Multilaser and high spatially resolved multipoint Thomson scattering system for the JT-60U tokamak

Abstract

The design and operation performance of the latest ruby Thomson scattering system for the JT-60U are described, which includes many novel approaches to attain the repetitive measurement of 60 spatial points with high resolution (8 mm), precision, and reliability especially for a high temperature and large size tokamak device. A beam combiner composed of a polarizer and a Faraday rotator for two ruby lasers has provided the transient measurement with the minimum time interval of 2 ms in burst operation and the multitime-slice measurement with the repetition rate of 0.5 Hz in normal operation. A newly developed photodiode array detector with high repetitive ability of 1 ms has been used for the high temperature core plasma measurement. A quantitative alignment of collection fiber object field has been utilized for the reliable ne profile measurement. By using Rayleigh scattering light, an in situ inferring method for a coated viewing window transmission has been found to have an effect on the precise correction of electron temperature Te and density ne underestimate for high Te plasmas. Making the most use of this diagnostic in a series of the recent JT-60U reversed shear experiments, the formation of an internal transport barrier even for electrons has been revealed from the clear existence of a steep gradient in both Te and ne profile shapes.