Progress of the synthetic HCOOH laser diagnostic system on HL-2A tokamak

A synthetic formic-acid laser (HCOOH, lambda = 432.5 mu m) diagnostic system, which includes a Michelson Interferometer, a Faraday-effect Polarimeter and a Far-forward collective scattering diagnostic, has been successfully developed on HL-2A tokamak for plasma operation and physics research. This paper describes the progress made to improve the diagnostic system: (1) For the Interferometer, the data processing/acquisition system was greatly improved, and the high-speed refractive memory card was firstly utilized in the real-time density feedback control. (2) For the Polarimeter, the main interference source of Faraday rotation angle measurement was identified to be the stay light, and preliminary result indicated that the stray light coming from the detector surface can be largely suppressed by using the optic-isolator which was made up of a polarizer and a quarter wave plate. (3) The newly developed Far-forward collective scattering diagnostic based on two circularly polarized waves was widely used to investigate broadband density fluctuations in recent experimental campaign.