In the quest for cleaner, more efficient energy, scientists are continually pushing the boundaries of what’s possible in nuclear fusion research. A recent study published in the journal “Nuclear Fusion” (translated from the original Latin title) offers new insights into achieving edge-localized mode (ELM) suppression in double-null (DN) plasma configurations, a challenge that has thus far eluded researchers. The findings, led by P. Lunia from the Department of Applied Physics and Applied Mathematics at Columbia University, could have significant implications for the future of fusion energy.
Edge-localized modes are sudden releases of energy and particles from the edge of fusion plasmas, which can damage the walls of the containment vessel. Suppressing these ELMs is crucial for the longevity and efficiency of fusion reactors. Resonant magnetic perturbations (RMPs) have been used successfully to suppress ELMs in single-null (SN) configurations, but achieving the same in DN configurations has proven difficult.
Lunia and his team used the GPEC code to model plasmas spanning shapes from single to double-null on the DIII-D tokamak. Their findings reveal that the high-field side response is reduced closer to DN shaping, a factor that has likely contributed to the previous lack of success in ELM suppression in these configurations. “The synthetic diagnostic measurements from our modeling are consistent with what has been observed in experiments on DIII-D,” Lunia explained. “This validates our plasma response model in this regime.”
The study found that common metrics for suppression do not illustrate a clear distinction between SN and DN cases. However, the pedestal top resonant field shows a significant decrease at DN shaping in modeling. This suggests that achieving ELM suppression in DN configurations may require at least 1.5 times greater RMP coil currents than what has been used in experiments to date.
Furthermore, the analysis from drift kinetic simulations indicates that up to two times larger critical island widths are required at the pedestal top for tearing mode growth compared to SN cases. Effective island widths inferred from 3D ideal magnetohydrodynamics (MHD) were also analyzed, revealing a threshold of approximately 18–24 times the ion gyroradius for sufficient profile flattening for ELM suppression.
These results suggest that ELM suppression may indeed be possible in DN configurations, provided that sufficiently large RMP coil amplitudes are used. The study also highlights the potential benefits of exploring lower triangularity shapes in future research.
The implications of this research are significant for the energy sector. Achieving ELM suppression in DN configurations could open up new possibilities for fusion reactor design, potentially leading to more efficient and cost-effective energy production. As Lunia noted, “Our findings provide a roadmap for future experiments aimed at achieving RMP ELM suppression in DN configurations. This could be a game-changer for the fusion energy sector.”
In the broader context, this research underscores the importance of continued investment in fusion energy research. While challenges remain, the progress being made in understanding and controlling plasma behavior brings us one step closer to realizing the promise of clean, abundant fusion energy. As the global demand for energy continues to grow, the insights gained from studies like this one will be crucial in shaping the future of the energy sector.