The development of novel technologies to simplify the design and construction of stellarator fusion systems has brought two new public-private collaborations to the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL).
The two collaborations, awarded in the latest round of the DOE's Innovation Network for Fusion Energy (INFUSE) program, brings PPPL into a one-year partnership with Princeton Stellarators Inc. (PSI), a start-up cofounded by physicist David Gates who until recently led stellarator development at the Laboratory and now is chief technology officer (CTO) of PSI.
David Gates explains innovative stellarator concepts and plans to launch PSI. (Video produced by Princeton University)
Harnessing fusion energy
The stellarator, which historically had a complex twisted-coil design, and the tokamak are the main systems with which scientists around the world are seeking to capture and control fusion energy as a clean and abundant source of power to generate electricity and mitigate climate change. Their goal is to facilitate harnessing on Earth the same fusion energy that powers the sun and stars.
The two PPPL collaborations, which will receive nearly $500,000 in total funding, are among the 10 recently announced INFUSE-funded projects totaling $2.3 million.
"The companies and DOE scientists will build on advances from the national labs with the entrepreneurial spirit of the private sector to advance our understanding of fusion," said Secretary of Energy Jennifer Granholm in announcing the awards.
The new projects bring the number of INFUSE-supported PPPL collaborations to 17 since the DOE launched the program in 2019, according to PPPL physicist Walter Guttenfelder, who has succeeded PPPL colleague Ahmed Diallo as INFUSE deputy director. Diallo now serves as a program director for the Advanced Research Projects Agency-Energy (ARPA-E), which funds the early stages of high-potential energy projects. For INFUSE, private partners are responsible for 20% of the costs.
The new PPPL collaborations:
PPPL, whose technology PSI has licensed, was focused on replacing the complex and costly stellarator magnets that spiral like candy cane stripes around the system, with cubic permanent magnets akin to those that people use to stick things on refrigerator doors. PSI similarly simplifies stellarator systems, however its approach utilizes arrays of planar and individually controllable electromagnetic coils, rather than permanent magnets. Electric current produces the magnetism in such coils, whereas the magnetism in permanent magnets is always "on."
The goal of the first partnership will be to analyze the behavior of particles that are injected into plasma to help heat it to million-degree temperatures - as well as the behavior of particles born of fusion events within the plasma. Such particles move faster and are harder to control than standard background plasma particles. New stellarator methods attempt to reproduce the kind of symmetry that allows tokamaks to retain these particles, and these new theories will be evaluated for use in designing future stellarator systems. This collaboration will help PSI to design a magnetic trap tailored to confine these essential particles, the company said.
The second collaboration will use modified PPPL computer codes to simulate the behavior of the plasma in planned system magnetic fields. Actual experiments have found stellarator plasma to be much more stable than the extensively used simplified models that are easier to evaluate have predicted. Using higher-fidelity computer codes like those at PPPL will simulate plasma stability.
Bootstrap currents
The code will include self-generated "bootstrap currents" that arise in a plasma. The bootstrap currents are predicted to mitigate areas called "magnetic islands" that allow essential heat to leak out. This impact can flatten the islands and likely improve the confinement of stellarator heat that is crucial to fusion reactions beyond the improvement predicted by current codes, according to the company.
Collaborating on these projects are PPPL physicists Phillip Bonofiglo, who will analyze the behavior of fast particles, and Adelle Wright who will evaluate the impact of bootstrap current on magnetic islands. Contributing at PSI are Charles Swanson, a former PPPL physicist who will help analyze the fast particles, and Mike Martin, a computational physicist and former staff scientist at Sandia National Laboratories who will contribute to the evaluation of the bootstrap current. Cofounders of PSI together with Gates include Brian Berzin, chief executive officer, and Matt Miller, president.
PSI places high stock in these collaborations. Successfully carrying them out, it says, will lead to "a new, radically simplifying system that allows for a more practical and cost-effective approach to fusion." Adds PSI CTO David Gates, "These INFUSE awards show what both sides bring to a public-private partnership. New breakthroughs in physics and engineering are allowing PSI to design more practical systems to bring commercial fusion to market."
