Thomson scattering measurements in the divertor region of the TCV Tokamak plasmas

In order to better study conventional and alternative divertor configurations, the TCV Tokamak was recently upgraded. In-vessel graphite baffles were installed in the TCV chamber to delimit a separate divertor chamber from the core that required enhanced diagnostic capabilities. To date, TCV’s Thomson scattering diagnostic provided electron temperature and density profiles of the hot core and the pedestal of the plasma with an array of 96 polychromators. To study the new divertor region, an upgrade added 20 new polychromators specifically to diagnose the plasma in the relatively cold divertor region. New 4-channel polychromators were designed to provide Te measurements down to ~1eV with ne~1.5x1019m-3. Interference filters of only 1.9nm FWHM were required to achieve this goal. Te and ne measurements from the TCV divertor region have been obtained for the first time. Specific diverted plasma discharges where the outer divertor leg is scanned in and out of the TS laser beam’s path are used to demonstrate the diagnostic’s new capabilities and potential with measurements of Te as low as 1.4eV obtained for electron densities of 2 x1018m-3. The system’s 16mm integration length along the laser line is providing, for the first time, Te and ne profiles with sufficient spatial resolution across the divertor legs to resolve the divertor plasma dynamics.