Speaker
Description
As a conventional reflectometry, W-band Poloidal Correlation Reflectometry (PCR) has been operated successfully on EAST tokamak since 2018 and has become a key diagnostic tool for measuring electron density fluctuation in plasma core. In this report, a new experimental observation that the turbulence spectrum detected by this PCR system exhibits an asymmetry and induced Doppler shift f_D during internal kink mode (IKM) rotation phase, will be presented. This Doppler shift f_D is the target measurement of Doppler reflectometry, but captured by this conventional reflectometry. Results show that the Doppler shift f_D is modulated by the periodic changes in the effective angle between the probing wave and cutoff layer normal, but not by plasma turbulence during IKM rotation. Fishbone mode and saturated long-live mode (LLM) are typical IKMs on EAST NBI-heating plasmas, and this modulation phenomenon is observed in both cases. In addition, the value of Doppler shift f_D is positively correlated with the amplitude of IKM, even when the latter is small. However, the positive and negative frequency components of the Doppler shift f_D can be asymmetric, which is related to the plasma configuration. A simulated analysis is performed by ray-tracing to verify these observations. These results establish a clear link between the Doppler shift f_D and IKM rotation, and are beneficial to study the characteristics of IKM and related physical phenomena.
