E×B Flux Driven Detachment Bifurcation in the DIII-D Tokamak

Area of Science:

• Plasma Physics
• Fusion Energy Research

Background:

• Tokamak fusion devices require precise control of plasma conditions within the divertor region.
• Understanding plasma detachment is critical for managing heat and particle exhaust in future fusion reactors.

Purpose of the Study:

• To investigate the observed bifurcative step transition in DIII-D tokamak divertor conditions.
• To provide a theoretical explanation and numerical validation for this transition's dependence on plasma parameters and magnetic field direction.

Main Methods:

• Experimental observation of plasma transitions in DIII-D tokamak.
• Development of a theoretical model explaining the bifurcation mechanism.
• Numerical simulations to reproduce the observed phenomena and parameter dependencies.

Main Results:

• A step transition from attached to detached divertor conditions was experimentally observed with increasing plasma density.
• The transition was found to be dependent on the high confinement mode and the direction of the B×∇B drift.
• The theoretical model successfully reproduced the bifurcation, attributing it to the interplay of E×B-drift fluxes, electric potential, and divertor conditions.

Conclusions:

• The study provides the first theoretical explanation for a density-driven bifurcative transition in tokamak divertor plasmas.
• The findings highlight the critical role of E×B-drift dynamics and electric potential in controlling plasma detachment.
• Results have significant implications for optimizing divertor power exhaust and detachment control strategies in next-generation fusion devices.