Initial operation of the divertor Thomson scattering diagnostic on DIII–D (abstract)

The first Thomson scattering measurements of ne and Te in the divertor region of a tokamak are reported. These data are used as input to boundary physics codes such as UEDGE and DEGAS and to benchmark the predictive capabilities of these codes. These measurements have also contributed to the characterization of tokamak disruptions. A Nd:YAG laser (20 Hz, 1 J, 15 ns, 1064 nm) is directed vertically through the lower divertor region of the DIII–D tokamak. A custom, aspherical collection lens (f/6.8) images the laser beam from 1 to 21 cm above the target plates into eight spatial channels with 1.5 cm vertical and 0.3 cm radial resolution. Two-dimensional mapping of the divertor region is achieved by sweeping the divertor X-point location radically through the fixed laser beam location. Fiber optics carry the light to polychromators whose interference filters have been optimized for low-Te measurements. Silicon avalanche photodiodes measure both the scattered and plasma background light. Temperatures and dens...