Research on the Real-Time Phase Jump Process Method for Plasma Electron Density Measurement in HL-2A Tokamak*

In the real-time plasma electron density measurement using far infrared (FIR) laser interferometry, the plasma electron density can be calculated by measuring the real time phase difference between the reference signal and the probe signal. A novel Real-time Phase Jump Process (RPJP) method is applied to the HL-2A tokamak. With this method, the phase difference precision is up to 1/3600 fringe (1 fringe is equal to a phase shift of 2π), and the dynamic measurement range is extensible 65536 fringes. The time resolution of the phase difference is 80 ns, while the feedback delay is 180 μs.