Development of the cross-polarization scattering system for the measurement of internal magnetic fluctuations on HL-3 tokamak

In this work, the design, test and the first experimental result of a new cross-polarization scattering (CPS) diagnostic is presented, which is based on the scattering of an incident microwave beam into the orthogonal polarization by magnetic fluctuations [1-4]. The new CPS diagnostic focus on the measurement of local density and magnetic field fluctuations simultaneously. With the help of the rotatable polarizer, the effect of the polarization mismatch is analyzed in detail and the conditions for a well polarized matching were confirmed. The response of the CPS receiver, the isolation of the polarizer, and the isolation of electronics system were tested in the laboratory. The plasma test results of polarization purity, signal amplitude and power spectral respond indicate the new CPS diagnostic can measure the density and magnetic field fluctuations simultaneously when the polarization is well matched. In the future, the CPS diagnosis will be used to study the electrostatic and electromagnetic turbulence behavior of the high-performance plasma on the HL-3 tokamak.