Design of a scanning 2D Divertor Thomson scattering system on DIII-D

Measurement of plasma electron temperature and density in the divertor region of high triangularity advanced Tokamak discharges is critical for characterization of boundary performance and for model validation. Previous divertor Thomson scattering (DTS) measurements in DIII-D were restricted to spatial locations along a fixed vertical Nd:YAG laser beam path optimized for low triangularity and without pumping access. With a single chord, the plasma has to be radially swept across the fixed laser path in order to study the full divertor. Recently, DIII-D has demonstrated the capability to redirect the radial measurement location using in-vessel optics. A further expansion is proposed by dynamically scanning a 50 Hz laser beam inside the Tokamak to up to 16 radial chords using an external fast steering mirror. A novel method of synchronizing the collection optics to follow the laser beam has been tested. This expansion will greatly enhance the capability of DTS for study of high performance plasmas and study of core-edge integration. The system will be described and initial prototype results will be presented.