Observation of Doppler shift f_D modulated by the internal kink mode using conventional reflectometry in the EAST tokamak

【摘要】 In this paper we present a new experimental observation using a conventional reflectometry technique,poloidal correlation reflectometry(PCR),in the Experimental Advanced Superconducting Tokamak(EAST).The turbulence spectrum detected by the PCR system exhibits an asymmetry and induced Doppler shift f_D during the internal kink mode(IKM)rotation phase.This Doppler shift f_D is the target measurement of Doppler reflectometry,but captured by 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.The fishbone mode and saturated long-lived mode are typical IKMs,and this modulation phenomenon is observed in both cases.Moreover,the value of the Doppler shift f_D is positively correlated with the amplitude of the 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 f_D and IKM rotation,and are helpful for studying the characteristics of IKM and related physical phenomena.更多还原

【Abstract】 In this paper we present a new experimental observation using a conventional reflectometry technique,poloidal correlation reflectometry(PCR),in the Experimental Advanced Superconducting Tokamak(EAST).The turbulence spectrum detected by the PCR system exhibits an asymmetry and induced Doppler shift f_D during the internal kink mode(IKM)rotation phase.This Doppler shift f_D is the target measurement of Doppler reflectometry,but captured by 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.The fishbone mode and saturated long-lived mode are typical IKMs,and this modulation phenomenon is observed in both cases.Moreover,the value of the Doppler shift f_D is positively correlated with the amplitude of the 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 f_D and IKM rotation,and are helpful for studying the characteristics of IKM and related physical phenomena.更多还原