  The effect of island width on the multi-scale interactions between magnetic
island (MI) and ion temperature gradient (ITG) turbulence has been investigated
based on the global gyrokinetic approach. It is found that the coupling between
the island and turbulence is enhanced when the MI width (w) becomes larger. A
vortex flow that is highly sensitive to the width of the magnetic island can be
triggered, ultimately resulting in a potent shear flow and a consequent
reduction in turbulent transport. The shearing rate induced by the vortex flow
is minimum at the O-point while it is maximum at both of the two reconnection
points of the island, i.e., the X-points, regardless of the island width. There
exists a nonmonotonic relationship between zonal flow (ZF) amplitude and island
width, showing that the ZF is partially suppressed by medium-sized MIs whereas
enhanced in the case of large island. A larger MI can tremendously damage the
ITG mode structure, resulting in higher turbulent transport at the X-point
whereas a lower one at the O-point, respectively. Such phenomenon will be less
distinct at very small island widths below w/a =8% (a is the minor radius),
where it shows that turbulence near the X-point is hardly affected although it
is still suppressed inside the island. Furthermore, the influence of different
island sizes on turbulence transport level is also discussed.
