Speaker
Makoto Sasaki
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1095.pdf
Spatio-temporal dynamics of turbulence coupling with zonal flows
M. Sasaki1,2 , T. Kobayashi3 , K. Itoh2,3,4 , N. Kasuya1,2 , Y. Kosuga1,2 ,
A. Fujisawa1,2 , S. Inagaki1,2 , S.-I. Itoh1,2,5
1 Research Institute for Applied Mechanics, Kyushu University, Kasuga, 816-8580, Japan
2 Research Center for Plasma Turbulence, Kyushu University, Kasuga, 816-8580 Japan
3 National Institute for Fusion Science, Toki, 509-5292, Japan
4 Institute of Science and Technology Research, Chubu University, Aichi, 487-8501, Japan
5 Department of Innovative Energy Science and Engineering, Graduate School of Engineering,
Chubu University, Aichi, 487-8501, Japan
Formation mechanism of spatial profile of turbulence is one of important subjects in fusion
plasma research. There are mechanisms to determine the spatial profile of the turbulence; one
is the propagation, such as the avalanche and turbulence spreading [1], and the other is the in-
teraction with the sheared flows, where the effects of flow shear [2] and of flow curvature [3]
have been theoretically predicted. Experimental observations on the spatial profiles of turbu-
lence within the scale of flow shears have been reported [4]. Therefore, a unified model that can
predict the spatial structure of turbulence, including the mechanisms of the propagation and the
interaction with the sheared flows, is required.
In this study, we investigate the phase-space dynamics of turbulence coupling with the zonal
flows, based on the wave-kinetic framework. We focus on the oscillatory branch of zonal flows,
which is called geodesic acoustic modes (GAMs), on which there are many experimental obser-
vations. Spatio-temporal structures of the turbulence and GAMs are obtained numerically. Due
to the turbulence trapping by the GAM [5], the turbulence is accumulated at regions where the
curvature of the GAM (spatial-second-derivative of the flow) is negative, and the turbulence is
suppressed at the positive curvature region. The roles of the flow shear and curvature on the tur-
bulence spatial profile are illustrated. The phase relation is sustained with the propagation of the
GAM [6]. Hence, there appear a new global characteristic velocity for turbulence propagation,
in addition to the local group velocity and that of the turbulence spreading.
References
[1] O. D. Gurcan, P. H. Diamond, T. S. Hahm, Z. Lin, Phys. Plasmas, 12, 032303 (2005).
[2] H. Biglari, P. H. Diamond, P. W. Terry, Phys. Plasmas, 2, 1 (1990).
[3] K. Itoh, et. al., Plasma Phys. Control. Fusion, 57, 075008 (2015).
[4] T. Tokuzawa, Nucl. Fusion, 57, 025001 (2017).
[5] M. Sasaki, et. al., Sci. Rep. 7, 16767 (2017).
[6] M. Sasaki, et. al., Phys. Plasmas, 25, 012316 (2018).
