Public-private partnership to bring new exhaust system to DIII-D

The DIII-D National Fusion Facility announced last week that it will partner with Kyoto Fusioneering to design, manufacture, install, and operate a new power exhaust system in the DIII-D tokamak to advance a negative triangularity approach for commercialization.

This effort builds on the company's partnership with Oak Ridge National Laboratory, which was announced earlier this year.

Testing negative triangularity: For the past few years, researchers at DIII-D have been exploring an approach to tokamak operations that flips the shape of the plasma: While most tokamaks currently use plasma with a cross section that looks like a D following the shape of the tokamak cross section, negative triangularity puts the rounded side of the D facing the center of the tokamak.

While negative triangularity had been considered in the 1970s and 1980s, positive triangularity became the dominant approach. But an increasing body of research into the negative triangularity approach suggests it exhibits high performance while avoiding damaging heat burst instabilities and easing engineering requirements for the device wall by dissipating heat loads through benign radiative processes.

According to DIII-D, this approach is being pursued by private companies designing fusion pilot plants, but negative triangularity exhibits unique plasma heat and particle exhaust features that have yet to be evaluated with a commercially relevant divertor.

A new divertor: When DIII-D was conducting a negative triangularity campaign in 2023, the tokamak's interior was modified with special armor tiles in a temporary divertor region.

"The campaign was incredibly exciting-we produced high-performance plasmas on DIII-D for weeks without seeing a single [edge-localized mode]. No one had ever accomplished something comparable before," said Kathreen Thome, an associate professor at Columbia University and one of the lead researchers on this campaign. "[Negative triangularity] is a potentially revolutionary way to design and operate a tokamak for fusion energy."

Now, through this new collaboration, DIII-D will be outfitted with a negative triangularity divertor such that subsequent experimentation will operate under the conditions relevant to a fusion energy plant.

DIII-D and Kyoto Fusioneering will collaborate on designing the divertor, and then the company will manufacture and supply the necessary tiles. Kyoto Fusioneering, alongside partners at Columbia University, will work with DIII-D to use the new setup to investigate issues including core-edge integration, power exhaust, diagnostic composition and performance, and stress to plasma-facing components.

According to the announcement, "As data are shared freely within the program and capabilities are available to all members of the DIII-D program, this work is expected to have broader benefits that support work by additional fusion pilot plant developers."

Suk-Ho Hong, DIII-D fusion technology outreach coordinator, said, "Our need to understand negative triangularity in a commercially relevant device setup led to the collaboration between DIII-D and Kyoto Fusioneering. This new capability will enable us to fully evaluate this promising approach together, continuing DIII-D's legacy of providing a rapid, cost-effective platform to test cutting-edge technologies and approaches for fusion energy."