Phase-locking of magnetic islands diagnosed by ECE-imaging

Area of Science:

• Plasma physics
• Fusion energy research
• Magnetohydrodynamics

Background:

• Tokamak devices are crucial for fusion energy research.
• Understanding plasma behavior, including magnetic islands, is key to controlling fusion reactions.
• Neoclassical tearing modes can destabilize plasma confinement.

Purpose of the Study:

• To investigate the interactions between multiple magnetic island chains in high-confinement tokamak discharges.
• To analyze the impact of these interactions on plasma rotation and tearing stability.
• To identify the criteria for wave coupling and its effect on plasma dynamics.

Main Methods:

• Utilizing millimeter-wave imaging diagnostics to measure the 2D power spectral density, S(ω, kpol).
• Analyzing phase-locking and 3-wave coupling selection criteria among magnetic island chains.
• Examining nonlinear coupling among neoclassical tearing modes with different toroidal mode numbers (n-number).

Main Results:

• Millimeter-wave imaging successfully identified phase-locking and 3-wave coupling criteria in multiple magnetic island chains.
• Nonlinear coupling between modes, especially those not satisfying specific poloidal mode number criteria, was observed.
• These interactions were found to reduce core plasma rotation and flow shear near the magnetic islands.

Conclusions:

• Millimeter-wave imaging provides localized internal measurements crucial for understanding complex plasma phenomena.
• Nonlinear coupling among magnetic islands significantly influences plasma rotation and stability in tokamaks.
• The findings highlight the importance of mode coupling in tokamak performance and suggest potential targets for control strategies.