7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Island-induced transport barrier due to turbulence-driven Vortex-Flow
M. Leconte1, Y.W. Cho1 and K. Ida2
1Korea Institute of Fusion Energy (KFE)
2
National Institute for Fusion Sciencee-mail (speaker): mleconte@kfe.re.kr

We predict a new state of plasma selforganization in presence of magnetic islands,
namely turbulence-driven island Vortex-Flows,which are non-axisymmetric flows. Theinteraction between an ExB sheared Vortex-Flowand the Drift-Wave (DW) turbulence driving it isderived in presence of a coherent static
magnetic island, based on Ref. [1]. The
turbulence is driven by a 3D density profile due
to quasi-linear island-induced profile flattening.
The Drift-Waves thus follow the local electron
diamagnetic direction along the island. The
metrix tensor is introduced, making the analysis
transparent in island geometry. An extended
Charney-Hasegawa-Mima [2] equation describes
the DW turbulence-Vortex Flow interaction, fromwhich a wave-kinetic equation is obtained inisland geometry. This yields a DW-Vortex Flow
predator-prey model which predicts a nonlinear
threshold for island Vortex-Flow formation. TheVortex-Flow threshold decreases as the inversesquare of the island width (normalized to thegyroradius), which shows that the turbulence
around wider islands may more easily drive
flows. Our previous turbulence-driven VortexFlow Predator-Prey model [3] is extended toinclude the coupling to the island pressure
gradient and associated mean Vortex-Flow.The
turbulence-driven Vortex-Flow is driven by
nonlinear coupling to turbulence, and damped
by viscous dissipation, whereas the mean
Vortex-Flow is set by the island pressure

dynamics of turbulence, turbulence-driven
Vortex-Flow energy and island pressure gradient
are shown [Fig 1]. Here, the heat source isconstant in time corresponding to the flat-top
regime while the island-width is slowly rampedup (black line), as in the experiment [4] which
triggers the transition to the ITB-like regime,
once the threshold island-width is reached. The
model predicts that the island-width threshold is
proportional toρ (rho star), which is favorable

for future devices like ITER. Once the islandwidth threshold is reached, the following
observations can be made, based on thispredator-prey model: i) The turbulence (blue)
starts to be suppressed, ii) The turbulencedriven Vortex-Flow energy (red) increases. The
island-averagedpressure
gradient(andassociated mean Vortex-Flow) increases (yellow),which correspond to the island-induced ITB.
References[1] T.S. Hahm et al., Phys. Plasmas 28, 022302 (2021)[2] A. Hasegawa and K. Mima, Phys. Fluids 21, 87(1978)[3] M. Leconte and Y.W. Cho, Nucl. Fusion 63, 034002(2023)[4] K. Ida et al., Phys. Rev. Lett. 88, 015002 (2002)

gradient via a generalization of radial force
balance to the island topology. The islandpressure gradient is driven by the heat source
Q, and suppressed by turbulence due toquasilinear flattening. The role of the mean
Vortex-Flow is to lock-in the transition to the ITBlike state, by analogy with the L-H transition.The

Fig. 1: dynamics of the island Vortex-Flow
predator-prey model