Part 2 of 2 Parts (Please read Part 1 first)
Ahmed Diallo is a PPPL principal research physicist and co-author of the paper. He compares tritium-burn efficiency to the efficiency of a gas stove. Diallo said, “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.”
The PPPL team consulted the fusion community and the broader community involved in spin polarization in their quest to find ways to enhance tritium-burn efficiency. Parisi said, “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.”
Quantum spin is very different from the physical spin that a pitcher can put on a baseball. A good pitcher can throw the ball with many different spins. There is a whole continuum of possibilities. However, there are only a few discrete options for the quantum spin on a particle such as up and down.
When two fusion fuel ions have the same quantum spin, it is more likely that they will fuse. Parsi said, “By amplifying the fusion cross section, more power can be produced from the same amount of fuel.”
While current spin-polarization methods don't align every ion, the gains shown in the PPPL model don't require one hundred percent spin alignment. In fact, the study demonstrates that even small levels of spin polarization can substantially improve the efficiency of the tritium burn, improving overall efficiency and reducing tritium consumption.
With less tritium required, the size of the fusion power plant can be reduced, making it easier to license, situate and construct. This should lower the operating costs of the fusion system.
Tritium is radioactive, and its radiation is relatively short-lived compared to the spent fuel from nuclear fission reactors. This reduction in the amount of tritium required has safety benefits because it decreases the risk of tritium leakage or contamination.
Parisi said, “The less tritium you have flowing through your system, the less of it will get into the components.” The storage and processing facilities necessary for the tritium can also be made much smaller and more efficient. This makes nuclear licensing easier.
Parsi continued, “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.”
More work is needed to investigate things that will be needed to implement the proposed system but have yet to be fully explored. Schwartz said, “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 said there are also potential problems related to polarization methods, but these create opportunities. He said, “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.”