Experimental study of core MHD events in EAST advanced scenarios by microwave reflectometry

Abstract Fishbone modes and Alfvén eigenmodes (AEs) are two of the most significant core magnetohydrodynamic (MHD) events observed in advanced scenarios on the Experimental Advanced Superconducting Tokamak. Microwave reflectometry, with its excellent spatial and temporal resolution, has been utilized to study their behaviors. During the fishbone event, the density profile and its gradient ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi mathvariant="normal">∇</mml:mi> <mml:mrow> <mml:msub> <mml:mi>n</mml:mi> <mml:mrow> <mml:mtext>e</mml:mtext> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> ), measured by density profile reflectometry, in the vicinity of the fishbone mode are modulated by the rotation of internal kink modes. Furthermore, the position of the maximum density gradient ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi mathvariant="normal">∇</mml:mi> <mml:mrow> <mml:msub> <mml:mi>n</mml:mi> <mml:mrow> <mml:mrow> <mml:mtext>e,max</mml:mtext> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> ) aligns with the fishbone location, and its value exhibits a positive correlation with the amplitude of the internal kink modes. Additionally, the fishbone can be detected by monitoring the center of gravity oscillations in a conventional reflectometry called multi-channel poloidal correlation reflectometry (PCR). Furthermore, the spectrogram of density fluctuation amplitude, measured by the PCR, reveals AEs more distinctly than commonly used diagnostics such as electron cyclotron emission and high frequency Mirnov coils. These findings not only help to better understand the characteristics of these MHD behaviors, but also contribute to the q -profile reconstruction and investigating the related physical processes.