Enhancement and suppression of turbulence by energetic-particle-driven geodesic acoustic modes

We propose a novel mechanism of enhancement of turbulence by energetic-particle-driven geodesic acoustic modes (EGAMs). The dynamics of drift-wave-type turbulence in the phase space is investigated by wave-kinetic equation. Spatially inhomogeneous turbulence in the presence of a transport barrier is...

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Bibliographic Details
Published in:Scientific reports 2017-12, Vol.7 (1), p.16767-7, Article 16767
Main Authors: Sasaki, M., Itoh, K., Hallatschek, K., Kasuya, N., Lesur, M., Kosuga, Y., Itoh, S.-I.
Format: Article
Language:English
Subjects:
639/766/189
639/766/1960/1136
Acoustics
Humanities and Social Sciences
Investigations
multidisciplinary
Propagation
Science
Science (multidisciplinary)
Turbulence
Velocity
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Summary:We propose a novel mechanism of enhancement of turbulence by energetic-particle-driven geodesic acoustic modes (EGAMs). The dynamics of drift-wave-type turbulence in the phase space is investigated by wave-kinetic equation. Spatially inhomogeneous turbulence in the presence of a transport barrier is considered. We discovered that trapping of turbulence clumps by the EGAMs is the key parameter that determines either suppress or enhance turbulence. In regions where turbulence is unstable, EGAM suppresses the turbulence. In contrast, in the stable region, EGAM traps clumps of turbulence and carries them across the transport barrier, so that the turbulence can be enhanced. The turbulence trapped by EGAMs can propagate independent of the gradients of density and temperature, which leads to non-Fickian transport. Hence, there appear a new global characteristic velocity, the phase velocity of GAMs, for turbulence dynamics, in addition to the local group velocity and that of the turbulence spreading. With these effect, EGAMs can deteriorate transport barriers and affect turbulence substantially. This manuscript provides a basis to consider whether a coherent wave breaks or strengthen transport barriers.
ISSN:2045-2322
2045-2322
DOI:10.1038/s41598-017-17011-y