Improvement of q profile by the polarimeter/interferometer system on EAST tokamak

A novel equilibrium fitting method, which combining the polarimeter/interferometer (POINT) measurements with the external magnetic measurements, has been developed to improve the accuracy of safety factor (q) profile on the EAST tokamak. The POINT system, measuring the accurate line-integrated electron density and Faraday rotation angle, provides the magnetic field information inside the plasma. By adding these data to the equilibrium constraints, the fitting results with new method show clear difference with the initial equilibrium and the difference becomes larger gradually from boundary to core of the plasma. This method, overcoming the difference of the EFIT results from the external magnetic measurements, shows a great improvement on q profile, especially in the core plasma. Results with and without these corrections are presented, comparisons of the corrected results and experimental results are also shown and these are found consistent with each other. The feasibility and reliability of the correction process are also discussed in this paper.