Fusion milestone plus headline hype

In the indirect-drive method used at the National Ignition Facility, a UV laser is fired at a cylinder called a hohlraum rather than at the hydrogen fuel. The hohlraum then emits x rays, which compress the fuel inside. Credit: Lawrence Livermore National Laboratory

The headline writers went overboard on this latest fusion accomplishment. The below articles go a bit beyond the headlines and share some key points around this fusion milestone. Three of those:

1. On December 5, 2022, the National Ignition Facility shot a pellet of fuel with 2 million joules of laser energy – about the amount of power it takes to run a hair dryer for 15 minutes – all contained within a few billionths of a second. This triggered a fusion reaction that released 3 million joules. 
2. While the laser energy of 2 million joules was less than the fusion yield of 3 million joules, it took the facility nearly 300 million joules to produce that laser light energy. And there was a lot of uncounted energy consumed for making the deuterium-tritium fuel pellet and its diamond coating.  So, the total energy imput was >100 times the fusion energy liberated.
3. In the milstone experiment, laser light was impinged upon a small cylindrical chamber known as a hohlraum, which converts the UV to x rays. Suspended inside was a diamond-coated, peppercorn-size capsule containing deuterium–tritium fuel, which the x rays imploded.

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from https://physicstoday.scitation.org/do/10.1063/PT.6.2.20221213a/full/:

13 Dec 2022 in Politics & Policy

National Ignition Facility surpasses long-awaited fusion milestone

The shot at Lawrence Livermore National Laboratory on 5 December is the first-ever controlled fusion reaction to produce an energy gain.

David Kramer

Thirteen years after completion of the $3.5 billion National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL), the goal embodied in the giant laser’s name has finally been achieved. For the first time in the nearly 70-year history of controlled fusion research, a fusion reaction has yielded more energy than it took to spark it.

According to Mark Herrmann, program director for weapons physics and design at LLNL, a laser shot performed on 5 December produced about 3.15 megajoules of fusion energy from the 2.05 MJ of laser light that reached the small cylindrical chamber known as a hohlraum, which converts the UV to x rays. Suspended inside was a diamond-coated, peppercorn-size capsule containing deuterium–tritium fuel, which the x rays imploded.

The results were officially announced by Energy secretary Jennifer Granholm, Office of Science and Technology Policy director Arati Prabhakar, and other officials on 13 December. The findings have not been peer reviewed, and Herrmann says he would have preferred they be released through a scientific journal. But the results were sure to leak out, and it was important that the advance be reported correctly, he adds.

The yield surpasses the criteria for ignition established by the National Research Council in 2007. By other measures, such as the amount of energy deposited on the fuel capsule—around 250 kilojoules—the gain, or Q, is around 10, says Michael Campbell, who led NIF construction until 1999. Yet the amount of fusion energy from the record shot amounts to just 1% of the 300 MJ from the grid that’s required to power the 192-beam NIF laser, Herrmann says. Thus, although the lab’s achievement is a significant step, inertial fusion is still a long way from becoming a viable energy source.

Ignition is a key process in nuclear weapons, says Herrmann, and will enable experiments in which materials can be exposed to highly intense fluxes of the 14 MeV neutrons that are produced in fusion reactions. That, he says, has direct application to maintaining the weapons stockpile—NIF’s primary mission.

The success caps what has been a tortuous path for NIF, which was controversial even before its construction began in 1997. The project began as a lifeline to LLNL, which faced an existential threat in the post-Cold War era, says Victor Reis, former assistant secretary for defense programs at the Department of Energy and a progenitor of DOE’s science-based program to maintain the nuclear stockpile without testing. One DOE advisory commission had recommended consolidating weapons research at Los Alamos National Laboratory. “People were saying we don’t need Livermore,” Reis says. “You really needed some big science projects that [would] test the laboratories. NIF was that for Livermore.”

