Research On Data Processing Of EAST Multi-channel Far-Infrared Laser Polarimeter Interferometer System

Electron density,current density and their distribution are key parameters for studying the behaviors of plasma confinement,transport,and MHD instability in tokamak devices.The accurate measurements and distribution calculations of the electron density and current density are crucial for tokamak experiments.The far-infrared laser diagnostic is an effective method to measure the line-integrated electron density and Faraday rotation angle of the plasma.The electron density profile and magnetic field information can be given by combining the measured data with appropriate inversion methods.At present,there are two sets of diagnostics on the Experimental Advanced Superconducting Tokamak that can measure the line-integrated density of the plasma,including the hydrogen cyanide(HCN)interferometer system and the polarimeter/interferometer(POINT)system.The line-integrated electron density in the vertical(3 chords)and horizontal(11 chords)directions were measured by HCN and POINT system separately.In addition,the POINT system can also measure the Faraday rotation information of the plasma.The POINT system on EAST tokamak has undergone two stages of development.Before 2015,the POINT system only has 5 measuring chords.Using the line-integrated electron density data measured by POINT system,combined with the boundary electron density profile measured by the microwave reflectometer system on the EAST device,a density inversion procedure based on the PARK-matrix method was developed and accurate electron density profile has been obtained.After 2015,the measuring chords of POINT has been increased to 11.This paper has further upgraded and optimized the density inversion procedure based on the upgraded system.The calibrations and statistics of the data of microwave reflectometer system and the POINT system have been performed.The coefficients between the line-integrated electron density in the boundary area that cannot be covered by the measuring channels of the POINT system and the measured values of the first and eleventh chords of the POINT system are obtained.These coefficients are used to strengthen the constraints on the electron density profile in the boundary region during the electron density inversion.In the upgraded density inversion procedure,the input data is provided by the POINT system only,and also ensuring the accuracy of the calculation results.In addition,the upgraded density inversion procedure optimizes data input,the zero drift and the lack of diagnostic data are all taken into consideration to make the procedure more convenient and user-friendly.During the development of high-parameter operation on the EAST device,the change of the density profile during the formation and collapse of the internal transport barrier(ITB)was studied using the high time resolution and high-precision electron density profile.Conducting the derivation of the density on the position can further investigate this physical process quantitatively and provide important supports for the study.Based on the high time resolution and high-precision electron density profile,the current density profile inversion on the EAST tokamak was further improved,and a more accurate current density profile was obtained.The data obtained from the external magnetic measurements combined with equilibrium fit(EFIT)code can give the initial plasma magnetic surfaces and current density profile,and then by adding the Faraday rotation information measured by the POINT system,the plasma in the core region can be further constrained and the calculation results will be more accurate.During the poloidal magnetic flux(magnetic field)correction process,the procedure does not rely on the EFIT program to iterate but pays more attention to the correction of the local area.Experiments with high normalized beta were performed on the EAST tokamak,the electron density profile during the formation and collapse of ITB was evoled using the POINT data,and the Faraday rotation information was used for the constraint of the safety factor(q)profile.The corrected safety factor profile was checked by using the special physical phenomena in the experiments,such as sawtooth and fishbone instability.The results show that the calculated results are in good agreement with the phenomena,and the feasibility of this method is verified.