Microturbulence Suppression by Alfvén Eigenmodes in the DIII-D Tokamak

Area of Science:

• Plasma Physics
• Fusion Energy Research
• Magnetohydrodynamics

Background:

• Low-k turbulence is a significant challenge in fusion energy research, potentially degrading plasma confinement.
• Toroidicity-induced Alfvén eigenmodes (TAEs) are known to interact with and influence plasma turbulence.

Purpose of the Study:

• To investigate the nonlinear evolution of TAEs and their effect on low-k turbulence.
• To understand the mechanisms behind turbulence mitigation and suppression driven by TAEs.

Main Methods:

• Analysis of experimental data from DIII-D tokamak.
• Observing the nonlinear evolution of TAEs and their polarization.
• Measuring turbulence characteristics and shear flow generation.

Main Results:

• TAEs were observed to mitigate and suppress low-k turbulence during their nonlinear evolution.
• A transition to a new TAE state characterized by discrete modes and localized structures was identified.
• A shear flow layer, driven by Reynolds stress, was found to exceed the turbulence decorrelation rate, causing suppression.

Conclusions:

• The nonlinear evolution of TAEs can lead to significant turbulence mitigation and suppression.
• An imbalance between Reynolds and Maxwell stress forces plays a crucial role in shear flow generation and turbulence reduction.
• These findings offer insights into controlling plasma turbulence in fusion devices.