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Increased nonlinear coupling between turbulence and low-frequency fluctuations at the L-H transition
R A Moyer1, G R Tynan, C Holland
1Mechanical and Aerospace Engineering Department, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA.
Physical Review Letters
|October 3, 2001
Summary
Transient turbulence coupling in tokamaks precedes improved confinement. This nonlinear interaction, crucial for H-mode transitions, involves turbulence suppression and sheared flow development, then returns to baseline levels.
Area of Science:
- Plasma physics
- Fusion energy research
- Turbulence dynamics
Background:
- Tokamak devices are key to fusion energy.
- Understanding plasma turbulence is vital for confinement.
- Improved confinement modes (like H-mode) are crucial for efficient fusion.
Purpose of the Study:
- Investigate the role of turbulence coupling during tokamak transitions.
- Examine the nonlinear interaction between small-scale turbulence and large-scale fluctuations.
- Clarify the sequence of events leading to improved confinement in tokamaks.
Main Methods:
- Analysis of nonlinear coupling in DIII-D tokamak data.
- Observing transient changes in turbulence and fluctuations during confinement transitions.
- Correlation of coupling changes with turbulence suppression and E x B shear-flow development.
Main Results:
- Nonlinear coupling transiently increases during transitions to improved confinement.
- This increase precedes turbulence suppression and E x B shear-flow development.
- Coupling levels return to baseline (L-mode) after the H-mode transition.
Conclusions:
- Results support the theory of turbulence-driven sheared flow triggering improved confinement.
- The findings highlight the dynamic interplay of turbulence during H-mode transitions.
- Transient coupling is a key indicator of spontaneous H-mode access.