Liam Stanton Helps Put the Keys in the Fusion Ignition
To create fusion ignition, National Ignition Facility’s laser energy is converted into x rays inside the hohlraum, which then compress a fuel capsule until it implodes, creating a high temperature, high pressure plasma. Photo by John Jett and Jake Long/LLNL.
Unless you’re a scientist, it’s possible that the significance of the headline “US scientists repeat fusion ignition breakthrough for 2nd time” may have been lost on you. Maybe you breezed past it, thinking that maybe on a less busy day you’d go back and get into the nitty gritty of what it all meant.
But the significance shouldn’t be lost on anyone, because this fusion ignition breakthrough is a big deal. If scientists can harness fusion energy, it could mean a clean energy revolution and something like “global stability,” possibly even “freely available energy” that may allow humans to travel beyond our solar system. “The holy grail in all energy production is fusion energy,” Liam Stanton, associate professor of applied mathematics at San José State, says.
Stanton’s models were put into the codes used to design this research into fusion energy, including a breakthrough series of similar experiments on August 8, 2021 and December 5, 2022, and then again in July and October 2023 at Lawrence Livermore National Laboratory (LLNL). He’s listed as an author among nearly 1,000 others worldwide, in the initial paper announcing the breakthrough as well as a follow-up paper released in February detailing the December 2022 experiment. Stanton completed a postdoc at Lawrence Livermore National Laboratory and then worked there as a staff scientist for a decade before coming to San José State.
The basics of fission vs. fusion
When people talk about nuclear power, they are usually referring to nuclear fission, when a heavy (as in, towards the end of the periodic table, like uranium and plutonium) atom breaks apart into smaller atoms when struck by a neutron. This converts nuclear mass into energy via Einstein’s famous E = mc2, and also emits more neutrons. These neutrons enable a “chain reaction” where fission begets more fission in a potentially uncontrolled way. Fission energy has been in use in various capacities for roughly 70 years (including nuclear power plants and, of course, atomic bombs).
Fusion, however, is when two light (as in, towards the beginning of the periodic table, like hydrogen) atoms are fused together. This also creates energy, and significantly more than fission. Fission energy is already about a million times more powerful than chemical energy (the energy that powers our bodies, for example), and fusion energy is about 10-100 times more powerful than that fission energy. Fusion energy’s power is evident whenever you look up: the sun itself is a massive fusion reactor, powering all life on Earth.
Fusion power also has other advantages over fission: A fusion power plant wouldn’t have the same meltdown issues that fission power (like the Fukushima and Chernobyl nuclear power plants) is known for occasionally causing. If an asteroid hit a fusion power plant, every part of the energy production would stop because the conditions needed to produce fusion energy are so “finicky.” As Stanton explains, “A fission power plant is maintaining a chain reaction just slightly below an uncontrolled level. Fusion is instead designed to operate safely in its most reactive state, so that any disruption ‘breaks’ the reactor and shuts it off.”
Fusion energy also produces “much less radioactive material than fission energy, with much shorter half-lives (10s to 100s of years vs. 10,000s of years) and no material useful for constructing nuclear weapons (like uranium and plutonium from fission).” It is therefore considered to be “a sustainable form of energy” that “checks every box.” It has the potential to be a game changer.
The only problem is that for decades, even after governments worldwide had invested billions and billions of dollars into research, no one had successfully produced “fusion ignition.” As Stanton explains, pushing two atoms together is like pushing magnets together – you squish them one way, they go the other way. You squish them the other direction, they move back again. The general strategy is to get the atoms hitting each other, which can be done by heating them up, pushing them together, or both. You need to contain the atoms in a relatively small space in order to fuse them, but this is also extremely difficult.
Fusion schemes rely on heating matter to enormous temperatures around 100 million degrees Kelvin – a very tall order on planet Earth, which is a mere 300 Kelvin. Fusion’s grand challenge for decades has been “ignition,” or getting enough fusion heating to overcome the energy lost in keeping the fuel hot and dense. This is like lighting the charcoal in a grill with lighter fluid and a match: once the fire catches, it sustains itself without more energy input. Stars are only able to do it because of their mass and gravity, and it’s hard to reproduce a star’s power here on Earth.
