Two-color CO2 laser long-distance interference measurements with long-time stabilization in JT-60SA.

We have developed a two-color CO2 laser interferometer in JT-60SA, which features a long transmission line and a long-time stabilization system. We inject two laser beams with an optimized beam size into the plasma of JT-60SA. A newly developed beam axis stabilizing system stabilizes the laser beam line to the plasma, which constitutes one fourth of the total line length of 214 m, for more than 11 hours, ensuring no beam line loss during the integrated commissioning phase of JT-60SA. It is possible to measure the line-integrated electron densities of JT-60SA plasmas with a resolution of 2 × 1019 m-2. The typical NeL = 1.4 × 1020 m-2. Experimental evidence also demonstrates the challenge of compensating for line-integrated electron density errors, even with a two-color interferometer.