Reviewed by Lexie CornerNov 20 2024
A recent study published in Nuclear Fusion by experts at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory suggests that a novel combination of fuels with improved properties could help address some of the main challenges in making fusion a more feasible energy source.
An artist’s interpretation of spin-aligned atoms during the process of fusion. Image Credit: Kyle Palmer / PPPL Communications Department
The proposed strategy continues to use deuterium and tritium, which are considered the most promising fuels for fusion energy. However, the quantum properties of the fuel would be optimized for maximum efficiency using an existing technique known as spin polarization. In addition to spin polarizing half of the fuel, the proportion of deuterium would be increased from the typical 60 % or higher.
Scientists developed models showing how this approach enhances tritium combustion while maintaining fusion power. This could significantly reduce the amount of tritium needed to initiate and sustain fusion reactions, leading to more compact and cost-effective fusion devices.
Fusion is really, really hard, and nature doesn’t do you many favors. So, it was surprising how big the improvement was.
Jason Parisi, Study First Author and Staff Research Physicist, Princeton Plasma Physics Laboratory
The study estimates that the method could increase tritium combustion efficiency by up to ten times. It also highlights PPPL's leadership in fusion research, particularly in systems like the one explored in Parisi’s work, where gases are superheated to create a plasma confined by magnetic fields in the shape of a cored apple.
The National Spherical Torus Experiment-Upgrade (NSTX-U), the lab's primary fusion device, shares a similar shape to the one considered by the researchers when testing their approach.
This is the first time researchers have looked at how spin-polarized fuel could improve tritium-burn efficiency.
Jacob Schwartz, Study Co-Author and Staff Research Physicist, Princeton Plasma Physics Laboratory
Minimizing Tritium Requirements by Maximizing Burn Efficiency
Ahmed Diallo, PPPL’s principal research physicist and co-author on the study, compares tritium-burn efficiency to that of a gas stove.
When gas comes out of a stove, you want to burn all the gas. In a fusion device, typically, the tritium isn’t fully burned, and it is hard to come by. So, we wanted to improve the tritium-burn efficiency.
Ahmed Diallo, Study Co-Author and Principal Research Scientist, Princeton Plasma Physics Laboratory
As part of its efforts to improve tritium-burn efficiency, the PPPL team spoke with the fusion community and the larger spin polarization group.
Parisi added, “Fusion is one of the most multidisciplinary areas of science and engineering. It requires progress on so many fronts, but sometimes there are surprising results when you combine research from different disciplines and put it together.”
A Different Kind of Spin
Quantum spin is fundamentally different from the physical spin of a baseball. For instance, a pitcher can throw a baseball with various spins, offering a range of possibilities. However, a particle’s quantum spin has only a few discrete options, such as up or down.
When two fusion fuel atoms share the same quantum spin, they are more likely to fuse.
“By amplifying the fusion cross section, more power can be produced from the same amount of fuel,” Parisi noted.
While current spin-polarization methods do not align every atom, the improvements in the PPPL model do not require complete spin alignment. In fact, the study demonstrates that even small amounts of spin polarization can significantly enhance the efficiency of tritium burn, improving overall efficiency and reducing tritium usage.
Improving Efficiency to Reduce Tritium Requirements
With less tritium required, the overall size of the fusion power plant can be reduced, making it easier to license, locate, and construct. This should also help lower the operational costs of the fusion system.
Since tritium is radioactive, reducing its use also offers safety benefits by decreasing the risk of tritium leakage or contamination, even though it has a shorter half-life compared to spent fuel from nuclear fission reactors.
Parisi stated, “The less tritium you have flowing through your system, the less of it will get into the components.”
The tritium storage and processing facilities can also be significantly reduced in size and increased in efficiency, which makes tasks like nuclear licensing easier.
Parisi added, “People think that the site boundary size is somewhat proportional to how much tritium you have. So, if you can have a lot less tritium, your plant could be smaller, faster to get approved by regulators, and cheaper.”
New Avenues to Explore
The DOE's Office of Science has supported separate research on several of the technologies needed to inject spin-polarized fuel into the fusion vessel. However, further research is necessary to understand the components required to implement the proposed system, which has not yet been fully explored.
Schwartz noted, “Whether it’s possible to have integrated scenarios that maintain a high-grade fusion plasma with these specific flows of excess fuel and ash from the plasma needs to be determined.”
Diallo stated that while polarization approaches have possible drawbacks, they also present opportunities.
He concluded, “One challenge would be to demonstrate techniques to produce spin-polarized fuel in large quantities and then store them. There’s a whole new technology area that would open up.”
Journal Reference:
Parisi, J. F. et. al. (2024) Simultaneous enhancement of tritium burn efficiency and fusion power with low-tritium spin-polarized fuel. Nuclear Fusion. doi.org/10.1088/1741-4326/ad7da3