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

The design and operation performance of the latest ruby Thomson scattering system for the JT-60U are described, which includes many novel approaches t o attain the repetitive measurement of 60 spatial points with high resoluti on (8 mm), precision, and reliability especially for a high temperature and large size tokamak device. A beam combiner composed of a polarizer and a F araday rotator for two ruby lasers has provided the transient measurement w ith 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 quan titative alignment of collection fiber object field has been utilized for t he reliable n(e) profile measurement. By using Rayleigh scattering light, a n in situ inferring method for a coated viewing window transmission has bee n found to have an effect on the precise correction of electron temperature T-e and density n(e) underestimate for high T-e plasmas. Making the most u se of this diagnostic in a series of the recent JT-60U reversed shear exper iments, the formation of an internal transport barrier even for electrons h as been revealed from the clear existence of a steep gradient in both T-e a nd n(e) profile shapes. (C) 1999 American Institute of Physics. [S0034-6748 (99)63901-6].