Study of a DCN laser interferometer/polarimeter for EAST tokamak

The experimental advanced superconducting tokamak (EAST) is a non-circular advanced steady-state experimental device. The first plasma discharge has been achieved successfully on the EAST in 2006. Single-null (SN) and double-null (DN) diverter plasmas discharges have also been achieved successfully on the EAST Tokamak in 2007. A five-channel vertical DCN laser interferometer/polarimeter system will be constructed on the EAST device. The system will be used mainly for getting electron density profile and poloidal current profile, and for a density feedback control simultaneously. Three 195 mu m(1.54 THz) continuous-wave glow discharge deuterium cyanide(DCN) lasers are implemented as beam sources. The system employs a three-wavelength configuration that simultaneously produces interferometric phase shift and Faraday rotation polarimetric data from a single detector for each channel. The optical system including optics inside the completely sealed frame has been designed in the consideration of long beam paths in a narrow diagnostics port and avoiding loss of laser power when laser passes through the moist atmosphere. By the same token, high sensitivity THz InSb detector system will be used in this interferometer/polarimeter system.