Optical design of vertical edge Thomson scattering on HL-2M tokamak

A vertical edge Thomson scattering (ETS) diagnostic system on HL-2M tokamak has been designed. The ETS system collects the scattered light from Nd: YAG laser (1064 nm, 2 J, 30 Hz, 15 ns). The laser beam propagates vertically through the plasma region and the polarization is parallel to the toroidal magnetic field. A special designed Galileo-type telescope with long Rayleigh length is applied to focus the laser size and ensure collimation. A group of double-Gaussian collection lenses image the 600 mm vertical scattered region onto rectangular fiber arrays with a spatial resolution of 10 mm. The 2.20 mm × 2.86 mm fiber optic bundle consists of 130 low hydroxyl (OH) 200/220 μm (core/cladding) diameter fibers with numerical aperture NA = 0.22, carrying the light to remotely located multi-channel polychromators. Effect of oblique incidence on narrow band filter has been analyzed. The designed electron temperatures range from 5 to 1000 eV and electron densities from 5 × 10¹⁸ to 1 × 10²⁰ m^-3.