On completion, the Joint European Torus (JET) will he the largest nuclear fusion experiment constructed. We are currently developing a novel system to measure radial electron temnerature/density profiles and central ion temperatures within the plasma using a 10Hz rep-rate CO2 laser. The large dimensions and expected neutron fluxes represent significant constraints on this design. Specifically the input and collected scattered radiation have to he relayed between shielded lasers/detectors and the torus, ~ 30m away, and the alignment maintained remotely. This system, containing ~ 75 mirrors and designed with the aid of a computer ray-tracing program, is described together with some details of the spectrometer and laser.
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