After delays and budget overruns, NIF opened for experiments in 2009. The facility then missed its original 2012 target for ignition. In a 2016 report, DOE’s National Nuclear Security Administration (NNSA) expressed doubt that what remains the world’s most energetic laser could ever attain its eponymous mission. The agency toned down the ignition objective, emphasizing NIF’s ongoing experiments to investigate materials’ behavior under extreme densities and pressures in support of nuclear stockpile maintenance. About 10% of NIF’s shots are reserved for unclassified research by academic researchers.

Many scientists believed that the laser’s energy was insufficient to overcome laser–plasma instabilities, which create pancake- or sausage-shaped asymmetric implosions. In response, NIF researchers have tried out numerous capsule and hohlraum configurations and materials. Campbell credits NIF’s latest achievement to advances in the last four to five years in the understanding of hohlraums and improved capsule fabrication, with contributions from other labs and the private sector.

As with the previous record shot in August 2021, the lab used nanocrystalline diamond–coated capsules for experiments. When blasted with x rays, the diamond shell blows off like a rocket, creating the implosion. The shell used in last week’s shot was about 10% thicker than those in previous attempts.

“We’ve always known we’re sensitive to defects in the capsules, but we had been blind to some of the defects in our metrology and the types of defects that were actually significant,” says Herrmann. “When we did follow-on experiments, we found there was more mixing of the capsule material into the fusion fuel, which was lowering the performance of implosions. Over the last year, we’ve put together a picture that says we have accounted for the degradations we observe.”

Another major contributor to last week’s success was the 10% increase to NIF’s original 1.9 MJ maximum laser energy. “It’s not that the laser couldn’t produce more energy,” Herrmann says, “but we didn’t want to break the laser.” In recent years, laser and optical scientists have succeeded in hardening the optics.

Campbell predicts the achievement will spark another frenzy of interest in fusion as an energy source. But laser fusion energy has a long list of engineering hurdles to overcome, such as finding ways to mass manufacture fusion capsules, to conduct laser shots continually, and to breed tritium.

“Ignition is a necessary but not sufficient condition for stewardship, because you’d want higher gain for stewardship, but it’s a really good start,” says Campbell, who retired last year as director of the DOE-supported Laboratory for Laser Energetics at the University of Rochester. “It shows the quality of the science and technology that NIF represents.”

Herrmann agrees that “the more the output, the more the utility for stockpile stewardship.” He thinks NIF could one day routinely produce laser pulses of 2.6–3 MJ to help initiate higher-gain reactions. “That will take many years, and we are discussing that with NNSA.”

There shouldn’t be any concerns about the size of the explosions inside NIF’s target chamber. It’s currently rated to safely accommodate yields up to 45 MJ, Herrmann says, and modest upgrades could increase that to 100 MJ.

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from https://interestingengineering.com/science/nuclear-fusion-improve-latest-breakthrough:

Nuclear fusion: How scientists can improve after latest breakthrough
American scientists have announced what they have called a major breakthrough in a long-elusive goal of creating energy from nuclear fusion.

The Conversation
Created: Dec 17, 2022 03:36 AM EST
SCIENCE

LAWRENCE LIVERMORE NATIONAL LABORATORY'S NATIONAL IGNITION FACILITY TARGET CHAMBER
U.S. Department of Energy 

American scientists have announced what they have called a major breakthrough in a long-elusive goal of creating energy from nuclear fusion.

The U.S. Department of Energy said on December 13, 2022, that for the first time – and after several decades of trying – scientists have managed to get more energy out of the process than they had to put in.

But just how significant is the development? And how far off is the long-sought dream of fusion providing abundant, clean energy? Carolyn Kuranz, an associate professor of nuclear engineering at the University of Michigan who has worked at the facility that just broke the fusion record, helps explain this new result.
What happened in the fusion chamber?

Fusion is a nuclear reaction that combines two atoms to create one or more new atoms with slightly less total mass. The difference in mass is released as energy, as described by Einstein’s famous equation, E = mc2 , where energy equals mass times the speed of light squared. Since the speed of light is enormous, converting just a tiny amount of mass into energy – like what happens in fusion – produces a similarly enormous amount of energy.

