Laser fusion approaches the milestone of ignition

18 August 2021

The USA's National Ignition Facility has achieved a record fusion yield that it says puts it "at the threshold of fusion ignition". The record laser shot produced 25 times more than the facility's next best experiment.

A technician inside NIF's laser chamber. A pellet of fusion fuel is held in target position within the small cylindrical hohlraum, top (Image: LLNL)

"This result is a historic step forward for inertial confinement fusion research," said Kim Budil, director of Lawrence Livermore National Laboratory, where the National Ignition Facility (NIF) is located. It opens "a fundamentally new regime for exploration and the advancement of our critical national security missions," she added.

The NIF facility covers an area equivalent to more than three football fields and generates 192 intense laser beams which are focused on a pellet of deuterium-tritium fusion fuel only a few millimetres in diameter.

The lasers instantly heat the pellet to temperatures of more than 3 million degrees Celsius causing its surface to blow off with a corresponding effect that compresses the deuterium and tritium to densities at which their atoms fuse. These fusion reactions release copious amounts of energy referred to as the yield.

LLNL said preliminary analysis of the experiment on 8 August showed a yield of 1.3 megajoules, which would be some 25 times more than its previous best of 55 kilojoules which it achieved in January 2018.

The ultimate goal of NIF is to trigger 'ignition', which is when the radiation released by fusion is enough to heat surrounding fuel and cause it to fuse too. This would create a self-sustaining fusion reaction. LLNL said that its latest record brings it to the "threshold" of that level.

"Looking ahead, access to this new experimental regime will inspire new avenues for research and provide the opportunity to benchmark modelling used to understand the proximity to ignition" said LLNL. "Plans for repeat experiments are well underway, although it will take several months for them to be executed."

LLNL is clear that, "The central mission of NIF is to provide experimental insight and data for the National Nuclear Security Administration's science-based Stockpile Stewardship Programme" - in other words, the maintenance and modernisation of US nuclear weapons - but the science it produces also plays an important role in the peaceful goal of creating power plants based on nuclear fusion.

LLNL said the new record came after several improvements across the NIF process: new diagnostics; improvements in the manufacturing of the hohlraum device that holds the fusion fuel pellet; and improved laser precision, among other things.

The preliminary result of a 1.3 megajoule yield must go through peer review and the process of publishing in a scientific journal before it will be official, LLNL noted.

Researched and written by World Nuclear News