New Capabilities of the Incoherent Thomson Scattering Diagnostics in the TCV Tokamak: Divertor and Real-Time Measurements

This work reports developments of the incoherent TS diagnostic capabilities in the Tokamak a Configuration Variable (TCV). Their goals are to (i) diagnose the TCV divertor region, and (ii) provide Te and ne profiles of the plasma bulk in real-time. These two new TS diagnostic capabilities are implemented within the framework of a TCV upgrade that will insert baffles in the lower divertor region. 20 new TS spectrometers are being installed to access electron temperatures down to similar to 1 eV, for densities above similar to 1.5 x 10(19) m(-3) within the TCV divertor region. They will measure the Thomson light scattered along the vertical propagation path of the three legacy Nd:YAG lasers. The light at each of the 20 measurement plasma volumes is collected by three optical fibers with a laser-mapped spatial resolution of 5-6 mm each, providing a vertical spatial resolution of 15-18mm. Interference filters with central. Interference filters with central wavelengths from 1025 to 1061 nm and widths as low as similar to 2 nm are employed to obtain the spectroscopic resolution required at these low temperatures. The acquisition chain and analysis of the TS signal will be integrated into the TCV monitoring and control system to provide electron density and temperature profiles in real-time, at a sampling rate up to 60 Hz. The real time electron property profiles complement existing systems provided by the far-infrared interferometer and the soft X-ray diagnostics. The latter are restricted to provide integrated values of the electron density and temperature respectively, but at higher sampling rates (10 kHz and 20 kHz respectively). The whole diagnostic ensemble will be integrated into TCV's control system to improve the accuracy and robustness of real-time plasma profile and equilibrium estimation for control purposes.