Scientists repeat energy gain through fusion – 08/08/2023 – Science

US government scientists have achieved a net energy gain in a fusion reaction for the second time, a result that should boost optimism about progress towards the dream of unlimited carbon-free energy.

Since the 1950s, physicists have sought to harness the fusion reaction that powers the Sun, but as of December, no group has managed to produce more energy from the reaction than it consumes, a condition also known as ignition.

Researchers at the Lawrence Livermore National Laboratory in California, who achieved ignition for the first time last year, repeated the finding in an experiment on July 30 that produced a higher energy than in December, according to three people briefed on the preliminary results.

The lab confirmed that energy gain was achieved again in its laser facility, adding that analysis of the results is ongoing.

“Since demonstrating fusion ignition for the first time at the National Ignition Facility (NIF) in December 2022, we have continued to run experiments to study this exciting new scientific regime. , we repeated the ignition,” he said. “As is our standard practice, we plan to report these results at upcoming scientific conferences and in peer-reviewed publications.”

Fusion is achieved by heating two isotopes of hydrogen – usually deuterium and tritium – to such extreme temperatures that atomic nuclei fuse, releasing helium and large amounts of energy in the form of neutrons.

While many scientists believe that fusion power plants are still decades away, the technology’s potential is hard to ignore. Fusion reactions do not emit carbon, do not produce long-lived radioactive waste, and a small cup of hydrogen fuel could theoretically power a home for hundreds of years.

The most widely studied approach, known as magnetic confinement, uses huge magnets to hold fuel in place while it is heated to temperatures higher than that of the sun.

NIF uses a different process called inertial confinement, in which it fires the world’s largest laser into a tiny capsule of fuel, causing an implosion.

US Secretary of Energy Jennifer Granholm in December described the achievement of ignition as “one of the most impressive scientific feats of the 21st century”. In this experiment, the reaction produced about 3.15 megajoules, about 150% of the 2.05 MJ of the lasers.

Initial data from the July experiment indicated an energy output of more than 3.5 MJ, said two of the people familiar with the preliminary results. That energy would be approximately enough to power a household iron for an hour.

Achieving net energy gain has for decades been considered a crucial step in proving that commercial fusion power plants are possible. However, there are still several obstacles to be overcome.

The energy gain in this context compares only the energy generated with the energy in the lasers, not with the total amount of energy extracted from the grid to feed the system, which is much higher. Scientists estimate that commercial fusion will require reactions that generate between 30 and 100 times the energy of lasers.

The NIF also does a maximum of one shot per day, whereas an indoor confinement plant would likely need to complete several shots per second.

However, the improved NIF result, “just eight months” after the initial breakthrough, was yet another sign that the pace of progress is picking up, said one of the people briefed.