Researchers at the U.S. Government’s National Ignition Facility in California have demonstrated, for the first time, what is known as “fusion ignition.” Ignition is when a fusion reaction produces more energy than is being put into the reaction from an outside source and becomes self-sustaining.

The technique used at the National Ignition Facility involved shooting 192 lasers at a 0.04 inch (1 mm) pellet of fuel made of deuterium and tritium – two versions of the element hydrogen with extra neutrons – placed in a gold canister. When the lasers hit the canister, they produce X-rays that heat and compress the fuel pellet to about 20 times the density of lead and to more than 5 million degrees Fahrenheit (3 million Celsius) – about 100 times hotter than the surface of the Sun. If you can maintain these conditions for a long enough time, the fuel will fuse and release energy.

The fuel and canister get vaporized within a few billionths of a second during the experiment. Researchers then hope their equipment survived the heat and accurately measured the energy released by the fusion reaction.

So what did they accomplish?

To assess the success of a fusion experiment, physicists look at the ratio between the energy released from the process of fusion and the amount of energy within the lasers. This ratio is called gain.

Anything above a gain of 1 means that the fusion process released more energy than the lasers delivered.

On December 5, 2022, the National Ignition Facility shot a pellet of fuel with 2 million joules of laser energy – about the amount of power it takes to run a hair dryer for 15 minutes – all contained within a few billionths of a second. This triggered a fusion reaction that released 3 million joules. That is a gain of about 1.5, smashing the previous record of a gain of 0.7 achieved by the facility in August 2021.
How big a deal is this result?

Fusion energy has been the “holy grail” of energy production for nearly half a century. While a gain of 1.5 is, I believe, a truly historic scientific breakthrough, there is still a long way to go before fusion is a viable energy source.

While the laser energy of 2 million joules was less than the fusion yield of 3 million joules, it took the facility nearly 300 million joules to produce the lasers used in this experiment. This result has shown that fusion ignition is possible, but it will take a lot of work to improve the efficiency to the point where fusion can provide a net positive energy return when taking into consideration the entire end-to-end system, not just a single interaction between the lasers and the fuel.
What needs to be improved?

There are a number of pieces of the fusion puzzle that scientists have been steadily improving for decades to produce this result, and further work can make this process more efficient.

First, lasers were only invented in 1960. When the U.S. government completed construction of the National Ignition Facility in 2009, it was the most powerful laser facility in the world, able to deliver 1 million joules of energy to a target. The 2 million joules it produces today is 50 times more energetic than the next most powerful laser on Earth. More powerful lasers and less energy-intensive ways to produce those powerful lasers could greatly improve the overall efficiency of the system.

Fusion conditions are very challenging to sustain, and any small imperfection in the capsule or fuel can increase the energy requirement and decrease efficiency. Scientists have made a lot of progress to more efficiently transfer energy from the laser to the canister and the X-ray radiation from the canister to the fuel capsule, but currently, only about 10% to 30% of the total laser energy is transferred to the canister and to the fuel.

Finally, while one part of the fuel, deuterium, is naturally abundant in sea water, tritium is much rarer. Fusion itself actually produces tritium, so researchers are hoping to develop ways of harvesting this tritium directly. In the meantime, there are other methods available to produce the needed fuel.

These and other scientific, technological, and engineering hurdles will need to be overcome before fusion will produce electricity for your home. Work will also need to be done to bring the cost of a fusion power plant well down from the US$3.5 billion of the National Ignition Facility. These steps will require significant investment from both the federal government and private industry.

It’s worth noting that there is a global race around fusion, with many other labs around the world pursuing different techniques. But with the new result from the National Ignition Facility, the world has, for the first time, seen evidence that the dream of fusion is achievable.

Author: Carolyn Kuranz, Associate Professor of Nuclear Engineering, University of Michigan

This article is republished from The Conversation under a Creative Commons license. Read the original article here.