Ground-Breaking Efforts Overcome an Operational Limit of Tokamaks, Advancing Efforts to Achieve Fusion Energy

By achieving very high density and confinement quality at the same time, researchers make new strides toward fusion energy.

The Science

To be economical, pilot fusion power plant designs based on the tokamak approach aim to increase efficiency by maximizing the pressure (temperature times density) of magnetically confined fusion fuel. Physics defines the optimal fuel temperature, so this variable can’t be changed. Instead, researchers can maximize fuel pressure by increasing density. However, fuel density has historically been constrained by limits in tokamak design. Now, researchers at the DIII-D National Fusion Facility have, for the first time, gone beyond this density limit while simultaneously maintaining high confinement quality. Reaching this new and attractive operational space involved pushing the known limits of a specific approach for fusion device operation.

The Impact

This research simultaneously achieved plasma density above a key milestone as well as confinement quality much better than typical with a standard high-confinement operational approach. Achieving these conditions together is a key feature of many economically-viable, fusion power plant designs. However, these conditions have historically been mutually exclusive. The new operational approach also produced a relatively cool and stable plasma edge. This points to a possible solution for a common challenge for tokamaks. This work has important implications for the design of advanced tokamak-based fusion power plants around the world.

Summary

Foundational experiments performed at the DIII-D National Fusion Facility provide new insights for a path toward the future commercialization of fusion energy, specifically for advanced tokamak-based fusion power plants. Decades of experience have shown that plasmas must be confined at high density for an extended period to achieve the power and efficiency needed for commercial energy production. However, prior fusion experiments failed to achieve the needed confinement quality and density at the same time.

DIII-D scientists experimented with the advanced high poloidal beta scenario to address this issue. This regime exhibits a self-organized magnetic geometry with good confinement quality, high pressure, and self-generated plasma. In this study, the team discovered new notable synergies. Increased core density gradients produced greater plasma turbulence suppression and increased confinement quality, which subsequently increased density. In addition, the increased density at the plasma edge suppressed edge instabilities typical of high-confinement plasmas and reduced plasma temperature near the surrounding walls, both effects extremely favorable for wall durability in a fusion power plant. This maintenance of a stable and cool plasma edge with high power in the core – referred to as “core-edge integration” – addresses another main challenge for tokamaks. Thus, the simultaneous achievement of very high density and confinement quality with edge instability suppression suggests this regime as a potential solution for economically-attractive fusion power plant designs.

Contact

Siye Ding
General Atomics
[email protected]

Andrea Garofalo
General Atomics
[email protected]

Funding

This work was supported by the Department of Energy (DOE) Office of Science, Office of Fusion Energy Sciences, using the DIII-D National Fusion Facility, a DOE Office of Science user facility.

Publications

Ding, S., et al., A high-density and high-confinement tokamak plasma regime for fusion energy, Nature 629, 555–560 ( (2024). [DOI: 10.1038/s41586-024-07313-3]

Highlight Categories

Program: FES

Performer: University , DOE Laboratory , DIII-D