Design of new Thomson scattering diagnostic system on COMPASS tokamak

Two new Thomson scattering (TS) diagnostic systems are being built on the COMPASS tokamak to get radial profiles of both electron temperature and electron density. The core TS system will measure at 24 spatial points with ≈10 mm resolution across the core plasma while the edge TS system will measure at 32 spatial points with ≈ (3–5) mm resolution across the edge plasma. Two independent Nd:YAG lasers (1.5 J, 30 Hz each) could be combined to produce a repetition rate of 60 Hz. The lasers will follow separate beam paths to the COMPASS vessel. Scattered light will be collected by two objectives: one for the core region, the second for the plasma edge. Both TS systems are based on Nd:YAG/APD (Avalanche photodiodes) technology. Scattered light is spectrally resolved in polychromators equipped with a set of spectral filters and APDs. The output signal is digitized by fast sampling (GS/s) 8 bit analog digital converters (ADCs).