Real-Time Dynamic Spectrum Analysis for Plasma Electron Density and Faraday Rotation Angle Measurement on HL-2A*

Electron density and Faraday rotation angle are important physical parameters in nuclear fusion research. To measure them simultaneously, the three-wave polarimeter/interferometer diagnostic system is applied. Both the final probe output signal and the reference signal contain three frequency components. The time-varying phase difference curve of each frequency component can be measured by the Real-time Dynamic Spectrum Analysis (RDSA) method based on Field-Programmable Gate Array (FPGA). The phase difference precision is better than 0.1° and the real-time feedback delay is less than 1 ms, which satisfy the requirements of HL-2A.