Achievement of Reactor-Relevant Performance in Negative Triangularity Shape in the DIII-D Tokamak.

Area of Science:

• Nuclear Fusion Science
• Plasma Physics
• Tokamak Research

Background:

• Tokamak devices are crucial for magnetic confinement fusion energy research.
• Plasma shaping, particularly triangularity, influences confinement and stability.
• High confinement mode (H-mode) is a key operational regime for efficient fusion.

Purpose of the Study:

• To investigate plasma performance and turbulent fluctuations in negative triangularity shapes.
• To compare negative triangularity discharges with positive triangularity H-mode discharges.
• To assess the impact of heating methods on plasma behavior in different triangularity configurations.

Main Methods:

• Creation of inner-wall-limited plasma discharges in the DIII-D tokamak.
• Utilizing negative triangularity (δ=-0.4) and positive triangularity (δ=+0.4) configurations.
• Employing electron cyclotron heating and neutral beam injection heating.
• Measuring turbulent fluctuations across various radial positions (0.5<ρ<0.9).

Main Results:

• Negative triangularity plasmas achieved high normalized beta (βN=2.7) and H-mode confinement (H98y2=1.2) without edge pressure pedestals or ELMs.
• Global performance was comparable to positive triangularity ELMing H-mode discharges.
• Turbulent fluctuations were reduced by 10-50% in negative triangularity plasmas compared to positive triangularity plasmas.

Conclusions:

• Negative triangularity shapes offer a promising pathway to achieve high-performance tokamak plasmas with suppressed ELMs.
• Reduced turbulent fluctuations in negative triangularity configurations contribute to improved confinement.
• These findings have significant implications for future fusion reactor designs and operational strategies.