Development Of ECE Imaging Diagnostics And Study Of MHD Behavior In Core Plasms On EAST

This paper mainly describe the development of 384 channel Electron Cyclotron Emission Imaging(ECEI),which has been installed on EAST tokamak,and some study on MHD behavior of core plasma.In the development of the Electron Cyclotron Emission Imaging diagnostic system,we designed an ECEI system for EAST tokamak and obtained the first successful commissioning in the spring of 2012.We have obtained some meaningful data in core plasma.Some unique features were introduced as compared with other ECEI systems:wider sampling volume,longer focal length and higher spatial resolution.In our design,the bandwidth of electronics was widen from 2～8GHz to 2～18GHz,so the radial range of sampling volume was widen.The arrangement of detector array was optimized:the deliectric lens and detector unit are one-to-one,it can improve the effciency of pumping local oscillator,and reduce the difference of singnal quality between side and core channels.The study of MHD instability in core plasma can be divided into two parts:the structure of MHD mode during the start-up phase of plasma current,and the sawtooth oscillation.During the start-up phase of plasma current,we found the coupling of multiple tearing modes:the inner m/n=1/1 mode and outer m/n=2/1 mode rotate with same frequency and poloidal direction.We also observed the interaction between different m/n=1/1 modes with m/n=0/0 mode which mode number is same as the zonal field,this phenomenon has never been reported.The m/n=1/1 mode which couples with m/n=2/1 mode interacts with a higher frequency m/n=1/1 mode to generate an m/n=0/0 mode,then the m/n=0/0 mode modulats the higher frequency m/n=1/1 mode to create another m/n=1/1 mode.We demonstrated the profile of tearing mode and some sawtooth crash with new character which is consistent with Wesson interchange model.In the research of sawtooth oscillation,we observed that the sawtooth crash took place with asymmetry of 3D structure in toroidal direction through ECEI and ECE which has been installed in different toroidal position,put forward a new model for sawtooth crash,and then discuss some problems in the measurement of sawtooth crash time.We found,during sawtooth crash the precursor mode changes its direction before and after the L-H transition.The sawtooth crash with high harmonic mode of m/n=1/1 mode will be shown by ECE Imaging map at the first time.