Magnets vs. lasers
There are two basic approaches, vastly oversimplified into the magnetic approach and the laser approach. The magnetic approach (which usually uses a device called a “tokamak”) essentially involves a gigantic donut-shaped reactor. Inside the donut, as Stanton describes, a plasma composed of hydrogen “flies around, you have big, big, giant magnetic coils, and it flies around the circle really, really fast and gets really, really hot.” This approach has so far failed to produce either fusion ignition or breakeven (when a fusion system as a whole produces more energy than it consumes), but it is still believed to be one of the most promising paths toward creating a fusion power plant.
The laser approach, Stanton explains, uses “a pellet with some light material (such as plastic, beryllium or the current favorite, diamond) on the outside and hydrogen on the inside. In some approaches, lasers directly crush the pellet – in others, they hit a golden cylinder called a ‘hohlraum’ which subsequently emits x-rays that then crush the target. And that’s called inertial confinement fusion (or ICF).”
LLNL has been studying ICF since the late 1950’s, with experiments beginning in the 1960’s. Between 2021 and now, it has achieved ignition five times, and breakeven has been exceeded three times. Stanton calls this a massive “breakthrough” and “proof of principle.” In fact, the highest energy gain to date is almost 2.4, meaning that the scientists got over twice as much energy out of the fusion reaction than the lasers put into it.
Stanton is quick to say that a fusion power plant is most likely decades away. Right now, the cost and the scale are prohibitive factors. The pellet they use at LLNL is the size of a BB and sitting in a facility the size of three football fields, with about 200 of the world’s most powerful lasers blasting down to a single point — a scale that’s difficult to replicate, to say the least. But people are already starting to create start-ups based on the possibilities.
Transport physics
Stanton’s work on this project explores both applied mathematics and physics questions. LLNL’s facility is state-of-the-art, but these experiments are extremely expensive to run.
“Every single time you push that button and all the lasers go off, you’re setting off the world’s largest laser experiment, and they probably do six of those shots a week right now,” he explains.
In order to conserve resources, experimentalists turn to simulation models to help pinpoint how exactly they should be running their experiments, “so they can set those shots up as well as they possibly can.” And that’s where Stanton comes in.
LLNL has supercomputers that can run massive simulations, but these simulations need the hands of physicists, mathematicians and computer scientists to help guide them. These simulations model fluids, much in the way you would model liquid sloshing around in a water bottle. Adding nuclear reactions and all the micro-physics occurring at the atomic scale to these equations can muddy the waters, and requires mathematicians to set parameters to help make the simulations more accurate.
These parameters, called “transport coefficients,” are the meat of Stanton’s research contributions. Stanton helped develop the models that go into the codes. These codes are then used to improve the accuracy of simulations, and the experimentalists use the simulations to design their laser tests. Essentially, the transport coefficients get plugged into the hydrodynamic equations which then simulate some of the implosions that the scientists are attempting.
And the code is flexible, too, allowing experimentalists to ask questions like, “What happens if we use this material? What should this pellet be made out of? What happens if you add a layer of gold?”
As Stanton explains, he and his research partner Michael Murillo, professor of computational mathematics, science and engineering at Michigan State University, “wrote a paper like a manual that just said, ‘here’s how to input those in your codes.’ Other people had tons of models for these transport coefficients, but we came up with ones that were not only accurate but also easy to use over a very broad range of temperature and density.”
Stanton’s work involves creating equations (sometimes with pen and paper, sometimes with computers) that can then be fed into supercomputers like the one at Lawrence Livermore National Lab. “I work through the math, and I have a set of equations, and I screw around with them,” he describes. “I tend to work on problems where I’m making approximations to really cut down on the cost; I try to develop mathematical models that can be solved.”
“A way to save humanity”
Many scientists thought they’d never live to see successful fusion ignition. Stanton remembers an older scientist at his retirement saying, “The two things I thought I was sure I’d see before retiring would be ignition and that BART would come to Livermore,” and by the time he’d completed 45 years in the lab, he’d seen neither.
But ignition happened – and then it happened again. Excitement is building.
“The idea is that we can reproduce it more and more reliably,” Stanton says. “If we can get a higher and higher energy yield each time, those are the steps that we have to take to get closer to fusion power as a way to save humanity. It’s that level of importance.”
