Improvements of CO₂ Laser Heterodyne Imaging Interferometer for Electron Density Profile Measurements on LHD

抄録

After installation of CO₂ laser (wavelength 10.6 μm) heterodyne imaging interferometer (CO₂ HI) in 2001, continuous developments have been carried out to improve the measurements capability and stability of operation. The CO₂ HI works almost without phase jumping at high electron density (> 1 × 10²⁰ m^-3), where the existing far infrared laser (wavelength 118.9 μm) interferometer suffers from fringe jump due to the reduction of signal intensity caused by refraction. However a second interferometer is required to compensate mechanical vibration. A YAG laser (wavelength 1.06 μm) heterodyne imaging interferometer (YAG HI) is presently used for the vibration compensation. In the 10th LHD experimental campaign (2006∼2007), sixty four channels of CO₂ HI to measure electron density profile and ten channels of YAG HI to measure mechanical vibration are working. A measurement example of a pellet fuelled high-density discharge is reported.