A Movable Thomson Scattering System Based on Optical Fibers (TS-Probe)

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This paper proposes a movable compact Thomson scattering (TS) system based on optical fibers (TS-probe). The TS-probe consists of a probe head, optical fibers, a laser diode, a polychromator, and lock-in amplifiers. Laser beam optics and light collection optics are mounted rigidly on a probe head with a fixed scattering position. Laser light and scattered light are transmitted by flexible optical fibers, enabling us to move the TS-probe head freely during plasma discharge. The light signal scattered from an amplitude-modulated laser is detected against the plasma light based on the principle of the lock-in amplifier. With a modulated laser power of 300 W, the scattered signal from a sheet plasma 15 mm deep with ne ∼1019 m−3 can be measured with 10 % accuracy by setting the integrating time to 0.1 s. The TS-probe head is similar to a 1/20 model of the currently operating Large Helical Device-TS.