Laser fusion discovery has greater energy explosion – 09/26/2023 – Science

In July, scientists at Lawrence Livermore National Laboratory in California generated a burst of energy by bombarding a hydrogen pellet with 192 lasers, briefly replicating the fusion process that powers the Sun. It was a repeat of an experiment carried out in last December, but this time scientists generated even more energy, with almost double the gain compared to the energy of the incoming lasers.

“We repeated the ignition again,” Richard Town, associate director of the laser fusion program at Livermore, said in an interview. He gave a talk about the July experiment this Monday (25) at a conference in Denver, USA.

The Livermore results raise hopes that fusion could one day be used to generate abundant amounts of electricity without producing greenhouse gases or long-lived radioactive waste.

Key number: 3.88 megajoules

The experiment in December generated a flood of praise when it produced about three megajoules of energy — equivalent to about 1.5 pounds of TNT, or about 1.5 times the energy of the incoming lasers. It was the first time that a fusion reaction in a laboratory environment produced more energy than was needed to start the reaction.

The July experiment was essentially identical to the December experiment. “We expected a similar yield,” Town said. “On the order of three megajoules.”

The production was 3.88 megajoules.

The better-than-expected result indicates that, with some changes, laser fusion can become significantly more efficient. But tiny variations can also result in fusion failures.

A fusion experiment in June, just a month earlier, was also predicted to produce about three megajoules, but only generated between 1.6 and 1.7 megajoules, Town said.

A more recent attempt this month, as part of efforts to maintain nuclear weapons without underground nuclear tests, produced just over two megajoules, equaling laser energy.

“It was a little surprising that we didn’t get ignition on all of them,” Town said.

Analyzing the results, Livermore scientists now think they better understand what’s going on.

Why This Matters: So Much More to Learn

For one thing, the 192 lasers aren’t perfect. “There are some variations every time you fire the laser,” Town said.

Instead of the laser energy arriving perfectly balanced to compress the hydrogen fuel capsule, a slight imbalance pushes the capsule in one direction. Some of the energy is lost and the internal implosion does not heat the hydrogen that much.

There are also slight variations in the fuel capsules that affect fusion reactions. Computer simulations now indicate that there can be a wide range in output energy.

“It could drop to as low as 1.4 megajoules,” Town said. “And if everything goes right and everything works perfectly, it could be up to seven megajoules.”

What happens next: Updating and optimizing the experiment

Siegfried Glenzer, a scientist at the SLAC National Accelerator Laboratory in Menlo Park, California, who led the initial fusion experiments at the Livermore facility years ago, said of the July breakthrough: “The fact that the gain increased in the last shot is a encouraging news and shows that current implosions are not yet fully optimized.”

A new series of experiments is about to begin at the National Ignition Facility as it aims to generate higher fusion yields more consistently. The facility’s laser energy is being upgraded to 2.2 megajoules, up from 2.05 previously. The most recent advances came after the last 1.9 megajoule update. Additional power is expected to lead to further improvements.

“If you can effectively couple more power to the hot spot, you should get more throughput,” Town said. “You can do that by having a bigger hammer.”