SCI-FI-TEK
Gas injection setup in new fusion system is guided by public-private research
Simulations showed that six valves provided the ideal setup for rapidly dispersing cooling gas
DOE/Princeton Plasma Physics Laboratory
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Six gas valves, shown here as yellow-pink puffs, provided the most effective cooling in highly sophisticated computer models created using a PPPL computer code known as M3D-C1. This code creates simulations from slices through the plasma that are unevenly spaced. In the image above, these slices are shown as vertical lines. The researchers intentionally generated more slices closer to the gas valves as they believe this is where the most important dynamics occur.
view moreCredit: Andreas Kleiner / PPPL
When the plasma inside a fusion system starts to misbehave, it needs to be quickly cooled to prevent damage to the device. Researchers at Commonwealth Fusion Systems believe the best bet is a massive gas injection: essentially, a well-timed, rapid blast of cooling gas inside their fusion system, which is known as SPARC. But how many gas valves does it take to quickly tame a plasma that is hotter than the sun? The team has to strike the perfect balance: with too few valves, some parts of SPARC might overheat. With too many, valuable space inside the vessel would be wasted.
To answer this question, researchers turned to a computer code known as M3D-C1, which is developed and maintained by scientists at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL). The code was used to model different valve configurations, and the results show that spacing six gas valves around the fusion vessel, with three on the top and three on the bottom, provides optimal protection.
The research, conducted by a team from PPPL, the Massachusetts Institute of Technology (MIT), General Atomics and Commonwealth Fusion Systems, is featured in a paper in Nuclear Fusion. The project was partially funded by the Innovation Network for Fusion Energy (INFUSE) program, an initiative designed to accelerate collaboration between national laboratories, universities, and private fusion companies. By advancing disruption mitigation strategies, the research team is helping bring fusion power one step closer to reality.
“This work also demonstrates that M3D-C1 can model a rapid shutdown via a massive gas injection using narrow and more realistic gas jets than in previous simulations,” said Andreas Kleiner, a staff research scientist at PPPL and the study’s lead author. “Our research also had a direct influence on the design of SPARC,” he said, noting that design plans for SPARC now incorporate six gas valves based in large part on this research.
Once completed, SPARC will use powerful magnetic fields to hold plasma in a shape that looks much like a doughnut. While SPARC will be an experimental fusion system, the hope is that one day similar devices will be refined enough to generate power for the electrical grid. A key part of this refinement is creating a system to prevent jets of ultrahot particles from damaging the inner walls of the fusion vessel. This problem is amplified in fusion systems such as SPARC, which use particularly strong magnetic fields to hold the plasma.
“Massive gas injection mitigation is needed to make sure that we can rapidly restart SPARC after a disruption,” said Ryan Sweeney, a co-author of the paper and disruption scientist at Commonwealth Fusion Systems.
Instabilities also need to be managed to ensure a long life for the fusion vessel.
“We don’t currently have any material that can withstand the power per area that may be deposited during such an event,” said Kleiner. That’s why it is critical to get the details right for the massive gas injection system that’s intended to cool the plasma down rapidly. “If there is no management of these events, the heat that is ejected toward the first wall can melt it.”
The most comprehensive disruption simulations to date
The simulations considered symmetric configurations with six, four and two gas valves spaced evenly around the fusion vessel, with half the valves on the top and half on the bottom. The simulations also considered asymmetric configurations with one injector and five valves. Each simulation is extremely time intensive — taking weeks to run — even though the team used extremely powerful, exascale computers.
“These are the most comprehensive disruption simulations that had been done to that point,” said Nate Ferraro, deputy head of theory at PPPL and a co-author of the study.
M3D-C1 has been a cornerstone of fusion research, and Ferraro played a central role in its development. Ferraro, who built the initial code as a graduate student alongside PPPL Principal Research Physicist Stephen Jardin, has spent years refining its capabilities. “Our ability to model the interaction between injected gas and plasma instabilities has grown significantly, making this study possible,” he said.
Specifically, the version of M3D-C1 that was used incorporates a more realistic representation of features like gas valves. It also offers a new approach to creating simulations called non-equidistant meshing, which enables finer resolution where it matters most. The M3D-C1 mesh divides the tokamak into slices. But the gas jets are small –– roughly a centimeter wide –– compared to roughly 10 meters of distance around the tokamak, so resolving these jets accurately would take hundreds of slices if they were uniformly spaced. But with non-equidistant meshing, scientists can slice the plasma unevenly. For the SPARC models, more slices were made closer to the gas valves because the scientists expected that’s where the most important changes would happen. The researchers say the approach made for a more realistic simulation overall.
“We could have modeled this before, but not with this level of accuracy,” Kleiner said.
This study highlights the importance of public-private partnerships in advancing fusion technology. PPPL worked closely with Commonwealth Fusion Systems, General Atomics and MIT to provide the high-fidelity simulations necessary for SPARC’s design optimization. This, in turn, will help with designs for Commonwealth Fusion System’s ARC power plant that will be built in Chesterfield County, Virginia.
“Running a code like M3D-C1 is very complicated. It’s a very niche skill,” said Sweeney. “PPPL has very unique expertise in being able to develop and run these types of codes, so it’s fantastic to be able to interface with the Lab.”
Ferraro said working with private partners also benefits PPPL because working on new machines allows Lab scientists the opportunity to apply their knowledge to new systems and learn new techniques. “This project is a good example of how when it comes to fusion, it’s not public versus private research. We are working together. We both have a role to fill to get to fusion.”
