Thermal and optical analyses of retro-reflector for poloidal polarimeter on ITER

Imazawa, Ryota; Kawano, Yasunori; Ono, Takehiro; Kusama, Yoshinori

This paper describes results from the first integrated analysis on the feasibility of a retro-reflector (RR) installed in the ITER vacuum vessel. We make thermal and structural analyses of passively-cooled RR and terrace retro-reflector array (TERRA) by using heat load conditions on ITER. In the case of RR, the temperature reaches over 600C, and the flatness of deformed mirror surface forming RR is approximately 80 m. Although the maximal displacement of mirror surface is large, 69% of the incident-laser power returns to a diagnostic room, disturbance of phase is and rotation angle of polarization plane is less than 0.06 . On the other hand, the temperature of TERRA is approximately 350C, and the flatness of the deformed mirror surface is less than 10 m. The flatness of the mirror surface of the deformed TERRA is much smaller than laser wavelength (118 m), but the global shape is curved to ruin the coherent phase of laser light. The curvature radius of TERRA is 21 m, and 49% of the incident-laser power returns to the diagnostic room, disturbance of phase is , and rotation angle of polarization plane is less than 0.06. Since the optimized incident angles of flat and curved TERRA are different, a real-time feedback control of the incident angle is necessary for applying TERRA to ITER poloidal polarimeter.