Producing energy from fusion – the clean nuclear reaction that mimics what happens in the solar core – could be simpler than expected. This is what emerges from a study by Princeton University published in the scientific journal Physical Review Letterswho identified an alternative theoretical path to reach the trigger of nuclear fusion (or ignition), the moment in which reactions can be self-sustaining thanks to the energy they release. A crucial step to transform fusion into a usable energy source: if the shortcut to ignition proposed by American researchers is confirmed with real experiments, fusion could in fact be achieved more quickly – and therefore more economically – than predicted by previous models.
The strategy to get to the trigger
Fusion is the atomic process that powers stars: the nuclei of light elements combine to form heavier nuclei and release energy. To reproduce it on Earth, the fuel must be brought to very high temperatures, until it becomes plasma, in order to overcome the resistance of the forces that keep the atomic nuclei separate. And heating it is not enough: the generated plasma must not lose energy too quickly, so that it can continue to independently power the fusion without needing to continue introducing heat from the outside, otherwise the energy balance of the reactor would be negative, making it useless as an energy source.
For decades, the conditions necessary for fusion to reach ignition have been evaluated with the so-called Lawson criterion, a series of parameters formulated by the English engineer John Lawson in 1955. However, the criterion indicates the goal, not the best way to get there. This is why the authors of the study decided to work to expand the Lawson criterion, taking into account factors that influence the energy balance of the plasma, such as spent fuel in the form of helium ash, impurities coming from the reactor walls, the radiation emitted and the heat that is lost. And in this way, they wondered if it was possible to find a shortcut to reach the goal: if we consider the ignition as a valley between two mountain peaks – they explain – the goal was to find a way to go around the mountains, instead of having to climb them.
The new model
Calculations published by the researchers indicate that a promising strategy is to first heat the plasma and then increase its density, rather than proceeding in the reverse order, as previously thought. In this way, according to the model, it would be less expensive to achieve the conditions necessary for self-sustaining fusion, and therefore improve the energy balance of fusion reactors, by taking a simple shortcut.
The practical impact mainly concerns the design of reactors. If confirmed, this path could help engineers choose more efficient configurations, reducing ineffective attempts, development time and costs. A potentially important contribution for a technology that promises to produce energy without direct carbon dioxide emissions during operation.
How long until the commercial merger?
The study also highlights a real problem: Even small amounts of tungsten, a high-temperature metal used or considered for the walls of some reactors, can hinder ignition. Impurities can in fact steal energy from the plasma, making it more difficult to maintain the conditions necessary for reactions. Controlling contamination will therefore be essential.
For now, commercial nuclear fusion remains a relatively distant dream: to achieve it, numerous technological challenges will have to be overcome, ranging from plasma management to the creation of plants capable of operating reliably, and above all conveniently. The intuition published in the new study (as we said, still to be confirmed) however offers a useful indication: better understanding how to achieve the trigger could avoid wasting resources and bring fusion closer to concrete use, step by step.