Alongside Kleiner, Ferraro and Sweeney, co-authors of the study include Brendan Lyons of General Atomics and Matthew Reinke of Commonwealth Fusion Systems. This work was supported by the INFUSE program and the DOE under grant numbers DE-AC02-09CH11466 and DE-AC02-05CH11231.
PPPL is mastering the art of using plasma — the fourth state of matter — to solve some of the world’s toughest science and technology challenges. Nestled on Princeton University’s Forrestal Campus in Plainsboro, New Jersey, our research ignites innovation in a range of applications including fusion energy, nanoscale fabrication, quantum materials and devices, and sustainability science. The University manages the Laboratory for the U.S. Department of Energy’s Office of Science, which is the nation’s single largest supporter of basic research in the physical sciences. Feel the heat at https://energy.gov/science and https://www.pppl.gov.
Journal
Nuclear Fusion
Article Title
Extended-MHD simulations of disruption mitigation via massive gas injection in SPARC
Listen to quantum atoms talk together thanks to acoustics
Ecole Polytechnique Fédérale de Lausanne
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(From left to right): Mathieu Padlewski, Romain Fleury and Hervé Lissek standing with their metamaterial. More photos available in the press kit.
view moreCredit: Alain Herzog / EPFL
What happens when a quantum physicist is frustrated by the limitations of quantum mechanics when trying to study densely packed atoms? At EPFL, you get a metamaterial, an engineered material that exhibits exotic properties.
That frustrated physicist is PhD student Mathieu Padlewski. In collaboration with Hervé Lissek and Romain Fleury at EPFL’s Laboratory of Wave Engineering, Padlewski has built a novel acoustic system for exploring condensed matter and their macroscopic properties, all the while circumventing the extremely sensitive nature that is inherent to quantum phenomena. Moreover, the acoustic system can be tweaked to study properties that go beyond solid-state physics. The results are published in Physical Review B.
“We’ve essentially built a playground inspired by quantum mechanics that can be adjusted to study various systems. Our metamaterial consists of highly tunable active elements, allowing us to synthesize phenomena that extend beyond the realm of nature,” says Padlewski. “Potential applications include manipulating waves and guiding energy for telecommunications, and the setup may one day provide clues for harvesting energy from waves for instance.”
Schrödinger’s cat, the quantum conundrum
In quantum mechanics, the cat is both dead and alive inside of the box until you interfere with the system by measuring it, which is done in this case by opening the box. From a purely quantum perspective, the cat is in a superposition of two probable states: a probable state of being dead and a probable state of being alive, until you open the box only to observe if the cat is actually dead or alive. A cat cannot be both dead and alive at the same time, and that’s the essence of Schrödinger cat, a thought experiment devised by Erwin Schrödinger in 1935 that illustrates the complexities of quantum concepts when imagined beyond the quantum scale, like the scale of a cat.
The sensitive nature of quantum physics that makes observation of solid states so difficult comes from the act of measuring the system, which forces the quantum system into a state, instead of allowing the system to exist – uninterrupted – in a superposition of probability states. That said, physicists know how to probe the electronic states indirectly and infer their corresponding properties.
Modeling quantum phenomena with sound waves
But there is another phenomenon for which Schrödinger’s cat makes perfect sense in the macroscopic world, and it’s one that we can interact with: sound.
If we take the sound of one’s voice for instance, we know that the reason why someone’s voice is unique and rich is because we hear the whole spectrum of frequencies. The frequency spectrum is characteristic for a given voice, but it also explains why the piano has its unique timbre, or why the trumpet sounds differently from the trombone. In principle, we can simultaneously hear the fundamental frequency, aka the fundamental state, plus all of the higher frequencies known as the harmonics. Borrowing language from quantum physics, we are actually hearing a superposition of many states at once. Or by analogy with Schrödinger’s cat, the cat is both dead and alive, and we can hear it!
“Quantum probability waves are waves after all – why not model them with sound?” says Padlewski. “Probing the electronic states of a solid state, directly without perturbation, would be like having a blind person tread through a busy street without a cane. But in acoustics, we can probe waves directly, in phase and in amplitude without destroying the state – which is nice.”
Engineering an acoustic metamaterial
The acoustic metamaterial built at EPFL consists of a line of “acoustic atoms”, essentially 16 small cubes connected to one another with openings to allow for the placement of multiple speakers or microphones. Speakers generate sound waves that are to propagate through the line of acoustic atoms in a controlled way, microphones measure sound waves for feedback control. The cubes can be viewed as building blocks for building more complex systems that go beyond a simple line.
“When you see the cochlea, the ear’s organ responsible for hearing, it resembles our active acoustic metamaterial in its structure and functionality,” says Lissek. “The cochlea consists of a perfect line of cells that amplify different frequencies. Our metamaterial could potentially be tuned to function the same way and study hearing problems like tinnitus.”
Towards a quantum inspired analog computing
Padlewski is also keen to use the metamaterial building blocks to investigate ways to build one of the first acoustic analog computers capable of generating non-separable states. Inspired by the work of Pierre Deymier of Arizona University, this computer would essentially be an acoustic equivalent of a quantum computer. It would allow for the direct observation of superposed states without interfering with the system, because acoustic waves are not as fragile as quantum ones.
“An acoustic quantum analog computer would be more like a crystal lattice – a periodic array of cells just as atoms are arranged in crystals,” adds Padlewski. “The acoustic approach to quantum computation has the potential to offer an alternate way of processing vast amounts of information simultaneously.”
