Nuclear fusion breakthrough gets a bigger blast of laser energy

Key number: 3.88 MJ.

The experiment in December generated a whirlwind of accolades when it produced about three megajoules of energy, the equivalent of about 1.5 pounds of TNT, or about 1.5 times the energy of the incoming lasers. This was the first time that a fusion reaction in a laboratory setting produced more energy than it took to start the reaction.

The July experience was essentially identical to the December experience. “We expected a similar return,” Dr. Towne said. “On the order of three megajoules.”

The actual output was 3.88 megajoules.

The better-than-expected result indicates that with some modifications, laser fusion can become significantly more efficient. But small differences can produce failed fusion bombs, too.

The fusion experiment conducted in June, just a month ago, was also expected to produce about three megajoules, but only produced between 1.6 and 1.7 megajoules, Dr. Town said.

A more recent attempt this month, as part of efforts to preserve nuclear weapons without underground nuclear testing, yielded just over two megajoules, the equivalent of laser energy.

“It was a bit surprising that we didn’t achieve ignition in all of them,” Dr. Towne said.

Why it matters: Lots to learn.

By analyzing the results, Livermore scientists now believe they better understand what is going on.

First, the 192 lasers are not perfect. “There are some differences each time the laser is fired,” Dr. Towne said.

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

There are also slight differences in the fuel capsules that affect fusion reactions. Computer simulations now indicate that there may be a wide range in output power.

“It could be as low as 1.4 megajoules,” Dr. Towne said. “And if the stars align and everything works perfectly, it could be up to seven megajoules.”

What happens next: Upgrade and improve the experience.

“The fact that the gain went up in the last shot is encouraging news and shows that the current implosion has not It is fully improved yet.

A new series of experiments is about to begin at the National Ignition Facility as they aim to generate higher fusion yields more consistently. The facility’s laser power is being upgraded to 2.2 megajoules from 2.05. The latest developments occurred after the recent upgrade of 1.9 MJ. The additional power is expected to lead to further improvements.

“If you can effectively attach more energy to the hotspot, you should get more return,” Dr. Town said. “You can do that by having a bigger hammer.”