Fusion power facilities need to produce and maintain the plasma conditions required for fusion reactions in order to be economically feasible. Nonetheless, gradients in temperature and density are frequently developed by plasmas at high temperatures and densities. Edge localized modes (ELMs), for example, are instabilities that can develop from these gradients.

ELMs can potentially harm the adjacent reactor wall since they arise in the plasma edge. The plasma’s cross-sectional shape is one characteristic that may have an impact on ELMs.

The degree to which the form of the plasma differs from an oval shape is referred to by researchers as its “plasma triangularity.” The majority of plasmas under study exhibit positive triangularity, which is characterized by a D-shaped cross-section with the vertical part of the “D” located close to the tokamak center post.

Scientists have recently examined negative triangularity, which is the opposite shape with the vertical portion close to the outer wall. Gradient self-regulation is known to exist in negative triangularity plasmas. The researchers demonstrated that this shape was intrinsically devoid of instabilities under a range of plasma conditions by means of a thorough review of data from the DIII-D National Fusion Facility collaboration. Physical Review Letters is the journal where the work is published.

This study demonstrated that without compromising fusion performance, negative triangularity plasmas are free of potentially harmful instabilities in the edge region of the plasma. This implies that instabilities in the plasma edge are stabilized by negative triangularity shaping.

Simultaneously, it attains the elevated core performance and edge conditions required to realize the burning plasma conditions required by future fusion power plants. This finding implies that designing fusion power plants with negative triangularity shaping might be the best course of action.

Utilizing the DIII-D National Fusion Facility tokamak, experiments were conducted to investigate the application of negative triangularity shaping in controlling the formation of extremely unstable and energetic ELMs. The project was a part of a broader effort on negative triangularity that involved nearly all US institutions conducting fusion research.

Although the study indicated that negative triangularity shaping prevented the development of temperature and pressure gradients that can grow into ELMs in the plasma edge, ELMs are frequent under the high-performance plasma conditions important to fusion power plants.

Interestingly, at the high heating power and core performance that usually result in ELMs, plasmas with strong negative triangularity (less than -0.15) did not exhibit any instabilities. Comprehensive examination of a large-scale DIII-D dataset spanning a variety of circumstances, such as the high core performance and edge compatibility required for fusion reactors, repeatedly demonstrated this ELM-free nature.

The thorough, high-fidelity diagnostics of the DIII-D tokamak made this work possible, and advancements in modeling reinforced the findings that indicated enhanced stability over the enlarged range of circumstances.

Additionally, the ELM suppression obtained through alternative methods—such as operating in an ELM-free regime or using resonant magnetic perturbations to suppress ELMs—was not as strong as this intrinsic stability. So, negative triangularity shaping could constrain the high-energy destructive plasma instabilities that are a major design concern for fusion power plants today. This suggests that the negative triangularity technique should be looked at more thoroughly before being used in the construction of fusion power plants.