Accurate measurement and interpretation of the heat flux to the divertor in TEXT Upgrade

To obtain accurate measurements of the heat flux to divertor tiles for comparison with probe data in the SOL and with models, digitized infrared camera data were calibrated and corrected for tile emissivity to provide true tile surface temperatures. The surface temperature T(x,y,t) was analysed with a full three dimensional heat flux code, including temperature dependent thermal properties, to extract the heat flux to the divertor tiles in the TEXT Upgrade tokamak. Each of the complexities in the analysis proved necessary for precise results. The parallel heat flux at the separatrix was generally consistent with independently measured edge parameters: a sheath transmission coefficient of ∼ 5 is inferred. The flux to the tiles varied with cos θinc as expected. The decay length for heat flux in the SOL did not vary significantly with conditions and remained ∼ 2.5 mm (traced to the outer midplane), which is significantly shorter than that implied by density and temperature scale lengths in the SOL. (author)