NSTX-U could serve as the model for a pilot fusion plant, PPPL says

April 18, 2022, 9:30AMNuclear News
PPPL physicist Walter Guttenfelder with figures from the paper he coauthored with members of the NSTX-U team and 23 collaborative institutions worldwide. (Photo: Elle Starkman/PPPL Office of Communications. Collage: Kiran Sudarsanan)

According to the Department of Energy’s Princeton Plasma Physics Laboratory, recent simulations and analysis demonstrate that the design of its flagship fusion facility, the National Spherical Torus Experiment Upgrade (NSTX-U), which is currently under repair, could serve as a model for an economically attractive next-generation fusion pilot plant.

"It's all about trying to project whether this route is favorable for a cost-effective pilot plant and beyond," said PPPL principal physicist Walter Guttenfelder, the lead author of a paper published in the International Atomic Energy Agency journal Nuclear Fusion, titled "NSTX-U Theory, Modeling and Analysis Results," which details the latest findings.

According to PPPL, the operating capabilities of the relatively compact and cost-effective NSTX-U are greatly enhanced over its pre-upgraded predecessor.

Trending up: “The primary motivation for NSTX-U is to push up to even higher powers, higher magnetic fields supporting high-temperature plasmas to see if previously observed favorable trends continue,” Guttenfelder said. According to PPPL, recent theory, analysis, and modeling from the NSTX-U research team predict that many of these trends should be demonstrated in new NSTX-U experiments.

Predicted operating conditions for the spherically shaped device include the following:

  • Starting up plasma. Modeling has been developed to efficiently optimize plasma initiation and ramp up, and it was applied to help a spherical tokamak facility in the United Kingdom produce its first plasma.
  • Understanding the plasma edge. New models simulate the dynamics between the edge of the plasma and the tokamak wall that can determine whether the core of the plasma will reach the 150 million-degree temperatures needed to produce fusion reactions.
  • Applying artificial intelligence. AI machine learning has developed a rapid path for optimizing and controlling plasma conditions that closely match predicted test targets.
  • Novel techniques. Simulations suggest many novel techniques for shielding interior NSTX-U components from blasts of exhaust heat from fusion reactions. Among these concepts is the use of vaporized lithium to reduce the impact of heat flux.
  • Stable performance. Studies found that a window for NSTX-U performance can remain stable in the face of instabilities that could degrade operations.
  • What to avoid. Increased understanding of the conditions to avoid come from excellent agreement between the predicted range of unstable plasmas and a large experimental database

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