Measurements of the E × B velocity fluctuation associated with the fishbone instability using the Doppler reflectometry on EAST

Abstract Velocity fluctuations are of significant importance in plasma transport
in magnetic confinement devices. Measurements of the E × B velocity fluctuation
(˜v E×B ) in the core region associated with the fishbone instability have been carried
out on EAST using a W-band X-mode Doppler reflectometry (DR). For internal kink-
like mode, Doppler shift fluctuations of probing beams due to deformation or advection
of the cut-off layer are negligible. The ˜vE×B amplitude inside the resonant surface is
measured to be 1 ∼ 5 km/s and is linearly proportional to the poloidal magnetic
fluctuation, as expected from the ideal MHD instabilities. Furthermore, the radial
velocity fluctuation (˜v r ) inferred from the density fluctuation is comparable to ˜v E×B ,
which is consistent with the plasma incompressibility. This is the first quantitative
measurement on the poloidal flow fluctuation generated by fishbone bursts. The
potential impact of such significant flow fluctuations on turbulence in core plasma
through flow shear or dynamo effect is a subject that merits further investigation.