Fusion has the potential to produce massive amounts of clean energy with few inputs, little fuel and little carbon dioxide emissions. A fusion plasma that is “ignited” will continue to burn as long as it is held in place. However, fusion reactions have proven difficult to control, and no fusion experiment had previously produced more energy than was put in to get the reaction started.

For more than 70 years, scientists have tried to use thermonuclear fusion – the power source of stars – to generate energy. In a new study, scientists hailed a “real breakthrough” as a fusion reaction successfully generated more energy than was used to create it. They achieved this holy grail at the Lawrence Livermore National Laboratory’s National Ignition9 Facility (NIF) in the US by producing more energy than the laser pulse used to heat the fuel.

The laser pulse had an energy output of 2.05 megajoules, the equivalent of two Martian chocolate bars or the energy needed to boil six kettles of water. Compared to the energy of the laser pulse, the energy of fusion reactions was 50% higher. This released high-energy neutrons.

Professor Jeremy Chittenden, co-director of the Center for Inertial Fusion Studies at Imperial College London, said: “Everyone who works on fusion has been trying for more than 70 years to show that it is possible to get more energy out of fusion than you put into it. This is a real breakthrough moment, which is extremely exciting. It proves that the long-sought goal, the ‘holy grail’ of fusion, can be achieved. This brings us closer to generating fusion power on a much larger scale.”

“To turn fusion into an energy source, we need to increase the energy gain even further. We will also have to find a way to reproduce the same effect much more often and more cheaply before we can turn this into a power plant. It’s hard to say how quickly we can get to that point. If everything lines up, we could see fusion power in use in a decade, but it could take much longer. Most importantly, with today’s results, we know that fusion power is within reach.”

Professor Steven Rose, also co-director of the Center for Inertial Fusion Studies at Imperial, said: “This wonderful result shows that inertial fusion operates on the megajoule scale, providing a huge boost to its development as a source of energy and as a tool for basic science.”

Dr. Brian Appelbe, a research fellow at the Center for Inertial Fusion Studies at Imperial, said: “Not only is this experiment an important step towards fusion power, it is also exciting because it will allow us to study matter at temperatures and densities never before achieved in the laboratory. All kinds of interesting physics can take place under these conditions, such as the formation of antimatter, and the NIF experiments will give us a glimpse into this world.”