Scientists have repeatedly been able to produce more energy than was put into a nuclear fusion reaction after successfully doing so for the first time a year ago.
Having achieved the initial milestone last December, scientists from Lawrence Livermore National Laboratory have been able to replicate the process, known as ignition, several times this year.
Now with four confirmed successful tests, the scientific journal Nature said the prospect of the first being an accident could now be ruled out.
Nuclear fusion sees atomic nuclei bound together to create a single heavier atom and is how the sun is powered.
Given the process can release more energy than is put in, scientists have long viewed nuclear fusion as a means of providing the world with limitless clean energy.
However, the incredibly high temperatures needed mean the process is difficult to successfully carry out.
“We now know it will work,” physicist Carmen Menoni, who is set to head up a fusion research lab at Colorado University, said, following the tests.
Tokamak Energy and First Light Fusion are among British-based companies involved in the development of fusion power plants.
The former, which has developed “super” magnets to control its reactor, reported in September that it attained a plasma temperature of 100 million degrees Celsius, the threshold required for commercial fusion energy.
Both are targeting the rollout of their respective commercial fusion power plants in the 2030s, meanwhile.