Clark J G, Bowden M D, Scannell R
Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool L69 3GJ, United Kingdom.
UKAEA/CCFE, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB, United Kingdom.
Rev Sci Instrum. 2021 Apr 1;92(4):043545. doi: 10.1063/5.0043813.
A new divertor Thomson scattering system has been developed for the MAST-U tokamak. The diagnostic will produce electron density and temperature profiles along the Super-X strike leg. The existing polychromator design has been adapted for low temperature measurements. A new 1061 nm channel with 2 nm bandwidth has been added to enable measurements down below the previous ∼5 eV limit on the core system. The optical filters used in the system have OD6 light rejection alongside a 1064.1 nm laser line filter to reduce stray light in the digitized channels. A new averaging technique has been applied to the scattered signal traces to improve the core Thomson data in the scrape-off layer. The technique reduces the systematic noise level in this region. This leads to a reduction in the error values for electron density and temperature measurements and, in particular, the digitizer noise. The technique has been applied to produce a radial profile for a number of L-mode MAST discharges down to very low densities of ∼1 × 10 m.
