Meet Q. No, not the mercurial omnipotent being played by John de Lancie in Star Trek, The Next Generation. In the context of nuclear energy, “Q” is the fusion energy gain factor, or ratio between the amount of energy put into a fusion reaction, and the amount of energy released.
Scientists have been trying…and failing…to get Q to a value above one for decades. This would mean they’ve “broken even” in the reaction and got at least as much energy out as they put in. But the closest they’ve gotten was the Joint European Torus’ (JET) record run in 1997, which yielded a Q of 0.67. (They injected 24MW of thermal power to heat the fuel, which produced 16MW of fusion power.)
That is, until very recently.
By now, you’ve probably heard that the National Ignition Facility (NIF) had this breakthrough in fusion energy on December 5th. Secretary of Energy Jennifer Granholm said that “the president has a decadal vision, to get to a commercial fusion reactor within 10 years.” Maybe you heard also that her announcement was probably hopelessly premature.
But it doesn’t mean that what happened wasn’t incredibly important. I was able to catch up with Gerrit Bruhaug, a PhD candidate at the University of Rochester’s Laboratory for Laser Energetics. It’s the only university lab able to do Inertial Confinement Fusion (ICF), the technique used by the NIF team to achieve their record shot.
A wild Q appeared
There’s an old joke that fusion energy is always 30 years in the future. Sometimes in the joke it’s 50, or 20. But always elusively out of reach. To be honest, in retrospect, early scientists were insanely optimistic.
“They thought fusion energy was going to be easy, hilariously enough,” said Bruhaug, “when you first look at the confinement conditions as a physicist, it just didn’t seem that complicated.”
What they didn’t take into account was plasma really does not like to behave in any kind of a stable manner. Comprising of atoms stripped of some of their electrons, plasma is like a swirling, angry cloud — fast, hot and out of control.
Even the now-triumphant NIF started with a solid decade of being humbled by their mission. It’s calle the NIF — National Ignition Facility — because they kinda expected to achieve ignition on their first shot. They even invited reporters around and everything. But their first shot in 2011 at igniting the tiny deuterium-tritium fuel capsule with two megajoules (MJ) of lasers was a damp squib, yielding roughly nothing at all, or a measly 2.5 kilojoules (kJ) if you want to be precise.
“Ignition is a runaway event, like striking a match” explained Bruhaug, “it is not a linear process.” After eating crow for a decade, the actual breakthrough caught the scientists at NIF by surprise. In August 2021, output for one of the runs shot up to 1.3MJ whereas it has never topped 0.2MJ on any of the previous runs. The NIF actually took some damage from the shot, losing some light bulbs and dinging some of the detectors.
Everything is different once you reach the break even point because instead of being dependent on power of the laser, the ignited plasma is dominated by its own self-generated energy. As far as Bruhaug is concerned, that was the Q>1 event right there, in August 2021.
Bruhaug explained that the NIF uses something called “indirect drive.” The laser does not directly hit the target fuel capsule. Instead, it shoots into a chamber containing the capsule called a “hohlraum” to heat it and create an X-ray “bath.” It’s those X-rays that ultimately hit the capsule with about 180 kJ of energy. By that measure, the 1.3MJ produced by the August 2021 event “blew past” the amount of energy applied to it.
However, the National Academy of Science has set the standard for Q for laser fusion as “equal or more energy than the laser energy used.” This simpler, more unambiguous metric was the one finally reached on the December 5th 2022 run. Upon putting 2.05MJ of laser energy into the system, the fusion reaction triggered produced 3.15MJ of energy, producing a Q of about 1.5.
How much is 3.15MJ? Some have used “the heat required to boil 20 kettles of water.”
“We’re American,” said Bruhaug, “we say it’s about the calories in a stick of butter.”
A good Q to ask
It is kind of an arbitrary choice to take the power of the lasers as the energy input to the fusion reaction because how do you define the boundaries of the energy system? As we just said, the actual amount of energy reaching the fuel capsule is less.
On the other hand, the amount of electrical energy used to create that laser is much, much more. If energy production is the goal, wouldn’t a better measure of Q encompass all the electricity inputs of the system compared to the electricity we get out?
While acknowledging that fusion people can be too blase about the engineering challenges, Bruhaug encourages us to shelve the skepticism for now and just enjoy the historic moment…the achievement of a self-heating fusion reaction outside of a nuclear weapon.
“We should be able to get more yield relatively easily,” said Bruhaug, “It wouldn’t shock me if NIF goes on to achieve 10 or even 100MJ.” Of course, that would not come close to the actual electricity input of the NIF, which takes 300MJ of electrical energy to produce each 2MJ laser shot.
Ultimately, what Bruhaug is excited about are the new ICF (inertial confinement fusion) facilities that would be triggered by the breakthrough. NIF uses super inefficient lasers which made sense back in 1992. Today’s lasers get efficiencies of 18% or better.
“None of this means we will have ICF power plants any time soon,” said Bruhaug, “but ICF has jumped the hurdle of ignition. That’s more than can be said for any other approach to fusion.”
