms are joined together under extraordinary temperatures and pressures. Such conditions, which are intense enough to simulate those of stars, are necessary for nuclei to overcome the electrostatic force repelling them, thus binding the two nuclei with strong nuclear force. The result is the formation of a single heavier nucleus and the release of energy.

In the NIF experiment, 192 energetic laser beams were fired at a capsule containing a mixture of two heavy isotopes of hydrogen: deuterium and tritium. As the beams heated the capsule to a few million degrees Celsius, the mixture became momentarily hotter and denser than the Sun. Under such phenomenal conditions, the hydrogen nuclei were prompted to fuse together, thereby ejecting alpha particles and generating 3.15 MJ of energy. 

Scientists regard the observed net gain in energy as a sustainable source insofar as the reagents used to generate it are found in the chemical structure of water and are thus virtually limitless and carbon-free. Additionally, the reaction produces no greenhouse gases or long-lived nuclear waste; in fact, its resulting alpha particles simply constitute an inert, non-toxic gas, with no known negative effects on the environment. 

Nuclear fusion is not to be confused with its similar-sounding counterpart, nuclear fission. The latter is essentially the opposite, as it requires the splitting of a heavier atomic nucleus into two smaller fragments of roughly equal mass, resulting in the release of energy. All modern nuclear power plants generate heat and electricity by means of fission, often irradiating Uranium-235 (U-235) with neutrons, whereupon U-235 subdivides into more neutrons and into nuclei of smaller atomic numbers — such as barium and krypton. 

Yet, unlike the reagents for fusion, U-235 is non-renewable and toxic, and its extraction from metal ores has deleterious effects on human health and the environment, albeit not as many as the effects from the consumption of fossil fuels for energy. Such a process also generates unstable radioactive nuclei, some of which persist for millions of years. 

Notwithstanding its disadvantages, fission energy remains in widespread use in the modern world, as it is relatively easy to generate in substantial quantities, requiring only the absorption of neutrons in the atomic structure of unstable U-235 nuclei. Unlike fusion, no extraordinary high-energy conditions that simulate the Sun must be present in order to generate a net amount of usable power. 

On the whole, nuclear fusion can be a cleaner and more sustainable energy source than the conventional sources that currently power our electric grid. However, various developmental, scientific and regulatory issues mean that years, if not decades, are likely necessary before nuclear fusion energy can be brought to scale commercially. 

As humanity is on a race against the clock to fight climate change, some scientists argue that more investment should be directed instead towards solar, wind, and hydropower, where significant research and advancements have already been made. Although wide-scale fusion energy still remains elusive, the science community has at least witnessed — for the first time in history — that the dream of a clean energy future is indeed possible for humanity.