Polarimeter–interferometer diagnostic using terahertz solid-state sources for fluctuation measurements on Keda Torus eXperiment (KTX)

A multi-channel polarimeter–interferometer has been developed on the Keda Torus eXperiment (KTX) for the study of equilibrium dynamics and internal magnetic fluctuations. A three-wave technique based on terahertz solid-state sources (~650 GHz) is applied for simultaneous measurements of electron density and Faraday rotation angle. The output power of the microwave source is 2 mW. Faraday rotation effect using a rotating wave plate is tested with phase noise less than 0.8°, and the density phase noise is less than 0.9°. Measurement of Faraday rotation angle and density for discharges on KTX have demonstrated high sensitivity to internal MHD activities.