Conceptual design of laser transfer system of the JT-60SA Thomson scattering diagnostic

JT-60SAトムソン散乱計測のレーザー伝送系の概念設計

東條 寛; 波多江 仰紀; 濱野 隆; 伊丹 潔

Tojo, Hiroshi; Hatae, Takaki; Hamano, Takashi; Itami, Kiyoshi

JT-60SA Thomson scattering system will measure electron temperature and density profile. A YAG laser will be toroidally injected to the JT-60SA on its equatorial plane. We designed beam transfer optics as long as using a relay image technique. The beam transfer optics designed for the JT-60SA tokamak can transfer the image of initial beam profile (flat-top). The laser beam is transferred from the laser room to the last convex lens placed before the plasma and its size is suppressed within a preferable scale ( 30 mm). The resultant beam width in the JT-60SA plasma can be minimized as less than 1 mm. Coping with stray light is another important issue. When the laser goes through the vacuum window, diffuse reflection at the window generates stray light. The stray light can significantly affect signal-to-noise ratio because the Thomson scattered cross section is very small (710 m). Numerical ray tracing to simulate suitable number of baffle boards for JT-60SA suggested that more than four baffle boards are necessary to suppress the stray light. We adapted six baffle boards which reduces stray light by compared with the case without baffle boards.