CO laser collective Thomson scattering diagnostic of -particles in burning plasmas

Kondoh, Takashi; Hayashi, Toshimitsu; Kawano, Yasunori; Kusama, Yoshinori; Sugie, Tatsuo; Hirata, Mafumi*; Miura, Yukitoshi

A diagnostic of fusion-generated -particles is important for the understanding of their contribution to plasma heating and plasma instabilities in burning plasmas. However, an effective measurement method has not yet been established. In International Thermonuclear Experimental Reactor (ITER), measurement of velocity and spatial distributions of confined -particles requires temporal resolution of 0.1 s and spatial resolution of a/10, where a is the plasma minor radius of ITER. A collective Thomson scattering (CTS) diagnostic for the measurement of particles is being developed using carbon dioxide (CO) lasers. The CTS based on the CO laser (wavelength 10.6 m) has an advantage of small plasma refraction, simplifying the tracking of the scattered radiation. To realize the CTS diagnostic, a high-repetition Transversely Excited Atmospheric (TEA) CO laser is being developed. The laser was designed based on a commercially available laser, TEA CO marking laser. Maximum output energy of 36 J has been obtained with a cavity configuration of stable resonator. 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 10 J at a frequency of 10 Hz has been achieved with single-mode output. Proof-of-principle test will be performed with the improved laser system on the JT-60U tokamak. In this paper, we will describe development of the new TEA laser system, measurement results of the CTS on the JT-60U tokamak. Application of the CTS diagnostic to the mirror systems will be also described.