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

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.