A multipoint Thomson scattering apparatus under development for the measurement of spatial Te and ne profiles in the ETA-BETA II reverse field pinch experiment is described. The apparatus is based upon the two-channel analysis method already adopted in the TFR tokamak. The 90° scattered light is collected simultaneously from seven spatial positions along a plasma diameter by means of high-efficiency, quartz, fiber-optic light guides. The detection system consists of a set of high aperture (f/2.4), plane grating, Littrow spectrometers developed to match the high throughput of the collection optics. These instruments employ photomultipliers with a GaAs photocathode (quantum efficiency ≂20%, λ=700 nm) and have a stray light rejection ratio of 3×10−4. Laboratory tests and preliminary measurements in ETA-BETA II have shown good sensitivity and a S/N ratio sufficient to diagnose plasmas with ne≥1013 cm−3.
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Bassan et al. (1985) studied this question.
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