Scientists demonstrate effective fusion "spark plugs" in groundbreaking experiments

Researchers from the Laser Energy Laboratory at the University of Rochester led the experiment and demonstrated an efficient "spark plug" for direct driving of inertial confinement fusion. In two studies published in the journal Nature Physics, the team shared their findings and detailed the potential to expand these methods with the aim of successful nuclear fusion in future facilities.

LLE is the largest university project of the US Department of Energy, equipped with the OMEGA laser system, which is the world's largest academic laser, but its energy is still almost one percent of that of the Lawrence Livermore National Laboratory National Ignition Facility in California. Through Omega, Rochester's scientists successfully attempted several times to emit 28 kilojoules of laser energy into small capsules filled with deuterium and tritium fuel, causing the capsules to implode and generate enough hot plasma to trigger fusion reactions between fuel nuclei. These experiments triggered fusion reactions, generating energy that exceeded the energy in the central thermal plasma.

The OMEGA experiment uses direct laser illumination of capsules, which is different from the indirect driving method used on NIF. When using indirect driving methods, the laser is converted into X-rays, which in turn drive the capsule to implode. NIF uses an indirect driver to irradiate the capsule with X-rays using approximately 2000 kilojoules of laser energy. This led to NIF achieving a breakthrough in fusion ignition in 2022- a fusion reaction that generates net energy gain from the target.

"Generating more fusion energy than the internal energy content of the fusion site is an important threshold," said Dr. Connor Williams' 23, the lead author of the first paper, who is currently a radiation and ICF target design scientist at Sandia National Laboratory. This is a necessary requirement for anything you want to accomplish in the future, such as burning plasma or achieving ignition.

By demonstrating that they can achieve this level of implosion performance with only 28 kilojoules of laser energy, the Rochester team is excited about the prospect of applying direct drive methods to lasers with more energy. Showcasing spark plugs is an important step, however, Omega is too small to compress enough fuel to ignite.

"If you can ultimately manufacture spark plugs and compress fuel, then compared to indirect driving, direct driving has many characteristics that are beneficial for fusion energy," said Dr. Varchas Gopalaswamy'21, a LLE scientist who led the second study that explored the effects of using direct driving methods on megajoule level lasers, similar in size to NIF. After amplifying the OMEGA results to a few megajoules of laser energy, it is expected that the fusion reaction will become self-sustaining, a situation known as' burning plasma '.

Gopalaswamy said that direct driving of ICF is a promising method for achieving thermonuclear ignition and net energy in laser fusion.
"A major factor contributing to the success of these latest experiments is the development of a novel implosion design method based on statistical prediction and validated by machine learning algorithms," said Robert L. McCrory, Professor of Mechanical Engineering and Physics and Astronomy at LE. These predictive models enable us to narrow down the pool of promising candidate designs before conducting valuable experiments.

Source: Laser Net