Explaining Cold-Pulse Dynamics in Tokamak Plasmas Using Local Turbulent Transport Models.

Area of Science:

• Plasma physics
• Fusion energy research
• Tokamak transport phenomena

Background:

• A persistent puzzle in plasma physics involves understanding energy transport in fusion devices.
• Experiments on the Alcator C-Mod tokamak showed core electron heating during edge cooling, faster than energy confinement times, suggesting nonlocal transport.

Purpose of the Study:

• To investigate the underlying mechanisms of plasma transport during cold-pulse experiments.
• To determine if nonlocal transport phenomena are essential for explaining experimental observations in tokamak plasmas.

Main Methods:

• Utilized computational modeling of cold-pulse experiments performed on the Alcator C-Mod tokamak.
• Employed a recent local quasilinear turbulent transport model to simulate plasma behavior.

Main Results:

• The local transport model accurately reproduced steady-state plasma profiles observed in experiments.
• The model successfully captured the rise time and density dependence of core electron heating during cold pulses.
• Simulations demonstrated that the observed phenomena can be explained without invoking nonlocal transport.

Conclusions:

• The study resolves a long-standing enigma in plasma transport by demonstrating the efficacy of local transport models.
• Nonlocal transport is not necessary to explain the behavior and time scales observed in tokamak cold-pulse experiments.
• Findings support the validity of local transport models for understanding energy dynamics in fusion plasmas.