Promising High-Confinement Regime for Steady-State Fusion

Area of Science:

• Nuclear Fusion Energy
• Plasma Physics

Background:

• Achieving stable, high-confinement plasma regimes is crucial for future fusion power plants.
• Edge-localized modes (ELMs) are plasma instabilities that can disrupt fusion reactions.
• Mitigating ELMs is essential for steady-state operation of fusion reactors.

Purpose of the Study:

• To investigate the underlying physics of a reproducible stationary high-confinement regime with small edge-localized modes (ELMs).
• To understand the role of the edge transport barrier (pedestal) characteristics in enabling this regime.
• To provide a physics basis for mitigating ELMs in future steady-state fusion reactors.

Main Methods:

• Experimental achievement of a stationary high-confinement regime in the Experimental Advanced Superconducting Tokamak.
• Analysis of pedestal properties, including density gradient and density ratio.
• Nonlinear simulations to reveal the mechanism of small ELM crashes.

Main Results:

• A reproducible stationary high-confinement regime with small ELMs was achieved in a metal-walled tokamak with low plasma rotation.
• This regime is characterized by a wide edge transport barrier (pedestal) with a low density gradient and high pedestal foot-to-top density ratio.
• Nonlinear simulations identified the upper movement of the peeling boundary, induced by localized pedestal collapse, as the mechanism preventing further instability growth.

Conclusions:

• The identified mechanism provides a physics basis for mitigating ELMs in future steady-state fusion reactors.
• The findings contribute to the development of stable operating regimes for fusion energy.
• The study highlights the importance of pedestal structure in controlling plasma instabilities.