New advanced operational regime on the W7-AS stellarator.

Area of Science:

• Plasma physics
• Stellarator research
• Fusion energy

Background:

• The Wendelstein stellarator W7-AS is a key facility for magnetic confinement fusion research.
• Optimizing plasma operational regimes is crucial for achieving stable and efficient fusion reactions.

Purpose of the Study:

• To discover and characterize a new promising plasma operational regime in the Wendelstein stellarator W7-AS.
• To investigate the properties and potential benefits of this novel regime for fusion energy applications.

Main Methods:

• Experimental operation of the Wendelstein stellarator W7-AS.
• Analysis of plasma parameters including density profiles, energy confinement, and impurity transport.
• Investigation of radiation levels and divertor target plate interactions.
• Demonstration of electron Bernstein wave heating via linear mode conversion.

Main Results:

• Discovery of a new plasma regime above a threshold density, characterized by flat density profiles.
• Achieved high energy confinement (up to twice standard scaling) and low impurity confinement times.
• Observed edge-localized radiation and avoided impurity accumulation.
• Realized quasistationary discharges with high line-averaged densities (up to 4 x 10^20 m^-3) and radiation levels up to 90%.
• Demonstrated partial plasma detachment at divertor targets and achieved an average beta value of 3.1% at 0.9 T.

Conclusions:

• The newly discovered plasma regime offers significant advantages for stellarator operation, including improved energy confinement and impurity control.
• This regime facilitates high-density, high-beta plasma conditions suitable for advanced heating methods like electron Bernstein wave heating.
• The findings represent a promising step towards efficient and stable operation of future fusion devices.