Estimation of ExB flow velocity and related flow physics from the measured poloidal velocities of density fluctuations in KSTAR L-mode plasmas

Abstract

The apparent poloidal rotations of ion-scale density fluctuations in the laboratory frame were measured with the microwave imaging reflectometer (MIR) system in KSTAR [1, 2]. The measured apparent poloidal velocities are 5−10 km/s in ion diamagnetic direction at r/a ∼ 0.4−0.7 of 1.43 MW neutral beam (NB) heated L-mode discharges. The apparent poloidal velocities are close to the E×B flow velocities when the intrinsic phase velocity of dominant density turbulence is negligible compared to the apparent poloidal velocity (i.e., the estimated intrinsic phase velocity is ∼0.4 km/s in a linear gyro-kinetic simulation with GYRO). The E×B flow shear is smaller than the maximum growth rate and the shear is mostly induced by poloidal flow shear. The measured apparent poloidal velocities will be compared with the results from a nonlinear gyro-kinetic simulation performed with GTS. Here, the adiabatic (equilibrium velocity from force balance) and non-adiabatic (perturbed distribution function of associated gradient driven physics) terms will be compared with the experimental results.