Ion gyroscale fluctuation measurement with microwave imaging reflectometer on KSTAR

Abstract

Ion gyroscale turbulent fluctuations with the poloidal wavenumber k(theta) similar to 3 cm(-1) have been measured in the core region of the neutral beam (NB) injected low confinement (L-mode) plasmas on Korea superconducting tokamak advanced research. The turbulence poloidal wavenumbers are deduced from the frequencies and poloidal rotation velocities in the laboratory frame, measured by the multi-channel microwave imaging reflectometer. Linear and nonlinear gyrokinetic simulations also predict the unstable modes with the normalized wavenumber k(theta)rho(s) similar to 0.4, consistent with the measurement. Comparison of the measured frequencies with the intrinsic mode frequencies from the linear simulations indicates that the measured ones are primarily due to the E x B flow velocity in the NB-injected fast rotating plasmas.