Robust Avoidance of Edge-Localized Modes alongside Gradient Formation in the Negative Triangularity Tokamak Edge
A O Nelson1, L Schmitz2, C Paz-Soldan1
1Columbia University, New York, New York 10027, USA.
Physical Review Letters
|November 24, 2023
Summary
Strong negative triangularity (NT) plasma shaping effectively suppresses edge-localized mode (ELM) instabilities in fusion devices. This finding supports NT
Area of Science:
- Fusion Energy Research
- Plasma Physics
- Tokamak Operations
Background:
- Edge-localized modes (ELMs) are transient instabilities in tokamak plasmas that can damage reactor walls.
- Controlling ELMs is crucial for sustained fusion energy production.
- Plasma shaping, particularly negative triangularity (NT), is explored as a method for ELM suppression.
Purpose of the Study:
- To investigate the effectiveness of strong negative triangularity (NT) shaping in suppressing edge-localized mode (ELM) activity.
- To determine the range of plasma conditions under which NT robustly suppresses ELMs.
- To assess the implications of NT for future fusion reactor designs.
Main Methods:
- Conducted high-performance diverted discharges on the DIII-D tokamak.
- Systematically varied plasma parameters including line-averaged density, auxiliary heating power, and toroidal magnetic field.
- Analyzed edge plasma profiles and stability limits.
Main Results:
- Strong NT shaping robustly suppressed all observed ELM activity across a wide range of plasma conditions.
- Experimental pressure profiles remained at or below the infinite-n ballooning stability limit, consistent with theory.
- Edge pressure gradients in NT plasmas approached H-mode levels, exceeding those in typical L-mode plasmas.
Conclusions:
- Negative triangularity plasma shaping is a viable strategy for robust ELM suppression in fusion devices.
- The observed stability is attributed to magnetic shear in the NT edge inhibiting access to ELMing H-mode regimes.
- NT configurations show promise for future fusion reactor designs due to improved edge plasma confinement and stability.
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