A terahertz solid-state source interferometer-polarimeter designed for long pulse discharges on EAST

A 0.65 THz Solid-state Source Interferometer-Polarimeter (SSIP) with vertical viewing has been installed for line-integrated density and Faraday rotation measurements on Experimental Advanced Superconducting Tokamak (EAST). The SSIP utilizes three independent solid-state diode sources based on frequency multiplier (X48) to provide the probing beam at a fixed frequency of 0.65 THz with ∼2.5 mW output power, which provide an Intermediate Frequency (IF) with wide range, and the highest IF is up to ∼10 MHz. The mixers optimized for high sensitivity, ∼750 mV/mW, are used in the SSIP system, which permits multichannel interferometer-polarimeter on EAST with a low phase noise. The resolution of the integrated density is 3.3 × 1017 m-2, and the Faraday rotation is about 1.5°. The density measurement has been implemented with IF ∼0.85 MHz, in a plasma with plasma current ∼300 kA on EAST. The line-averaged density, 3.5 × 1019 m-3, measured by the SSIP shows good agreement with the results measured by the POlarimeter-INTerferometer (POINT) system and the CO2 dispersion interferometer system in the same discharge.