European scientists have taken a significant step closer to mastering a technology that could allow them to one day harness nuclear fusion, providing a clean and almost limitless source of energy, British officials said Wednesday.

Researchers at the Joint European Torus experiment near Oxford managed to produce a record amount of heat energy over a five-second period, which was the duration of the experiment, the U.K. Atomic Energy Authority said.

The 59 megajoules of sustained fusion energy produced were more than double the previous record achieved in 1997.

The agency said the result was “the clearest demonstration worldwide of the potential for fusion energy to deliver safe and sustainable low-carbon energy.”

“If we can maintain fusion for five seconds, we can do it for five minutes and then five hours as we scale up our operations in future machines,” said Tony Donne, program manager for EUROfusion. “This is a big moment for every one of us and the entire fusion community.”

Ian Chapman, CEO of the U.K. Atomic Energy Authority, said the results were a “huge step closer to conquering one of the biggest scientific and engineering challenges of them all.”

The facility, also known as JET, is home to the world’s largest and most powerful operational tokamak — a donut-shaped device that is considered one promising method for performing controlled fusion.

Scientists who were not involved in the project believed it was a significant result, but still a very long way from achieving commercial fusion power.