Nuclear fusion, a reaction in which two light atomic nuclei combine to form a heavier one, is the process that powers the Sun and the stars, capable of releasing enormous quantities of energy. But then, if it works so well in nature, why can’t we reproduce it on Earth too? Nuclear fusion is clean, safe, practically inexhaustible. To get it on Earth, you have to replicate extreme conditions of temperature and pressure, similar to those of the solar nucleus, to overcome the repulsion between the nuclei and force them to merge. The main technological challenge is precisely to create and maintain these conditions in a controlled way.
What is nuclear fusion
Nuclear fusion is a reaction in which two light atomic nucleilike those of hydrogen, come together to form a heavier nucleus, releasing energy. It is the opposite of fission – used in nuclear power plants – where a heavy nucleus splits into two lighter ones. The most studied reaction is the one between deuterium And tritiumtwo isotopes of hydrogen:
Deuterium + Tritium → Helium + Neutron + Energy
This reaction is exothermic, i.e produces energyand it is what powers the stars. But replicating it on Earth is technically complex.
What are the most important technical difficulties
There are several technical difficulties that make nuclear fusion complex to achieve on Earth.
- Overcome the repulsion between the two nuclei: atomic nuclei are positively chargedso they reject each other. To make them melt, you have to bring them very close, exceeding the electrostatic barrier. You can do it with very high temperaturesof the order of 100 million degrees Celsius!
- Confine the plasma: at those temperatures the matter becomes plasmaa gas of ionized charged particles. To contain it and trap the plasma they are used magnetic fields very strong.
- Durability and stability: the plasma must remain stable long enough for the merger to occur. But since the plasma is turbulent and unstable, it tends to “escape” from magnetic fields. Maintaining the reaction for more than a few seconds, therefore, is a challenge.
- Energy balance: So far, experiments and systems that try to produce energy with nuclear fusion have required more energy than it producescone to fuel the entire process. The goal to be achieved in the future will be to reach a positive energy balance. The first step to achieve it is the so-called break-eventhat is, when the energy produced by the reaction exceeds that introduced.
In 2022, the NIF laboratory in the USA made progress, producing more energy than was put into the reaction. However, its performance is still far from energetically balancing all the auxiliary services that power the experiment, such as cooling systems or servers.
Technologies in the field
There are various technologies that allow the creation of plasma and its confinement. There exists the tokamakwith a donut shape, which uses magnetic fields to confine the plasma. The ITER project is an example under construction.
Then they also exist laser very powerful with inertial fusion, which compress fuel capsules and trigger fusion. It is the method used by National Ignition Facility (NIF) in the United States. Finally the Stellaratorwith a more complex geometry, designed to improve plasma stability. The reactor Wendelstein 7-X in Germany it is one of the most advanced.
Because we care so much
Nuclear fusion could revolutionize the world of energy: it does not produce greenhouse gases And does not generate long-lasting radioactive waste. Deuterium fuel is plentiful and is found in sea water. Finally it is safe and it can’t explode. In practice, it would be like having a miniature Sun on Earthcapable of providing clean and practically infinite energy.