Inertial vs. Magnetic confinement
When most people think of a fusion experiment, they are likely picturing a “tokamak” device in their head. A tokamak uses powerful magnets to hold the plasma used for fusion in the shape of a doughnut. The world’s largest fusion experiment, ITER, is a tokamak. Secretary Graham described magnetic confinement as “a lot further along” than inertial confinement using lasers, which is what NIF used.
In fact, it’s often said that the goal of ICF is not power production at all, but “stockpile stewardship,” that is, the management of America’s aging nuclear arsenal. In the absence of more testing, laser fusion experiments are a good way to figure out if those nuclear weapons are still good. The Department of Defense are keen to know and generous with funding.
But it would be mistaken to think of ICF as a one-trick pony though. Now that an ICF device got to ignition first, it is every bit as promising as magnetic confinement when it comes to finding a way to power production, said Bruhaug.
Remember the “angry cloud” of plasma? It’s a hell of a thing to manage, especially with the super magnets that needs to be kept at near absolute zero, or colder than the dark side of the moon, to work. Especially since the plasma inside the tokamak reaches 150 million degrees Celsius, or ten times hotter than the core of our sun. Managing the extreme temperature differential is not the only headache…the “angry cloud” is also buzzing with energetic fast neutrons which will slam into every surface of the device, causing the material to become damaged and radioactive.
In inertial confinement fusion, on the other hand, you have the luxury of keeping your expensive lasers a nice distance away from your target fuel capsule. The capsule, ignited at a distance, only burns for a few trillionth of a second, compared to a few seconds for magnetic confinement. But that’s OK, said Bruhaug, that’s how it’s supposed to work.
“We’re not trying to keep it lit. We’re not trying to control it at all,” said Bruhaug.
The reason why it’s called “inertial confinement” is because the only thing doing the confinement is the inertia exerted by the shell of the capsule as it is vaporized by the energy from the lasers. This pushes the shell inwards towards the deuterium-tritium fuel, compressing it in all directions until the fusion reaction occurs. Instead of lasers you can slam the fuel with particle beams or even shoot the target through a rail gun. As long as the fuel reaches the correct compression conditions, it will go. “There’s a beautiful simplicity to that.” To output power, you will need a steady stream of targets reaching ignition at machine-gun pace, rather like a Diesel engine ignites at every stroke.
Tokamak experiments like ITER will reach Q eventually too, Bruhaug is sure. But it will take a while and cost a pretty penny compared to NIF. The US Department of Energy has estimated ITER costs through 2025 to be $65 billion. That’s when it is supposed to start fusion plasma experiments. In comparison, while NIF went “way over-budget,” it still got done at a relatively-low US$3.5 billion of Department of Defense money.
Supernova in a lab
It took nuclear fission 14 years to go from Enrico Fermi’s first criticality to Calder Hall, the first commercial nuclear power plant. If we are to consider NIF’s ignition event fusion’s first spark, how long will it take before we get the fusion version of Calder hall?
“We’ll see pilot projects for fusion power plants in our lifetimes,” said Bruhaug, hardly a detractor for fusion, “but I don’t know about commercial.”
The increase in private funding in fusion since 2017 or so has been “stunning” and is at about US$4 billion this year. Despite being such a long shot, energy is a $10 trillion dollar a year business with an addressable market of the entire world. Venture capital do love a wild card.
Above all, it’s a triumph for science.
“It’s so exciting to have a source of burning plasma! That little fusion ball will be the brightest source of X-rays on earth. It’s a supernova in a lab. We can probe all sorts of things to understand the universe,” said Bruhaug.
THE ELEMENTAL TAKE
The recent breakthrough is nuclear fusion is stunning and deserving of celebration, but not the hype. I do worry that breathless pronouncements that makes it sound like infinite energy is just around the corner could distract from nuclear fission, which has been producing rock-solid low-carbon power for decades and is in fact what we need to power the world.
In truth, every fusion expert I know is also a fission fan and recognize it would be pretty stupid to wait for fusion when fission already exists and does most of the job that people hope fusion will do one day — provide a massively scalable source of low-carbon energy.
Instead of fission and fusion being in opposition, there is in fact enormous common cause and opportunities for cooperation. In fact, the tritium used as fusion fuel comes from CANDU reactors. And Copenhagen Atomic’s highly-purified salts are also snapped up by fusion start-ups. Incredibly, they even have very similar headaches with the Nuclear Regulatory Commission in the US.
Just as I cover different fission technologies in various stages of maturity from meat-and-potatoes Light Water Reactors to thorium molten salt, I hope to occasionally cover exciting advancements in fusion going forward.
After all, it’s all elemental energy!
It's pretty interesting how there's the view of magnetic confinement being ahead, but then I read pieces like this on the physics, and it seems like inertial confinement is far ahead and magnetic confinement has far more unanswered questions. https://inference-review.com/article/the-quest-for-fusion-energy
Pretty good article.