Development of CO laser for collective Thomson scattering diagnostics

Kondoh, Takashi; Hayashi, Toshimitsu; Kawano, Yasunori; Kusama, Yoshinori; Sugie, Tatsuo

A diagnostic of fusion-generated alpha-particles is important for burning plasmas, however, an effective measurement method has not yet been established. A collective Thomson scattering (CTS) diagnostic for the measurement of alpha particles is being developed using carbon dioxide (CO) lasers. To realize the CTS diagnostic, a high-repetition Transversely Excited Atmospheric (TEA) CO laser is being developed. In order to obtain single-mode output, which is needed for CTS diagnostic, seed laser is injected to the cavity with unstable resonator. Using this technique, output energy of 17 J in frequency of 15 Hz has been achieved with single-mode output. These results gives a prospect for the CTS diagnostic on International Thermonuclear Experimental Reactor (ITER), which requires energy of 20 J with repetition rate of 40 Hz. Proof-of-principle test will be performed with the improved laser system on the JT-60U tokamak.