Polarization Interferometer System Based on Terahertz Solid State Source on KTX Experiment

The magnetic configuration distribution in the magnetic confinement fusion device determines the operation mode of the device, and the instability of the magnetohydrodynamic (MHD) is closely related to the confinement performance of the device. Therefore, the measurement of the magnetic field equilibrium and fluctuation is of great significance to the physics research and the development of the control technology of magnetic confinement fusion. The measurement of the magnetic field equilibrium helps us to invert the magnetic surface more accurately for the discharge operation of the device, and the measurement of the magnetic field fluctuation helps to study the MHD instability. We developed a three-wave polarization interferometer system based on a 650GHz terahertz solid state microwave source on the Keda Torus eXperiment (KTX) at the University of Science and Technology of China, and successfully completed the collinear and polarization state tests, which verified the feasibility of the diagnostic system. The system can measure the interference signal caused by electron density and the Faraday rotation angle signal caused by magnetic field effect respectively. Compared with traditional laser systems in the same band, the design based on microwave source improves the stability and operability of the system, and realizes the miniaturization of the system at the same time. In the next step, we will perform the magnetic surface based on EFIT program, combined with diagnostic data such as boundary magnetic probe. The measured fluctuation data is used to analyze the MHD instability in the device.